Cd80, also known as B7-1, is a transmembrane glycoprotein belonging to the B7 family and a crucial molecule in T cell modulation. Its ligands mainly include CD28, PD-L1, and CTLA-4. It plays a significant role in the immune system, especially during T-cell activation, and is involved in immune-related pathways such as the CTLA4-CD80/86 axis which is important in immune response regulation [3,4]. It is expressed on antigen-presenting cells and also on the surface of some tumor cells, thus being relevant in both anti-tumor immune responses and autoimmune diseases [3].

In a knock-in mouse model where cis -PD-L1/CD80 interactions do not occur, tumor immunity and autoimmune responses were greatly attenuated by PD-1. This indicates that CD80 on antigen-presenting cells limits the PD-1 coinhibitory signal while promoting CD28-mediated costimulation, highlighting its importance in inducing optimal immune responses [1]. In another study, treating mammary tumors with chemotherapy followed by targeting the CD80 axis led to marked T cell accumulation, although tumors were not fully eradicated, revealing the role of CD80 in immune-modulatory programs of breast cancer cells surviving chemotherapy [2]. Also, in CD80 -/- mice infected with HSV-1, the absence of CD80 led to increased inflammation and reduced latency but no effect on reactivation, suggesting that CD80 plays a role in HSV-1-induced immunopathology [5].

In conclusion, Cd80 is essential in T-cell activation and immune response modulation. Gene-knockout mouse models have revealed its role in various disease conditions such as tumor immunity, autoimmune responses, breast cancer survival post-chemotherapy, and HSV-1-related immunopathology. Understanding Cd80's functions through these models provides insights into immune-related disease mechanisms and potential therapeutic strategies.