Allogeneic cell therapy in murine B-cell leukemia (BCL1): 2. The role of non-activated and rIL-2-activated CD4+ and CD8+ T cells in immunotherapy for leukemia

Graft-versus-leukemia (GVL) effects play a key role in the elimination of residual leukemia cells in the course of allogeneic bone marrow transplantation (alloBMT). GVL effects can also be induced by donor lymphocyte infusion following alloBMT. We have investigated the role of CD4+ and CD8+ T cells in the development of GVL in mice with B-cell leukemia/lymphoma (BCL1) following allogeneic cell therapy. Sublethally irradiated (C57BL/6 x BALB/c)F1 mice were intravenously inoculated with 10(5) BCL1 cells and given untreated or recombinant human Interleukin-2 (rIL-2)-activated C57BL/6 spleen cells. Effective elimination of clonogenic BCL1 cells was confirmed by adoptive transfer of spleen cells obtained from treated mice into secondary BALB/c recipients. GVL effects were maintained after inactivation of CD4+ cells with monoclonal anti-CD4 antibodies in the inoculum, while inactivation of CD8+ cells with monoclonal anti-CD8 antibodies resulted in complete loss of GVL effects induced both by resting and rIL-2-activated allogeneic spleen lymphocytes. These results indicate that Thy-1 cells play the major role in the induction of GVL effects, mediated by C57BL/6 effector T cells in this model. Since the number of natural killer (NK) cells also increased during in vitro culture with rIL-2, their contribution, especially that of CD8+ NK cells, in GVL effects mediated by rIL-2-activated CD8+ cells cannot be ruled out.