An emerging field of mRNA technology is in vivo encoding immune proteins or immunomodulatory proteins that can be used therapeutically, such as antibodies and cytokines.

One of the main challenges of protein immunotherapy is to deliver mRNA to all target organs and cells in order to achieve the best therapeutic effect. ​For example, some proteins need further PTM (such as glycosylation and proteolysis) to function fully. The modification effect of PTM on protein may be tissue-dependent, not just dependent on the sequence of mRNA, which further indicates that mRNA needs to be specifically delivered to the target tissue.

When mRNA is administered systemically with LNP as a carrier, the LNP complex will tend to be distributed to liver tissue as apolipoprotein E can bind to the LNP surface and hepatocyte surface receptors will induce hepatocyte uptake of LNP. The specific tissue distribution of non-liver, such as the targeted delivery of lung endothelial cells or spleen, can be achieved by adjusting the lipid composition (including adjusting the proportion and composition of lipids) in LNP. Recently, LNP has specifically targeted bone marrow endothelial cells in hematopoietic stem cell niches by regulating the lipid structure of PEG- and changing the surface properties of LNP.

Therefore, compared with vaccines, mRNA protein immunotherapy poses new challenges in preparation delivery, protein production effectiveness, and tolerance. This may also be why the development of mRNA therapeutic drugs is slower than that of mRNA vaccines.

mRNA Coding Monoclonal Antibody Therapy

Direct delivery of mRNA to specific tissues or organs is a barrier to mRNA drug development. As long as the drug is safe and the dosage is designed reasonably to control the protein expression level, systemic administration of mRNA drug is an appropriate way of drug administration. mRNA-1944 is an mRNA drug that encodes monoclonal antibodies (mAb). The drug uses LNP as the carrier and encodes a mAb that recognizes the chikungunya virus. Data from the first clinical trial based on healthy subjects showed that neutralizing antibodies could be detected in all trial doses (0.1, 0.3, 0.6 mg/kg). However, in the highest dose group, infusion-related reactions occurred in 3 of the 4 subjects, including grade 3 tachycardia, elevated white blood cell count, grade 2 nausea, vomiting and fever, and transient inverted T waves on ECG. However, there was no grade 3 adverse reaction in the other group treated with steroids at the same dose, but the level of chikungunya virus specific antibody (Emax) decreased 1.7 times.

Generating antibodies with mRNA has attracted a lot of attention, and there are several collaborations in this area currently underway in the industry. For example, CureVac is collaborating with Cenmab on an mRNA-based mAb antitumor therapy, and Neurimmune and Ethirs have collaborated on an inhaled mRNA drug encoding an anti-neocrown mAb. The key factor to consider here is why mRNA is used to encode antibodies in vivo instead of the traditional recombinant production process. The most promising approach requires a comprehensive consideration of factors such as dose, duration, PTM type, delivery system and the safety of the target antibody.

mRNA Encodes Immunostimulatory Protein

Another anti-tumor method is to inject mRNA that encodes a protein with a direct therapeutic effect, which can attack the tumor by stimulating the immune system, such as OX40 ligand (OX40L) or IL. For example, mRNA-2416 is an mRNA drug that encodes the immune checkpoint regulatory molecule OX40L. In a clinical study, intratumoral monotherapy in 41 patients with multiple malignant tumors did not meet the criteria for partial remission specified in the Response Evaluation Criteria in Solid Tumors. Currently, sponsors plan to conduct a clinical phase II extended cohort study in combination with Duvalizumab in the treatment of ovarian cancer.

The mRNA drug ECI-006, which encodes a variety of different immunomodulators, is a combination of TriMix [mRNA, which encodes multiple molecules that activate DC cells (CD40L, CD70 and caTLR4)] and melanoma-specific TAA (tyrosine, gp100, MAGE A3, MAGEC2 and PRAME mRNA). The drug is in phase I clinical trials in patients with melanoma.

Another idea is to produce immunomodulatory fusion proteins. MEDI1191 encodes a single-stranded fusion protein containing IL-12 α and IL-12 β subunits, and the two subunits are bound by a connecting group. Intratumoral injection of this drug is expected to improve systemic tolerance to recombinant IL-12.

mRNA in Adoptive Immunocyte Therapy

Adoptive immunotherapy is a relatively new method of treatment, which collects autoimmune cells from patients, treats them in vitro and infuses them back into patients to achieve the purpose of tumor treatment. Research shows that intratumoral injection of T cells transfected with chimeric antigen receptor (CAR) mRNA targeting c-Met was well tolerated and could induce the immune response in tumor tissues.

Nano-preparations help deliver mRNA to different immune cells, such as macrophages, B cells and T cells, which further expands the application prospects of immunotherapy. ​For example, T-cell targeted mRNA delivery technology creates the possibility of producing CAR-T cells in vivo and opens up a new way of tumor therapy.