CD8A and breast cancer: Notably, the number of double-negative T cells (CD3+CD4- CD8-) accounted for ~31.0% of all T cells in breast cancer but only 1–5% in healthy humans.154,155 Double-negative T cells play a key role in inflammation and autoimmunity.152,153 However, three independent clusters with high levels of effector markers (GZMA, GZMB, and IFN-γ), regulatory markers (FOXP3 and IL2RA), and naïve markers (CCR7) indicate that double-negative T cell function is important and complex in the TNBC microenvironment.