Similar to the situation inside a Toxoplasma-infected cell, tumor microenvironments (TME) have limiting amounts of TRP, and this depletion is thought to be mediated by constitutive and regulated IDO1 (and possible TDO2) expression in infiltrating myeloid cells and tumor cells themselves, combined with the anabolic requirements of the tumor mass (Murray, 2016). Here, TDO2 is linked to neoplasm.