1
A single BNT162b2 mRNA dose elicits antibodies with Fc-mediated effector functions and 1
boost pre-existing humoral and T cell responses 2
3
Alexandra Tauzin
1,2
*, Manon Nayrac
1,2,
*, Mehdi Benlarbi
1
, Shang Yu Gong
1,3
, Romain Gasser
1,2
, 4
Guillaume Beaudoin-Bussières
1,2
, Nathalie Brassard
1
, Annemarie Laumaea
1,2
, Dani Vézina
1
, 5
Jérémie Prévost
1,2
, Sai Priya Anand
1,3
, Catherine Bourassa
1
, Gabrielle Gendron-Lepage
1
, Halima 6
Medjahed
1
, Guillaume Goyette
1
, Julia Niessl
1,2,12,§
, Olivier Tastet
1
, Laurie Gokool
1
, Chantal 7
Morrisseau
1
, Pascale Arlotto
1
, Leonidas Stamatatos
4,5
, Andrew T. McGuire
4
, Catherine 8
Larochelle
1,6
, Pradeep Uchil
7
, Maolin Lu
7
, Walther Mothes
7
, Gaston De Serres
8
, Sandrine 9
Moreira
9
, Michel Roger
1,2,9
, Jonathan Richard
1,2
, Valérie Martel-Laferrière
1,2
, Ralf Duerr
10
, Cécile 10
Tremblay
1,2,#
, Daniel E. Kaufmann
1,11,12,#
, and Andrés Finzi
1,2,3,#
11
12
1
Centre de Recherche du CHUM, Montréal, QC, Canada 13
2
Département de Microbiologie, Infectiologie et Immunologie, Université de Montréal, Montreal, QC, 14
Canada 15
3
Department of Microbiology and Immunology, McGill University, Montreal, QC, Canada 16
4
Fred Hutchinson Cancer Research Center, Vaccine and Infectious Disease Division, Seattle, WA, USA 17
5
University of Washington, Department of Global Health, Seattle, WA 98109, USA 18
6
Département des Neurosciences, Université de Montréal, Montreal, QC, Canada 19
7
Department of Microbial Pathogenesis, School of Medicine, New Haven, CT, USA 20
8
Institut National de Santé Publique du Québec, Quebec, QC, Canada 21
9
Laboratoire de Santé Publique du Québec, Institut national de santé publique du Québec, Sainte-Anne-22
de-Bellevue, QC, Canada 23
10
Department of Microbiology, New York University School of Medicine, New York, NY, USA 24
11
Département de Médecine, Université de Montréal, Montreal, QC, Canada 25
12
Consortium for HIV/AIDS Vaccine Development (CHAVD), La Jolla, CA, USA 26
27
28
*Contributed equally 29
§
Current affiliation: Center for Infectious Medicine, Department of Medicine Huddinge, 30
Karolinska Institutet, Stockholm, Sweden 31
32
#
Correspondance 33
Cécile Tremblay – c.tremblay@umontreal.ca
34
Daniel E. Kaufmann - daniel.kaufmann@umontreal.ca
35
Andrés Finzi - andres.finzi@umontreal.ca 36
37
Key Words: Coronavirus, COVID-19, SARS-CoV-2, Spike glycoproteins, mRNA vaccine, 38
Variants, Antibodies, Humoral responses, Neutralization, ADCC, T-cell responses, Activation-39
induced marker assay, Intracellular cytokine staining 40
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 18, 2021. ; https://doi.org/10.1101/2021.03.18.435972doi: bioRxiv preprint
2
Abstract 41
The standard dosing of the Pfizer/BioNTech BNT162b2 mRNA vaccine validated in clinical trials 42
includes two doses administered three weeks apart. While the decision by some public health 43
authorities to space the doses because of limiting supply has raised concerns about vaccine 44
efficacy, data indicate that a single dose is up to 90% effective starting 14 days after its 45
administration. We analyzed humoral and T cells responses three weeks after a single dose of 46
this mRNA vaccine. Despite the proven efficacy of the vaccine at this time point, no neutralizing 47
activity were elicited in SARS-CoV-2 naïve individuals. However, we detected strong anti-receptor 48
binding domain (RBD) and Spike antibodies with Fc-mediated effector functions and cellular 49
responses dominated by the CD4
+
T cell component. A single dose of this mRNA vaccine to 50
individuals previously infected by SARS-CoV-2 boosted all humoral and T cell responses 51
measured, with strong correlations between T helper and antibody immunity. Neutralizing 52
