PDCD1 and acute lymphoblastic leukemia: Specifically, two exhausted T cell clusters (CD4_Exhau and CD8_Exhau) were shown in B‐ALL patients, which were characterized with high levels of the exhaustion markers LAG3, PDCD1, TIGIT, and HAVCR2[21] (Figure 1C; Figures S1F,G, S2A,B, and Table S2, Supporting Information).