Considerations on the Design of Lipid-based mRNA Vaccines Against Cancer.

Throughout the last decades, mRNA vaccines have been developed as a cancer immunotherapeutic and the technology recently gained momentum during the COVID-19 pandemic. Recent promising results obtained from clinical trials investigating lipid-based mRNA vaccines in cancer therapy further highlighted the potential of this therapy. Interestingly, while the technologies being used in authorized mRNA vaccines for the prevention of COVID-19 are relatively similar, mRNA vaccines in clinical development for cancer vaccination show marked differences in mRNA modification, lipid carrier, and administration route. In this review, we describe findings on how these factors can impact the potency of mRNA vaccines in cancer therapy and provide insights into the complex interplay between them. We discuss how lipid carrier composition can affect passive targeting to immune cells to improve the efficacy and safety of mRNA vaccines. Finally, we summarize strategies that are established or still being explored to improve the efficacy of mRNA cancer vaccines and include next-generation vaccines that are on the horizon in clinical development.

Alpha-galactosylceramide improves the potency of mRNA LNP vaccines against cancer and intracellular bacteria.

Although various types of mRNA-based vaccines have been explored, the optimal conditions for induction of both humoral and cellular immunity remain rather unknown. In this study, mRNA vaccines of nucleoside-modified mRNA in lipoplexes (LPXs) or lipid nanoparticles (LNPs) were evaluated after administration in mice through different routes, assessing mRNA delivery, tolerability and immunogenicity. In addition, we investigated whether mRNA vaccines could benefit from the inclusion of the adjuvant alpha-galactosylceramide (αGC), an invariant Natural Killer T (iNKT) cell ligand. Intramuscular (IM) vaccination with ovalbumin (OVA)-encoding mRNA encapsulated in LNPs adjuvanted with αGC showed the highest antibody- and CD8+ T cell responses. Furthermore, we observed that addition of signal peptides and endocytic sorting signals of either LAMP1 or HLA-B7 in the OVA-encoding mRNA sequence further enhanced CD8+ T cell activation although reducing the induction of IgG antibody responses. Moreover, mRNA LNPs with the ionizable lipidoid C12-200 exhibited higher pro-inflammatory- and reactogenic activity compared to mRNA LNPs with SM-102, correlating with increased T cell activation and antitumor potential. We also observed that αGC could further enhance the cellular immunity of clinically relevant mRNA LNP vaccines, thereby promoting therapeutic antitumor potential. Finally, a Listeria monocytogenes mRNA LNP vaccine supplemented with αGC showed synergistic protective effects against listeriosis, highlighting a key advantage of co-activating iNKT cells in antibacterial mRNA vaccines. Taken together, our study offers multiple insights for optimizing the design of mRNA vaccines for disease applications, such as cancer and intracellular bacterial infections.

Continuous freeze-drying of messenger RNA lipid nanoparticles enables storage at higher temperatures.

Messenger RNA (mRNA) lipid nanoparticles (LNPs) have emerged at the forefront during the COVID-19 vaccination campaign. Despite their tremendous success, mRNA vaccines currently require storage at deep freeze temperatures which complicates their storage and distribution, and ultimately leads to lower accessibility to low- and middle-income countries. To elaborate on this challenge, we investigated freeze-drying as a method to enable storage of mRNA LNPs at room- and even higher temperatures. More specifically, we explored a novel continuous freeze-drying technique based on spin-freezing, which has several advantages compared to classical batch freeze-drying including a much shorter drying time and improved process and product quality controlling. Here, we give insight into the variables that play a role during freeze-drying by evaluating the impact of the buffer and mRNA LNP formulation (ionizable lipid to mRNA weight ratio) on properties such as size, morphology and mRNA encapsulation. We found that a sufficiently high ionizable lipid to mRNA weight ratio was necessary to prevent leakage of mRNA during freeze-drying and that phosphate and Tris, but not PBS, were appropriate buffers for lyophilization of mRNA LNPs. We also studied the stability of optimally lyophilized mRNA LNPs at 4 °C, 22 °C, and 37 °C and found that transfection properties of lyophilized mRNA LNPs were maintained during at least 12 weeks. To our knowledge, this is the first study that demonstrates that optimally lyophilized mRNA LNPs can be safely stored at higher temperatures for months without losing their transfection properties.

