IDH1 and central nervous system cancer: Notably, IDH-Mut tumors exhibit immune-cold signatures characterized by a general paucity of immune cells.40 Furthermore, IDH-mut gliomas exhibit greater myeloid-to-lymphoid cell ratios, ostensibly predominated by microglial transcriptional signatures.41,42 Perhaps non-coincidentally, histone-mutant tumors are also largely immune cold.43 IDH-A tumors contain more myeloid cells (microglia and macrophages) than IDH-O tumors,20 and are enriched for monocytic-lineage cells from circulation.