CD34⁺ stem cell augmentation of elutriated allogeneic bone marrow grafts: Results of a phase II clinical trial of engraftment and graft-versus-host disease prophylaxis in high-risk hematologic malignancies

Although T cell depletion of allografts used in BMT has reduced GVHD, it has been associated with inferior engraftment and an increased risk of relapse. We have found that T cell depletion by counterflow centrifugal elutriation (CCE) also results in depletion of CD34⁺ stem cells. In order to determine if the discarded CD34⁺ cells would improve engraftment, we undertook a phase II trial of allogeneic BMT in which 110 patients (median age 43) with a variety of hematologic malignancies received CD34⁺ stem cell augmented, elutriated marrow grafts. The T cell-depleted grafts were tightly controlled and contained a mean of 4.3 x 10⁷ mononuclear cells/kg, 3.3 x 10⁶ CD34⁺ cells/kg, 1.5 x 10⁵ CFU-GM/kg and 5.5 x 10⁵ CD3⁺ T cells/kg. Median time to engraftment of granulocytes (> 500/μl) was 16 days and of platelets (> 50,000/μl) was 25 days, comparable to that seen with unmanipulated marrow. No mixed hematopoietic chimerism was observed that was not associated with disease relapse. The four patients (3.6%) who failed to engraft were all at high risk because of prior donor transfusions or underlying marrow disorders. The incidence of GVHD was dependent on the duration of cyclosporin A (CsA) immunosuppression. In patients who received CsA for ≥ 80 days, the incidence of clinically significant acute GVHD (> stage 1) and extensive, chronic GVHD was 5% and 11%, respectively. Peritransplant (≤ 100 day post-BMT) mortality for this group of patients was 15%. Event-free survival in selected subsets of patients compared favorably to previous studies in which patients received unmanipulated marrow allografts.