Bioactive SL-13R Peptide Expands Human Umbilical Cord Blood Hematopoietic Stem Cells and Maintains Long-Term Reconstitution Ability

Hematopoietic stem cell (HSC) transplantation is a curative treatment of hematological disorders that has been utilized for several decades. Although umbilical cord blood (UCB) is a promising source of HSCs, the presence of an insufficient number of HSCs in these preparations limits their use, prompting need for ex vivo HSC amplification. To establish a more efficient method to expand UCB HSCs, we developed the SL-13R peptide and cultured UCB CD34⁺ cells with peptide in serum-free medium containing a cytokine cocktail. Following 9 days of culture with peptide, the number of total cells, CD34⁺CD38^- cells and hematopoietic colonies significantly increased relative to control cells grown without peptide. Transplantation of these cells into immunodeficient NOD/Shi-scid/IL-2Rγ knockout mice confirmed that they possess long-term reconstitution ability. To understand how the peptide promotes HSC expansion, we identified PLEC and ERLIN2 proteins as peptide interactors and undertook loss-of-function analysis to determine whether either was required for peptide function in our culture system. PLEC knockdown UCB CD34⁺ cells cultured with peptide showed a decreased number of hematopoietic colonies relative to peptide-treated, non-knockdown controls. By contrast, ERLIN2 knockdown had little effect in the presence of peptide. This work suggests that PLEC functions in HSC expansion promoted by SL-13R. In summary, we have identified a novel peptide promoting expansion of UCB CD34⁺ cells with long-term reconstitution ability. Its use may facilitate clinical use of UCB HSCs.