Antibodies have driven the development of research and medicine. Their specificity, stability, and reduced immunogenicity have made them one of the most desirable biopharmaceuticals and reagents in the last decades. Today, the use of antibodies spans from therapeutics, diagnostics, and fundamental research. However, typical monoclonal antibody production processes have difficulties keeping up with the increasing demand for these biomolecules.
Limitations of conventional monoclonal antibody production processes
A typical monoclonal antibody production process starts by cloning antibody-encoding genes and transfecting mammalian cell lines for recombinant production. However, the transfection of mammalian cell lines is difficult due to the inherent complexity of their genetic machinery. Moreover, teaching these cells on how to make high amounts of new antibodies is not feasible during devastating pandemics or epidemics.
Early in 2019, a team of scientists at Vanderbilt University Medical Center (VUMC) showed it may be possible to bypass the hurdles of conventional monoclonal antibody production processes. Instead of relying on conventional methods of antibody production, they went for a radically different approach – mRNA antibody delivery.
By teaching the cells to manufacture specific antibodies, we could grant risk groups (medical staff, elderly, children, etc.) passive protection and give them a better chance of fighting and surviving devastating infections when urgent solutions are necessary.
Would passive immunization be a better solution than vaccination?
In a recent paper, Rob Hooft van Huijsduijnen and his team argue that although vaccination has proven the be effective against many deadly pathogens, we should not overlook the benefits of passive immunization in the fight against infectious diseases.
According to their exhaustive literature review on the topic, antibodies are becoming affordable enough to be used to protect the fragile or immunocompromised population against viruses, bacteria, and fungi. Moreover, in cases where it is hard to develop a vaccine conferring long-term protection (e.g. influenza, HIV, fungal infections, etc.), antibody therapy may hold the key to mitigate the effects of devastating epidemics.
But the question remains, is this approach feasible and effective?
Scientists at Vanderbilt University Medical Center (VUMC) have tried to answer that question by developing the first mRNA encoded therapeutic antibody ever to enter clinical trials. The biotherapeutic, developed in partnership with Moderna Inc., binds the mosquito-borne chikungunya virus to which no cure or treatment is known.
The clinical trial (NCT03829384) is now recruiting participants to test the safety of the lipid-encapsulated mRNA. But it is still too soon to know how effective in situ production will prove to be.
The rationale that keeps driving the development of this technology is the promise that it could overcome the typical hurdles of conventional monoclonal antibody production processes. By delivering the mRNA instead of the protein itself, we would be bypassing the need to produce these complex biomolecules in vitro.
RNA and DNA consist of only 4 different building blocks and can be easily synthesized in vitro. But proteins, specifically immunoglobulins, can be composed of up to 20 different amino acids and possess a complex glycosylation pattern, deemed essential to modulate the effector functions of these molecules.
If we teach the body to produce these molecules, we may significantly reduce the time-frame associated with typical monoclonal antibody production processes. Moreover, it could allow us to test more antibodies against a single disease in shorter periods of time.
But has this technology been tested for antibody delivery?
The first proof-of-concept on mRNA antibody delivery was published only in 2017. A group of scientists led by Drew Weissman (University of Pennsylvania, USA), compared the performance of VRC01, an anti-HIV-1 antibody, when delivered as protein or lipid-encapsulated mRNA to mice. The study proved two things: that the antibody could be produced in situ by the infected mice model and that it could even outperform the purified mAb in terms of therapeutic effectiveness.
Further studies on other disease models achieved similar results, indicating that lipid-encapsulated mRNA delivery could provide long-lasting protection and that it did not cause inflammation of the liver (the target organ of these constructs).
But, until now, no antibody-encoding mRNA has proven to be effective in clinical trials. For this reason, more studies are necessary to understand the dynamics of antibody production in situ and how the efficiency of this approach compares to conventional therapeutic antibody delivery.
Despite the promising preliminary results, mRNA delivery of antibodies is still an immature technology facing many practical challenges. Thus, these obstacles need to be addressed before this technology can be useful in the face of epidemics or life-threatening diseases.
- Immunogenicity: in vitro transcribed mRNA is often immunogenic, activating the production of cytokines and other molecules involved in the inflammatory response. One way to modulate this response is to introduce specific modifications into the mRNA nucleotides, however, which modifications would be best suited to reduce the immunogenicity remains to be clarified.
- Delivery: like antibodies, mRNA has limited diffusion across membranes which limits its therapeutic effectiveness. One way to overcome this limitation is to encapsulate the mRNA in liposomes or polymers. Until now, lipid nanoparticles (LNPs) show the most promising results, however, more studies are necessary to ascertain their clinical safety and efficiency.
- Clinical data: the mAb encoding the anti-chikungunya antibody is only the first to successfully enter clinical trials. For this reason, we still lack crucial clinical data on the short-term efficiency and the long-term safety of mRNA therapeutics. These trials may reveal further challenges in the widespread adoption of this technology.
mRNA and DNA are emerging biologics for the treatment and prophylactics of multiple diseases. Although the in situ expression of foreign proteins has found applicability in vaccine design, it has still struggled with many limitations when used as a vehicle for antibody delivery.
mRNA delivery could significantly shorten the development of new therapeutics by overcoming the limitations of conventional monoclonal antibody production processes. However, more in vitro and in vivo studies are necessary until we are able to leverage the full potential of this new technology.
- Kose, N. et al. A lipid-encapsulated mRNA encoding a potently neutralizing human monoclonal antibody protects against chikungunya infection. Sci Immunol. 2019; 4(35):pii: eaaw6647. doi: 10.1126/sciimmunol.aaw6647
- Pardi, N. et al. Administration of nucleoside-modified mRNA encoding broadly neutralizing antibody protects humanized mice from HIV-1 challenge. Nat Commun. 2017; 8:14630. doi: 10.1038/ncomms14630
- Schlake, T. et al. mRNA: A Novel Avenue to Antibody Therapy? Mol Ther. 2019; 27(4):773-784. doi: 10.1016/j.ymthe.2019.03.002
- Snyder, B. VUMC chikungunya antibody set to enter clinical trial. VUMC reporter. February 21, 2020. Retrieved from https://news.vumc.org/2019/02/21/chikungunya-antibody-set-to-enter-clinical-trial/
- Van Hoecke, L. and Roose, K. How mRNA therapeutics are entering the monoclonal antibody field. J Transl Med. 2019; 17:54. doi: 10.1186/s12967-019-1804-8
- van Huijsduijnen, R. H. et al. Reassessing therapeutic antibodies for neglected and tropical diseases. PLoS Negl Trop Dis. 2020; 14(1): e0007860. doi: 10.1371/journal.pntd.0007860