Antibody-bound Viral Antigens
Reporter: Larry H. Bernstein, MD, FCAP
The following presentations are closely related to other similar pieces, except that this uniquely envisions the release and presentation of antibody-bound VIRAL antigens in targeting cancer cells. The approach compares the lifelong immunity conferred by immunity to herpesvirus to immunosuppression of cancer targets by high affinity cytotoxic T-lymphoctes targeting the cancer in vivo.
Abstract 2893: Engineered release and presentation of antibody-bound viral antigens: A highly specific and novel immunotherapeutic approach to target cancer in vivo
David G. Millar, Laura Morton, Manuela Carvalho Gaspar, …, Guy E. Pratt, and Mark Cobbold
Cancer Res Oct 1, 201474; 2893 http://dx. doi.org:/10.1158/1538-7445.AM2014-2893
Harnessing the power of adaptive immunity to combat cancer has been a long-term goal of translational immunotherapy. Tumor-specific immunity, where present, is typically at low frequency and affinity with compromised effector function. By contrast, immunity against persistent herpesviruses in man is characterised by high affinity cytotoxic T-lymphocytes (CTL) at high frequency with potent effector function. Furthermore, the immunosubversive mechanisms employed by herpesviruses show striking parallels to tumors, yet the associated anti-viral immunity limits these to life-long asymptomatic infections.
We reasoned that the delivery of immunodominant viral peptide epitopes to the tumor surface might facilitate passive-loading of peptides into empty MHC class-I molecules, effectively mimicking viral infection, rendering tumors susceptible to lysis by anti-viral immunity.
To address this we developed a new class of targeting antibodies: APEC (Antibody Peptide Epitope Complexes) that are able to deliver an antigenic payload at the cell surface through proteolytic release of covalently-coupled peptide antigens. As a proof-of-concept we used clinically-validated antibodies cetuximab (anti-EGFR) and rituximab (anti-CD20) to develop APECs that are able to target human tumors.
We screened 15 HLA-A*0201+ EGFR-expressing NCI-60 cell lines, CD20+ lymphoma cell lines, 20 primary CD20+ CLL tumor samples and four healthy B-cells against a library of 190 cetuximab-APECs (cAPEC) or rituximab (rAPEC) incorporating the immunodominant cytomegalovirus (CMV) pp65495-503 epitope and candidate protease cleavage sites following co-incubation with CMV-specific CTL (CMV-CTL). The most effective cAPEC and rAPEC were those incorporating MMP2, MMP9, Cathepsin B and Cathepsin D protease recognition domains. Very few (2/190) rAPEC were able to redirect CMV-CTL against healthy cells. Heterogeneity was observed for primary CLL tumors but a limited number of rAPEC were effective in all cases (5/190).
Mechanistic studies demonstrated that: (i) peptide loading occurred at the cell surface, (ii) required the expression of target antigens at the cell surface and (iii) T-cell recognition could be inhibited by unconjugated antibody (92%) or by incubation with protease inhibitors (83%).
T-cell specificity was examined using rAPEC treated tumor targets co-incubated with various HLA-matched effector T-cell populations. No activation of CD4+ was observed including CD4+CD25hi regulatory T-cell populations. Incubation with CD8+ T-cells revealed that only pp65495-503-specific CD8+ T-cells engaged with APEC-treated tumor cells. Lastly, xenograft studies using EGFR+ and CD20+ tumor cell lines demonstrated efficacy of both cAPEC and rAPEC to eliminate tumors in vivo by redirecting anti-viral CTL.
These data indicate that APECs represent a powerful new approach to combat cancer.
Citation Format: David G. Millar, Laura Morton, Manuela Carvalho Gaspar, Punam Mistry, Hugo De La Peña, Ricky Joseph, Sarah Penny, Oliver C. Goodyear, Margaret Goodall, Guy E. Pratt, Mark Cobbold. Engineered release and presentation of antibody-bound viral antigens: A highly specific and novel immunotherapeutic approach to target cancer in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2893. doi:10.1158/1538-7445.AM2014-2893
Re-directing the anti-viral T cell response towards cancer
Early ex vivo work using Chronic Lymphocytic Leukaemia (CLL) patient cells has shown the ability of Rituximab APEC to re-direct anti-viral T cells towards primary CLL cells. Furthermore, early in vivo murine models using the Cetuximab APEC have demonstrated efficacy of the APEC with tumour clearance seen up to 32 days post-APEC treatment.
Conclusion In summary, this novel approach promises to provide existing therapeutic antibodies with a new mechanism of action that allows them to engage with highly potent T cells in an antigen-specific manner. Further in vivo work is on-going with the aim of pushing this work toward the clinic.
APEC antibodies
cyclic di-nucleotides
CTLA4 and PD1 antibodies
STING
STING pathway activators
NK cell immunotherapies
T cell activation
CRC Surface Phosphopeptides
tumor — Surface MHC
Tumor-specific neoantigens
CD8+ T-cells
O-GlcNAcylation
HLA-A2-tyrosinase complex
disease-specific MHC-peptide complexes
TCR-like antibodies
two-state electronic antigen and a chimeric cell receptor
antigen targeting via the human DCIR receptor
Toll-like receptor (TLR) 7/8 agonist
DC subsets
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This is very insightful. There is no doubt that there is the bias you refer to. 42 years ago, when I was postdocing in biochemistry/enzymology before completing my residency in pathology, I knew that there were very influential mambers of the faculty, who also had large programs, and attracted exceptional students. My mentor, it was said (although he was a great writer), could draft a project on toilet paper and call the NIH. It can’t be true, but it was a time in our history preceding a great explosion. It is bizarre for me to read now about eNOS and iNOS, and about CaMKII-á, â, ã, ä – isoenzymes. They were overlooked during the search for the genome, so intermediary metabolism took a back seat. But the work on protein conformation, and on the mechanism of action of enzymes and ligand and coenzyme was just out there, and became more important with the research on signaling pathways. The work on the mechanism of pyridine nucleotide isoenzymes preceded the work by Burton Sobel on the MB isoenzyme in heart. The Vietnam War cut into the funding, and it has actually declined linearly since.
A few years later, I was an Associate Professor at a new Medical School and I submitted a proposal that was reviewed by the Chairman of Pharmacology, who was a former Director of NSF. He thought it was good enough. I was a pathologist and it went to a Biochemistry Review Committee. It was approved, but not funded. The verdict was that I would not be able to carry out the studies needed, and they would have approached it differently. A thousand young investigators are out there now with similar letters. I was told that the Department Chairmen have to build up their faculty. It’s harder now than then. So I filed for and received 3 patents based on my work at the suggestion of my brother-in-law. When I took it to Boehringer-Mannheim, they were actually clueless.