Development of a fully human t-cell engaging bispecific antibody for the treatment of multiple myeloma.

Abstract

60 Background: T-cell engaging bispecific antibody (T-BsAb) therapies are highly efficacious and well suited for targets with low expression on tumor cells. Recently, T-BsAbs with high activation of CD3 have been shown to overstimulate T cells, leading to toxicity and decreased efficacy. Teneobio has developed a fully human BCMA-specific T-BsAb using a low-activating αCD3 that is highly effective in vitro and in vivo against MM but stimulates minimal cytokine release. Methods: UniRats were immunized with either CD3 or BCMA antigens and antigen-specific UniAbs were identified by Ab repertoire sequencing and high-throughput gene assembly, expression, and screening. Antigen-specific VH sequences with the desired target affinity were selected using recombinant proteins and cells. In vitro efficacy studies included T-cell activation by cytokine- and tumor cell kill by calcein-release assays. In vivo efficacy of the molecules was evaluated in NSG mice harboring myeloma cells and human PBMCs. Results: BCMA-specific UniAbs bound plasma cells with sub-nM affinity. Strong and weak T cell agonists were identified that bound human T cells with high and low affinities respectively. T-BsAbs with a strong and a weak αCD3 demonstrated T-cell activation and tumor-cell cytotoxicity in vitro; T-BsAbs with a weak αCD3 showed markedly reduced cytokine production even at doses that showed maximum tumor cell lysis. In vivo, BCMAxCD3 T-BsAbs reduced tumor load and increased survival when co-administered with human PBMCs as compared to controls. Conclusions: Our results suggest that T-BsAbs with low-activating αCD3 arms may have a favorable toxicity profile while maintaining efficacy in the treatment of MM.