Transport by circulating myeloid cells drives liposomal accumulation in inflamed synovium.

The therapeutic potential of liposomes to deliver drugs into inflamed tissue is well documented. Liposomes are believed to largely transport drugs into inflamed joints by selective extravasation through endothelial gaps at the inflammatory sites, known as the enhanced permeation and retention effect. However, the potential of blood-circulating myeloid cells for the uptake and delivery of liposomes has been largely overlooked. Here we show that myeloid cells can transport liposomes to inflammatory sites in a collagen-induced arthritis model. It is shown that the selective depletion of the circulating myeloid cells reduces the accumulation of liposomes up to 50-60%, suggesting that myeloid-cell-mediated transport accounts for more than half of liposomal accumulation in inflamed regions. Although it is widely believed that PEGylation inhibits premature liposome clearance by the mononuclear phagocytic system, our data show that the long blood circulation times of PEGylated liposomes rather favours uptake by myeloid cells. This challenges the prevailing theory that synovial liposomal accumulation is primarily due to the enhanced permeation and retention effect and highlights the potential for other pathways of delivery in inflammatory diseases.

Nanobody-mediated SPECT/CT imaging reveals the spatiotemporal expression of programmed death-ligand 1 in response to a CD8+ T cell and iNKT cell activating mRNA vaccine.

Rationale: Although promising responses are obtained in patients treated with immune checkpoint inhibitors targeting programmed death ligand 1 (PD-L1) and its receptor programmed death-1 (PD-1), only a fraction of patients benefits from this immunotherapy. Cancer vaccination may be an effective approach to improve the response to immune checkpoint inhibitors anti-PD-L1/PD-1 therapy. However, there is a lack of research on the dynamics of PD-L1 expression in response to cancer vaccination. Methods: We performed non-invasive whole-body imaging to visualize PD-L1 expression at different timepoints after vaccination of melanoma-bearing mice. Mice bearing ovalbumin (OVA) expressing B16 tumors were i.v. injected with the Galsome mRNA vaccine: OVA encoding mRNA lipoplexes co-encapsulating a low or a high dose of the atypical adjuvant α-galactosylceramide (αGC) to activate invariant natural killer T (iNKT) cells. Serial non-invasive whole-body immune imaging was performed using a technetium-99m (99mTc)-labeled anti-PD-L1 nanobody, single-photon emission computerized tomography (SPECT) and X-ray computed tomography (CT) images were quantified. Additionally, cellular expression of PD-L1 was evaluated with flow cytometry. Results: SPECT/CT-imaging showed a rapid and systemic upregulation of PD-L1 after vaccination. PD-L1 expression could not be correlated to the αGC-dose, although we observed a dose-dependent iNKT cell activation. Dynamics of PD-L1 expression were organ-dependent and most pronounced in lungs and liver, organs to which the vaccine was distributed. PD-L1 expression in lungs increased immediately after vaccination and gradually decreased over time, whereas in liver, vaccination-induced PD-L1 upregulation was short-lived. Flow cytometric analysis of these organs further showed myeloid cells as well as non-immune cells with elevated PD-L1 expression in response to vaccination. SPECT/CT imaging of the tumor demonstrated that the expression of PD-L1 remained stable over time and was overall not affected by vaccination although flow cytometric analysis at the cellular level demonstrated changes in PD-L1 expression in various immune cell populations following vaccination. Conclusion: Repeated non-invasive whole-body imaging using 99mTc-labeled anti-PD-L1 nanobodies allows to document the dynamic nature of PD-L1 expression upon vaccination. Galsome vaccination rapidly induced systemic upregulation of PD-L1 expression with the most pronounced upregulation in lungs and liver while flow cytometry analysis showed upregulation of PD-L1 in the tumor microenvironment. This study shows that imaging using nanobodies may be useful for monitoring vaccine-mediated PD-L1 modulation in patients and could provide a rationale for combination therapy. To the best of our knowledge, this is the first report that visualizes PD-L1 expression upon cancer vaccination.