We developed a new preclinical model of spontaneous T1D in YES mice engineered to express the human co-activation hB7.1 gene in β cells by injecting a HIV-derived recombinant lentiviral vector in which a RIP-hB7.1 transgene has been inserted as previously reported (17), in addition to expression of human MHC and insulin genes instead of the corresponding mouse genes (16). The gene discussed is HLA-C; the disease is type 1 diabetes mellitus.