So what advantages do bsAbs offer? At the risk of stating the obvious, bsAbs can simultaneously bind to two different antigens. In immunotherapy for example, their “Y” shape allows the first prong of the antibody to find and locate a receptor tyrosine kinase ROR1 protein, which is only present on the surface of cancer cells. The second bsAb prong attracts and binds to killer T-cells. This binding activates the killer T-cell to release toxins that can destroy the cancer cell.
Two decades of work have delivered a range of recombinant bispecific antibody formats, with more than 50 different formats now available. This variety has accelerated their use for a range of therapeutic applications. For example, bsAb developers have recently created bispecific fragments with Fc regions allowing the mediation of Fc effector functions. Due to their smaller size, these fragments have better solid-tumor penetration rates. Additionally, because they are rapidly cleared from a patient’s bloodstream, developers can more easily can adjust the size, valency, flexibility, and half-life of the bsAbs to best meet application needs.
The current success of bispecific antibodies has been made possible by overcoming significant manufacturing challenges. In the earlier days of bsAb development, wild-type IgG sequences were used. Wild-type IgG sequences led to the random association of chains and combinatorial associations of the two heavy and light chains, creating up to ten different products.”Early attempts to produce bispecific antibodies relied on the conjugation of antibody fragments or on the fusion of two different hybridomas to generate a quadroma. These approaches were suitable for research purposes but not for clinical applications as the source material was not easily scalable,” a recent paper published in BioDrugs entitled “Expanding the Boundaries of Biotherapeutics with Bispecifc Antibodies” stated.
While various therapeutic approaches tend to have their strengths and weakness, there are indications that bsAbs might provide a simpler and more feasible path to success in some cases. For example, bluebird bio and partner Celgene has been working on a therapeutic to treat patients with aggressive multiple myeloma. The Celgene-bluebird therapeutic, bb2121, relies on engineering a patients T-cells to express a chimeric antigen receptor (CAR-T) that recognizes beta cell maturation antigen (BCMA). This approach requires patients to spend a few days in the hospital so that they can be treated with lymphodepleting chemotherapy. Their T-cells are then removed and shipped to a manufacturing site, where they are then trained to express the needed CAR-T.
This approach poses obvious unpleasantries for patients, high costs and an inefficient production process. On the other hand, Amgen’s therapeutic, AMG-420, looks like it might be superior in terms of efficacy, manufacturability and administration efficiency. The Motley Fool’s Cory Renauer recently reported, “AMG-420 is part of a drug class called bi-specific T-cell engagers (BiTEs), which are just two-sided proteins that can be taken off a shelf and plugged into a patient’s IV drip. Despite being easier to manufacture, warehouse, and administer to patients, AMG-420 accomplishes the same complex task as bb2121 by clinging to BCMA with one arm, while the opposite side engages T-cells and holds them in place until they cause the cancerous cell to burst.”
These studies are in their early days and it is much too soon to jump to any conclusions. But, AMG-420 is an example of how with key enabling development and manufacturing technologies now in place, bsAbs are poised for a bright future.