Immune correlates of protection by mRNA-1273 vaccine against SARS-CoV-2 in nonhuman primates

Passively transferred mRNA-1273-immune NHP IgG is sufficient to mediate protection against SARS-CoV-2 challenge or disease in hamsters.

“Passively transferred NHP antibodies were sufficient to mediate protection against SARS-CoV-2 challenge in hamsters, emphasizing that antibodies are mechanistic correlates.”

• Also stated in: § Passively transferred mRNA-1273–induced IgG mediates protection against SARS-CoV-2 · plain

  “Thus, mRNA-1273 immune IgG alone is sufficient to mediate protection from disease in vivo against SARS-CoV-2 infection.”

• Also stated in: § Discussion · plain

  “vaccine-elicited antibodies are sufficient for protection against disease in the highly pathogenic golden Syrian hamster model of SARS-CoV-2 infection.”

mRNA-1273 vaccination elicits S-specific binding antibody responses in a dose-dependent manner.

“Binding antibody titers increased compared with control animals in a dose-dependent manner, ranging from a median of 55 to 5800 IU/ml at 0.3 and 100 μg, respectively, for S-specific IgG and 66 to 10,400 IU/ml for RBD-specific IgG (Fig. 1, A and B).”

• Also stated in: § mRNA-1273 vaccination elicits antibody responses in a dose-dependent manner · boosted

  “All measures were significantly correlated with dose (P < 0.0001), as determined by Spearman’s correlation test.”

S-specific binding antibody reached median reciprocal end-point titers of 7900 and 64,000 by 4 weeks after prime and after boost, respectively, after immunization with 30 μg of mRNA-1273.

“S-specific binding antibody (2, 3) was increased over baseline after each immunization, reaching 7900 and 64,000 median reciprocal end-point titers by 4 weeks after prime and after boost, respectively, after immunization with 30 μg of mRNA-1273 (fig. S2A).”

Antibody binding and neutralizing responses were highly correlated with one another.

“Assessments of antibody binding and neutralizing responses were highly correlated with one another, suggesting that mRNA-1273 immunization and elicitation of high-titer S-binding antibody responses predicts functional antibody responses (Fig. 2).”

30 μg of mRNA-1273 elicited 1400 and 21,300 AUC IgA in BAL and nasal washes, respectively.

“The dose-dependent trend for S-specific IgA was similar albeit at lower levels where 30 μg of mRNA-1273 elicited 1400 and 21,300 AUC IgA in BAL (Fig. 1I) and nasal washes (Fig. 1J), respectively.”

There was a dose-dependent reduction in median ACE2-binding inhibition comparing 100 μg with 1 μg of mRNA-1273, reaching a maximum difference of 270-fold.

“There was also a dose-dependent reduction in median ACE2-binding inhibition comparing 100 μg with 1 μg of mRNA-1273 (Fig. 1C), reaching a maximum difference between these two dose groups of 270-fold.”

Nasal wash S-specific IgG titers ranged from 86 to 142,200 AUC.

“Nasal wash S-specific IgG titers ranged from 86 to 142,200 AUC (Fig. 1H).”

Live viral neutralization of the alpha (B.1.1.7) variant was not appreciably decreased compared with D614G.

“Live viral neutralization of the alpha (B.1.1.7) variant (21), which is highly transmissible and has previously been circulating worldwide (22), was not appreciably decreased compared with D614G (fig. S3A).”

S-specific IgG titers ranged from a median of 55 to 5800 IU/ml at 0.3 and 100 μg, respectively.

“Binding antibody titers increased compared with control animals in a dose-dependent manner, ranging from a median of 55 to 5800 IU/ml at 0.3 and 100 μg, respectively, for S-specific IgG and 66 to 10,400 IU/ml for RBD-specific IgG (Fig. 1, A and B).”

BAL S-specific IgG levels after 0.3 and 30 μg of mRNA-1273 ranged from a median of 110 to 280,000 AUC.

“BAL S-specific IgG levels after 0.3 and 30 μg of mRNA-1273 ranged from a median of 110 to 280,000 area under the curve (AUC) (Fig. 1G).”

RBD-specific IgG titers ranged from a median of 66 to 10,400 IU/ml at 0.3 and 100 μg, respectively.

“Binding antibody titers increased compared with control animals in a dose-dependent manner, ranging from a median of 55 to 5800 IU/ml at 0.3 and 100 μg, respectively, for S-specific IgG and 66 to 10,400 IU/ml for RBD-specific IgG (Fig. 1, A and B).”

