IDO1 and Ewing sarcoma: MAX et al., on the other hand, used transgenic techniques to study the CD137/CD137L pathway on Ewing sarcoma expression of IDO regulation of the CD137L transgenic tumor cells expressing IDO was significantly suppressed, and regulation of CD137/CD137L pathway was effective in reducing the expression of Ewing sarcoma cells by IL-2 stimulated expression of IDO (112).