By targeting genomic sequences in the constant regions of the endogenous α or β subunits of the TCR or disrupting HLA-A locus of MHC gene complex, the expression of TCR or the HLA class I antigens is abrogated, and the resulting T cells are not capable of recognizing allogeneic antigens, thus leading to the elimination of GVHD. This evidence concerns the gene HLA-A and graft versus host disease.