Synthetic modified vaccinia Ankara vaccines confer cross-reactive and protective immunity against mpox virus

Abstract

Background: Although the mpox global health emergency caused by mpox virus (MPXV) clade IIb.1 has ended, mpox cases are still reported due to low vaccination coverage and waning immunity. COH04S1 is a clinically evaluated, multiantigen COVID-19 vaccine candidate built on a fully synthetic platform of the highly attenuated modified vaccinia Ankara (MVA) vector, representing the only FDA-approved smallpox/mpox vaccine JYNNEOS. Given the potential threat of MPXV resurgence and need for vaccine alternatives, we aimed to assess the capacity COH04S1 and its synthetic MVA (sMVA) backbone to confer MPXV-specific immunity.

Methods: We evaluated orthopoxvirus-specific and MPXV cross-reactive immune responses in samples collected during a Phase 1 clinical trial of COH04S1 and in non-human primates (NHP) vaccinated with COH04S1 or its sMVA backbone. MPXV cross-reactive immune responses in COH04S1-vaccinated healthy adults were compared to responses measured in healthy subjects vaccinated with JYNNEOS. Additionally, we evaluated the protective efficacy of COH04S1 and sMVA against mpox in mpox-susceptible CAST/EiJ mice.

Results: COH04S1-vaccinated individuals develop robust orthopoxvirus-specific humoral and cellular responses, including cross-reactive antibodies to MPXV-specific virion proteins as well as MPXV cross-neutralizing antibodies in 45% of the subjects. In addition, NHP vaccinated with COH04S1 or sMVA show similar MPXV cross-reactive antibody responses. Moreover, MPXV cross-reactive humoral responses elicited by COH04S1 are comparable to those measured in JYNNEOS-vaccinated subjects. Finally, we show that mice vaccinated with COH04S1 or sMVA are protected from lung infection following challenge with MPXV clade IIb.1.

Conclusions: These results demonstrate the capacity of sMVA vaccines to elicit cross-reactive and protective orthopox-specific immunity against MPXV, suggesting that COH04S1 and sMVA could be developed as bivalent or monovalent mpox vaccine alternatives against MPXV.

Fig. 1. MVA-specific humoral and cellular responses in COH04S1-vaccinated healthy adults.

a COH04S1 schedule and dosing in healthy adults. Large circles indicate time of vaccination. MVA-specific humoral responses. MVA-specific IgG endpoint titers (b), and neutralizing antibodies (NAb) (c) were measured by ELISA and neutralization assay in subjects before vaccination, post-prime vaccination, and at one- and five-months post-booster vaccination with COH04S1 at dose-level (DL) 1 (DL1/DL1 [lavender circles] and DL1/placebo/DL1 [upward purple triangles]), DL2 (DL2/DL2 [downward pink triangles]), and DL3 (DL3/DL3 [green squares]) (n = 5 subjects/group). Placebo controls (n = 4 subjects [gray diamonds]) were included. c MVA-specific cellular responses. MVA-specific CD8⁺ and CD4 + T cells co-expressing CD107 (blue circles and downward pink triangles, respectively) or CD69 (upward purple triangles and green squares, respectively) markers were measured by intracellular IFNγ staining in subjects described in b-c. Box plots show 25th–75th percentiles, lines indicate medians, whiskers go from minimum to maximum values. Two-way ANOVA followed by Tukey’s multiple comparison test was used in (b, c) after log transformation. Two-tailed Wilcoxon paired T test was used in (d). P values < 0.05 are shown. Dotted lines in b-c represent the lower limit of detection of the assay.

Fig. 2. MPXV-specific humoral response in COH04S1- and JYNNEOS-vaccinated individuals.

MPXV-specific IgG endpoint titers to MPXV virion proteins B6R, A35, M1R, and H3 (a) and MPXV-cross reactive neutralizing antibody titers (PRNT50) (b) were measured by ELISA and MPXV PRNT assay in healthy adults (n = 5 subjects/group) one-month post-booster vaccination with COH04S1 at dose-level (DL) 1 (DL1/DL1 [lavender circles] and DL1/placebo/DL1 [upward purple triangles]), DL2 (DL2/DL2 [downward pink triangles]), and DL3 (DL3/DL3 [green squares]). Placebo controls (n = 4 subjects [gray diamonds]) were included. MPXV-specific IgG endpoint titers to MVA and MPXV virion proteins B6R, A35, M1R, and H3, (c) and MPXV-cross reactive neutralizing antibody titers (PRNT50) measured in the presence or absence of complement (d) were evaluated in healthy adults vaccinated with COH04S1 as described for (a, b) (n = 20 subjects [dark blue circles]), and healthy adults vaccinated with two doses of JYNNEOS (n = 19 subjects [light blue circles]). Red open circles indicate volunteers born before 1973 who likely had smallpox vaccination during childhood. Box plots show 25th–75th percentiles, lines indicate medians, whiskers go from minimum to maximum values. Two-way ANOVA followed by Tukey’s multiple comparison test was used after log transformation. P values < 0.05 are indicated. IMV intracellular mature virions, EEV extracellular enveloped virions.

Fig. 3. COH04S1 and sMVA immunogenicity and protective efficacy against mpox in CAST/EiJ mice.

a Study design. CAST/EiJ mice were intramuscularly (IM) vaccinated two times with sMVA at 1 × 10⁶ (n = 9 mice, upward pink triangles. One mouse died post-prime due to vaccine-unrelated causes), 1 × 10⁷ (n = 9 mice, purple squares), and 1 × 10⁸ pfu (n = 9 mice, light blue circles. One mouse died post-boost due to vaccine-unrelated causes), or COH04S1 at 1 × 10⁶ (n = 9 mice, brown diamonds), 1 × 10⁷ (n = 9 mice, downward teal triangles), and 1 × 10⁸ pfu (n = 9 mice, light green hexagons). Unvaccinated mice were used as controls (n = 10 mice [dark green stars]). Serum samples were collected at baseline, day 28 and day 56 for immunological analysis. Mice were intranasally (IN) challenged with mpox clade IIb.1 at day 56 and weight was recorded for 5 days. At day 5, lungs were collected for viral load (VL) assessment. b Neutralizing antibody (NAb) titers. NAb were evaluated at days 28 (post-prime) and 56 (post-boost) using a plaque reduction neutralization test (PRNT). 50% PRNT titers are shown. Dotted line indicates lower detection limit. c Body weight. Shown are body weight changes compared to baseline. d Lung VL. A 50% tissue culture infectious dose (TCID50) assay was used to evaluate lung VL at day 5 post-challenge. Dotted line indicates lower detection limit. Data are presented as box plots extending from 25th to 75th percentiles, with lines indicating medians, and whiskers going from minimum to maximum values. Two-way (b, c) or one-way (d) ANOVA followed by Tukey’s multiple comparison test were used following log transformation. In (d), ****=p  <  0.0001 when comparing each vaccine group to unvaccinated controls.