Targeting Cancer Neoantigens and Metabolic Change in T-cells

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Targeting Cancer Neoantigens and Metabolic Change in T-cells

May 19, 2016 by larryhbern

Targeting Cancer Neoantigens and Metabolic Change in T-cells

Curator: Larry H. Bernstein, MD, FCAP

WordCloud created by Noam Steiner Tomer 8/10/2020

Updated 5/28/2016

Updated 6/1/2016

Updated 6/11/2021

Fighting Cancer with Borrowed Immunity

http://www.genengnews.com/gen-news-highlights/fighting-cancer-with-borrowed-immunity/81252754/

Outsource a part of the T cell’s immune value chain, propose cancer immunotherapy researchers, from patient T cells to donor T cells. The novel allogeneic approach could rely on T-cell receptor gene transfer to generate broad and tumor-specific T-cell immune responses. [NIAID]

A new cancer immunotherapy approach could essentially outsource a crucial T-cell function. This function, T-cell reactivity to specific cancer antigens, is sometimes lacking in cancer patients. Yet, according to a new proof-of-principle study, these patients could benefit from T cells provided by healthy donors. Specifically, the healthy donors’ T cells could be used to broaden the T-cell receptor repertoires of the cancer patients’ T cells.

Ultimately, this approach relies on a cancer immunotherapy technique called T-cell receptor (TCR) transfer, or the genetic transfer of TCR chains. TCR transfer can be used to outsource the T cell’s learning function, the process by which a T cell acquires the ability to recognize foreign antigens—in this case, the sort of proteins that can be expressed on the surface of cancer cells. Because cancer cells harbor faulty proteins, they can also display foreign protein fragments, also known as neoantigens, on their surface, much in the way virus-infected cells express fragments of viral proteins.

The approach was detailed in a paper that appeared May 19 in the journal Science, in an article entitled, “Targeting of Cancer Neoantigens with Donor-Derived T Cell Receptor Repertoires.” This article, by scientists based at the Netherlands Cancer Institute and the University of Oslo, describes a novel strategy to broaden neoantigen-specific T-cell responses. Such a strategy would be useful in overcoming a common limitation seen in the immune response to cancer: Neoantigen-specific T-cell reactivity is generally limited to just a few mutant epitopes, even though the number of predicted epitopes is large.

“We demonstrate that T cell repertoires from healthy donors provide a rich source of T cells that specifically recognize neoantigens present on human tumors,” the study’s authors wrote. “Responses to 11 epitopes were observed, and for the majority of evaluated epitopes, potent and specific recognition of tumor cells endogenously presenting the neoantigens was detected.”

First, the researchers mapped all possible neoantigens on the surface of melanoma cells from three different patients. In all three patients, the cancer cells seemed to display a large number of different neoantigens. But when the researchers tried to match these to the T cells derived from within the patient’s tumors, most of these aberrant protein fragments on the tumor cells went unnoticed.

Next, the researchers tested whether the same neoantigens could be seen by T cells derived from healthy volunteers. Strikingly, these donor-derived T cells could detect a significant number of neoantigens that had not been seen by the patients’ T cells.

“Many of the T cell reactivities [among donor T cells] involved epitopes that in vivo were neglected by patient autologous tumor-infiltrating lymphocytes,” the authors of the Science article continued. “T cells re-directed with T cell receptors identified from donor-derived T cells efficiently recognized patient-derived melanoma cells harboring the relevant mutations, providing a rationale for the use of such ‘outsourced’ immune responses in cancer immunotherapy.”

“In a way, our findings show that the immune response in cancer patients can be strengthened; there is more on the cancer cells that makes them foreign that we can exploit. One way we consider doing this is finding the right donor T cells to match these neoantigens,” said Ton Schumacher, Ph.D., a principal investigator at the Netherlands Cancer Institute. “The receptor that is used by these donor T cells can then be used to genetically modify the patient’s own T cells so these will be able to detect the cancer cells.”

“Our study shows that the principle of outsourcing cancer immunity to a donor is sound,” added Johanna Olweus, M.D., Ph.D., who heads a research group at the University of Oslo. “However, more work needs to be done before patients can benefit from this discovery. Thus, we need to find ways to enhance the throughput.”

“We are currently exploring high-throughput methods to identify the neoantigens that the T cells can ‘see’ on the cancer and isolate the responding cells. But the results showing that we can obtain cancer-specific immunity from the blood of healthy individuals are already very promising.”

Targeting of cancer neoantigens with donor-derived T cell receptor repertoires

Erlend Strønen¹,², Mireille Toebes³, Sander Kelderman³,…., Fridtjof Lund-Johansen²,⁵, Johanna Olweus¹,²,*,†, Ton N. Schumacher³,*,† + Author Affiliations
Science 19 May 2016: http://dx.doi.org:/10.1126/science.aaf2288

Metabolic maintenance of cell asymmetry following division in activated T lymphocytes.

Verbist KC¹, Guy CS¹, Milasta S¹, Liedmann S¹, Kamiński MM¹, Wang R², Green DR^{1
Nature. 2016 Apr 21; 532(7599):389-93. http://dx. doi.org:/10.1038/nature17442. Epub 2016 Apr 11}

Asymmetric cell division, the partitioning of cellular components in response to polarizing cues during mitosis, has roles in differentiation and development. It is important for the self-renewal of fertilized zygotes in Caenorhabditis elegans and neuroblasts in Drosophila, and in the development of mammalian nervous and digestive systems. T lymphocytes, upon activation by antigen-presenting cells (APCs), can undergo asymmetric cell division, wherein the daughter cell proximal to the APC is more likely to differentiate into an effector-like T cell and the distal daughter is more likely to differentiate into a memory-like T cell. Upon activation and before cell division, expression of the transcription factor c-Myc drives metabolic reprogramming, necessary for the subsequent proliferative burst. Here we find that during the first division of an activated T cell in mice, c-Myc can sort asymmetrically. Asymmetric distribution of amino acid transporters, amino acid content, and activity of mammalian target of rapamycin complex 1 (mTORC1) is correlated with c-Myc expression, and both amino acids and mTORC1 activity sustain the differences in c-Myc expression in one daughter cell compared to the other. Asymmetric c-Myc levels in daughter T cells affect proliferation, metabolism, and differentiation, and these effects are altered by experimental manipulation of mTORC1 activity or c-Myc expression. Therefore, metabolic signalling pathways cooperate with transcription programs to maintain differential cell fates following asymmetric T-cell division.

Review mTORC1 regulates CD8+ T-cell glucose metabolism and function independently of PI3K and PKB.[Biochem Soc Trans. 2013]

mTORC1 regulates CD8+ T-cell glucose metabolism and function independently of PI3K and PKB.

Finlay DK.Biochem Soc Trans. 2013 Apr; 41(2):681-6.
Review Integrating canonical and metabolic signalling programmes in the regulation of T cell responses.[Nat Rev Immunol. 2014]
Phosphorylation-dependent interaction between antigenic peptides and MHC class I: a molecular basis for presentation of transformed self
NIHPA Author Manuscripts. 2008 Nov; 9(11)1236

AMPK Is Essential to Balance Glycolysis and Mitochondrial Metabolism to Control T-ALL Cell Stress and Survival.

