Immune suppressive checkpoint interactions in the tumour microenvironment of primary liver cancers.

Liver cancer is one of the most prevalent cancers, and the third most common cause of cancer-related mortality worldwide. The therapeutic options for the main types of primary liver cancer-hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA)-are very limited. HCC and CCA are immunogenic cancers, but effective immune-mediated tumour control is prevented by their immunosuppressive tumour microenvironment. Despite the critical involvement of key co-inhibitory immune checkpoint interactions in immunosuppression in liver cancer, only a minority of patients with HCC respond to monotherapy using approved checkpoint inhibitor antibodies. To develop effective (combinatorial) therapeutic immune checkpoint strategies for liver cancer, in-depth knowledge of the different mechanisms that contribute to intratumoral immunosuppression is needed. Here, we review the co-inhibitory pathways that are known to suppress intratumoral T cells in HCC and CCA. We provide a detailed description of insights from preclinical studies in cellular crosstalk within the tumour microenvironment that results in interactions between co-inhibitory receptors on different T-cell subsets and their ligands on other cell types, including tumour cells. We suggest alternative immune checkpoints as promising targets, and draw attention to the possibility of combined targeting of co-inhibitory and co-stimulatory pathways to abrogate immunosuppression.

Modelling immune cytotoxicity for cholangiocarcinoma with tumour-derived organoids and effector T cells.

BACKGROUND: Immunotherapy with immune checkpoint inhibitors (ICIs) is being explored to improve cholangiocarcinoma (CCA) therapy. However, it remains difficult to predict which ICI will be effective for individual patients. Therefore, the aim of this study is to develop a co-culture method with patient-derived CCA organoids and immune cells, which could represent anti-cancer immunity in vitro. METHODS: CCA organoids were co-cultured with peripheral blood mononuclear cells or T cells. Flow cytometry, time-lapse confocal imaging for apoptosis, and quantification of cytokeratin 19 fragment (CYFRA) release were applied to analyse organoid and immune cell behaviour. CCA organoids were also cultured in immune cell-conditioned media to analyse the effect of soluble factors. RESULTS: The co-culture system demonstrated an effective anti-tumour organoid immune response by a decrease in live organoid cells and an increase in apoptosis and CYFRA release. Interpatient heterogeneity was observed. The cytotoxic effects could be mediated by direct cell-cell contact and by release of soluble factors, although soluble factors only decreased viability in one organoid line. CONCLUSIONS: In this proof-of-concept study, a novel CCA organoid and immune cell co-culture method was established. This can be the first step towards personalised immunotherapy for CCA by predicting which ICIs are most effective for individual patients.

Activated CD4+ T Cells and Highly Differentiated Alloreactive CD4+ T Cells Distinguish Operationally Tolerant Liver Transplantation Recipients.

Spontaneous operational tolerance to the allograft develops in a proportion of liver transplantation (LT) recipients weaned off immunosuppressive (IS) drugs. Several studies have investigated whether peripheral blood circulating T cells could play a role in the development or identify operational tolerance, but never characterized alloreactive T cells in detail due to the lack of a marker for these T cells. In this study, we comprehensively investigated phenotypic and functional characteristics of alloreactive circulating T cell subsets in tolerant LT recipients (n = 15) using multiparameter flow cytometry and compared these with LT recipients on IS drugs (n = 23) and healthy individuals (n = 16). Activation-induced CD137 was used as a marker for alloreactive T cells upon allogenic stimulation. We found that central and effector memory CD4+ T cells were hyporesponsive against donor and third-party splenocyte stimulation in tolerant LT recipients, whereas an overall hyperresponsiveness was observed in alloreactive terminally differentiated effector memory CD4+ T cells. In addition, elevated percentages of circulating activated T helper cells were observed in these recipients. Lastly, tolerant and control LT recipients did not differ in donor-specific antibody formation. In conclusion, a combination of circulating hyperresponsive highly differentiated alloreactive CD4+ T cells and circulating activated T helper cells could discriminate tolerant recipients from a larger group of LT recipients.

The biological process of lysine-tRNA charging is therapeutically targetable in liver cancer.

