Hypothesizing that the relative infiltration levels of CD8+ T lymphocytes and CD68+CD163+ macrophages capture the interplay between anti- and pro-tumoural aspects of the immune microenvironment, we generated a combined immune biomarker by computing the ratio of CD8+ cell density to the sum of the densities of CD8+ and CD68+CD163+ cells, and termed it the ‘Signature of Immune Activation’ (SIA) (Fig. 1f). The gene discussed is CD8A; the disease is neoplasm.