CD133⁺ Hematopoietic Cells Successfully Reconstitute Hematopoiesis Following Autologous Peripheral Blood Stem Cell Transplantation.

CD133 is a unique antigen found on hematopoietic precursor cells, with a limited expression on non-hematopoietic cells. These features make it an attractive marker for obtaining tumor-free hematopoietic grafts. We conducted a prospective clinical trial for patients with solid tumors and lymphomas who required autologous HSCT. 11 children (6 male, 5 female) had CD133+ peripheral blood stem cells (PBSC) collected for subsequent autologous HSCT. The median age was 12.4 yrs (range, 2.2–26). Diagnosis included Hodgkin lymphoma (1 stable disease, 2 PR), neuroblastoma (2 PR), NHL (2PR), Ewing sarcoma (1 stable disease), CNS PNET (1 PR), and desmoplastic small round cell tumor (1 PR). All had received priming chemotherapy with growth factor support. PBSC were collected in 1 or 2 procedures when the absolute CD34+ count was ≥ 40/ul. A stem cell product was cryopreserved as a backup. The PBSC product was processed on the CliniMACS device with positive selection methodology using the CD133 antigen. Prior to CD133 selection, the graft contained 0.3–4.9% CD34⁺ cells and 0.3–4.4% CD133⁺ cells. Following CD133 selection, the graft contained 45.1–98.4% CD34⁺ cells and 45.9–98.8% CD133⁺ cells. The stem cell products contained a median of 5.4 x 10⁶ CD34⁺/kg (range, 2.61–7.89) and 5.3 x 10⁶ CD133⁺/kg (range, 2.54–8.04). One patient who had PBSC collected has not yet proceeded to HSCT. All were conditioned with busulfan 37.5 mg/m²/dose for 16 doses and melphalan 70 mg/m² for 2 doses. A cell dose from 2 x 10⁶ CD133⁺/kg to a maximum of 8 X 10⁶ CD133⁺/kg was infused. G-CSF 5 mcg/kg/day was initiated on day +5 and continued until ANC ≥ 3,000/mm³ for 2 consecutive days. All 10 patients engrafted and no patient required infusion of the back-up stem cell product. No infusion reactions were observed during infusion of the stem cell product. The median time to ANC ≥ 500/mm³ was day + 11 (range, 10–13) for all 10 patients. Of the 8 evaluable patients (1 had hemorrhagic cystitis, 1 severe epistaxis), all achieved an unsupported platelet count of greater than 20,000/mm³ at a median of day + 17 (range, 12–20). This trial demonstrates that infusion of CD133+ hematopoietic cells can reconstitute hematopoiesis following myeloablative HSCT. Further studies are needed to describe the ability of CD133 selection to obtain tumor free hematopoietic grafts.