By Scott Ripley, PhD, and Tracy Humphries
Scientists have always dreamed big. Before the COVID-19 pandemic, investigators working on RNA therapeutics were able to envisage its potential and impact on the field of medicine. The success of mRNA-based COVID-19 vaccines accelerated the market for RNA-based medicines and enabled manufacturers to gain traction.
mRNA-based therapies gained popularity for several reasons:
- mRNA is a versatile molecule that can be easily synthesized and modified.
- mRNA-based therapies are considered safe and are used in COVID-19 vaccines.
- mRNA-based therapies have the potential to treat a wide range of diseases.
RNA can target specific cells, encode proteins, and trigger immune responses, enabling its use in vaccines and cell and gene therapies. However, the development of mRNA-based vaccines and therapies can still face challenges, such as targeted delivery, efficacy, stability, and scalability.
Nevertheless, the potential of mRNA therapeutics is significant. Their rise has been exponential, and the number of therapies in clinical trials continues to increase. mRNA-based therapies show promise for the treatment of cancer, genetic disorders, and infectious diseases.
The technology that the coronavirus vaccine is built upon is now widely known. Moderna and BioNTech were at the forefront of mRNA technology, with their COVID-19 vaccines being the first to receive emergency use authorization.
mRNA vaccines, which deliver genetic instructions to cells to make a specific protein to trigger an immune response, are highly adaptable and can be quickly designed and manufactured to target new pathogens. Further vaccines are in development, not only for COVID-19, but for other infectious diseases such as influenza, Zika virus, cytomegalovirus, and respiratory syncytial virus. Companies working on such vaccines include Moderna, Pfizer, BioNTech, CureVac, and Sanofi.
mRNAs to form CAR proteins
An exciting branch of RNA therapeutics is mRNA-based immunotherapy. It involves the delivery of chimeric antigen receptor (CAR)-encoding mRNA to T cells. Essentially, the approach uses mRNA to reprogram T cells so that they target and kill cancer cells. It has the potential to treat a wide range of cancers, including leukemia and lymphoma.
The production of CAR T cells in vivo has been demonstrated to treat cardiac injury by delivering modified mRNA in T-cell-targeted lipid nanoparticles. Conventional CAR T-cell therapies have high manufacturing costs due to the infrastructure and reagents needed. Lipid nanoparticle–based mRNA therapy negates the need to expand T cells outside the body and can be a more cost-effective method.
Combinatorial therapies are also promising, as BioNTech has shown with BNT211, which is a synergistic approach combining the company’s CAR T-cell and FixVac platform technologies to develop a highly tumor-specific CAR T-cell therapy product, which is enhanced by a CAR T-cell amplifying RNA vaccine (CARVac).
mRNA as a cancer vaccine
The success of the mRNA-based COVID-19 vaccines owes much to the research that was originally focused on cancer vaccines. To accelerate the development of the Pfizer/BioNTech and Moderna COVID-19 vaccines, all the companies leveraged their cancer vaccine experience. There are many clinical trials in progress for mRNA vaccine treatment of melanoma and colorectal and pancreatic cancer.
mRNA cancer vaccines can work with a one-vaccine-to-many-people approach, or as a personalized therapy. Dendritic cells take up mRNA from the vaccine and present it to T cells, teaching them to search out and destroy cancer cells.
Personalized vaccines are manufactured based on molecular features of tumors from individuals to identify genetic mutations that could give rise to neoantigens. Algorithms are used to predict which neoantigens will bind to T-cell receptors and create an immune response. Speed of manufacturing is particularly important in this case, which is one of the reasons that mRNA is a suitable modality.
Companies working in this space include eTheRNA, Moderna, BioNTech, Merck & Co., and Genentech.
Gene therapy protein replacement
Protein replacement therapies address protein deficiencies, raising protein levels that are too low, or substituting functional for nonfunctional proteins. mRNA can be used to produce therapeutic proteins within the body—for example, by instructing cells to produce a specific protein that corrects a disease-causing genetic effect. In cystic fibrosis, mRNA can encode a functional copy of the cystic fibrosis transmembrane conductance regulator protein, which is deficient in patients, an approach used by Vertex Pharmaceuticals and Moderna. Likewise, Arcturus Therapeutics has presented data establishing proof of principle of a novel mRNA replacement therapy to treat phenylketonuria.
RNA therapeutics may have an advantage over more invasive and permanent gene editing procedures. mRNA protein replacement therapies will, however, require much larger doses than traditional vaccines. Other RNA modalities, such as circular RNA (circRNA) and self-amplifying RNA (saRNA), allow for lower mRNA requirements per dose.
Gene editing approach
mRNA can deliver gene editing tools such as CRISPR-Cas9 to cells and tissues, making it possible for the tools to correct deleterious mutations that cause genetic disorders. For example, mRNA-delivered gene editing tools can correct mutations in the HBB gene that lead to sickle-cell disease. Similarly, mRNA-delivered gene editing tools can eliminate aberrant splicing sites that cause b-thalassemia. mRNA can also deliver gene editing tools to cancer cells, enabling precise genomic modifications that make the cells more vulnerable to immune attack.
When gene therapies are delivered by mRNA, “one dose and done” treatments are possible. In contrast, mRNA therapies that rely on mRNA to express therapeutic proteins typically involve repeat doses.
At GreenLight Biosciences, mRNA delivery technology is part of the company’s strategy to develop an in vivo gene therapy for sickle-cell disease. The company is also assessing treatments for HIV. Besides GreenLight, companies in this space include Editas Medicine, Beam Therapeutics, CRISPR Therapeutics, and Intellia Therapeutics.
CircRNAs for apoptosis and aging
CircRNAs are noncoding closed RNAs that appear to work in conjunction with microRNAs. Several circRNAs have been found to enhance or inhibit tumor progression in various types of human cancer. They have also been found to be involved in adipose metabolism. In addition, they are believed to influence aging, to function in multiple disorders, to regulate gene expression, and to modulate programmed cell death pathways such as apoptosis pathways.
As circRNAs are stable and expressed in a tissue type– or cell type–specific manner, they are also being explored as therapeutic targets. Expanding our knowledge of circRNA functional mechanisms and approaches to target in vivo will be key to unlocking circ-based therapeutics.
Several RNA therapeutic approaches have been mentioned in this article. In general, each approach has been treated singularly. However, there are many ways these approaches may be merged, resulting in combinatorial therapies. In addition, the RNA therapeutic approaches described here may be combined with other modalities not mentioned in this article.
There is a lot of potential for RNA therapeutics, especially since they facilitate a toolbox approach to treatment modalities. For a given target, the right modality or modalities can be selected, with RNA therapies augmenting or serving as alternatives to more traditional approaches. By offering compatibility or disruptiveness, as needed, RNA therapies also support more innovative thinking. Ultimately, they promise to expand the genomic medicine universe.
Scott Ripley, PhD, is general manager and Tracy Humphries is marketing leader of the nucleic acid therapeutics business at Cytiva.