Using this CD200-directed peptide before the subcutaneous delivery of an autologous tumor lysate vaccine doubled survival relative to animals given tumor lysate alone, and was associated with the suppressed expression of inhibitory CD200R receptor on T-cells, and APCs, thereby overriding the CD200-mediated suppression of a glioblastoma microenvironment overexpressing immunosuppressive CD200 protein. The gene discussed is CD200; the disease is glioblastoma.