Kishton RJ¹, Barnes CE², Nichols AG¹, Cohen S¹, Gerriets VA², Siska PJ³, Macintyre AN², Goraksha-Hicks P², …, Gershon TR⁸, Rathmell WK⁴, Richards KL⁸, Locasale JW⁹, Rathmell JC^{10
Cell Metab. 2016 Apr 12;23(4):649-62. http://dx.doi.org:/10.1016/j.cmet.2016.03.008.}

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive malignancy associated with Notch pathway mutations. While both normal activated and leukemic T cells can utilize aerobic glycolysis to support proliferation, it is unclear to what extent these cell populations are metabolically similar and if differences reveal T-ALL vulnerabilities. Here we show that aerobic glycolysis is surprisingly less active in T-ALL cells than proliferating normal T cells and that T-ALL cells are metabolically distinct. Oncogenic Notch promoted glycolysis but also induced metabolic stress that activated 5′ AMP-activated kinase (AMPK). Unlike stimulated T cells, AMPK actively restrained aerobic glycolysis in T-ALL cells through inhibition of mTORC1 while promoting oxidative metabolism and mitochondrial Complex I activity. Importantly, AMPK deficiency or inhibition of Complex I led to T-ALL cell death and reduced disease burden. Thus, AMPK simultaneously inhibits anabolic growth signaling and is essential to promote mitochondrial pathways that mitigate metabolic stress and apoptosis in T-ALL.

Review AMPK: opposing the metabolic changes in both tumour cells and inflammatory cells?[Biochem Soc Trans. 2013]

AMPK: opposing the metabolic changes in both tumour cells and inflammatory cells?

Dandapani M, Hardie DG.Biochem Soc Trans. 2013 Apr; 41(2):687-93.
Review The multifaceted activities of AMPK in tumor progression–why the “one size fits all” definition does not fit at all?[IUBMB Life. 2013]
The multifaceted activities of AMPK in tumor progression–why the “one size fits all” definition does not fit at all?
Bonini MG, Gantner BN.IUBMB Life. 2013 Nov; 65(11):889-96.

Glutamine Modulates Macrophage Lipotoxicity.

He L^1,², Weber KJ^3,⁴, Schilling JD^5,^6,^{7
Nutrients. 2016 Apr 12;8(4). pii: E215. http://dx.doi.org:/10.3390/nu8040215}

Obesity and diabetes are associated with excessive inflammation and impaired wound healing. Increasing evidence suggests that macrophage dysfunction is responsible for these inflammatory defects. In the setting of excess nutrients, particularly dietary saturated fatty acids (SFAs), activated macrophages develop lysosome dysfunction, which triggers activation of the NLRP3 inflammasome and cell death. The molecular pathways that connect lipid stress to lysosome pathology are not well understood, but may represent a viable target for therapy. Glutamine uptake is increased in activated macrophages leading us to hypothesize that in the context of excess lipids glutamine metabolism could overwhelm the mitochondria and promote the accumulation of toxic metabolites. To investigate this question we assessed macrophage lipotoxicity in the absence of glutamine using LPS-activated peritoneal macrophages exposed to the SFA palmitate. We found that glutamine deficiency reduced lipid induced lysosome dysfunction, inflammasome activation, and cell death. Under glutamine deficient conditions mTOR activation was decreased and autophagy was enhanced; however, autophagy was dispensable for the rescue phenotype. Rather, glutamine deficiency prevented the suppressive effect of the SFA palmitate on mitochondrial respiration and this phenotype was associated with protection from macrophage cell death. Together, these findings reveal that crosstalk between activation-induced metabolic reprogramming and the nutrient microenvironment can dramatically alter macrophage responses to inflammatory stimuli.

Immunoregulatory Protein B7-H3 Reprograms Glucose Metabolism in Cancer Cells by ROS-Mediated Stabilization of HIF1α

Sangbin Lim1, Hao Liu1,2,*, Luciana Madeira da Silva1, Ritu Arora1,…., Gary A. Piazza1, Oystein Fodstad1,4,*, and Ming Tan1,5,*
Cancer Res April 5, 2016 http://dx.doi.org:/10.1158/0008-5472.CAN-15-1538

B7-H3 is a member of B7 family of immunoregulatory transmembrane glycoproteins expressed by T cells. While B7-H3 overexpression is associated with poor outcomes in multiple cancers, it also has immune-independent roles outside T cells and its precise mechanistic contributions to cancer are unclear. In this study, we investigated the role of B7-H3 in metabolic reprogramming of cancer cells in vitro and in vivo. We found that B7-H3 promoted the Warburg effect, evidenced by increased glucose uptake and lactate production in B7-H3–expressing cells. B7-H3 also increased the protein levels of HIF1α and its downstream targets, LDHA and PDK1, key enzymes in the glycolytic pathway. Furthermore, B7-H3 promoted reactive oxygen species–dependent stabilization of HIF1α by suppressing the activity of the stress-activated transcription factor Nrf2 and its target genes, including the antioxidants SOD1, SOD2, and PRX3. Metabolic imaging of human breast cancer xenografts in mice confirmed that B7-H3 enhanced tumor glucose uptake and tumor growth. Together, our results illuminate the critical immune-independent contributions of B7-H3 to cancer metabolism, presenting a radically new perspective on B7 family immunoregulatory proteins in malignant progression. Cancer Res; 76(8); 1–12. ©2016 AACR.

TLR-Mediated Innate Production of IFN-γ by CD8+ T Cells Is Independent of Glycolysis.

Salerno F¹, Guislain A², …, Wolkers MC².
J Immunol. 2016 May 1;196(9):3695-705. http://dx.doi.org:/10.4049/jimmunol.1501997. Epub 2016 Mar 25.

CD8(+) T cells can respond to unrelated infections in an Ag-independent manner. This rapid innate-like immune response allows Ag-experienced T cells to alert other immune cell types to pathogenic intruders. In this study, we show that murine CD8(+) T cells can sense TLR2 and TLR7 ligands, resulting in rapid production of IFN-γ but not of TNF-α and IL-2. Importantly, Ag-experienced T cells activated by TLR ligands produce sufficient IFN-γ to augment the activation of macrophages. In contrast to Ag-specific reactivation, TLR-dependent production of IFN-γ by CD8(+) T cells relies exclusively on newly synthesized transcripts without inducing mRNA stability. Furthermore, transcription of IFN-γ upon TLR triggering depends on the activation of PI3K and serine-threonine kinase Akt, and protein synthesis relies on the activation of the mechanistic target of rapamycin. We next investigated which energy source drives the TLR-induced production of IFN-γ. Although Ag-specific cytokine production requires a glycolytic switch for optimal cytokine release, glucose availability does not alter the rate of IFN-γ production upon TLR-mediated activation. Rather, mitochondrial respiration provides sufficient energy for TLR-induced IFN-γ production. To our knowledge, this is the first report describing that TLR-mediated bystander activation elicits a helper phenotype of CD8(+) T cells. It induces a short boost of IFN-γ production that leads to a significant but limited activation of Ag-experienced CD8(+) T cells. This activation suffices to prime macrophages but keeps T cell responses limited to unrelated infections.

