Leaders in Pharmaceutical Business Intelligence (LPBI) Group

The SCID Pig II: Researchers Develop Another SCID Pig, And Another Great Model For Cancer Research

 

Writer. Reporter: Stephen J. Williams, Ph.D.

 

 

The choice of suitable animal model of disease may define future success or failure for drug development, basic and translational research, or biomarker discovery projects.   Indeed, as highlighted in one of my earlier posts “Heroes in Medical Research: Developing Models for Cancer Research”, the choice of animal to model a human disease can have drastic implications in the basic researchers ability to understand metabolic and genetic factors causally associated with disease development. As described in that post the King rat model led to our understanding of the genetics of early development and sex determination while early mouse models helped us to understand the impact of microenvironment on cell fate and the discovery of stem cells. In addition, transgenic and immunodeficient mice resulted in transformational studies on our understanding of cancer. Small rodent models are ideal for following reasons:

• Ease of genetic manipulation
• Availability of well-defined models
• Ease of low cost of use

Regardless of these benefits many investigators in industry and academia are looking to models of human disease in animals more closely resembling human anatomy, physiology, and genetics.

 

There is a growing need for alternative animal models in cancer research.

 

As I had discussed in another of my earlier posts “The SCID Pig: How Pigs are becoming a Great Alternate Model for Cancer Research”, the pig is gaining notoriety and acceptance as a very suitable animal to model human disease as minipigs and humans have:

• Similar physiology
• Similar genetics: >90% homology
• Similar anatomic dimensions: i.e. Adult Gottingen minipigs are 70kg (adult human male weight)
• Similar organ size and structure to humans organ size and structure
• Pig genome sequencing project nearly complete
• Ability to manipulate pig genetics

The post had discussed the development of a severe combined immunodeficient (SCID) pig by investigators at Iowa State and Kansas State University. This line of pigs, selected on a specific diet, could act as recipients for human cancer cell lines, a proof of their SCID phenotype.

A report featured on Fierce Biotech Research “MU Scientists Successfully Transplant, Grow Stem Cells in Pigs” discussed the development of a new genetically-modified immunodeficient porcine model by researchers at the University of Missouri, recently published in Proceedings of the National Academy of Sciences[1].

These pigs are available from the National Swine Resource and Research Center (http://nsrrc.missouri.edu).

For the report on Fierce Biotech Research please follow the link below:

http://www.fiercebiotechresearch.com/press-releases/mu-scientists-successfully-transplant-grow-stem-cells-pigs

 

The report in FierceBiotech highlights the type of studies an immunocompromised pig model would be useful for including:

• Regenerative medicine
• Xenotransplantation
• Tumor growth and efficacy studies

 

Comments in the post from the investigators explained the benefits of developing such a porcine model system including:

“The rejection of transplants and grafts by host bodies is a huge hurdle for medical researchers,” said R. Michael Roberts, Curators Professor of Animal Science and Biochemistry and a researcher in the Bond Life Sciences Center. “By establishing that these pigs will support transplants without the fear of rejection, we can move stem cell therapy research forward at a quicker pace.”

The studies main investigators, Drs. Randall Prather and R. Michael Roberts, both of University of Missouri, along with first authors Kiho Lee, Deug-Nam Kwon and Toshihiko Ezashi, used biallellic mutation of the RAG2 gene in Gottingen minipig fibroblasts and then subsequent somatic cell nuclear transfer (SCNT) to produce the RAG2-/- animals. (Rag2 is a protein involved in V(D)J recombination of antibodies during early B and T cell development. See GeneCard link above)

As proof of their SCID phenotype the authors showed that

1. these RAG2-/- animals could act as host for human induced pluripotent stem cells
2. act as recipient for allogeneic porcine stem cells
3. reduced levels of (CD21+) B cells and (CD3+) T cells
4. growth retardation if housed under standard, non-sterile conditions

Details of the study are given below:

Methodology Used

For Production of Gottingen minipigs carrying the RAG2 mutation

To produce targeted mutations in RAG2:

• TALENS () were constructed to produced mutation in exon 2 of RAG2
• Constructed TALENS and reporter electroporated in fetal-derived pig fibroblasts
• SCNT used to transfer RAG2 mutant nuclei to donor oocytes
• 9 embryo transfers resulted in 22 live piglets
• Piglets genotyped as either monoallelic or biallelic RAG2 mutant
• RAG2wild-type and mutants housed in either pathogen-free or normal housing conditions

To verify SCID phenotype of litter by either

1. Graft acceptance of human iPSCs and teratoma formation

–          Fibroblasts from human umbilical cord reprogrammed to pluripotency; verified by pluripotent markers POUSF1, NANOG, SSEA-3)

–          Two human and porcine iPSC lines with trophoblastic properties[2] were injected subcutaneously in ear or flank

–          Tumor formation analyzed by immunohistochemistry using markers:

CTNNBI (B-catenin)

VWF (von Willebrand

DES and ACTG2

GFAP and ENO2

Human specific MFN1 (both antibody and gene primers)

1. Flow Cytometry

–          Analysis of piglet spleen cells for B cell population (CD21)

–          Analysis of piglet spleen cell for T cell population (CD3)

C.    Histology

– histo evaluation of thymus, spleen

– marker evaluation of spleen using anti-CD79A (B cells), CD3 (T cells),

CD335 (NK cells)

Results

TALEN produced a variety of indels (insertion/deletions) and three RAG2 mutatnt colonies (containing monoallelic, mix of mono and biallelic) used for SCNT.

Three litters produced 16 piglets (eight survived [four mono and four biallelic]

Biallelic RAG2 mutants showed slower weight gain than wild type or monoallelic mutants with signs of inflammation and apoptosis in spleen and designated “failure to thrive” in standard housing…needed a clean environment to thrive.

Biallelic mutant pigs lacked mature CD21 B cells and CD3 T cells but contained macrophages and NK cells.

Implantation of human and allogenic porcine pluripotent stem cells (trophoblastic) showed rapid development of teratomas.
References

1. Lee K, Kwon DN, Ezashi T, Choi YJ, Park C, Ericsson AC, Brown AN, Samuel MS, Park KW, Walters EM et al: Engraftment of human iPS cells and allogeneic porcine cells into pigs with inactivated RAG2 and accompanying severe combined immunodeficiency. Proceedings of the National Academy of Sciences of the United States of America 2014, 111(20):7260-7265.
2. Ezashi T, Matsuyama H, Telugu BP, Roberts RM: Generation of colonies of induced trophoblast cells during standard reprogramming of porcine fibroblasts to induced pluripotent stem cells. Biology of reproduction 2011, 85(4):779-787.

 

Other posts on this site related to Cancer Research Tools include

The SCID Pig: How Pigs are becoming a Great Alternate Model for Cancer Research

Heroes in Medical Research: Developing Models for Cancer Research

Reprogramming Induced Pleuripotent Stem Cells

The Cancer Research Concentration @ Leaders in Pharmaceutical Business Intelligence

A Synthesis of the Beauty and Complexity of How We View Cancer

Guidelines for the welfare and use of animals in cancer research

Gene Therapy and the Genetic Study of Disease: @Berkeley and @UCSF – New DNA-editing technology spawns bold UC initiative as Crispr Goes Global