Pre-Existing Anti-Inflammatory Immune Conditions Influence Early Antibody Avidity and Isotype Profile Following Comirnaty® Vaccination in Mice

Abstract

Background/objectives: Vaccine immunogenicity is often suboptimal in vulnerable populations such as the elderly, infants, and individuals in low- and middle-income countries. One contributing factor may be pre-existing immunomodulatory conditions, including helminth infections. This study investigates the impact of Fasciola hepatica (F. hepatica) derived molecules on the early humoral response to the COVID-19 mRNA vaccine Comirnaty^® in a mouse model.

Methods: BALB/c mice were pretreated with a F. hepatica protein extract (FH) or complete Freund's adjuvant (CFA) prior to vaccination. Cytokine production and antibody responses were assessed at 0, 14, and 21 days post-vaccination (dpv) through serum analysis and ex vivo splenocyte stimulation with the SARS-CoV-2 receptor-binding domain (RBD) or LPS.

Results: At 0 dpv, FH-treated mice showed increased serum IL-10, while CFA treatment induced IL-12. FH- but not CFA-treated splenocytes secreted IL-10 upon RBD or LPS stimulation. At 21 dpv, FH-treated mice lacked IFN-γ production but maintained IL-10 and showed elevated IL-4, consistent with a Th2-skewed profile. Although total anti-RBD IgG levels were similar between groups, FH-treated mice exhibited reduced IgG avidity and a higher IgG1/IgG2 ratio. CFA-treated mice showed delayed avidity maturation.

Conclusions: Prior exposure to F. hepatica antigens can modulate the early immune response to Comirnaty^®, affecting both cellular activation and antibody quality. This altered response may reflect a reduced early protective capacity of the vaccine, which might need to be considered when designing or evaluating vaccination strategies using mRNA vaccines in helminth-endemic regions.

Keywords: early immune response; helminth proteins; immunomodulation; mRNA vaccine; trained immunity.

Figure 1

Schematic diagram illustrating the pre-vaccination treatments, vaccination schedule, and corresponding sampling time points.

Figure 2

Effects of the in vivo innate training. (A) Splenocytes from animals treated in presence or absence of FH or CFA were isolated 7 days after treatment (0 dpv) and stimulated ex vivo with RDB, LPS or PBS (mock). (B) Serum cytokine levels in animals treated with FH or CFA at 0 dpv. Concentration of cytokines was estimated from a standard curve using ELISA. Asterisks indicate statistically significant differences between groups calculated with two-way Anova followed by a Tukey multiple comparison test: * p < 0.05; ** p < 0.01; *** p < 0.001; ns = not significant (p > 0.05).

Figure 3

RBD-specific antibody immune response in F. hepatica treated (blue), CFA-treated (orange) or control (green) mice. (A) Total anti-RBD IgG kinetics and (B) compared levels at 14 and 21 dpv. (C) Kinetics of the avidity maturation expressed as avidity index (AI%) and (D) compared levels at 14 and 21 dpv. (E) IgG1 to IgG2 ratio kinetics, and (F) comparisons at 14 and 21 dpv with line dotted line indicating equal concentration of both IgG subtypes. Asterisks indicate statistically significant differences between infected and control animals calculated with two-way Anova followed by a Tukey multiple comparison test: * p < 0.05; ** p < 0.01; *** p < 0.001; ns = not significant (p > 0.05).

Figure 4

Splenocytes from vaccinated animals pre-treated, or not pre-treated, with FH or CFA and vaccinated with one dose of Comirnaty^® Vaccine (legends, “Animals”) were isolated at 21 dpv. Cells were stimulated ex vivo (indicated by “Cells”) with RBD, LPS or mock-treated and IFN-γ (A), IL-10 (B) and IL-4 (C) concentrations were estimated by ELISA. * p < 0.05; ** p < 0.01; ns = not significant (p > 0.05).