Inactivation Methods for Experimental Nipah Virus Infection.

Nipah virus (NiV) is an emerging zoonotic paramyxovirus that causes severe disease in humans and livestock. Due to its high pathogenicity in humans and the lack of available vaccines and therapeutics, NiV needs to be handled in biosafety level 4 (BSL-4) laboratories. Safe inactivation of samples containing NiV is thus necessary to allow further processing in lower containment areas. To date, there is only limited information available on NiV inactivation methods validated by BSL-4 facilities that can be used as a reference. Here, we compare some of the most common inactivation methods in order to evaluate their efficacy at inactivating NiV in infected cells, supernatants and organs. Thus, several physical and chemical inactivation methods, and combinations thereof, were assessed. Viral replication was monitored for 3 weeks and NiV presence was assessed by RT-qPCR, plaque assay and indirect immunofluorescence. A total of nineteen methods were shown to reduce NiV infectious particles in cells, supernatants and organs to undetectable levels. Therefore, we provide a list of methods for the safe and efficient inactivation of NiV.

Metagenomic Snapshots of Viral Components in Guinean Bats.

To prevent the emergence of zoonotic infectious diseases and reduce their epidemic potential, we need to understand their origins in nature. Bats in the order Chiroptera are widely distributed worldwide and are natural reservoirs of prominent zoonotic viruses, including Nipah virus, Marburg virus, and possibly SARS-CoV-2. In this study, we applied unbiased metagenomic and metatranscriptomic approaches to decipher the virosphere of frugivorous and insectivorous bat species captured in Guéckédou, Guinea, the epicenter of the West African Ebola virus disease epidemic in 2013-2016. Our study provides a snapshot of the viral diversity present in these bat species, with several novel viruses reported for the first time in bats, as well as some bat viruses closely related to known human or animal pathogens. In addition, analysis of Mops condylurus genomic DNA samples revealed the presence of an Ebola virus nucleoprotein (NP)-derived pseudogene inserted in its genome. These findings provide insight into the evolutionary traits of several virus families in bats and add evidence that nonretroviral integrated RNA viruses (NIRVs) derived from filoviruses may be common in bat genomes.

Melanoma-associated fibroblasts impair CD8+ T cell function and modify expression of immune checkpoint regulators via increased arginase activity.

This study shows that melanoma-associated fibroblasts (MAFs) suppress cytotoxic T lymphocyte (CTL) activity and reveals a pivotal role played by arginase in this phenomenon. MAFs and normal dermal fibroblasts (DFs) were isolated from surgically resected melanomas and identified as Melan-A-/gp100-/FAP+ cells. CTLs of healthy blood donors were activated in the presence of MAF- and DF-conditioned media (CM). Markers of successful CTL activation, cytotoxic degranulation, killing activity and immune checkpoint regulation were evaluated by flow cytometry, ELISPOT, and redirected killing assays. Soluble mediators responsible for MAF-mediated effects were identified by ELISA, flow cytometry, inhibitor assays, and knock-in experiments. In the presence of MAF-CM, activated/non-naïve CTLs displayed dysregulated ERK1/2 and NF-κB signaling, impeded CD69 and granzyme B production, impaired killing activity, and upregulated expression of the negative immune checkpoint receptors TIGIT and BTLA. Compared to DFs, MAFs displayed increased amounts of VISTA and HVEM, a known ligand of BTLA on T cells, increased L-arginase activity and CXCL12 release. Transgenic arginase over-expression further increased, while selective arginase inhibition neutralized MAF-induced TIGIT and BTLA expression on CTLs. Our data indicate that MAF interfere with intracellular CTL signaling via soluble mediators leading to CTL anergy and modify immune checkpoint receptor availability via L-arginine depletion.

Skin-homing CD8+ T cells preferentially express GPI-anchored peptidase inhibitor 16, an inhibitor of cathepsin K.

