Immunogenicity and safety of a recombinant adenovirus type-5 COVID 19 vaccine in adults: data from a randomised, double-blind, placebo-controlled, single-dose, phase 3 trial in Russia

BackgroundTo determine the immunogenicity, efficacy, reactogenicity, and safety of a single dose of recombinant adenovirus type-5 vectored COVID-19 vaccine (Ad5-nCoV, 5 x 1010 viral particles per 0.5 mL dose), we conducted a single-dose, randomised, double-blind, placebo-controlled, parallel group (3:1 Ad5-nCoV:placebo), phase 3 trial (Prometheus). MethodsFrom 11-September-2020 to 05-May-2021, across six sites in the Russian Federation, 496 participants were injected with either placebo or Ad5-nCoV expressing the full-length spike (S) protein from the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). ResultsSeroconversion (the primary endpoint) rates of 78.5% (95% CI: 73.9; 82.6) against receptor binding domain (RBD), 90.6% (95% CI: 87.2; 93.4) against S protein and 59% (95% CI: 53.3; 64.6) against neutralising SARS-CoV2 antibodies 28 days post-vaccination. Geometric mean titres (GMTs) were also elevated for antibodies against the RBD (405.32 [95% CI: 361.58; 454.46]) and S protein (678.86 [95% CI: 607.44; 754.40]) compared to the GMT of neutralising antibodies against SARS-CoV-2 (16.73 [95% CI: 15.36; 18.22]). Using an IFN-{gamma} ELISpot assay after stimulating the cells with full-length S protein we showed that the Ad5-nCoV vaccine induced the most robust cellular immune response on Days 14 and 28. Up to Day 28, the primary and all secondary endpoints of the Ad5-nCoV vaccine were statistically superior to the placebo ([p] <0.001). Systemic reactions were reported in 113 of 496 (22.8%) participants (Ad5-nCoV, 26.9%; Placebo, 10.5%), and local reactions were reported in 108 (21.8%) participants (Ad5-nCoV, 28.5%; Placebo, 1.6%). These were generally mild and resolved within 7 days after vaccination. Of the six serious adverse events reported, none of the events were vaccine related. There were no deaths or premature withdrawals. ConclusionA single-dose of Ad5-nCoV vaccine induced a marked specific humoral and cellular immune response with a favourable safety profile. Trial RegistrationClinicalTrials.gov: NCT04540419

A prospective study of the protective effect of SARS-CoV-2-specific antibodies and T cells in Moscow residents

Rapid spread of COVID-19 pandemic made a substantial share of the world population immunised by SARS-CoV-2 antigens. Infection induces the development of virus-specific antibodies and T cells. Ample evidence on the antibody-mediated protection is contrasted by the elusive role of T cells in preventing infection. To explore the impact of T cells and to quantify the protective levels of the immune responses we conducted a large prospective study: 5,340 Moscow residents were evaluated for the antibody and cellular immune responses to SARS-CoV-2 and monitored for COVID-19 up to 300 days. The antibody and cellular responses were tightly interconnected, their magnitude inversely correlated with infection probability. Similar maximal level of protection was reached by individuals positive for both types of responses and by individuals with antibodies alone. Meanwhile, T cells in the absence of antibodies provided an intermediate level of protection. The real-world data on the protective effects of T cells have important implications for T cell immunology and development of the strategies to fight the pandemic.

Structural basis for recognition of two HLA-A2-restricted SARS-CoV-2 spike epitopes by public and private T cell receptors

T cells play a vital role in combatting SARS-CoV-2 and in forming long-term memory responses. Whereas extensive structural information is available on neutralizing antibodies against SARS-CoV-2, such information on SARS-CoV-2-specific T cell receptors (TCRs) bound to their peptide-MHC targets is lacking. We determined structures of a public and a private TCR from COVID-19 convalescent patients in complex with HLA-A2 and two SARS-CoV-2 spike protein epitopes (YLQ and RLQ). The structures revealed the basis for selection of particular TRAV and TRBV germline genes by the public but not the private TCR, and for the ability of both TCRs to recognize natural variants of YLQ and RLQ but not homologous epitopes from human seasonal coronaviruses. By elucidating the mechanism for TCR recognition of an immunodominant yet variable epitope (YLQ) and a conserved but less commonly targeted epitope (RLQ), this study can inform prospective efforts to design vaccines to elicit pan-coronavirus immunity.

SARS-CoV-2 epitopes are recognized by a public and diverse repertoire of human T-cell receptors

Understanding the hallmarks of the adaptive immune response to SARS-CoV-2 is critical for fighting the COVID-19 pandemic. We assessed the antibody and T-cell reactivity in COVID-19 convalescent patients and healthy donors sampled both prior to and during the pandemic. The numbers of SARS-CoV-2-specific T cells were increased in healthy donors examined during COVID-19. Combined with the absence of symptoms and humoral response across that group, this finding suggests that some individuals might be protected by T-cell cross-reactivity. In convalescent patients we observed public and diverse T-cell response to SARS-CoV-2 epitopes, revealing T-cell receptor motifs with germline-encoded features. Bulk CD4+ and CD8+ T-cell responses to Spike glycoprotein were mediated by groups of homologous T-cell receptors, some of them shared across multiple donors. Overall, our results demonstrate that T-cell response to SARS-CoV-2, including the identified set of specific T-cell receptors, can serve as a useful biomarker for surveying viral exposure and immunity.