Abstract 124: Parthenogenetic Stem Cell-derived Cardiomyocytes Express Major Histocompatibility Complex-I only after Inflammatory Stimulation

Background: Pluripotent parthenogenetic stem cells (PSCs) can be directed towards a cardiac fate and utilized in tissue engineered heart repair. In vivo applications of tissue engineered allografts are compromised by expression of mismatching major histocompatibility complex proteins (MHC; encoded in the murine H2 locus). Here we investigated whether PSC-derived cardiomyocytes (CM) express MHC-I. Methods: Mouse PSCs (A3-line from B6D2F1 strain with haploidentical H2Kd-locus) expressing a CM-specific neomycin-resistance and GFP were differentiated and purified for CM by addition of G418 (85% purity by FACS for actinin). To simulate heart muscle biology in vitro, we made use of engineered heart muscle (EHM) constructed from PSC-derived CM (75%), growth-inhibited murine embryonic fibroblasts (MEF (25%); NMRI mice), and collagen type I. MHC class-I H2Kd (MHC-I) expression was assessed on CM and Non myocytes before EHM assembly and from enzymatically digested EHMs (cultured for 10 days) by FACS. Interferon gamma (IFNγ) was added for 48 h to stimulate MHC-I expression. As a reference, we investigated MHC-I expression in CM from neonatal mice and adult mouse hearts by FACS and by immunofluorescence staining. Results: EHM showed a positive ionotropic response to beta-adrenergic stimulation which could be reduced by muscarinergic stimulation. A3-CM, in contrast to Non myocytes, showed negligible expression of MHC-I (1±0.5% vs. 60±10% positive cells; n=3). EHM culture did not change MHC-I expression in CM. IFNγ treatment resulted in a marked increase of MHC-I-expression in CM monolayer culture (40±6%; n=3) and in EHM (30±8%; n=3). For comparison, 30% (n=2) neonatal CM expressed MHC-I while MHC-I was not detectable in adult CM. Conclusion: PSC-derived CM show a similarly low expression of MHC-I as adult CM and respond with MHC-I upregulation to IFNγ stimulation. This suggests a mature immunological response in PSC-CM with important implications for in vivo applications, i.e., MHC-I matching will likely be a prerequisite for successful allografting of PSC-EHM.