This study sought to identify novel CD8+ T cell homing markers by studying acute graft versus host disease (aGvHD), typically involving increased T cell homing to the skin and gut. FACS-sorted skin-homing (CD8ß+ /CLA+ ), gut-homing (CD8ß+ /integrinß7+ ), and reference (CD8ß+ /CLA- /integrinß7- ) T cells were compared in patients affected by cutaneous and/or gastrointestinal aGVHD. Microarray analysis, qPCR, and flow cytometry revealed increased expression of peptidase inhibitor 16 (PI16) in skin-homing CD8+ T cells. Robust association of PI16 with skin homing was confirmed in all types of aGvHD and in healthy controls, too. PI16 was not observed on CLA+ leukocytes other than T cells. Induction of PI16 expression on skin-homing T cells occurred independently of vitamin D3. Among skin-homing T cells, PI16 expression was most pronounced in memory-like CD45RO+ /CD127+ /CD25+ /CD69- /granzyme B- cells. PI16 was confined to the plasma membrane, was GPI-anchored, and was lost upon restimulation of memory CD8+ T cells. Loss of PI16 occurred by downregulation of PI16 transcription, and not by Phospholipase C (PLC)- or Angiotensin-converting enzyme (ACE)-mediated shedding, or by protein recycling. Inhibitor screening and pull-down experiments confirmed that PI16 inhibits cathepsin K, but may not bind to other skin proteases. These data link PI16 to skin-homing CD8+ T cells, and raise the possibility that PI16 may regulate cutaneous cathepsin K.

Unique patterns of CD8+ T-cell-mediated organ damage in the Act-mOVA/OT-I model of acute graft-versus-host disease.

T-cell receptor (TCR)-transgenic models of acute graft-versus-host disease (aGvHD) offer a straightforward and highly controlled approach to study the mechanisms and consequences of T-cell activation following allogeneic hematopoietic stem cell transplantation (aHSCT). Here, we report that aHSCT involving OT-I mice as donors, carrying an ovalbumin-specific CD8+ TCR, and Act-mOVA mice as recipients, expressing membrane-bound ovalbumin driven by the ß-actin promoter, induces lethal aGvHD in a CD8+ T-cell-dependent, highly reproducible manner, within 4-7 days. Tracking of UBC-GFP/OT-I graft CD8+ T cells disclosed heavy infiltration of the gastrointestinal tract, liver, and lungs at the onset of the disease, and histology confirmed hallmark features of gastrointestinal aGVHD, hepatic aGvHD, and aGvHD-associated lymphocytic bronchitis in infiltrated organs. However, T-cell infiltration was virtually absent in the skin, a key target organ of human aGvHD, and histology confirmed the absence of cutaneous aGVHD, as well. We show that the model allows studying CD8+ T-cell responses in situ, as selective recovery of graft CD45.1/OT-I CD8+ T cells from target organs is simple and feasible by automated tissue dissociation and subsequent cell sorting. Assessment of interferon-gamma production by flow cytometry, granzyme-B release by ELISA, TREC assay, and whole-genome gene expression profiling confirmed that isolated graft CD8+ T cells remained intact, underwent clonal expansion, and exerted effector functions in all affected tissues. Taken together, these data demonstrate that the OT-I/Act-mOVA model is suitable to study the CD8+ T-cell-mediated effector mechanisms in a disease closely resembling fatal human gastrointestinal and hepatic aGVHD that may develop after aHSCT using HLA-matched unrelated donors.

Complement receptor type 1 (CR1/CD35) expressed on activated human CD4+ T cells contributes to generation of regulatory T cells.

The role of complement in the regulation of T cell immunity has been highlighted recently by several groups. We were prompted to reinvestigate the role of complement receptor type 1 (CR1, CD35) [corrected] in human T cells based on our earlier data showing that activated human T cells produce C3 (Torok et al. (2012) [48]) and also by results demonstrating that engagement of Membrane Cofactor Protein (MCP, CD46) induces a switch of anti-CD35-activated [corrected] helper T cells into regulatory T cells (Kemper et al. (2003) [17]). We demonstrate here that co-ligation of CD46 and CD35, [corrected] the two C3b-binding structures present on activated CD4+ human T cells significantly enhances CD25 expression, elevates granzyme B production and synergistically augments cell proliferation. The role of CR1 in the development of the Treg phenotype was further confirmed by demonstrating that its engagement enhances IL-10 production and reduces IFNγ release by the activated CD4+ T cells in the presence of excess IL-2. The functional in vivo relevance of our findings was highlighted by the immunohistochemical staining of tonsils, revealing the presence of CD4/CD35 [corrected] double positive lymphocytes mainly in the inter-follicular regions where direct contact between CD4+ T cells and B lymphocytes occurs. Regarding the in vivo relevance of the complement-dependent generation of regulatory T cells in secondary lymphoid organs we propose a scenario shown in the figure. The depicted process involves the sequential binding of locally produced C3 fragments to CD46 and CD35 [corrected] expressed on activated T cells, which - in the presence of excess IL-2 - leads to the development of Treg cells.