IFNG and neoplasm: Although we and others have previously demonstrated that upon IFN-γ mediated activation, GBM cell lines are able to generate Kyn when cultured with tryptophan10,13, here we show that these tumor cells do not have the capacity to independently complete this metabolic pathway in its entirety, as QA was not present when GBM cell lines were cultured with either tryptophan or Kyn (Fig. 1f).