Combination of interleukin-2-stimulated lymphocytes and bispecific antibodies that efficiently lyse leukemic cells does not affect bone marrow CD34-positive stem cell function in vitro.

We have recently reported that a combination of lymphokine-activated killer (LAK) cells and bispecific antibodies (BsAb) efficiently lysed autologous and allogeneic leukemic blasts that had surface antigens reactive with the BsAb. The effector cells used in that experiment were peripheral blood mononuclear cells stimulated with interleukin-2 (IL-2) for 2 weeks, with the initial addition of anti-CD3 moAb; these were termed T3-LAK effector cells. In this study, we examined the effects of T3-LAK cells and BsAb on autologous normal CD34+ BM cells in both cytotoxicity and colony formation assays. When T3-LAK cells were incubated with CD34+ BM cells, low levels of cytotoxicity were induced against the CD34+ BM cells and the cytotoxicity was enhanced by the addition of anti-CD3 Fab' x anti-CD 13 Fab' BsAb but not by the addition of anti-CD3 Fab' x anti-CD10 Fab' BsAb. This enhancement appeared to be due to the lysis of CD34+CD13+ BM cells. When T3-LAK cells were preincubated with CD34+ BM cells in the presence or absence of the BsAb and plated for colony assay, neither the T3-LAK cells nor the BsAb affected granulocyte-macrophage or mixed-cell colony formation by CD34+ BM cells. Taken together with our previous finding that T3-LAK cells used in combination with the BsAb markedly inhibited colony formation by leukemic progenitor cells, these results indicate that this combination provides a potential new strategy for CD34+ BM cell purging in autologous BMT.