mRNA is a single-stranded molecule that carries the genetic information from DNA to the ribosomes, where it is translated into proteins. mRNA has emerged as a versatile and powerful platform for various applications in cancer immunotherapy, such as vaccines, monoclonal antibodies, chimeric antigen receptors (CARs), and immunomodulatory proteins. The advantages of mRNA include its high potency, specificity, flexibility, rapid and large-scale production, low-cost manufacturing, and safety. However, mRNA also faces some challenges, such as its instability, low transfection efficiency, and potential immunogenicity.
mRNA anti-cancer vaccines are designed to elicit immune responses against specific tumor antigens (TAs) that are expressed by cancer cells. TAs can be either tumor-associated antigens (TAAs) or tumor-specific antigens (TSAs). TAAs are non-mutated proteins that are overexpressed or aberrantly expressed in cancer cells, such as differentiation antigens, products of silent genes, universal tumor antigens, and oncoviral antigens. TSAs are mutated proteins that are exclusively expressed by cancer cells, such as neoantigens. mRNA vaccines can encode either TAAs or TSAs, or a combination of both, to induce both humoral and cellular immune responses against cancer cells.
There are two main types of mRNA anti-cancer vaccines: self-amplifying mRNA (saRNA) vaccines and conventional mRNA (cmRNA) vaccines. saRNA vaccines are derived from viral genomes and have the ability to replicate in the cytoplasm of transfected cells, resulting in high-level and sustained expression of the encoded antigen. cmRNA vaccines are linear mRNA molecules that are capped and polyadenylated, but do not have the replication machinery. Both types of mRNA vaccines can be modified with various chemical modifications, such as pseudouridine, 5-methylcytosine, and 2'-O-methylribonucleotides, to enhance their stability, transfection efficiency, and immunogenicity.
The design and preparation of mRNA anti-cancer vaccines involve several steps, such as antigen selection, mRNA synthesis, formulation, and delivery. Antigen selection is a critical step that determines the specificity and efficacy of the vaccine. For TAAs, antigen selection can be based on the expression level, immunogenicity, and clinical relevance of the candidate antigens. For TSAs, the antigen selection can be based on the identification of neoantigens from tumor sequencing data, using bioinformatic tools and algorithms to predict the immunogenicity and presentation of the neoantigens. mRNA synthesis is the process of generating mRNA molecules that encode the selected antigens using in vitro transcription or enzymatic synthesis. Formulation is the process of incorporating the mRNA molecules into suitable carriers, such as lipids, polymers, or nanoparticles, to protect them from degradation and enhance their delivery. Delivery is the process of administering the mRNA vaccine to the target tissue, such as by intramuscular, intradermal, or intranodal injection.
Several mRNA anti-cancer vaccines have been tested in clinical trials, showing promising results in terms of safety, immunogenicity, and efficacy. For example, a personalized mRNA vaccine encoding over 30 neoantigens, combined with an anti-PD-1 antibody, showed a significant decrease in the risk of post-surgical recurrence or death in patients with melanoma, compared to antibody alone. Another mRNA vaccine encoding four TAAs combined with an anti-PD-1 antibody, showed an objective response rate in melanoma, with durable responses and manageable safety profile. A saRNA vaccine encoding four TAAs administered intratumorally or intracutaneously, showed tumor regression and immune activation in patients with various solid tumors.
mRNA CAR-T cells are a novel form of cancer immunotherapy that uses T cells that are transiently engineered with mRNA to express a chimeric antigen receptor (CAR) that can recognize and kill tumor cells. CARs are synthetic molecules that consist of an extracellular domain that binds to a specific tumor antigen and an intracellular domain that activates the T cell upon antigen recognition. mRNA CAR-T cells have several advantages over conventional CAR-T cells that are permanently modified with viral vectors or genome editing tools. First, mRNA CAR-T cells can reduce the risk of unwanted side effects, such as cytokine release syndrome, neurotoxicity, or autoimmunity, because the CAR expression is short-lived and can be controlled by the dose and frequency of mRNA administration. Second, mRNA CAR-T cells can be produced quickly and easily, allowing for flexible and personalized treatment options. Third, mRNA CAR-T cells can be engineered with multiple CARs or other functional molecules, such as cytokines, chemokines, or suicide genes, to improve their efficacy, specificity, and safety.
