Age-related persistent clonal expansions of CD28(-) cells: phenotypic and molecular TCR analysis reveals both CD4(+) and CD4(+)CD8(+) cells with identical CDR3 sequences.

In a small group of subjects we had identified persistent expansions (range 6-72%) of CD4(+)CD8(+) double-positive (DP) peripheral blood (PB) cells which express the CD8 alpha/alpha homodimer. Here, DP cells present in a larger cohort were further investigated and found by FACS analysis to express a single or a dominant TCRBV family. In these subjects, with a mean age of about 64 years, expansions of CD4(+) cells with the same TCRBV family specificity as in the respective DP cells also were consistently detected. TCR heterogeneity of the dominant TCRBV family was specifically evaluated: The amplified CDR3 region was cloned and found to consist of one single or two largely dominant sequence patterns. Furthermore, cloning of the CDR3 region from FACS-sorted DP, CD4(+), or CD8(+) cells indicates that both DP and CD4(+), but not CD8(+) cells, isolated from the same individual possess a striking identity of the CDR3 regions. As indicated by FACS analysis, the clonally expanded cells occur in the CD4(+)CD28(-) cells. Taken together, these results suggest that expanded CD4(+)CD28(-) cells might also acquire CD8 alpha/alpha expression and become DP and imply that CD4 clonality is a more frequent phenomenon than previously suspected. In conclusion, the persistent expansions described in this report represent a novel group of age-related benign clonal expansions of still undefined significance of a rare CD28(-) T cell subset.