Loss of programmed death ligand-1 expression on donor T cells lessens acute graft-versus-host disease lethality

The PD-1/PD-L1 pathway plays an important role in regulation of alloimmune responses and in induction and maintenance of peripheral tolerance. Because GVHD is driven by donor T cells and PD-L1 expression can be markedly elevated on T cells during activation, we investigated the functional significance of PD-L1 expressed by donor T cells in regulating murine models of acute GVHD. PD-L1 expression was up-regulated on donor CD4 and CD8 T cells during GVHD. We considered the possibility that PD-L1 expression on activated donor T cells might inhibit GVHD by down regulating donor anti-host T cell responses, consistent with PD-L1 co-inhibitory activity when expressed on host parenchymal cells during GVHD. Surprisingly, T cell mediated GVHD lethality was markedly reduced in recipients of PD-L1-/- compared to WT donor T cells in both B6 to BALB/c model of GVHD(P<0.0001; Fig 1A) and in B6 to B10.BR model (P=0.0047; Fig 1B), suggesting that PD-L1 expression on donor T cells is involved in interactions that enhance T cell mediated effector function. Survival data confirmed that PD-L1-/- Teffs and not Tregs were responsible for reduced lethality in recipients of PD-L1-/- donor T cells (Fig 1C). During GVHD, PD-L1-/- donor CD4 and CD8 T cells had reduced expression of gut homing receptors (Fig 1D), and recipients of PD-L1-/- donor T cells had reduced T cell infiltration into lymphoid organs and gut, retained intestinal epithelial integrity, and had lower inflammatory cytokine production. PD-L1-/- donor CD4 and CD8 T cells had increased expression of multiple inhibitory receptors (Fig 1E, 1F), reduced T cell proliferation, and increased T cell apoptosis by transcriptional profiling and cell surface marker expression. Four pathways, including proteasome activity showed decreased expression in PD-L1-/- donor T cells. In vitro T cell activation in the presence of single (PD-L1:B7-1) vs. dual (PD-L1:B7-1 and PD-L1:PD-1) pathway blocking anti-PD-L1 mAb confirmed that T-T interaction between PD-1 and PD-L1 is important for proliferation and survival, whereas sensitive in vitro assays with supported lipid bilayers found no evidence for a functionally relevant cis interaction of PD-L1 and PD-1 on T cells. We found a significant increase in glucose transporter (GLUT1) expression in proliferating WT vs. PD-L1-/- donor CD4 and CD8 T cells, along with increased glycolysis, OXPHOS, glutamine consumption and glutamate production. We also observed increased fatty acid (FA) uptake and FA oxidation, and enhanced pharmacologic inhibition of FA oxidation in WT donor T cells, suggesting that PD-1:PD-L1 interactions are important for FA metabolism, which may further support T cell survival. Studies using stable isotope carbon tracers highlighted the divergent roles for glutamine and glucose in energy generation and biosynthetic pathways. Given the importance of acetyl-CoA as a high energy thioester intermediate in the TCA cycle and a lipogenic precursor for T cells undergoing expansion, significantly enhanced production of acetyl-CoA from glucose by WT donor T cells support the notion that PD-L1 on T cells promotes clonal expansion of alloreactive T cells. In summary, these data are the first to show that PD-L1 expression on donor T cells can provide positive signals for T cell survival, activation, and metabolism. Greater understanding of the function of PD-L1 expression by activated donor T cells will provide new insight into the regulation of GVHD and suggest strategies to selectively inhibit PD-L1 on donor T cells that may be clinically useful to prevent GVHD

Programmed death ligand-1 expression on donor T cells drives graft-versus-host disease lethality.

Programmed death ligand-1 (PD-L1) interaction with PD-1 induces T cell exhaustion and is a therapeutic target to enhance immune responses against cancer and chronic infections. In murine bone marrow transplant models, PD-L1 expression on host target tissues reduces the incidence of graft-versus-host disease (GVHD). PD-L1 is also expressed on T cells; however, it is unclear whether PD-L1 on this population influences immune function. Here, we examined the effects of PD-L1 modulation of T cell function in GVHD. In patients with severe GVHD, PD-L1 expression was increased on donor T cells. Compared with mice that received WT T cells, GVHD was reduced in animals that received T cells from Pdl1-/- donors. PD-L1-deficient T cells had reduced expression of gut homing receptors, diminished production of inflammatory cytokines, and enhanced rates of apoptosis. Moreover, multiple bioenergetic pathways, including aerobic glycolysis, oxidative phosphorylation, and fatty acid metabolism, were also reduced in T cells lacking PD-L1. Finally, the reduction of acute GVHD lethality in mice that received Pdl1-/- donor cells did not affect graft-versus-leukemia responses. These data demonstrate that PD-L1 selectively enhances T cell-mediated immune responses, suggesting a context-dependent function of the PD-1/PD-L1 axis, and suggest selective inhibition of PD-L1 on donor T cells as a potential strategy to prevent or ameliorate GVHD

A Strong B-cell Response Is Part of the Immune Landscape in Human High-Grade Serous Ovarian Metastases

