T-CELL RECEPTOR V-DELTA-2-C-ALPHA TRANSCRIPTS ARE PRESENT IN THE THYMUS BUT VIRTUALLY ABSENT IN THE PERIPHERY

To investigate whether the V delta 2-(D)-J alpha gene configuration, c haracteristically associated with the major subset of acute lymphoblas tic leukemias in humans, might have a physiologic role in T cell ontog eny, we have looked for V delta 2-C alpha transcripts in the thymus an d peripheral blood of normal donors. Here we show by PCR analysis that these transcripts are virtually absent in the PBMC, whereas they are present in fetal and postnatal thymus. Interestingly, over 80% of 43 V delta 2-C alpha cDNAs randomly isolated from one postnatal thymus app eared to maintain an open reading frame. This suggests that in the thy mus the V delta 2-C alpha. products might be exposed to selective pres sure. Furthermore, in two of three thymuses tested for J alpha. usage, it was found overrepresented in a J alpha element (J alpha 58) locate d 2 kb downstream to a pseudo-J (J alpha 61), known to be a hot spot o f recombination in alpha beta committed cells. A possible alternative pathway to alpha beta T cell differentiation via a V delta 2-J alpha i ntermediate is discussed.