Cord blood CD34+ cells expanded on Wharton's jelly multipotent mesenchymal stromal cells improve the hematopoietic engraftment in NOD/SCID mice

Objective This study aims to investigate the capability of Wharton's jelly multipotent mesenchymal stromal cells (WJ-MSC) to support the in vitro expansion of hematopoietic stem/progenitor cells (HSPC) derived from cord blood (CB) in the absence of exogenous cytokines, and the effect on engraftment of the expanded cells in a mouse model. Methods CB-CD34+ cells were seeded on WJ-MSC layer and cultured in HP01 serum-free medium. Day-7 and day-13 expanded cells were transplanted in NOD/SCID mice. After 8 wk, engraftment was evaluated in mouse bone marrow as percentage of human CD45+ cells. Results CD34+ population was expanded without increasing the differentiation rate. Co-culture increased the expansion of the CD34+ cells by 2.0 and 7.3 times after 7 and 13 d, respectively, and maintained the CD34+ cells up to day 20. In particular, earlier CD34+/CD90+ and CD34+/CD33− subtypes were increased. An advantage of the day-7 co-cultured HSPC in respect of HSPC at day 0 in the engraftment of NOD/SCID mice was obtained both as percentage of mice engrafted (100% vs. 75%) and as percentage of chimerism. Conclusions Although the increase in hematopoietic progenitors is not dramatic as in the presence of added cytokines, this study demonstrates the effectiveness of the WJ-MSC not only to preserve the CD34+ population but also to improve the repopulating efficacy of the amplified HSPC, also in the absence of added cytokines and growth factors.