Following the stunning success of IVT mRNA COVID-19 vaccines, therapeutic applications based on this new efficient and accessible modality are rapidly evolving. As evidenced by this year’s AACR meeting, IVT mRNA is providing innovative solutions to improve cancer immunotherapies. Below, we highlight clinical and preclinical studies expanding the reach of mRNA medicines in cancer.
As part of the Clinical Trials Plenary Session: “Harnessing the Immune System in the Clinic,” Dr. Jeffrey S. Weber, NYU Langone Medical Center, provided an update on the open-label phase 2 mRNA-4157-P201/Keynote-942 trial.
AACR 2023-Clinical Trials Plenary Session. A personalized cancer vaccine mRNA-4157, combined with pembrolizumab versus pembrolizumab alone in patients with resected high-risk melanoma: Efficacy and safety results from the randomized, open-label Phase 2 mRNA-4157-P201/Keynote-942 trial.
Currently, checkpoint inhibitor monotherapy, the standard of care for high-risk resected melanoma, has a ~55% survival rate without relapse in 5 years. However, notwithstanding these significant benefits, a large portion of patients require more effective options. Therefore, this randomized study was designed to evaluate the safety and efficacy of a personalized neoantigen cancer vaccine in combination with the anti-PD-1 checkpoint inhibitor, pembrolizumab.
Cancer vaccines may be prophylactic or therapeutic, thereby preventing tumor growth or eliminating an existing tumor. For example, prophylactic cancer vaccines, such as those approved by the FDA, Cervarix, and Engerix-B, target viral antigens to prevent human papillomavirus (HPV) and (hepatitis B virus) HBV-associated cancers (Abd-Aziz and Poh 2022). In contrast, personalized neoantigen cancer vaccines leverage novel tumor-specific antigens formed through mutagenesis processes to induce strong tumor-killing immune responses.
Neoantigens are tumor-specific and discovered through whole exome sequencing. Once identified, these antigens may be leveraged as peptides, DNA, or mRNA for personalized vaccines to stimulate T cell immunity and epitope spreading. In this phase 2 study, the mRNA-4157 vaccine was designed to encode up to ~34 personalized neoantigens concatenated into one sequence. Patients received either pembrolizumab alone (18 cycles) for 1 year or combined with 9 doses of the personalized mRNA-4157 vaccine.
Promisingly, evaluation of efficacy after 18 months of treatment showed significant differences between groups, with over 78% recurrence-free survival for patients treated with the mRNA-4157 vaccine and pembrolizumab, as opposed to ~62% for those receiving the PD-1 inhibitor alone. Additionally, the study demonstrated that despite some serious adverse events, which were similar between the combination treatment and pembrolizumab alone, mostly transient minimal toxicities, such as fatigue, injection site-related inflammation, and chills, were associated with the mRNA-4157 vaccine.
Although this phase 2 study remains in progress, treatment outcomes support the benefits of combining a personalized neoantigen vaccine and checkpoint inhibition in melanoma patients. In agreement with these findings, the combination of mRNA-4157 vaccine and pembrolizumab received FDA “Breakthrough Therapy” designation in February 2023 and EMA “PRIME” designation in April 2023.
From Nutcracker Therapeutics, Dr. Ole Audun W. Haabeth presented a poster as part of the “Oncolytic Viruses, Anticancer Vaccines, and Other Immunomodulatory Therapies” session. Nutcracker is an early-stage mRNA-based therapeutic development and manufacturing company. In their quest to support the development of effective mRNA-based medicines, Dr. Haabeth shared a new approach to improve exogenous antigen presentation.
For cancer vaccines to work effectively, tumor-relevant antigens, such as tumor-associated (TAA) or tumor-specific antigens (TSA), must be presented by the Major Histocompatibility Complex class I and class II (MHC I and MHC II) transmembrane proteins to ensure strong anti-tumor adaptive immune responses. Therefore, Nutcracker is leveraging tumor-relevant antigens encoded by IVT mRNA in conjugation with endolysosomal targeting sequences to maximize MHC presentation. In this approach, antigens are flanked by the signal peptide and cytoplasmic tail sequences of the CD1 isoform CD1d. Previous work has demonstrated the role of CD1’s cytoplasmic tail for its intracellular trafficking, interaction with adaptor-protein complexes, and distribution into various endosomal compartments (Moody and Porcelli 2003).
MHC Class I and II Antigen Presentation Pathways. “Created with BioRender.com.”
By leveraging CD1d-derived sequences as part of IVT mRNA-encoded antigens, scientists at Nutcracker hoped to promote efficient presentation by MHC I and MHC II receptor complexes. Their studies with an antigen consisting of “CD1d signal sequence-HPV16E6E7-CD1d cytoplasmic tail” delivered as IVT mRNA demonstrated preferential antigen localization to multivesicular bodies for processing and MHC II presentation. Significantly, in vitro studies showed that the antigen-CD1d construct improved MHC II presentation, leading consequently to greater CD4 T cell activation. Additionally, in vivo studies demonstrated improved cellular (CD8 T cells) and humoral immunogenic responses.
Dr. Thomas E. Prod'homme, Myeloid Therapeutics, presented a poster in the “Late-Breaking Research: Experimental and Molecular Therapeutics 1” session. Their work showcased how engineering myeloid cells for tumor-cell killing is emerging as a promising strategy to re-target and leverage the therapeutic potential of these cells.
The myeloid cell compartment comprises heterogeneous cell populations of macrophages, monocytes, dendritic cells, neutrophils, and granulocytes. Among these, macrophages and monocytes are most abundant in the solid tumor microenvironment (TME), where they play both pro-and anti-tumorigenic roles. In general, the presence of macrophages with immunosuppressive phenotypes within the TME, “TH2-skewed,” is associated with immune evasion and poor prognosis (Cotechini et al. 2013, Balakrishnan and Dubey 2022).
Therefore, new strategies aim to re-direct myeloid cells’ activities to promote tumor cell killing. Myeloid Therapeutics has developed a new platform for preferential in vivo engineering of myeloid cells. Their strategy leverages a chimeric antigen receptor (CAR) construct consisting of an anti-tumor scFv fused to FcαRI (CD89), which requires FcRγ constitutively expressed by monocytes and macrophages, to achieve cell surface expression. Once on the surface, the CD89-FcRγ association enables signaling for the activation of phagocytic activity and the release of inflammatory mediators by myeloid cells (van der Boog et al. 2002).
Myeloid IgA Fc receptor FcαRI (CD89). The transmembrane region of the CD89 receptor interacts with the signaling molecule FcRγ chain. “Created with BioRender.com.”
Dr. Prod'homme shared how in vivo delivery of CAR-CD89 mRNA via lipid nanoparticles (LNPs) effectively reduced tumor volume in different tumor models. Furthermore, this effect was associated with increased dendritic cell activation and improved CD8+ T cell cytolytic activity within tumors. Significantly, the CAR-CD89 fused construct expression was predominant in monocytes in mice and cynomolgus monkeys, providing support for this receptor pairing strategy to achieve preferentially in vivo delivery of CAR constructs to specific immune cells.
Overall, these clinical and preclinical studies demonstrate the far-reaching possibilities of IVT mRNA as a therapeutic modality in cancer. Whether used as a prophylactic or therapeutic vaccine or in the delivery of anti-tumor CARs, IVT mRNA can help improve current treatment standards and enable new immunotherapy strategies. In addition, compared to protein and DNA-based therapeutics, the simpler and expedited mRNA manufacturing workflow offers more opportunities for personalized medicines.
Guide to IVT mRNA Parts Infographic
