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

Abstract

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.