VSV-based pseudovirus and live-virus neutralization followed the same significant trend of dose dependency.

“Vesicular stomatitis virus (VSV)–based pseudovirus (Fig. 1E) and live-virus (Fig. 1F) neutralization followed the same significant trend of dose dependency.”

There was a dose-dependent increase in BAL and nasal wash S-specific IgG and IgA after two doses of mRNA-1273.

“There was a dose-dependent increase in BAL and nasal wash S-specific IgG and IgA after two doses of mRNA-1273 (Fig. 1, G to J).”

The beta (B.1.351) variant exhibited a ninefold reduction in neutralization compared with D614G in the 100-μg dose group.

“The beta (B.1.351) variant, which contains multiple mutations in RBD and NTD and has been reported to show the greatest reduction of neutralization by vaccine-induced sera (16, 23, 24), exhibited a ninefold reduction compared with D614G in the 100-μg dose group.”

mRNA-1273 vaccination elicits S-specific IgG and IgA antibodies in both the upper and lower airways.

“Thus, mRNA-1273 vaccination elicits S-specific IgG and IgA antibodies in both the upper and lower airways, which potentially provide immediate protection at the site of infection and limit transmission.”

There was a direct correlation between dose and the proportion of TH1 cells among peripheral blood memory CD4 T cells (P = 0.006).

“There was a direct correlation between dose and the proportion of T helper type 1 (TH1) cells [interleukin 2–positive (IL-2+), tumor necrosis factor–positive (TNF+), and/or interferon-γ–positive (IFN-γ+)] among peripheral blood memory CD4 T cells (P = 0.006), because all animals in the 30-μg dose group had TH1 responses (fig. S6A).”

In control animals, SARS-CoV-2 infection caused patchy, moderate to severe inflammation often involving small airways and adjacent alveolar interstitium.

“In the control animals, SARS-CoV-2 infection caused patchy, moderate to severe inflammation that often involved the small airways and the adjacent alveolar interstitium, consistent with previous reports (29–31).”

TH2 responses were low to undetectable in all vaccine dose groups.

“By contrast, TH2 responses (IL-4+and/or IL-5+) were low to undetectable in all vaccine dose groups (fig. S6B).”

No animals with an S-binding titer of >488 IU/ml exhibited higher N-specific primary antibody responses after challenge above the background value at the time of challenge.

“Finally, no animals with an S-binding titer of >488 IU/ml exhibited higher N-specific primary antibody responses after challenge above the background value at the time of challenge.”

For all six antibody measurements, dose was not significantly predictive of sgRNA in BAL after adjusting for antibody levels.

“For all six antibody measurements, the dose was not significantly predictive of sgRNA in the BAL after adjusting for antibody levels (table S2A).”

There was limited to no lung pathology or viral antigen detected in animals with <10,000 sgRNA copies/ml in BAL.

“Additionally, there was limited to no lung pathology or viral antigen detected in animals with <10,000 sgRNA copies/ml in BAL, providing additional evidence that mRNA-1273–vaccinated animals were protected from lower airway disease.”

There was a direct correlation between dose and magnitude of S-specific IL-21 TFH cell responses (P = 0.010).

“There was also a direct correlation between dose and magnitude of S-specific IL-21 TFH cell responses (P = 0.010) (fig. S6D).”

Seroconversion to N was observed only in control animals and animals immunized with <3 μg of mRNA-1273.

“When prechallenge N-specific IgG responses were compared with postchallenge responses, we only observed seroconversion in the control animals and animals immunized with <3 μg of mRNA-1273 (fig. S9D).”

There was a vaccine dose effect for protection against viral replication in the upper and lower airways.

“We observed a vaccine dose effect for protection against viral replication in the upper and lower airways.”

The reduction in sgRNA in nasal swabs was primarily limited to animals receiving 30 μg of mRNA-1273 compared with control animals.

“By contrast, the reduction in sgRNA in nasal swabs was primarily limited to animals receiving 30 μg of mRNA-1273 compared with control animals (Fig. 3B and fig. S7B).”

There was a strong correlation between sgRNA in the upper and lower airways.

“Although we observed a strong correlation between sgRNA in the upper and lower airways, there was a time-dependent loss of concordance in the correlations with upper and lower airways samples (Fig. 3, C to E), suggesting distinct mechanisms for viral clearance in the two compartments.”

