Effector T cell function rather than survival determines extent and duration of hepatitis in mice

BACKGROUND & AIMS

Acute hepatitis is often mediated by cytotoxic T lymphocytes (CTLs); however, the intrinsic parameters that limit CTL-mediated liver injury are not well understood.

METHODS

To investigate whether acute liver damage is limited by molecules that decrease the lifespan or effector function of CTLs, we used a well-characterized transgenic (Tg) mouse model in which acute liver damage develops upon transfer of T cell receptor (TCR) Tg CD8 T cells. Recipient Tg mice received donor TCR Tg T cells deficient for either the pro-apoptotic molecule Bim, which regulates CTL survival, or suppressor of cytokine signaling-1 (SOCS-1), which controls expression of common gamma chain cytokines; the effects of anti-PD-L1 neutralizing antibodies were also assessed.

RESULTS

Use of Bim-deficient donor T cells and/or PD-L1 blockade increased the number of intrahepatic T cells without affecting the degree and kinetic of acute hepatitis. In contrast, SOCS-1-deficient T cells induced a heightened, prolonged acute hepatitis caused by their enhanced cytotoxic function and increased expansion. Although they inflicted more severe acute liver damage, SOCS-1-deficient T cells never precipitated chronic hepatitis and became exhausted.

CONCLUSIONS

The degree of acute hepatitis is regulated by the function of CD8 T cells, but is not affected by changes in CTL lifespan. Although manipulation of the examined parameters affected acute hepatitis, persistent hepatitis did not ensue, indicating that, in the presence of high intrahepatic antigen load, changes in these factors in isolation were not sufficient to prevent T cell exhaustion and mediate progression to chronic hepatitis.

Long-term results after in-situ split (ISS) liver resection

PURPOSE

In-situ split (ISS) liver resection is a novel method to induce rapid hypertrophy of the contralateral liver lobe in patients at risk for postoperative liver failure due to insufficient liver remnant. So far, no data about oncological long-term survival after ISS liver resection is available.

METHODS

We retrospectively analyzed our patients treated with ISS liver resection at the Department of Surgery of the University of Regensburg, the first center worldwide to perform ISS.

RESULTS

Between 2007 and 2014, ISS liver resection was performed in 16 patients. Two patients (12.5 %) were lost in early postoperative phase (90 days) and one was lost to follow-up. Thirteen patients with a follow-up period of more than 3 months were included into oncologically focused analyses. Median follow-up was 26.4 months (range 3.2-54.6). Seven patients had suffered from colorectal liver metastases (CRLM) and six from various other liver malignancies (non-CRLM). The ISS procedure had led to a median increase of 86.3 % of the left lateral liver lobe after a median of 9 days (range 4-28 days). Median disease-free survival (DFS) was 14.6 months and median overall survival (OS) was 41.7 months (26.4 months when including 90-days mortality). Three-year survival was calculated with 56.4 and 48.9 % when including perioperative mortality, respectively (CRLM 64.3 % vs. non-CRLM 50 %).

CONCLUSION

ISS liver resection can provide long-term survival of selected patients with advanced liver malignancies that otherwise are not eligible for liver resection due to insufficient liver remnant.

Retrograde stapling of a free cervical jejunal interposition graft: a technical innovation and case report

Background

Free jejunal interposition is a useful technique for reconstruction of the cervical esophagus. However, the distal anastomosis between the graft and the remaining thoracic esophagus or a gastric conduit can be technically challenging when located very low in the thoracic aperture. We here describe a modified technique for retrograde stapling of a jejunal graft to a failed gastric conduit using a circular stapler on a delivery system.

Case presentation

A 56 year-old patient had been referred for esophageal squamous cell carcinoma at 20 cm from the incisors. On day 8 after thoracoabdominal esophagectomy with gastric pull-up, an anastomotic leakage was diagnosed. A proximal-release stent was successfully placed by gastroscopy and the patient was discharged. Two weeks later, an esophagotracheal fistula occurred proximal to the esophageal stent. Cervical esophagostomy was performed with cranial closure of the gastric conduit, which was left in situ within the right hemithorax. Three months later, reconstruction was performed using a free jejunal interposition. The anvil of a circular stapler (Orvil®, Covidien) was placed transabdominally through an endoscopic rendez-vous procedure into the gastric conduit. A free jejunal graft was retrogradely stapled to the proximal end of the conduit. Microvascular anastomoses were performed subsequently. The proximal anastomosis of the conduit was completed manually after reperfusion.

