Umbilical Cord Blood (UCB) Graft T-Cells Correlate with Myeloid Recovery in Adults with Hematologic Malignancies Treated with Reduced Intensity Conditioning (RIC) and Single Unit Infusion.

Experience with unrelated allogeneic UCB stem cell transplantation in the non-myeloablative setting is limited because of concerns of graft failure due to limited cell content. Dual UCB graft infusion has been explored to overcome cell dose limitations, but influence on engraftment is unclear. This single institution phase I trial examined RIC followed by single UCB transplantation for patients unable to tolerate fully myeloablative regimens and lacking a matched adult donor. Conditioning consisted of TBI 200 cGy, fludarabine 175 mg/m², cyclophosphamide 2 gm/m², ATG 60 mg/kg. Trial design specified selection of UCB grafts to be matched at 4/6 HLA loci or better with one unit infused if cryopreserved nucleated cell dose exceeded 2.5 x 10⁷/kg recipient weight. If no adequate single UCB unit to meet these criteria was available, study patients received 2 UCB units containing a combined cell dose exceeding 1.5 x 10⁷/kg. Grafts were analyzed via flow cytometry post thaw for stem cell and lymphocyte expression of surface antigens, among them CD4, CD8, CD7, CD34, CD38, CD45RA, CD45RO. 23 patients have been enrolled, the majority diagnosed with AML (n=17). Median age was 47 (range 25–68) years. Single UCB units meeting stated criteria were identified for all but one study patient, who was excluded from graft analysis. The time to engraftment was measured from the date of transplantation to the date of 3 successive days ANC≥500/μL attained. In addition, we assessed time to peripheral blood donor lymphocyte chimerism ≥ 60%. Patients were censored at the date of last follow-up or the date of death. 94% (95%CI: 77-.99%) of patients achieved ANC≥500/μL by T+36 with median of 26.5 ( range 11–55) days. 68% (95%CI: 48–85%) of patients (n=15) achieved >60% donor derived chimerism by median of 22 (range 14–35) days. Median cryopreserved and infused total nucleated cell dose was 2.85 x 10⁷ and 2.5 x 10⁷ cells/kg, respectively. Median infused CD34 cell dose was 1.71 (range 0.21–5.39) x 10⁵ cells/kg. By univariate analysis the dose of infused UCB graft T-cells including CD4 and CD8 T-cells co-expressing CD45RO, and CD34 stem cells co-expressing CD7 and CD38 correlated with neutrophil recovery, p=0.046, 0.008, and 0.033, respectively. Median overall survival at this early interim analysis has not been reached; with 86% and 65% survival at 3 and 24 months, respectively. Event free survival is 78% and 44.5% at 3 and 24 months, respectively. In summary, in this heavily pretreated group of advanced age patients, RIC and single unit unrelated allogeneic UCB stem cell transplantation is safe. Identification of a single UCB graft of HLA match 4/6 meeting cell dose requirement 2.5x10⁷/kg is identified in the vast majority of full size adult patients. Engraftment and survival rates are higher than reported in single UCB transplants following administration of myeloablative regimens and similar to recent reports for RIC with double UCB graft infusion. The potential benefit of infusion of 1 vs. 2 UCB units after RIC in adult patients remains to be fully evaluated.