Preliminary In Vivo Studies Leading to Possible Immunotherapeutic Roles for NK Cells and Macrophages against Neoplasia
Leonhardt, James Gates
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Natural killer (NK) cells are thought to participate in the destruction and growth suppression of tumor cells in vivo, and the role of NK cells in the control of metastatic spread by the elimination of tumor cells entering the blood stream was examined. The ability of BALB/c nude and C57BL/6 mice to eliminate tumor cells from the blood stream and lungs was severely impaired after a single inoculation of 0.2 mI. of anti-asialo GM1 (asGM1) serum, diluted 1:40 to 1:320. The number of i.v. inoculated Yac-1 cells surviving in the lungs of BALB/c nude mice pretreated with anti-asGM1 serum was 28 times higher than in the control nude mice. The increase in the initial survival of tumor cells in the mice that is induced by pre-treatment with anti-asGM1 resulted in a substantial increase in the number of artificial lung metastases that developed. In C57BL/6 +/+ mice treated with anti-asGM1, and in C57BL/6beige mice, i.v. inoculation of B16 melanoma cells induced ten times more metastatic foci in the lungs than in the control C57BL/6 +/+ mice. In beige mice and in C57BI/6 +/+ treated with anti-asGM1, multiple metastatic foci developed in the liver. whereas in control C57BL/6 +/+ and nude mice, no extrapulmonary metastases were found. These data indicate that B16 melanoma cells are able to grow in the liver, but their growth is ordinarily prevented by NK cells. These experiments demonstrate that NK cells may play an important role in the elimination of metastatic cells, and in the control of metastatic spread and growth of tumor cells in mice. In order to investigate the role of macrophages in the anti-tumor host response, macrophages were adoptively transferred into mice and the subsequent response was evaluated. Adoptively transferred peptone elicited macrophages from C57BL/6 mice migrated to the spleen, and initially (24 hours) to the liver in greater numbers than did adoptively transferred thioglycolate elicited macrophages. Thioglycolate elicited macrophages migrated to the lungs in far greater numbers than did peptone elicited macrophages. Activation of the peptone elicited macrophages increased the number of these cells that traveled to the liver, and had no significant effect on the number of cells that migrated to the spleen or lungs. Activation of the thioglycolate elicited macrophages slightly decreased the number of these cells that migrated to the lungs, and had no effect on migration to the liver or spleen. C57BL/6 mice inoculated with 4 x 10 4 B16 melanoma cells and 0.1 mI. of anti-asGM1 had a median of 39 lung metastatic foci, and 10 liver metastatic foci, 25 days after inoculation. These mice also received unactivated thioglycolate elicited macrophages. Similarly treated animals that received activated thioglycolate elicited maqrophages had a median of 24 lung nodules, and only 2 liver nodules. Activation was carried out in vivo with 100 ug of polyinosinic polycytidylic acid for 3 hours. These data demonstrate the effects of anti-asGM1, as well as the importance of the NK system. The data also shows the cytotoxic effects of activated macrophages, which are significant in the reduction of liver metastases, and possibly in the reduction of lung metastases.