Bispecific monoclonal antibody

Source: Wikipedia, the free encyclopedia.

A bispecific monoclonal antibody (BsMAb, BsAb) is an artificial

epitopes on the same antigen.[1] Naturally occurring antibodies typically only target one antigen. BsAbs can be manufactured in several structural formats. BsAbs can be designed to recruit and activate immune cells, to interfere with receptor signaling and inactivate signaling ligands, and to force association of protein complexes.[2] BsAbs have been explored for cancer immunotherapy, drug delivery, and Alzheimer's disease.[1][3]

Development history

The original concept of BsAbs was proposed by Nisonoff and his collaborators in the 1960s, including the first idea of antibody architecture and other findings.

quadroma) technology.[7] In 1988, the single-chain variable fragment (scFv) was invented by the Huston team to minimize the refolding problems, which contains the incorrect domain pairing or aggregation of two-chain species.[8] In 1996, the BsAbs became more developed when the knobs-into-holes technology emerged.[1][9]

Structural types and manufacturing methods

Three types of bispecific antibodies: trifunctional antibody, chemically linked Fab and bi-specific T-cell engager (bottom row). Blue and yellow parts distinguish parts from separate monoclonal antibodies.

There are many formats of BsAbs, but the two main categories are IgG-like and non-IgG-like.[3] The main types of manufacturing methods are quadromas, chemical conjugation, and genetic recombination, and each method results in a unique format.[3][10]

IgG-like

This format retains the traditional

quadroma, or the hybrid hybridoma, method.[11][12][13]

DVD-Ig Knob in Hole
The "knobs into holes" approach for manufacturing IgG-like bsMabs is shown on the left, while a diagram depicting the DVD-Ig format is on the right. The red dot indicates a possible site for introducing mutations in the heavy chain. Blue and yellow correspond to separate monoclonal antibodies.

However, the quadroma method relies on random chance to form usable BsAb, and can be inefficient. Another method for manufacturing IgG-like BsAb is called "knobs into holes," and relies on introducing a mutation for a large amino acid in the heavy chain from one mAb, and a mutation for a small amino acid in the other mAb's heavy chain. This allows the target heavy chains (and their corresponding light chains) to fit together better, and makes the production of BsAbs more reliable.[3][10]

Non-IgG-like

There are other BsAbs that lack an Fc region entirely, and thus leads to relatively simple design strategies.

variable domains of two antibodies. The furthest developed of these newer formats are the bi-specific T-cell engagers (BiTEs), which uses the G4S linker to connect two ScFvs-one CD3 antibody ScFv and one tumor-associated antigen (TAA) or tumor-specific ScFv-to redirect T cells to cancer cells for target killing.[14][15][16] Other platforms include tetravalent antiparallel structure (TandAbs) and VH only (Bi-Nanobody). The TandAb platform is formed by a tetravalent antibody molecule containing two binding sites for each of two antigens.[17] In this platform, the reverse pairing of two peptide chains forms a homodimer molecule. As an example, AFM11 is based on the TandAbs platform and targets both CD3 and CD19 to achieve therapeutic effects. AFM11 showed dose-dependent inhibition of Raji tumors in vivo.[18] The Bi-Nanobody platform forms multi-specific binding through the connection between the VH regions of two or more antibody molecules. The products that are designed based on this platform are small molecules and these small molecules have high stability and better tissue permeability in vivo.[19] Even though non-IgG-like BsAbs have low molecular weight and thus high tumor tissue permeability, their half-life is relatively short and they require multiple doses.[1]

Despite the considerable differences between the various types and formats of bispecific antibodies, their manufacturing processes correspond in several steps:

Mechanism of action

The mechanism of action of a BsAb, exemplified by catumaxomab, representing the first approved bispecific trifunctional antibody.

Recruiting and activating of immune cells

The binding of a BsAb to its target antigens can lead to a variety of effects. The most widely used application of this approach is in

antibody-dependent cell-mediated cytotoxicity or complement-dependent cytotoxicity.[13][15]

live cell imaging
microscope.

