CD274 and acute lymphoblastic leukemia: Following oncogene inactivation, vascular remodeling and clearance of acute lymphoblastic leukemia (ALL) cells are promoted through PDGF secretion by CD4+ T cells.379 In chronic lymphocytic leukemia (CLL), exosomes enriched with noncoding RNAs (e.g., hY4) are secreted by tumor cells, which induce PD-L1 expression and the release of protumor factors (CCL2 and IL-6) via TLR7 signaling activation in monocytes, thereby establishing an immunosuppressive niche.380 The dormancy-activation transition of tumor cells is profoundly influenced by stromal-leukemic cell crosstalk.