responses were increased in both potency and breadth, with distinctive capacity to neutralize 53
emerging variant strains. Our results highlight the importance of vaccinating uninfected and 54
previously-infected individuals and shed new light into the potential role of Fc-mediated effector 55
functions and T cell responses in vaccine efficacy. They also provide support to spacing the doses 56
of two-vaccine regimens to vaccinate a larger pool of the population in the context of vaccine 57
scarcity against SARS-CoV-2. 58
59
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3
Introduction 60
The Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is the etiological 61
agent of the Coronavirus disease 2019 (COVID-19), responsible for the current pandemic that 62
infected over 120 million people and led to more than 2.66 million deaths worldwide
1,2
. This 63
pandemic caused a race for the elaboration of an effective vaccine against SARS-CoV-2
3,4
. 64
Currently approved vaccines target the highly immunogenic trimeric Spike (S) glycoprotein that 65
facilitates SARS-CoV-2 entry into host cells via its receptor-binding domain (RBD) that interacts 66
with angiotensin-converting enzyme 2 (ACE-2)
5,6
. Among these vaccines, four are approved in 67
many countries (Pfizer/BioNtech BNT162b2, Moderna mRNA-1273, AstraZeneca ChAdOx1 and 68
Janssen Ad26.COV2S). The Pfizer/BioNtech BNT162b2 vaccine was developed using a novel 69
technology based on mRNA
7
. This technology consists in intramuscular injection of a lipid 70
nanoparticle-encapsulated synthetic mRNA vaccine encoding the viral Spike glycoproteins of 71
SARS-CoV-2, which has shown to elicit a robust efficacy against the Wuhan-Hu-1 strain, which 72
served as template for their development
8,9
. This vaccine encodes for a membrane-anchored 73
SARS-CoV-2 full-length spike, stabilized in a prefusion conformation by mutating the furin 74
cleavage site and introducing two prolines in the S2 fusion machinery
7,10
. However, the 75
emergence of mutations in the SARS-CoV-2 S glycoprotein could affect different properties of the 76
virus including affinity for its receptor, resulting in increased infectivity, transmissibility and evasion 77
from humoral responses elicited by natural infection or vaccination
11
. 78
The D614G Spike mutation appeared very early in the pandemic and is now highly 79
prevalent in all circulating strains
12
. The B.1.1.7 variant was first identified in the United Kingdom 80
and has been spread rapidly to many countries since its identification. This variant contains 81
several mutations in its S glycoproteins (ΔH69-V70, ΔY144, N501Y, A570D, P681H, T716I, 82
S982A and D1118H) and has increased infectivity
13,14
. Among the mutations present in the 83
B.1.1.7 strain, the N501Y is also present in many other circulating variants (B.1.351 and P.1) and 84
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4
increases the affinity for the ACE-2 receptor
15,16
. The E484K mutation, is part of the South African 85
B.1.351 variant and is now found in several SARS-CoV-2 genomes worldwide that spread 86
rapidly
17
. Studies have shown that this mutation increases affinity of the S glycoprotein for ACE-87
2
18
and confers resistance to neutralization mediated by mAbs and plasma from naturally-infected 88
and vaccinated individuals
19–22
. The S477N mutation confers a higher affinity for the ACE-2 89
receptor and has rapidly spread to many countries in Oceania and Europe
23–28
. The S477N and 90
N501S mutations are found in several SARS-CoV-2 genomes in Quebec (Laboratoire de Santé 91
Publique du Québec, unpublished data). 92
93
In spite of the proven clinical efficacy of BNT162b2, there are still limitations in the 94
understanding of the protective components of the immune responses elicited by this vaccine. 95
