Intranasal M2SR (M2-Deficient Single Replication) H3N2 Influenza Vaccine Provides Enhanced Mucosal and Serum Antibodies in Adults

Joseph Eiden, Carlos Fierro, Howard Schwartz, Mark Adams, Kimberly J Ellis, Roger Aitchison, Renee Herber, Yasuko Hatta, David Marshall, Michael J Moser, Robert Belshe, Harry Greenberg, Kathleen Coelingh, Yoshihiro Kawaoka, Gabriele Neumann, Pamuk Bilsel, Joseph Eiden, Carlos Fierro, Howard Schwartz, Mark Adams, Kimberly J Ellis, Roger Aitchison, Renee Herber, Yasuko Hatta, David Marshall, Michael J Moser, Robert Belshe, Harry Greenberg, Kathleen Coelingh, Yoshihiro Kawaoka, Gabriele Neumann, Pamuk Bilsel

Abstract

Background: We previously demonstrated that an intranasal dose of 108 50% tissue culture infectious dose (TCID50) M2-deficient single replication (M2SR) influenza vaccine protected against highly drifted H3N2 influenza challenge in a subset of subjects who demonstrated ≥2-fold increase in microneutralization (MN) antibodies to Belgium2015 (the challenge strain) after vaccination. Here, we describe a phase 1b, observer-blinded, dose-escalation study demonstrating an increased proportion of responders with this signal of immune protection.

Methods: Serosusceptible subjects aged 18-49 years were randomized to receive 2 doses (108-109 TCID50) of M2SR or placebo administered 28 days apart. Clinical specimens were collected before and after each dose. The primary objective was to demonstrate safety of M2SR vaccines.

Results: The vaccine was well tolerated at all dose levels. Against Belgium2015, ≥ 2-fold increases in MN antibodies were noted among 40% (95% confidence interval [CI], 24.9%-56.7%) of subjects following a single 108 TCID50 M2SR dose and among 80.6% (95% CI, 61.4%-92.3%) after 109 dose (P < .001). A single 109 TCID50 dose of M2SR generated ≥4-fold hemagglutination inhibition antibody seroconversion against the vaccine strain in 71% (95% CI, 52.0%-85.8%) of recipients. Mucosal and cellular immune responses were also induced.

Conclusions: These results indicate that M2SR may provide substantial protection against infection with highly drifted strains of H3N2 influenza.

Clinical trials registration: NCT03999554.

Keywords: H3N2; drift; influenza; intranasal; live; mucosal; vaccine.

Conflict of interest statement

Potential conflicts of interest. J. E. is a consultant to FluGen. R. B., H. G., and K. C. serve on FluGen's Clinical Advisory Board. Y. K. and G. N. are founders of FluGen. R. H., Y. H., D. M., M. M., and P. B. are employees of FluGen. All other authors: No reported conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

© The Author(s) 2022. Published by Oxford University Press on behalf of Infectious Diseases Society of America.

Figures

Figure 1.
Figure 1.
Trial profile. Abbreviations: Bris2007, H3N2 A/Brisbane/10/2007; Sing2016, H3N2 A/Singapore/INFIMH-16-0019/2016.
Figure 2.
Figure 2.
Treatment-related adverse events. A, Proportion of subjects with treatment-emergent adverse events (TEAE) 8 days after the first dose. B, Proportion of subjects with TEAE 8 days after the second dose.
Figure 3.
Figure 3.
Serum HAI and neutralizing antibody responses after intranasal vaccination. A, Proportion of subjects with ≥4-fold rise in HAI titer 28 days after the first dose against matched and drifted H3N2 influenza virus strains. B, Proportion of subjects with ≥4-fold rise in HAI titer 28 days after the second dose against matched and drifted H3N2 influenza virus strains. Error bars are 95% CI. C, Proportion of subjects with ≥2-fold rise in MNT 28 days after the first dose against matched and drifted H3N2 influenza virus strains. Error bars are 95% CI. H3N2 test strains are: Singapore 2016, A/Singapore/INFIMH-16-0019/2016; Hong Kong 2019, A/Hong Kong/2671/2019; Switzerland 2017, A/Switzerland/8060/2017; Belgium 2015, A/Belgium/4217/2015; Kansas 2017, A/Kansas/14/2017; Kansas 2017 cell, A/Kansas/14/2017 cell-based; Kansas 2017 egg, A/Kansas/14/2017 egg-based; Brisbane 2007, A/Brisbane/10/2007. ***P < .001, **P < .01, *P < .05. Abbreviations: CI, confidence interval; HAI, hemagglutination inhibition; MNT, microneutralization titer; TCID50, tissue culture infectious dose.
Figure 4.
Figure 4.
Serum neuraminidase inhibition antibody titers after intranasal vaccination. Shown are proportion of subjects with ≥2-fold and ≥4-fold rise in neuraminidase inhibition 28 days after the first dose against H6N2 reassortant influenza virus encoding the neuraminidase from A/Switzerland/9715293/2013. Error bars are 95% confidence interval. ***P < .001, **P < .01, *P < .05. Abbreviations: Bris2007, H3N2 A/Brisbane/10/2007; Sing2016, H3N2 A/Singapore/INFIMH-16-0019/2016; TCID50, tissue culture infectious dose.
Figure 5.
Figure 5.
Mucosal sIgA and serum IgA antibody ELISA titers in nasal swabs after intranasal vaccination. A, GMFR from baseline in sIgA titer 28 days after first dose and 28 days after second dose. Anti-Sing2016 HA ELISA titers were normalized to total sIgA in the nasal specimens. B, Proportion of subjects demonstrating ≥2-fold rise in sIgA titer 28 days after first dose and 28 days after second dose. ***P < .001; **P < .01, M2SR dose levels versus placebo. #P < .05, 109 M2SR versus 108 M2SR. C, GMFR from baseline in anti-Sing2016 HA serum IgA ELISA titer 28 days after first dose and 28 days after second dose. D, Proportion of subjects demonstrating ≥2-fold rise in serum IgA titer 28 days after first dose and 28 days after second dose. ***P < .001, **P < .01, *P < .05. Abbreviations: ELISA, enzyme-linked immunosorbent assay; GMFR, geometric mean fold rise; HA, hemagglutinin; M2SR, M2-deficient single replication; sIgA, secretory immunoglobulin A; Sing2016, H3N2 A/Singapore/INFIMH-16-0019/2016; TCID50, tissue culture infectious dose.
Figure 6.
Figure 6.
Cell-mediated immune responses after intranasal M2SR vaccination. Geometric mean ELISpot responses (SFC per 106 PBMC) on day 1 (baseline) and day 28 after vaccination. PBMC were stimulated with a nucleoprotein peptide pool. Error bars are 95% confidence interval. Abbreviations: M2SR, M2-deficient single replication; PBMC, peripheral blood mononuclear cell; Sing2016, H3N2 A/Singapore/INFIMH-16-0019/2016; SFC, spot forming cell; TCID50, 50% tissue culture infectious dose.

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