The present invention relates to a novel heterocyclic compound, a pharmaceutical composition comprisining said compound, a method and use of said compound for clinical treatment of medical conditions which may benefit from immunomodulation, e.g. rheumatoid arthritis, multiple sclerosis, diabetes, asthma, transplantation, systemic lupus erythematosis and psoriasis. More particularly the present invention relates to novel heterocyclic compounds, which are CD80 antagonists capable of inhibiting the interactions between CD80 and CD28. A method of screening compounds for their ability of inhibiting ligand-induced co-stimulatory receptor internalization pathways in immune competent human cells is described. Said immune competent human cells are incubated at conditions capable of inducing co-stimulatory receptor internalization in the presence of at least one test compound and the suppression of the ligand-induced co-stimulatory receptor internalization determined. There is also described a kit for use in such a method, as well as an immunoregulatory drug capable of blocking down-modulation of a ligand-induced receptor.