The effects of chronic administration of cyclophosphamide on haemopoietic stem cells

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.

Evaluation of Doxorubin Toxicity on Normal Hemopoietic Stem Cells

The effect of administration of Doxorubicin (Dx) on the bone marrow CFUs, CFUe and CFUe has been evaluated in mice following injection of scalar single doses of the drug or during its repeated (3 times in 5 days) or prolonged (5 or 10 weeks) administration. In the first experiment the dose survival curves were exponential and the sensitivity of the 3 types of hemopoietic progenitors assayed was almost similar. During repeated or prolonged administration of Doxorubicin the CFUs appeared to be less affected by the drug than the committed progenitors.

Examination of bone marrow, immunologic parameters and host susceptibility following pre- and postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The effects of pre/postnatal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on various immunological, bone marrow and host susceptibility assays were examined in B6C3F1 hybrid mice. Exposure was accomplished by maternal dosing on Day 14 of gestation and again on Days 1, 7, and 14 following birth, employing dosages of 0, 1.0, 5.0 or 15.0 micrograms/kg body weight. The 15.0 micrograms/kg dosage was lethal to 70% of the offspring with the remainder of that dosage group revealing overt toxicity. Bone marrow toxicity occurred in both the 15.0 and 5.0 micrograms/kg dosage groups as evidenced by bone marrow hypocellularity and depressed colony formation of macrophage-granulocyte progenitor cells and pleuripotent stem cells. Evidence was presented that depression of lymphoproliferative responses following mitogen stimulation in TCDD-immunosuppressed mice was due to a functional defect of lymphocyte activation rather than suppressor cell activity. Administration of either Listeria monocytogenes or syngeneic PYB6 tumor cells in mice exposed to relatively low levels of TCDD during pre- and postnatal development increased their susceptibility to either bacterial or tumor challenge.