Combination of a bispecific antibody and costimulatory antibody-ligand fusion proteins for targeted cancer immunotherapy.

Initiation of a tumor-directed immune response and appropriate modulation of its progress are key issues in cancer immunotherapy. Combinatorial strategies addressing both aspects might therefore be especially suitable. Here, we report a targeted approach combining a bispecific antibody with 2 costimulatory antibody-ligand fusion proteins. According to the concept, the bispecific antibody (scDbFAP×CD3) retargets T cells in a MHC-independent manner to tumor cells, providing an artificial first signal that allows the costimulatory antibody-ligand fusion proteins (B7.2-Db and scFv-4-1BBL) likewise targeted to the tumor cells to modulate the T-cell response. In our model system, the target cells coexpress the fibroblast activation protein (FAP) and endoglin as antigens. ScDbFAPCD3 and B7.2-Db are targeted to FAP although by different antibody moieties, whereas scFv-4-1BBL is directed against endoglin. ScDbFAPCD3-induced T-cell stimulation could be enhanced by the addition of either B7.2-Db or scFv-4-1BBL and even further by the combination of both as shown in terms of cytokine release (interleukin-2/interferon γ), proliferation and activation marker expression (CD25). By combined costimulation, overall T-cell population strongly increased in activation-experienced memory phenotype accompanied by a decrease in naive phenotype. ScFv-4-1BBL-mediated costimulation of naive CD8+ T cells promoted the expansion and development of cytotoxic T cells with strong effector potential. Thus, combining a bispecific antibody with antibody-ligand fusion protein-mediated CD28 and 4-1BB costimulation in a targeted approach shows great potential to generate and shape an immune response at the tumor site. Therefore, the adaptation of this approach to other immune modulatory ligands and tumor-relevant targets seems to be promising.