Conclusions

This modified technique allows stapling of a jejunal interposition graft located deep in the thoracic aperture and is therefore a useful method that may help to avoid reconstruction by colonic pull-up and thoracotomy.

Differential migration of passenger leukocytes and rapid deletion of naive alloreactive CD8 T cells after mouse liver transplantation

Donor passenger leukocytes (PLs) from transplanted livers migrate to recipient lymphoid tissues, where they are thought to induce the deletion of donor-specific T cells and tolerance. Difficulties in tracking alloreactive T cells and PLs in rats and in performing this complex surgery in mice have limited progress in identifying the contribution of PL subsets and sites and the kinetics of T cell deletion. Here we developed a mouse liver transplant model in which PLs, recipient cells, and a reporter population of transgenic CD8 T cells specific for the graft could be easily distinguished and quantified in allografts and recipient organs by flow cytometry. All PL subsets circulated rapidly via the blood as soon as 1.5 hours after transplantation. By 24 hours, PLs were distributed differently in the lymph nodes and spleen, whereas donor natural killer and natural killer T cells remained in the liver and blood. Reporter T cells were activated in both liver and lymphoid tissues, but their numbers dramatically decreased within the first 48 hours. These results provide the first unequivocal demonstration of the differential recirculation of liver PL subsets after transplantation, and show that alloreactive CD8 T cells are deleted more rapidly than initially reported. This model will be useful for dissecting early events leading to the spontaneous acceptance of liver transplants.

Both passenger leucocytes and hepatic parenchyma contribute to activation and deletion of graft-reactive CD8 T cells in liver transplantation (P2130)

Unlike most solid organs, liver transplants are spontaneously accepted across MHC mismatch and induce donor-specific tolerance. The mechanisms and site of tolerance induction remain unclear. Both recipient lymphoid tissues (RLT) where donor passenger leukocytes (PL) migrate, and the liver parenchyma itself are thought to contribute to this process by inducing abortive activation of alloreactive T cells. To determine the relative contribution of these compartments to alloreactive T cell fate, we developed a murine liver transplant model in which we traced the fate of PL and a naïve alloreactive CD8 T cell reporter population specific for donor MHC. Ly5.2+C57BL/6 livers were transplanted into allogeneic Ly5.1+B10.BR recipients. Directly allograft reactive Des-TCR transgenic T cells specific for donor H-2Kb were adoptively transferred as a reporter population. Donor and recipient leukocyte location and fate were traced by flow cytometry and radiolabelling. All Des T cells were rapidly activated in RLT and liver but numbers dropped dramatically within 48h, with cells resident in RLT predominantly dying in situ, while most circulating Des T cells were deleted in the liver. Intrahepatic clearance was associated with degradation of Des T cells in hepatocyte lysosomal compartments. In conclusion, these results show that both PL and the hepatic parenchyma contribute to deletion of graft reactive T cells, and reveal a novel mechanism of tolerance induction within the hepatic allograft.

The magnitude of acute hepatitis is more limited by regulation of cytokine signalling than apoptosis of liver-infiltrating effector CD8 T cells (P4174)

Acute hepatitis is often mediated by CD8 T cells that kill target cells or secrete hepatotoxic cytokines. However, the parameters regulating CD8 T cell-mediated acute hepatitis are not well understood. We used the well-characterized Met-Kb Tg mouse model of acute hepatitis, in which hepatitis is mediated by lymph node activated TCR Tg CD8 recognizing their cognate antigen in the liver. To investigate whether cytokine regulation or apoptosis of CD8 T cells were critical in limiting acute hepatocellular injury, adoptive transfer experiments were performed using TCR Tg T cells deficient for either suppressor of cytokine signaling (SOCS-1) or the pro-apoptotic molecule Bim. Although there was a substantial accumulation of Bim-/- Tg cells, the outcome of hepatitis remained unchanged, suggesting that effector T cell survival was not a critical parameter in limiting liver damage. In contrast, SOCS-1-/- Tg T cells induced a heightened severity of hepatitis than their wt counterparts. SOCS-1-/- Tg cells isolated from the liver displayed upregulated IL-2Rα, required for the high affinity IL-2 receptor, and was associated with higher levels of IFN-γ expression, CTL activity, and proliferation rates, consistent with enhanced effector function. These data support a critical role for cytokines in CTL function, and demonstrate that the propensity of CD8 T cells to mediate acute hepatitis is determined by the quality rather than the number of CTLs infiltrating the liver.

