CROI 2025 Abstract eBook

Abstract eBook

Poster Abstracts

473

Spike Ferritin Nanoparticle (SpFN) Recalls Memory B Cells in SARS-CoV-2 Experienced Donors Lauren Smith 1 , Kerri Lal 1 , Bonnie Slike 2 , Huy Nguyen 3 , Emilie Goguet 1 , Peifang Sun 4 , Allison Malloy 5 , Simon Pollett 1 , Edward Mitre 5 , Andrew Letizia 3 , Sandhya Vasan 1 , Julie Ake 2 , Nelson Michael 6 , Gordon Joyce 2 , Shelly Krebs 2 1 Henry M Jackson Foundation, Bethesda, MD, USA, 2 United States Military HIV Research Program, Bethesda, MD, USA, 3 Naval Medical Research Unit INDO PACIFIC, Singapore, Singapore, 4 Naval Medical Research Command, Silver Spring, MD, USA, 5 Uniformed Services University of the Health Sciences, Bethesda, MD, USA, 6 Walter Reed Army Institute of Research, Silver Spring, MD, USA Background: The FDA issued emergency use authorization (EUA) for mRNA- and protein-based vaccines that were effective in addressing the SARS-CoV-2 pandemic. The EUA is updated yearly to match the current circulating variants; XBB.1.5-based vaccination was recommended for 2023-2024. The Walter Reed Army Institute of Research (WRAIR) developed a SARS-CoV-2 vaccine candidate using a ferritin nanoparticle to display the SARS-CoV-2 Wu-1 D614G spike trimers (SpFN) incorporated in adjuvanted liposome, which elicits robust cross-neutralizing antibodies against SARS-CoV-2 variants and SARS-CoV-1 in SARS-CoV-naïve participants. In this study we aimed to determine the ability of the SpFN vaccine molecule to recall memory B cells in SARS-CoV-2-experienced participants compared to the recommended XBB.1.5 vaccine to evaluate the potential of SpFN as a vaccine boost. Methods: Participants (n=10) with prior exposure to SARS-CoV-2 via either immunization(s) and/or natural infection were used to determine the frequency of memory B cells that engaged either SpFN or XBB.1.5 trimer (S2P) molecules through flow cytometry. Additionally, to confirm that the recalled B cells could differentiate into antibody-secreting cells (ASCs), B cell enzyme-linked immunosorbent spot (ELISpot) assays were used to compare the frequency of antibody secreting cells specific to SpFN or the XBB.1.5 trimer in samples from SARS-CoV-2-exposed participants (N=16), with and without prior XBB.1.5 exposure. Results: A higher frequency of memory B cells from SARS-CoV-2-experienced participants bound to the SpFN molecule (median=0.87%) compared to XBB.1.5 S2P (median=0.58; p=0.009) (Fig. 1a). Similarly, in the presence of SpFN, antibody-secreting cells developed more spot-forming units (SFUs) (median=645) compared to the XBB.1.5 molecule (median= 420, p=0.001) (Fig 1b). The frequency of memory B cells binding to SpFN or XBB.1.5 was higher in participants with XBB.1.5 exposure within 2-3 months prior to sampling (m=0.69% and m=0.96%, p=0.05). Conclusions: Here we show SpFN is able to engage SARS-CoV-2-specific memory B cells at levels higher than that of the recommended 2023-2024 vaccine immunogen, XBB.1.5, in samples collected cross-sectionally prior to 2024. These data demonstrate the ability of SpFN to recall memory B cells and differentiate into antibody secreting cells previously generated through SARS-CoV-2 infection and/or vaccination, underlining the potential of SpFN as a vaccine booster strategy.

