H-Y-Incompatible Stem Cell Transplantation Causes Rejection of Nucleus Matched Cell

Objectives: Due to their pluripotency, embryonic stem cells (ESCs) are promising candidates for cell-based regenerative therapies for heart failure. However, transplantation of ESC-derived cells or tissue will trigger an immune response and will lead to rejection based on the major histocompatibility antigen (HLA) mismatch. Less is known about the relevance of the H-Y antigens, a class of minor histocompatibility antigens encoded by the Y chromosome. In this study, we sought to investigate the antigenicity of H-Y in a mouse model.

Methods: Pluripotent murine ESCs (mESCs, BALB/c background, male karyotype) were culture expanded and transplanted in 1x10⁶ doses. Unidirectional ELISPOT assays were conducted to investigate the Th1-specific IFNγ response and teratoma formation was analyzed as parameter for cell survival. Neonatal female BALB/c mice were injected with male mESCs according to the Medawar protocol. Unidirectional ELISPOT and mixed lymphocyte reaction (MLR) assays were performed to evaluate immune activation.

Results: Our results show an increased immune activation in the H-Y mismatched syngeneic model. ELISPOT assays showed a significantly stronger response in syngeneic BALB/c females than in BALB/c males (p < 0.0001). Female BALB/c nude mice lacking T cells generated a significantly lower ELISPOT frequency than BALB/c wildtype (p < 0.0001), which reveals that T cells are necessary for the H-Y-dependent immune response. Teratoma formation occurred in 100% of male BALB/c and 100% of female BALB/c nude as well as in 100% of immunodeficient SCID beige animals. Female BALB/c did not show any teratoma formation (0%). In the Medawar experiments, male mESCs were injected into female BALB/c during the neonatal period. After these mice were challenged again in adulthood with mESC grafts, the ELISPOT response (IFNγ, p < 0.0001) as well as the T cell proliferation (p < 0.0001) was significantly lower than in regular female recipients. This proves that tolerance against H-Y can be induced in the neonatal phase.

Conclusion: Our results clearly indicate that H-Y-associated antigens by themselves are strong enough to cause rejection of MHC-identical mESC grafts. Due to relevant implications for both experimental as well as clinical applications, the immunobiology of the Y-chromosome has to be considered in the development of ESC-based tissue and organ regenerative strategies and therapies.

No conflict of interest has been declared by the author(s).