Processing of G-CSF Mobilized Peripheral Blood Hematopoietic Progenitor Cells (PB-HPC) from Matched- Related or Unrelated Donors Undergoing CD34 Enrichment with T Cell Addback in Children, Adolescents and Adults with Malignant and Nonmalignant Diseases: Rapid Engraftment, Immune Cell Reconstitution and Sustained Donor Chimerism

Sixty to seventy percent of patients undergoing HLA identical transplants will develop grade II-IV acute GVHD, despite using prophylactic immunosuppressants. Several studies have demonstrated that manipulation utilizing ex-vivo CD34+ positively selected grafts result in 4-5 log T-cell depletion with limited T-cell add back follow with early engraftment and decreased aGVHD (Silva et al, Blood Journal, 2015 & Chakrabarti et al, BMT, 2003). We previously demonstrated the safety and efficiency of CD34+ enriched cells with 2 × 105 CD3 (MNC)/kg add back in pediatric SCD patients resulting in rapid engraftment, donor chimerism, and low incidence of aGVHD (Geyer/Cairo et al, BJH, 2012). Utilizing CD34+ cell selection, children, adolescents, and adults with a matched or partially matched family donor or matched unrelated donors allogeneic PB-HPC transplant can safely receive and tolerate with a low incidence of serious (Grade III/IV) acute and chronic GVHD. Patients received CD34+ enriched products processed by using the CliniMACS CD34+ Reagent System (Miltenyi Biotec, Bergisch Gladbach, Germany). The CD34+ enriched HPC product was either a fresh infusion or cryopreserved and stored until time of transplantation. A target of 5 × 106 CD34+enriched/kg recipient weight with a T cell add back of 2 × 105 CD3+/kg (MNC) was infused. Sixteen patients underwent BMT with median age of 55 years (23 months to 71 years). Patients' disease status was as follows: complete remission (CR) 2 in four AML patients, CR1 in 9 AML patients, Lymphohistiocytosis (n=1), Macrophage Activating Syndrome (n=1), CR2 in one Non-Hodgkins Lymphoma patient. Nine patients received 10/10 HLA-matched unrelated donor BMT, two 9/10 HLA-matched unrelated donors, five had 6/6 HLA-matched sibling transplant. PB-HPC products contained 0.59 × 1010 CD3/kg (±0.23), and 6.77 × 106 CD34/kg (±1.27). After CD34 enrichment, the PB-HPC CD34% recovery was 73.1±3.08% with a log T cell depletion of 4.9 (±0.11). The target transplant dose per patient was 5 × 106 CD34 enriched/kg. Sixteen and patients had myeloid and 13 patients had platelet engraftment with a median of 11.5 days and 16 days, respectively (Fig. 1a and Fig. 1b). Two patients died prior to platelet engraftment one due to multi-organ system failure following septic shock and the other patient due to refractory AML. One patient died after myeloid and platelet engraftment secondary to disease progression. Early and late peripheral blood chimerism were ≥ 98.4% at 19.9 days (±12) and 92.5% at 180 days (n=4). The probability of grade II-IV aGVHD was 20% (CI95: 0.1-66.9) (Fig 2). One patient had grade II skin aGVHD and one patient had grade II gut aGVHD. No patient had cGVHD. This study demonstrates the safety and efficiency of CD34+ enriched PB-HPC products with T-cell addback in AlloSCT recipients with a low probability of acute GVHD.