Antitumor Effector Mechanism at a Distant Site in the Double Grafted Tumor System of PSK, a Protein-bound Polysaccharide Preparation

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Abstract
The antitumor effect at a distant site of PSK, a Coriolus preparation, was analyzed with the double grafted tumor system in which BALB/c mice received stimultaneous intradermal inoculations of Meth-A tumor in the right (106 cells) and left (2 .times. 105 cells) flanks and were then injected with PSK in the right-flank tumor on day 3. PSK inhibited the growth of not only the right but also the left (non-treated) tumor. Immunized spleen cells were taken from mice which had been cured by the intratumoral administration of 5 mg of PSK and were injected into the Meth-A tumor on day 3. Adoptive transfer of PSK immunized spleen cells caused the complete regression of Meth-A tumors. The effector cell activity was lost only after treatment with anti-Lyt-1 monoclonal antibody plus complement. Spleen cells and right and left regional lymph node cells prepared from PSK immunized mice were examined for Thy-1, Lyt-1, Lyt-2 and asialo GM1 phenotypes. The number of Lyt-1-positive lymphocytes increased in the right regional lymph nodes after intratumoral administration of PSK. A massive accumulation of macrophages and polymorphonuclear leukocytes was found in the right tumor and an infiltration of macrophages and Lyt-2-positive lymphocyts was found in the left (non-treated) tumor by immunohistochemical analyses. These results suggest that intratumoral administration of PSK induces Lyt-1-positive cells first in regional lymph nodes, then in the spleen, and subsequently induces macrophages and Lyt-2-positive cells in the left (non-treated) tumor, thus bringing about the regression of metastatic tumors.