474

Optimized ACE2-Fc With Picomolar Pan-Neutralization of SARS-CoV-2 Variants, Including JN.1 and KP.2 Ferran Abancó i Espuga 1 , Ferran Tarrés-Freixas 2 , Rosalba Lepore 3 , Elisa Molina 1 , Edwards Pradenas 1 , Dalia Raïch-Regué 1 , Bonaventura Clotet 1 , Alfonso Valencia 3 , Júlia Vergara-Alert 2 , Joaquim Segalés 2 , Jorge Carrillo 1 , Nuria Izquierdo-Useros 1 , Julià Blanco 1 , Benjamin Trinité 1 1 IrsiCaixa, Badalona, Spain, 2 Universitat Autònoma de Barcelona, Barcelona, Spain, 3 Centro Nacional de Supercomputación, Barcelona, Spain Background: Many neutralizing monoclonal antibodies capable of providing sterilizing immunity against SARS-CoV-2 have been developed and temporarily approved for emergency clinical use as prophylactics. However, the rapid evolution of SARS-CoV-2 progressively renders these treatments obsolete. Several groups have been exploring the use of ACE2-based Fc fusion proteins to obtain a pan-variant neutralizing molecule. In this work we designed ACE2-Fc candidates effective (IC50<100pM) against all variant tested. Methods: A catalytically inactivated ACE2 peptidase domain was fused to the N-terminal end of a human IgG1 Fc, either directly or via a flexible linker. In silico predicted point mutations were introduced into the ACE2 sequence to increase both spike receptor binding domain (RBD) affinity and protein stability. Using pseudovirus and full virus-based neutralization assays, all candidates were functionally validated and compared to the monoclonal antibody Sipavibart (AZD3152), against a large panel of pre-Omicron and Omicron-derived variants, including JN.1 and KP.2. Results: We identified 3 points of improvement: (1) the addition of the flexible linker which systematically improved both the production (up to 10-fold) and neutralizing activity (5-fold); (2) a combination of four ACE2 mutations which, benefited the neutralizing activity (10-fold); (3) the addition of a second ACE2 at the Fc C-terminal end, to generate a tetrameric protein, greatly improved the potency (117-fold). The combination of the linker and binding mutations synergized to increase the neutralizing activity (27-fold) but did not improve the potency of the tetrameric molecule suggesting that its activity was already optimal. Finally, while Sipavibart showed loss of activity against JN.1 and KP.2 variants (IC50 of 660 pM and >3456 pM, respectively), our ACE2 molecules demonstrated increased potency against these latest variants (IC50 down to 12 pM and 4 pM, respectively). Conclusions: Our results demonstrate the relevance of ACE2 recombinant proteins to neutralize all SARS-CoV-2 variants. While the development and validation of traditional monoclonal antibodies is long and costly. ACE2-Fc molecules could provide an off-the-shelf solution ready to protect the immunocompromised and other risk groups against the rapidly evolving SARS CoV-2 variants and any coronaviruses using ACE2 as receptor. Long COVID Is Associated With Lower Percentages of Mature, Cytotoxic NK-Cell Phenotypes Tasha Tsao, Amanda M. Buck, Lilian Grimbert, Brian Lafranchi, Belen Altamirano Poblano, Dylan Ryder, Avery Eun, Kathleen Bellon Pizarro, Melissa Buitrago, Kofi Asare, Emily Fehrman, Peter W. Hunt, Michael Peluso, Oscar A. Aguilar, Timothy J. Henrich, for the Long-term Impact of Infection with Novel Coronavirus (LIINC) Study Group University of California San Francisco, San Francisco, CA, USA Background: Long COVID (LC) is associated with dysregulated adaptive immune function and inflammation, which may originate from or contribute to the persistence of SARS-CoV-2 in post-acute COVID-19. COVID-19 can also induce adaptive NK cell responses during the acute phase, but our understanding of NK cell phenotypes in the post-acute phase and their relationship to LC is unknown. Methods: Using PBMCs cryopreserved 4 months after initial SARS-CoV-2 infection, we studied individuals with LC (n=21), defined as ongoing COVID attributed symptoms >3 months post-COVID, in comparison to matched comparators who had fully recovered from COVID-19 (n=14). All samples were collected in the pre-Omicron era, prior to confounders like vaccination or reinfection. Most participants (74%) had been outpatients with mild/moderate COVID-19. We performed NK cell phenotyping using high-dimensional spectral flow cytometry and examined associations between NK cell parameters and clinical factors. Results: The frequencies of CD56+/CD3- NK cells were similar across groups. However, in comparison to those who fully recovered, the mean percentage of mature, cytotoxic CD56dim/CD16+ NK cells was lower in those with LC (69% vs. 57.9%; P=0.037). An even lower percentage was seen in those with severe LC (>5 symptoms; 50.6%; P=0.004), and in participants reporting

Poster Abstracts

475

CROI 2025 118