BACKGROUND & AIMS: Mature transfer RNAs (tRNA) charged with amino acids decode mRNA to synthesize proteins. Dysregulation of translational machineries has a fundamental impact on cancer biology. This study aims to map the tRNAome landscape in liver cancer patients and to explore potential therapeutic targets at the interface of charging amino acid with tRNA. METHODS: Resected tumour and paired tumour-free (TFL) tissues from hepatocellular carcinoma (HCC) patients (n = 69), and healthy liver tissues from organ transplant donors (n = 21), HCC cell lines, and cholangiocarcinoma (CC) patient-derived tumour organoids were used. RESULTS: The expression levels of different mature tRNAs were highly correlated and closely clustered within individual tissues, suggesting that different members of the tRNAome function cooperatively in protein translation. Interestingly, high expression of tRNA-Lys-CUU in HCC tumours was associated with more tumour recurrence (HR 1.1; P = .022) and worse patient survival (HR 1.1; P = .0037). The expression of Lysyl-tRNA Synthetase (KARS), the enzyme catalysing the charge of lysine to tRNA-Lys-CUU, was significantly upregulated in HCC tumour tissues compared to tumour-free liver tissues. In HCC cell lines, lysine deprivation, KARS knockdown or treatment with the KARS inhibitor cladosporin effectively inhibited overall cell growth, single cell-based colony formation and cell migration. This was mechanistically mediated by cell cycling arrest and induction of apoptosis. Finally, these inhibitory effects were confirmed in 3D cultured patient-derived CC organoids. CONCLUSIONS: The biological process of charging tRNA-Lys-CUU with lysine sustains liver cancer cell growth and migration, and is clinically relevant in HCC patients. This process can be therapeutically targeted and represents an unexplored territory for developing novel treatment strategies against liver cancer.

HHLA2 is expressed in pancreatic and ampullary cancers and increased expression is associated with better post-surgical prognosis.

BACKGROUND: HHLA2 is a recently discovered member of the B7-family of immune checkpoint molecules with limited expression in normal tissues but overexpression in several types of cancer. The aim was to determine the expression, prevalence and biological relevance of HHLA2 protein expression in two closely related human cancer types, namely pancreatic cancer and ampullary cancer. METHODS: HHLA2 expression levels were retrospectively determined by immunohistochemistry in tissue micro-arrays of surgically resected tumours of 122 pancreatic cancer patients and 72 patients with ampullary cancer of the pancreato-biliary subtype. RESULTS: HHLA2 was expressed at variable levels by tumour cells in 67% of pancreatic tumours and 93% of ampullary tumours. In the combined cohort high tumoural HHLA2 expression levels were significantly associated with delayed cancer recurrence and improved post-operative cancer-specific survival. The association of HHLA2 expression with cancer-specific survival and recurrence was statistically significant for the pancreatic cancer subgroup while a similar trend was found for the ampullary cancer subgroup. In multivariable analysis together with clinicopathologic characteristics, higher HHLA2 expression was an independent predictor of cancer-specific survival. CONCLUSION: The wide expression of HHLA2 in tumour cells and its association with cancer recurrence and patient survival suggest that HHLA2 represents a relevant immune checkpoint molecule in pancreatic and ampullary cancers.

Enrichment of the tumour immune microenvironment in patients with desmoplastic colorectal liver metastasis.

BACKGROUND: Patients with resected colorectal liver metastasis (CRLM) who display only the desmoplastic histopathological growth pattern (dHGP) exhibit superior survival compared to patients with any non-desmoplastic growth (non-dHGP). The aim of this study was to compare the tumour microenvironment between dHGP and non-dHGP. METHODS: The tumour microenvironment was investigated in three cohorts of chemo-naive patients surgically treated for CRLM. In cohort A semi-quantitative immunohistochemistry was performed, in cohort B intratumoural and peritumoural T cells were counted using immunohistochemistry and digital image analysis, and in cohort C the relative proportions of individual T cell subsets were determined by flow cytometry. RESULTS: One hundred and seventeen, 34, and 79 patients were included in cohorts A, B, and C, with dHGP being observed in 27%, 29%, and 15% of patients, respectively. Cohorts A and B independently demonstrated peritumoural and intratumoural enrichment of cytotoxic CD8+ T cells in dHGP, as well as a higher CD8+/CD4+ ratio (cohort A). Flow cytometric analysis of fresh tumour tissues in cohort C confirmed these results; dHGP was associated with higher CD8+ and lower CD4+ T cell subsets, resulting in a higher CD8+/CD4+ ratio. CONCLUSION: The tumour microenvironment of patients with dHGP is characterised by an increased and distinctly cytotoxic immune infiltrate, providing a potential explanation for their superior survival.

