UNIQUE PHENOTYPE AND DISTINCT TCR V-BETA-REPERTOIRE IN HUMAN PERIPHERAL-BLOOD ALPHA-BETA-TCR-, AND CD8- DOUBLE-NEGATIVE T-CELLS(, CD4)

TCR-alphabeta+ CD4- CD8 double-negative (DN) T cells represent a small , poorly defined T cell subset in human peripheral blood that has been postulated to be potentially autoreactive. To define some of the char acteristics of this subset of T cells, DN cells and CD4+ and CD8+ sing le-positive (SP) cells were purified from the peripheral blood of six unrelated individuals by a combination of positive selection and deple tion using mAb conjugated to immunomagnetic beads. Purified DN cells w ere found to be enriched in cells expressing HLA-DR and the NK cell ma rker, CD56, when compared to the SP population. Furthermore, in contra st to SP cells that express the adhesion marker CD44, DN cells were fo und to express very little, if any, CD44. When the Vbeta TCR repertoir es of DN and SP (CD4+ and CD8+) cells, determined by quantitative (q) PCR, were compared all three populations were found to be considerably different. Furthermore, several Vbeta segments (Vbeta11 and Bbeta19) were consistently expressed at higher levels on DN cells than on SP ce lls. The TCR repertoires of both DN and SP cells were frequently chara cterized by dominance of one or more Vbeta segments that could in some instances be shown to be restricted to the CD45RO+ (''memory'') popul ation. However, differences in TCR repertoire between DN and SP cells were observed even when CD45RO+ cells were removed before qPCR analysi s. These studies suggest that the TCR repertoires of DN and SP cells a re determined by different selection mechanisms and that DN and SP cel ls are directed against different Ag.