CD8 T cell responses were low to undetectable in all vaccine dose groups.

“By contrast, CD8 T cell responses were also low to undetectable in all vaccine dose groups (fig. S6E).”

On days 2 and 4 after challenge, there were approximately two and five log10 reductions in sgRNA_N in BAL compared with control animals at doses of 1 and 30 μg, respectively.

“On days 2 and 4 after challenge, there were approximately two and five log10 reductions in sgRNA_N in BAL compared with control animals at doses of 1 and 30 μg, respectively (Fig. 3A).”

Viral antigen was detected in both control animals but only sporadically across vaccinated animals in various dose groups.

“Viral antigen was detected in both control animals but only sporadically across vaccinated animals in various dose groups (table S1).”

In sera, there was no postchallenge increase in S-specific, RBD-specific, or neutralizing antibodies in the 3-, 10-, or 30-μg dose groups.

“In sera, there was no postchallenge increase in S-specific (fig. S9A), RBD-specific (fig. S9B), or neutralizing antibodies (fig. S9C) in the 3-, 10-, or 30-μg dose groups.”

There was a time-dependent loss of concordance in the correlations with upper and lower airways samples.

“Although we observed a strong correlation between sgRNA in the upper and lower airways, there was a time-dependent loss of concordance in the correlations with upper and lower airways samples (Fig. 3, C to E), suggesting distinct mechanisms for viral clearance in the two compartments.”

There was a strong negative correlation between prechallenge S-specific antibodies and postchallenge N-specific antibodies.

“Consistent with this, there was a strong negative correlation between prechallenge S-specific antibodies and postchallenge N-specific antibodies (Fig. 4M).”

By day 4 after challenge, most animals vaccinated with 1 μg or higher had low to undetectable sgRNA_E in BAL.

“Moreover, by day 4 after challenge, most animals vaccinated with 1 μg or higher had low to undetectable sgRNA_E in BAL (fig. S7A).”

mRNA-1273 vaccination induces TH1- and TFH-skewed CD4 T cell responses.

“Thus, in agreement with previous results (13, 25, 26), mRNA-1273 vaccination induces TH1- and TFH-skewed CD4 T cell responses.”

• cites [13] 13. Corbett K. S., Flynn B., Foulds K. E., Francica J. R., Boyoglu-Barnum S., Werner A. P., Flach B., O’Connell S., Bock K. W., Minai M., Nagata B. M., Andersen H., Martinez D. R., Noe A. T., Douek N., Donaldson M. M., Nji N. N., Alvarado G. S., Edwards D. K., Flebbe D. R., Lamb E., Doria-Rose N. A., Lin B. C., Louder M. K., O’Dell S., Schmidt S. D., Phung E., Chang L. A., Yap C., Todd J. M., Pessaint L., Van Ry A., Browne S., Greenhouse J., Putman-Taylor T., Strasbaugh A., Campbell T.-A., Cook A., Dodson A., Steingrebe K., Shi W., Zhang Y., Abiona O. M., Wang L., Pegu A., Yang E. S., Leung K. sourceNot checked yet

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• cites [25] 25. Corbett K. S., Edwards D., Leist S. R., Abiona O. M., Boyoglu-Barnum S., Gillespie R. A., Himansu S., Schäfer A., Ziwawo C. T., DiPiazza A. T., Dinnon K. H., Elbashir S. M., Shaw C. A., Woods A., Fritch E. J., Martinez D. R., Bock K. W., Minai M., Nagata B. M., Hutchinson G. B., Bahl K., Garcia-Dominguez D., Ma L., Renzi I., Kong W. P., Schmidt S. D., Wang L., Zhang Y., Stevens L. J., Phung E., Chang L. A., Loomis R. J., Altaras N. E., Narayanan E., Metkar M., Presnyak V., Liu C., Louder M. K., Shi W., Leung K., Yang E. S., West A., Gully K. L., Wang N., Wrapp D., Doria-Rose N. A., StewartNot checked yet

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• cites [26] 26. Pardi N., Hogan M. J., Naradikian M. S., Parkhouse K., Cain D. W., Jones L., Moody M. A., Verkerke H. P., Myles A., Willis E., LaBranche C. C., Montefiori D. C., Lobby J. L., Saunders K. O., Liao H.-X., Korber B. T., Sutherland L. L., Scearce R. M., Hraber P. T., Tombácz I., Muramatsu H., Ni H., Balikov D. A., Li C., Mui B. L., Tam Y. K., Krammer F., Karikó K., Polacino P., Eisenlohr L. C., Madden T. D., Hope M. J., Lewis M. G., Lee K. K., Hu S.-L., Hensley S. E., Cancro M. P., Haynes B. F., Weissman D., Nucleoside-modified mRNA vaccines induce potent T follicular helper and germinal cente sourceNot checked yet

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The virus was more rapidly cleared from BAL compared with nasal swab samples.

