Recombinant human CD137L for cancer immunotherapy: effects of different fusions and linkers on its activity.

Co-stimulatory molecules can be efficiently produced as a recombinant protein in E. coli with a large range of applications in the fields of immunotherapy. However, whether, different fusions that would affect their functions have rarely been analyzed. To explore the effects of different fusions and linkers on the molecular conformation and activity of CD137 ligand (CD137L), a recombinant human CD137L protein (rhCD137L) library, which consists of the entire extracellular domain of human CD137L fused to N- or C-terminal His-tag through different linkers, was constructed and all rhCD137Ls were, respectively, expressed in E. coli BL21 (DE3) strain carrying a chaperone plasmid pG-Tf2. After purification of the soluble rhCD137Ls, the recombinant fusion proteins could markedly promote the growth of activated T cells, but their effects on cytokine productions were different from each other. The present work indicated that, although all rhCD137Ls have desired biological activity, different fusions and linkers did affect their structures and functions. Consequently, rational design of a library is a necessary and feasible approach for fusion proteins in order to obtain a satisfactory drug candidate for further development.