CD8A and neoplasm: More importantly, this enzyme seems to promote tumor progression, by predominantly acting on regulatory T cells (Tregs), effector cytotoxic CD8+ T cells (Teff), and natural killer cells (NK) (Munn and Mellor 2016); these lymphocytes exert a protective activity by reducing tumor progression and improving antitumor immunity, but kynurenine can suppress CD8+ T and NK cells and bias Tregs differentiation (Muller et al. 2018).