Action and clinical significance of CCAAT/enhancer-binding protein delta in hepatocellular carcinoma.

CCAAT/enhancer-binding protein delta (CEBPD) is associated with the regulation of apoptosis and cell proliferation and is a candidate tumor suppressor gene. Here, we investigated its role in hepatocellular carcinoma (HCC). We observe that CEBPD mRNA expression is significantly downregulated in HCC tumors as compared with adjacent tissues. Protein levels of CEBPD are also lower in tumors relative to adjacent tissues. Reduced expression of CEBPD in the tumor correlates with worse clinical outcome. In both Huh7 and HepG2 cells, shRNA-mediated CEBPD knockdown significantly reduces cell proliferation, single cell colony formation and arrests cells in the G0/G1 phase. Subcutaneous xenografting of Huh7 in nude mice show that CEBPD knockdown results in smaller tumors. Gene expression analysis shows that CEBPD modulates interleukin-1 signaling. We conclude that CEBPD expression uncouples cancer compartment expansion and clinical outcome in HCC, potentially by modulating interleukin-1 signaling. Thus, although our results support the notion that CEBPD acts as a tumor suppressor in HCC, its action does not involve impairing compartment expansion per se but more likely acts through improving anticancer immunity.

Modeling liver cancer and therapy responsiveness using organoids derived from primary mouse liver tumors.

The current understanding of cancer biology and development of effective treatments for cancer remain far from satisfactory. This in turn heavily relies on the availability of easy and robust model systems that resemble the architecture/physiology of the tumors in patients to facilitate research. Cancer research in vitro has mainly been based on the use of immortalized 2D cancer cell lines that deviate in many aspects from the original primary tumors. The recent development of the organoid technology allowing generation of organ-buds in 3D culture from adult stem cells has endowed the possibility of establishing stable culture from primary tumors. Although culturing organoids from liver tumors is thought to be difficult, we now convincingly demonstrate the establishment of organoids from mouse primary liver tumors. We have succeeded in culturing 91 lines from 129 liver tissue/tumors. These organoids can be grown in long-term cultures in vitro. About 20% of these organoids form tumors in immunodeficient mice upon (serial) transplantation, confirming their tumorigenic and self-renewal properties. Interestingly, single cells from the tumor organoids have high efficiency of organoid initiation, and a single organoid derived from a cancer cell is able to initiate a tumor in mice, indicating the enrichment of tumor-initiating cells in the tumor organoids. Furthermore, these organoids recapitulate, to some extent, the heterogeneity of liver cancer in patients, with respect to phenotype, cancer cell composition and treatment response. These model systems shall provide enormous opportunities to advance our research on liver cancer (stem cell) biology, drug development and personalized medicine.

GITR ligation enhances functionality of tumor-infiltrating T cells in hepatocellular carcinoma.

No curative treatment options are available for advanced hepatocellular carcinoma (HCC). Anti-PD1 antibody therapy can induce tumor regression in 20% of advanced HCC patients, demonstrating that co-inhibitory immune checkpoint blockade has therapeutic potential for this type of cancer. However, whether agonistic targeting of co-stimulatory receptors might be able to stimulate anti-tumor immunity in HCC is as yet unknown. We investigated whether agonistic targeting of the co-stimulatory receptor GITR could reinvigorate ex vivo functional responses of tumor-infiltrating lymphocytes (TIL) freshly isolated from resected tumors of HCC patients. In addition, we compared GITR expression between TIL and paired samples of leukocytes isolated from blood and tumor-free liver tissues, and studied the effects of combined GITR and PD1 targeting on ex vivo TIL responses. In all three tissue compartments, CD4+ FoxP3+ regulatory T cells (Treg) showed higher GITR- expression than effector T-cell subsets. The highest expression of GITR was found on CD4+ FoxP3hi CD45RA- activated Treg in tumors. Recombinant GITR-ligand as well as a humanized agonistic anti-GITR antibody enhanced ex vivo proliferative responses of CD4+ and CD8+ TIL to tumor antigens presented by mRNA-transfected autologous B-cell blasts, and also reinforced proliferation, IFN-γ secretion and granzyme B production in stimulations of TIL with CD3/CD28 antibodies. Combining GITR ligation with anti-PD1 antibody nivolumab further enhanced tumor antigen-specific responses of TIL in some, but not all, HCC patients, compared to either single treatment. In conclusion, agonistic targeting of GITR can enhance functionality of HCC TIL, and may therefore be a promising strategy for single or combinatorial immunotherapy in HCC.