“The virus was more rapidly cleared from BAL compared with nasal swab samples.”

At doses below 1 μg, there were increased S-specific, RBD-specific, and neutralizing antibody responses at day 28 after challenge compared with before challenge.

“By contrast, at doses below 1 μg, there were increased S-specific (fig. S9A), RBD-specific (fig. S9B), and neutralizing antibody responses (fig. S9C) at day 28 after challenge compared with before challenge.”

Both BAL and nasal wash S-specific IgG and IgA were predictive for reducing sgRNA in these compartments.

“Both BAL and nasal wash S-specific IgG and IgA were predictive for reducing sgRNA in these compartments.”

A 10-fold increase in S-binding titers was associated with ~10-fold reductions in viral replication in BAL and NS after challenge.

“We have shown that a 10-fold increase in S-binding titers was associated with ~10-fold reductions in viral replication in BAL and NS after challenge.”

There were no anamnestic S-specific responses or increase in N-specific responses in blood or BAL within 28 days after infection in the >3-μg dose groups compared with prechallenge.

“There were no anamnestic S-specific responses or increase in N-specific responses in blood or BAL within 28 days after infection in the >3-μg dose groups compared with prechallenge, consistent with these doses inducing higher antibody responses and preventing viral replication.”

After adjustment for S-specific IgG, CD40L+ TFH and TH1 cell responses did not remain significantly associated with sgRNA levels in BAL.

“After adjustment for S-specific IgG, neither of these remained significantly associated with sgRNA levels in the BAL, suggesting that these T cell measures do not predict sgRNA independently of the binding antibody measured in BAL.”

Hamsters that received preimmune IgG or 2 μg of mRNA-1273-immune IgG showed ~10% weight loss by day 6.

“Hamsters that received preimmune IgG or 2 μg of mRNA-1273–immune IgG showed ~10% weight loss by day 6 (32).”

Hamsters that received 10 μg of mRNA-1273-immune NHP IgG showed little to no weight loss after challenge.

“By contrast, hamsters that received 10 μg of mRNA-1273–immune NHP IgG showed little to no weight loss after challenge (Fig. 5E).”

There are no studies to date that have specifically defined immune correlates of protection in upper and lower airways after vaccination with any COVID-19 vaccine approved for use in humans.

“Although immune responses associated with protection after primary infection have been assessed in NHPs (15), there are no studies to date that have specifically defined immune correlates of protection in upper and lower airways after vaccination with any COVID-19 vaccine approved for use in humans.”

• cites [15] 15. McMahan K., Yu J., Mercado N. B., Loos C., Tostanoski L. H., Chandrashekar A., Liu J., Peter L., Atyeo C., Zhu A., Bondzie E. A., Dagotto G., Gebre M. S., Jacob-Dolan C., Li Z., Nampanya F., Patel S., Pessaint L., Van Ry A., Blade K., Yalley-Ogunro J., Cabus M., Brown R., Cook A., Teow E., Andersen H., Lewis M. G., Lauffenburger D. A., Alter G., Barouch D. H., Correlates of protection against SARS-CoV-2 in rhesus macaques. Nature 590, 630–634 (2021). 10.1038/s41586-020-03041-6 sourceNot checked yet

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Protection of the lower respiratory tract required lower serum antibody concentrations than protection of the upper respiratory tract.

“Protection of the lower respiratory tract required lower serum antibody concentrations, possibly explaining why most current vaccines are highly effective against severe lower airway disease.”

• Also stated in: § Discussion · plain

  “Thus, a lower antibody level is needed for the reduction of viral replication in the lower airway than in the upper airway.”

The NHP model exhibits upper and lower airway infection and pathology similar to clinical presentations of mild COVID-19 in humans.

“This model exhibits upper and lower airway infection and pathology similar to clinical presentations of mild COVID-19 in humans (14).”

