Bispecific Antibodies
To enhance efficacy and reduce risk of drug resistance and toxicity from combination therapies, bispecific antibodies are engineered to target two antigenic epitopes. By performing two functions in one molecule—binding tumor cells and recruiting cytotoxic immune cells, for example—bispecific antibodies can do more with less drug and potentially fewer side effects. As of 2023, seven bispecific antibodies have been approved for cancer therapy, with many more expected to come to market in the future. Bispecific antibodies can be either IgG-based or fragment-based. Antibody fragment formats carry advantages in yield, cost, and tumor penetration but require careful engineering to ensure optimal affinity and valency.16 The known advantages of VHH, including increased solubility and thermal stability, can be harnessed into bispecific or even trispecific VHH, in which two or three VHH domains are connected by a flexible peptide linker. Multispecific VHH are undergoing investigation for treatment of solid tumors and conditions like psoriatic arthritis and psoriasis.17
Antibody-Drug Conjugates
Advances in antibody engineering have enabled more precise payload targeting, allowing for highly specific therapies that deliver treatments directly to disease sites. Beyond standard mAb treatment, antibody-based therapy has expanded to include other types of drug products, such as antibody-drug conjugates (ADCs). ADCs combine a mAb with a cytotoxic payload and a linker that releases the payload once inside a tumor cell.18 As of 2023, thirteen ADC products have been FDA-approved for certain solid and hematologic cancers.19
This mechanism of payload targeting has been expanded to antibody-antibiotic conjugates (AAC), which enable highly selective delivery of antibiotics to target bacteria-infected cells and enhancing phagocytosis while minimizing off-target effects.20 While no AAC products have been FDA-approved as of the time of publication, several are in preclinical or clinical trials for major infectious diseases like Staphylococcus aureus.
CAR-T for Cancer Therapy
For the treatment of hematological malignancies, chimeric antigen receptor T-cell (CAR-T) therapy provides new second- or third-line treatment options for some patients. Six CAR-T therapies have been approved in the US and most of these use single-chain fragment variables (scFvs) as targeting domains. However, use of scFvs for CAR-T design may have limitations, such as the potential for folding instability and changes in binding affinity when engineered into a CAR using a linker. To overcome some of these issues, VHH are being explored for numerous CAR-T therapies and offer advantages in stability, low immunogenicity, binding affinity, and modularity that could lead to improvements in CAR-T efficacy.21
Beyond CAR-T
CAR therapies employing other immune cells, such as Natural Killer cells (CAR-NK), macrophages (CAR-M), and B cells (CAR-B), have been tested in numerous studies. Since most of the cytokines released by NK cells do not induce systemic inflammation, CAR-NK therapies have potential to reduce undesirable side effects of CAR therapy. CAR-NK therapies assembled with MICA-specific VHH have been recently shown to selectively kill MICA-positive lung tumor cells in mice, opening up more avenues for immunotherapy development.22
The first in-human trial testing macrophages engineered to target phagocytic activity against tumors began recruiting in 2022. In mouse xenograft models, these CAR-M cells reduced tumor burden and prolonged overall survival.23 Studies also observed that CAR-M engineering converted the macrophage phenotype from M2 to M1, cross-presented antigens to T cells, and contributed to dendritic cell maturation. Researchers have also started to investigate the possibility of designing B cells and dendritic cells against specific tumor cells, primarily integrating scFv antibodies in their construction.24
Antibodies for Agricultural and Industrial Applications
The potential of antibodies extends into other fields such as environmental monitoring. Immunosensors are favored for their high sensitivity, selectivity, and ability to assess the immunoreaction in real-time. Monitoring programs, regulatory agencies, and environmental researchers leverage antibodies to assess for the presence of herbicides and toxins in water, soil, air, and plants.25 For example, a mAb has been leveraged in an immunoassay to screen for excess levels of forchlorfenuron (CPPU) in cucumber samples—a plant growth regulator that can harm environmental and human health when used excessively.26 Additionally, antibodies are used to diagnose and monitor pathogens that affect crops and livestock. VHH have been engineered into ELISA tests for certain toxins, pathogens, and herbicides in crops like zucchini.27
Full-length rmAb or VHH can also be employed to produce pathogen-resistant plants. This method can help overcome risks associated with older pathogen resistance approaches, such as expressing a DNA sequence that disrupts a pathogenic life cycle, which is effective for viruses but runs the risk of recombination events. Since the late 1980s, engineered antibody expression has been used in numerous crops, such as tomatoes, beets, and citrus, to improve pathogen resistance and create a more secure global food supply.28 Researchers have also successfully used VHH as a component in tailored plant immune receptors to confer pathogen resistance to new species. For instance, blocking crops susceptible to broad bean mottle virus and grapevine fanleaf virus and engineered with VHH recognizing these viral targets improved resistance to a potentially widespread crop disease. VHH can also enhance delivery of bioactive compounds to insects and reduce the amount of insecticide that needs to be administered.27
Future Trends in Antibody Applications
The future of antibodies is wide open. Ongoing research into the capabilities of smaller and multispecific antibodies will unlock new classes of diagnostics and therapeutics for diseases that are not amenable to traditional mAb approaches. The potential of VHH to cross the blood-brain barrier, for example, could unlock possibilities in brain cancer, migraine, Alzheimer’s disease, and more.18 Investments into continuous drug manufacturing processes and scalability will increase yields and permit the distribution of products for chronic conditions.29 And artificial intelligence (AI) and machine learning are beginning to be integrated into the screening and discovery process.30
Fueled by these leaps, the next generation of antibody technology will continue to focus on overcoming barriers of conventional antibody design and engineering, making highly efficacious antibodies accessible to more people and for more conditions. We should expect to see improvements in precision, stability, manufacturing, and administration options.31