Anti-Metastatic Activity Induced by the In Vivo Activation of Purified Protein Derivative (PPD)Recognizing Thl Type CD4 + T Cells

Abstract

The Th1 type CD4 + T cell clone (MH2), which is capable of recognizing purified protein derivative from Mycobacterium tuberculosis (PPD), was examined for its anti-metastatic activity against melanoma. In using an in vitro proliferative assay, MH2 was able to recognize PPD-derived antigen in a major histocompatibility complex class 11-restricted manner. MH2 showed neither any natural killer (NK) activity nor cytolytic activity against syngeneic B16 melanoma. This clone produced interferon-γ, tumor necrosis factor and interleukin-2, but not interleukin-4, when co-cultured with PPD and irradiated syngeneic C57BL/6 spleen cells, suggesting that this clone could thus be assigned to the Th1 subset. An intraperitoneal (i.p.) co-injection of 2 x 10 6 MH2 and 50μg PPD increased the NK activity of the peritoneal exudate cells (PEC) and the percentage of NK1.1 + cells in the PEC. These activated NK cells showed a low but significant cytolytic activity against B16 melanoma. The augmented NK activity induced by the co-injection of MH2 and PPD was maintained by the weekly additional i.p. injections of PPD alone. Using a murine metastatic model, an i.p. co-injection of MH2 and PPD-induced antimetastatic activity against B16 melanoma. This anti-metastatic activity was then abrogated by the in vivo administration of anti-asialo GMt serum. In addition, the NK activity in both peripheral blood and metastatic lungs was significantly augmented in the mice which were co-injected with MH2 and PPD. Taken together, these findings indicate that the in vivo activation of Tht type CD4+ T cells augmented the NK activity in vivo and thus could potentially be an efficient immunotherapeutic weapon against metastasis of melanoma. These results also imply that adoptive immunotherapy could induce antimetastatic activity through cytokine production but not through any direct cytolytic activity.