CROI 2024 Abstract eBook

Abstract eBook

Poster Abstracts

Omicron BA.5 spike proteins, were developed to enhance immune responses against the BA.5 sublineage. However, studies have shown that these bivalent vaccines do not induce stronger T cell responses to the BA.5 spike protein than monovalent vaccines containing only ancestral spike mRNA. We tested the hypothesis that this was due to the preferential expansion of cross-reactive memory T cells rather than naive BA.5 mono-reactive T cells. Methods: We used the ELISpot assay to determine the targeted epitopes and the functional expansion of specific T Cells (FEST) assay to assess the percentage of CD4+ T cells that cross-recognized both ancestral and BA.5 spike proteins compared to those that were mono-reactive for each protein. We conducted this analysis in two distinct cohorts: 20 healthy donors (HDs) and 20 people living with HIV (PLWH) on suppressive antiretroviral therapy. All the participants received either the Pfizer-BioNTech (BNT162b2) or Moderna (mRNA-1273) SARS CoV-2 ancestral spike/BA.5 spike bivalent vaccine. Results: We found robust T cell responses to both ancestral and BA.5 spike proteins in both HDs and PLWH. Importantly, the FEST assay revealed that a predominant percentage of these responses were cross-reactive CD4+ T cells. Specifically, only 8.9% and 3.8% of spike-specific CD4+ T cell receptors were mono-reactive to BA.5 spike protein in HDs and PLWH respectively. Additionally, we conducted an in-depth analysis of the individual ancestral spike protein epitopes targeted by T cells in bivalent vaccine recipients. We found that more than 80% of these epitopes were ones that did not contain BA.5 mutations. Conclusion: In conclusion, our study suggests that the current bivalent vaccines do not effectively induce substantial BA.5-mono-reactive T cell responses; instead, cross-reactive T cells dominate the spike-specific T cell response. These findings have significant implications for future COVID vaccine strategies. Spike-V987H Vaccination Protects Animal Models From SARS-COV-2– Induced Severe Disease Carlos Ávila Nieto 1 , Julia Vergara-Alert 2 , Pep Amengual-Rigo 3 , Erola Ainsua Enrich 1 , Edwards Pradenas 1 , Jordi Rodon 2 , Victor Urrea 1 , Ester Ballana 1 , Nuria Izquierdo-Useros 1 , Alfonso Valencia 3 , Julià Blanco 1 , Victor Guallar 3 , Bonaventura Clotet 1 , Joaquim Segalés 2 , Jorge Carrillo 1 1 IrsiCaixa Institute for AIDS Research, Badalona, Spain, 2 Animal Health Research Center (CReSA), Bellaterra, Spain, 3 Barcelona Supercomputing Center (BSC), Barcelona, Spain Background: Most SARS-CoV-2 vaccines are based on a two-prolines (K986P and V987P) stabilized Spike (S) glycoprotein (S-2P). Although these mutations improve S stability and immunogenicity, S-2P is produced at low levels yet. Here we explored new S protein stabilization approaches. Methods: We have investigated the immunogenicity and efficacy of a novel set of stabilizing mutations selected by computational modelling and screened by recombinant S yield and RBD exposure. S variants were produced by transient transfection in Expi293 cells, and yield and RBD exposure were analyzed by ELISA. Immunogenicity and efficacy studies were conducted in K18-hACE2 mice and golden Syrian hamsters (GSH) challenged with SARS-CoV-2 D614G, Beta or Omicrom BQ1.1 variants. We measured weight changes, and viral loads in different biological samples: oropharyngeal swab, nasal turbinate, lung and brain. In addition, we performed histopathological analysis of tissue samples. Humoral and T cell responses were analyzed by ELISA and neutralizing assays, and by ELISPOT, respectively. Results: When compared with the S-2P, a single V987H mutation increased RBD exposure and production, and showed equivalent immunogenicity (determined as anti-RBD, anti-S IgG levels, and IFN-g ELIspot). S-V987H- immunization induced neutralizing antibodies against Wuhan, Beta and Delta variants and gained activity against Omicron after viral challenge. S-V987H immunized mice showed lower viral loads and immunohistochemistry score than non immunized animals and were protected from severe disease induced by SARS CoV-2. These results were confirmed in the GSH model. Conclusion: Here, we identified a novel single mutation that increased the yield of S protein, maintaining its immunogenicity and improving the protective efficacy against the development of SARS-CoV-2-induced severe disease in two animal models. These results could contribute to the development of novel vaccines for other respiratory viruses.

