TILs were an obvious choice for the second interaction because TILs isolated from tumors recognize a variety of tumor-specific antigens and release IFNγ.25 To test this hypothesis, we successfully generated 3 independent CSV+ PDX tumors: SA127 (undifferentiated sarcoma), SA117 (osteosarcoma), and SA174 (osteosarcoma) in vivo and their matched autologous TILs in vitro, following a large number of attempts. Here, IFNG is linked to undifferentiated (embryonal) sarcoma.