Fc-gamma receptor-dependent antibody effector functions are required for vaccine protection against infection by antigenic variants of SARS-CoV-2

Emerging SARS-CoV-2 variants with antigenic changes in the spike protein are neutralized less efficiently by serum antibodies elicited by legacy vaccines against the ancestral Wuhan-1 virus. Nonetheless, these vaccines, including mRNA-1273 and BNT162b2, retained their ability to protect against severe disease and death, suggesting that other aspects of immunity control infection in the lung. Although vaccine-elicited antibodies can bind Fc gamma receptors (Fc{gamma}Rs) and mediate effector functions against SARS-CoV-2 variants, and this property correlates with improved clinical COVID-19 outcome, a causal relationship between Fc effector functions and vaccine-mediated protection against infection has not been established. Here, using passive and active immunization approaches in wild-type and Fc-gamma receptor (Fc{gamma}R) KO mice, we determined the requirement for Fc effector functions to protect against SARS-CoV-2 infection. The antiviral activity of passively transferred immune serum was lost against multiple SARS-CoV-2 strains in mice lacking expression of activating Fc{gamma}Rs, especially murine Fc{gamma}R III (CD16), or depleted of alveolar macrophages. After immunization with the preclinical mRNA-1273 vaccine, protection against Omicron BA.5 infection in the respiratory tract also was lost in mice lacking Fc{gamma}R III. Our passive and active immunization studies in mice suggest that Fc-Fc{gamma}R engagement and alveolar macrophages are required for vaccine-induced antibody-mediated protection against infection by antigenically changed SARS-CoV-2 variants, including Omicron strains.

Fc mediated pan-sarbecovirus protection after alphavirus vector vaccination

Two group 2B {beta}-coronaviruses (sarbecoviruses) have caused regional and global epidemics in modern history. The mechanisms of cross protection driven by the sarbecovirus spike, a dominant immunogen, are less clear yet critically important for pan-sarbecovirus vaccine development. We evaluated the mechanisms of cross-sarbecovirus protective immunity using a panel of alphavirus-vectored vaccines covering bat to human strains. While vaccination did not prevent virus replication, it protected against lethal heterologous disease outcomes in both SARS-CoV-2 and clade 2 bat sarbecovirus HKU3-SRBD challenge models. The spike vaccines tested primarily elicited a highly S1-specific homologous neutralizing antibody response with no detectable cross-virus neutralization. We found non-neutralizing antibody functions that mediated cross protection in wild-type mice were mechanistically linked to FcgR4 and spike S2-binding antibodies. Protection was lost in FcR knockout mice, further supporting a model for non-neutralizing, protective antibodies. These data highlight the importance of FcR-mediated cross-protective immune responses in universal pan-sarbecovirus vaccine designs.

Waning and boosting of functional humoral immunity to SARS-CoV-2

Since the emergence of the SARS-CoV-2 virus, we have witnessed a revolution in vaccine development with the rapid emergence and deployment of both traditional and novel vaccine platforms. The inactivated CoronaVac vaccine and the mRNA-based Pfizer/BNT162b2 vaccine are among the most widely distributed vaccines, both demonstrating high, albeit variable, vaccine effectiveness against severe COVID-19 over time. Beyond the ability of the vaccines to generate neutralizing antibodies, antibodies can attenuate disease via their ability to recruit the cytotoxic and opsinophagocytic functions of the immune response. However, whether Fc-effector functions are induced differentially, wane with different kinetics, and are boostable, remains unknown. Here, using systems serology, we profiled the Fc-effector profiles induced by the CoronaVac and BNT162b2 vaccines, over time. Despite the significantly higher antibody functional responses induced by the BNT162b2 vaccine, CoronaVac responses waned more slowly, albeit still found at levels below those present in the systemic circulation of BNT162b2 immunized individuals. However, mRNA boosting of the CoronaVac vaccine responses resulted in the induction of significantly higher peak antibody functional responses with increased humoral breadth, including to Omicron. Collectively, the data presented here point to striking differences in vaccine platform-induced functional humoral immune responses, that wane with different kinetics, and can be functionally rescued and expanded with boosting.

Intra-host evolution provides for continuous emergence of SARS-CoV-2 variants

Variants of concern (VOC) in SARS-CoV-2 refer to viral genomes that differ significantly from the ancestor virus and that show the potential for higher transmissibility and/or worse clinical progression. VOC have the potential to disrupt ongoing public health measures and vaccine efforts. Yet, little is known regarding how frequently different viral variants emerge and under what circumstances. We report a longitudinal study to determine the degree of SARS-CoV-2 sequence evolution in 94 COVID-19 cases and to estimate the frequency at which highly diverse variants emerge. 2 cases accumulated [≥]9 single-nucleotide variants (SNVs) over a two-week period and 1 case accumulated 23 SNVs over a three-week period, including three non-synonymous mutations in the Spike protein (D138H, E554D, D614G). We estimate that in 2% of COVID cases, viral variants with multiple mutations, including in the Spike glycoprotein, can become the dominant strains in as little as one month of persistent in patient virus replication. This suggests the continued local emergence of VOC independent of travel patterns. Surveillance by sequencing for (i) viremic COVID-19 patients, (ii) patients suspected of re-infection, and (iii) patients with diminished immune function may offer broad public health benefits.

High-density amplicon sequencing identifies community spread and ongoing evolution of SARS-CoV-2 in the Southern United States

SARS-CoV-2 is constantly evolving. Prior studies have focused on high case-density locations, such as the Northern and Western metropolitan areas in the U.S. This study demonstrates continued SARS-CoV-2 evolution in a suburban Southern U.S. region by high-density amplicon sequencing of symptomatic cases. 57% of strains carried the spike D614G variant. The presence of D614G was associated with a higher genome copy number and its prevalence expanded with time. Four strains carried a deletion in a predicted stem loop of the 3 untranslated region. The data are consistent with community spread within the local population and the larger continental U.S. No strain had mutations in the target sites used in common diagnostic assays. The data instill confidence in the sensitivity of current tests and validate "testing by sequencing" as a new option to uncover cases, particularly those not conforming to the standard clinical presentation of COVID-19. This study contributes to the understanding of COVID-19 by providing an extensive set of genomes from a non-urban setting and further informs vaccine design by defining D614G as a dominant and emergent SARS-CoV-2 isolate in the U.S.