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

The human tumor necrosis factor (TNF) receptor superfamily member, herpesvirus entry mediator (TNFRSF14; HVEM), is frequently targeted by viral pathogens and in human cancer. HVEM activates NF-κB signaling following ligation with its ligands LIGHT, B and T lymphocyte attenuator (BTLA), and CD160. Additionally, HVEM binding to BTLA receptors activates inhibitory signaling in lymphocytes while HVEM binding to CD160 receptors activates inflammatory signaling in natural killer (NK) cells. The human cytomegalovirus opening reading frame UL144 is an ortholog of HVEM that selectively binds and activates BTLA, avoiding activation of inflammatory signaling initiated by CD160 in NK 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 trans or in cis, that is shared with a BTLA antibody agonist. In human lymphoma the HVEM gene is frequently mutated with predominant mutations focused in the extracellular domain. However, it is unclear whether these HVEM mutants regulate ligand binding and HVEM activated signaling. We additionally show that these mutations specifically target ligand binding, resulting in specific loss of interactions with CD160 compared to LIGHT or BTLA, translating into inability to activate ligand-mediated signaling. On the basis of this selectivity we observe in the UL144 protein, and in several HVEM mutants in lymphoma, we engineered a BTLA-selective HVEM protein to understand the basis for 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. Support or Funding Information This study was supported by grants from the US National Institutes of Health (AI048073, AI067890, CA164679, and CA177322 to C.F.W.), a gift from the Perkins Family Foundation (to C.F.W.), the American Heart Association (AHA-14BGIA20380277 to J.R.S.), the National Psoriasis Foundation (NPF2015 to J.R.S.), the Slovak Research and Development Agency (APVV-14-0839 to I.N.) and the Scientific Grant Agency of the Slovak Republic (2/0103/15 to I.N.), and a research contract from Pfizer Centers for Therapeutic Innovation. I.N. is a Marie Curie Fellow financed by the SASPRO Program, co-funded by the EU and the Slovak Academy of Sciences. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.