In C.B17 mice on a BALB/c background (except C57BL/Ka IgMb), spontaneous leukemia/lymphoma generation also occurs, as illustrated by early generation from anti-thymocyte/Thy-1 autoreactive (ATA) BCR B1a cells in ATAμκ transgenic (Tg) mice and anti-non-muscle myosin IIA (aMyIIA) BCR B1a cells in aMyIIA VHQ52/D/J knock-in (KI) mice6,7,9. The gene discussed is BCR; the disease is lymphoma.