We examined the possibility that Th1 type CD4+ T cells may be an effector against three kinds of syngeneic tumors such as highly immunogenic B16 melanoma (B16) and two poorly immunogenic lines of MCA fibrosarcoma (MCA) and 3LL carcinoma (3LL). In a proliferation assay, the Th1 type CD4+ T cell clone (MH2) recognized the purified protein derivatives (PPD) derived from Mycobacterium tuberculosis. In a tumor-neutralizing assay, MH2 showed anti-tumor activity against both B16 and MCA. In a model of pulmonary metastasis, MH2 also showed anti-tumor activity against both B16 and 3LL. In an assay of cytolysis, MH2 showed a moderate level of tumor necrosis factor-dependent cytolytic activity only against MCA. In a cytostasis assay, MH2 showed a high level of interferon γ-dependent cytostatic activity against the three tumors in the presence of macrophages. The anti-tumor activity of MH2 against B16 and 3LL was suggested to be, at least in part, attributable to the augmented natural killer activity. Taken together, these findings suggest that we may potentially be able to utilize Th1 type CD4+ T cells as an effector for immunotherapy against poorly immunogenic tumors.
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