| Description |
In this thesis, the in vitro culture of mouse neoplasms has been investigated as a source of altered, attenuated, viable cells to act as a potential immunizing agents in conferring resistance to the fully virulent neoplasm. The intent of the research was to establish a practical animal immunization procedure which might have application to altering and attenuating tumor cells for the preparation of human cancer vaccines. Many recent studies of resistance to neoplasia in mice have sought to alter tumor cells for use as immunogens by using various chemical or mechanical treatments such as X-irradiation, nitrogen mustard, pheno1, or formalin. Such studies have concluded that metabolizing or partially viable cells are more effective than non-viable cells in conferring resistance to subsequent challenge with the same tumor. Excessive treatment with such agents results in a decrease in the effectiveness of the treated cells as immunogens. Like-wise, work with human viral vaccines has demonstrated the desirability of using "live" attenuated agents rather than "killed" ones for establishing maximum immunizing protection. The above observations suggested in vitro culture of tumor cells as a logical, convenient source of viable, potentially immunogenic cells. Also contributing to the value of this approach were the prospects that the cells in culture might undergo (a) slight morphological or biochemical changes to render them more antigenic that host tumor cells in being recognized as "not self" or (b) changes in virulence to yield an attenuated strain of cells. The specific objectives of the research reported in the thesis included the following: (a) in vitro culture of Ehrlich ascites tumor cells (EAT), Sarcoma-37 ascites tumor cells (S-37), and other, solid neoplasms of the mouse; (b) LD50 determinations of virulence for mouse-passage and in vitro strains of EAT and S-37; (c) immunogenicity studies of the resulting in vitro strains; and (d) retained virulence and immunogenicity of refrigerated S-37 cells. The latter objective was included to test the refrigerated cells as an alternate source of viable, altered, potentially immunogenic cells. Initial efforts to achieve successful in vitro culture of EAT cells using several media under a variety of conditions yielded only limited success. Subcultures of another, tissue culture strain of EAT were maintained successfully for over one year. Culture attempts with solid tumors of inbred strains of mice gave few positive results. S-37 ascites tumor cells and subsequently the first EAT strain were passaged through subculture for over six weeks with sufficient cells being harvested for succeeding mouse reinoculation studies on a pilot basis. Determinations of LD50 values for mouse-passage strains of EAT and S-37 revealed good correlation with former values, indicating stability of the virulence characteristics of the tumor cells upon continued mouse passage. An LD50 determination for EAT cells after six weeks in culture demonstrated and apparent decrease in the virulence of this in vitro strain in comparison to the observed LD50 values of the mouse passage strain. An insufficient yield of cell from further subcultures prevented the continuation of comparative virulence studies for both EAT and S-37. Immunogenicity of these cells, likewise, could not be demonstrated under these condition. No discernible trends cold be observed in the results of the experiments designed to test for retained virulence and immunogenicity of the refrigerated S-37 tumor cells. Comparison of the mortality ratios for mice treated with refrigerated cells and those of immune and normal controls exhibited no statistically significant differences. |
