Butyrophilin 3A1 binds phosphorylated antigens and stimulates human γδ T cells.

Human T cells that express a T cell antigen receptor (TCR) containing γ-chain variable region 9 and δ-chain variable region 2 (Vγ9Vδ2) recognize phosphorylated prenyl metabolites as antigens in the presence of antigen-presenting cells but independently of major histocompatibility complex (MHC), the MHC class I-related molecule MR1 and antigen-presenting CD1 molecules. Here we used genetic approaches to identify the molecule that binds and presents phosphorylated antigens. We found that the butyrophilin BTN3A1 bound phosphorylated antigens with low affinity, at a stoichiometry of 1:1, and stimulated mouse T cells with transgenic expression of a human Vγ9Vδ2 TCR. The structures of the BTN3A1 distal domain in complex with host- or microbe-derived phosphorylated antigens had an immunoglobulin-like fold in which the antigens bound in a shallow pocket. Soluble Vγ9Vδ2 TCR interacted specifically with BTN3A1-antigen complexes. Accordingly, BTN3A1 represents an antigen-presenting molecule required for the activation of Vγ9Vδ2 T cells.

An abnormal phenotype of lung Vγ9Vδ2 T cells impairs their responsiveness in tuberculosis patients.

Antigen-specific γδ T cells represent an early innate defense known to play an important role in anti-mycobacterial immunity. We have investigated the immune functions of Vγ9Vδ2 T cells from Broncho-Alveolar lavages (BAC) samples of active TB patients. We observed that BAC Vγ9Vδ2 T cells presented a strong down-modulation of CD3 expression compared with Vγ9Vδ2 T cells from peripheral blood. Furthermore, Vγ9Vδ2 T cells mainly showed a central memory phenotype, expressed high levels of NK inhibitory receptors and TEMRA cells showed low expression of CD16 compared to circulating Vγ9Vδ2 T cells. Interestingly, the ability of BAC Vγ9Vδ2 T cells to respond to antigen stimulation was dramatically reduced, differently from blood counterpart. These observations indicate that γδ T cell functions are specifically impaired in situ by active TB, suggesting that the alveolar ambient during tuberculosis may affect resident γδ T cells in comparison to circulating cells.

MAIT and Vδ2 unconventional T cells are supported by a diverse intestinal microbiome and correlate with favorable patient outcome after allogeneic HCT.

Microbial diversity is associated with improved outcomes in recipients of allogeneic hematopoietic cell transplantation (allo-HCT), but the mechanism underlying this observation is unclear. In a cohort of 174 patients who underwent allo-HCT, we demonstrate that a diverse intestinal microbiome early after allo-HCT is associated with an increased number of innate-like mucosal-associated invariant T (MAIT) cells, which are in turn associated with improved overall survival and less acute graft-versus-host disease (aGVHD). Immune profiling of conventional and unconventional immune cell subsets revealed that the prevalence of Vδ2 cells, the major circulating subpopulation of γδ T cells, closely correlated with the frequency of MAIT cells and was associated with less aGVHD. Analysis of these populations using both single-cell transcriptomics and flow cytometry suggested a shift toward activated phenotypes and a gain of cytotoxic and effector functions after transplantation. A diverse intestinal microbiome with the capacity to produce activating ligands for MAIT and Vδ2 cells appeared to be necessary for the maintenance of these populations after allo-HCT. These data suggest an immunological link between intestinal microbial diversity, microbe-derived ligands, and maintenance of unconventional T cells.

γδ T cells cross-link innate and adaptive immunity in Mycobacterium tuberculosis infection.

Protective immunity against mycobacterial infections such as Mycobacterium tuberculosis is mediated by interactions between specific T cells and activated antigen presenting cells. To date, many aspects of mycobacterial immunity have shown that innate cells could be the key elements that substantially may influence the subsequent adaptive host response. During the early phases of infection, innate lymphocyte subsets play a pivotal role in this context. Here we summarize the findings of recent investigations on γδ T lymphocytes and their role in tuberculosis immunity.

Microbiota stimulation generates LCMV-specific memory CD8+ T cells in SPF mice and determines their TCR repertoire during LCMV infection.

