Identification of an H-2 K^b-presented Moloney murine leukemia virus cytotoxic T-lymphocyte epitope that displays enhanced recognition in H-2 D^b mutant bm13 mice

Upon infection with the Moloney murine sarcoma virus-murine leukemia virus (MuLV) complex, H-2^b C57BL/6 (B6) mice respond with a class I D^b-restricted cytotoxic T-lymphocyte (CTL) response, which protects against virus-induced tumorigenesis. In the B6-derived D^b mutant B6.CH-2^bm13 (bm13) strain, part of the class I D^b antigen-presenting groove is shaped by a class I K^b- encoded sequence. Like B6 mice, bm13 mice reject Moloney virus-induced tumors, but the protective CTL response is K^b restricted. In this study we show enhanced levels of Moloney MuLV-specific CTLp with a restriction for K^b in bm13 mice. Through the use of CTL clones from Moloney virus-immunized bm13 mice, the class I K^b-presented CTL epitope was identified. The epitope is located in the Moloney virus gp70 envelope protein region {Moloney envelope, amino acids 189 to 196 [Mol env (189-196)]}, SSWDFITV and has the K^b allele-specific binding motif. The D^bm13 molecule does not present the env(189 to 196) epitope to K^b-restricted bm13 CTL. In B6 mice, Mol env(189- 196)-specific CTL could be induced by peptide vaccination. B6 mice thus have CTL precursors specific for this epitope but at considerably lower levels than do bm13 mice. We hypothesize that additional positive selection of K^b- restricted CTL on the D^bm13 molecule in bm13 mice explains this difference in precursor frequencies. We examined related strains of MuLV for the presence of Mol env(189-196) sequence equivalents. Rauscher, Friend, and AKV MuLV-encoded Mol env(189-196) epitope equivalents were properly recognized in cytotoxicity assays, both as synthetic and as endogenously expressed (Rauscher MuLV) peptides. In contrast, the mink cell focus-forming virus MuLV-encoded epitope equivalent, lacking a K^b anchor residue, was not presented for CTL recognition and hence can be excluded as an important CTL epitope for mink cell focus-forming viruses.