Reduction of immunosuppressive tumor microenvironment in cholangiocarcinoma by ex vivo targeting immune checkpoint molecules.

BACKGROUND & AIMS: Cholangiocarcinoma is an aggressive hepatobiliary malignancy originating from biliary tract epithelium. Whether cholangiocarcinoma is responsive to immune checkpoint antibody therapy is unknown, and knowledge of its tumor immune microenvironment is limited. We aimed to characterize tumor-infiltrating lymphocytes (TILs) in cholangiocarcinoma and assess functional effects of targeting checkpoint molecules on TILs. METHODS: We isolated TILs from resected tumors of patients with cholangiocarcinoma and investigated their compositions compared with their counterparts in tumor-free liver (TFL) tissues and blood, by flow cytometry and immunohistochemistry. We measured expression of immune co-stimulatory and co-inhibitory molecules on TILs, and determined whether targeting these molecules improved ex vivo functions of TILs. RESULTS: Proportions of cytotoxic T cells and natural killer cells were decreased, whereas regulatory T cells were increased in tumors compared with TFL. While regulatory T cells accumulated in tumors, the majority of cytotoxic and helper T cells were sequestered at tumor margins, and natural killer cells were excluded from the tumors. The co-stimulatory receptor GITR and co-inhibitory receptors PD1 and CTLA4 were over-expressed on tumor-infiltrating T cells compared with T cells in TFL and blood. Antagonistic targeting of PD1 or CTLA4 or agonistic targeting of GITR enhanced effector molecule production and T cell proliferation in ex vivo stimulation of TILs derived from cholangiocarcinoma. The inter-individual variations in TIL responses to checkpoint treatments were correlated with differences in TIL immune phenotype. CONCLUSIONS: Decreased numbers of cytotoxic immune cells and increased numbers of suppressor T cells that over-express co-inhibitory receptors suggest that the tumor microenvironment in cholangiocarcinoma is immunosuppressive. Targeting GITR, PD1 or CTLA4 enhances effector functions of tumor-infiltrating T cells, indicating that these molecules are potential immunotherapeutic targets for patients with cholangiocarcinoma. LAY SUMMARY: The defense functions of immune cells are suppressed in cholangiocarcinoma tumors. Stimulating or blocking "immune checkpoint" molecules expressed on tumor-infiltrating T cells can enhance the defense functions of these cells. Therefore, these molecules may be promising targets for therapeutic stimulation of immune cells to eradicate the tumors and prevent cancer recurrence in patients with cholangiocarcinoma.

Antibodies Against Immune Checkpoint Molecules Restore Functions of Tumor-Infiltrating T Cells in Hepatocellular Carcinomas.

BACKGROUND & AIMS: Ligand binding to inhibitory receptors on immune cells, such as programmed cell death 1 (PD-1) and cytotoxic T-lymphocyte associated protein 4 (CTLA4), down-regulates the T-cell-mediated immune response (called immune checkpoints). Antibodies that block these receptors increase antitumor immunity in patients with melanoma, non-small-cell lung cancer, and renal cell cancer. Tumor-infiltrating CD4+ and CD8+ T cells in patients with hepatocellular carcinoma (HCC) have been found to be functionally compromised. We analyzed HCC samples from patients to determine if these inhibitory pathways prevent T-cell responses in HCCs and to find ways to restore their antitumor functions. METHODS: We collected HCC samples from 59 patients who underwent surgical resection from November 2013 through May 2017, along with tumor-free liver tissues (control tissues) and peripheral blood samples. We isolated tumor-infiltrating lymphocytes (TIL) and intra-hepatic lymphocytes. We used flow cytometry to quantify expression of the inhibitory receptors PD-1, hepatitis A virus cellular receptor 2 (TIM3), lymphocyte activating 3 (LAG3), and CTLA4 on CD8+ and CD4+ T cells from tumor, control tissue, and blood; we studied the effects of antibodies that block these pathways in T-cell activation assays. RESULTS: Expression of PD-1, TIM3, LAG3, and CTLA4 was significantly higher on CD8+ and CD4+ T cells isolated from HCC tissue than control tissue or blood. Dendritic cells, monocytes, and B cells in HCC tumors expressed ligands for these receptors. Expression of PD-1, TIM3, and LAG3 was higher on tumor-associated antigen (TAA)-specific CD8+ TIL, compared with other CD8+ TIL. Compared with TIL that did not express these inhibitory receptors, CD8+ and CD4+ TIL that did express these receptors had higher levels of markers of activation, but similar or decreased levels of granzyme B and effector cytokines. Antibodies against CD274 (PD-ligand1 [PD-L1]), TIM3, or LAG3 increased proliferation of CD8+ and CD4+ TIL and cytokine production in response to stimulation with polyclonal antigens or TAA. Importantly, combining antibody against PD-L1 with antibodies against TIM3, LAG3, or CTLA4 further increased TIL functions. CONCLUSIONS: The immune checkpoint inhibitory molecules PD-1, TIM3, and LAG3 are up-regulated on TAA-specific T cells isolated from human HCC tissues, compared with T cells from tumor-free liver tissues or blood. Antibodies against PD-L1, TIM3, or LAG3 restore responses of HCC-derived T cells to tumor antigens, and combinations of the antibodies have additive effects. Strategies to block PD-L1, TIM3, and LAG3 might be developed for treatment of primary liver cancer.

