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Fc/CD16 Interaction Is the Major Contributor to ADCC of HIV-Infected CD4 T Cells
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CROI 2026 Feb 22-25 Denver
Claudia Melo1, Teresa Murphy1, Carissa Holmberg1, Elyse McMahon1, Jonathan Lochner1, Rebecca Lynch, 1 and Alberto Bosque1 1Department of Microbiology, Immunology, and Tropical Medicine, George Washington University, Washington, District of Columbia
Program abstract
Background: Latent HIV reservoirs remain a barrier to cure. Natural killer (NK) cells control infection via natural cytotoxicity and antibody-dependent cellular cytotoxicity (ADCC), making them attractive effectors for HIV cure strategies. However, NK cell function is often impaired during chronic infection, and CD16 surface expression, critical for ADCC, is downregulated. We investigated how cytokine stimulation and Fc-engineered broadly neutralizing antibodies (bNAbs) influence NK-mediated clearance of HIV-infected cells across viral subtypes.
Methods: NK cells were isolated from PBMCs of HIV-negative donors and stimulated overnight with IL-12 (10 ng/mL), IL-15 (50 ng/mL), and IL-18 (50 ng/mL), with or without the ADAM17 inhibitor TAPI-1 (10 μ
M). CD69, CD16, and IFN-γ expression were assessed by flow cytometry. For cytotoxic assays, autologous CD4+ T cells were activated, infected with HIV-1 strains representing subtypes A, B, C, D, AE, and co-cultured with NK cells in the presence or absence of bNAbs N6, or VRC07-523LS wild-type or Fc-modified antibodies GASDALIE, LPLIL, AAA, or Fc-null GRLR (1 μ
M). CD16 engagement was assessed with a Jurkat-Lucia NFAT-CD16 reporter assay. Surface envelope binding, %remaining p24+cells, and ADCC activity were quantified by flow cytometry. Data were analyzed using Two-Way ANOVA, Friedman test, or Spearman’s correlation, with N=7-16 for functional assays and N=3-4 for envelope-binding assays. Sex- and agestratified analyses were included. Clustering of %remaining p24+ cells and %ADCC across conditions and viral subtypes was performed using ClustVis.
Results: Cytokine stimulation enhanced NK activation and IFN-γ production (p<0.01) but reduced CD16 surface expression (p=0.0055). TAPI-1 restored CD16 expression but did not improve ADCC. In contrast, Fc-enhanced VRC07-523LS variants GASDALIE and LPLIL consistently improved clearance of HIV-infected cells across all seven viral strains, independent of cytokine priming or ADAM17 inhibition. Surface envelope binding varied across subtypes, but Fc-optimized bNAbs rescued killing even with limited binding.
Conclusions: While restoring CD16 expression alone is insufficient to improve ADCC, Fc-engineered bNAbs that enhance CD16 engagement robustly boost ADCC, even under conditions of reduced envelope binding. These findings support combining NK-activating cytokines with Fc-optimized bNabs to enhance clearance of HIV-infected cells across subtypes.
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