Human Cytomegalovirus mRNA-1647 Vaccine Candidate Elicits Potent and Broad Neutralization and Higher Antibody-Dependent Cellular Cytotoxicity Responses Than the gB/MF59 Vaccine

Abstract

Background: MF59-adjuvanted gB subunit (gB/MF59) vaccine demonstrated approximately 50% efficacy against human cytomegalovirus (HCMV) acquisition in multiple clinical trials, suggesting that efforts to improve this vaccine design might yield a vaccine suitable for licensure.

Methods: A messenger RNA (mRNA)-based vaccine candidate encoding HCMV gB and pentameric complex (PC), mRNA-1647, is currently in late-stage efficacy trials. However, its immunogenicity has not been compared to the partially effective gB/MF59 vaccine. We assessed neutralizing and Fc-mediated immunoglobulin G (IgG) effector antibody responses induced by mRNA-1647 in both HCMV-seropositive and -seronegative vaccinees from a first-in-human clinical trial through 1 year following third vaccination using a systems serology approach. Furthermore, we compared peak anti-gB antibody responses in seronegative mRNA-1647 vaccinees to that of seronegative gB/MF59 vaccine recipients.

Results: mRNA-1647 vaccination elicited and boosted HCMV-specific IgG responses in seronegative and seropositive vaccinees, respectively, including neutralizing and Fc-mediated effector antibody responses. gB-specific IgG responses were lower than PC-specific IgG responses. gB-specific IgG and antibody-dependent cellular phagocytosis responses were lower than those elicited by gB/MF59. However, mRNA-1647 elicited higher neutralization and antibody-dependent cellular cytotoxicity (ADCC) responses.

Conclusions: Overall, mRNA-1647 vaccination induced polyfunctional and durable HCMV-specific antibody responses, with lower gB-specific IgG responses but higher neutralization and ADCC responses compared to the gB/MF59 vaccine.

Clinical trials registration: NCT03382405 (mRNA-1647) and NCT00133497 (gB/MF59).

Keywords: durability; gB/MF59 vaccine; human cytomegalovirus; mRNA-1647 vaccine; pentametric complex.

Figure 1.

mRNA-1647 vaccine–induced long-lasting antigen-specific immunoglobulin G (IgG) antibody responses in human cytomegalovirus-seropositive and -seronegative vaccinees. The soluble glycoprotein B (gB)–specific (A), pentameric complex (PC)–specific (B), and TB40/E virion-bound (C) IgG antibody titers (effective dose 50 [ED₅₀]) were determined via enzyme-linked immunosorbent assay for both seronegative (left panels) and seropositive (right panels) vaccinees, respectively, at the indicated time points including the 1-year follow-up after last vaccination. The dotted line indicates the limit of detection (ED₅₀ = 30). D, IgG-binding activities to Merlin gB-transfected cells were evaluated for seronegative (left panel) and seropositive (right panel) vaccinees at the indicated time points via flow cytometry–based assay. P values from Wilcoxon matched-pairs signed-rank test are reported. *P < .05, ***P < .001.

Figure 2.

Durable neutralizing antibody responses elicited by the mRNA-1647 vaccine in both seropositive and seronegative vaccine recipients. A, Fibroblast neutralization reactivities against Towne virus in HFF-1 cells were compared before (month 0) and after (month 7) vaccination for both seronegative (left panel) and seropositive (right panel) vaccinees. Similarly, fibroblast neutralization responses against AD169r virus in HFF-1 cells (B) and epithelial neutralization antibody responses against AD169r in ARPE-19 cells (C) were monitored before vaccination (month 0) and months 7, 12, and 18 after vaccination for both seronegative (left panels) and seropositive (right panels) vaccinees, respectively, to assess durability. P values from Wilcoxon matched-pairs signed-rank test are reported. *P < .05, **P < .01, ***P < .001. Abbreviation: ID₅₀, 50% inhibitory dose.

Figure 3.

Fc receptor (FcR) binding magnitude and immunoglobulin G (IgG) Fc-portion mediated functionalities induced by the mRNA-1647 vaccine in both seropositive and seronegative vaccinees. Glycoprotein B (gB)–specific (A) and pentameric complex–specific (B) IgG Fc antibody (FcγR1A, FcγR2A [H131], FcγR2B, FcγR3A [V158], and FcRN) responses were plotted for both seronegative and seropositive vaccinees before vaccination (month 0 [M0]) and at the peak timepoint (month 7 [M7]). MFI, mean fluorescense intensity. Vaccine-induced IgG antibody Fc-mediated AD169r virion antibody-dependent cellular cytotoxicity (ADCC) (C) and antibody-dependent cellular phagocytosis (ADCP) (D) responses were assessed for both seronegative (S–) and seropositive (S+) vaccinees. P values from Wilcoxon matched-pairs signed-rank test are reported. Open diamond symbols indicate seronegative samples and open circles indicate seropositive samples. *P < .05, **P < .01, ***P < .001.

