Immunologic enhancement of tumor xenografts by pepsin-degraded immunoglobulin.

The serums from guinea pigs previously injected with mouse Ehrlich ascites tumor cells were fractionated to obtain gamma(2)-immunoglobulin. This immunoglobulin was degraded with pepsin to obtain an F(ab')(2) fragment. Fresh tumor cells were incubated with immunoglobulin or the fragment and injected into normal guinea pigs. The growth of these cells as tumor xenografts was inhibited by the gamma(2)-immunoglobulin and enhanced by the F(ab')(2) fragment. Similar incubation of tumor cells with normal guinea pig gamma(2)-globulin or its derived F(ab')(2) fragment did not alter subsequent tumor growth.