Dynamics of Proliferative and Quiescent Stem Cells in Liver Homeostasis and Injury.

BACKGROUND & AIMS: Adult liver stem cells are usually maintained in a quiescent/slow-cycling state. However, a proliferative population, marked by leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), was recently identified as an important liver stem cell population. We aimed to investigate the dynamics and functions of proliferative and quiescent stem cells in healthy and injured livers. METHODS: We studied LGR5-positive stem cells using diphtheria toxin receptor and green fluorescent protein (GFP) knock-in mice. In these mice, LGR5-positive cells specifically coexpress diphtheria toxin receptor and the GFP reporter. Lineage-tracing experiments were performed in mice in which LGR5-positive stem cells and their daughter cells expressed a yellow fluorescent protein/mTmG reporter. Slow-cycling stem cells were investigated using GFP-based, Tet-on controlled transgenic mice. We studied the dynamics of both stem cell populations during liver homeostasis and injury induced by carbon tetrachloride. Stem cells were isolated from mouse liver and organoid formation assays were performed. We analyzed hepatocyte and cholangiocyte lineage differentiation in cultured organoids. RESULTS: We did not detect LGR5-expressing stem cells in livers of mice at any stage of a lifespan, but only following liver injury induced by carbon tetrachloride. In the liver stem cell niche, where the proliferating LGR5+ cells are located, we identified a quiescent/slow-cycling cell population, called label-retaining cells (LRCs). These cells were present in the homeostatic liver, capable of retaining the GFP label over 1 year, and expressed a panel of progenitor/stem cell markers. Isolated single LRCs were capable of forming organoids that could be carried in culture, expanded for months, and differentiated into hepatocyte and cholangiocyte lineages in vitro, demonstrating their bona fide stem cell properties. More interestingly, LRCs responded to liver injury and gave rise to LGR5-expressing stem cells, as well as other potential progenitor/stem cell populations, including SOX9- and CD44-positive cells. CONCLUSIONS: Proliferative LGR5 cells are an intermediate stem cell population in the liver that emerge only during tissue injury. In contrast, LRCs are quiescent stem cells that are present in homeostatic liver, respond to tissue injury, and can give rise to LGR5 stem cells, as well as SOX9- and CD44-positive cells.

Donor-specific anti-HLA antibodies are not associated with nonanastomotic biliary strictures but both are independent risk factors for graft loss after liver transplantation.

Donor-specific alloantibodies (DSA) have been associated with rejection and shorter graft survival after orthotopic liver transplantation (OLT). We examined the role of DSA in nonanastomotic biliary strictures (NAS) after OLT. Patients receiving first OLT who developed NAS (n = 68) and a control group without NAS (n = 83), with pre-OLT and 12 months post-OLT serum samples, were included. DSA were specified using the Luminex single antigen test. Risk factors for NAS and graft survival were analyzed. The presence of preformed DSA was not significantly different between patients with NAS and controls (P = .89). After 12 months, 26.5% of NAS patients and 16.9% of controls had generated de novo DSA (P = .15). Neither de novo class I DSA nor de novo class II DSA were associated with NAS. De novo DSA generally developed after the diagnosis of NAS. Time-dependent regression analysis identified both NAS (aHR 8.05, CI 3.28 - 19.77, P < .01) and de novo class II DSA (aHR 2.84, CI 1.38 - 5.82, P < .01) as independent risk factors for graft loss. Preformed or de novo DSA were not associated with the development of NAS. However, NAS as well as de novo class II DSA were independent risk factors for graft loss after OLT.

