Universal embryonic stem cell donor lines would greatly facilitate stem cell based regenerative medicine and permit facile testing of human pluripotent stem cell derived grafts in xenogeneic settings. Because HLA-G overcomes immune cell mediated attack of foetal tissues during pregnancy and inhibits T-cell responses and dendritic cell antigen maturation in vitro and in vivo, it is an attractive candidate molecule for achieving this goal. Here we investigated whether enforced expression of either the soluble or the membrane bound form of the HLA-G mouse homologue, H2-Bl, in human and mouse ES cell lines would allow engraftment in immunocompetent mice. Despite evidence for robust expression of soluble or membrane bound H2-Bl molecules and effective inhibition of CD8+ T-cell proliferation by all H2-Bl engineered ES cell lines, all failed to generate teratomas in immunocompetent mice, despite doing so in NOD-SCID mice. We conclude that expression of H2-Bl in human and mouse embryonic stem cells alone is insufficient to overcome xenogeneic rejection.

ABSTRACT:Ataxia telangiectasia (A-T) is an autosomal recessive disorder associated with early childhood ataxia, neurodegeneration, immune deficiency, radiosensitivity, sterility, and an increased susceptibility to cancer. In spite of numerous years of research, there is still no curative treatment for A-T, nor a reliable animal model that recapitulates the prominent neurological phenotypes observed in patients. To address these deficiencies and investigate potential therapeutic approaches I have attempted to generate a universal donor pluripotent stem cell line, utilized radiological imaging to investigate a novel rat model of A-T, and tested whether bone marrow transplantation (BMT) could provide benefit in the treatment of hematological defects associated with A-T. Animal models are likely to play a key role in the development of therapeutic strategies for the treatment of A-T. While multiple mouse models of A-T currently exist and recapitulate some of the phenotypes attributed to the human disease, prominent neurodegeneration has not been observed in these animal. As such, our research group has produced a gene knock-out model in the rat, utilizing Zinc Finger Nuclease technology. Approximately 50% of the Atm -/-rats show dilated blood vessels in the eyes, microgliosis, and develop hind limb paralysis, suggesting this model may recapitulate some of the neurological defect observed in A-T patients. Magnetic resonance imaging (MRI) was utilized to assess structural changes in the brain and spinal cord. Surprisingly, no significant differences in cerebellar volume or gray/white matter ratios were observed in the brain or spinal cord of healthy animals.However, lymphomas were detected in the T12-L3 region of the spine in all of the paralysed animals tested. I utilized PET/MRI in conjunction with the radiotracer ( 18 F)PBR111, which is highly selective for the TSPO receptor of activated microglia in the brain, to assess microglial activation in vivo in 5 month old control and ATM null nonparalysed rats, three of each. No differences were observed in the cerebellum of these rats relative to WT rats, as well as multiple other brain regions assessed in healthy animals. These data provide evidence that paralysis in the A-T rat model is associated with the presence of lymphomas within the spinal column.