PTPRC (CD45) is a transmembrane protein tyrosine phosphatase expressed on virtually all hematopoietic cells except mature erythrocytes, serving as an essential regulator of T and B cell antigen receptor signaling 1. As a receptor tyrosine phosphatase, CD45 functions upstream of T cell receptor (TCR) signaling by excluding itself from the immunological synapse, thereby maintaining the activation threshold for immune responses 23. CD45 can be modulated by extracellular ligands—including adenoviral proteins like E3/49K—that dimerize CD45 and suppress its phosphatase activity, consequently inhibiting T cell activation 3. Pathologically, CD45 expression on circulating tumor cells enables immune evasion through homophilic CD45-CD45 interactions with T cells, reducing TCR signaling and promoting metastasis 4. Clinically, CD45-based imaging effectively detects inflammation across multiple disease contexts, outperforming standard methods 5. Genetic variants in PTPRC (rs10919563 A allele) are associated with poor response to TNF-blocking therapy in rheumatoid arthritis, suggesting utility for personalized treatment prediction 6. Disruption of PTPRC-mediated signaling balance can result in immunodeficiency, autoimmunity, or malignancy 1.