No abstract

The Ad26.COV2.S vaccine [1][2][3] has demonstrated clinical efficacy against symptomatic COVID-19, including against the B.1.351 variant that is partially resistant to neutralizing antibodies 1 . However, the immunogenicity of this vaccine in humans against SARS-CoV-2 variants of concern remains unclear. Here we report humoral and cellular immune responses from 20 Ad26.COV2.S vaccinated individuals from the COV1001 phase 1/2 clinical trial 2 against the original SARS-CoV-2 strain WA1/2020 as well as against the B.1.1.7, CAL.20C, P.1., and B.1.351 variants of concern. Ad26.COV2.S induced median pseudovirus neutralizing antibody titers that were 5.0-and 3.3-fold lower against the B.1.351 and P.1 variants, respectively, as compared with WA1/2020 on day 71 following vaccination. Median binding antibody titers were 2.9-and 2.7-fold lower against the B.1.351 and P.1 variants, respectively, as compared with WA1/2020. Antibody-dependent cellular phagocytosis, complement deposition, and NK cell activation responses were largely preserved against the B.1.351 variant. CD8 and CD4 T cell responses, including central and effector memory responses, were comparable among the WA1/2020, B.1.1.7, B.1.351, P.1, and CAL.20C variants. These data show that neutralizing antibody responses induced by Ad26.COV2.S were reduced against the B.1.351 and P.1 variants, but functional non-neutralizing antibody responses and T cell responses were largely preserved against SARS-CoV-2 variants. These findings have implications for vaccine protection against SARS-CoV-2 variants of concern.

The prevention of infectious disease via prophylactic immunization is a mainstay of global public health efforts. Vaccine design would be facilitated by a better understanding of the type and durability of immune responses generated by different vaccine vectors. We report here the results of a comparative immunogenicity trial of six different vaccine vectors expressing the same insert antigen, cowpox virus B5 (CPXV-B5). Of those vectors tested, recombinant adenovirus (rAd5) was the most immunogenic, inducing the highest titer anti-B5 antibodies and conferring protection from sublethal vaccinia virus challenge in mice after a single immunization. We tested select heterologous primeboost combinations and identified recombinant vesicular stomatitis virus (rVSV) and recombinant Venezuelan equine encephalitis virus replicons (VRP) as the most synergistic regimen. Comparative data such as those presented here are critical to efforts to generate protective vaccines for emerging infectious diseases as well as for biothreat agents.

HIV infection can be treated but not cured with antiretroviral therapy, motivating the development of new therapies that instead target host immune responses. Three such immunotherapies were recently tested in non-human primates -a TLR7-agonist, therapeutic vaccine, and broadly-neutralizing antibody -and cured a subset of animals by preventing or controlling viral rebound after antiretrovirals were stopped. However, their mechanism of action remains unknown; for example, whether they reduced the pool of latently-infected cells versus boosted antiviral immunity, and whether they acted independently or synergistically. Here we conduct a detailed analysis of the kinetics of viral rebound after immunotherapy, and use mathematical models combined with rigorous statistical fitting to quantify the impact of these interventions on viral dynamics. We find that the vaccine reduced reactivation of latent virus by 4-fold, and boosted the avidity of antiviral immune responses by 17-fold when alone and 210-fold when combined with the TLR7-agonist. In the context of later initiation of antiretroviral therapy only, the TLR7-agonist reduced latent reservoir reactivation by 8-fold, but also slightly increased target cell availability (1.5-fold). The antibody boosted immune response avidity (8-fold) and displayed no detectable synergy with the TLR7-agonist. To predict the impact of these immunotherapies in clinical trials, we calibrated a model of HIV rebound to human treatment interruption trials and simulated the effect of adding each therapy. Overall, our results provide a framework for understanding the relative contributions of different mechanisms of preventing viral rebound and highlight the multifaceted roles of TLR7-agonists for HIV/SIV cure.