Assessment of Anti-Carbohydrate Immunity Against SARS-CoV-2

Background: The outbreaks of viral disease caused by bat-derived coronaviruses (CoVs) in this decade-the severe acute respiratory syndrome coronavirus (SARS-CoV), the Middle East respiratory syndrome coronavirus (MERS-CoV), and the 2019-nCoV (SARS-CoV-2) responsible for the present pandemic of COVID-19 pneumonia-highlight the urgent and long-term needs of broad-spectrum antiviral biodefense strategies. Due to the genetic diversities and hyper-mutation rates of this class of RNA viruses, it is highly challenging to develop such biodefense strategies to combat unpredictable outbreak of SARS-related CoVs (Sr-CoVs). Carbohydrates represent a class of important immunological targets of microbial pathogens. In our FY17 PRMRP study, we obtained compelling evidence the glycan shields of CoV virions are decorated with conserved carbohydrate moieties that are likely suitable for antibody-mediated broad-spectrum virus neutralization. In the current FY21 Expansion Award application, we plan to further investigate whether or not these conserved viral glycan shield components are immunogenic in humans and if SARS-CoV-2 natural infection or vaccines elicit antibody responses to these targets and protect humans from infection. Relevance to Focus Area(s): Our application targets the FY21 PRMRP Topic Area of Emerging Viral Diseases and is highly relevant to the following Areas of Encouragement: (a) "rapid prediction of protective antigens/epitopes and testable correlates of protection on emerging or novel pathogens with an emphasis on emerging respiratory viruses with epidemic potential" and (b) "development of meaningful and relevant immunological and virological readouts that translate and/or predict human responses to vaccination or infection." Hypothesis/Objective: We hypothesize SARS-CoV-2 virions are generally decorated with N-glycan cryptic glyco-determinants that are potentially immunogenic. Human antibodies targeting these glyco-epitopes can effectively neutralize a broad spectrum of SARS-CoV2 strains, including the variant of concern (VOC) clinical isolates that may emerge continuously to challenge our biodefense capacity. Specific Aims: We propose the following specific experimental investigations to critically examine our hypothesis: Aim 1: Determine whether current SARS-CoV-2 vaccines elicit characteristic serological responses to the conserved CoV-glycan shield components (Year 1). Aim 2: Determine whether SARS-CoV-2 natural infection elicits antibody responses to the conserved viral glycan targets and if detection of glycan-specific antibody signatures predicts clinical outcomes of SARS-CoV-2 infection (Years 1-2). Aim 3: Determine whether human monoclonal antibodies (mAbs) specific for these viral glycan targets effectively neutralize SARS-CoV-2 and VOC isolates to significantly contribute to antiviral immunity (Years 2-3). Study Design: The most conventional immunoassays based on S glycoproteins detect both protein- and glycan-specific antibodies without differentiation. These assays are not suitable for use in deciphering the anti-protein and anti-glycan specificities that may be elicited by a natural infection or vaccine. We will take advantage of our established synthetic glycoconjugate and antigen microarray technologies to overcome these expected technical challenges in our serological study (Aims 1 and 2). Moreover, we will produce human mAbs using the glycan-specific B-cells isolated from the subjects that produce the desired neutralizing antibodies to precisely correlate glycan-targeting specificity to antiviral activity of each mAb (Aim 3). Impact: We expect to uncover critical information to critically evaluate the potential of anti-carbohydrate immunity in protecting humans from SARS-CoV-2 infection and treating patients with severe COVID-19. Since the proposed targets are highly conserved in viral glycome, this study may lead to development of a new class of broadly virus-neutralizing antibodies to combat future emergence of unexpected Sr-CoVs. Relevance to Military Health: Military and medical personnel often encounter a wide variety of infectious agents, including various emerging and re-emerging viral pathogens. Developing versatile antiviral therapeutic and prophylactic agents against CoVs is, therefore, a pressing need in military medicine. Our proposed work aims at developing a new class of broad-range biodefense agents that are readily applicable for use in response to unexpected emerging viral pathogens. Thus, the results of our research may benefit both military personnel and the general population. Less