Immunometabolism of regulatory T cells

Newton R, Priyadharshini B & Laurence A Turk
Nature Immunology 2016;17:618–625 http://dx.doi.doi.org:/10.1038/ni.3466

The bidirectional interaction between the immune system and whole-body metabolism has been well recognized for many years. Via effects on adipocytes and hepatocytes, immune cells can modulate whole-body metabolism (in metabolic syndromes such as type 2 diabetes and obesity) and, reciprocally, host nutrition and commensal-microbiota-derived metabolites modulate immunological homeostasis. Studies demonstrating the metabolic similarities of proliferating immune cells and cancer cells have helped give birth to the new field of immunometabolism, which focuses on how the cell-intrinsic metabolic properties of lymphocytes and macrophages can themselves dictate the fate and function of the cells and eventually shape an immune response. We focus on this aspect here, particularly as it relates to regulatory T cells.

Figure 1: Proposed model for the metabolic signatures of various T_reg cell subsets.

http://www.nature.com/ni/journal/v17/n6/carousel/ni.3466-F1.jpg

(a) Activated CD4⁺ T cells that differentiate into the T_eff cell lineage (green) (T_H1 or T_H17 cells) are dependent mainly on carbon substrates such as glucose and glutamine for their anabolic metabolism. In contrast to that, pT_reg cells…

T-bet is a key modulator of IL-23-driven pathogenic CD4⁺ T cell responses in the intestine

Krausgruber T, Schiering C, Adelmann K & Harrison OJ.
Nature Communications 7; Article number:11627 http://dx.doi.org:/10.1038/ncomms11627

IL-23 is a key driver of pathogenic Th17 cell responses. It has been suggested that the transcription factor T-bet is required to facilitate IL-23-driven pathogenic effector functions; however, the precise role of T-bet in intestinal T cell responses remains elusive. Here, we show that T-bet expression by T cells is not required for the induction of colitis or the differentiation of pathogenic Th17 cells but modifies qualitative features of the IL-23-driven colitogenic response by negatively regulating IL-23R expression. Consequently, absence of T-bet leads to unrestrained Th17 cell differentiation and activation characterized by high amounts of IL-17A and IL-22. The combined increase in IL-17A/IL-22 results in enhanced epithelial cell activation and inhibition of either IL-17A or IL-22 leads to disease amelioration. Our study identifies T-bet as a key modulator of IL-23-driven colitogenic responses in the intestine and has important implications for understanding of heterogeneity among inflammatory bowel disease patients.

Th17 cells are enriched at mucosal sites, produce high amounts of IL-17A, IL-17F and IL-22, and have an essential role in mediating host protective immunity against a variety of extracellular pathogens1. However, on the dark side, Th17 cells have also been implicated in a variety of autoimmune and chronic inflammatory conditions, including inflammatory bowel disease (IBD)2. Despite intense interest, the cellular and molecular cues that drive Th17 cells into a pathogenic state in distinct tissue settings remain poorly defined.

The Th17 cell programme is driven by the transcription factor retinoid-related orphan receptor gamma-t (RORγt) (ref. 3), which is also required for the induction and maintenance of the receptor for IL-23 (refs 4, 5). The pro-inflammatory cytokine IL-23, composed of IL-23p19 and IL-12p40 (ref. 6), has been shown to be a key driver of pathology in various murine models of autoimmune and chronic inflammatory disease such as experimental autoimmune encephalomyelitis (EAE)7, collagen induced arthritis8 and intestinal inflammation9, 10, 11, 12. Several lines of evidence, predominantly derived from EAE, suggest that IL-23 promotes the transition of Th17 cells to pathogenic effector cells9, 10, 11, 12. Elegant fate mapping experiments of IL-17A-producing cells during EAE have shown that the majority of IL-17A+IFN-γ+ and IL-17A−IFN-γ+ effector cells arise from Th17 cell progeny13. This transition of Th17 cells into IFN-γ-producing ‘ex’ Th17 cells required IL-23 and correlated with increased expression of T-bet. The T-box transcription factor T-bet drives the Th1 cell differentiation programme14 and directly transactivates the Ifng gene by binding to its promoter as well as multiple enhancer elements15. Indeed, epigenetic analyses have revealed that the loci for T-bet and IFN-γ are associated with permissive histone modifications in Th17 cells suggesting that Th17 cells are poised to express T-bet which could subsequently drive IFN-γ production16, 17.

A similar picture is emerging in the intestine where IL-23 drives T-cell-mediated intestinal pathology which is thought to be dependent on expression of T-bet18 and RORγt (ref. 19) by T cells. In support of this we have recently shown that IL-23 signalling in T cells drives the emergence of IFN-γ producing Th17 cells in the intestine during chronic inflammation20. Collectively these studies suggest a model whereby RORγt drives differentiation of Th17 cells expressing high amounts of IL-23R, and subsequently, induction of T-bet downstream of IL-23 signalling generates IL-17A+IFN-γ+ T cells that are highly pathogenic. Indeed, acquisition of IFN-γ production by Th17 cells has been linked to their pathogenicity in several models of chronic disease13, 21, 22, 23, 24 and a population of T cells capable of producing both IL-17A and IFN-γ has also been described in intestinal biopsies of IBD patients25, 26.

However, in the context of intestinal inflammation, it remains poorly defined whether the requirement for RORγt and T-bet reflects a contribution of Th17 and Th1 cells to disease progression or whether Th17 cells require T-bet co-expression to exert their pathogenic effector functions. Here, we use two distinct models of chronic intestinal inflammation and make the unexpected finding that T-bet is dispensable for IL-23-driven colitis. Rather the presence of T-bet serves to modify the colitogenic response restraining IL-17 and IL-22 driven pathology. These data identify T-bet as a key modulator of IL–23-driven colitogenic effector responses in the intestine and have important implications for understanding of heterogeneous immune pathogenic mechanisms in IBD patients.

Figure 1: IL-23 signalling is required for bacteria-driven T-cell-dependent colitis and the emergence of IL-17A⁺IFN-γ⁺ T cells.

http://www.nature.com/ncomms/2016/160519/ncomms11627/images_article/ncomms11627-f1.jpg

C57BL/6 WT and Il23r^−/− mice were infected orally with Hh and received weekly i.p. injections of IL-10R blocking antibody. Mice were killed at 4 weeks post infection and assessed for intestinal inflammation. (a) Colitis scores. (b) Typhlitis sores. (c) Representative photomicrographs of colon and caecum (× 10 magnification; scale bars, 200 μM). (d) Representative flow cytometry plots of colonic lamina propria gated on viable CD4⁺ T cells. (e) Frequencies of IL-17A⁺ and/or IFN-γ⁺ CD4⁺ T cells present in the colon. Data represent pooled results from two independent experiments (n=12 for WT, n=10 for Il23r^−/−). Bars are the mean and each symbol represents an individual mouse. *P<0.05, ***P<0.001 as calculated by Mann–Whitney U test.