Such protection is mediated through a complex interplay between innate, humoral and cell-96
mediated immunity
29,30
. Several reports showed that administration of the mRNA vaccine induced 97
a strong humoral response after two doses, especially against the RBD domain
31,32
. Robust CD4
+
98
and CD8
+
memory T cell responses are induced after SARS-CoV-2 infection
33,34
and play 99
important roles in resolution of the infection
35
including modulating disease severity in humans
36
100
and reducing viral load in non-human primates (NHP)
37
. However, the detection of these specific 101
memory T cells has been poorly studied in the SARS-CoV-2 vaccine development and represent 102
a gap in the understanding of the induced cellular adaptative immune responses which are likely 103
to also play an important role
8,38
. Among CD4
+
T cells, the T follicular helper (Tfh) subset is of 104
particular interest, as it provides help for B cell maturation and development of high affinity 105
antibody responses in the germinal center (GC) of secondary lymphoid organs. Studies have 106
shown that a subset of CXCR5
+
in blood, called circulating Tfh (cTfh)
39,40
has clonal, phenotypic 107
and functional overlap with GC Tfh and reflect at least in part responses in tissues
41,42
. 108
Results from phase III clinical trials have shown a vaccine efficacy of >90% starting 14 109
days after the injection of a single dose of BNT162b2 mRNA vaccine, thus before the 110
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5
administration of a second dose
7,9,43
. In this report, we characterized the humoral and T cell 111
immune responses in cohorts of SARS-CoV-2 naïve and naturally-infected individuals prior and 112
three weeks after a first dose of the BNT162b2 mRNA vaccine. 113
114
Results 115
Here we analyzed humoral and cellular responses in blood samples from 16 SARS-CoV-116
2 naïve donors prior and after vaccination (median [range]: 21 days [16-26 days]). In addition, we 117
examined the same immunological features in 16 individuals that were previously infected around 118
9 months before vaccination (median [range]: 266 days [116-309 days]) and three weeks after 119
vaccination (median [range]: 21 days [17-25 days]). For 11 of these donors, we also longitudinally 120
monitored evolution of the humoral response, from 6 weeks post-symptom onset (PSO, median 121
[range]: 40 days [16-62 days]) to 3 weeks after vaccination. Basic demographic characteristics 122
are summarized in Table 1. In the SARS-CoV-2 naïve group, the average age of donors was 48 123
years old (range: 21-59 years old), and samples were from 3 males and 13 females. In the group 124
of previously-infected individuals, the average age of the donors was 48 years old (range: 23-65 125
years old), and samples were from 8 males and 8 females (Table 1). 126
127
Elicitation of SARS-CoV-2 antibodies against the full Spike and its receptor binding domain 128
To evaluate vaccine responses in SARS-CoV-2 naïve and previously-infected individuals, 129
we first measured the presence of RBD-specific antibodies (IgG, IgM, IgA) using a previously 130
described enzyme-linked immunosorbent (ELISA) RBD assay
44–46
. As expected, in the SARS-131
CoV-2 naïve group, we did not observe RBD-specific immunoglobulins (Ig) in samples recovered 132
before vaccination (Figure 1A-D). Three weeks after the first dose, we found a significant increase 133
in the total RBD-specific immunoglobulin levels with the exception of one donor from the SARS-134
CoV-2 naïve group who didn’t respond to the vaccine at this time-point. With the exception of 135
IgM, vaccination induced similar levels of immunoglobulins (IgA and IgG) targeting the RBD to 136
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