Figure 4.

mRNA-1647 induced higher pentameric complex (PC)–specific immunoglobulin G (IgG) responses than glycoprotein B (gB)–specific responses in the same formulation. The magnitude of mRNA-1647 vaccine–induced total IgG responses and IgG subclass (IgG1, IgG2 and IgG3) responses were compared between gB-specific and PC-specific responses for both seronegative (A) and seropositive (B) vaccinees at month 7. The total IgG responses were measured by enzyme-linked immunosorbent assay, while the IgG subclass (IgG1, IgG2, and IgG3) responses were detected via binding antibody multiplex assay. P values from Wilcoxon matched-pairs signed-rank test are reported. The level of IgG Fc antibody responses (FcγR1A, FcγR2A, FcγR2B, FcγR3A, and FcRN) were compared among gB and PC antigen components in the same vaccine formulation in both seronegative (C) and seropositive (D) vaccinees in the mRNA-1647 vaccine cohort. P values from nonparametric t tests are reported (Mann–Whitney test). *P < .05, **P < .01, ***P < .001. Abbreviations: ED₅₀, 50% effective dose; gB, glycoprotein B; IgG, immunoglobulin G; MFI, mean fluorescense intensity; PC, pentameric complex.

Figure 5.

Comparison of glycoprotein B (gB)–specific peak immunoglobulin G (IgG) binding antibody and neutralizing antibody responses. A, Soluble gB-specific total IgG antibody titers (left panel) and relative avidity index (RAI) (right panel) were compared between the 2 vaccine cohorts. B, TB40/E virion-bound IgG titers (left panel) and RAI (right panel) were also compared between the 2 vaccine cohorts. C, Similarly, Towne (left panel) and Merlin gB (right panel) cell-associated IgG antibody responses were compared among the 2 vaccine cohorts. D, The epithelial neutralizing antibody against AD169r in ARPE-19 cells (left panel) and fibroblast neutralizing antibody against AD169r (middle panel) and Towne (right panel) in HFF-1 cells were compared between the mRNA-1647 and gB/MF59 vaccine cohorts. Additionally, the human cytomegalovirus (HCMV)–infected individuals were also included for the comparison. Open blue circles denote the seropositive samples at baseline from the mRNA-1647 vaccine cohort while open purple circles denote the in-house HCMV-seropositive individuals in some assays to increase the statistical power. However, the statistical analysis indicated that the increased sample number did not change the conclusion. P values from nonparametric t tests are reported (Mann–Whitney test). ***P < .001. Abbreviations: ED₅₀, 50% effective dose; gB, glycoprotein B; ID₅₀, 50% inhibitory dose; IgG, immunoglobulin G; MFI, mean fluorescense intensity; S+, human cytomegalovirus seropositive.

Figure 6.

The glycoprotein B (gB)/MF59 vaccine elicited higher peak Fc receptors (FcRs) and antibody-dependent cellular cytotoxicity (ADCP) but lower antibody-dependent cellular cytotoxicity (ADCC) functional antibody responses than the mRNA-1647 vaccine candidate. gB-specific FcγR1A, -2A, -2B, -3A, and FcRN antibody responses were compared between the 2 vaccine cohorts indicative of overall higher-level responses except for FcγR1A response in the gB/MF59 vaccine cohort (A); AD169r virion ADCC (B) and ADCP (C) effector antibody responses were compared between 2 vaccine cohorts, suggesting elevated ADCC responses, but lower ADCP responses were found in the mRNA-1647 cohort. Additionally, the human cytomegalovirus–infected individuals (S+) were also included in the comparison. Open blue circle denotes the seropositive samples at baseline from the mRNA-1647 vaccine. P values from nonparametric t tests are reported (Mann–Whitney test). *P < .05, **P < .01, ***P < .001. Abbreviations: ADCC, antibody-dependent cellular cytotoxicity; ADCP, antibody-dependent cellular phagocytosis; MFI, mean fluorescense intensity; S+, human cytomegalovirus seropositive.