CD3 Depleted Hematopoietic Peripheral Blood Stem Cell Grafts in Children with Refractory Hematologic Malignancies Undergoing Transplantation from Mismatched Related Donors.

Allogeneic HSCT is the only curative intervention for patients with persistent disease or who recur after transplantation; however, these patients are often not considered for HSCT because of their persistent disease or high risk for regimen-related toxicity. We conducted a prospective study for patients who had hematologic malignancies with refractory disease or who relapsed after allogeneic HSCT using mismatched family member donors and a reduced intensity conditioning regimen in an effort to allow GVHD to occur to reduce disease recurrence in this high risk patient population. The conditioning regimen consisted of fludarabine (40 mg/m²/day for 5 days), melphalan (60 mg/m²/day for 2 days), and thiotepa (10 mg/kg/day for one day). One dose of melphalan was omitted in 6 patients who were aplastic at the time of transplantation. OKT3 was administered from day −9 to +17 for prevention of graft rejection. GVHD prophylaxis consisted of MMF initiated on day −2. Rituximab 375 mg/m² was administered on day 0 as EBV prophylaxis. Patients received G-CSF starting on day +6 until ANC ≥ 2000/mm³ for two consecutive days. Peripheral blood grafts were obtained after mobilization with G-CSF and GM-CSF. Grafts were depleted of T-lymphocytes on the CliniMACS device using the anti-CD3 antibody OKT3. 25 patients were treated in this manner: 10 with refractory disease and 15 requiring another allogeneic HSCT (14 had one prior HSCT, one had 2 prior HSCT). For refractory patients, diagnoses included AML (2 secondary AML, 1 persistent disease (PD)) JMML (n=1, PD), ALL (n=3, PD), and NHL (n=3, PD including one after autologous HSCT). For patients who had failed prior allogeneic HSCT, diagnoses included AML (n=7), ALL (n=7), and CML (n=1, blast crisis). Patients had failed HSCT from matched sibling donors (n=5), unrelated donors (n=5), unrelated cord blood grafts (n=2), and haploidentical parents (n=3). Patients were a median of 11 years old at HSCT (range, 1–26). The median number of CD34⁺cells/kg infused was 13.64 x 10⁶/kg (range, 2.23–42.46); the median number of CD3+ cells/kg infused was 0.122 x 10⁶/kg (range, 0.006–0.45). Two patients suffered primary graft rejection: one with refractory JMML recovered with persistent disease after OKT3 and a re-infusion of paternal PBSCs. The second underwent infusion of the original unrelated donor cells and engrafted. The 23 evaluable patients had a median time to ANC ≥ 500/mm³ of 10 days (range, 7–12) post-HSCT. One patient undergoing second HSCT developed secondary graft rejection requiring infusion of original sibling donor marrow. 13 patients developed acute GVHD, but only 2 developed grade 3–4 acute GVHD. 5 patients developed chronic GVHD. None developed VOD. Of the refractory patients, 7 died of relapse and 1 of regimen-related toxicity. Of those undergoing subsequent HSCT, 6 died of relapse and 2 of regimen-related toxicity. With a median followup of 472 days, (range, 147–767), 9 remain alive. Transplantation of mismatched related donor PBSC grafts using OKT3 for ex vivo T-cell depletion following a reduced intensity conditioning regimen produces favorable outcomes with acceptable toxicity in this this high-risk patient population.