O1051: Transamniotic Fetal mRNA Vaccination: Active Immunization Against Zika Virus in a Rodent Model

Background: Gestational Zika virus (ZIKV) infection carries a major disease burden globally, often with devastating permanent consequences such as microcephaly or fetal loss. Active fetal immunizations with mRNA vaccines are hindered by poor placental crossing of encapsulated mRNA from the mother to the fetus. It has been shown that encapsulated mRNA injected into the amniotic fluid can reach the placenta and fetal circulation via hematogenous routing after transport through the amnio-placental interface. We investigated whether transamniotic fetal mRNA vaccination could be a viable strategy for perinatal immunization against ZIKV infection, first utilizing a human ZIKV antigen in a rodent model.

Methods: After IACUC approval, twenty pregnant Sprague Dawley dams underwent volume-matched intra-amniotic injections in all their fetuses (n=280) of either a suspension of a custom-made mRNA encoding for the ZIKV pre-membrane (ZIVK-prM) and envelope (ZIKV-E) structural proteins encapsulated in a semi-synthetic composite lipopolyplex (vaccinated, n=153), or of the same lipopolyplex without mRNA (control, n=127) on gestational day 17-18 (E17-18; term=E21-22). Pup serum levels of ZIKV-E antigen-specific IgG antibodies were measured by ELISA at term and postnatally on days 5 (P5), 11 (P11), 16 (P16), 1 month, 2 months, and 3 months of age. In addition, splenocyte and lymph node cell suspensions were incubated with either enriched media or enriched media combined with ZIKV-E recombinant protein for 5 days, followed by flow cytometry of culture supernatants to assess T-cell response. Placentas from an additional 27 fetuses were screened for ZIKV-E antigen production. Statistical analyses included the Fisher’s exact test, the Wilcoxon rank sum test, and the Kruskal-Wallis test (all p< 0.05).

Results: Survival in the vaccinated and control groups were respectively 47.1% (72/153) and 53.5% (68/127), not significantly different. When controlled by mRNA-free injections, ZIKV-E-specific IgG was not detected in the serum of term fetuses, however, levels were significantly elevated in vaccinated pups from P5 to P16 (p=0.005-0.002) (figure 1). Splenocytes from vaccinated pups showed significant increases in IL-6 and IFN-γ productions after the antigen-specific challenge at 2 and 3 months (p=0.049 to 0.003 vs. non-challenged cells), along with a significant decrease in IL-13 production at 3 months (p=0.006) (figure 2). Lymph node cell suspensions from vaccinated pups also demonstrated increased production of IFN-γ following antigen-specific challenge (p < 0.001 vs. non-challenged cells), albeit solely at 3 months, along with a significant decrease in IL-13 production at 3 months (0.014 vs. non-challenged cells) (figure 2). No ZIKV-E antigen production was detected in the placental samples.

Conclusion: Transamniotic fetal mRNA delivery of a Zika virus antigen can induce an adaptive humoral and cellular immune response extending into the neonatal period in a healthy rat model. Fetal mRNA vaccination via the minimally invasive transamniotic route could become a novel strategy for prevention of perinatal Zika virus infection.