Preliminary Results of a Pilot Trial of Unrelated Umbilical Cord Blood Transplantation (UCBT) Augmented with Cytokine-Primed Aldehyde Dehydrogenase-Bright (ALDHbr) Cells.

Umbilical cord blood (UCB) transplantation results in delayed myeloid and platelet engraftment, likely due to lower cell dosing with cord blood. One strategy to overcome this problem is to augment the graft with ex vivo expanded cells. Previous studies have shown large expansion of progenitor cells in vitro, but when infused, these cells had little to no effects on hematopoietic reconstitution in the recipient. We hypothesized that these cells may have terminally differentiated in culture, loosing the potential for further expansion in vivo. The ALDHbr fraction of non-erythroid, non-monocytic cells is enriched for stem and progenitor cells. We performed preclinical studies showing that ALDHbr cells cultured ex vivo in SCF, FLT-3 and IL-7 expanded several fold with survival of both differentiated and immature cells. We designed a clinical trial to test whether infusion of primed (but not expanded) ALDHbr cells would be safe and would impact engraftment and survival after unrelated donor UCB transplantation (UCBT). ALDHbr cells were isolated from the 20% fraction of cryopreserved cord blood units (CBU) 6 days before thei nfusion of donor cells. The cells were cultured in SCF/FLT3/IL7 for 5 days. Release criteria included TNC with viability, negative bacterial/fungal cuture taken 2 days before planned infusion and negative gram stain. After written informed consent, patients were assigned to receive sorted cells (n=3) or sorted and primed cells (n=8) augmenting a standard UCBT which was administered with the 80% fraction of the CBU. The study cells were given 4 hours after the standard infusion on day 0. The primary study endpoint was safety and secondary endpoints: engraftment, Graft versus Host Disease (GvHD) and overall survival. Thus far, 11 patients (55% male, 82% Caucasian, median age 1.26 years) with pediatric malignant (n=5) or non-malignant (n=6) diagnoses have been infused. The median precryopreservation cell dose of the CBU was 13.89×10e7/kg and median cell dose infused 9.53×10e7/kg (range 4.13–18.6). The cell yield post sort ranged from 50,000–100,000 ALDHbr cells. After priming, the TNC content remained stable. Cells were infused without clinical reactions. The cummulative incidence (CI) of neutrophil engraftment by day +42 was 90.9% (95% CI 78–100) and no patient experienced graft failure. The CI of platelet engraftment (50K by 100 days) was 79.5% (95% CI 63.6–95.5). The median day to neutrophil (ANC 500/uL) and platelet engraftment (50K) were 17 (range 12–33) and 50 (range 38–90). Median CD4 counts at 100 and 180 days were 123, and 257/uL, higher than those seen with standard transplants. Overall survival at latest followup (1–9 months) was 90.9% (95% CI 73.9–100%). One death occurred in a newborn with a metabolic disease from congenital pulmonary hypertension, unrelated to the study. Although the study population is small, these results compare favorably to a similar population of patients in the COBLT study where the CI of ANC engraftment by day 42 was 78% (p=0.001), platelet engraftment was 50% and overall survival was 57%(p=.2). We conclude that isolation and priming of ALDHbr cells is feasible, infusion is safe and effects on engraftment and survival appear promising.