Monkeypox virus-infected individuals mount comparable humoral immune responses as Smallpox-vaccinated individuals

Abstract

In early 2022, a cluster of monkeypox virus (MPXV) infection (mpox) cases were identified within the UK with no prior travel history to MPXV-endemic regions. Subsequently, case numbers exceeding 80,000 were reported worldwide, primarily affecting gay, bisexual, and other men who have sex with men (GBMSM). Public health agencies worldwide have offered the IMVANEX Smallpox vaccination to these individuals at high-risk to provide protection and limit the spread of MPXV. We have developed a comprehensive array of ELISAs to study poxvirus-induced antibodies, utilising 24 MPXV and 3 Vaccinia virus (VACV) recombinant antigens. Panels of serum samples from individuals with differing Smallpox-vaccine doses and those with prior MPXV infection were tested on these assays, where we observed that one dose of Smallpox vaccination induces a low number of antibodies to a limited number of MPXV antigens but increasing with further vaccination doses. MPXV infection induced similar antibody responses to diverse poxvirus antigens observed in Smallpox-vaccinated individuals. We identify MPXV A27 as a serological marker of MPXV-infection, whilst MPXV M1 (VACV L1) is likely IMVANEX-specific. Here, we demonstrate analogous humoral antigen recognition between both MPXV-infected or Smallpox-vaccinated individuals, with binding to diverse yet core set of poxvirus antigens, providing opportunities for future vaccine (e.g., mRNA) and therapeutic (e.g., mAbs) design.

Fig. 1. Heatmap of ELISA results of serum samples from negative (pre-vaccination or paediatric), vaccinated (IMVANEX or ACAM2000) or MPXV-infected individuals using individual MPXV, VACV or a pool of MPXV and VACV recombinant antigens.

Colour scale represents the OD. Top panel: MPX antigens, split according to the different sample groups. Middle panel: VACV antigens, split according to the different sample groups. Bottom panel: Using a pool of four MPXV and one VACV recombinant antigens. n is equal to the number of biologically independent samples.

Fig. 2. Pearson correlation matrix of VACV and MPXV antigens in those vaccinated or MPXV-infected.

Groups include those with no prior infection or smallpox vaccination (negatives), IMVANEX vaccinated (dose 1, dose 2 and dose 3), ACAM2000-vaccinated and convalescent MPXV-infected individuals (Clade IIb and IIa). Two-tailed correlation was performed using all ELISA data for MPXV and VACV antigens. Only significant correlations are shown, with blank cells indicating a non-significant (p ≥ 0.05) correlation. Data produced using the CorrPlot package.

Fig. 3. Principal component analysis to identify similar antibody responses between IMVANEX-vaccinated and MPXV-infected individuals.

a Principal component analysis (PCA) of antibody binding to 23 MPXV and 3 VACV recombinant antigens, plotted and coloured by group. Coloured circles represent all samples within that cohort. b Biplot of PCA, highlighting that a number of ELISAs using specific antigens can be used for each particular group. Arrows highlighting recombinant MPXV antigens B2, M1 and A27. Note: C18L was excluded from the principal component analysis due to non-specific antibody binding. n is equal to the number of biologically independent samples.

Fig. 4. Differential antibody responses between vaccinated and MPXV-infected individuals.

Differential MPXV poxvirus antigens used to determine: a Prior MPXV infection or ACAM2000 vaccination using MPXV A27 and b recent IMVANEX vaccination using MPXV M1. Cutoffs used are those defined in Table 3. P values above each column were generated using an ordinary one-way ANOVA with a multiple comparison follow-up test comparing the mean of each column with the mean of the negative column. Bars represent the mean ± standard deviation. Differential binding to the c VACV B5 and MPXV B6 and d VACV A33 and MPXV A35 protein homologues between the MPXV-infected individuals and MVA-vaccinated (IMVANEX and ACAM2000: VACV) individuals. Those with MVA vaccination show stronger binding to the VACV B5 and A33 protein compared to the MPXV B6 and A35 homologue, whilst MPXV-infected individuals show higher binding to the B6 and A35 protein. n is equal to the number of biologically independent samples.

Fig. 5. Antibody responses to different MPXV antigens longitudinally in IMVANEX-vaccinated individuals.

Longitudinal sampling of individuals receiving IMAVENEX vaccination against: a a panel of 24 MPXV and 3 VACV antigens or the pooled antigen ELISA. Bars represent the mean ± standard error of the mean. n is equal to the number of biologically independent samples. b Evaluation of the pooled antigen ELISA to determine sensitivity and specificity. Bars represent the mean ± standard deviation. Each dot represents a biologically independent sample. c Using the pooled antigen ELISA, endpoint titres were determined for positive groups. Bars represent the mean ± standard error of the mean. Each dot represents a biologically independent sample. Comparison of the ELISA results of MPXV-infected and Smallpox-vaccinated serum samples using individual antigens relative to the pool of antigens (d) split by antigen, or e linear regression of individual antigen results relative to pooled antigen ELISA results (n = 121 biologically independent samples). Dotted lines represent the 95% confidence intervals. Black lines represent X = Y. P values for d were generated using a paired t test and each pair of dots joined by a line represents a biologically independent sample.