CAPACITY OF MICROSOMALLY-ACTIVATED CYCLOPHOSPHAMIDE TO INDUCE IMMUNOSUPPRESSION INVITRO

Abstract

Cyclophosphamide (CY) was activated in vitro with washed rat liver microsomes and cofactors. Pretreatment of mouse spleen cells in vitro with the activated drug abolished their capacity to give a primary antibody respnse to SRBC [sheep erythrocytes] and levan on transfer to irradiated syngeneic recipients. Responsiveness returned if challenge was delayed for 7 or more days after transfer. Part of this was shown to be of donor origin by an allotype marker. The treatment of normal spleen cells with activated CY in vitro also prevented B [bone marrow derived] cells from regenerating their immunoglobulin receptors after capping with anti-immunoglobulin serum. The induction of suppression required contact between lymphocytes and activated CY for at least 30 min at 37.degree. C and did not appear following incubation for 1 h at 0.degree. C. Since the antibody response of drug-treated spleen cells to SRBC could not be restored with purified normal B or T [thymus derived] cells, B and T lymphocytes are both probably susceptible to suppression by activated CY in vitro. Similar pretreatment abrogated the graft vs. host (GVH) reactivity of spleen cells as measured by survival and in a popliteal lymph node assay. B cell chimerism in F1 recipients of drug-treated parental spleen cells was demonstrated by the presence of congenic allotype markers. This suggests a possible approach for the attenuation of GVH disease which is associated with bone marrow transplantation in man.