Butyrophilin-2A1 Directly Binds Germline-Encoded Regions of the Vγ9Vδ2 TCR and Is Essential for Phosphoantigen Sensing.

Vγ9Vδ2 T cells respond in a TCR-dependent fashion to both microbial and host-derived pyrophosphate compounds (phosphoantigens, or P-Ag). Butyrophilin-3A1 (BTN3A1), a protein structurally related to the B7 family of costimulatory molecules, is necessary but insufficient for this process. We performed radiation hybrid screens to uncover direct TCR ligands and cofactors that potentiate BTN3A1's P-Ag sensing function. These experiments identified butyrophilin-2A1 (BTN2A1) as essential to Vγ9Vδ2 T cell recognition. BTN2A1 synergised with BTN3A1 in sensitizing P-Ag-exposed cells for Vγ9Vδ2 TCR-mediated responses. Surface plasmon resonance experiments established Vγ9Vδ2 TCRs used germline-encoded Vγ9 regions to directly bind the BTN2A1 CFG-IgV domain surface. Notably, somatically recombined CDR3 loops implicated in P-Ag recognition were uninvolved. Immunoprecipitations demonstrated close cell-surface BTN2A1-BTN3A1 association independent of P-Ag stimulation. Thus, BTN2A1 is a BTN3A1-linked co-factor critical to Vγ9Vδ2 TCR recognition. Furthermore, these results suggest a composite-ligand model of P-Ag sensing wherein the Vγ9Vδ2 TCR directly interacts with both BTN2A1 and an additional ligand recognized in a CDR3-dependent manner.

A Photo-Crosslinkable Biotin Derivative of the Phosphoantigen (E)-4-Hydroxy-3-Methylbut-2-Enyl Diphosphate (HMBPP) Activates Vγ9Vδ2 T Cells and Binds to the HMBPP Site of BTN3A1.

Vγ9Vδ2 T cells play an important role in the cross talk of the innate and adaptive immune system. For their activation by phosphoantigens (PAgs), both cell surface receptors, the eponymous Vγ9Vδ2 T cell antigen receptors (Vγ9Vδ2 TCRs) on Vγ9Vδ2 T cells and butyrophilin 3A1 (BTN3A1) on the phosphoantigen-"presenting" cell, are mandatory. To find yet undetected but further contributing proteins, a biotinylated, photo-crosslinkable benzophenone probe BioBP-HMBPP (2) was synthesized from a known allyl alcohol in nine steps and overall 16 % yield. 2 is based on the picomolar PAg (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP, 1). Laser irradiation of 2 at 308 nm initiated the photo-crosslinking reaction with proteins. When the B30.2 domain of BTN3A1, which contains a positively charged PAg-binding pocket, was exposed to increasing amounts of HMBPP (1), labeling by BioBP-HMBPP (2) was reduced significantly. Because BSA labeling was not impaired, 2 clearly binds to the same site as natural ligand 1. Thus, BioBP-HMBPP (2) is a suitable tool to identify co-ligands or receptors involved in PAg-mediated T cell activation.

Successful adoptive transfer and in vivo expansion of haploidentical γδ T cells.

BACKGROUND: The primary aim of this pilot study was to determine the feasibility and safety of an adoptive transfer and in vivo expansion of human haploidentical γδ T lymphocytes. METHODS: Patients with advanced haematological malignancies who are not eligible for allogeneic transplantation received peripheral blood mononuclear cells from half-matched family donors. For that, a single unstimulated leukapheresis product was incubated with both the anti-CD4 and anti-CD8 antibodies conjugated to paramagnetic particles. The depletion procedure was performed on a fully automated CliniMACS device according to the manufacturer's instructions. On average, patients received 2.17 × 106/kg (range 0.9-3.48) γδ T cells with <1% CD4- or CD8-positive cells remaining in the product. All patients received prior lymphopenia-inducing chemotherapy (fludarabine 20-25 mg/m² day -6 until day -2 and cyclophosphamide 30-60 mg/kg day -6 and -5) and were treated with 4 mg zoledronate on day 0 and 1.0 x 106 IU/m² IL-2 on day +1 until day +6 for the induction of γδ T cell proliferation in vivo. RESULTS: This resulted in a marked in vivo expansion of donor γδ T cells and, to a lower extent, natural killer cells and double-negative αß T cells (mean 68-fold, eight-fold, and eight-fold, respectively). Proliferation peaked by around day +8 and donor cells persisted up to 28 days. Although refractory to all prior therapies, three out of four patients achieved a complete remission, which lasted for 8 months in a patient with plasma cell leukaemia. One patient died from an infection 6 weeks after treatment. CONCLUSION: This pilot study shows that adoptive transfer and in vivo expansion of haploidentical γδ T lymphocytes is feasible and suggests a potential role of these cells in the treatment of haematological diseases.