Interfering with receptor signaling and inactivating signaling ligands

The growth of tumor cells can be simulated or modulated by receptor tyrosine kinase (RTKs), including members of the Her family or insulin-like growth factor (IGF). The RTKs are therefore preferred targets in cancer therapy. Although monospecific RTK-targeting IgGs have already been available in the market, such as cetuximab (Erbitux) and panitumumab (Vectibix), both of which are directed against HER1. However, cancer cells can switch to a different pathway to escape the growth inhibition generated by blocking one signaling pathway. To improve the therapeutic efficacy, simultaneously interfering/blocking of two (or more) RTK signaling pathways, achieved through the mediation of BsAb to inactivate either the RTKs or their ligand, reduces the possibility of the escape mechanisms adopted by the tumor cells.[21][22]

In addition, in working with Ebolavirus vaccines, a study has shown that a DVD-Ig antibody can be used to prevent viral escape from the endosome. Ebolaviruses infect cells by receptor-mediated endocytosis. Researchers developed DVD-Igs where the outer variable regions bind to the surface glycoproteins of the viral coat and enter the cell with the virus. These outer regions are cleaved in the viral endosome, revealing the inner variable regions that then bind to both the virus and internal receptors in the endosome. Blocking the interaction between the virus and endosomal proteins prevents viral escape from the endosome and further infection.[23]

Forcing association of protein complexes

As an example, emicizumab (formerly RG6013) is an IgG derivative containing H-chain heterodimerization motifs, which was combined with the common light chain approach to prevent L-chain mispairing issues.[24][25] With a bivalent composition, emicizumab brings two protein antigens together into one complex. Factor IXa and Factor X in the coagulation cascade are the cognate antigens which are bound by RG6013. These two factors are brought together by coagulation factor VIIIa in a healthy individual, while patients with bleeding disorder hemophilia A do not have VIIIa. Current treatment of this disorder is to supplement the patients with FVIII to reduce bleeding complications. But FVIII can be recognized as a foreign protein in these patients due to the absence of this protein and thus an immune response will be generated against this protein. Besides, FVIII has a short half-life (less than 15 hours) and thus is cleared rapidly. However, the humanized BsAb has lower immunogenicity and long serum half-life compared with FVIII and thus provide a better treatment for hemophilia.[2]

Advantages over ordinary monoclonal antibodies

orders of magnitude lower than with ordinary antibodies.[26] For non-IgG-like BsAbs, their smaller size allows them to reach antigens usually unavailable to conventional antibodies.[3] In the case of Ebola vaccines, this method allows the antibody to target intracellular targets not usually accessible by traditional monoclonal antibody treatments.[23]

Additionally, targeting more than one molecule can be useful to circumvent the regulation of parallel pathways and avoid resistance to the treatment. Binding or blocking multiple targets in a pathway can be beneficial to stopping disease, as most conditions have complicated multifaceted effects throughout the body.[28] Together with combination therapies, BsAbs are being used more and more to treat certain types of cancers, as, over time, some tumors develop resistances to checkpoint inhibitors and/or co-stimulatory molecules.[29]

Current Scenario of bsAb drugs

Currently, nine bsAb drugs have been approved by the US FDA / EMA and over 180 are currently in clinical trials. The first bispecific antibody to gain regulatory approval, blinatumomab, targets CD19 on B cells and CD3 on T cells, leading to the activation of T cells and the destruction of B cells.[30] A total of eight more bispecific antibody drugs have since been approved by the US FDA: blinatumomab, emacizumab, amivantamab, tebentafusp, faricimab, teclistamab, mosunetuzumab, epcoritamab, glofitamab.[31] Among the bsAb programs currently under development, the combination of CD3 and tumor surface targets are the most popular targets pairs. Other popular targets are CD3, HER2, PD-1, PD-L1, EGFR, CTLA-4, etc., which as well as immune targets of PD-1, PD-L1, BCMA, CD47, CTLA-4, LAG-3, 4 -1BB.[32] Additionally, with the approval of the several new bsAb since 2022, and new mechanisms for improving efficacy like development of hetero-dimer bispecific molecules, several additional possibilities of target pairs have emerged.[32]

Problems and current disadvantages

IgG-like antibodies can be immunogenic, which means the Fc region could cause detrimental downstream immune responses caused by cells that are activated by Fc receptors.[3] The therapeutic use of BsAbs as a whole is still largely in development, with many clinical trials currently ongoing that are determining the efficacy and safety of BsAbs for treatment.[14]

Applications

Bispecific antibodies have a wide variety of applications in diagnosis and therapy. BsAbs can be combined with HRPO, can be used in pre-targeting strategies, and can be used to provide better imaging for early detection in diagnosis. To treat cancer, BsAbs can target immune cells precisely, help and reactive the immune cells, fine-tune the fate and function of immune cells, improve the tolerance of immune cells, and promote the return to immune homeostasis. BsAbs can also be applied to treat other diseases, including hemophilia A, diabetes, Alzeimer's disease, and ophthalmological diseases.[1]

BsAbs on the market

Three bispecific antibodies are presently in clinical use.

non-small cell lung cancer (NSCLC) with epidermal growth factor receptor (EGFR) exon 20 insertion mutations.[35]

References

Public Domain This article incorporates

U.S. National Cancer Institute
.

External links