Mechanistic insight into the CD32-driven enhancement of HIV-1 susceptibility of resting CD4 T cells

Gapp, Madeleine (2024): Mechanistic insight into the CD32-driven enhancement of HIV-1 susceptibility of resting CD4 T cells. Dissertation, LMU München: Medizinische Fakultät

Abstract

The current treatment of HIV-1-infected patients relies on life-long antiretroviral therapy (ART) that can suppress virus replication, but not eradicate the pathogen. The persistence of latent and ART-resistant viral reservoirs, particularly in resting CD4 T cells, remains the major bar-rier to HIV cure. The current limitation of strategies aiming at reversal of HIV latency or killing of infected cells in a clinical setting, in part results from a lack of biomarkers that are selec-tively exposed on latently HIV-1-infected, resting CD4 T cells. This knowledge could facilitate the selective elimination of the viral reservoir in infected individuals. Several candidate bi-omarkers were recently proposed, including the Fcγ receptor (FcγR)-IIa (CD32a), but its role has remained controversial. Here we show, that the FcγR CD32 (FcγRII) is not expressed de novo by HIV-1-infected CD4 T cells, but acquired from CD32-positive cells such as macro-phages under conditions of close cell-to-cell contact. This cell communication process is re-ferred to as FcγR-mediated trogocytosis. To study it, we established a cell line-based FcγR-mediated trogocytosis model. Here, we tested the functionality and auto-transfer of three isoforms of CD32, i.e. CD32A, B and C, as well as a panel of CD32A and B mutants. This re-vealed that CD32 drives the transient, cell contact-dependent transfer of itself, but also the co-transfer of other cell surface receptors (CD32B>CD32C≥CD32A) including chemokine core-ceptors for HIV-1. Additionally, we explored the role of antibodies in modulating CD32-mediated trogocytosis. We found that the HIV-1 broadly neutralizing antibody (bNAb) PGT151 is autoreactive to CD4 T cells and thereby enhances trogocytosis. Intriguingly, also a subset of patients with chronic HIV-1 infection harbors T cell-reactive IgG autoantibodies with this capacity in their blood. Moreover, in co-cultures of primary macrophages with primary CD4 T cells we detected the transfer of CD32 as well as the co-transfer of a number of other recep-tors from the plasma membrane of macrophages to that of T cells. Transferred receptors were able to confer cell migration and adhesion properties to recipient cells. By confocal microsco-py we were able to visualize transferred receptors on T cells within distinct membrane patch-es, which originated from the donor cells. Importantly, these macrophage-derived membrane patches served as hotspots for binding and fusion of HIV-1 particles and rendered resting CD4 T cells susceptible to infection. In order to further elucidate mechanisms that may be directly involved in preferential HIV-1 binding to membrane patches transferred by trogocytosis we investigated a set of receptors, previously implicated in HIV-1 binding to macrophages. While being able to detect the co-transfer of such HIV-1 binding receptors, including DC-SIGN, CD206 and CD11a/b/c, we ex-cluded their functional contribution in this process using highly efficient knockout approaches in donor macrophages. Unexpectedly, we observed that CD4 endogenously expressed by T cells aggregated within transferred CD32+ ganglioside GM1+ membrane patches. Based on gene perturbation and antibody inhibition studies, we show that the recruited CD4 is an im-portant factor for preferential virion binding and fusion at these hotspots, resulting in increased infection of these viral reservoir cells. Taken together, the antibody-enhanced, CD32-driven trogocytotic transfer of membrane patches containing a number of surface receptors can change the proteomic and functional plasticity of primary CD4 T cells. On a more general level, FcγR-mediated trogocytosis should be taken into account when investigating primary immune cells in co-culture and analyzing the expression and functionality of cell surface markers untypical for the respective cell lineage. Even though we can exclude CD32 as a bona fide biomarker for latently HIV-1-infected cells, the discovery of FcγR-driven trogocytosis which enhances the HIV-1 infection rate of resting CD4 T cells is important as this process may contribute to seeding and expansion of the latent reservoir in patients.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: CD32, HIV reservoir, autoantibodies, immune cell communication, trogocytosis
• Themengebiete: 600 Technik, Medizin, angewandte Wissenschaften ; 600 Technik, Medizin, angewandte Wissenschaften > 610 Medizin und Gesundheit
• Fakultäten: Medizinische Fakultät
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 13. März 2024
• 1. Bericht­erstatter:in: Keppler, Oliver