All-trans retinoic acid (ATRA) enhances maintenance of primitive human hematopoietic progenitors and skews them towards myeloid differentiation in a stroma-noncontact culture system

OBJECTIVE: We have previously shown that hematopoietic progenitor cells (HPCs) from umbilical cord blood (UCB) can be maintained in a cytokine-supplemented stroma-noncontact (SNC) system. Here, we tested if all-trans retinoic acid (ATRA), known to improve expansion of murine hematopoietic stem cells, would enhance human HPC maintenance in a SNC culture system. METHODS: CD34+CD38-Lin- cells from UCB were cultured in transwells above AFT024 in the presence of Flt-3 ligand (FLT) and thrombopoietin (TPO), with or without ATRA. Total nucleated cells (TNC), colony-forming units (CFUs), long-term culture-initiating cells (LTC-ICs), myeloid-lymphoid initiating cells (ML-ICs) and SCID repopulating cells (SRCs) were evaluated 1 to 5 weeks after culture. RESULTS: All-trans retinoic acid (1 mumol/L) reduced expansion of CD34+CD38-Lin- TNC and CFUs after 2 to 5 weeks of culture. However, it significantly increased LTC-IC expansion after 1 to 3 and, even more so, 5 weeks of culture. ATRA also increased recovery of more primitive ML-ICs and SRCs. Increased HPC recovery appeared dependent on the presence of stromal cells, as LTC-IC expansion was significantly reduced when ATRA was added to stroma-free cultures. CONCLUSION: All-trans retinoic acid increases expansion of early HPCs in a stromal cell-dependent fashion.