The progression of a productive immune response requires that a number of immunological
checkpoints be passed. Passage may require the presence of excitatory costimulatory
signals or the avoidance of negative or coinhibitory signals, which act to dampen or
terminate immune activity. The immunoglobulin superfamily occupies a central importance
in this coordination of immune responses, and the CD28/cytotoxic T‐lymphocyte antigen‐4
(CTLA‐4): B7. 1/B7. 2 receptor/ligand grouping represents the archetypal example of these …