EXAMPLE 41
To verify if the CD28-Fc binding clones could also bind to the native form of the CD28 antigen, serial dilutions of purified protein preparations of such clones were allowed to bind to the human Jurkat T-cell line, which expresses human CD28. Binding of putative CD28 reactive Nanobodies clones was detected using unlabeled anti-c-myc tag mouse monoclonal antibody 9E10, followed by a phycoerythrin conjugated F(ab′)2 derived from goat-anti-mouse IgG (human and bovine crossabsorbed), and read on a BD FACSarray instrument. Dead cells were excluded from the analysis by gating out TOPRO3 vital dye positive scoring cells. Binding of the Nanobodies to cells was evaluated in BD FACS array control software as PE channel histograms. Based on these FACS experiments, all CD28-Fc binding Nanobody clones bound cell expressed CD28. Results of a representative experiment are depicted in
