MAP4K1 encodes hematopoietic progenitor kinase 1 (HPK1), a serine/threonine kinase that serves as a negative regulator of T-cell receptor signaling and immune responses. The protein functions by phosphorylating adaptor proteins SLP-76 and Gads, thereby dampening T-cell activation 1. MAP4K1 also participates in the Hippo signaling pathway, acting upstream of LATS1/2 to control organ size and tumor suppression [UniProt reference]. In cancer contexts, MAP4K1 demonstrates complex roles: high expression correlates with T-cell exhaustion and worse patient survival across multiple cancer types 2, while in glioblastoma, it facilitates tumor growth by modulating cytokine-chemokine networks and reducing CD8+ T-cell infiltration 3. Conversely, heterozygous loss-of-function variants cause immune dysregulation through amplified T-cell responses, leading to hyperproduction of proinflammatory cytokines like IFN-γ and TNF 1. Clinically, MAP4K1 represents a promising therapeutic target for cancer immunotherapy, with genetic depletion or pharmacological inhibition improving CAR-T cell efficacy in preclinical models 2. The protein's dual role as both a tumor promoter and immune suppressor makes it an attractive druggable target, with small molecule inhibitors currently in clinical development 4.