Priming of thymus-grafted, bone marrow-reconstituted, RIP-mOVA mice does not lead to the generation of OVA-specific CTL. Mice were thymectomized at 4–5 wk, reconstituted with B6 bone marrow at 7 wk, and then grafted with a B6 neonatal thymus at 11 wk. After another 19 wk, to allow T cell reconstitution, a RIP-mOVA mouse (B) or a nontransgenic littermate (A) was injected with OVA peptide in complete Freund’s adjuvant. Then, 1 wk later, their spleens were removed and cultured in vitro with OVA-loaded spleen as previously described (8). After another 6 days, cultures were assayed for OVA-specific lytic activity by assessing their ability to lyse the OVA257–264 peptide-coated EL4 cells (■) or uncoated EL4 cells (□).