eIg-based bispecific T-cell engagers targeting EGFR: Format matters

A bispecific antibody that targets the membrane-proximal region of mesothelin and retains high anticancer activity in the presence of shed mesothelin

Mesothelin (MSLN) is a cell-surface protein that is expressed on many cancers, which makes it a popular target for antibody-based cancer therapy. However, MSLN is shed from cancer cells at high levels via proteases that cleave at its membrane-proximal C-terminal region. Shed MSLN accumulates in patient fluids and tumors and can block antibody-based MSLN-targeting drugs from killing cancer cells. A previously established monoclonal antibody (mAb), 15B6, binds MSLN at its protease-sensitive C-terminal region and does not bind shed MSLN. 15B6 variable fragment (Fv)-derived chimeric antigen receptor (CAR) T cells are not inhibited by shed MSLN and kill tumors in mice more effectively than mAb SS1 Fv-derived CAR T cells, which bind an epitope retained in shed MSLN. Here, we have established 15B6 Fv-derived MSLN x CD3 bispecific antibodies (BsAbs) that target MSLN-expressing cancers. We identified our lead candidate, BsAb 5, after screening multiple 15B6-derived BsAb formats in vitro for cytotoxic activity. BsAb 5 activates T cells to kill various cancer cell lines in a MSLN-specific manner. MSLN 296-591 His, a recombinant protein mimicking shed MSLN, does not inhibit 15B6-derived BsAb 5 but completely inhibits humanized SS1-derived BsAb 7. Furthermore, BsAb 5 inhibits and delays tumor growth and is not inhibited by MSLN 296-585 His in mice. Our findings indicate that by targeting the protease-sensitive region of MSLN, BsAb 5 has high MSLN-specific anticancer activity that is not inhibited by shed MSLN. BsAb 5 may be a promising immunotherapy candidate for MSLN-expressing cancers.

Design and engineering of bispecific antibodies: insights and practical considerations

Bispecific antibodies (bsAbs) have attracted significant attention due to their dual binding activity, which permits simultaneous targeting of antigens and synergistic binding effects beyond what can be obtained even with combinations of conventional monospecific antibodies. Despite the tremendous therapeutic potential, the design and construction of bsAbs are often hampered by practical issues arising from the increased structural complexity as compared to conventional monospecific antibodies. The issues are diverse in nature, spanning from decreased biophysical stability from fusion of exogenous antigen-binding domains to antibody chain mispairing leading to formation of antibody-related impurities that are very difficult to remove. The added complexity requires judicious design considerations as well as extensive molecular engineering to ensure formation of high quality bsAbs with the intended mode of action and favorable drug-like qualities. In this review, we highlight and summarize some of the key considerations in design of bsAbs as well as state-of-the-art engineering principles that can be applied in efficient construction of bsAbs with diverse molecular formats.

Facilitating high throughput bispecific antibody production and potential applications within biopharmaceutical discovery workflows

A major driver for the recent investment surge in bispecific antibody (bsAb) platforms and products is the multitude of distinct mechanisms of action that bsAbs offer compared to a combination of two monoclonal antibodies. Four bsAb products were granted first regulatory approvals in the US or EU during 2023 and the biopharmaceutical industry pipeline is brimming with bsAb candidates across a broad range of therapeutic applications. In previously reported bsAb discovery campaigns, following a hypothesis-based choice of two specific target proteins, selections and screening activities have often been performed in mono-specific formats. The conversion to bispecific modalities has usually been positioned toward the end of the discovery process and has involved small numbers of lead molecules, largely due to challenges in expressing, purifying, and analyzing large numbers of bsAbs. In this review, we discuss emerging strategies to facilitate the production of expanded bsAb panels, focusing particularly upon combinatorial methods to generate bsAb matrices. Such technologies will enable screening in. bispecific formats at earlier stages of discovery campaigns, not only widening the accessible protein space to maximize chances of success, but also advancing empirical bi-target validation activities to assess initial target selection hypotheses.

Engineering bispecific T-cell engagers to deplete eosinophils for the treatment of severe eosinophilic asthma

Severe eosinophilic asthma (SEA) is characterized by elevated eosinophil counts in the blood and airway mucosa. While monoclonal antibody therapies targeting interleukin-5 (IL-5) and its receptor (IL-5Rα) have improved treatment, some patients remain unresponsive. We propose an alternative approach to eliminate eosinophils using T cells by engineering IL-5Rα × CD3 bispecific T-cell engagers (bsTCEs) that target both IL-5Rα on eosinophils and CD3 on T cells. We designed different formats of IL-5Rα × CD3 bsTCEs, incorporating variations in valency, geometry, and affinity for the target antigen binding. We identified the single-chain variable fragment (scFv)-Fc format with the highest affinity toward the membrane-proximal domain of IL-5Rα in the IL-5Rα-binding arm showed the most potent cytotoxicity against IL-5Rα-expressing peripheral eosinophils by activating autologous primary T cells from healthy donors. This study proposes IL-5Rα × CD3 bsTCEs as potential alternatives for SEA treatment. Importantly, it demonstrates the first application of bsTCEs in eliminating disease-associated cells, including eosinophils, beyond cancer cells.