Prognostic value of intra-tumoral CD8+ /FoxP3+ lymphocyte ratio in patients with resected colorectal cancer liver metastasis.

BACKGROUND AND OBJECTIVES: Patients with isolated colorectal-cancer-liver-metastases (CRCLM) frequently undergo metastatectomy. Tumor-infiltrating-lymphocytes (TILs) have prognostic potential in the setting of primary colorectal cancer, however, their role in CRCLM is less studied. We aimed to study the spatial distribution and prognostic role of tumor-infiltrating CD8+ cytotoxic T-cells and FoxP3+ regulatory T-cells at the metastatic site of CRCLM patients. METHODS: TILs were isolated from fresh metastatic tissues of 47 patients with CRCLM. Archived paraffin-embedded tissue, from the same patients, was retrieved. CD8+ and FoxP3+ cells, both in the intra-tumoral and the peri-tumoral compartments, were measured by immunohistochemistry on full tissue sections. Proportions of cytotoxic T-cells (CD8+ ) and regulatory T-cells (CD4+ CD25+ FoxP3+ ), within CD45+ TILs, were measured by flow-cytometry. RESULTS: By immunohistochemistry, individual densities of intra-tumoral or peri-tumoral CD8+ and FoxP3+ cells were not prognostic of survival. However, the intra-tumoral, but not the peri-tumoral, CD8+ /FoxP3+ ratio was an independent predictor of survival (HR 0.43, 95%CI 0.19-0.95, P = 0.032). By flow cytometry, the intra-tumoral CD8+ /regulatory T-cell ratio was also an independent predictor of survival (HR 0.45, 95%CI 0.20-0.99, P = 0.044). CONCLUSIONS: The ratio of cytotoxic (CD8+ ) to regulatory (FoxP3+ ) T-cells, in the intra-tumoral compartment, but not in the peri-tumoral compartment, can predict survival after resection of CRCLM.

Tumor cell expression of immune inhibitory molecules and tumor-infiltrating lymphocyte count predict cancer-specific survival in pancreatic and ampullary cancer.

Understanding the mechanisms of immune resistance in pancreatic and ampullary cancers is crucial for the development of suitable biomarkers and effective immunotherapeutics. Our aim was to examine the expression of the immune inhibiting molecules PD-L1, Galectin-9, HVEM, IDO and HLA-G, as well as CD8+ and FoxP3+ tumor infiltrating lymphocytes (TIL), in pancreatic and ampullary cancers, and to relate their individual, as well as their combined expression, to cancer survival. Tumor tissue from 224 patients with resected pancreatic (n = 148) and ampullary (n = 76) cancer was used to construct tissue-microarrays. Expression of immune inhibitory molecules and TIL was examined by immunohistochemistry. We show that immune inhibitory molecules are prevalently expressed. Moreover, high tumor expression of PD-L1 (p = 0.002), Gal-9 (p = 0.003), HVEM (p = 0.001), IDO (p = 0.049), HLA-G (p = 0.004) and high CD8/FoxP3 TIL ratio (p = 0.006) were associated with improved cancer-specific survival. All immune biomarkers, with the exception of IDO, were individually predictive of cancer-specific survival when adjusted for clinicopathologic characteristics. For every additional immune biomarker present survival was almost two-fold prolonged (HR 0.57 95%CI 0.47-0.69, p < 0.0001). When patients with pancreatic and ampullary cancer were analyzed separately the results were similar. We conclude that pancreas and ampullary cancers are rich in expression of immune-inhibitory molecules. These molecules can be targets for future immunotherapeutics, as well as form powerful immunological biomarkers. We propose that such immune biomarker panels be included in future prospective immunotherapy trials.

Cytomegalovirus-Induced Expression of CD244 after Liver Transplantation Is Associated with CD8+ T Cell Hyporesponsiveness to Alloantigen.

