Class II Major Histocompatibility Complex Transactivator (CIITA) Knockdown Prevents Immune Rejection of Allogeneic Bone Marrow Stem Cells in Cardiac Regeneration

Introduction: Allogeneic young mesenchymal stem cells (MSCs) are excellent candidates for cardiac repair due to their great regenerative potential and immunoprivilege. However, their differentiation increases major histocompatibity complex II (MHC II) expression which induces transition from an immunoprivileged to an immunogenic state. The expression of MHC II is transcriptionally regulated by the class II MHC transactivator (CIITA). We assayed the effects of blocking MHC II upregulation using CIITA gene knockdown (CIITA − ) on survival of allogeneic MSCs in vitro and in vivo . Methods: In vitro, wild-type (WT) or CIITA knockout (CIITA − ) mouse MSCs were induced to differentiate using 5-azacytidine or cytokines. A co-culture system with allogeneic leukocytes was used to evaluate cytotoxicity (LDH release and leukocyte proliferation). Human MSCs (hMSCs) were treated with interferon-γ (INF-γ) to induce MHC II expression. siRNA was used to knockdown CIITA and evaluate immunoprivilege. In vivo, WT or CIITA − MSCs were allogeneically implanted into infarcted myocardium. Allo-antibody formation in the recipients, cell survival, and cardiac function were assessed for the duration of the 5 week experiment. Results: Mouse data - MSC differentiation induced MHC II expression in WT cells whereas CIITA knockout completely prevented MHC II upregulation in differentiated MSCs. When these cells were co-cultured with allogeneic leukocytes, immune rejection was observed in differentiated WT-MSCs but immune tolerance was achieved with differentiated CIITA (-) -MSCs. In vivo : knocking out CIITA in MSCs alleviated allogeneic immune response after cell therapy and prevented the rejection of transplanted cells, improving post-infarction cardiac function when compared to WT MSCs ( P Human data - MHC II upregulation by INF-γ exposure was associated with increased immunogenicity of hMSCs. Knocking down CIITA restored the immunoprivilege in the in vitro co-culture system. Conclusions: CIITA is a key factor which regulates the switch of allogeneic MSCs from an immunoprivileged to an immunogenic phenotype in vitro and in vivo . CIITA knockdown rescued MSC immunoprivilege and prolonged the beneficial effect of allogeneic MSC therapy for cardiac repair.