Concurrent IDO and TS downregulation sensitized cancer cells to pemetrexed more effectively than knockdown of IDO alone (Fig 7A and 7C): when pooled data from the 3 control clones and 2 anti-IDO shRNA clones were compared, knockdown of IDO alone increased sensitivity to pemetrexed by approximately 17% (Fig 7C, bar 3 vs bar 4) and knockdown of TS alone (TS siRNA #3) by 60% (Fig 7C, bar 5 vs bar 7), but knockdown of both IDO and TS (TS siRNA #3) increased sensitivity by 95% (Fig 7C, bar 8). This evidence concerns the gene IDO1 and cancer.