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IL-23 signals are dispensable for T-bet and RORγt expression

RORγt but not T-bet is required for T cell transfer colitis

Figure 2: RORγt but not T-bet expression by CD4⁺ T cells is required for the development of T cell transfer colitis.

http://www.nature.com/ncomms/2016/160519/ncomms11627/images_article/ncomms11627-f2.jpg

C57BL/6 Rag1^−/− mice were injected i.p. with 4 × 10⁵ CD4⁺CD25⁻CD45RB^hi T cells from C57BL/6 WT,Rorc^−/− or Tbx21^−/− donors. Mice were killed when recipients of Tbx21^−/− T cells developed clinical signs of disease (4–6 weeks) and assessed for intestinal inflammation. (a) Colitis scores. (b) Representative photomicrographs of proximal colon sections (× 10 magnification; scale bars, 200 μM). (c) Concentration of cytokines released from colon explants into the medium after overnight culture. Data represent pooled results from two independent experiments (n=14 for WT, n=11 for Rorc^−/−, n=14 forTbx21^−/−). Bars are the mean and each symbol represents an individual mouse. Bars are the mean and error bars represent s.e.m. *P<0.05, **P<0.01, ***P<0.001 as calculated by Kruskal–Wallis one-way ANOVA with Dunn’s post-test.

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T-bet is dispensable for IL-17A⁺IFN-γ⁺ intestinal T cells

Figure 3: T-bet expression by CD4⁺ T cells is not required for the emergence of IL-17A⁺IFN-γ⁺ T cells.

http://www.nature.com/ncomms/2016/160519/ncomms11627/images_article/ncomms11627-f3.jpg

C57BL/6 Rag1^−/− mice were injected i.p. with 4×10⁵ CD4⁺CD25⁻CD45RB^hi T cells from C57BL/6 WT,Rorc^−/− or Tbx21^−/− donors. Mice were killed when recipients of Tbx21^−/−T cells developed clinical signs of disease (4–6 weeks). (a) Representative plots of IL-17A and IFN-γ expression in colonic CD4⁺ T cells. (b) Frequencies of IL-17A⁺ and/or IFN-γ⁺ cells among colonic CD4⁺ T cells. (c) Total numbers of IL-17A⁺and/or IFN-γ⁺ CD4⁺ T cells present in the colon. Data represent pooled results from three independent experiments (n=20 for WT, n=18 for Tbx21^−/−, n=12 for Rorc^−/−). Bars are the mean and each symbol represents an individual mouse. *P<0.05, **P<0.01, ***P<0.001 as calculated by Kruskal–Wallis one-way ANOVA with Dunn’s post-test.

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T-bet deficiency promotes an exacerbated Th17-type response

Our transfer of Tbx21^−/− T cells revealed a striking increase in the frequency of IL-17A⁺IFN-γ⁻cells (Fig. 3) and we reasoned that T-bet-deficiency could impact on Th17 cell cytokine production. Therefore, we transferred WT or Tbx21^−/− CD4⁺ T cells into Rag1^−/− recipients and measured the expression of RORγt, IL-17A, IL-17F and IL-22 by CD4⁺ T cells isolated from the colon. In agreement with our earlier findings, Tbx21^−/− T cells gave rise to significantly increased frequencies of RORγt-expressing T cells capable of producing IL-17A (Fig. 4a). Furthermore, T-bet deficiency also led to a dramatic expansion of IL-17F and IL-22-expressing cells, which constituted only a minor fraction in WT T cells (Fig. 4a,b). By contrast, the frequency of granulocyte-macrophage colony-stimulating factor (GM-CSF) and IFN-γ producing cells was significantly reduced in T-bet-deficient T cells as compared with WT T cells. When analysed in more detail we noted that the production of IL-17A, IL-17F and IL-22 increased specifically in T-bet-deficient IL-17A⁺IFN-γ⁺ T cells as compared with WT T cells whereas IFN-γ production decreased overall in the absence of T-bet as expected (Supplementary Fig. 4A). Similarly, GM-CSF production was also generally reduced in Tbx21^−/− CD4⁺ T cells further suggesting a shift in the qualitative nature of the T cell response.

Figure 4: T-bet-deficient CD4⁺ T cells promote an exacerbated Th17-type inflammatory response.

http://www.nature.com/ncomms/2016/160519/ncomms11627/images_article/ncomms11627-f4.jpg

C57BL/6 Rag1^−/− mice were injected i.p. with 4×10⁵ CD4⁺CD25⁻CD45RB^hi T cells from C57BL/6 WT orTbx21^−/− donors. Mice were killed when recipients of Tbx21^−/−T cells developed clinical signs of disease (4–6 weeks). (a) Representative plots of cytokines and transcription factors in WT or Tbx21^−/− colonic CD4⁺ T cells. (b) Frequency of IL-17A⁺, IL-17F⁺, IL-22⁺, GM-CSF⁺ or IFN-γ⁺ colonic T cells in WT orTbx21^−/−. (c) quantitative reverse transcription PCR (qRT-PCR) analysis of mRNA levels of indicated genes in colon tissue homogenates. (d) Total number of neutrophils (CD11b⁺ Gr1^high) in the colon. (e) Primary epithelial cells were isolated from the colon of steady state C57BL/6 Rag1^−/− mice and stimulated with 10 ng ml⁻¹ cytokines for 4 h after which cells were harvested and analysed by qRT-PCR for the indicated genes. Data in b–d represent pooled results from two independent experiments (n=14 for WT, n=11 for Tbx21^−/−). Bars are the mean and error bars represent s.e.m. Data in e are pooled results from four independent experiments, bars are the mean and error bars represent s.e.m. *P<0.05, **P<0.01,***P<0.001 as calculated by Mann–Whitney U test.

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………

T-bet-deficient colitis depends on IL-23, IL-17A and IL-22

In the present study we show that bacteria-driven colitis is associated with the IL-23-dependent emergence of IFN-γ-producing Th17 cells co-expressing RORγt and T-bet. Strikingly, while RORγt is required for the differentiation of IFN-γ-producing Th17 cells and induction of colitis, T-bet is dispensable for the emergence of IL-17A⁺IFN-γ⁺ T cells and intestinal pathology. Our results show that instead of a mandatory role in the colitogenic response, the presence of T-bet modulates the qualitative nature of the IL-23-driven intestinal inflammatory response. In the presence of T-bet, IL-23-driven colitis is multifunctional in nature and not functionally dependent on either IL-17A or IL-22. By contrast, in the absence of T-bet a highly polarized colitogenic Th17 cell response ensues which is functionally dependent on both IL-17A and IL-22. T-bet-deficient T cells are hyper-responsive to IL-23 resulting in enhanced STAT3 activation and downstream cytokine secretion providing a mechanistic basis for the functional changes. These data newly identify T-bet as a key modulator of IL-23-driven colitogenic CD4⁺ T cell responses.

