CD4⁺ bias in T cells cloned from a CML patient with active graft versus leukemia effect

Background: The ability to generate a GvL response by infusion of donor leukocytes (DL) in patients following relapse after BMT is now well documented and has been demonstrated to be particularly effective in patients with CML. Methods: We generated T-cell lines from a patient who was undergoing an active GvL response following withdrawal of immunosuppression for cytogenetic relapse of CML. Cryopreserved pre-transplant leukemic cells were used as stimulators, to generate T-cell lines and oligoclonal lines from the lymphocytes. In total 38 sub-lines were generated from different bulk cultures. The lines were tested for their proliferative and cytotoxic capability to patient pre-transplant leukemic cells, PHA-transformed lymphoblasts, allogeneic CML cells, and autologous and allogeneic B-LCL. Results: Four of the cloned lines tested recognized the patient's pre-transplant leukemic cells. Specifically, two were both cytotoxic and proliferative in response to patient leukemic cells and two were cytotoxic only. Six clonal lines recognized PHA blasts only and were proliferative, one was specific for PHA blasts and CML cells. The sub-lines were phenotyped for cell-surface markers and all were CD4⁺ CD8^- CD 16/56^-. The proliferative response of the leukemia-specific clonal lines could be blocked with anti-MHC Class II MAbs. Discussion: These data suggest that CD4⁺ cells play a crucial role in mediating the GvL effect in CML patients. Our observations can be used to delineate strategies for enhancing and investigating the GvL effect in CML.