The role of the skin in active specific immunization against leukemia in guinea pigs

The L(2)C 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(-6) or 10(-7) dilution) 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(-2) dilution, 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.