Induction by cyclophosphamide administration of two distinct anti-tumor effector cells at tumor site and spleen of mice transplanted with MOPC-104E plasmacytoma.

BALB/c mice were inoculated intraperitoneally (i.p.) with MOPC-104E syngeneic plasmacytoma cells and seven days later the mice were treated with i.p. cyclophosphamide (CY). All mice exhibited a complete regression of MOPC-104E, and in addition acquired the resistance to second challenge of MOPC-104E, but not to syngeneic Meth-A fibrosarcoma. Following CY treatment, a large number of viable MOPC-104E cells were seen in the peritoneal cavity of the mice on day 7, and then they decreased and disappeared on day 14. By contrast, athymic BALB/c nude mice with MOPC-104E did not respond to CY and died. Only a transient decrease in the number of tumor cells was observed in the peritoneal cavity of nude mice. Following CY treatment, whole peritoneal cells (tumor cells and peritoneal exudate cells) was not transplanted to conventional mice, while transplantation was possible following treatment of whole peritoneal cells with anti-Thy1, anti-Lyt 1 or anti-Lyt 2 plus complement (C). The in vivo anti-tumor activity of spleen cells of mice in regression was nullified by treatment with anti-Thy 1 and anti-Lyt 1 plus C, but not anti-Lyt 2 plus C. These results indicate that CY administration results in only a transient decrease of tumor cell number and that an induction of Lyt 1 +, Lyt 2 + T cells in the peritoneal cavity and Lyt 1 + T cells in spleen may be responsible for a complete disappearance of tumor cells.