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). This evidence concerns the gene INS and type 1 diabetes mellitus.