Both mouse and human harbour memory phenotype CD8+ T cells specific for antigens in hosts that have not been previously exposed to these antigens. The origin and the nature of the stimuli responsible for generation of CD44hi CD8+ T cells in specific pathogen-free (SPF) mice remain controversial. It is known that microbiota plays a crucial role in the prevention and resolution of systemic infections by influencing myelopoiesis, regulating dendritic cells, inflammasome activation and promoting the production of type I and II interferons. By contrast, here we suggest that microbiota has a direct effect on generation of memory phenotype CD44hiGP33+CD8+ T cells. In SPF mice, it generates a novel GP33+CD44hiCD8+ T cell sub-population associating the properties of innate and genuine memory cells. These cells are highly enriched in the bone marrow, proliferate rapidly and express immediate effector functions. They dominate the response to LCMV and express particular TCRß chains. The sequence of these selected TCRß chains overlaps with that of GP33+CD8+ T cells directly selected by microbiota in the gut epithelium of SPF mice, demonstrating a common selection mechanism in gut and peripheral CD8+ T cell pool. Therefore microbiota has a direct role in priming T cell immunity in SPF mice and in the selection of TCRß repertoires during systemic infection. We identify a mechanism that primes T cell immunity in SPF mice and may have a major role in colonization resistance and protection from infection.

"Shock and kill" effects of class I-selective histone deacetylase inhibitors in combination with the glutathione synthesis inhibitor buthionine sulfoximine in cell line models for HIV-1 quiescence.

Latently infected, resting memory CD4+ T cells and macrophages represent a major obstacle to the eradication of HIV-1. For this purpose, "shock and kill" strategies have been proposed (activation of HIV-1 followed by stimuli leading to cell death). Histone deacetylase inhibitors (HDACIs) induce HIV-1 activation from quiescence, yet class/isoform-selective HDACIs are needed to specifically target HIV-1 latency. We tested 32 small molecule HDACIs for their ability to induce HIV-1 activation in the ACH-2 and U1 cell line models. In general, potent activators of HIV-1 replication were found among non-class selective and class I-selective HDACIs. However, class I selectivity did not reduce the toxicity of most of the molecules for uninfected cells, which is a major concern for possible HDACI-based therapies. To overcome this problem, complementary strategies using lower HDACI concentrations have been explored. We added to class I HDACIs the glutathione-synthesis inhibitor buthionine sulfoximine (BSO), in an attempt to create an intracellular environment that would facilitate HIV-1 activation. The basis for this strategy was that HIV-1 replication decreases the intracellular levels of reduced glutathione, creating a pro-oxidant environment which in turn stimulates HIV-1 transcription. We found that BSO increased the ability of class I HDACIs to activate HIV-1. This interaction allowed the use of both types of drugs at concentrations that were non-toxic for uninfected cells, whereas the infected cell cultures succumbed more readily to the drug combination. These effects were associated with BSO-induced recruitment of HDACI-insensitive cells into the responding cell population, as shown in Jurkat cell models for HIV-1 quiescence. The results of the present study may contribute to the future design of class I HDACIs for treating HIV-1. Moreover, the combined effects of class I-selective HDACIs and the glutathione synthesis inhibitor BSO suggest the existence of an Achilles' heel that could be manipulated in order to facilitate the "kill" phase of experimental HIV-1 eradication strategies.

Calcineurin-mediated IL-2 production by CD11chighMHCII+ myeloid cells is crucial for intestinal immune homeostasis.

The intestinal immune system can respond to invading pathogens yet maintain immune tolerance to self-antigens and microbiota. Myeloid cells are central to these processes, but the signaling pathways that underlie tolerance versus inflammation are unclear. Here we show that mice lacking Calcineurin B in CD11chighMHCII+ cells (Cnb1 CD11c mice) spontaneously develop intestinal inflammation and are susceptible to induced colitis. In these mice, colitis is associated with expansion of T helper type 1 (Th1) and Th17 cell populations and a decrease in the number of FoxP3+ regulatory T (Treg) cells, and the pathology is linked to the inability of intestinal Cnb1-deficient CD11chighMHCII+ cells to express IL-2. Deleting IL-2 in CD11chighMHCII+ cells induces spontaneous colitis resembling human inflammatory bowel disease. Our findings identify that the calcineurin-NFAT-IL-2 pathway in myeloid cells is a critical regulator of intestinal homeostasis by influencing the balance of inflammatory and regulatory responses in the mouse intestine.

IL-15-dependent balance between Foxp3 and RORγt expression impacts inflammatory bowel disease.

The ability of CD4+ T cells to change their phenotype and to specialize into different functional subsets may enhance the risk of autoimmune diseases. Here we investigate how a pleiotropic cytokine interleukin (IL)-15 may modify the functional commitment of CD4+ T cells expressing the lineage-associated transcription factors: forkhead box P3 (Foxp3; Treg) and RORγt (Th17) in the context of inflammatory bowel disease (IBD). We demonstrate in mice that impaired delivery of IL-15 to CD4+ T cells in the colon downmodulates Foxp3 expression (diminishing STAT5 phosphorylation) and enhances RORγt expression (by upregulating the expression of Runx1). In consequence, CD4+ T cells deprived of IL-15 rapidly trigger IBD characterized by enhanced production of pro-inflammatory cytokines (interferon-γ, IL-6) and accumulation of Th1/Th17 cells. Overall, our findings indicate a potentially beneficial role of IL-15 in IBD by fine-tuning the balance between Treg and Th17 cells and controlling intestinal inflammation.

