CD8A and colorectal cancer: However, comparison of pre- and post-treatment tumor biopsies from a patient with advanced colorectal cancer indicated a shift from a suppressive tumor microenvironment at baseline, characterized by Tregs and GITR expression, toward a tumor microenvironment characterized by a lack of Tregs, increased numbers of CD8+ T-cell infiltrates, and 10-fold less GITR expression (10% to 1%), indicating tumor target coverage in this patient (Fig. 3c).