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Long-Term Immunodominant Profile of SARS-CoV-2 T-Cell Responses in Hybrid Immunity Raúl Pérez-Caballero 1 , Laia Bernad 1 , Athina Kilpeläinen 1 , Oscar Blanch Lombarte 1 , Luis Romero 1 , Ruth Peña 1 , Gabriel F. Rodríguez-Lozano 1 , Josep Maria Manresa-Dominguez 2 , Bonaventura Clotet 1 , Alex Olvera 1 , Christian Brander 1 , Eva María Martínez Cáceres 2 , Concepción Violán 3 , Pere Torán‐Monserrat 3 , Julia G. Prado 1 1 IrsiCaixa Institute for AIDS Research, Badalona, Spain, 2 Hospital Germans Trias i Pujol, Badalona, Spain, 3 Institut Universitari d’Investigació en Atenció Primària Jordi Gol (IDIAP Jordi Gol), Barcelona, Spain Background: Characterization of long-term T-cell immunity against SARS CoV-2 proteome is critical for understanding the implications of virus-specific hybrid immunity in protecting against re-infection and advancing novel vaccine designs. Here, we conducted a high-resolution mapping of the breadth and magnitude of T-cell responses to the entire SARS-CoV-2 proteome over a 2-year follow-up period in individuals with hybrid immunity. Methods: We selected cryopreserved PBMC from 38 healthcare workers, including 19 SARS-CoV-2 infected (CoV2+, tested at 124 days from symptoms onset, DfSO) and 19 uninfected (CoV2-) participants in the ProHEpiC-19 cohort study (NCT04885478). Longitudinal PBMC were available from 18 individuals after a 3- dose mRNA vaccination, including 13 CoV2+ (CoV2+Vac+, 825 DfSO) and 5 CoV2- who became infected during the follow-up period (Vac+CoV2+, 302 DfSO). We measured the breadth and magnitude of IFN-y T-cell responses by ELISpot assay using a 15-mer overlapping peptide (OLP) library of 2,790 SARS-CoV-2 peptides in 100 pools using a Mega Matrix approach, and we deconvoluted the matrix using single peptides by ELISpot assay. Results: We identified immunodominant T-cell responses to 13 regions across the SARS-CoV-2 proteome within S, Nsp3, NC, Env, and M proteins across groups and time. In addition, we observed a booster vaccination effect in these immunodominant regions with the strongest responses targeting S and Nsp3 proteins. In addition, CoV2+Vac+ individuals had broader T-cell responses than Vac+CoV2+ and showed an exclusive targeting of ORF3a, M, upORFs, Nsp2, 3C_LP, Nsp10 and Hel regions across the SARS-CoV-2 proteome. At the single peptide level, we identified differential frequency in the optimal T-cell responses across groups as the CoV2+Vac+ showed a preferential targeting of S1 (58%), S2 (17%) and ORF1ab/8 (25%) compared to Vac+CoV2+ with almost exclusive recognition of S2 (86%). Conclusion: Our results define immunodominant long-term T-cell responses in S, Nsp3, NC, Env, and M proteins in SARS-CoV2 proteome in the context of hybrid immunity. Our data demonstrate broader and exclusive T-cell responses in CoV2+Vac+ individuals compared to Vac+CoV2+. Overall, we identify differences in long-term T-cell hybrid immunity primed by infection or vaccination with implications for protection from re- infection and future vaccine design. Bivalent mRNA COVID Vaccines Elicit Predominantly Cross-Reactive CD4+ T-Cell Clonotypes Joel Sop , Arbor G. Dykema, Caroline C. Traut, Christie R. Basseth, Annukka A. Antar, Kellie N. Smith, Joel N. Blankson The Johns Hopkins University School of Medicine, Baltimore, MD, USA Background: The emergence of the Omicron BA.5 sublineage in February 2022 raised concerns due to its ability to escape neutralizing antibodies induced by ancestral spike mRNA vaccines and natural infection with prior SARS-CoV-2 variants. Bivalent COVID-19 vaccines, containing mRNA for both ancestral and

Poster Abstracts

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CROI 2024