Contrary to our expectations T-bet expression by CD4 T cells was not required for their pathogenicity. In keeping with the negative effect of T-bet on Th17 differentiation^{40, 41, 42}, we observed highly polarized Th17 responses in T-bet-deficient intestinal T cells. Early studies demonstrated that IFN-γ could suppress the differentiation of Th17 cells⁴⁰ and thus the reduced IFN-γ production by Tbx21^−/−T cells could facilitate Th17 cell generation. However, our co-transfer studies revealed unrestrained Th17 differentiation of Tbx21^−/− T cells even in the presence of WT T cells, suggesting a cell autonomous role for T-bet-mediated suppression of the Th17 programme. Indeed, the role of T-bet as a transcriptional repressor of the Th17 cell fate has been described recently. For example, T-bet physically interacts with and sequesters Runx1, thereby preventing Runx1-mediated induction of RORγt and Th17 cell differentiation⁴³. In addition, T-bet binds directly to and negatively regulates expression of many Th17-related genes^{15, 34} and we identified IL23r to be repressed in a T-bet-dependent manner. In line with this we show here that T-bet-deficient intestinal T cells express higher amounts of Il23r as well as Rorc. This resulted in enhanced IL-23-mediated STAT3 activation and increased production of IL-17A and IL-22. It has also been suggested that T-bet activation downstream of IL-23R signalling is required for pathogenic IL-23-driven T cell responses^{43, 44}. However, we did not find a role for IL-23 in the induction and/or maintenance of T-bet expression and colitis induced by T-bet-deficient T cells was IL-23 dependent. Collectively, these findings demonstrate that T-bet deficiency leads to unrestrained expansion of colitogenic Th17 cells, which is likely mediated through enhanced activation of the IL-23R-STAT3 pathway.

The observation that T-bet-deficient T cells retain their colitogenic potential is in stark contrast to earlier studies. Neurath et al.¹⁸ convincingly showed that adoptive transfer of Tbx21^−/− CD4⁺ T cells into severe combined immunodeficiency (SCID) recipients failed to induce colitis and this correlated with reduced IFN-γ and increased IL-4 production. Another study revealed that IL-4 plays a functional role in inhibiting the colitogenic potential of Tbx21^−/− T cells, as recipients ofStat6^−/−Tbx21^−/− T cells developed severe colitis³⁷. Importantly, the intestinal inflammation that developed in recipients of Stat6^−/−Tbx21^−/− T cells could be blocked by administration of IL-17A neutralizing antibody, suggesting that the potent inhibitory effect of IL-4/STAT6 signals on Th17 differentiation normally prevent colitis induced by Tbx21^−/− T cells³⁷. Various explanations could account for the discrepancy between our study and those earlier findings. First, in contrast to the published reports, we used naïve Tbx21^−/− CD4⁺ T cells from C57BL/6 mice instead of BALB/c mice. An important difference between Tbx21^−/− CD4⁺ T cells from these genetic backgrounds appears to be their differential susceptibility to suppression by IL-4/STAT6 signals. We found that transfer of Tbx21^−/− T cells induced IL-17A-dependent colitis despite increased frequencies of IL-4-expressing cells in the intestine. This discrepancy may be due to higher amounts of IL-4 produced by activated CD4⁺ T cells from BALB/c versus C57BL/6 mice⁴⁵, leading to the well-described Th2-bias of the BALB/c strain⁴⁵. Second, differences in the composition of the intestinal microbiota between animal facilities can have a substantial effect on skewing CD4⁺ T cells responses. In particular, the Clostridium-related segmented filamentous bacteria (SFB) have been shown to drive the emergence of IL-17 and IL-22 producing CD4⁺ T cells in the intestine⁴⁶. Importantly, the ability of naïve CD4⁺ T cells to induce colitis is dependent on the presence of intestinal bacteria, as germ-free mice do not develop pathology upon T cell transfer⁴⁷. In line with this, we previously described that colonization of germ-free mice with intestinal microbiota containing SFB was necessary to restore the development of colitis⁴⁷. Since our Rag1^−/− colony is SFB⁺ and the presence of SFB was not reported in the previous studies, it is possible that differences in SFB colonization status contributed to the observed differences in pathogenicity ofTbx21^−/− T cells.

It is important to note that T-bet-deficient T cells did not induce more severe colitis than WT T cells but rather promoted a distinct mucosal inflammatory response. Colitis induced by WT T cells is characterized by a multifunctional response with high amounts of IFN-γ and GM-CSF and a lower IL-17A and IL-22 response. Consistent with this, we have shown that blockade of GM-CSF abrogates T cell transfer colitis⁴⁸ as well as bacteria-driven intestinal inflammation⁴⁹ in T-bet sufficiency whereas blockade of IL-17A or IL-22 fails to do so. By contrast T-bet deficiency leads to production of high amounts of IL-17A and IL-22 in the colon and neutralization of either was sufficient to reduce intestinal pathology. Our in vitro experiments suggest that IL-17A and IL-22 synergise to promote intestinal epithelial cell responses, which may in part explain the efficacy of blocking IL-17A or IL-22 in colitis induced by T-bet-deficient T cells. A similar synergistic interplay has been described in the lung where IL-22 served a tissue protective function in homeostasis but induced airway inflammation in the presence of IL-17A (ref. 50). This highlights the complexity of the system in health and disease, and the need for a controlled production of both cytokines. We describe here only one mechanism of how IL-17A/IL-22 induce a context-specific epithelial cell response that potentially impacts on the order or composition of immune cell infiltration. Overall, these results provide a new perspective on T-bet, revealing its role in shaping the qualitative nature of the IL-23-driven colitogenic T cell response.

We also describe here the unexpected finding that a substantial proportion of T-bet-deficient intestinal T cells retain the ability to express IFN-γ. To investigate the potential mechanisms responsible for T-bet-independent IFN-γ production by intestinal CD4⁺ T cells we focused on two transcription factors, Runx3 and Eomes. Runx3 has been shown to promote IFN-γ expression directly through binding to the Ifng promoter³⁸ and Eomes is known to compensate for IFN-γproduction in T-bet-deficient Th1 cells³⁷. We found IL-23-mediated induction of Runx3 protein in WT and Tbx21^−/− T cells isolated from the intestine, thus identifying Runx3 downstream of IL-23R signalling. By contrast, we could only detect Eomes protein and its induction by IL-23 in T-bet-deficient but not WT T cells. Thus, Runx3 and Eomes are activated in response to IL-23 in T-bet-deficient cells and are likely to be drivers of T-bet-independent IFN-γ production. In support of this we found that the majority of T-bet-deficient IL-17A⁻IFN-γ⁺ T cells expressed Eomes. However, only a minor population of IL-17A⁺IFN-γ⁺ T cells stained positive for Eomes, suggesting the existence of alternative pathways for IFN-γ production by Th17 cells. Intriguingly, a recent study identified Runx3 and Runx1 as the transcriptional regulators critical for the differentiation of IFN-γ-producing Th17 cells⁵¹. The author’s demonstrated that ectopic expression of Runx transcription factors was sufficient to induce IFN-γ production by Th17 cells even in the absence of T-bet. These findings, combined with our data on Runx3 activation downstream of IL-23R signalling strongly suggest that Runx3 rather than Eomes is driving IFN-γ expression by intestinal Th17 cells.

We have not formally addressed the role of IFN-γ in colitis driven by T-bet-deficient T cells. A recent report by Zimmermann et al.⁵² found that antibody-mediated blockade of IFN-γ ameliorates colitis induced by WT or T-bet-deficient T cells suggesting IFN-γ also contributes to the colitogneic response mediated by T-bet-deficient T cells as originally described for WT T cells^{53, 54}. By contrast with our results the Zimmerman study found that IL-17A blockade exacerbated colitis following transfer of Tbx21^−/− T cells. The reason for the differential role of IL-17A in the two studies is not clear but it is notable that the Zimmerman study was performed in the presence of co-infection with SFB and Hh, and this strong inflammatory drive may alter the pathophysiological role of particular cytokines. Together the data indicate that T-bet deficiency in T cells does not impede their colitogenic activity but that the downstream effector cytokines of the response are context dependent.