The chronic presence of viral Ags can induce T cell exhaustion, which is characterized by upregulation of coinhibitory receptors and loss of T cell function. We studied whether a similar phenomenon occurs after liver transplantation (LTx), when there is continuous exposure to alloantigen. Expression of coinhibitory receptors on circulating CD4(+) and CD8(+) T cells was analyzed longitudinally in 19 patients until 6 mo after LTx and cross-sectionally in 38 patients late (1-12 y) after LTx. Expression of the coinhibitory receptors CD160 and CD244 on circulating CD8(+) T cells was already higher 6 mo after LTx compared with pre-LTx, and the elevated expression was sustained late after LTx, with CD244 showing the more prominent increase. The strongest upregulation of CD244 on circulating CD8(+) T cells was observed in patients who experienced CMV infection after LTx. CMV infection also was associated with reduced CD8(+) T cell proliferation and cytotoxic degranulation in response to alloantigen late after LTx. Purified CD244(+)CD8(+) T cells from LTx patients showed lower proliferative responses to alloantigen, as well as to polyclonal stimulation, than did their CD244(-) counterparts. In addition, the CD244(+)CD8(+) T cell population contained the majority of CMV peptide-loaded MHC class I tetramer-binding cells. In conclusion, CMV infection after LTx, rather than persistence of alloantigen, induces the accumulation of dysfunctional CD244(+)CD8(+) T cells in the circulation that persist long-term, resulting in reduced frequencies of circulating alloreactive CD8(+) T cells. These results suggest that CMV infection restrains CD8(+) T cell alloresponses after LTx.

Counter-regulation of rejection activity against human liver grafts by donor PD-L1 and recipient PD-1 interaction.

BACKGROUND & AIMS: Co-inhibitory receptor-ligand interactions fine-tune immune responses by negatively regulating T cell functions. Our aim is to examine the involvement of co-inhibitory receptor-ligand pair PD-1/PD-L1 in regulating rejection after liver transplantation (LT) in humans. METHODS: PD-L1/PD-1 expression in liver allograft was determined by immunohistochemistry or flow cytometry, and the effect of blockade was studied using graft-infiltrating T cells ex vivo. Five single nucleotide polymorphisms within PD-1 and PD-L1 genes were genotyped in 528 LT recipients and 410 donors, and associations with both early (⩽6months) and late (>6months) acute rejection were analyzed using Cox proportional-hazards regression model. The effect of PD-L1 rs4143815 on PD-L1 expression was analyzed using donor hepatic leukocytes. RESULTS: PD-L1 was expressed by hepatocytes, cholangiocytes and along the sinusoids in post-transplant liver allografts, and PD-1 was abundantly expressed on allograft-infiltrating T cells. PD-L1 blockade enhanced allogeneic proliferative responses of graft-infiltrating T cells. In the genetic association analysis, donor PD-L1 rs4143815 (CC/CG vs. GG; HR=0.230; p=0.002) and recipient PD-1 rs11568821 (AA/AG vs. GG; HR=3.739; p=0.004) were associated with acute rejection late after LT in multivariate analysis. Recipients carrying the PD-1 rs11568821 A allele who were transplanted with liver grafts of PD-L1 rs4143815 GG homozygous donors showed the highest risk for late acute rejection. PD-L1 rs4143815 is associated with differential PD-L1 expression on donor hepatic dendritic cells upon IFN-γ stimulation. CONCLUSION: Our data suggest that interplay between donor PD-L1 and recipient PD-1 counter-regulates rejection activity against liver grafts in humans.

Differential Sensitivities of Fast- and Slow-Cycling Cancer Cells to Inosine Monophosphate Dehydrogenase 2 Inhibition by Mycophenolic Acid.

