The Role of the Skin in Active Specific Immunization against Leukemia in Guinea Pigs

The L2C leukemia strain, which originated as spontaneous leukemia in ``strain 2'' guinea pigs, is transmissible by cell-graft in animals of this line; on subcutaneous inoculation it induces consistently generalized and progressive stem-cell leukemia in 99% of the inoculated animals. The leukemia thus induced never regresses. However, when very small doses of leukemic cell suspensions (0.05 ml of a 10-6or 10-7dilution) were inoculated intradermally, 86 out of 180 intradermal tumors (48%) regressed spontaneously. Most of the animals that recovered from the intradermal tumors were resistant to a challenging reinoculation of leukemic cells. This resistance could be substantially increased by a second intradermal inoculation of leukemic cells. Females were more resistant than males. When 55 immunized females and 36 males received a challenging subcutaneous reinoculation (0.5 ml each) of a leukemic cell suspension of 10-2dilution, only two females and six males developed leukemia; the remaining 83 animals (91%) remained in good health. In a control experiment, 126 untreated ``strain 2'' guinea pigs were inoculated subcutaneously with the same dose, and all but one (99%) developed leukemia. The immunity thus induced could not be transferred to other animals by a serum collected from immunized guinea pigs.