Previous studies have shown that single-stranded RNA (ssRNA) mixed with protamine forms particles and activates immune cells through Toll-like receptors (TLRs). We have found that the size of protamine-RNA particles generated depends on the electrolyte content when mixing the 2 components. Moreover, we have evidenced that (1) nanometric particles induce production of interferon-α, whereas (2) micrometric particles mainly induce production of tumor necrosis factor-α (TNF-α) in human immune cells. We found that the mechanisms underlying these observations are (1) nanoparticles but not microparticles are selectively phagocytosed by plasmacytoid dendritic cells (pDCs), which produce interferon-α and (2) monocytes that produce TNF-α have a higher activation threshold than that of pDCs. Thus, at the same time as sensing pathogen-associated molecular patterns such as ssRNA, the immune system distinguishes the size of the associated structure in such a way as to trigger the adapted antivirus (nanometric) or antibacterial/antifungal (micrometric) immune response. Our results introduce a new dimension in danger signaling—how size qualitatively affects innate response.

Protamine is a natural cationic peptide mixture mostly known as a drug for the neutralization of heparin and as a compound in formulations of slow-release insulin. Protamine is also used for cellular delivery of nucleic acids due to opposite charge-driven coupling. This year marks 60 years since the first use of Protamine as a transfection enhancement agent. Since then, Protamine has been broadly used as a stabilization agent for RNA delivery. It has also been involved in several compositions for RNA-based vaccinations in clinical development. Protamine stabilization of RNA shows double functionality: it not only protects RNA from degradation within biological systems, but also enhances penetration into cells. A Protamine-based RNA delivery system is a flexible and versatile platform that can be adjusted according to therapeutic goals: fused with targeting antibodies for precise delivery, digested into a cell penetrating peptide for better transfection efficiency or not-covalently mixed with functional polymers. This manuscript gives an overview of the strategies employed in protamine-based RNA delivery, including the optimization of the nucleic acid’s stability and translational efficiency, as well as the regulation of its immunostimulatory properties from early studies to recent developments.

Purpose: Most chimeric antigen receptor (CAR) T-cell strategies against glioblastoma have demonstrated only modest therapeutic activity and are based on persistent gene modification strategies that have limited transgene capacity, long manufacturing processes, and the risk for uncontrollable off-tumor toxicities. mRNA-based T-cell modifications are an emerging safe, rapid, and cost-effective alternative to overcome these challenges, but are underexplored against glioblastoma. Experimental Design: We generated mouse and human mRNA-based multifunctional T cells coexpressing a multitargeting CAR based on the natural killer group 2D (NKG2D) receptor and the proinflammatory cytokines IL12 and IFNα2 and assessed their antiglioma activity in vitro and in vivo. Results: Compared with T cells that either expressed the CAR or cytokines alone, multifunctional CAR T cells demonstrated increased antiglioma activity in vitro and in vivo in three orthotopic immunocompetent mouse glioma models without signs of toxicity. Mechanistically, the coexpression of IL12 and IFNα2 in addition to the CAR promoted a proinflammatory tumor microenvironment and reduced T-cell exhaustion as demonstrated by ex vivo immune phenotyping, cytokine profiling, and RNA sequencing. The translational potential was demonstrated by image-based single-cell analyses of mRNA-modified T cells in patient glioblastoma samples with a complex cellular microenvironment. This revealed strong antiglioma activity of human mRNA-based multifunctional NKG2D CAR T cells coexpressing IL12 and IFNα2 whereas T cells that expressed either the CAR or cytokines alone did not demonstrate comparable antiglioma activity. Conclusions: These data provide a robust rationale for future clinical studies with mRNA-based multifunctional CAR T cells to treat malignant brain tumors.

In the race for a vaccine against SARS-CoV-2, the synthetic mRNA format has been shown to be the fastest one and proved to be safe and highly efficient, even at the very low dose of a few µg per injection. The mRNA vaccines are not new: vaccines that are based on attenuated mRNA viruses, such as Mumps, Measles, and Rubella, immunize by delivering their mRNAs into the cells of the vaccinated individual, who produces the viral proteins that then prime the immune response. Synthetic mRNA in liposomes can be seen as a modern, more refined, and thereby a safer version of those live attenuated RNA viruses. The anti-COVID-19 mRNA vaccine (coding the SARS-CoV-2 spike protein) is the third synthetic RNA therapeutic being approved. It follows the aptamer Macugen^® (which neutralizes VEGF) and the siRNA Onpattro^® (which destroys the transthyretin-coding mRNA). Remarkably, the 30 µg of mRNA that are contained in the first approved anti-COVID-19 vaccine are sufficient for generating high levels of neutralizing antibodies against the virus in all injected volunteers (including participants over 65 years old). The efficacy and safety data are stunning. The distribution of these vaccines throughout the world will bring a halt to the coronavirus pandemic.

Particle‐mediated epidermal delivery (PMED) is a potent genetic vaccination method. However, a recent report found PMED only poorly and infrequently triggered antigen‐specific cytotoxic T‐cells in cancer patients. Here, we show that injection of the chemotherapeutic drug Gemcitabine in mice results in improvement of the efficacy of subsequent PMED vaccination against NY‐ESO‐1. We found in mice and in cancer patients that administration of Gemcitabine induces a transient reduction in the percentage of regulatory T‐cells among CD4‐positive cells. The higher relative sensitivity of regulatory T‐cells compared to other CD4‐positive T‐cells toward cytostatic drugs can be linked to the higher frequency of proliferating cells in the regulatory compartment compared to the nonregulatory CD4‐compartment in healthy people and cancer patients. Thus, by affecting regulatory T‐cells more than other lymphocyte subsets, chemotherapeutic agents can create a transient hyperimmunoreactive window. Such a window would provide an ideal timepoint to administer a vaccine expected to induce a therapeutically relevant anticancer cytotoxic T‐cell response.