CD160 isoforms and regulation of CD4 and CD8 T-cell responses

BACKGROUND: Coexpression of CD160 and PD-1 on HIV-specific CD8(+) T-cells defines a highly exhausted T-cell subset. CD160 binds to Herpes Virus Entry Mediator (HVEM) and blocking this interaction with HVEM antibodies reverses T-cell exhaustion. As HVEM binds both inhibitory and activatory receptors, our aim in the current study was to assess the impact of CD160-specific antibodies on the enhancement of T-cell activation. METHODS: Expression of the two CD160 isoforms; glycosylphosphatidylinositol-anchored (CD160-GPI) and the transmembrane isoforms (CD160-TM) was assessed in CD4 and CD8 primary T-cells by quantitative RT-PCR and Flow-cytometry. Binding of these isoforms to HVEM ligand and the differential capacities of CD160 and HVEM specific antibodies to inhibit this binding were further evaluated using a Time-Resolved Fluorescence assay (TRF). The impact of both CD160 and HVEM specific antibodies on enhancing T-cell functionality upon antigenic stimulation was performed in comparative ex vivo studies using primary cells from HIV-infected subjects stimulated with HIV antigens in the presence or absence of blocking antibodies to the key inhibitory receptor PD-1. RESULTS: We first show that both CD160 isoforms, CD160-GPI and CD160-TM, were expressed in human primary CD4(+) and CD8(+) T-cells. The two isoforms were also recognized by the HVEM ligand, although this binding was less pronounced with the CD160-TM isoform. Mechanistic studies revealed that although HVEM specific antibodies blocked its binding to CD160-GPI, surprisingly, these antibodies enhanced HVEM binding to CD160-TM, suggesting that potential antibody-mediated HVEM multimerization and/or induced conformational changes may be required for optimal CD160-TM binding. Triggering of CD160-GPI over-expressed on Jurkat cells with either bead-bound HVEM-Fc or anti-CD160 monoclonal antibodies enhanced cell activation, consistent with a positive co-stimulatory role for CD160-GPI. However, CD160-TM did not respond to this stimulation, likely due to the lack of optimal HVEM binding. Finally, ex vivo assays using PBMCs from HIV viremic subjects showed that the use of CD160-GPI-specific antibodies combined with blockade of PD-1 synergistically enhanced the proliferation of HIV-1 specific CD8(+) T-cells upon antigenic stimulation. CONCLUSIONS: Antibodies targeting CD160-GPI complement the blockade of PD-1 to enhance HIV-specific T-cell responses and warrant further investigation in the development of novel immunotherapeutic approaches. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12967-014-0217-y) contains supplementary material, which is available to authorized users

VanX, a bacterial <scp>d</scp> -alanyl- <scp>d</scp> -alanine dipeptidase: Resistance, immunity, or survival function?

The zinc-containing d -alanyl- d -alanine ( d -Ala- d -Ala) dipeptidase VanX has been detected in both Gram-positive and Gram-negative bacteria, where it appears to have adapted to at least three distinct physiological roles. In pathogenic vancomycin-resistant enterococci, vanX is part of a five-gene cluster that is switched on to reprogram cell-wall biosynthesis to produce peptidoglycan chain precursors terminating in d -alanyl- d -lactate ( d -Ala- d -lactate) rather than d -Ala- d -Ala. The modified peptidoglycan exhibits a 1,000-fold decrease in affinity for vancomycin, accounting for the observed phenotypic resistance. In the glycopeptide antibiotic producers Streptomyces toyocaensis and Amylocatopsis orientalis , a vanHAX operon may have coevolved with antibiotic biosynthesis genes to provide immunity by reprogramming cell-wall termini to d -Ala- d -lactate as antibiotic biosynthesis is initiated. In the Gram-negative bacterium Escherichia coli , which is never challenged by the glycopeptide antibiotics because they cannot penetrate the outer membrane permeability barrier, the vanX homologue ( ddpX ) is cotranscribed with a putative dipeptide transport system ( ddpABCDF ) in stationary phase by the transcription factor RpoS (σ s ). The combined action of DdpX and the permease would permit hydrolysis of d -Ala- d -Ala transported back into the cytoplasm from the periplasm as cell-wall crosslinks are refashioned. The d -Ala product could then be oxidized as an energy source for cell survival under starvation conditions. </jats:p