Division of labor and cooperation between different butyrophilin proteins controls phosphoantigen-mediated activation of human γδ T cells.

Butyrophilin (BTN)-3A and BTN2A1 molecules control TCR-mediated activation of human Vγ9Vδ2 T-cells triggered by phosphoantigens (PAg) from microbes and tumors, but the molecular rules governing antigen sensing are unknown. Here we establish three mechanistic principles of PAg-action. Firstly, in humans, following PAg binding to the BTN3A1-B30.2 domain, Vγ9Vδ2 TCR triggering involves the V-domain of BTN3A2/BTN3A3. Moreover, PAg/B30.2 interaction, and the critical γδ-T-cell-activating V-domain, localize to different molecules. Secondly, this distinct topology as well as intracellular trafficking and conformation of BTN3A heteromers or ancestral-like BTN3A homomers are controlled by molecular interactions of the BTN3 juxtamembrane region. Finally, the ability of PAg not simply to bind BTN3A-B30.2, but to promote its subsequent interaction with the BTN2A1-B30.2 domain, is essential for T-cell activation. Defining these determinants of cooperation and division of labor in BTN proteins deepens understanding of PAg sensing and elucidates a mode of action potentially applicable to other BTN/BTNL family members.

A distinct topology of BTN3A IgV and B30.2 domains controlled by juxtamembrane regions favors optimal human γδ T cell phosphoantigen sensing.

Butyrophilin (BTN)-3A and BTN2A1 molecules control the activation of human Vγ9Vδ2 T cells during T cell receptor (TCR)-mediated sensing of phosphoantigens (PAg) derived from microbes and tumors. However, the molecular rules governing PAg sensing remain largely unknown. Here, we establish three mechanistic principles of PAg-mediated γδ T cell activation. First, in humans, following PAg binding to the intracellular BTN3A1-B30.2 domain, Vγ9Vδ2 TCR triggering involves the extracellular V-domain of BTN3A2/BTN3A3. Moreover, the localization of both protein domains on different chains of the BTN3A homo-or heteromers is essential for efficient PAg-mediated activation. Second, the formation of BTN3A homo-or heteromers, which differ in intracellular trafficking and conformation, is controlled by molecular interactions between the juxtamembrane regions of the BTN3A chains. Finally, the ability of PAg not simply to bind BTN3A-B30.2, but to promote its subsequent interaction with the BTN2A1-B30.2 domain, is essential for T-cell activation. Defining these determinants of cooperation and the division of labor in BTN proteins improves our understanding of PAg sensing and elucidates a mode of action that may apply to other BTN family members.

Reduced expression of the mevalonate pathway enzyme farnesyl pyrophosphate synthase unveils recognition of tumor cells by Vgamma9Vdelta2 T cells.

Human Vgamma9Vdelta2 T cells are characterized by a unique specificity for certain tumors (e.g., Daudi), cells presenting so-called phosphoantigens such as isopentenyl pyrophosphate (IPP), or cells treated with aminobisphosphonates. We now report conversion of hematopoietic and nonhematopoietic tumor cell lines into Vgamma9Vdelta2 T cell activators by means of short hairpin RNA-mediated knockdown of expression of the IPP-consuming enzyme, farnesyl pyrophosphate synthase (FPPS). FPPS knockdown cells activated Vgamma9Vdelta2 T cells, as measured by increased levels of CD69 and CD107a, killing of FPPS knockdown cells, and induction of IFN-gamma secretion. The IPP-synthesis-inhibiting drug mevastatin reduced Vgamma9Vdelta2 T cell activation by FPPS knockdown cells but not activation by the phosphoantigen bromohydrin pyrophosphate. In conclusion, our data support the concept of Vgamma9Vdelta2 T cells as sensors of a dysregulated isoprenoid metabolism and suggest therapeutic down-modulation of FPPS expression as an additional tool to target tumor cells to Vgamma9Vdelta2 T cell-mediated immunosurveillance.

Inhibition of phosphoantigen-mediated gammadelta T-cell proliferation by CD4+ CD25+ FoxP3+ regulatory T cells.

