Background There are limited global data on head-to-head comparisons of vaccine platforms assessing both humoral and cellular immune responses, stratified by pre-vaccination serostatus. The COVID-19 vaccination drive for the Indian population in the 18 to 45-year age-group began in April 2021 when seropositivity rates in the general population were rising due to the Delta wave in April-May 2021. Methods Between 30 June 2021 and 28 January 2022, we enrolled 691 participants in the 18-45 age group across 4 clinical sites in India. In this non-randomized and laboratory blinded study, participants received either two doses of Covaxin® 4 weeks apart or two doses of Covishield™ 12 weeks apart per the national vaccination policy. The primary outcome was the seroconversion rate and the geometric mean titer (GMT) of antibodies against the SARS-CoV-2 spike and nucleocapsid proteins. The secondary outcome was the frequency of cellular immune responses pre- and post-vaccination. Findings When compared to pre-vaccination baseline, both vaccines elicited statistically significant seroconversion and binding antibody levels in both seronegative and seropositive individuals. In the per-protocol cohort, Covishield™ elicited higher antibody responses than Covaxin® as measured by seroconversion rate (98.3% vs 74.4%, p<0.0001 in seronegative individuals; 91.7% vs 66.9%, p<0.0001 in seropositive individuals) as well as by anti-spike antibody levels against the ancestral strain (GMT 1272.1 vs 75.4 BAU/ml, p<0.0001 in seronegative individuals; 2089.07 vs 585.7 BAU/ml, p<0.0001 in seropositive individuals). Not all sites recruited at the same time, therefore site-specific immunogenicity was impacted by the timing of vaccination relative to the Delta and Omicron waves. Surrogate neutralizing antibody responses against variants-of-concern were higher in Covishield™ recipients than in Covaxin® recipients and in seropositive than in seronegative individuals after both vaccination and asymptomatic Omicron infection. T cell responses are reported from only one of the four site cohorts where the vaccination schedule preceded the Omicron wave. In seronegative individuals, Covishield™ elicited both CD4+ and CD8+ spike-specific cytokine-producing T cells whereas Covaxin® elicited mainly CD4+ spike-specific T cells. Neither vaccine showed significant post-vaccination expansion of spike-specific T cells in seropositive individuals. Interpretation Covishield™ elicited immune responses of higher magnitude and breadth than Covaxin® in both seronegative individuals and seropositive individuals, across cohorts representing the pre-vaccination immune history of the majority of the vaccinated Indian population.
HIV-1 causes diverse immunomodulatory responses in the host, including the down-regulation of co-stimulatory proteins CD80/86, mediated by HIV-1 protein Nef, blunting T-cell activation. Using a screening cascade of biochemical and cell-based assays, we identified potent small molecules representing three chemical scaffolds namely amino pyrimidine, phenoxy acetamide and bi-aryl heteroaryl carbamate which target the protein-protein interaction interface of CD80/86 and Nef with sub-micromolar potency. These molecules restore CD80/86 surface levels in HIV-1-Nef infected antigen presenting cells and T-cell activation. Nef-CD80 interface and small molecule binding sites were mapped by using computational docking and structural studies, followed by validation by mutational analysis. This analysis resulted in the identification of two key residues, K99 and R111, which were associated with down-modulation of CD80 surface levels by Nef and important for small molecule binding. Targeting these interacting residues disabled Nef-mediated down-modulation of CD80 surface levels, consequently restoring T-cell activation. Thus, we validate a new target, the Nef-CD80/86 protein-protein interaction interface, with a potential to develop new inhibitors to counteract the immunomodulatory consequences of HIV-1.
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