Ex vivo manipulations alter the reconstitution potential of mobilized human CD34+ peripheral blood progenitors

The phenotype and functions of CD34⁺ cells isolated from peripheral blood (PB) of steady-state healthy volunteers (ssPB-CD34), and of patients or healthy volunteers after mobilization (mPB-CD34) were investigated. ssPB-CD34⁺ cells contain a lymphoid cell population that co-express T or B cell markers, while mPB-CD34⁺ cells lack this population. After 5-day culture, significantly higher levels of expansion in cell, CD34⁺ cell, and HPP-CFC numbers were induced in ssPB-CD34⁺ cells, as compared to mPB-CD34⁺ cells. Hematopoietic reconstitution potential of these ex vivo manipulated CD34⁺ PBPC was evaluated in SCID-hu mice. It was found that ssPB-CD34⁺ cells retained the potential to reconstitute human bone marrow (BM), as well as thymus implanted in SCID animals. In contrast, only very low levels of reconstitution were detected in human hematopoietic tissues injected with cultured mPB-CD34⁺ cells. Reconstitution was restricted to myeloid cells, and no B cell reconstitution in bone marrow, or T cell reconstitution in thymus was achieved by these cells. The loss of B cell reconstitution potential of mPB-CD34⁺ cells was shown to be induced in a time-dependent manner during culture. These results indicate that mPB-CD34⁺ cells have different phenotypic and functional properties from ssPB-CD34⁺ cells. This may affect the efficacy of cell and gene therapy with mobilized PBPC.