CROI 2025 Abstract eBook

Abstract eBook

Oral Abstracts

147

Immunological Impact of Short-Term BCL2 Inhibition at ART Initiation on SIV-Infected Rhesus Macaques Tomas Raul Wiche Salinas 1 , Justin Harper 2 , Kevin Nguyen 2 , James Auger 2 , Hannah Flores 2 , Laurence Raymond Marchand 3 , Greg Laird 4 , Gregory K. Tharp 2 , Steven Bosinger 2 , Andrew D. Badley 5 , R. Brad Jones 6 , Guido Silvestri 2 , Deanna A. Kulpa 7 , Mirko Paiardini 1 1 Emory University, Atlanta, GA, USA, 2 Emory National Primate Research Center, Atlanta, GA, USA, 3 University of Montreal, Montreal, Canada, 4 Accelevir Diagnostics, Baltimore, MD, USA, 5 Mayo Clinic, Rochester, MN, USA, 6 Weill Cornell Medicine, New York, NY, USA, 7 Yerkes National Primate Research Center, Atlanta, GA, USA Background: The anti-apoptotic molecule BCL-2 promotes the establishment, maintenance, and expansion of the CD4 T cell reservoir. In SIV-infected rhesus macaque (RMs), we found that BCL-2 inhibition at antiretroviral therapy (ART) initiation (ARTi) promotes a rapid and sustained reduction of the SIV reservoir in blood CD4 T cells. To determine mechanisms for reservoir decrease, we assess the immunological impact of a BCL-2 inhibitor, venetoclax (vtx), in SIV-infected RMs. Methods: 24 RMs were infected with barcoded SIVmac239M and initiated ART at 14 days post-infection (p.i.). 8 RMs received ART alone; 8 RMs received 10 daily doses of vtx starting at ARTi; and 8 RMs received vtx in combination with a single dose of the anti-CD8a depleting antibody MT807R1 at ARTi. RMs were followed until d294 p.i. Immunological signatures in purified CD4 T cells were assessed at the end of vtx treatment (d25 p.i.) and of the follow-up period (d294 p.i.) by flow cytometry and RNA-seq. Results: At d25 p.i., we found a reduction of central and effector memory CD4 T cells in RMs treated with vtx alone or with MT807R1. The remaining CD4 T cells showed significant enrichment of the 'Regulation of apoptosis' gene set, consistent with BCL-2 inhibition. Additionally, pathways such as 'inflammasomes' and 'NOD signaling' were enriched, with upregulation of CARD9, PYCARD, caspase-1, and caspase-4—key mediators of pyroptosis, an alternative cell death process. Notably, there was also increased expression of anti-apoptotic molecules like clusterin, NOL-3 and BCL-2, which counteract pro-apoptotic Bax, indicating activation of pathways promoting resistance to cell death following BCL-2 inhibition in the remaining cells. Consistently, genes associated with vtx resistance in cancer patients, such as BCL-XL, CLEC7A, and CD14, were upregulated in blood CD4 T cells. At d294 p.i., gene and pathway expression had normalized, except for the T-cell receptor beta chain variable region, which remained suppressed, suggesting vtx may reduce clonotype diversity during ART. Conclusions: BCL-2 inhibition via vtx promotes rapid changes in gene expression within CD4+ T cells, associated with reduced size of the SIV reservoirs. While key cell death mediators were upregulated, anti-apoptotic mechanisms also emerged, suggesting resistance to BCL-2 inhibition. These findings provide a rationale for targeting BCL-2 in people with HIV and identifying additional anti-apoptotic molecules to target in a combination approach to eradicate the SIV reservoir. Bispecific Antibody VRC07/PGT121 Protects Against High-Dose Intravenous SHIV-BG505 Challenge Matthew S. Parsons 1 , Decha Silsorn 1 , Jumpol Sopanaporn 1 , Panupat Nadee 1 , Dutsadee Inthawong 1 , Rawiwan Imerbsin 1 , Michelle Zemil 2 , Victoria Polonis 3 , Diane Bolton 4 , Manoj S. Nair 5 , Jian Yu 5 , Yaoxing Huang 5 , David D. Ho 5 , Sandhya Vasan 2 , Julie Ake 4 1 Armed Forces Research Institute of Medical Sciences in Bangkok, Bangkok, Thailand, 2 Henry M Jackson Foundation, Bethesda, MD, USA, 3 US Military HIV Research Program, Bethesda, MD, USA, 4 United States Military HIV Research Program, Bethesda, MD, USA, 5 Aaron Diamond AIDS Research Center, New York, NY, USA Background: Non-human primate (NHP) and human clinical studies highlight the utility of broadly neutralizing antibodies (bNAbs) for immunoprophylaxis against HIV-1. Passively delivered bNAbs protect against viral strains susceptible to antibody-mediated neutralization. To protect against HIV-1 strains resistant to individual antibodies, endeavors to improve bNAb breadth are required. A key strategy to enhance the neutralization breadth of individual bNAbs is to generate designer bispecific bNAbs. Methods: We implemented CrossMAb technology to generate a bispecific anti-HIV-1 Env bNAb with antigen-binding arms derived from the VRC07 and PGT121 bNAbs. We screened the antibody for viral neutralization in a pseudovirus neutralization assay and assessed for in vivo anti-viral activity in humanized NSG mice infected with HIV-1 JRCSF (n=8). We then implemented an NHP high-dose intravenous viral exposure model to assess antibody-mediated

