Developing co-stimulatory agonists targeting CD28 therefore represents a promising strategy to enhance the efficacy of T cell based anti-tumor immunotherapy.<h4>Results</h4>In this study, we isolated 34 VHHs (VHHs) from a phage-display immune library generated using PBMCs of a Bactrian camel immunized with recombinant human CD28 protein. Here, CD28 is linked to neoplasm.