Restricted TCR-α CDR3 Diversity Disadvantages Natural Regulatory T Cell Development in the B6.2.16 β-Chain Transgenic Mouse

Abstract

To date, analysis of mice expressing TCR-beta transgenes derived from CD4(+) T cell clones has demonstrated equivalent or higher TCR diversity in naturally occurring regulatory CD4(+) T cells (Tregs) versus conventional CD4(+) T cells (Tcons). However, TCR-alpha-chain diversity in these mice may be influenced by the inherent bias toward the CD4(+) lineage in the selected repertoires. We wished to determine whether the choice of TCR-beta-chain influences the relative diversity of the Treg and Tcon repertoires, examining as a model the B6.2.16beta-transgenic mouse, in which the fixed beta-chain is derived from a CD8(+) T cell clone. B6.2.16beta Treg thymocytes showed significantly lower TRAV17 (AV9) CDR3 sequence diversity than both syngeneic Tcon thymocytes, and Treg and Tcon thymocytes from wild-type C57BL/6 (B6) mice. The ratio of single-positive CD4(+)/single-positive CD8(+) thymocytes in B6.2.16beta mice was similar to that in B6, yet both the proportional frequency and absolute number of CD4(+)Foxp3(+) cells was significantly lower in the thymi and peripheral lymph nodes of B6.2.16beta mice. Furthermore, B6 + B6.2.16beta-->B6 mixed bone marrow chimeras revealed that the transgenic beta-chain disadvantaged Treg development in a competitive environment. These data underline the importance of the beta-chain in assessments of Treg alpha-chain diversity and provide further support for the notion that interclonal competition for entry into the Treg lineage is a significant factor in determining the composition of this lineage.