• cites [14] 14. Munster V. J., Feldmann F., Williamson B. N., van Doremalen N., Pérez-Pérez L., Schulz J., Meade-White K., Okumura A., Callison J., Brumbaugh B., Avanzato V. A., Rosenke R., Hanley P. W., Saturday G., Scott D., Fischer E. R., de Wit E., Respiratory disease in rhesus macaques inoculated with SARS-CoV-2. Nature 585, 268–272 (2020). 10.1038/s41586-020-2324-7 sourceNot checked yet

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Antibodies are mechanistic correlates of protection.

“emphasizing that antibodies are mechanistic correlates.”

• Also stated in: § Discussion · boosted

  “this study establishes the critical role of antibodies as a correlate of protection against SARS-CoV-2 in the NHP model”

High-titer S-binding antibody responses predict functional antibody responses after mRNA-1273 immunization.

“suggesting that mRNA-1273 immunization and elicitation of high-titer S-binding antibody responses predicts functional antibody responses (Fig. 2).”

The mRNA-1273 dose may have a profound effect on eliciting neutralizing antibodies against the beta variant.

“However, these data further suggest that the mRNA-1273 dose may have a profound effect on eliciting neutralizing antibodies against the beta variant.”

Vaccine-elicited immune responses, particularly at high doses, were protective.

“The reduction of viral replication as determined by sgRNA coupled with limited pathology in the lung and no detectable anamnestic S responses or induction of primary responses to N provide three distinct measures suggesting that vaccine-elicited immune responses, particularly at high doses, were protective.”

The dose effect on day 2 sgRNA in NS and BAL appears to be fully captured by adjustment for S-specific IgG.

“Thus, the dose effect on day 2 sgRNA in NS and BAL appears to be fully captured by the adjustment for S-specific IgG.”

mRNA-1273-vaccinated animals were protected from lower airway disease.

“providing additional evidence that mRNA-1273–vaccinated animals were protected from lower airway disease.”

S-specific IgG meets prespecified criteria to be considered a correlate of sgRNA levels in NS and BAL.

“Moreover, in this model, S-specific IgG meets our prespecified criteria to be considered as a correlate of sgRNA levels in NS and BAL.”

Viral clearance in the upper and lower airways involves distinct mechanisms.

“suggesting distinct mechanisms for viral clearance in the two compartments.”

The antibody titers required in this high-dose challenge NHP model for a reduction in viral replication may be a conservative estimate for what is required to prevent clinical disease in humans.

“The antibody titers required in this high-dose challenge NHP model for a reduction in viral replication may be a conservative estimate for what is required to prevent clinical disease in humans.”

Immune correlates may differ in their ability to confer protection against severe disease in the lung versus mild infection in the upper airway.

“Moreover, these data highlight how immune correlates may differ in their ability to confer protection against severe disease in the lung versus mild infection in the upper airway, which has potential implications for determining whether higher immune responses will be required to limit transmission and if this will require additional boosting.”

For mRNA-1273, S-specific binding antibody is a surrogate marker of protection.

“In conclusion, this study establishes the critical role of antibodies as a correlate of protection against SARS-CoV-2 in the NHP model and shows that, for mRNA-1273, S-specific binding antibody is a surrogate marker of protection.”

Parallelism between the MSD reference standard and the WHO international standard was established for SARS-CoV proteins S-2P, RBD, and N.

“Parallelism between MSD reference standard and the WHO international standard was established for SARS-CoV proteins (S-2P, RBD, and N).”

T cell measures do not predict sgRNA independently of the binding antibody measured in BAL.

“suggesting that these T cell measures do not predict sgRNA independently of the binding antibody measured in BAL.”

The boosting of vaccine-induced antibodies may occur after upper airway infection in animals that have minimal viral replication in the lower airway.

“Thus, the boosting of vaccine-induced antibodies may occur after upper airway infection in animals that have minimal viral replication in the lower airway.”

Clearance of virus from BAL and NS have distinct immunological requirements.

“Thus, clearance of virus from BAL and NS have distinct immunological requirements (Fig. 3, C to E).”

The strong correlation and proportional changes between S-specific binding titers with serum-neutralizing activity support using easy-to-measure binding titers as the primary metric for defining a correlate of protection in humans, at least for mRNA-based vaccines delivering similar antigens and eliciting similar patterns of immunogenicity.

“The strong correlation and proportional changes between S-specific binding titers with serum-neutralizing activity support using easy-to-measure binding titers as the primary metric for defining a correlate of protection in humans, at least for mRNA-based vaccines delivering similar antigens and eliciting similar patterns of immunogenicity.”