Mesenchymal stem cells are short-lived and do not migrate beyond the lungs after intravenous infusion

Mesenchymal stem cells (MSC) are under investigation as a therapy for a variety of disorders. Although animal models show long term regenerative and immunomodulatory effects of MSC, the fate of MSC after infusion remains to be elucidated. In the present study the localization and viability of MSC was examined by isolation and re-culture of intravenously infused MSC. C57BL/6 MSC (500,000) constitutively expressing DsRed-fluorescent protein and radioactively labeled with Cr-51 were infused via the tail vein in wild-type C57BL/6 mice. After 5 min, 1, 24, or 72 h, mice were sacrificed and blood, lungs, liver, spleen, kidneys, and bone marrow removed. One hour after MSC infusion the majority of Cr-51 was found in the lungs, whereas after 24 h Cr-51 was mainly found in the liver. Tissue cultures demonstrated that viable donor MSC were present in the lungs up to 24 h after infusion, after which they disappeared. No viable MSC were found in the other organs examined at any time. The induction of ischemia-reperfusion injury in the liver did not trigger the migration of viable MSC to the liver. These results demonstrate that MSC are short-lived after i.v. infusion and that viable MSC do not pass the lungs. Cell debris may be transported to the liver. Long term immunomodulatory and regenerative effects of infused MSC must therefore be mediated via other cell types.

Role of the hepatic parenchyma in liver transplant tolerance: a paradigm revisited

Unlike other solid organs, liver transplants are spontaneously accepted in a wide range of animal models. In the clinic, transplanted livers also display privileged immunological properties allowing weaning of immunosuppression therapy in up to 20% of selected patients. To explain this phenomenon, many studies have focused on the role of donor-derived 'passenger' leukocytes that are thought to induce antigen-specific tolerance by migrating from the graft into recipient secondary lymphoid tissues. Although convincing evidence exists that these cells are able to elicit antiallograft T cell hyporesponsiveness, several studies argue against an exclusive role for this cell population and even question whether it is critical in conferring donor MHC-specific tolerance. Instead, these studies suggest that the hepatic parenchyma plays a more critical role in this phenomenon. In this review we will reinterpret the results of old and more recent literature in light of recent advances in the field of liver immunology to explain the contribution of both passenger leukocytes and liver tissue in the liver tolerance effect.

Safety and feasibility of third-party multipotent adult progenitor cells for immunomodulation therapy after liver transplantation--a phase I study (MISOT-I)

BACKGROUND

Liver transplantation is the definitive treatment for many end-stage liver diseases. However, the life-long immunosuppression needed to prevent graft rejection causes clinically significant side effects. Cellular immunomodulatory therapies may allow the dose of immunosuppressive drugs to be reduced. In the current protocol, we propose to complement immunosuppressive pharmacotherapy with third-party multipotent adult progenitor cells (MAPCs), a culture-selected population of adult adherent stem cells derived from bone marrow that has been shown to display potent immunomodulatory and regenerative properties. In animal models, MAPCs reduce the need for pharmacological immunosuppression after experimental solid organ transplantation and regenerate damaged organs.

METHODS

Patients enrolled in this phase I, single-arm, single-center safety and feasibility study (n = 3-24) will receive 2 doses of third-party MAPCs after liver transplantation, on days 1 and 3, in addition to a calcineurin-inhibitor-free "bottom-up" immunosuppressive regimen with basiliximab, mycophenolic acid, and steroids. The study objective is to evaluate the safety and clinical feasibility of MAPC administration in this patient cohort. The primary endpoint of the study is safety, assessed by standardized dose-limiting toxicity events. One secondary endpoint is the time until first biopsy-proven acute rejection, in order to collect first evidence of efficacy. Dose escalation (150, 300, 450, and 600 million MAPCs) will be done according to a 3 + 3 classical escalation design (4 groups of 3-6 patients each).

