ENHANCED HOMEOSTATIC PROLIFERATION OF T LYMPHOCYTES AFTER CYCLOPHOSPHAMIDE INJECTION IN C57BL/6 MICE

Chemotherapeutic agents are used in medicine to treat cancer. They can damage immune system and lead to the secondary immunodeficiency. T cells are most severely affected during chemotherapy. Restoration of the T lymphocytes is an important topic in research to understand pathogenesis of damaging effects caused by cytostatics and searching ways to correct the resulting disorders. The aim of our study was to follow the process of T cell recovery, and to understand the role of its homeostatic proliferation. 33 female C57BL/6 mice were included into the experiment. The experimental group (25 mice) received a single injection of cyclophosphamide (Cy) at a dose of 125 mg/kg; the control group did not receive the drug. Biomaterials for the study were splenocytes isolated on days 5, 10, 20, 30 and 60 after the drug administration. Flow cytometry was used to measure the recovery of T helpers (CD3CD4) and cytotoxic T lymphocytes (CTL, CD3CD8), as well as their “age-related” phenotype assayed for naive (Tnaive) and central memory (Tcm) T cells. The level of homeostatic proliferation was determined by the Tnaive/Tcm ratio. The total amount of splenocytes, T helpers, CTLs and the CD4/CD8 ratio showed a statistically significant increase at the early terms after Cy administration (day 5). Further, a decrease in splenocytes and their subpopulations was observed. We found that the CTL subpopulation didn’t recover even 2 months after the drug administration and was more sensitive to the action of cyclophosphamide than the T helper subpopulation. We have also revealed that naive T helpers and naive CTLs are most susceptible to the Cy action; these subpopulations also failed to recover 60 days after the drug administration. At the same time, the amount of central memory T cells predominated by the end of the experiment, showing conversion of the T cell phenotype. Thus, we have shown an increase in homeostatic proliferation, along with conversion of naive T cell phenotype to the central memory T cells after Cy administration accompanied by deficiency of naive T cells. Such changes cause skewing of TCR repertoire. This shift may cause premature aging of immune system and increases the risk of autoimmune diseases.