immunoprophylaxis. This model mimics exposure via a large unscreened blood transfusion but is also relevant to lower-dose intravenous exposures such as through sharing drug injection equipment. Experimental (n=8) and control (n=8) Indian-origin rhesus macaques were infused with VRC07/PGT121 (30 mg/kg) or an equivalent volume of saline, respectively, one hour before intravenous challenge with SHIV-BG505 (40 X 10 6 viral RNA copies). Plasma bNAb concentration was monitored by ELISA. Starting at week eight post-challenge, anti-CD8 alpha antibody (45 mg/kg) was administered in animals lacking evidence of plasma viremia and with VRC07/PGT121 plasma concentrations <1 µg/ml for at least two weeks to reveal possible subclinical infections. Results: The VRC07/PGT121 bispecific bNAb neutralized >90% of a panel of 64 global HIV-1 strains (geometric mean IC 50 =0.64 µg/ml) and reduced viremia in HIV-1-infected humanized mice (average viral load decline ~1.0-1.5 log 10 for three weeks). The high-dose intravenous SHIV-BG505 challenge infected all eight control animals (peak log 10 viral load range: 6.3-7.3 copies/ml). We have yet to observe evidence of viral replication in animals pre-treated with VRC07/PGT121 before SHIV-BG505 exposure, including during the post-CD8 depletion period (animals are currently between one- and five-weeks post-depletion). Conclusions: Bispecific anti-HIV-1 bNAbs are potentially valuable biomedical interventions for ongoing efforts to achieve HIV-1 immunoprophylaxis, as evidenced in this very stringent IV challenge model. Time-to-Rebound Measurements in ATI Trials With bNAb Intervention Are Confounded by Autologous NAbs Mauro Garcia 1 , Junlin Zhuo 1 , Emmanouil Papasavvas 2 , Brianna Lopez 1 , Anthony Abeyta-Lopez 1 , Beril Aydin 3 , Joseph Varriale 1 , Jun Lai 1 , Livio Azzoni 2 , Kenneth Lynn 4 , Karam Mounzer 5 , Pablo Tebas 4 , Luis J. Montaner 2 , Robert F. Siliciano 1 , Janet M. Siliciano 1 1 The Johns Hopkins University School of Medicine, Baltimore, MD, USA, 2 The Wistar Institute, Philadelphia, PA, USA, 3 The Johns Hopkins University, Baltimore, MD, USA, 4 University of Pennsylvania, Philadelphia, PA, USA, 5 Philadelphia FIGHT, Philadelphia, PA, USA Background: Many HIV cure trials use time-to-rebound during an analytic treatment interruption (ATI) as a primary outcome measurement. In a previously described ATI study with no intervention, the fraction of replication-competent outgrowth viruses neutralized by contemporaneous autologous neutralizing antibodies (aNAbs) prior to ART interruption correlated with time to rebound. Therefore, aNAbs may also contribute to delayed rebound in trials that include a broadly neutralizing antibody (bNAb) intervention or other interventions. Participants in the NCT03588715 (BEAT2) clinical trial received six infusions of the bNAbs 3BNC117 and 10-1074, and thirty doses of IFNa2b. Following cessation of all immunotherapies, BEAT2 participants had variable times to rebound (4-25 weeks), and we hypothesized that aNAbs may be a critical contributing factor. Methods: Inhibition of viral outgrowth by aNAbs was assessed at baseline using a modified quantitative viral outgrowth assay in which resting CD4+ T cells were activated by PHA and cultured in the presence of contemporaneous autologous IgG, HIV-negative donor IgG, or no IgG for 14 days. Viral outgrowth was measured by HIV-1 p24 ELISA and env genes sequenced. Results: The fraction of replication-competent outgrowth viruses neutralized by contemporaneous aNAbs at baseline varied widely (0 to 100%) among participants and correlated significantly (p=0.0342) with time-to-rebound following cessation of all immunotherapies. HIV-1 env sequencing and phylogenetic analyses revealed critical differences between aNAb-sensitive and aNAb-resistant outgrowth virus. aNAb-resistant reservoir variants detected prior to the ATI may be genetically similar or identical to rebound virus. Conclusions: The study participants had a variable fraction of inducible, replication-competent reservoir viruses neutralized by contemporaneous aNAbs prior to receiving immunotherapy (bNAbs and IFNa2b) and undergoing ART interruption. Higher proportions of replication-competent outgrowth viruses neutralized by aNAbs was associated with a more delayed time-to-rebound following cessation of all immunotherapies. ATI studies must consider the role of pre-existing aNAbs in potentially confounding time-to-rebound measurements.

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CROI 2025