To determine whether the BM microenvironment in pediatric AML is characterized by high (‘hot’) or low (‘cold’) T cell infiltration, we performed immunohistochemistry (IHC) with antibodies against CD3 and CD8 on 82 FFPE BM biopsies from pediatric patients with treatment-naïve de novo AML (n = 72), and age- and sex-matched non-leukemic individuals (n = 10; Fig. 1A; representative images shown in Fig. 1B, C; collectively referred to as ‘primary study cohort’). This evidence concerns the gene CD8A and acute myeloid leukemia.