DISCUSSION

If MAPCs are safe for patients undergoing liver transplantation in this study, a phase II/III trial will be conducted to assess their clinical efficacy.

The impact of poloxamer 407 on the ultrastructure of the liver and evidence for clearance by extensive endothelial and kupffer cell endocytosis

Poloxamer 407 (P407) is a non-ionic detergent that is used widely in pharmaceutical formulations and personal care products. In animals, P407 causes hyperlipidaemia. P407 is taken up by the liver and causes loss of fenestrations in liver sinusoidal endothelial cells (LSEC), which contributes to the pathogenesis of hyperlipidaemia. Here the short-term (1-15 days) effects of P407 on all liver cells were investigated in mice using electron and light microscopy. As expected, P407 was associated with hyperlipidaemia. Kupffer cells became massively engorged with vacuoles and took on a marked honeycomb morphology. LSECs also became engorged with vacuoles and endocytosis was activated. The diameter of lipoproteins in the space of Disse was less than those in the lumen, consistent with a filtering effect of fenestrations. Defenestration of the LSEC was noted. Hepatocyte endocytosis of lipoproteins and P407 particles was also noted; however, hepatocyte steatosis was not evident. Hepatic stellate cells did not appear to be abnormal. In conclusion, P407 is taken up by the liver mostly through endocytosis by LSECs and Kupffer cells.

[The liver as an immunological organ]

In many species, liver transplants induce antigen-specific immunological tolerance. Furthermore, the liver seems to play an important role in oral tolerance although the exact mechanisms as to how the liver induces immunological tolerance still need to be defined. Apart from the presence of an unusual subset of effector cells of the innate immune system, the liver is rich in CD 8+ T cells with an activated and preapoptotic phenotype. In this article, we discuss the suggested hypothesis to explain this phenotype. In addition, we discuss the different cell types that have been suggested to serve as antigen-presenting cells (APC) for naïve T cells. Interestingly, different APCs seem to use different mechanisms to induce tolerance while hepatic stellate cells were reported to induce an effective immune response.

Invading macrophages play a major role in the liver progenitor cell response to chronic liver injury

BACKGROUND & AIMS

Although a strong association between liver progenitor cells (LPCs) and inflammation exists in many chronic liver diseases, the exact role of the immune system in LPC-mediated hepatic regeneration remains unclear. A number of pro-inflammatory factors were identified in cytokine knockout mice in which the LPC response was attenuated but neither the mechanism nor the producing cells are known.

METHODS

To identify the critical immune cells and cytokines required in the LPC response, we compared two diet-induced models of liver injury with two recently established transgenic models of immune-mediated hepatitis.

RESULTS

Despite severe inflammation being observed in all models, the generation of LPCs was highly dependent on the cause and kinetics of liver damage. The LPC response was associated with an increase of macrophages and CD8(+) T cells but not natural killer cells. T cell-deficient mice were able to mount a LPC response, albeit delayed, suggesting that T cells are not essential. Mice mounting an LPC response showed elevated numbers of Kupffer cells and invading CX(3)CR1(high)CCR2(high) macrophages secreting persistent high levels of tumour necrosis factor alpha (TNFalpha), a major cytokine involved in the LPC response.

CONCLUSIONS

Liver macrophages are an important determinant of LPC expansion during liver regeneration in models of diet- and immune-mediated liver injury. Invading macrophages in particular provide pro-mitogenic cytokines such as TNFalpha that underpin the process. LPC themselves are a source of chemokines (CCL2, CX(3)CL1) that attract infiltrating macrophages.

