A herpesvirus entry mediator mutein with selective agonist action for the inhibitory receptor B and T lymphocyte attenuator

Abstract

The human cytomegalovirus opening reading frame UL144 is an ortholog of the TNF receptor superfamily member, herpesvirus entry mediator (HVEM; ). HVEM binds the TNF ligands, LIGHT and LTa; the immunoglobulin inhibitory receptor, B and T lymphocyte attenuator (BTLA); and the natural killer cell-activating receptor CD160. However, UL144 selectively binds BTLA, avoiding activation of inflammatory signaling initiated by CD160 in natural killer cells. BTLA and CD160 cross-compete for binding HVEM, but the structural basis for the ligand selectivity by UL144 and how it acts as an anti-inflammatory agonist remains unclear. Here, we modeled the UL144 structure and characterized its binding with BTLA. The UL144 structure was predicted to closely mimic the surface of HVEM, and we also found that both HVEM and UL144 bind a common epitope of BTLA, whether engaged in or in, that is shared with a BTLA antibody agonist. On the basis of the UL144 selectivity, we engineered a BTLA-selective HVEM protein to understand the basis for ligand selectivity and BTLA agonism to develop novel anti-inflammatory agonists. This HVEM mutein did not bind CD160 or TNF ligands but did bind BTLA with 10-fold stronger affinity than wild-type HVEM and retained potent inhibitory activity that reduced T-cell receptor, B-cell receptor, and interferon signaling in B cells. In conclusion, using a viral immune evasion strategy that shows broad immune-ablating activity, we have identified a novel anti-inflammatory BTLA-selective agonist.

Past and ongoing adaptation of human cytomegalovirus to its host

“…For instance, several selected sites in gB map within ADs (Fig 2C), and in gH (UL75) positively selected sites localize to a structural epitope within antigenic site 7 [43] (Fig 5A). Additional details on the location of positively selected sites, sequence polymorphism, and ADs for gB, gH, gM and gO are reported in S6 Fig. As for UL144, positively selected sites are directly involved in BTLA (B and T lymphocyte attenuator) binding ( Fig 5B) [44].…”

Structure of human cytomegalovirus UL144, an HVEM orthologue, bound to the B and T cell Lymphocyte Attenuator

“…This suggests that UL144 has evolved as a true viral mimic of HVEM in its ability to bind to BTLA. Recently published mutagenesis data has identified seven critical UL144 residues (E27, Q33, P36, G41, Y42, T52 and L68) that are required for BTLA binding (27). Based on our solved crystal structure, not all of these UL144 residues directly contact BTLA.…”

“…However, in UL144, the lysine residue is not conserved, and in the UL144/BTLA complex the loss of this interaction is compensated by Thr 57 of UL144 that forms a novel contact with Figure 5C). As the Y42A mutant of UL144 and Y61A mutant of HVEM (25,27) are dead for BTLA-binding, we assessed the impact of Leu 123 on binding by transfecting 293T cells with plasmid encoding WT and a L123A mutant of BTLA. While the L123A mutant of BTLA showed decreased binding towards HVEM, interestingly UL144 binding was not impacted ( Figure 5D).…”

Immune Checkpoints as Therapeutic Targets in Autoimmunity

“…Šedý et al studied the structure of UL144 to guide their design of a mutated HVEM-Fc protein capable of binding BTLA with 10 fold higher affinity than wildtype HVEM and with no binding to the receptors LIGHT or CD160. In vitro this construct regulated B, T, and NK cell cytokine production ( 66 ). There are numerous other viral proteins that have evolved to mimic inhibitory ligands, which presents an opportunity to further explore these compounds as therapeutic agents and once again highlights the potential merits of exploiting signaling through inhibitory receptors to switch off unwanted immune responses.…”