SARS-CoV-2 infection causes respiratory insufficiency and neurological manifestations, including loss of smell and psychiatric disorders, and can be fatal. Most vaccines are based on the spike antigen alone, and although they have shown efficacy at preventing severe disease and death, they do not always confer sterilizing immunity. Here, we interrogate whether SARS-CoV-2 vaccines could be improved by incorporating nucleocapsid as an antigen. We show that after 72 hr of challenge, a spike-based vaccine confers acute protection in lung, but not in brain. However, combining a spike-based vaccine with a nucleocapsid-based vaccine confers acute protection in both lung and brain. These findings suggest that nucleocapsid-specific immunity can improve the distal control of SARS-CoV-2, suggesting the inclusion of nucleocapsid in next-generation COVID-19 vaccines.

An important focus in vaccine research is the design of vaccine vectors with low seroprevalence and high immunogenicity. Replication-incompetent lymphocytic choriomeningitis virus (rLCMV) vectors do not elicit vector-neutralizing antibody responses, and homologous prime-boost regimens with rLCMV vectors induce boostable and protective T cell responses to model antigens in mice. However, cellular and humoral immune responses following homologous rLCMV vaccine regimens have not been rigorously evaluated in non-human primates (NHPs). To test whether rLCMV vectors constitute an effective vaccine platform in NHPs, we developed rLCMV vectors expressing SIVmac239 Env and Gag antigens and assessed their immunogenicity in mice and cynomolgus macaques. Immunization with rLCMV vaccine vectors expressing SIV Env and Gag was effective at generating SIV-specific T cell and antibody responses in both mice and NHPs. Epitope mapping using SIV Env in C57BL/6 mice demonstrated that rLCMV vectors induced sustained poly-functional responses to both dominant and subdominant epitopes. Our results suggest the potential of rLCMV vectors as vaccine candidates. Future SIV challenge experiments in rhesus macaques will be needed to assess immune protection by these vaccine vectors.

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

The PDL-1:PD-1 pathway is involved in T cell exhaustion after chronic viral infection. PD-1 can bind to either PDL-1 or PDL-2, whereas PDL-1 can bind to either PD-1 or B7.1. We tested the effect of combining standard aPDL-1 blockade with a4-1BB (3H3 agonistic antibody) treatment to determine T cell restoration effects in a model of chronic infection with lymphocytic choriomeningitis virus (LCMV). We chose 4-1BB because it has been shown to be an important costimulatory pathway. It appears that a4-1BB treatment enhances the effect of aPDL-1 blockade if given in a low dose (50 μg, once). Conversely, if a4-1BB is given in a high dose (200 μg, five times), it results in sudden increase of antigen-specific T cells by day 7, but massive T cell death by day 14 post treatment. These results show the importance for 4-1BB costimulation in aPDL-1 mediated T cell restoration.