Microvesicles secreted by CoCl₂-primed mesenchymal stromal cells boost the functionality of hematopoietic stem cells...

Rapid hematopoietic regeneration post-hematopoietic stem cell transplantation (HSCT) is vital for prompt immune recovery, infection prevention, and averting complications such as anemia and thrombocytopenia. The hematopoietic stem cells (HSCs) produce mature blood cells through a process known as hematopoiesis that is tightly regulated by the hypoxic bone marrow microenvironment. However, the limited number of HSCs present in the bone marrow is one of the major challenges for successful HSCT. Hence, developing novel ex vivo expansion strategies that address the clinical limitations of the current HSCT becomes imperative. Our prior work demonstrated that priming of mesenchymal stromal cells (MSCs) with a hypoxia-mimetic compound, cobalt chloride (CoCl_2; CoCl₂-MSCs) promotes the expansion of functional HSCs co-cultured with them. In this study, we investigated the role of CoCl₂-MSCs-derived microvesicles (Co-MVs) and exosomes (Co-Exo) in regulating hematopoietic stem and progenitor cells (HSPCs). MVs and exosomes from naïve and atmospheric hypoxia (1% O₂)-primed MSCs were used as controls. We found that CoCl₂ induces the expression of Jagged-1-specific mRNA in the MSCs, which gets selectively partitioned into the Co-MVs. These Co-MVs, in turn, upregulate the expression of Notch2 and Hes1 in the HSPCs cultured with them. Furthermore, Co-MVs induce the expression of quiescence and self-renewal genes in the HSPCs and boost their long-term engraftment ability. These beneficial effects of Co-MVs on the functionality of HSPCs hold significant clinical implications as cell-free and cost-effective therapeutics in improving the success rate of HSCT.