Successful generation of p190-BCR ABL-specific T-cell lines for prophylaxis/treatment of minimal residual disease in HSCT recipients with Ph+ acute lymphoblastic leukaemia

Recent studies by our groups have demonstrated the presence of BM-homing, BCR-ABL specific cytotoxic T cells (CTL) in Philadelphia chromosome positive acute lymphoblastic leukemia (Ph+ALL) patients during sole Imatinib mesylate maintenance treatment, that inversely correlated with minimal residual disease (MRD). This observation supports the notion that anti-tumor T lymphocytes may effectively participate in the control of Ph+ leukemic proliferation, and represents the rationale for a BCR-ABL-targeted cell therapy approach to prophylactically treat leukemic relapse after HSCT in patients with Ph+ALL. The aim of this study was to evaluate the feasibility of expanding BCR-ABL specific CTL from HSCT donors, to be employed as specific DLI after HSCT for Ph+ALL. We conducted scale-up experiments to validate an in vitro culture method to expand BCR-ABL specific CTL from HSCT donors, by peripheral blood mononuclear cell (PBMC) stimulation with 9-20mer peptide pools derived from the p190 BCR-ABL fusion region. T-cell lines, that included a median 70% CD4+ and 29% CD8+ T lymphocytes, were successfully generated from 5/6 individuals. The T-cell lines showed specific INFg production in Elispot assays consistently higher (median 130 SFU/10e5 cells, range 0-198) than non-cultured donor PBMC (median 4 SFU/10e5 cells). In a standard 51chromium release assay, 5 of 6 T-cell lines presented specific cytotoxic activity against PHA blasts pulsed with BCR-ABL peptide mix (median lysis 30%, range 6-65), CD3-redirected activity against P815 cells (median lysis 38%, range 36-52) with minimal residual alloreactivity (median lysis 4%, range 0-15). Our data indicate that BCR-ABL-specific T-cell lines with limited alloreactivity may be expanded from HSCT donors after stimulation with BCR-ABL fusion region-derived peptides. Their efficacy in containment of MRD after allogeneic HSCT for Ph+ALL remains to be evaluated in clinical trials.