Ex Vivo Modulation of Mobilized Peripheral Blood: Characterization of HSC and T-Cell Responses to Prostaglandin E2
Authors: Robbins David , Le Thuy , Troung Christopher , Foster Heather , Rezner Betsy , Mitchell Leah , Guerrettaz Lisa , Multani Pratik S. , Shoemaker Daniel 
Published: October 2019

Abstract
16,16 dimethyl prostaglandin E2 (FT1050) was previously identified to be a critical regulator of hematopoetic stem cell (HSC) homeostasis and we hypothesized that a brief ex vivo modulation could improve patient outcomes in umbilical cord blood (UCB) transplantation by increasing the “effective dose” of HSCs. Using preclinical models, we have demonstrated that pulse treating human HSCs with FT1050 significantly enhances the homing and engraftment of donor cells to the bone marrow niche, in part by upregulating CXCR4.
To date, preclinical and clinical translation of this therapeutic paradigm has focused on UCB. In an initial clinical evaluation, ex vivo modulation of UCB with FT1050 (2 hours, on site, just prior to infusion) was found to accelerate neutrophil recovery (median 17.5 vs 21 days, p = 0.045) in adult patients undergoing double UCB transplantation (Cutler, 2013). In this Phase 1b study, we also observed low rates of viral reactivation (17% incidence of CMV viremia vs. 42-67% reported in the literature) and GvHD, suggesting that FT1050 may also be having a therapeutically relevant effect on the T-cell compartment of the treated UCB units. To explore the potential therapeutic application of ex vivo modulation of other allogeneic HSC sources, we conducted a series of in vitro studies characterizing the effect of FT1050 on HSCs and T-cells derived from mobilized peripheral blood (mPB).
CD34+ cells isolated from mPB or UCB were treated with 10μM FT1050 for 2 hours at 37ºC. We showed that FT1050 binds to the EP2 and EP4 receptors on the cell surface, activating adenylate cyclase which results in a rapid increase in intracellular cAMP levels. Results of a competitive antibody binding assay demonstrated robust and comparable increases in cAMP levels in CD34+ cells from both UCB and mPB. Genome-wide expression analysis of FT1050 treated CD34+ cells showed a highly similar expression response in cells isolated from mPB and UCB, including a 20-fold increase in the key HSC homing receptor CXCR4. We also observed similar FT1050-dependent increases in the surface CXCR4 protein levels and significant improvements in transwell migration rates to gradients of SDF-1. Genome-wide expression analysis within the T-cell compartments from both UCB and mPB (e.g., CD8, CD4, NK, Tregs) revealed a highly similar set of FT1050 induced genes which are involved in cell cycle (e.g., CCND1, CCNE1), tolerance (e.g., DUSP5, FLT1) and anti-viral response (e.g., CD56, EFNB2). The results of this preclinical characterization study provides the basis upon which to explore the future use of FT1050 modulated mPB in a clinical setting.

Disclosures
Robbins: Fate Therapeutics: Employment, Equity Ownership. Le:Fate Therapeutics: Employment, Equity Ownership. Troung:Fate Therapeutics: Employment, Equity Ownership. Foster:Fate Therapeutics: Employment, Equity Ownership. Rezner:Fate Therapeutics: Employment, Equity Ownership. Mitchell:Fate Therapeutics: Employment, Equity Ownership. Guerrettaz:Fate Therapeutics: Employment, Equity Ownership. Multani:Fate Therapeutics: Employment, Equity Ownership. Shoemaker:Fate Therapeutics: Employment, Equity Ownership.