SummaryThe spike protein of SARS-CoV-2 is a critical antigen present in all approved SARS-CoV-2 vaccines. This surface viral protein is also the target for all monoclonal antibody therapies, but it is unclear whether antibodies targeting other viral proteins can also improve protection against COVID-19. Here, we interrogate whether nucleocapsid-specific antibodies can improve protection against SARS-CoV-2. We first immunized mice with a nucleocapsid-based vaccine, and then transferred sera from these mice into naïve mice. On the next day, the recipient mice were challenged intranasally with SARS-CoV-2 to evaluate whether nucleocapsid-specific humoral responses affect viral control. Interestingly, mice that received nucleocapsid-specific sera exhibited enhanced control of a SARS-CoV-2 infection. These findings provide the first demonstration that humoral responses specific to an internal coronavirus protein can help clear infection, warranting the inclusion of other viral antigens in next-generation SARS-CoV-2 vaccines and providing a rationale for the clinical evaluation of nucleocapsid-specific monoclonals to treat COVID-19.HighlightsA SARS-CoV-2 nucleocapsid vaccine elicits robust nucleocapsid-specific antibody responses.This nucleocapsid vaccine generates memory B cells (MBC).Nucleocapsid-specific humoral responses do not prevent SARS-CoV-2 infection.Nucleocapsid-specific humoral responses help control a SARS-CoV-2 infection.

Although SARS-CoV-2 vaccines have shown efficacy against SARS-CoV-2, it is unclear if they can also protect against other coronaviruses that may infect humans in the future. Here, we show that SARS-CoV-2 vaccination in humans elicits cross-reactive antibodies against other coronaviruses. Our studies in mice demonstrate that SARS-CoV-2 vaccination protects against a common cold coronavirus, and that SARS-CoV-1 vaccination protects against SARS-CoV-2. Similarly, infection with a common cold coronavirus also conferred enhanced protection from subsequent infections with other coronaviruses. Mechanistically, both T cells and antibodies mediated cross-protection. This is the first direct demonstration that coronavirus-specific immunity can confer heterologous protection in vivo, providing a rationale for universal coronavirus vaccines.

The SARS CoV-2 pandemic has killed millions of people. This viral infection can also result in substantial morbidity, including respiratory insufficiency and neurological manifestations, such as loss of smell and psychiatric diseases. Most SARS CoV-2 vaccines are based on the spike antigen, and although they have shown extraordinary efficacy at preventing severe lung disease and death, they do not always confer sterilizing immune protection. We performed studies in K18-hACE2 mice to evaluate whether the efficacy of SARS CoV-2 vaccines could be augmented by incorporating nucleocapsid as a vaccine antigen. We vaccinated mice with adenovirus-based vaccines encoding spike antigen alone, nucleocapsid antigen alone, or combined spike and nucleocapsid antigens. Mice were then challenged intranasally with SARS CoV-2, and acute viral loads were quantified at a proximal site of infection (lung) and a distal site of infection (brain). Interestingly, the spike-based vaccine conferred acute protection in the lung, but not in the brain. The spike-based vaccine conferred acute protection in the brain only if combined with the nucleocapsid-based vaccine. These findings suggest that nucleocapsid-specific immunity is important for the distal control of SARS CoV-2, warranting the inclusion of nucleocapsid in next-generation COVID-19 vaccines.

Persistent cognitive impairment and neuropsychiatric disorders are prevalent sequelae of SARS-CoV-2-induced COVID-19 in middle-aged adults. To model age-related neurological vulnerability to COVID-19, we induced respiratory SARS-CoV-2 MA10 infections by nasal inoculation in young (2 months) and middle-aged (12 months) mice. We hypothesized that aging and SARS-CoV-2 synergistically damage the blood-brain barrier (BBB) to worsen disease. Indeed, the combined action of aging and SARS-CoV-2 infection caused more fibrinogen leakage, T cell infiltration, and neuroinflammation in middle-aged SARS-CoV-2-infected mice than in similarly inoculated young adults. Mechanistically, SARS-CoV-2 exacerbated age-related increases in Caveolin-1 BBB transcellular permeability and loss of Wnt/β-catenin ligands, with no apparent changes in tight junction proteins. Finally, SARS-CoV-2 infection induced age-dependent neuropsychiatric abnormalities including bradykinesia and repetitive behavior. These observations indicate that cerebrovascular aging, including loss of Wnt suppression of Caveolin-1, heightens vulnerability to SARS-CoV-2-induced neuroinflammation and neuropsychiatric sequalae. Our work suggests that modulation of Wnt signaling or its downstream effectors at the BBB could be potential interventional strategies for Long COVID.

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) vaccines have shown extraordinary efficacy against SARS-CoV-2. Recently, we demonstrated that prime-boost coronavirus vaccine regimens can protect against heterologous coronaviruses (Dangi, The Journal of Clinical Investigation, 2021). However, it remains unclear whether boosters are required for such cross-protection. In this study, we show that booster immunizations are critical to elicit cross-protection against heterologous coronaviruses. We first vaccinated BALB/c mice intramuscularly with a poxvirus-based SARS-CoV-1 vaccine developed in 2004 (MVA-SARS-CoV-1) and compared cross-protection following an intranasal SARS-CoV-2 challenge, evaluating cross-protection after a prime-only regimen versus a prime-boost regimen. Interestingly, we show cross-protection only in mice that received boosters. We are currently testing the durability of cross-protection elicited by prime-boost vaccine regimens, and we are also extending these results to humans. Overall, our findings provide a rationale for universal coronavirus vaccines, and highlights the importance of boosters as a strategy to broaden cross-protection to other coronaviruses different than SARS-CoV-2. Supported by NIDA DP2 Avenir (1DP2DA051912-01) EREEP Grant Northwestern University