In conclusion, our data further underline the essential role for IL-23 in intestinal inflammation and demonstrate that T-bet is an important modulator of the IL–23-driven effector T cell response. The colitogenic T cell response in a T-bet sufficient environment is multifunctional with a dominant GM-CSF and IFN-γ response. By contrast T-bet-deficient colitogenic responses are dominated by IL-17A and IL-22-mediated immune pathology. These results may have significant bearing on human IBD where it is now recognized that differential responsiveness to treatment may reflect considerable disease heterogeneity. As such, identification of suitable biomarkers such as immunological parameters, that allow stratification of patient groups, is becoming increasingly important⁵⁵. Genome-wide association studies have identified polymorphisms in loci related to innate and adaptive immune arms that confer increased susceptibility to IBD. Among these are Th1 (STAT4, IFNG and STAT1) as well as Th17-related genes (RORC, IL23R and STAT3) (refs56, 57). Thus, detailed profiling of the T cell response in IBD patients may help identify appropriate patient groups that are most likely to benefit from therapeutic blockade of certain effector cytokines. Finally, our studies highlight the importance of IL-23 in the intestinal inflammatory hierarchy and suggest that IL-23 could be an effective therapeutic target across a variety of patient groups.

Yale study: How antibodies access neurons to fight infection

By Ziba Kashef

http://news.yale.edu/2016/05/18/yale-study-how-antibodies-access-neurons-fight-infection

Yale scientists have solved a puzzle of the immune system: how antibodies enter the nervous system to control viral infections. Their finding may have implications for the prevention and treatment of a range of conditions, including herpes and Guillain-Barre syndrome, which has been linked to the Zika virus.

Many viruses — such as West Nile, Zika, and the herpes simplex virus — enter the nervous system, where they were thought to be beyond the reach of antibodies. Yale immunobiologists Akiko Iwasaki and Norifumi Iijima used mice models to investigate how antibodies could gain access to nerve tissue in order to control infection.

In mice infected with herpes, they observed a previously under-recognized role of CD4 T cells, a type of white blood cell that guards against infection by sending signals to activate the immune system. In response to herpes infection, CD4 T cells entered the nerve tissue, secreted signaling proteins, and allowed antibody access to infected sites. Combined, CD4 T cells and antibodies limited viral spread.

“This is a very elegant design of the immune system to allow antibodies to go to the sites of infection,” said Iwasaki. “The CD4 T cells will only go to the site where there is a virus. It’s a targeted delivery system for antibodies.”

Access of protective antiviral antibody to neuronal tissues requires CD4 T-cell help

Norifumi Iijima & Akiko Iwasaki
Nature 533,552–556 (26 May 2016) http://dx.doi.org:/10.1038/nature17979

Circulating antibodies can access most tissues to mediate surveillance and elimination of invading pathogens. Immunoprivileged tissues such as the brain and the peripheral nervous system are shielded from plasma proteins by the blood–brain barrier¹ and blood–nerve barrier², respectively. Yet, circulating antibodies must somehow gain access to these tissues to mediate their antimicrobial functions. Here we examine the mechanism by which antibodies gain access to neuronal tissues to control infection. Using a mouse model of genital herpes infection, we demonstrate that both antibodies and CD4 T cells are required to protect the host after immunization at a distal site. We show that memory CD4 T cells migrate to the dorsal root ganglia and spinal cord in response to infection with herpes simplex virus type 2. Once inside these neuronal tissues, CD4 T cells secrete interferon-γ and mediate local increase in vascular permeability, enabling antibody access for viral control. A similar requirement for CD4 T cells for antibody access to the brain is observed after intranasal challenge with vesicular stomatitis virus. Our results reveal a previously unappreciated role of CD4 T cells in mobilizing antibodies to the peripheral sites of infection where they help to limit viral spread.

T Cells Help Reverse Ovarian Cancer Drug Resistance

http://www.genengnews.com/gen-news-highlights/t-cells-help-reverse-ovarian-cancer-drug-resistance/81252753/

http://www.genengnews.com/Media/images/GENHighlight/116057_web2151982472.jpg

T cells (red) attack ovarian cancer cells (green). [University of Michigan Health System]

Researchers at the University of Michigan have recently published the results from a new study that they believe underscores why so many ovarian tumors develop resistance to chemotherapy. The tumor microenvironment is made up of an array of cell types, yet effector T cells and fibroblasts constitute the bulk of the tissue. The investigators believe that understanding the interplay between these two cell types holds the key to how ovarian cancer cells develop resistance.

The new study suggests that the fibroblasts surrounding the tumor work to block chemotherapy, which is why nearly every woman with ovarian cancer becomes resistant to treatment. Conversely, the scientists published evidence that T cells in the microenvironment can reverse the resistance phenotype—suggesting a whole different way of thinking about chemotherapy resistance and the potential to harness immunotherapy drugs to treat ovarian cancer.

“Ovarian cancer is often diagnosed at late stages, so chemotherapy is a key part of treatment,” explained co-senior study author J. Rebecca Liu, M.D., associate professor of obstetrics and gynecology at the University of Michigan. “Most patients will respond to it at first, but everybody develops chemoresistance. And that’s when ovarian cancer becomes deadly.”

Dr. Liu continued, stating that “in the past, we’ve thought the resistance was caused by genetic changes in tumor cells. But we found that’s not the whole story.”

The University of Michigan team looked at tissue samples from ovarian cancer patients and separated the cells by type to study the tumor microenvironment in vitro and in mice. More importantly, the scientists linked their findings back to actual patient outcomes.

The results of this study were published recently in Cell through an article entitled “Effector T Cells Abrogate Stroma-Mediated Chemoresistance in Ovarian Cancer.”

Ovarian cancer is typically treated with cisplatin, a platinum-based chemotherapy. The researchers found that fibroblasts blocked platinum. These cells prevented platinum from accumulating in the tumor and protected tumor cells from being killed off by cisplatin.

http://www.genengnews.com/Media/images/GENHighlight/1s20S0092867416304007fx11564016520.jpg

Diagram depicting how T cells can reverse chemotherapeutic resistance. [Cell, Volume 165, Issue 5, May 19, 2016]

“We show that fibroblasts diminish the nuclear accumulation of platinum in ovarian cancer cells, resulting in resistance to platinum-based chemotherapy,” the authors wrote. “We demonstrate that glutathione and cysteine released by fibroblasts contribute to this resistance.”

T cells, on the other hand, overruled the protection of the fibroblasts. When researchers added the T cells to the fibroblast population, the tumor cells began to die off.

“CD8⁺ T cells abolish the resistance by altering glutathione and cystine metabolism in fibroblasts,” the authors explained. “CD8⁺ T-cell-derived interferon (IFN)γ controls fibroblast glutathione and cysteine through upregulation of gamma-glutamyltransferases and transcriptional repression of system xc⁻cystine and glutamate antiporter via the JAK/STAT1 pathway.”

By boosting the effector T cell numbers, the researchers were able to overcome the chemotherapy resistance in mouse models. Moreover, the team used interferon, an immune cell-secreted cytokine, to manipulate the pathways involved in cisplatin.

