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

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.