The in vitro growth of a cord blood-derived cell population enriched for CD34+ cells is influenced by its cell cycle status and treatment with hydroxyurea.

OBJECTIVE: Cell cycle plays a fundamental role in the physiology of hematopoietic stem and progenitor cells. In the present study we used a negative selection system to obtain an immature cell population-enriched for cord blood-derived CD34+ cells-and we determined its proliferation, expansion and differentiation patterns as a function of the cell cycle status. The effects of hydroxyurea (HU) were also assessed. RESULTS: As compared with cells in synthesis (S)/Gap2 (G2)/mitosis (M), cells in quiescent state (G0)/Gap1 (G1) showed a higher proliferation potential in vitro. At culture onset, G0, G1 and S/G2/M cells corresponded with 63%, 33% and 4%, respectively. Treatment with HU before culture resulted in an increase in the proportion of cells in G1 with a concomitant decrease in S/G2/M cells, without affecting the proportion of cells in G0. After 3 days of culture in the presence of recombinant cytokines, the vast majority of the cells (90%) were in G1, and by day 8, G0, G1 and S/G2/M cells corresponded with 18%, 67% and 15%, respectively. HU also induced an increase in colony-forming cell (CFC) frequency, in the proliferation and expansion capacities of cultured cells under myeloid conditions, and favored the development of the erythroid lineage. CONCLUSION: Our results show that the in vitro proliferation, expansion and differentiation potentials of immature hematopoietic cells are determined, at least in part, by their cell cycle status and that the cell cycle modifier HU significantly influences the growth of human hematopoietic cells. These results are of potential relevance for the development of ex vivo expansion protocols.

Sex-based differences in lymphocyte proliferation in the spleen after vanadium inhalation.

Vanadium (V) is a transition metal often adhered to particulate matter and released into the atmosphere as vanadium pentoxide (V2O5) by the burning of fossil fuels. This air pollutant causes adverse effects in the immune system. Lymphocytosis and splenomegaly have been reported with increased white pulp in mice after V inhalation. The effect of V on the immune system as related to sex has been poorly investigated. This study sought to determine if V inhalation (a) produced lymphoproliferation that could explain the changes previously observed in the spleen and in peripheral blood lymphocyte counts and (b) whether any observed effects differed due to gender. Immunohistochemical analyses of Ki-67, a specific proliferation marker, was made in the spleens of CD-1 male and female mice exposed for 1 h, twice a week, over a 12-week period to V2O5 (at 1.4 mg V2O5/m(3)) by whole-body inhalation; similar analyses were performed on spleens of control mice exposed to vehicle (filtered air). The results showed that in male mice there was a significant increase in percentage of Ki-67 immunopositive lymphocytes starting from the second week and until the end of the exposure. The Ki-67 signal was cytoplasmic and nuclear in the exposed males, while in controls the signal was only nuclear. In female mice, V inhalation singificantly increased the percentage of proliferating lymphocytes only after 1 week of exposure. Ki-67 signal was observed only in the nucleus of lymphocytes from the control and exposed females. The results here help to explain the splenomegaly and lymphocytosis observed previously in male mice and support the lymphoproliferative effect induced by V. Lastly, the finding that there was a sex difference in the effect of vanadium on lymphocyte proliferation suggests a role for sex hormones in potential protection against V immunotoxicity; however, further studies are needed to support this hypothesis.