As uncontrolled cell proliferation requires nucleotide biosynthesis, inhibiting enzymes that mediate nucleotide biosynthesis constitutes a rational approach to the management of oncological diseases. In practice, however, results of this strategy are mixed and thus elucidation of the mechanisms by which cancer cells evade the effect of nucleotide biosynthesis restriction is urgently needed. Here we explored the notion that intrinsic differences in cancer cell cycle velocity are important in the resistance toward inhibition of inosine monophosphate dehydrogenase (IMPDH) by mycophenolic acid (MPA). In short-term experiments, MPA treatment of fast-growing cancer cells effectively elicited G0/G1 arrest and provoked apoptosis, thus inhibiting cell proliferation and colony formation. Forced expression of a mutated IMPDH2, lacking a binding site for MPA but retaining enzymatic activity, resulted in complete resistance of cancer cells to MPA. In nude mice subcutaneously engrafted with HeLa cells, MPA moderately delayed tumor formation by inhibiting cell proliferation and inducing apoptosis. Importantly, we developed a lentiviral vector-based Tet-on label-retaining system that enables to identify, isolate and functionally characterize slow-cycling or so-called label-retaining cells (LRCs) in vitro and in vivo. We surprisingly found the presence of LRCs in fast-growing tumors. LRCs were superior in colony formation, tumor initiation and resistance to MPA as compared with fast-cycling cells. Thus, the slow-cycling compartment of cancer seems predominantly responsible for resistance to MPA.

Polarized release of hepatic microRNAs into bile and serum in response to cellular injury and impaired liver function.

BACKGROUND & AIMS: Extracellular microRNAs (miRNAs) in serum and bile are currently under intense investigation for biomarker purposes in liver disease. However, the directions and pathways by which miRNAs are released from hepatic cells remains largely unknown. Here, we investigated the release of hepatocyte and cholangiocyte-derived miRNAs (HDmiRs and CDmiRs) into blood and bile during various (patho)physiological hepatic conditions. METHODS: MiRNA release was analysed using longitudinally collected tissue and paired bile and serum samples (n = 124) that were obtained from liver transplant recipients during follow-up. RESULTS: Cell-type specificity of HDmiRs and CDmiRs was confirmed in liver and common bile duct biopsies (P < 0.001). Analysis of paired bile and serum samples showed up to 20-times higher miRNA-levels in bile compared to serum (P < 0.0001). Fractionation of bile showed the majority of miRNAs being present in the unpelletable supernatant, where protein conjunctions protect miRNAs against degradation (P < 0.0001). During episodes of liver injury and histologically proven rejection in liver transplant recipients, relative HDmiR-levels in bile decreased while its levels in serum increased (P ≤ 0.015). Simultaneously, relative CDmiR-levels in bile significantly increased, while their levels in serum decreased. Related to liver excretory function, a strong positive correlation was observed between HDmiR-122 levels and bilirubin excretion into bile (R = 0.694, P < 0.0001), whereas CDmiRs showed an inverse correlation (P < 0.05). CONCLUSION: During impaired excretory function and injury, the liver shows polarized release of extracellular HDmiRs and CDmiRs. This sheds new light on the biology of hepatic miRNA release which is relevant for the interpretation of hepatic miRNAs as biomarkers.

Intravenous immunoglobulin treatment in humans suppresses dendritic cell function via stimulation of IL-4 and IL-13 production.

High-dose i.v. Ig (IVIg) is a prominent immunomodulatory therapy for various autoimmune and inflammatory diseases. Recent mice studies suggest that IVIg inhibits myeloid cell function by inducing a cascade of IL-33-Th2 cytokine production causing upregulation of the inhibitory FcγRIIb, as well as by modulating IFN-γ signaling. The purpose of our study was to explore whether and how these mechanisms are operational in IVIg-treated patients. We show that IVIg in patients results in increases in plasma levels of IL-33, IL-4, and IL-13 and that increments in IL-33 levels correlate with rises in plasma IL-4 and IL-13 levels. Strikingly, no upregulation of FcγRIIb expression was found, but instead a decreased expression of the activating FcγRIIa on circulating myeloid dendritic cells (mDCs) after high-dose, but not after low-dose, IVIg treatment. In addition, expression of the signaling IFN-γR2 subunit of the IFN-γR on mDCs was downregulated upon high-dose IVIg therapy. In vitro experiments suggest that the modulation of FcγRs and IFN-γR2 on mDCs is mediated by IL-4 and IL-13, which functionally suppress the responsiveness of mDCs to immune complexes or IFN-γ. Human lymph nodes and macrophages were identified as potential sources of IL-33 during IVIg treatment. Interestingly, stimulation of IL-33 production in human macrophages by IVIg was not mediated by dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN). In conclusion, high-dose IVIg treatment inhibits inflammatory responsiveness of mDCs in humans by Th2 cytokine-mediated downregulation of FcγRIIa and IFN-γR2 and not by upregulation of FcγRIIb. Our results suggest that this cascade is initiated by stimulation of IL-33 production that seems DC-SIGN independent.