Optimization of Lipid Nanoparticles for Intramuscular Administration of mRNA Vaccines

Abstract

mRNA vaccines have the potential to tackle many unmet medical needs that are unable to be addressed with conventional vaccine technologies. A potent and well-tolerated delivery technology is integral to fully realizing the potential of mRNA vaccines. Pre-clinical and clinical studies have demonstrated that mRNA delivered intramuscularly (IM) with first-generation lipid nanoparticles (LNPs) generates robust immune responses. Despite progress made over the past several years, there remains significant opportunity for improvement, as the most advanced LNPs were designed for intravenous (IV) delivery of siRNA to the liver. Here, we screened a panel of proprietary biodegradable ionizable lipids for both expression and immunogenicity in a rodent model when administered IM. A subset of compounds was selected and further evaluated for tolerability, immunogenicity, and expression in rodents and non-human primates (NHPs). A lead formulation was identified that yielded a robust immune response with improved tolerability. More importantly for vaccines, increased innate immune stimulation driven by LNPs does not equate to increased immunogenicity, illustrating that mRNA vaccine tolerability can be improved without affecting potency.

Keywords: LNP; formulation; immunogenicity; intramuscular; lipids; mRNA; tolerability; vaccines.

Graphical abstract

Figure 1

Pharmacokinetics of LNPs containing MC3 after IM administration in mice Lipid concentration (nanograms per gram) after IM administration of modified mRNA encoding luciferase formulated in LNPs containing MC3 (gray triangles) in muscle, liver, and spleen up to 24 h post-injection (n = 3 per group per time point).

Figure 2

Expression and Immunogenicity from LNPs Containing Novel Ionizable Lipids in Mice (A) Thirty novel lipid LNPs, A through E′ were compared to a D (MC3) LNP control for expression and immunogenicity. Lipids are arranged left to right in order of pKa from low (A) to high (DOTAP). Expression measured by luminescence in flux (photons per second) 6 h after administration of modified mRNA encoding luciferase delivered at 0.5 mg/kg IV in CD-1 mice, 0.01 mg/kg IM or 0.001 mg/kg IM in BALB/c mice (n = 5 per group). Immunogenicity measured by H10-specific IgG titers measured 2 weeks after two doses administered 3 weeks apart delivered IM at 0.001 mg/kg IM in BALB/c mice (n = 5 per group). Data are represented as log₂ fold change compared to MC3. Squares containing an X indicate >4-fold change (log₂) lower than for MC3. (B) Log₂ fold increase in expression was compared to the log₂ fold change in immunogenicity at the low dose level administered IM (0.001 mg/kg). The five lead novel lipids and MC3 LNPs are labeled accordingly: MC3 (gray triangles), lipid H (green circles), lipid M (orange squares), lipid P (purple diamonds), lipid Q (tan inverted triangles), and lipid N (yellow hexagons). (C) Lipid pK_a versus fold increase in immunogenicity at 0.001 mg/kg IM for lipids A through E′. (D) Circulating IgG antibody (micrograms per milliliter of serum) 6 h after administration of 0.2 mg/kg modified mRNAs encoding the heavy chain and light chain of an influenza monoclonal antibody formulated at a 2:1 mass ratio in LNPs containing MC3 or novel lipids (n = 5 per group). *p < 0.05; **p < 0.01; ***p < 0.001; ****p < 0.0001, ordinary one-way ANOVA with Dunnett’s multiple comparisons test of each novel lipid versus MC3.

Figure 3

Chemical Structure and Pharmacokinetics of Lead Lipids (A) Chemical structures and pK_a of MC3 and novel lipids. (B–D) Lipid concentration (nanograms per gram) after IM administration of modified mRNA encoding luciferase formulated in LNPs containing lipid H (green circles), lipid M (orange squares), lipid P (purple diamonds), lipid Q (tan inverted triangles), and lipid N (yellow hexagons) in (B) muscle, (C) liver, and (D) spleen up to 48 h post-injection (n = 3 per group per time point).

Figure 4

Expression and Immunogenicity in Non-human Primates (A and B) Immunogenicity measured by H10-specific (A) ELISA or (B) HAI at days 0, 21 (3 weeks after the first dose), and 42 (3 weeks after the second dose). Each dose in cynomolgus monkeys contained 5 μg modified mRNA encoding H10N8 formulated in LNPs containing either MC3 (gray triangles), lipid H (green circles), lipid M (orange squares), lipid P (purple diamonds), lipid Q (tan inverted triangles), or lipid N (yellow hexagons) (n = 3 per group). (C) Circulating IgG levels (in micrograms per milliliter) after a 500-μg IM administration in cynomolgus monkeys of modified mRNA encoding heavy- and light-chain antibodies in a 2:1 weight ratio formulated in LNPs containing MC3 or novel lipids (n = 3 per group). (D and E) Site of injection was monitored for (D) edema and (E) erythema 1 and 3 days after injection. (F) Circulating IL-6 levels (in picograms per milliliter) 6 h after administration. ^#p > 0.05; ^##p > 0.001, two-way ANOVA with Dunnett’s multiple comparison test of each lipid versus MC3 at each time point. **p > 0.01; ****p > 0.0001, z test of areas under the curve (AUCs) for each novel lipid versus MC3.

Figure 5

Tolerability in Rats Serum concentrations (in picograms per milliliter) of cytokines (A) eotaxin, (B) GRO-alpha, (C) IP-10, (D) RANTES, and (E) MCP-1 were measured 6 h after a single IM administration of 0.01 mg or 0.1 mg modified mRNA encoding prM-E from Zika virus formulated in LNPs containing MC3 (gray), lipid H (green), lipid M (orange), lipid P (purple), lipid Q (tan), or lipid N (yellow) (n = 3 per group). (F–I) Representative histology sections stained with H&E 2 days after a single IM administration of 0.1 mg of modified mRNA encoding prM-E from Zika virus formulated in LNPs containing MC3 or lipid H in the (F and H) muscle and (G and I) skin. (F) MC3 muscle; (G) MC3 skin; (H) lipid H muscle; (I) lipid H skin.