This work was funded by Cancer Research UK (A16354), Swiss Cancer League (BIL KLS2883-02-2012); the European Research Council (ERC322566); Barts and The London Charity (467/1307 to ML and BLT 297/2249 to 2 PRC); Bloodwise (Bennett Fellowship to MC; ref 12002); UNC University Cancer Research Fund and UNC Oncology Clinical Translational Research Training Program (5K12CA120780; to BV); National Cancer Institute (P50 CA058223; to JSS)

Stromal Interferon-γ Signaling and Cross-Presentation Are Required to Eliminate Antigen-Loss Variants of B Cell Lymphomas in Mice

To study mechanisms of T cell-mediated rejection of B cell lymphomas, we developed a murine lymphoma model wherein three potential rejection antigens, human c-MYC, chicken ovalbumin (OVA), and GFP are expressed. After transfer into wild-type mice 60–70% of systemically growing lymphomas expressing all three antigens were rejected; lymphomas expressing only human c-MYC protein were not rejected. OVA expressing lymphomas were infiltrated by T cells, showed MHC class I and II upregulation, and lost antigen expression, indicating immune escape. In contrast to wild-type recipients, 80–100% of STAT1-, IFN-γ-, or IFN-γ receptor-deficient recipients died of lymphoma, indicating that host IFN-γ signaling is critical for rejection. Lymphomas arising in IFN-γ- and IFN-γ-receptor-deficient mice had invariably lost antigen expression, suggesting that poor overall survival of these recipients was due to inefficient elimination of antigen-negative lymphoma variants. Antigen-dependent eradication of lymphoma cells in wild-type animals was dependent on cross-presentation of antigen by cells of the tumor stroma. These findings provide first evidence for an important role of the tumor stroma in T cell-mediated control of hematologic neoplasias and highlight the importance of incorporating stroma-targeting strategies into future immunotherapeutic approaches

Bacteremia after hematopoietic stem cell transplantation: incidence and predictive value of surveillance cultures.

We studied 622 transplants undertaken between 1982 and 2001 to: (1) determine the incidence, timing and etiology of bacteremias, and (2) examine the ability of routine surveillance cultures to predict bacteremias. A total of 404 episodes (0.65 episode per patient) occurred in 248 patients, due to coagulase-negative staphylococci (n=171, 42%), Gram-negative bacteria (n=129, 32%), streptococci (n=48, 12%), other Gram-positive bacteria (n=33, 8%), anaerobes (n=9, 2%) and fungi (n=14, 3%). Bacteremias were more frequent in allogeneic (0.96 episode/patient) compared to autologous (0.44) transplants (P<0.0001). The overall incidence decreased from 0.92 episode/patient until 1990 to 0.66 in 1991-1996 and 0.55 in 1997-2001 (P<0.0001), but this was only observed in autologous transplants. Among them, 212 (53%) occurred before hospital discharge and 192 (47%) thereafter. This proportion was lower for coagulase-negative staphylococci, other Gram-positive bacteria and Gram-negative bacteria compared to other agents (P=0.001). In 50% of the cases, the agent responsible for the bacteremic episode was present in routine surveillance cultures previously. In conclusion: (1) bacteremias remain a frequent complication, particularly in allogeneic transplantation, even long after hospital discharge; (2) routine surveillance cultures can predict bacteremias in 50% of the cases, but the practical impact of this observation is limited in view of the costs

Bim regulates the survival and suppressive capability of CD8+ FOXP3+ regulatory T cells during murine GVHD

peer reviewedCD8+ Foxp3+ T cells (Tregs) are a potent regulatory population whose functional and ontological similarities to CD4+ Fox3+ T cells have not been well delineated. Using an experimental model of graft-versus-host disease (GVHD), we observed that CD8+ Tregs were significantly less potent than CD4+ Tregs for the suppression of GVHD. To define the mechanistic basis for this observation, we examined the T-cell repertoire and the transcriptional profile of in vivo-derived CD4+ and CD8+ Tregs that emerged early during this disease. Polyclonal and alloantigen-induced CD8+ Tregs had repertoire diversity that was similar to that of conventional CD8+ T cells, indicating that a restricted repertoire was not the proximate cause of decreased suppression. Transcriptional profiling revealed that CD8+ Tregs possessed a canonical Treg transcriptional signature that was similar to that observed in CD4+ Tregs, yet distinct from conventional CD8+ T cells. Pathway analysis, however, demonstrated that CD8+ Tregs had differential gene expression in pathways involved in cell death and survival. This was further confirmed by detailed mRNA sequence analysis and protein expression studies, which demonstrated that CD8+ Tregs had increased expression of Bim and reduced expression of Mcl-1. Transplantation with CD8+ Foxp3+ Bim-/- Tregs resulted in prolonged Treg survival and reduced GVHD lethality compared with wild-type CD8+ Tregs, providing functional confirmation that increased expression of Bim was responsible for reduced in vivo efficacy. Thus, Bim regulates the survival and suppressive capability of CD8+ Tregs, which may have implications for their use in regulatory T-cell therapy