Used in immunological research to study T-cell regulation and immune checkpoint pathways. Functions as a soluble receptor that binds to B7 molecules (CD80/CD86) on antigen-presenting cells, blocking the co-stimulatory signal required for T-cell activation. This makes it valuable in assays investigating immune inhibition, autoimmunity, and cancer immunotherapy. Commonly employed in ELISA, flow cytometry, and in vitro functional assays to modulate immune responses. Also used as a reference standard or capture/detection reagent in protein interaction studies involving the CTLA-4 pathway.