Granulocytic myeloid derived suppressor cells expansion during active pulmonary tuberculosis is associated with high nitric oxide plasma level.

Tuberculosis (TB) is still the principal cause of death caused by a single infectious agent, and the balance between the bacillus and host defense mechanisms reflects the different manifestations of the pathology. The aim of this work was to study the role of myeloid-derived suppressor cells (MDSCs) during active pulmonary tuberculosis at the site of infection. We observed an expansion of MDSCs in the lung and blood of patients with active TB, which are correlated with an enhanced amount of nitric oxide in the plasma. We also found that these cells have the remarkable ability to suppress T-cell response, suggesting an important role in the modulation of the immune response against TB. Interestingly, a trend in the diminution of MDSCs was found after an efficacious anti-TB therapy, suggesting that these cells may be used as a potential biomarker for monitoring anti-TB therapy efficacy.

Evaluation of the antiretroviral effects of a PEG-conjugated peptide derived from human CD38.

OBJECTIVE: Cell infection by HIV-1 is inhibited by both the expression of CD38 and a soluble peptide (sCD38p) corresponding to its extracellular membrane-proximal amino acid sequence (amino acids 51 - 74). We show here the effects of PEG conjugation to sCD38p and provide new insights into the mechanisms behind the anti-HIV-1 effects of CD38 and derived peptides. RESEARCH DESIGN/METHODS: In-vitro and in-silico study. RESULTS: PEGylation of sCD38p increased its ability to inhibit replication of HIV-1 in MT-4 cells and syncytia formation in cocultures of MT-2 and persistently HIV-1(IIIB)-infected H9(IIIB) cells. In silico modeling suggests that sCD38p and CD4 form stable heterodimers involving, among others, an interaction between lysine 57 (K57) of CD38 and a groove in the CD4 receptor, which, in CD4/gp120 complexes, is partially occupied by a lysine residue of the HIV-1 envelope glycoprotein. K57 substitution with a glycine in sCD38p impaired its ability to inhibit syncytia formation in MT-2/H9(IIIB) cell cocultures and gp120 binding to CD4 in a mouse T cell line expressing human but not mouse CD4. CONCLUSIONS: PEGylation significantly improves the anti-HIV-1 activity of sCD38p, whose effect is probably due to competition with gp120 for a common binding site on CD4 although other mechanisms cannot be excluded so far. The inhibitory concentrations of the sCD38p-PEG as well as its poor toxicity, merit further consideration in anti-HIV-1 strategies.

Response of feline immunodeficiency virus (FIV) to tipranavir may provide new clues for development of broad-based inhibitors of retroviral proteases acting on drug-resistant HIV-1.

The feline AIDS model for HIV-1 treatment failed in the 1990s, due to structural features resembling protease inhibitor (PI) resistant HIV-1 variants. Widespread drug-resistance to PIs now invokes the possibility of rescuing feline immunodeficiency virus (FIV) as a model for PI treatment. We here analyzed susceptibility of FIV to second generation PIs, lopinavir, atazanavir, and the structurally unrelated non-peptidic PI tipranavir. We found that FIV protease resembles HIV-1 protease drug resistance mutations limiting binding of lopinavir and atazanavir but not tipranavir. All three PIs were found to inhibit FIV replication in a concentration-dependent manner, but only tipranavir inhibited FIV similarly to HIV-1. This drug inhibited FIV synergistically with ritonavir. Inhibition of protease activity was confirmed by Western blot analysis. In molecular docking simulations, tipranavir displayed energetically favorable interactions with the catalytic cavity of the mature dimeric FIV protease. The calculated hydrogen bond network was similar to that found in HIV-1 protease/tipranavir complexes and involved atoms in the protein backbone. We also modeled the interaction of tipranavir with an immature protease monomer, suggesting that inhibition of protease dimerization may be a secondary modality for FIV inhibition by tipranavir. In conclusion, tipranavir is the first FDA-approved non-reverse transcriptase inhibitor of HIV-1 to show anti-FIV properties. The tipranavir response by FIV may 1) support the idea of using FIV as a small animal model for PI-resistant HIV-1, thus expanding access to animal AIDS models; and 2) pave the way for development of novel broad-based inhibitors for treatment of drug resistant HIV-1.