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.