Adhesion receptor expression by hematopoietic cell lines and murine progenitors: Modulation by cytokines and cell cycle status

Hematopoietic progenitor cells are incubated with cytokine combinations for in vitro expansion of stem cells and to enhance retrovirus-mediated gene t ransfer. Optimization of the engraftment of these treated cells would be cr itical to the success of stem cell transplantation or gene therapy. Previou s studies demonstrated that a 48-hour incubation of donor BALB/c bone marro w with a mixture of four cytokines (IL-3, IL-6, IL-11, and SCF), resulted i n expansion of primitive progenitor/stem cells but a loss of long-term engr aftment in non-myeloablated or myeloablated recipients. We have established the expression pattern for a number of adhesion receptors by normal hemato poietic progenitors and cell lines and the modulation in expression induced by cytokines or cell cycle progression to ascertain the molecular basis fo r such defective engraftment. Northern blot analysis demonstrated that the cytokine combination of IL-3, IL-6, IL-11, and SCF dramatically downregulat ed alpha(4) integrin receptor expression in HL-60 cells. Synchronized FDC-P 1 cells exhibited modulation of alpha(4) expression through cell cycle prog ression, both by quantitative RT-PCR and flow cytometry. Normal murine bone marrow lineage-depleted, Sca(+) cells expressed a number of adhesion recep tors, including alpha(L) alpha(1), alpha(3), alpha(4), alpha(5), alpha(6), beta(1), L-selectin, CD44, and PE-CAM as assessed by flow cytometry, immuno fluorescence, and RT-PCR. There was modulation of the expression of several of these receptors after incubation in the four cytokines for 24 and/or 48 hours: the proportion of cells expressing alpha L, alpha(5), alpha(6), and PECAM increased, whereas the proportion of cells expressing alpha(4) and b eta(1) decreased, after cytokine incubation. There was a demonstrable conco mitant decline in adhesion of these cells to fibronectin after the cytokine incubation, a finding that correlates with the decrease in expression of c u,. These changes in adhesion receptor expression and function with cytokin es and during cell cycle transit may be critical to stem cell homing and en graftment after transplantation, as multiple receptors could be involved in the process of rolling, attachment to endothelium, endothelial transmigrat ion, and migration within the marrow space. (C) 1999 International Society for Experimental Hematology. Published by Elsevier Science.