Background. Patients with advanced hematologic malignancies remain at risk for relapse following reduced-intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (allo-HSCT). We conducted a prospective clinical trial to test whether vaccination with whole leukemia cells early after transplantation facilitates the expansion of leukemia-reactive T cells and thereby enhances antitumor immunity. Methods. We enrolled 22 patients with advanced chronic lymphocytic leukemia (CLL), 18 of whom received up to 6 vaccines initiated between days 30 and 45 after transplantation. Each vaccine consisted of irradiated autologous tumor cells admixed with GM-CSF-secreting bystander cells. Serial patient PBMC samples following transplantation were collected, and the impact of vaccination on T cell activity was evaluated. Results. At a median follow-up of 2.9 (range, 1-4) years, the estimated 2-year progression-free and overall survival rates of vaccinated subjects were 82% (95% CI, 54%-94%) and 88% (95% CI, 59%-97%), respectively. Although vaccination only had a modest impact on recovering T cell numbers, CD8+ T cells from vaccinated patients consistently reacted against autologous tumor, but not alloantigen-bearing recipient cells with increased secretion of the effector cytokine IFN-γ, unlike T cells from nonvaccinated CLL patients undergoing allo-HSCT. Further analysis confirmed that 17% (range, 13%-33%) of CD8 + T cell clones isolated from 4 vaccinated patients by limiting dilution of bulk tumor-reactive T cells solely reacted against CLL-associated antigens. Conclusion. Our studies suggest that autologous tumor cell vaccination is an effective strategy to advance longterm leukemia control following allo-HSCT. Trial registration. Clinicaltrials.gov NCT00442130.
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