RAG2 and immune system disorder: Given the limited numbers of PDX there was no association between the immunodeficiency and HCC disease etiology. Mildly immunodeficient Rag2−/− mice prevented PDX formation from all four major HCC etiologies in the U.S. (HCV, ALD, NAFLD, and HBV) whereas Rag2−/− Il2rgnull and NRG mice allowed for PDX establishment from these four etiologies (Table 1). Of the 20 HCC specimens that could form PDX, five biopsy specimens were implanted in both Rag2−/−Il2rgnull and NRG mice.