Single-Chain Variable Fragment-Based Bispecific Antibodies: Hitting Two Targets with One Sophisticated Arrow

Abstract

Despite the success of monoclonal antibodies (mAbs) to treat some disorders, the monospecific molecular entity of mAbs as well as the presence of multiple factors and pathways involved in the pathogenesis of disorders, such as various malignancies, infectious diseases, and autoimmune disorders, and resistance to therapy have restricted the therapeutic efficacy of mAbs in clinical use. Bispecific antibodies (bsAbs), by concurrently recognizing two targets, can partly circumvent these problems. Serial killing of tumor cells by bsAb-redirected T cells, simultaneous blocking of two antigens involved in the HIV-1 infection, and concurrent targeting of the activating and inhibitory receptors on B cells to modulate autoimmunity are part of the capabilities of bsAbs. After designing and developing a large number of bsAbs for years, catumaxomab, a full-length bsAb targeting EpCAM and CD3, was approved in 2009 to treat EpCAM-positive carcinomas besides blinatumomab, a bispecific T cell engager antibody targeting CD19 and CD3, which was approved in 2014 to treat relapsed or refractory acute lymphoblastic leukemia. Furthermore, approximately 60 bsAbs are under investigation in clinical trials. The current review aims at portraying different formats of the single-chain variable fragment (scFv)-based bsAbs and shedding light on the scFv-based bsAbs in preclinical development, different phases of clinical trials, and the market.

Keywords: ESKAPE; HIV-1; autoimmune diseases; bacteria; bispecific antibody; cancer; monoclonal antibody; single-chain variable fragment.

Figure 1

The Schematic Representation of Various scFv-Based bsAb Formats These bsAbs either employing immune cells, such as T cells and NK cells, and bringing them close to the target cell or targeting two vital markers on the cell(s) could exert their therapeutic functions in a range of disorders, such as cancers, autoimmune diseases, and infectious diseases. (A) Whole antibody, (B) antigen-binding fragment (Fab), (C) single-chain variable fragment (scFv), (D) single-domain antibody (e.g., VHH), (E) tandem scFv (e.g., bispecific T cell engager), (F) diabody, (G) tandem antibody (TandAb), (H) dual-affinity retargeting (DART), (I) scFv₂-Fc, (J) scFv₂-scFv₂-Fc, (K) scFv-VHH-Fc, (L) anti-IGF-1R IgG-scFv₂, and (M) Fab₂-scFv₂-Fc (e.g., BiS4aPa) are shown.