PTGS2 and neoplasm: Other mechanisms of MDSC-induced suppression of effector T cells comprise induction of Tregs by IL-10 secretion in mouse models of colon carcinoma, B16 melanoma, and in patients with HPV-induced neoplasia [59]; depletion of cysteine, the essential aminoacid necessary for T cell activation [60]; secretion of high peroxynitrite levels, which lead to tumor progression [61] upregulation of Cox2/PGE2 [62].