Comparative study of the in vitro behavior of cord blood subpopulations after short-term cytokine exposure

Abstract

We investigated the effect of short-term cytokine exposure on defined cord blood subpopulations. CD34⁺Thy1⁺, CD34⁺Thy1⁻, CD34⁺38⁻, CD34⁺38⁺, CD34⁺DR⁺, CD34⁺DR⁻, CD34⁺Rhodamine123 (Rh123)⁻ and CD34⁺Rh123⁺ cells were incubated for 7 days in IMDM + 10% FCS + IL3 + IL6 + G-CSF + SCF (36GS) ± flt3L. We evaluated LTHC-IC, immunophenotype and nucleated cell count for each cell population before and after cytokine exposure. Short-term exposure of CD34⁺38⁺, CD34⁺Thy1⁻, CD34⁺DR⁺, CD34⁺DR⁻ and CD34⁺Rh123⁺cells to 36GS causes a significant increase in cell number, whereas CD34⁺38⁻, CD34⁺Thy1⁺, and CD34⁺Rh123⁻ cells show only a limited increase. CD34 status post cytokine incubation shows that CD34⁺38⁺, CD34⁺Thy1⁻, CD34⁺DR⁺, and CD34⁺Rh123⁺fractions have a lower proportion of cells remaining CD34⁺ than CD34⁺38⁻ CD34⁺Thy1⁺, CD34⁺DR⁻ and CD34⁺Rh123⁻fractions. LTHC-IC analyses among input subpopulations show a higher frequency among CD34⁺38⁺, CD34⁺Thy1⁻, CD34⁺DR⁺, CD34⁺DR⁻and CD34⁺Rh123⁺cells as compared with CD34⁺38⁻, CD34⁺Thy1⁺ and CD34⁺Rh123⁻ cells. However, when LTHC-IC were evaluated after cytokine exposure, CD34⁺38⁻, CD34⁺Thy1⁺, and CD34⁺Rh123⁻ cells showed a higher frequency of LTHC-IC as compared with other subpopulations. Addition of flt3L to 36GS doubled the numbers in all subpopulations without altering the proportion of CD34⁺ cells. Results suggest that CD34⁺38⁻, CD34⁺Thy1⁺ and CD34⁺Rh123⁻ cells have a limited proliferative response to cytokines, the stem cell component of these populations is largely maintained and that expansion is derived from mature cell populations.