Epstein-Barr virus (EBV) infection causes B cell lymphomas in humanized mouse models and contributes to a variety of different types of human lymphomas. T cells directed against viral antigens play a critical role in controlling EBV infection, and EBV-positive lymphomas are particularly common in immunocompromised hosts. We previously showed that EBV induces B cell lymphomas with high frequency in a cord blood-humanized mouse model in which EBV-infected human cord blood is injected intraperitoneally into NOD/LtSz-scid/IL2Rγnull (NSG) mice. Since our former studies showed that it is possible for T cells to control the tumors in another NSG mouse model engrafted with both human fetal CD34+ cells and human thymus and liver, here we investigated whether monoclonal antibodies that block the T cell inhibitory receptors, PD-1 and CTLA-4, enhance the ability of cord blood T cells to control the outgrowth of EBV-induced lymphomas in the cord-blood humanized mouse model. We demonstrate that EBV-infected lymphoma cells in this model express both the PD-L1 and PD-L2 inhibitory ligands for the PD-1 receptor, and that T cells express the PD-1 and CTLA-4 receptors. Furthermore, we show that the combination of CTLA-4 and PD-1 blockade strikingly reduces the size of lymphomas induced by a lytic EBV strain (M81) in this model, and that this anti-tumor effect requires T cells. PD-1/CTLA-4 blockade markedly increases EBV-specific T cell responses, and is associated with enhanced tumor infiltration by CD4+ and CD8+ T cells. In addition, PD-1/CTLA-4 blockade decreases the number of both latently, and lytically, EBV-infected B cells. These results indicate that PD-1/CTLA-4 blockade enhances the ability of cord blood T cells to control outgrowth of EBV-induced lymphomas, and suggest that PD-1/CTLA-4 blockade might be useful for treating certain EBV-induced diseases in humans.
SUMMARY
Invariant natural killer T (iNKT) cells are innate T lymphocytes that promote host defense against a variety of microbial pathogens. Whether microbial ligands are required for their protective effects remains unclear. Here, we show that iNKT cells stimulate human-monocyte-derived dendritic cells (DCs) to produce inflammatory mediators in a manner that does not require the presence of microbial compounds. Interleukin 2 (IL-2)-exposed iNKT cells selectively induced repeated cytoplasmic Ca2+ fluxes in DCs that were dependent on signaling by the P2X7 purinergic receptor and mediated by ATP released during iNKT-DC interactions. Exposure to iNKT cells led to DC cyclooxygenase 2 (PTGS2) gene transcription, and release of PGE2 that was associated with vascular permeabilization in vivo. Additionally, soluble factors were released that induced neutrophil recruitment and activation and enhanced control of Candida albicans. These results suggest that sterile interactions between iNKT cells and monocyte-derived DCs lead to the production of non-redundant inflammatory mediators that promote neutrophil responses.
The cytokine IL-1β plays a central role in inflammatory responses that are initiated by microbial challenges, as well as in those that are due to endogenous processes (often called “sterile” inflammation). IL-1β secretion that occurs independently of microbial stimulation is typically associated with the presence of endogenous alarmins, such as extracellular ATP (an indicator of cytopathic damage). Here we show that IL-2 activated human iNKT cells stimulate the secretion of IL-1β protein by human peripheral blood monocytes in a manner that requires neither the presence of microbial compounds nor signaling through the extracellular ATP receptor P2X7. Monocyte IL-1β production was specifically induced by iNKT cells, since similarly activated polyclonal autologous T cells did not have this effect. Secretion of IL-1β protein occurred rapidly (within 3-4 hours), and required cell contact between the iNKT cells and monocytes. Similar to IL-1β production induced by TLR stimulation, the iNKT-induced pathway appeared to entail a two-step process involving NFκB signaling and IL1B gene transcription, as well as assembly of the NLRP3 inflammasome and activation of caspase 1. However, in contrast to the classical inflammasome-mediated pathway of IL-1β production, activation of monocytes via P2X7 was dispensable for iNKT-induced IL-1β secretion and potassium efflux was not required. Moreover, the iNKT-induced effect involved caspase 8 activity, yet induced little monocyte death. These results suggest that IL-2 activated human iNKT cells induce monocytes to produce IL-1β through a distinctive pathway that does not require the presence of microbial danger signals or alarmins associated with cytopathic damage.
By binding to its ligand ICAM-1, LFA-1 is known to mediate both adhesion and costimulatory signaling for T cell activation. The constitutively high LFA-1 cell surface expression of invariant NKT (iNKT) cells has been shown to be responsible for their distinctive tissue homing and residency within ICAM-rich endothelial vessels. However, the functional impact of LFA-1 on the activation of iNKT cells and other innate T lymphocyte subsets has remained largely unexplored. In particular, it is not clear whether LFA-1 contributes to innate-like pathways of T cell activation, such as IFN-γ secretion in response to IL-12. Using a recombinant ICAM-1-Fc fusion protein to stimulate human iNKT cells in the absence of APCs, we show that LFA-1 engagement enhances their IL-12-driven IFN-γ production. Surprisingly, exposure to high densities of ICAM-1 was also sufficient to activate iNKT cell cytokine secretion independently of IL-12 and associated JAK/STAT signaling. LFA-1 engagement induced elevated cytoplasmic Ca and rapid ERK phosphorylation in iNKT cells, and the resulting IFN-γ secretion was dependent on both of these pathways. Analysis of freshly isolated human PBMC samples revealed that a fraction of lymphocytes that showed elevated LFA-1 cell surface expression produced IFN-γ in response to plate-bound ICAM-1-Fc. A majority of the responding cells were T cells, with the remainder NK cells. The responding T cells included iNKT cells, MAIT cells, and Vδ2 γδ T cells. These results delineate a novel integrin-mediated pathway of IFN-γ secretion that is a shared feature of innate lymphocytes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.