An enlarged subpopulation of T lymphocytes bearing two distinct gammadelta TCR in an HIV-positive patient.

Although T cell clone monospecificity is ensured by several allelic exclusion processes operating at either the genotypic or phenotypic levels, clones expressing two distinct alphabeta or gammadelta TCR have been described in several instances. Thus far, the origin of dual TCR-expressing cells and the homeostatic mechanisms controlling the size of this subset in the periphery remain poorly understood. In the course of a phenotypic analysis of gammadelta T cells in HIV-infected patients, we detected the presence of a T cell subset stained by both Vdelta2- and Vdelta3-specific mAb, which represented a large fraction (up to 16.5%) of gammadelta peripheral blood lymphocytes (PBL) in one HIV patient. The presence of two distinct functional delta chains on these cells was confirmed by phenotypic and molecular analysis of TCR transcripts expressed by Vdelta2+Vdelta3+ T cell clones derived from this patient. For 18 months, the absolute number of these cells varied similarly to the other PBL subsets, before becoming undetectable in blood samples. Moreover, most of these cells expressed CD8 receptors, which are classically found on activated, but not resting, gammadelta T cells. Taken together, these data suggest that dual TCR-expressing T cells are subjected to peripheral expansions and contractions presumably following antigen recognition, which would argue against a systematic counter-selection of these cells during peripheral antigen-driven responses.