Human T cell leukemia virus type II increases telomerase activity in uninfected CD34(+) hematopoietic progenitor cells

The aging process of long-term self-renewing hematopoietic stem/progenitor cells is not yet completely understood and recent studies on antiapoptotic cell pathways have demonstrated a close linkage between telomerase activati on and Bcl-2 deregulation in human cancer cells. The present work shows tha t human T cell leukemia virus type II (HTLV-II) Mo virions that have origin ated from the T cell line (C344), but not from the B cell line (BJAB), are critically involved in mediating survival and growth effects on hematopoiet ic precursors (represented by both the TF-1 CD34(+) cell line and by periph eral blood-derived CD34+ cells) through the maintenance or enhancement of t elomerase activity and the induction of bcl-2 expression. In addition, usin g an interleukin-3-dependent TF-1 cell line, it was demonstrated that IL-3 deprivation was sufficient to influence the levels of telomerase activity a nd Bcl-2 expression in CD34+ cells. Taken together, these findings suggest that, in appropriate conditions, extended hematopoietic progenitor cell sur vival and proliferation following HTLV-II exposure depends on a synergistic interaction between up-regulation of Bcl-2 and activation of telomerase ac tivity.