Identifying a Csmd3 ⁺ Microglial Subpopulation that Drives Cold‐to‐Hot Transition and Immune‐Cure in Glioblastoma

ABSTRACT Glioblastoma (GBM) is immunologically cold and responds poorly to immune‐based therapies owing to its highly heterogeneous and immunosuppressive tumor microenvironment (TME). However, strategies to achieve a cold‐to‐hot transition remain elusive, and suitable research models are still lacking. Here, TME profiling classifies our refractory G422 ^TN ‐GBM model as the TME ^Med (heterogeneous immune populations, “cold”) subtype of human GBM, which can be shifted toward the TME ^High (immune‐high, “hot”) subtype by inhibiting TGF‐β signaling. In the multi‐drug regimen, only αTGF‐β combining temozolomide chemoradiotherapy and αPD‐1 achieves immune‐cure (ICu, passing tumor rechallenge, 12.5%). ICu screening reveals a newly identified Csmd3 ⁺ microglial subset with innate immune memory potential, which likely initiates durable anti‐GBM immune memory and closely associates with effective GBM therapy and favorable prognosis. MG ^{OE• Csmd3 , BV2} ( Csmd3 ‐overexpressed microglial BV2) elicit robust anti‐GBM effects and achieve a notably 100% tumor rechallenge success in G422 ^TN ‐GBM mice via promoting TME ^Med ‐to‐TME ^High remodeling. Taken together, our findings identify an immunologically cold TME ^Med GBM mouse model and provide a proof‐of‐concept for microglia‐based TME reprogramming and cell therapy in GBM.