RAG2 and lung cancer: We do know that while expression of JSRV Env in lungs of immunodeficient Rag2-knockout mice that lack mature T and B cells can cause rapid development of tumors and death, immunocompetent mice are resistant to lung cancer induction by the same treatment [13] (although this result appears to be dependent of the strength of the promoter that drives JSRV Env expression [25]).