Background: To obtain a better understanding of the mechanism underlying different modalities of immunotherapy, we investigated the types of tumor-infiltrating cells present at the tumor site, with special attention to the presence of macrophages.
Experimental design: Frozen sections of carcinomas of the kidney, colon, breast, lung, ovary, and thyroid gland, as well as malignant melanoma were investigated with a panel of monoclonal antibodies against macrophage, T cell and NK cell associated antigens. Both type and pattern of the tumor-infiltrating cells were analyzed.
Results: All tumor-infiltrating cells accumulated preferentially in the stromal bands between tumor cells. In all types of tumor, CD11c+, CD14+, CD68+ and alpha-naphthyl-acetate-esterase positive monocytes/macrophages accounted for most tumor-infiltrating cells. Next in frequency were T lymphocytes (CD2+, CD3+, TCR alpha beta +). Only a few B lymphocytes (CD22+), and T cells expressing the T cell receptor gamma delta (TCR gamma delta) were found. Hardly any lymphoid cells with an NK phenotype (CD3-, CD56+) were present in the tumors studied. Large numbers of CD16+ cells were found, which could be identified as macrophages on the basis of their morphology, positive staining with a panel of monocyte/macrophage markers, and the results of double staining with CD11c.
Conclusions: We have demonstrated the presence of a large number of macrophages in the cellular infiltrates of several types of tumors. The largest numbers of CD16+ macrophages were found in renal cancer, melanoma, and colonic-carcinoma. These are the tumors that are most susceptible to immunotherapy with lymphokine activated killer cells, suggesting that these CD16+ macrophages may be involved in antitumor cytotoxicity. Furthermore, these findings suggest that new strategies of immunotherapy aimed at the use of macrophages present in many tumors could be developed.