Inhibition of human bone marrow and myeloid progenitors by interleukin 2-activated lymphocytes

We have shown that unstimulated and interleukin 2 (IL-2)-activated peripheral blood lymphocytes from both normal donors and cancer patients in remission significantly inhibited the proliferation and granulocyte-macrophage colony formation (granulocyte-macrophage colony-forming cells, GM-CFC) of autologous and allogeneic bone marrow (BM). The inhibition was mediated primarily by CD5+ T cells, although lower levels of inhibition were also displayed by CD56+, CD5- lymphocytes, most of which were CD16-. The CD5+ lymphocytes were also the major effectors responsible for lysis of BM. Inhibition of BM proliferation and GM-CFC colony formation was not dependent on proliferation of the effector cells or cell-to-cell contact, because it was also mediated by a soluble factor produced by IL-2-activated lymphocytes. The relevance of these findings to future approaches to leukemia treatment is discussed.