Increased nod/scid repopulating potential and primitive hematopoietic function of human CD34+ cells following exposure to ANTI-CXCR4

Abstract

Due to its demonstrated effects on migration of primitive hematopoietic progenitor cells (HPC), the CXCR4-SDF-1 receptor-ligand pair has been implicated in in vivo trafficking and homing of primitive HPC. To further define the role of CXCR4 in hematopoiesis, the contribution of CXCR4 to primitive hematopoietic function of normal human mobilized peripheral blood (MPB) and bone marrow (BM) CD34+ cells was investigated. MPB and BM were enriched for CD34+ cells, then stained for flow cytometric cell sorting with antibodies to CD34 only, or CD34 and CD90. Expression of CXCR4 on normal BM and MPB CD34+ CD90+ (++) cells ranged from < 1% to 10%. Primitive HPC activity (assayed as LTHC-IC and the ability to initiate and sustain long-term cultures, LTC) was 3- to 10-fold higher among ++ CXCR4- cells compared to ++ cells expressing CXCR4. To examine effects on primitive hematopoietic function, purified CD34+ or ++ cells were exposed, for up to 5 days, to anti-CXCR4 antibody (12G5) or an irrelevant isotype, then examined for hematopoietic potential in LTC and NOD/SCID recipients. Interestingly, LTC initiated with cells exposed to anti-CXCR4 produced up to 2-fold more CFU than control cultures, largely due to increased and sustained BFU-E production. This enhanced in vitro hematopoietic potential was paralled by an enhanced engraftment potential: chimerism in mice transplanted with ++ cells exposed to anti-CXCR4 was 13.4 ± 10.3% (n = 3), while that in mice receiving control cells was 3.9 ± 2.4% (n = 4). Production of human CD34+ cells and clonogenic HPC was also higher in NOD/SCID mice transplanted with cells exposed to CXCR4. While analysis of CD34+ or ++ cells after a 3–5 day exposure to anti-CXCR4 did not reveal differences in adhesion molecule phenotype, a consistent increase in CD34+ CD38−/lo cells was documented among CXCR4-exposed cells. These data suggest that activation of the CXCR4 receptor on MPB or BM CD34+ cells enhances primitive hematopoietic cell function, possibly by amplification of a primitive cell subset. Whether activation of CXCR4 effects more efficient in vivo homing remains to be examined.