PRDM1 (PR/SET domain 1) is a transcription factor that functions as a master regulator of immune cell differentiation and tissue residency. As a DNA-binding transcriptional repressor, PRDM1 negatively regulates gene expression programs that control lymphocyte development and function 1. In B cell development, PRDM1 drives the differentiation of B lymphocytes into immunoglobulin-secreting plasma cells, and its absence defines follicular helper T cells critical for germinal center formation 1. PRDM1 plays dual roles in T cell biology: elevated expression in tumor-infiltrating CAR T cells associates with exhaustion and reduced stemness, while PRDM1 knockout maintains early memory phenotypes and enhances anti-tumor efficacy 23. In autoimmune contexts, a primate-specific short isoform (PRDM1-S) promotes regulatory T cell dysfunction in multiple sclerosis by inducing SGK1 expression and destabilizing FOXP3, suggesting PRDM1 dysregulation contributes to autoimmune pathogenesis 4. Additionally, BLIMP1 (PRDM1 protein product) prevents transcriptional repression of oncogenes in diffuse large B cell lymphoma by blocking repressor binding to hypermutated super-enhancers 5. These findings establish PRDM1 as a critical epigenetic regulator with therapeutic relevance in cancer immunotherapy and autoimmune disease.