Cytotoxic and proliferative functions of T lymphocyte clones derived very shortly after allogeneic bone marrow transplantation.

In a search for mechanisms of potential graft-versus-leukaemia (GVL) activity after allogeneic bone marrow transplantation (BMT), peripheral lymphocytes from five patients (four chronic myeloid leukaemia, one acute lymphoblastic leukaemia) 24-39 days post-transplant were precultured with pretransplant host leukaemia cells and then cloned by limiting dilution with interleukin-2 (IL-2). Clones obtained were exclusively CD3+ CD56-, carried the alpha/beta form of the T cell receptor for antigen, and were mostly (88% of 138) CD4+. None of 143 clones, including CD8+ clones, convincingly lysed host pretransplant cells, although 35 (24.5%) manifested lytic potential in lectin-mediated cytotoxicity assays. Measuring the proliferative responses of 118 of these clones in the presence of exogenous IL-2 revealed that a small number of clones reacted more strongly to host leukaemia than to unrelated leukaemias or B lymphoblastoid cell lines. In the two cases tested, the donor's untransplanted lymphocytes cloned under the same conditions as post-transplant cells did not generate any clones reacting preferentially with host leukaemia cells. These results may suggest that some T cells appearing shortly after allogeneic BMT could potentially mediate anti-leukaemia activity not associated with cytolysis of target cells.