Continued expression of recombination‐activating genes and TCR gene recombination in human peripheral T cells

It has been reported that a small population of peripheral T lymphocytes are capable of expressing V(D)J recombinase and initiating secondary V(D)J rearrangements. To determine whether RAG‐expression and secondary TCR gene recombination in peripheral T cells are an antigen‐driven process in secondary lymphoid tissues, we examined naive CD4+ T cells, activated/memory CD4+ T cells, and germinal center T cells from human tonsils. Our results showed that low levels of RAG‐1 and RAG‐2 mRNA were present in all T cell subpopulations except CD3+/CD4– T cells. LM‐PCR analyses for double‐strand DNA breaks showed that all the T cell subsets expressing RAG genes contain double‐strand signal break ends, indicating ongoing TCR gene recombination. Continued RAG gene expression, introducing and repairing of double‐strand DNA breaks at the TCR loci in the periphery may have significant implications in the development of some T cell neoplasms.