Nicotinamide (NAM) Modulates Transcriptional Signature of Ex Vivo Cultured UCB CD34+ Cells (Omidubicel) and Preserves Their Stemness and Engraftment Potential

Historical efforts at expansion of umbilical cord blood (UCB) derived CD34+ hematopoietic stem cells (HSCs) ex vivo with cytokines yielded large numbers of progenitors for transplantation but impaired their long-term engraftment. We used nicotinamide (NAM), an allosteric inhibitor of NAD-enzymes, to create omidubicel, an investigational cell therapy designed to improve the expansion of CD34+ HSCs for bone marrow transplant. A Phase 1/2 clinical study in patients with high-risk hematologic malignancies showed rapid neutrophil engraftment in patients compared to historical controls [1]. We hypothesized that NAM treatment maintains the stemness and engraftment potential of omidubicel, which is associated with clinical benefit [2]. We performed transcriptome analysis to discern the mechanism of action of NAM after ex vivo expansion of CD34+ cells in omidubicel compared to CD34+ controls. Analysis revealed that HSCs expanded with cytokines alone led to an increase in genes responsible for cell proliferation, differentiation, and apoptosis, and in the production of reactive oxygen and nitrogen species (ROS, RNS), and matrix metalloproteinases (MMPs), all of which were attenuated by NAM. Transcription factor (TF) enrichment analysis demonstrated that NAM modulated TFs critically involved in activation of pathways for HSC differentiation, apoptosis, and migration. Specifically, NF-kB, C-Jun, LXR/RXR and PPARα/RXRα, and mTor signaling were all reduced in NAM-treated CD34+ cells compared to controls. NAM treatment upregulated genes linked to cellular metabolism including the Sirtuin family genes, TCA cycle genes, and HIF1a. NAM upregulated genes responsible for telomerase expression further validating our hypothesis that NAM preserves cell stemness. In summary, these data provide further scientific rationale for the favorable clinical engraftment and patient outcomes observed in the Phase 1/2 clinical study of omidubicel. An international, randomized, multi-center Phase 3 study of omidubicel in patients with high-risk hematologic malignancies is underway [2]. [1] Horwitz ME. et. al., J Clin Oncol. 2019 Feb 10;37(5):367-374. [2] ClinicalTrials.gov identifier NCT02730299.