“T cells are the soldiers of the immune system,” noted co-senior study author Weiping Zou, M.D., Ph.D., professor of surgery, immunology, and biology at the University of Michigan. “We already know that if you have a lot of T cells in a tumor, you have better outcomes. Now we see that the immune system can also impact chemotherapy resistance.”

The researchers suggest that combining chemotherapy with immunotherapy may be effective against ovarian cancer. Programmed death ligand 1 (PD-L1) and PD-1 pathway blockers are currently FDA-approved treatments for some cancers, although not ovarian cancer.

“We can imagine re-educating the fibroblasts and tumor cells with immune T cells after chemoresistance develops,” Dr. Zou remarked.

“Then we could potentially go back to the same chemotherapy drug that we thought the patient was resistant to. Only now we have reversed that, and it’s effective again,” Dr. Liu concluded.

Effector T Cells Abrogate Stroma-Mediated Chemoresistance in Ovarian Cancer

Weimin Wang, Ilona Kryczek, Lubomír Dostál, Heng Lin, Lijun Tan, et al.
Cell May 2016; 165, Issue 5:1092–1105. http://dx.doi.org/10.1016/j.cell.2016.04.009

Highlights

•Fibroblasts diminish platinum content in cancer cells, resulting in drug resistance
•GSH and cysteine released by fibroblasts contribute to platinum resistance
•T cells alter fibroblast GSH and cystine metabolism and abolish the resistance
•Fibroblasts and CD8⁺ T cells associate with patient chemotherapy response

Summary

Effector T cells and fibroblasts are major components in the tumor microenvironment. The means through which these cellular interactions affect chemoresistance is unclear. Here, we show that fibroblasts diminish nuclear accumulation of platinum in ovarian cancer cells, resulting in resistance to platinum-based chemotherapy. We demonstrate that glutathione and cysteine released by fibroblasts contribute to this resistance. CD8⁺ T cells abolish the resistance by altering glutathione and cystine metabolism in fibroblasts. CD8⁺ T-cell-derived interferon (IFN)γ controls fibroblast glutathione and cysteine through upregulation of gamma-glutamyltransferases and transcriptional repression of system xc⁻ cystine and glutamate antiporter via the JAK/STAT1 pathway. The presence of stromal fibroblasts and CD8⁺ T cells is negatively and positively associated with ovarian cancer patient survival, respectively. Thus, our work uncovers a mode of action for effector T cells: they abrogate stromal-mediated chemoresistance. Capitalizing upon the interplay between chemotherapy and immunotherapy holds high potential for cancer treatment.

Aurelian Udristioiu

Activation of effect or T cells leads to increased glucose uptake, glycolysis, and lipid synthesis to support growth and proliferation. Activated T cells were identified with CD7, CD5, CD3, CD2, CD4, CD8 and CD45RO. Simultaneously, the expression of CD95 and its ligand causes apoptotic cells death by paracrine or autocrine mechanism, and during inflammation, IL1-β and interferon-1α..
The receptor glucose, Glut 1, is expressed at a low level in naive T cells, and rapidly induced by Myc following T cell receptor (TCR) activation. Glut1 trafficking is also highly regulated, with Glut1 protein remaining in intracellular vesicles until T cell activation.
CD28 co-stimulation further activates the PI3K/Akt/mTOR pathway in particular, and provides a signal for Glut1 expression and cell surface localization.
Mechanisms that control T cell metabolic reprogramming are now coming to light, and many of the same oncogenes importance in cancer metabolism are also crucial to drive T cell metabolic transformations, most notably Myc, hypoxia inducible factor (HIF)1a, estrogen-related receptor (ERR) a, and the mTOR pathway. The proto-oncogenic transcription factor, Myc, is known to promote transcription of genes for the cell cycle, as well as aerobic glycolysis and glutamine metabolism.
Recently, Myc has been shown to play an essential role in inducing the expression of glycolytic and glutamine metabolism genes in the initial hours of T cell activation. In a similar fashion, the transcription factor (HIF)1a can up-regulate glycolytic genes to allow cancer cells to survive under hypoxic conditions

UPDATE 6/11/2021

Bispecific Antibodies Emerging as Effective Cancer Therapeutics

In Perspectives in the Journal Science

Bispecific antibodies

Source: https://science.sciencemag.org/content/372/6545/916

Ulrich Brinkmann1,
Roland E. Kontermann2

See all authors and affiliations

Science 28 May 2021:
Vol. 372, Issue 6545, pp. 916-917
DOI: 10.1126/science.abg1209

Bispecific antibodies (bsAbs) bind two different epitopes on the same or different antigens. Through this dual specificity for soluble or cell-surface antigens, bsAbs exert activities beyond those of natural antibodies, offering numerous opportunities for therapeutic applications. Although initially developed for retargeting T cells to tumors, with a first bsAb approved in 2009 (catumaxomab, withdrawn in 2017), exploring new modes of action opened the door to many additional applications beyond those of simply combining the activity of two different antibodies within one molecule. Examples include agonistic “assembly activities” that mimic the activity of natural ligands and cofactors (for example, factor VIII replacement in hemophilia A), inactivation of receptors or ligands, and delivery of payloads to cells or tissues or across biological barriers. Over the past years, the bsAb field transformed from early research to clinical applications and drugs. New developments offer a glimpse into the future promise of this exciting and rapidly progressing field.

Monoclonal antibodies (mAbs) comprise antigen-binding sites formed by the variable domains of the heavy and light chain and an Fc region that mediates immune responses. BsAbs, produced through genetic engineering, combine the antigen-binding sites of two different antibodies within one molecule, with a plethora of formats available (1). Conceptually, one can discriminate between bsAbs with combinatorial modes of action where the antigen-binding sites act independently from each other, and bsAbs with obligate modes of action where activity needs binding of both, either in a sequential (temporal) way or dependent on the physical (spatial) linkage of both (see the figure) (2). BsAbs approved as drugs are so far in the obligate dual-binding category: A T cell recruiter (blinatumomab) against cancer and a factor VIIIa mimetic to treat hemophilia A (emicizumab). Most but not all of the more than 100 bsAbs in clinical development address cancers. Some are in late stage (such as amivantamab, epcoritamab, faricimab, and KNO46), but most are still in early stages (2). Most of these entities enable effector cell retargeting to induce target cell destruction.

An increasing number of programs also explore alternative modes of action. This includes bsAbs that target pathways involved in tumor proliferation (such as amivantamab), invasion, ocular angiogenesis (such as faricimab), or immune regulation by blocking receptors and/or ligands, mainly in a combinatorial manner. Challenges for all of these entities are potential adverse effects, toxicity in normal tissues, and overshooting and systemic immune responses, especially with T cell retargeting or immune-modulating or activating entities. Such issues need to be carefully addressed.

Most of the bispecific T cell engagers comprise a binding site for a tumor-associated antigen and CD3 [a component of the T cell receptor (TCR) activation complex] as trigger molecule on T cells. To prevent or ameliorate “on-target, off-tumor” effects of T cell recruiters, approaches currently investigated include the modulation of target affinities and mechanisms to allow conditional activation upon target cell binding. Thus, a reduced affinity for CD3 increased tolerability by reducing peripheral cytokine concentrations that are associated with nonspecific or overshooting immune reactions (3). Similarly, reduced affinity for the target antigen was shown to ameliorate cytokine release and damage of target-expressing tissues (4). Tumor selectivity can be further increased by implementing avidity effects—for example, by using 2+1 bsAb formats with two low-affinity binding sites for target antigens and monovalent binding to CD3 (4).

