Lysis of Fresh Human Tumor Cells by Autologous Peripheral Blood Lymphocytes and Tumor-infiltrating Lymphocytes Activated hy PSK

The protein-bound polysaccharide PSK was tested for the ability to induce in vitro autologous tumor killing (ATK) activity in human cancer patients. Peripheral blood lymphocytes (PBL) and tumor-infiltrating lymphocytes (TIL) demonstrated various levels of cytotoxicity against autologous, freshly isolated tumor cells. When PBL and TIL were cultured overnight with PSK, ATK activity was induced in previously non-reactive cases and augmented in previously reactive samples. The PSK effect was observed with PSK concentrations of 10–100 μg/ml that could be obtained in the blood of cancer patients who received standard oral administration of PSK. The manifestation of PSK-induced ATK required active cell metabolism and RNA and protein syntheses, but not DNA synthesis of lymphocytes. PSK-induced enhancement of ATK was not abrogated by monoclonal antibodies (mAb) directed against interferon (IFN)α or IFNγ-. In addition, mAb that neutralized interleukin-2 (IL-2) or mAb reactive with α-chain or β -chain of IL-2 receptors (IL-2R) had no effect on PSK-induced ATK activity. Supernatants from PSK-stimulated lymphocyte cultures did not induce ATK. Cell fractiona-tion experiments revealed that CD3^-CD16⁺ large granular lymphocytes (LGL) and/or CD3⁺CD16^- T lymphocytes were responsible for both spontaneous and PSK-induced ATK. PSK-activated LGL, but not T lymphocytes expressed lysis of fresh allogeneic tumor cells. These results indicate that PSK activates PBL and TIL to exhibit ATK independently of IL-2/IL-2R systems.