Stem cell recovery from cyclophosphamide-induced myelosuppression requires the presence of CD4+ cells.
Recently, we have reviewed studies regarding the growth-stimulating effect of CD4+ cells on haematopoietic cells in culture (Pantel & Nakeff, 1989a). In the present study we have tested the physiologic relevance of this interaction using a drug-perturbed mouse model. The long-term application of cyclophosphamide (CY, 30 mg/kg/d, five i.p. injections per week over 7 weeks) in B6D2F1 mice resulted in initial CY-induced cytotoxicity to CFU-S followed by the reestablishment to pretreatment values of the femoral content of CFU-S within 2-3 weeks of CY-treatment. An examination of CY-metabolism in these treated mice excluded a pharmacological explanation for the compensation of CY-cytotoxicity. However, a three-fold increase in the cycling fraction of CFU-S (determined by in vivo hydroxyurea suicide) was observed concomitant with a two-fold increase in the femoral content of L3T4+ cells (the murine equivalent to human CD4+ cells), as compared to the corresponding values in untreated mice. Ablating these L3T4+ cells in vivo by means of a cytotoxic monoclonal antibody (MoAb) to the L3T4 determinant resulted in a decrease in the cycling fraction of CFU-S from 56 +/- 8% to essentially zero and a decrease in the femoral content of CFU-S when comparing mice receiving either CY alone or CY plus MoAb, respectively. It would appear that the CY-induced increase in the proliferative activity of CFU-S requires the presence of L3T4+ cells. These data constitute the first in situ evidence for the physiologic relevance of immunocompetent L3T4+ cells as regulators involved in the recovery of stem cells from drug-induced myelosuppression.
Pantel
K
K
Department of Internal Medicine, Wayne State University School of Medicine, Detroit, Michigan 48201.
Djuric
Z
Z
Nakeff
A
A
D000818:Animals; D015704:CD4 Antigens / Q000032:analysis*; D002450:Cell Communication / Q000276:immunology; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D003114:Colony-Forming Units Assay; D003520:Cyclophosphamide / Q000493:pharmacokinetics / Q000494:pharmacology*; D006412:Hematopoietic Stem Cells / Q000187:drug effects* / Q000502:physiology; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D013601:T-Lymphocytes / Q000502:physiology*
D015704:CD4 Antigens; D003520:Cyclophosphamide