Improved Immune Reconstitution with Low Incidence of Severe Graft-Versus-Host Disease after Transplantation of CD34⁺ or CD133⁺ Enriched Stem Cells with Add-Back of Ten Million T-Cells Per Kg.

Unrelated donors are commonly used for hematopoietic stem cell transplants, but graft-versus-host disease (GVHD) is a major problem. We investigated whether transplantation of CD34⁺ or CD133⁺ enriched stem cells with add-back of ten million T-cells per kg from unrelated donors would prevent acute GVHD in pediatric patients in combination with pharmacologic immunosuppression. Eighteen patients (1 CML in second chronic phase, 2 MDS, 4 ALL in CR1, 4 ALL in CR2, 1 JMML, 1 AML in CR1, 3 AML in CR2, 1 Wiskott-Aldrich syndrome and 1 NHL in CR2) were transplanted with G-CSF mobilized peripheral blood stem cells (PBSC) from HLA-matched unrelated donors (n = 18). Median of age was 8.9 years (0.5 to 18 years). Conditioning regimens were performed according to national therapy protocol guidelines. On the day of transplant patients received a median of 13.5 (4.5 to 30.0 x 10⁶) CD34⁺ or CD133⁺ enriched stem cells and an aliquot of unmanipulated PBSC containing 10 x 10⁶ T-cells per kg. GVHD prophylaxis consisted of cyclosporine A (CSA) and short course methotrexate (MTX) on day +1, +3 and +6. Engraftment was rapid with a median of 19.6 days in sixteen patients. Two patients failed to engraft at first. However, full donor chimerism and stable engraftment was achieved in both patients after cessation of CSA treatment and an additional stem cell boost without any reconditioning. One patient with ALL developed acute GVHD grade III (skin and gut) after cessation of CSA treatment, but responded well to treatment with CSA and steroids. None of the other 17 patients developed acute GVHD > grade I. Thirteen are alive and well with a median follow-up of 578 days (101 to 1095 days). Three patients died of severe infectious complications and two due to relapse (JMML, AML). Compared to a historical control group of patients transplanted with highly purified CD34⁺ selected cells, the group with add-back of 10 x 10⁶ T-cells per kg showed significantly higher T-cell counts (p=0.008, Wilcoxon Rank sum test) on day 90 after transplantation with a median number of six T-cells/μl in the control group and a median number of 294 T-cells/μl in the study group. We conclude that add-back of 10 x 10⁶ T-cells per kg in combination with CSA and short course MTX improves T-cell recovery and appears to be a safe T-cell dosage regarding acute GVHD in the setting of allogeneic peripheral blood stem cell transplantation from unrelated donors.