Transitional changes in immunophenotypic subpopulations of human peripheral blood CD34+ cells expanded in vitro

We determined the appropriate incubation period to expand human peripheral blood (PB) CD34+ cells for clinical application and the role of recombinant human (rh) interleukin-3 (rhIL-3) in the expansion and differentiation of these cells. The cells were purified up to 40 +/- 16% and transitional changes in immunophenotypic subpopulations in suspension culture were examined following stimulation with three different combinations of rh colony-stimulating factors (rhCSFs): 1) rhIL-3 alone, 2) rhIL-6, rhSCF, rhG-CSF, plus rhGM-CSF, and 3) the four CSFs plus rhIL-3. With all three CSF combinations, the total cells increased continuously after day 5 until day 14, and a combination of the five CSFs always gave rise to the highest number of total cells. Immunophenotypic analysis of the expanded cells showed that with all three CSF combinations CD34+ cells reached a maximal rate on day 5 and then decreased in an inverse correlation between the logarithm of CD34 positive rate and the duration of suspension culture. The maximum expansion of CD34+ cells and PB progenitor cells (PBPC) with rhIL-3 alone, the four CSFs, or the five CSFs was observed on day 5, 10, or 7, respectively. The combination of the five CSFs was identified as the most potent stimulus for expansion of PBPC and CD34+ cells, as it increased non-erythroid PBPC 89 +/- 69-fold, with a range of 24 to 204-fold on day 7. However, differences in the expansion rate of these cells on days 5, 7, and 10 were not statistically significant. The majority of purified CD34+ cells coexpressed CD38 (91 +/- 3%) but were negative for CD33 (85 +/- 4%), and one-half coexpressed CD13. With all three combinations of CSFs, the mature CD34+ cells that coexpressed CD38, CD33, or CD13 expanded in parallel with the total CD34+ cells, while an increase in relatively immature CD34+ cells, which do not express CD38, CD33, or CD13, was only statistically significant with the five CSFs. Thus, rhIL-3 played a critical role when combined with the four CSFs by increasing both mature and immature CD34+ cells.