Enhanced susceptibility to apoptosis in T cells recovering after autologous peripheral blood progenitor cell transplantation: Reversal by interleukin-15

T-cell number and competence are profoundly impaired after transplantation of autologous cytokine-mobilized peripheral blood progenitor cells (PBPC). The objective of the present study was to evaluate the occurrence of T-cell spontaneous apoptosis (Aspont) and its modulation in vitro by the interleukin-2 receptor (IL-2R) γ-chain (γc)-signaling cytokine interleukin-15 (IL-15) in the peripheral blood of patients transplanted with autologous PBPC for hematological malignancies. An average 45% ± 6% of CD4+ and 55% ± 6% of CD8+ T cells cultured in the absence of exogenous cytokines underwent Aspont; of interest, IL-15 and, to a lesser extent, its structural cousin IL-2 counteracted T-cell Aspont and upregulated Bcl-2 levels. IL-15 did not rescue T cells from Aspont by promoting proliferation, but rather it acted as a genuine survival factor. Furthermore, T-cell preincubation with a γc-blocking antibody was capable of abrogating both apoptosis inhibition and Bcl-2 induction by IL-15. These in vitro findings suggest that IL-15 might represent a promising immunomodulating agent to improve T-cell function after autologous PBPC transplantation.