CD86 (B7-2) is a costimulatory molecule expressed on antigen-presenting cells that plays a central role in T cell activation and immune regulation. Functionally, CD86 serves as a ligand for CD28 and CTLA-4 receptors on T cells, delivering costimulatory signals essential for productive immune responses 1. CD86 is the primary B7 homologue driving human T cell proliferation and proinflammatory cytokine production 1. However, CTLA-4 can capture CD86 from antigen-presenting cells through trans-endocytosis, depleting ligand availability and suppressing CD28-mediated costimulation, thereby functioning as a negative immune regulator 2. CD86 expression has significant disease relevance. Genetic polymorphisms in CD86 (particularly +1057G/A) are associated with increased susceptibility to brucellosis and pancreatic cancer 34. CD86 is highly expressed in B-cell malignancies, potentially facilitating tumor immune evasion 5. In cancer immunotherapy, CD86-specific blockade, distinct from broader checkpoint inhibition, can redirect immune responses toward productive CTL priming by preventing aberrant regulatory T cell activation following radiotherapy 6. Clinically, understanding CD86 biology informs development of immunotherapeutic strategies that selectively target costimulatory pathways rather than employing broad CTLA-4 or PD-1 blockade, particularly in lymphocyte-depleted malignancies 6.