Altered IgG4 Antibody Response to Repeated mRNA versus Protein COVID Vaccines

Abstract

Repeated mRNA SARS-CoV-2 vaccination has been associated with increases in the proportion of IgG4 in spike-specific antibody responses and concurrent reductions in Fcγ-mediated effector functions that may limit control of viral infection. Here, we assessed anti-Spike total IgG, IgG1, IgG2, IgG3 and IgG4, and surrogate markers for antibody-dependent cellular phagocytosis (ADCP, FcγRIIa binding), antibody-dependent cellular cytotoxicity (ADCC, FcγRIIIa binding), and antibody-dependent complement deposition (ADCD, C1q binding) associated with repeated SARS-CoV-2 vaccination with NVX-CoV2373 (Novavax Inc., Gaithersburg, MD). The NVX-CoV2373 protein vaccine did not induce notable increases in spike-specific IgG4 or negatively impact surrogates for Fcγ effector responses. Conversely, repeated NVX-CoV2373 vaccination uniquely enhanced IgG3 responses which are known to exhibit strong affinity for FcγRIIIa and have previously been linked to potent neutralization of SARS-CoV-2. Subsequent investigations will help to understand the immunological diversity generated by different SARS-CoV-2 vaccine types and have the potential to reshape public health strategies.

Keywords: COVID-19; IgG4; NVX-CoV2373; Vaccine; mRNA.

Figure 1.. IgG Subclass Serum Concentrations and Fc Effector Function Responses After Repeated COVID Vaccination.

Randomly selected serum samples from COVID vaccine recipients included participants from 2019nCoV-307 (ClinicalTrials.gov: NCT05463068) who received three homologous doses of Moderna (mRNA-1273, blue, n = 10) or Pfizer (BNT162b2, teal, n = 10) mRNA vaccine followed by one dose of Novavax (NVX-CoV2373), and from 2019nCoV-301 (ClinicalTrials.gov: NCT04611802) who received four homologous doses of Novavax (purple, n = 18). Serum was collected ≥6 months after the last dose for homologous three-dose samples (open circle) and ~4 weeks after fourth dose samples (filled circle). For each vaccine type, the GMFR between the third and fourth doses is indicated in bolded text above the fourth-dose data points. (A) Serum concentrations of anti–ancestral (Wuhan) rS–specific total IgG, IgG1, and IgG4 were measured using quantitative ELISA and reported as GMT with 95% CI. One subject (Moderna) was excluded due to a failed logic check. (B) ADCP, ADCC, and ADCD were analyzed using previously described surrogate SARS-CoV-2 ancestral rS–specific antibody Fc functional multiplex assays assessing median fluorescence intensity of FcγRIIa, FcγRIIIa, and C1q binding, respectively. One subject (Novavax) was excluded due to missing data (x3 Dose + Novavax). SAS^® 9.4 software (SAS Institute Inc., Cary, NC), PROC SGPLOT was used to detect far-outliers based on the log-transformed assay values, defined as Far-outliers = Observations > Q3 + 3*IQR or < Q1 – 3*IQR; none were found or excluded. Abbreviations: ADCC, antibody-dependent cellular cytotoxicity; ADCD, antibody-dependent complement deposition; ADCP, antibody-dependent cellular phagocytosis; CI, confidence interval; C1q complement component 1q; ELISA, enzyme-linked immunosorbent assay; FcγRIIa, Fcγ Receptor IIa; FcγRIIIa, Fcγ Receptor IIIa; GMFR, geometric mean fold rise; GMT, geometric mean titer; IgG, Immunoglobulin G; MFI, median fluorescent intensity; rS, recombinant spike protein; 3x, three-dose.