Complete regression of mouse hepatoma transplanted after partial hepatectomy and the immunological mechanism of such regression.

We have investigated the effect of partial hepatectomy (HEP) on tumor growth. MH-134 hepatoma cells, which were inoculated in syngeneic C3H/He mice from 3 to 10 days after HEP, grew with a linear increase in size until 7 days, began to regress, and disappeared 14 days after the inoculation. The survival rate was 100%, and the recurrence of tumor was not observed during the following 4 mo. On the other hand, the growth of another syngeneic tumor, X-5563, and of an allogeneic Ehrlich tumor was not affected by HEP. When MH-134 tumor cells were inoculated 7 days before or 15 days after HEP, tumor regression was not observed. The Winn assay showed the presence of tumor-neutralizing activity in spleen cells of MH-134 tumor-regressed mice. Cytotoxic activity against MH-134 tumor cells was also detected in the spleen cells. Analysis by using monoclonal antibodies showed that the effector cells were Thy-1+ and Lyt-2+ cells. Thus, HEP and the following liver cell regeneration may play a role in augmentation of specific immune response to the transplanted hepatoma cells.