(W1130-02-07) Biodistribution Study of a Bivalent SARS-CoV-2 mRNA Vaccine in Rat

Purpose: Novel SARS-CoV-2 mRNA vaccines delivered in lipid nanoparticle (LNP) are being developed to improve the potency and breadth of immune response against emerging SARS-CoV-2 variants. This presentation summarizes the biodistribution study of a bivalent mRNA vaccine in rats, one of the preclinical safety studies to support First in Human (FIH) trials.

Methods: Sprague Dawley rats were vaccinated by intramuscular administration with vehicle or a bivalent SARS-CoV-2 mRNA vaccine against both Wuhan D614G and Omicron BA.4/5 variants with a single dose of 10µg. Blood and various tissue samples including injection site, lymph nodes, spleen, heart, liver, kidney, lung, brain, ovaries/testis, bone marrow and thymus were collected on Day 1 (4 and 8 hours post-dose), Day 4, Day 8, Day 15, Day 29 and Day 43 for analyzing mRNA biodistribution by a validated TaqMan™. RT-qPCR method targeting the conserved region of the mRNA constructs. Serum samples were collected at the same timepoints for assessing immunogenicity by Spike protein-specific IgG ELISA assays.

Results: No vaccine-related clinical signs, body weight or food consumption changes were observed. All animals developed robust antibody titers against both spike proteins of Wuhan D614G and Omicron BA. 4/5 variants by Day 15. The biodistribution analysis by RT-qPCR showed that the vaccine mRNA copies in blood peaked with a mean of 2.9x10⁵ copies/μg RNA on Day 1 (4 hours post-dose) and dropped to a barely detectable 17.7 copies/μg RNA by Day 2 and became undetectable in all animals by Day 8. All tissues had detectable mRNA copies on Day 1 ranging from 10³ to 10⁷ copies/ug RNA, with higher levels detected in injection site, spleen and lymph nodes. The vaccine mRNA copies were sharply decreased by Day 2 in most of the tissues and became undetectable or near limit of detection in the bone marrow, brain, heart, ovary, testis, and thymus by Day 4; lung by Day 8; and kidney, liver, mesenteric lymph nodes, and injection sites by Day 29. On Day 43, only the spleen, inguinal, and axillary lymph nodes and injection site had very low detectable mRNA copies in a few animals.

Conclusion: Appropriate bioanalytical methods were developed and validated to assess the mRNA vaccine biodistribution. The biodistribution studies demonstrated that a 10mg dose novel mRNA vaccine elicited robust antibody response to both spike proteins and confirmed overall safety and biodistribution profile post-vaccination.