A self-amplifying mRNA SARS-CoV-2 vaccine candidate induces safe and robust protective immunity in preclinical models.

RNA vaccines have demonstrated efficacy against SARS-CoV-2 in humans, and the technology is being leveraged for rapid emergency response. In this report, we assessed immunogenicity and, for the first time, toxicity, biodistribution, and protective efficacy in preclinical models of a two-dose self-amplifying messenger RNA (SAM) vaccine, encoding a prefusion-stabilized spike antigen of SARS-CoV-2 Wuhan-Hu-1 strain and delivered by lipid nanoparticles (LNPs). In mice, one immunization with the SAM vaccine elicited a robust spike-specific antibody response, which was further boosted by a second immunization, and effectively neutralized the matched SARS-CoV-2 Wuhan strain as well as B.1.1.7 (Alpha), B.1.351 (Beta) and B.1.617.2 (Delta) variants. High frequencies of spike-specific germinal center B, Th0/Th1 CD4, and CD8 T cell responses were observed in mice. Local tolerance, potential systemic toxicity, and biodistribution of the vaccine were characterized in rats. In hamsters, the vaccine candidate was well-tolerated, markedly reduced viral load in the upper and lower airways, and protected animals against disease in a dose-dependent manner, with no evidence of disease enhancement following SARS-CoV-2 challenge. Therefore, the SARS-CoV-2 SAM (LNP) vaccine candidate has a favorable safety profile, elicits robust protective immune responses against multiple SARS-CoV-2 variants, and has been advanced to phase 1 clinical evaluation (NCT04758962).

Differential immune responses to HIV-1 envelope protein induced by liposomal adjuvant formulations containing monophosphoryl lipid A with or without QS21.

Liposomes have shown promise as constituents of adjuvant formulations in vaccines to parasitic and viral diseases. A particular type of liposomal construct, referred to as Army Liposome Formulation (ALF), containing neutral and anionic saturated phospholipids, cholesterol, and monophosphoryl lipid A (MPLA), has been used as an adjuvant for many years. Here we investigated the effects of physical and chemical changes of ALF liposomes on adjuvanted immune responses to CN54 gp140, a recombinant HIV-1 envelope protein. While holding the total amounts of liposomal MPLA and the gp140 antigen constant, different liposome sizes and liposomal MPLA:phospholipid molar ratios, and the effect of adding QS21 to the liposomes were compared for inducing immune responses to the gp140. For liposomes lacking QS21, higher titers of IgG binding antibodies to gp140 were induced by small unilamellar vesicle (SUV) rather than by large multilamellar vesicle (MLV) liposomes, and the highest titers were obtained with SUV having the MPLA:phospholipid ratio of 1:5.6. ALF plus QS21 (ALFQ) liposomes induced the same maximal binding antibody titers regardless of the MPLA:phospholipid ratio. ALF MLV liposomes induced mainly IgG1 and very low IgG2a antibodies, while ALF SUV liposomes induced IgG1≥IgG2a>IgG2b antibodies. Liposomes containing QS21 induced IgG1>IgG2a>IgG2b>IgG3 antibodies. ELISPOT analysis of splenocytes from immunized mice revealed that ALF liposomes induced low levels of IFN-γ, but ALFQ induced high levels. ALF and ALFQ liposomes each induced approximately equivalent high levels of IL-4. Based on antibody subtypes and cytokine secretion, we conclude that ALF liposomes predominantly stimulate Th2, while ALFQ strongly induces both Th1 and Th2 immunity. When CN54 gp140 was adjuvanted with either ALF or ALFQ liposomes, antibodies were induced that neutralized two HIV-1 tier 1 clade C strain pseudoviruses.

Adjuvants for vaccines to drugs of abuse and addiction.

Immunotherapeutic vaccines to drugs of abuse, including nicotine, cocaine, heroin, oxycodone, methamphetamine, and others are being developed. The theoretical basis of such vaccines is to induce antibodies that sequester the drug in the blood in the form of antibody-bound drug that cannot cross the blood brain barrier, thereby preventing psychoactive effects. Because the drugs are haptens a successful vaccine relies on development of appropriate hapten-protein carrier conjugates. However, because induction of high and prolonged levels of antibodies is required for an effective vaccine, and because injection of T-independent haptenic drugs of abuse does not induce memory recall responses, the role of adjuvants during immunization plays a critical role. As reviewed herein, preclinical studies often use strong adjuvants such as complete and incomplete Freund's adjuvant and others that cannot be, or in the case of many newer adjuvants, have never been, employed in humans. Balanced against this, the only adjuvant that has been included in candidate vaccines in human clinical trials to nicotine and cocaine has been aluminum hydroxide gel. While aluminum salts have been widely utilized worldwide in numerous licensed vaccines, the experience with human responses to aluminum salt-adjuvanted vaccines to haptenic drugs of abuse has suggested that the immune responses are too weak to allow development of a successful vaccine. What is needed is an adjuvant or combination of adjuvants that are safe, potent, widely available, easily manufactured, and cost-effective. Based on our review of the field we recommend the following adjuvant combinations either for research or for product development for human use: aluminum salt with adsorbed monophosphoryl lipid A (MPLA); liposomes containing MPLA [L(MPLA)]; L(MPLA) adsorbed to aluminum salt; oil-in-water emulsion; or oil-in-water emulsion containing MPLA.