Immunologic defenses against metastases: impairment by excision of an allotransplanted lymphoma.

Hamsters grafted with an allotransplantable lymphoma that does not metastasize develop a state of concomitant immunity which renders them refractory to reinoculation with cells of the same tumor. Removal of the tumor 7 days after transplantation rapidly leads to a decrease in immunity, the production of enhancing antibodies, and the appearance of metastatic deposits which are probably derived from preexisting tumor cells in the blood and lymphoid tissuces.