Tumour growth promotes the expansion of CD4(+) CD25(+) FoxP3(+) regulatory T cells (Tregs) which suppress various arms of immune responses and might therefore contribute to tumour immunosurveillance. In this study, we found an inverse correlation between circulating Treg frequencies and phosphoantigen-induced gammadelta T-cell proliferation in cancer patients, which prompted us to address the role of Tregs in controlling the gammadelta T-cell arm of innate immune responses. In vitro, human Treg-peripheral blood mononuclear cell (PBMC) co-cultures strongly inhibited phosphoantigen-induced proliferation of gammadelta T cells and depletion of Tregs restored the impaired phosphoantigen-induced gammadelta T-cell proliferation of cancer patients. Tregs did not suppress other effector functions of gammadelta T cells such as cytokine production or cytotoxicity. Our experiments indicate that Tregs do not mediate their suppressive activity via a cell-cell contact-dependent mechanism, but rather secrete a soluble non-proteinaceous factor, which is independent of known soluble factors interacting with amino acid depletion (e.g. arginase-diminished arginine and indolamine 2,3-dioxygenase-diminished tryptophan) or nitric oxide (NO) production. However, the proliferative activity of alphabeta T cells was not affected by this cell-cell contact-independent suppressive activity induced by Tregs. In conclusion, these findings indicate a potential new mechanism by which Tregs can specifically suppress gammadelta T cells and highlight the strategy of combining Treg inhibition with subsequent gammadelta T-cell activation to enhance gammadelta T cell-mediated immunotherapy.

A comprehensive analysis of primary acute myeloid leukemia identifies biomarkers predicting susceptibility to human allogeneic Vγ9Vδ2 T cells.

Allogeneic innate lymphocytes such as Vγ9Vδ2 T cells are attractive candidates for cancer immunotherapy as they provide MHC-unrestricted antitumor activity without clinical evidence for inducing graft-versus-host disease (GvHD). However, current cellular immunotherapy approaches lack predictive biomarkers identifying patient cohorts most susceptible to immune attack. For this purpose we performed a comprehensive analysis of clinical, genetic, metabolic, and immunophenotypic features of 19 primary acute myeloid leukemia (AML) samples and correlated these factors with AML blast recognition by allogeneic Vγ9Vδ2 T cells. We show that 36% of primary AML samples were intrinsically susceptible to allogeneic Vγ9Vδ2 T cells. Among several evaluated features, only UL-16 binding protein 1 (ULBP1) expression (P<0.01) determines intrinsic AML susceptibility to allogeneic Vγ9Vδ2 T cells. Within the intrinsically resistant AML samples, pretreatment of AML blasts with nitrogen-containing bisphosphonates (NBP) significantly induced Vγ9Vδ2 T-cell cytotoxicity in 50% of AML samples, whereas 50% of AML samples were consistently refractory to γδ T-cell cytolysis. Activity of the mevalonate pathway (P<0.05) and myelomonocytic differentiation of AML (P<0.05) correlated with sensitivity of primary AML samples toward NBP pretreatment. In conclusion, this study identifies subsets of AML patients most likely to benefit from allogeneic Vγ9Vδ2 T-cell-mediated immunotherapy.

Tumor-promoting versus tumor-antagonizing roles of γδ T cells in cancer immunotherapy: results from a prospective phase I/II trial.

Emerging evidence suggests that nitrogen-containing bisphosphonates have direct and indirect anticancer effects including immunomodulatory effects. Using in vivo targeting of bisphosphonate-reactive γδ T cells by adding low-dose interleukin-2 to zoledronic acid, we evaluated the safety, pharmacodynamics, and antitumor activity of this immunotherapy approach in 21 adults with advanced malignancies (renal cell carcinoma [RCC], malignant melanoma, and acute myeloid leukemia). A total of 58 treatment cycles were administered and the median number of treatment cycles was 2.7 (range, 1 to 6). The regimen was well tolerated, with no grade 3 to 4 drug-related adverse events, except for fever. No objective responses were observed in both cohorts of solid tumors (RCC and malignant melanoma), whereas 2 patients with acute myeloid leukemia (25%) achieved objective tumor responses (partial remission). Pharmacodynamic analyses showed significant in vivo activation (interferon-γ production) and expansion of γδ T cells in all evaluable patients. High pretreatment serum vascular endothelial growth factor (VEGF) levels and an unexpected increase in VEGF induced by zoledronic acid plus low-dose interleukin-2 were correlated with the lack of a clinical response. In conclusion, this study indicates that immunotherapy-induced VEGF can limit clinical innate tumor immune responses, especially for angiogenesis-dependent solid tumors. Our data challenge the current cellular immunotherapy paradigms in the treatment of cancer.