Public T Cell Receptor β-Chains Are Not Advantaged during Positive Selection1

Studies of human and murine T cells have shown that public TCR β-chain rearrangements can dominate the Ag-specific and naive repertoires of distinct individuals. We show that mouse T cells responding to the minor histocompatibility Ag HYDbSmcy share an invariant Vβ8.2-Jβ2.3 TCR gene rearrangement. The dominance of this rearrangement shows that it successfully negotiated thymic selection and was highly favored during clonal expansion in all animals examined. We hypothesized that such β-chains are advantaged during thymic and/or peripheral selection and, as a result, may be over-represented in the naive repertoire. A sequencing study was undertaken to examine the diversity of Vβ8.2-Jβ2.3 CDR3 loops from naive T cell repertoires of multiple mice. Public TCR β-chain sequences were identified across different repertoires and MHC haplotypes. To determine whether such public β-chains are advantaged during thymic selection, individual chains were followed through T cell development in a series of novel bone marrow competition chimeras. We demonstrate that β-chains were positively selected with similar efficiency regardless of CDR3 loop sequence. Therefore, the establishment and maintenance of public β-chains in the periphery is predominantly controlled by post-thymic events through modification of the primary, thymus-derived TCR repertoire.