CD14+ cells from peripheral blood positively regulate hematopoietic stem and progenitor cell survival resulting in increased erythroid yield

Expansion of erythroblasts from human peripheral blood mononuclear cells is 4- to 15-fold more efficient than that of CD34(+) cells purified from peripheral blood mononuclear cells. In addition, purified CD34(+) and CD34(-) populations from blood do not reconstitute this erythroid yield, suggesting a role for feeder cells present in blood mononuclear cells that increase hematopoietic output. Immunodepleting peripheral blood mononuclear cells for CD14(+) cells reduced hematopoietic stem and progenitor cell expansion. Conversely, the yield was increased upon co-culture of CD34(+) cells with CD14(+) cells (full contact or transwell assays) or CD34(+) cells re-constituted in conditioned medium from CD14(+) cells. In particular, CD14(++)CD16(+) intermediate monocytes/macrophages enhanced erythroblast outgrowth from CD34(+) cells. No effect of CD14(+) cells on erythroblasts themselves was observed. However, 2 days of co-culturing CD34(+) and CD14(+) cells increased CD34(+) cell numbers and colony-forming units 5-fold. Proliferation assays suggested that CD14(+) cells sustain CD34(+) cell survival but not proliferation. These data identify previously unrecognized erythroid and non-erythroid CD34(-) and CD34(+) populations in blood that contribute to the erythroid yield. A flow cytometry panel containing CD34/CD36 can be used to follow specific stages during CD34(+) differentiation to erythroblasts. We have shown modulation of hematopoietic stem and progenitor cell survival by CD14(+) cells present in peripheral blood mononuclear cells which can also be found near specific hematopoietic niches in the bone marrow.