IDO1 and neoplasm: Many immunosuppressive elements of the TME, including upregulation of PD-L1, production of indolamine-2,3-dioxygenase (IDO) and elevated numbers of Tregs, are induced as a consequence of the anti-tumor immune response itself.22 In order to investigate how activated T cells influence the phenotype of CAFs and vice versa we measured phenotypic and functional changes in both populations during co-culture in primary NSCLC samples.