The production and application of mRNA CAR-T cells involve several steps, such as antigen selection, mRNA synthesis, formulation, transfection, and expansion. The ideal tumor antigen should be highly and exclusively expressed on the surface of tumor cells but not on normal cells to avoid on-target off-tumor toxicity. However, most tumor antigens are either heterogeneously or variably expressed or shared with normal tissues, posing challenges for CAR-T cell therapy. Therefore, strategies such as targeting multiple antigens, using logic gates, or incorporating safety switches have been developed to improve the selectivity and controllability of CAR-T cells. mRNA synthesis is the process of generating mRNA molecules that encode the selected CAR using in vitro transcription or enzymatic synthesis. Formulation is the process of incorporating the mRNA molecules into suitable carriers, such as lipids, polymers, or nanoparticles, to protect them from degradation and enhance their delivery. Transfection is the process of delivering mRNA molecules into the cytoplasm of T cells, using physical methods such as electroporation or microfluidics, or chemical methods such as lipofection or polyfection. Expansion is the process of stimulating and proliferating the transfected T cells, using cytokines such as IL-2 or IL-7, or artificial antigen-presenting cells.
Several mRNA CAR-T cells have been evaluated in preclinical and clinical studies, showing promising results in terms of safety, efficacy, and versatility. For example, mRNA CAR-T cells targeting CD19, a common antigen in B-cell malignancies, showed similar anti-tumor activity and reduced toxicity compared to conventional CD19 CAR-T cells in mouse models of acute lymphoblastic leukemia and non-Hodgkin lymphoma. mRNA CAR-T cells targeting mesothelin, a tumor-associated antigen in mesothelioma and pancreatic cancer, showed potent anti-tumor activity and reduced cytokine release syndrome compared to conventional mesothelin CAR-T cells in mouse models of mesothelioma and pancreatic cancer. mRNA CAR-T cells targeting protein kinase Met (c-Met), a receptor tyrosine kinase involved in tumor growth and metastasis, showed anti-tumor activity and reduced neurotoxicity compared to conventional c-Met CAR-T cells in mouse models of breast cancer and melanoma. mRNA CAR-T cells targeting B-cell maturation antigen (BCMA), a plasma cell-specific antigen in multiple myeloma, showed anti-tumor activity and reduced toxicity compared to conventional BCMA CAR-T cells in mouse models of multiple myeloma.
mRNA antibodies and cytokines are mRNA molecules that encode therapeutic antibodies or cytokines that can modulate the immune system against cancer. Antibodies are proteins that can specifically bind to antigens and mediate various effector functions, such as neutralization, opsonization, complement activation, and antibody-dependent cellular cytotoxicity. Cytokines are proteins that can influence the differentiation, proliferation, activation, and migration of immune cells and modulate the inflammatory response. mRNA antibodies and cytokines have several advantages over recombinant antibodies or cytokines. First, mRNA antibodies and cytokines can be generated rapidly and easily, without the need for complex and costly protein purification and quality control processes. Second, mRNA cytokines and antibodies can be administered locally and transiently, avoiding the systemic and prolonged exposure that may cause adverse events such as toxicity, immunogenicity, or resistance. Third, mRNA antibodies and cytokines can be modified with various chemical modifications, such as pseudouridine, 5-methylcytosine, and 2'-O-methylribonucleotides, to enhance their stability, transfection efficiency, and immunogenicity.
The production and application of mRNA antibodies and cytokines also involve several steps, including antigen selection, mRNA synthesis, formulation, and delivery. For antibodies, the antigen selection can be based on the expression level, immunogenicity, and clinical relevance of the target antigen. For cytokines, antigen selection can be based on the desired immune response, such as pro-inflammatory, anti-inflammatory, or immunoregulatory. mRNA synthesis is the process of generating mRNA molecules that encode the selected antibody or cytokine, using in vitro transcription or enzymatic synthesis. Formulation is the process of incorporating the mRNA molecules into suitable carriers, such as lipids, polymers, or nanoparticles, to protect them from degradation and enhance their delivery. Delivery is the process of administering the mRNA antibody or cytokine to the target tissue, such as by intratumoral, intranodal, or intravenous injection.
Several mRNA antibodies and cytokines have been evaluated in preclinical and clinical studies, showing promising results in terms of safety, efficacy, and versatility. For example, mRNA encoding an anti-PD-L1 antibody, delivered intratumorally, showed anti-tumor activity and systemic immune activation in mouse models of melanoma and colon cancer. mRNA encoding an anti-CTLA-4 antibody, delivered intravenously, showed anti-tumor activity and reduced toxicity compared to the recombinant antibody in mouse models of melanoma and breast cancer. mRNA encoding an anti-HER2 antibody, delivered intravenously, showed anti-tumor activity and reduced cardiotoxicity compared to the recombinant antibody in mouse models of breast cancer. mRNA encoding IL-12, delivered intratumorally, showed anti-tumor activity and immune activation in mouse models of melanoma and colon cancer. mRNA encoding IL-2, delivered intravenously, showed anti-tumor activity and reduced toxicity compared to the recombinant cytokine in mouse models of melanoma and lymphoma.
In summary, mRNA-based cancer immunotherapy has the potential to revolutionize the treatment of cancer by providing a novel and effective way to modulate the immune system against tumor cells. However, further research and development are needed to optimize the design, delivery, and combination of mRNA-based cancer therapeutics and to explore their application in different cancer types and stages.
