Failure of Immunosurveillance Against Chemically Induced In Situ Tumors in Mice

Summary

Incipient tumors were produced by the administration of 5% 3-methylcholanthrene (MCA) pellets to normal and immunodepressed mice. Two months later, half the animals were subjected to full-thickness autografting of the area containing the MCA pellet. No tumors developed in autografted sites of normal mice. Normal mice with nongrafted sites and both groups of immunodepressed mice had significant tumor development. In a second experiment, spontaneous in situ neoplasms were simulated by implantation of weakly antigenic, heavily irradiated, mesenchymal or epidermal tumors into normal and lmmunedepressed mice. Half the animals had autografting of areas containing the implants. All mice were subsequently challenged with viable tumor fragments. The results indicate that no animal was immunized even though sites containing tumor were surgically manipulated. Both experiments suggest that in a natural situation where most tumors are small and weakly antigenic, immunosurveillance is ineffective because the weak antigenicity of tumors is not detectable and undisturbed tumors are not recognized by host immunity.