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Immunization of C58 Mice to Line I_b Leukemia¹

Department of Microbiology, The University of Michigan, School of Medicine, Ann Arbor, Michigan 48104

A study was done to define the conditions that had to be met to immunize C58 mice to line I_b transplantable leukemia (I_b cells). The relative immunogenicity of I_b cell preparations inactivated by a variety of methods was compared. Cell preparations were inactivated by exposure to UV light for up to 60 minutes. A cell concentration of 10⁶ to 10⁷ per ml exposed to UV light for 15 to 30 minutes was the most immunogenic. A dose of 10⁵ cells per ml was only weakly immunogenic. A dose of 10⁸ UV-irradiated cells killed all of the recipient mice. However, when 10⁸ cells were exposed to 15,000 R of X-irradiation they were strongly immunogenic; a 10⁵ cell dose exposed to 5,000–15,000 R was not immunogenic. A preparation of 10⁷ cells per ml exposed to 5,000–15,000 R was the most immunogenic. The optimum method for inactivating cells with formalin was by exposure to a 1:500 dilution for 18 hours at 4°C. A dose of 10⁷ cells per ml was the most immunogenic. Frozen-thawed, sonicated-lyophilized, and sonicated-filtered preparations were immunogenic, providing that the initial cell concentration was about 10⁸ per ml and that the proper dose regimen was used for immunization. Freund's complete adjuvant impaired the immune response of C58 mice to UV-, X-irradiated, or formalin-treated cell preparations.

Quantitative studies of cell-associated immunity to line I_b leukemia were carried out. Immune lymphoid cells were obtained from the spleen, lymph nodes, and peritoneal cavity of immune C58 mice. A ratio of 10 immune cells to 1 I_b cell was necessary to afford complete protection. When mice were immunized by a single injection of formalinized or UV-inactivated cells, immunity persisted at a high level for approximately 1 year.

¹ Supported by Grant 06639, National Cancer Institute, NIH, USPHS.

Received 9/20/67. Accepted 3/25/69.