Hierarchal utilization of different T-cell receptor V beta gene segments in the CD8(+)-T-cell response to an immunodominant Moloney leukemia virus-encoded epitope in vivo

The CD*(+)-T-cell response to Moloney murine leukemia virus (M-MuLV)-associ ated antigens in C57BL/6 mice is directed against an immunodominant gag-enc oded epitope (CCLCLTVFL) presented in the context of H-2D(b) and is restric ted primarily to cytotoxic T lymphocytes (CTL) expressing the V alpha 3.2 a nd V beta 5.2 gene segments. We decided to examine the M-MuLV response in c ongenic C57BL/6 V beta(a) mice which are unable to express the dominant V a lpha 3.2(+) V beta 5.2(+) T-cell receptor (TCR) due to a large deletion at the TCR locus that includes the V beta 5.2 gene segment. Interestingly, M-M uLV-immune C57BL/6 V beta(a) mice were still able to reject M-MuLV-infected tumor cells and direct ex vivo analysis of peripheral blood lymphocytes fr om these immune mice revealed a dramatic increase in CD8(+) cells utilizing the same V alpha 3.2 gene segment in association with two different V beta segments (V beta 3 and V beta 17). Surprisingly, all these CTL recognized the same immunodominant M-MuLV gag epitope. Analysis of the TCR repertoire of individual M-MuLV-immune (C57BL/6 x C57BL/6 V beta(a))F-1 mice revealed a clear hierarchy in V beta utilization, with a preferential usage of the V beta 17 gene segment, whereas V beta 3 and especially V beta 5.2 were used to much lesser extents. Sequencing of TCR alpha- and -beta-chain junctiona l regions of CTL clones specific for the M-MuLV gag epitope revealed a dive rse repertoire of TCR beta chains in V beta(a) mice and a highly restricted TCR beta-chain repertoire in V beta(b) mice, whereas TCR alpha-chain seque nces were highly conserved in both cases. Collectively, our data indicate t hat the H-2D(b)-restricted M-MuLV gag epitope can be recognized in a hierar chal fashion by different V beta domains and that the degree of beta-chain diversity varies according to V beta utilization.