Ex Vivo Pharmacologic Modulation in a Nutrient-Rich Medium to Accelerate Engraftment of Human Umbilical Cord Blood

Umbilical cord blood (UCB) offers many potential advantages as a source of hematopoietic stem cells (HSCs) for allogeneic transplantation, including ease of collection, rapid availability, flexibility of HLA-matching, lower rates of GvHD and potentially lower relapse rates. However, the low HSC content of UCB compared to other graft sources results in a prolonged time to engraftment, and higher rates of graft failure and early mortality.

Pulse ex vivo exposure of HSCs to 16,16-dimethyl PGE2 (FT1050) has been demonstrated to enhance HSC engraftment potential, which could benefit clinical UCB transplant. FT1050 modulation promotes multiple mechanisms, including increased proliferation, reduced apoptosis, and improved migration and homing [North 2007&2009; Hoggatt 2009]. Improved HSC homing is mediated by induction of CXCR4 gene expression leading to increased cell surface CXCR4. Further optimization of the UCB modulation process demonstrated that incubation with 10µM FT1050 for 2 hrs at 37C resulted in a maximal biological response of the FT1050-UCB (ProHema®).

A Phase 1 trial was performed to evaluate the safety of FT1050-UCB paired with an unmanipulated UCB unit in reduced-intensity double UCBT (dUCBT) [Cutler 2013]. We observed durable, multi-lineage engraftment of FT1050-UCB with acceptable safety. Earlier neutrophil engraftment was observed relative to historical controls (median 17.5 vs. 21 days (historical control), p=0.045), coupled with preferential engraftment of the FT1050-UCB unit in 10 of 12 subjects. A Phase 2 multi-center clinical trial of FT1050-UCB in adult patients undergoing dUCBT for hematologic malignancies was then initiated. Subjects are randomized 2:1 to FT1050-UCB-containing vs. standard dUCBT after high-dose conditioning. The primary endpoint is a categorical analysis of neutrophil engraftment using a pre-specified control median. Data on the initial 11 subjects, of which 8 were randomized to receive FT1050-UCB, continue to demonstrate acceptable safety with adverse events attributed to FT1050-UCB limited primarily to common infusion-related side effects. Of the 8 FT1050-UCB subjects, 1 died prior to neutrophil engraftment, with the remaining 7 subjects engrafting at a median of 28 days vs. 31 days for the 3 control subjects. With median overall follow-up of 16.1 months, 4 of 8 subjects on the FT1050-UCB arm are alive with a median survival not reached (> 11.0 months). 1 of 3 control subjects is alive with median survival of 6.0 months.

During the clinical translation process, the media used during FT1050 modulation of UCB was identified as a key variable. Standard UCB washing media, consisting of a nutrient-free saline solution of low molecular weight dextran and human serum albumin (LMD/HSA), is used clinically to stabilize fragile cells post-thaw by reducing lysis. This media was used in the Phase 1 trial and to initiate Phase 2. Early during the Phase 2 trial, we identified a novel cell-stabilizing nutrient-rich formulation (NRM), containing glucose, amino acids and other HSC-supporting nutrients that promoted full FT1050 modulation of UCB and increased cell viability. The expression of key FT1050-pathway genes was significantly higher with NRM compared to intermediate levels observed with LMD/HSA. Modulation of human CD34⁺ (hCD34⁺) cells with FT1050 in NRM led to an 8-fold increase over LMD/HSA in induced CXCR4 gene expression (20-fold total), which translated to significantly increased surface CXCR4 protein. In vivo homing models demonstrated that UCB CD34⁺ cells modulated with FT1050 in NRM resulted in a 2.2-fold homing increase relative to vehicle (p < 0.001) compared to a 1.6-fold increase with LMD/HSA (p = 0.002), with a significant difference between the two media conditions (p = 0.04). A xenotransplantation study in NSG mice with hCD34⁺ cells modulated with FT1050 in either NRM or LMD/HSA demonstrated a 2-fold increase in circulating hCD45⁺ cells 12-weeks post-transplant with NRM (p = 0.007; unpaired t-test). These findings supported the incorporation of NRM into the FT1050-UCB manufacturing process in order to further improve its clinical engraftment potential. Enrollment of a 60-patient Phase 2 trial has been initiated that incorporates this manufacturing change.