Abstract
Mouse lymphoma cells were inoculated into preirradiated syngeneic hosts after incubation with lymph‐node, spleen, liver or lymphoma cells from different sources in the presence of phytohemagglutinin. Neutralization of tumor growth was detected after incubation of lymphoma target cells with added untreated or X‐irradiated normal lymphoid or liver cells or with X‐irradiated intact or ultrasonically disintegrated lymphoma cells in all cases where the added cells contained H‐2 isoantigens which were foreign to the targets.