In further approaches, binders to CD3 were identified that efficiently trigger target cell destruction without inducing undesired release of cytokines, demonstrating the importance of epitope specificity to potentially uncouple efficacy from cytokine release (5). Complementing these T cell–recruiting principles, the nonclassical T cell subset of γ9d2 T cells with strong cytotoxic activity emerged as potent effectors, which can be retargeted with bsAbs binding to the γ9d2 TCR. Thereby, global activation of all T cells, including inhibitory regulatory T cells (T_reg cells), through CD3 binding, may be avoided (6). However, even these approaches might result in a narrow therapeutic window to treat solid tumors because of T cell activation in normal tissues.

Consequently, there are several approaches to conditionally activate T cells within tumors, including a local liberation of the CD3-binding sites or triggering local assembly of CD3-binding sites from two half-molecules. For example, CD3-binding sites have been masked by fusing antigen binding or blocking moieties—such as peptides, aptamers, or anti-idiotypic antibody fragments—to one or both variable domains. These moieties are released within the tumor by tumor-associated proteases, or through biochemical responses to hypoxia or low pH (7). This approach can also be applied to confer specific binding of antibody therapeutics, including bsAbs, to antigens on tumor cells (8).

An on-target restoration of CD3-binding sites requires application of two target-binding entities, each comprising parts of the CD3-binding site, which assemble into functional binding sites upon close binding of both half-antibodies. The feasibility of this approach was recently shown, for example, for a split T cell–engaging antibody derivative (Hemibody) that targets a cell surface antigen (9). Such approaches can also be applied to half-antibodies that recognize two different targets expressed on the same cell, further increasing tumor selectivity.

Regarding T cell engagers, increasing efforts are made to target not only cell-surface antigens expressed on tumor cells but also human leukocyte antigen (HLA)–presented tumor-specific peptides. This expands the target space of bsAbs toward tumor-specific intracellular antigens and can be achieved by using either recombinant TCRs or antibodies with TCR-like specificities combined with, for example, CD3-binding arms to engage T cell responses. A first TCR–anti-CD3 bispecific molecule is in phase I and II trials to treat metastatic melanoma (10). A challenge of this approach is the identification of TCRs or TCR-like antibodies that bind the peptide in the context of HLA with high affinity and specificity, without cross-reacting with related peptides to reduce or avoid off-target activities. Comprehensive screening tools and implementation of computational approaches are being developed to achieve this task.

A rapidly growing area of bsAbs in cancer therapy is their use to foster antitumor immune responses. Here, they are especially applied for dual inhibition of checkpoints that prevent immune responses—for example, programmed cell death protein 1 (PD-1) and its ligand (PD-L1), cytotoxic T lymphocyte–associated antigen 4 (CTLA-4), or lymphocyte activation gene 3 (LAG-3; for example, KNO46). Tumor-targeted bsAbs can also target costimulatory factors such as CD28 or 4-1BB ligand (4-1BBL) to enhance T cell responses when combined with PD-1 blockade or to provide an activity-enhancing costimulatory signal in combination with CD3-based bsAbs (11). Furthermore, bsAbs are being developed for local effects by targeting one arm to antigens that are expressed by tumor cells or cells of the tumor microenvironment (2).

Clinical application of bsAbs now expands to other therapeutic areas, including chronic inflammatory, autoimmune, and neurodegenerative diseases; vascular, ocular, and hematologic disorders; and infections. In contrast to mAbs, bsAbs can inactivate the signaling of different cytokines with one molecule to treat inflammatory diseases (12). Simultaneous dual-target binding is not essential to elicit activity for bsAbs against combinations of proinflammatory cytokines, such as tumor necrosis factor (TNF), interleukin-1α (IL-1α), IL-1β, IL-4, IL-13, IL-17, inducible T cell costimulator ligand (ICOSL), or B cell–activating factor (BAFF). This presumably also applies to blockade of immune cell receptors, although dual targeting might confer increased efficacy due to avidity effects and increased selectivity through simultaneous binding of two different receptors.

A further application of combinatorial dual targeting is in ophthalmology. Loss of vision in wet age-related macular degeneration (AMD) results from abnormal proliferation and leakiness of blood vessels in the macula. This can be treated with antibodies that bind and inactivate factors that stimulate their proliferation (13). In contrast to mAbs or fragments that recognize individual factors, bsAbs bind two such factors. For example, faricimab that binds vascular endothelial growth factor A (VEGF-A) and angiopoietin-2 (ANG2), demonstrated dual efficacy in preclinical studies, and is currently in phase 3 trials.

BsAbs with obligate modes of action that mandate simultaneous dual-target binding are “assemblers” that replace the function of factors necessary to form functional protein complexes. One of these bsAbs with an assembly role (emicizumab, approved in 2018) replaces factor VIIIa in the clotting cascade. Deficiency of factor VIII causes hemophilia A, which can be overcome by substitution with recombinant factor VIII. However, a proportion of patients develop factor VIII–neutralizing immune responses and no longer respond to therapy. To overcome this, a bsAb was developed with binding sites that recognize and physically connect factors IXa and X, a process normally mediated by factor VIIIa. Extensive screening of a large set of bsAbs was required to identify those that combine suitable epitopes with optimized affinities and geometry to serve as functional factor VIIIa mimetics (14). This exemplifies the complexity of identifying the best bsAb for therapeutic applications.

A mode of action requiring sequential binding of two targets is the transport of bsAbs across the blood-brain barrier (BBB). This is a tight barrier of brain capillary endothelial cells that controls the transport of substances between the blood and the cerebrospinal fluid—the brain parenchyma. Passage of large molecules, including antibodies, across the BBB is thereby restricted. Some proteins, such as transferrin or insulin, pass through the BBB by way of transporters on endothelial cells. Antibodies that bind these shuttle molecules, such as the transferrin receptor (TfR), can hitchhike across the BBB. BsAbs that recognize brain targets (such as β-amyloid for Alzheimer’s disease) and TfR with optimized affinities, epitopes, and formats can thereby enter the brain. Such bsAbs are currently in clinical evaluation to treat neurodegenerative diseases (15).

In the past years, there has been a transition from a technology-driven phase, solving hurdles to generate bsAbs with defined composition, toward exploring and extending the modes of action for new therapeutic options. The challenge of generating bsAbs is not only to identify suitable antigen pairs to be targeted in a combined manner. It is now recognized that the molecular composition has a profound impact on bsAb functionality (13). That more than 30 different bsAb formats are in clinical trials proves that development is now driven by a “fit for purpose” or “format defines function” rationale. Many candidates differ in their composition, affecting valency, geometry, flexibility, size, and half-life (1). Not all members of this “zoo of bsAb formats” qualify to become drugs. Strong emphasis is therefore on identifying candidates that exhibit drug-like properties and fulfill safety, developability, and manufacturability criteria. There is likely to be an exciting new wave of bsAb therapeutics available in the coming years.

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