Rapid engraftment after allogeneic transplantation using CD34-enriched marrow cells

Bone marrow cells expressing the surface antigen CD34 comprise approximately 1% of harvested marrow and are highly enriched for marrow progenitor cells, including the cells believed to be responsible for long-term engraftment following hone marrow transplantation (BMT). Selection of CD34-expressing cells was applied in allogeneic BMT (alloBMT) to decrease the number of T lymphocytes in the infused marrow in an attempt to prevent severe graft-versus-host disease (GVHD). We report 14 patients who underwent HLA-identical sibling-matched alloBMT with marrow-enriched for CD34 cells using the Isolex 300 SA device. Patients received total body irradiation, thiotepa, cyclophosphamide, antithymocyte globulin and methylprednisolone prior to marrow infusion. No post-transplantation immunosuppressive therapy was given except for a 5-week course of steroids. The purity of the infused marrow was 64.9 ± 6.0% (mean ± s.e.m.) CD34-positive cells and patients received a mean of 1.24 ± 0.21 x 10⁶ CD34 cells/kg. A mean of 9.4 ± 1.7 x 10⁴ CD3 T cells/kg were present in the CD34-enriched product, representing a 2.7 ± 0.1 log depletion. There were no graft rejections and patients achieved a sustained absolute granulocyte count of > 500 in a median of 10.5 days and a sustained platelet engraftment of > 20,000 untransfused in a median of 27 days. Patients were discharged a median of 21.5 days after marrow infusion. There were no instances of grade III or IV graft-versus-host disease (GVHD) and no unexpected adverse events during the transplant hospitalization. With a median follow-up of 12 months, the estimated 100 day survival is 86 ± 9%. CD34 selection in alloBMT permits rapid engraftment without unanticipated toxicities.