Figure 1 RAG-1-and perforin-deficient mice have tumor incidence similar to that of wild-type mice after injection of MCA.(a) RAG-1-deficient (Rag1–/–) and heterozygous (Rag1+/–) and homozygous (Rag1+/+) control littermates bred at our institute (originally obtained on a C57BL/6 genetic background) were injected intramuscularly with 25 µg MCA in 0.1 ml sesame oil, and tumor development was monitored. Mice bearing a tumor≥ 1 cm in diameter were considered tumor-positive. Similar results were obtained in a second experiment and in experiments using severe combined immunodeficient and nude mice.(b) C57BL/6 perforin-deficient (Prf1–/–) and wild-type (Prf1+/+) mice obtained from the Jackson Laboratories were injected intramuscularly with 25 µg MCA as described above. Similar results were obtained when 100 µg was injected intramuscularly, 50 µg was injected subcutaneously or 25 µg was injected subcutaneously into perforin-deficient mice and control littermates bred at our institute.