Immunosuppression by cytostatic drugs?

In the present study, an attempt was made to characterize the immunomodulating abilities of the cytostatic drugs cyclophosphamide, ifosfamide, vinblastine, vincristine, procarbazine, dacarbazine, 6-mercaptopurine, methotrexate, 5-fluorouracil and adriamycin in a defined experimental model. Varying combinations of drug plus transplantation alloantigen, (C3H-lymphocytes) were injected into Balb/c mice at different time intervals in vivo. The resulting T-effector cell reactivity was determined in vitro with the microcytotoxicity assay on day +5 for primary (1 degree) and day +7 for secondary (2 degrees) sensitized mice. According to the type of drug (alkylating agent vs. vinca alkaloid vs. antimetabolite vs. cytostatic antibiotic), the dosage (20% LD50 vs. 60% LD50), the state of sensitization (1 degree vs. 2 degrees sensitized recipients), and the time of drug application in relation to the antigen treatment on day 0 (in varying steps from day -6 to day +4), so-called "pharmacon-antigen-variation-effects" (PAVE) were established for each of the investigated drugs in form of reaction profiles. The results were as follows: For almost all substances, characteristic reaction profiles involving immunostimulation and/or immunosuppression could be established. Similarities in the profiles of different substances made it possible to classify the drugs according to different reaction types. The reaction type however is not definitely correlated to the biochemical mechanism of drug action. The PAVE are decisively influenced by some of the biological parameters, such as the time of drug application in relation to the antigen treatment and the state of sensitization but relatively little by the dosage of the drug. Considering the different processes occurring during primary and secondary immune responses, the PAVE may give hints for a distinct manipulation of the immunoregulation and thus information on the immunobiological mechanism of drug action.