IL4 and breast carcinoma: When we performed mouse orthotopic engraftment experiments with AC2M2 breast carcinoma cells expressing empty vector control or IL-4 in immune-compromised athymic nude mice or Rag2−/−; IL2Rγc−/− double-knockout mice, we observed the most pronounced differences in tumorigenesis and metastasis in Rag2−/−; IL2Rγc−/− mice.