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Suppressor T Cells Regulate the Cytolytic T Lymphocyte Response to Syngeneic Tumors Induced by Murine Sarcoma Virus (MSV) in the Mouse¹

From the Department of Genetics, Albert Einstein College of Medicine, Bronx, New York 10461; the Unit of Human Cancer Immunology, Lausanne Branch, Ludwig Institute for Cancer Research, Epalinges-sur-Lausanne, Switzerland; and Institut National de la Santé et de la Recherche Médicale (INSERM), Paris, France

Abstract

Studies were designed to analyze the immune activities of spleen cells from mice previously injected with murine sarcoma virus (MSV) and undergoing the processes of MSV tumor growth and rejection. Fractionation of MSV-primed spleen cells according to cell size by velocity sedimentation at unit gravity showed that MSV-specific cytolytic T lymphocytes (CTL) generated in vivo underwent an apparent transition in size from large to small cells as the tumor regressed. The majority of CTL precursors, however, were invariably recovered among small to medium-sized MSV-immune cells, as revealed by CTL generation in vitro in secondary mixed leukocyte-tumor cell cultures (MLTC). Evidence was obtained for the existence in MSV-immune spleens of two suppressor cell populations capable of inhibiting CTL generation in vitro: one population probably consisted of macrophages and could be removed by treatment with carbonyl iron; the second population was comparised of T cells and inhibited the differentiation of tumor-immune CTL precursors in a selective manner. These results provide a preliminary overview of the mechanisms regulating the generation, differentiation, and activity of tumor-specific CTL in a syngeneic model system.

Footnotes

¹ This work was supported in part by National Institutes of Health Grant RO1 CA 19931 and Training Grant 5T32 GM 7288, and by grants from the Swiss National Foundation for Scientific Research.

² Recipient of a research fellowship from the Cancer Research Institute, New York.