Analysis of effector cells in tumor-bearing mice pre-treated with active specific immunization followed by cyclophosphamide

In order to analyse the effector population in an immunization model, we tr eated BALB/c mice with intraperitoneal (i.p.) active specific immunization (ASI), which consists of interleukin (IL)-1-beta and sonicated tumor supern atant (SS) of a plasmacytoma MOPC-104E followed by i.p. injection of cyclop hosphamide (CY). This ASI-CY treatment provoked a protective immunity again st i.p. tumor inoculation more strongly than that of ASI alone. The main ef fector cells in tumor neutralizing assay were CD4+ T cells at this pont. Th e number of spleen cells of the ASI-CY treated mice were significantly lowe r than that of ASI alone treated mice but it increased significantly 6 days thereafter while this increase was not observed on the mice treated with A SI alone. The spleen cells of the ASI-CY treated mice responded to SS in vi tro in the presence of IL-2, more profoundly in CD4 enriched population whi ch produced high amount of TNF-alpha. In vivo tumor-neutralizing activity a t a later stage was dependent on CD8+ T cells in addition to CD4+ T cells. These results suggest that antitumor activity by ASI and CY is transduced b y sequential population shift from CD4 alone to both of CD4 and CD8.