[Case report--surgical therapy of a retroperitoneal liposarcoma weighing 45 kg]

Due to the late onset of symptoms, retroperitoneal liposarcoma are often diagnosed in advanced stages when adjacent organs have been infiltrated and the tumours have reached extensive sizes. Surgery remains the first choice of therapy. We report on the primary resection of a 45-kg liposarcoma that was removed en-bloc including the left kidney and descending colon with -tumour-free margins. Nine months later, the follow-up revealed a right-sided recurrence of the tumour, which was surgically removed including the right ureter. Since then, the patient has been without any signs of tumour recurrence or metastases. This report demonstrates that even extreme-ly large tumours can be removed safely and that the size is not a contraindication for primary surgical treatment. Local recurrence is common as seen in our case, and occurs even after R0 resection up to 10 years after the first operation. Recurrences should be surgically removed as this is the only treatment which has been shown to increase survival in even R1 and R2 situations.

Liver tolerance and the manipulation of immune outcomes

In recent years it has become apparent that the liver holds a distinct immunological position. Previously described as a "graveyard" for T cells activated in the periphery, emerging evidence indicates that this organ may have a more active role in mediating tolerance. Attenuated immune responses in the liver can be beneficial in the transplantation setting, as liver transplants are more readily accepted than other organ allografts even in the absence of immunosuppressive drugs. However, the ability of the liver to induce immunological unresponsiveness could be exploited by some pathogens, such as the hepatitis C virus (HCV), to establish chronic infections with potentially fatal outcomes. Understanding the mechanisms controlling the balance between intrahepatic tolerance and immunity is critical in order to design new strategies to enhance acceptance of solid organ allografts and to promote efficient immune responses against HCV. In this article, we will review current knowledge of the mechanisms regulating intrahepatic immunity and discuss how these mechanisms might potentially be targeted to achieve advantageous clinical outcomes in transplantation and persistent hepatotropic infections.

Intrahepatic murine CD8 T-cell activation associates with a distinct phenotype leading to Bim-dependent death

BACKGROUND & AIMS

Chronic infections by hepatotropic viruses such as hepatitis B and C are generally associated with an impaired CD8 T-cell immune response that is unable to clear the virus. The liver is increasingly recognized as an alternative site in which primary activation of CD8 T cells takes place, a property that might explain its role in inducing tolerance. However, the molecular mechanism by which intrahepatically activated T cells become tolerant is unknown. Here, we investigated the phenotype and fate of naïve CD8 T cells activated by hepatocytes in vivo.

METHODS

Transgenic mouse models in which the antigen is expressed in lymph nodes and/or in the liver were adoptively transferred with naïve CD8 T cells specific for the hepatic antigen.

RESULTS

Liver-activated CD8 T cells displayed poor effector functions and a unique CD25(low) CD54(low) phenotype. This phenotype was associated with increased expression of the proapoptotic protein Bim and caspase-3, demonstrating that these cells are programmed to die following intrahepatic activation. Importantly, we show that T cells deficient for Bim survived following intrahepatic activation.

CONCLUSIONS

This study identifies Bim for the first time as a critical initiator of T-cell death in the liver. Thus, strategies inhibiting the up-regulation of this molecule could potentially be used to rescue CD8 T cells, clear the virus, and reverse the outcome of viral chronic infections affecting the liver.

T cells in the liver: there is life beyond the graveyard

Influenza A virus infection of C57BL/6 mice is a well-characterized model for studying CD8+ T cell-mediated immunity. Analysis of primary and secondary responses showed that the liver is highly enriched for CD8+ T cells specific for the immunodominant H2D(b)NP(366-374) (D(b)NP(366)) epitope. Functional analysis established that these liver-derived virus-specific CD8+ T cells are fully competent cytotoxic effectors and IFN-gamma secretors. In addition, flow cytometric analysis of early apoptotic cells showed that these influenza-specific CD8+ T cells from liver are as viable as those in the spleen, bronchoalveolar lavage, mediastinal lymph nodes, or lung. Moreover, cytokine profiles of the influenza-specific CD8+ T cells recovered from different sites were consistent with the bronchoalveolar lavage, rather than liver population, being the most susceptible to activation-induced cell death. Importantly, adoptively transferred influenza virus-specific CD8+ T cells from the liver survived and were readily recalled after virus challenge. Together, these results show clearly that the liver is not a "graveyard" for influenza virus-specific CD8+ T cells.

The liver: a special case in transplantation tolerance

Liver transplants are not often rejected in patients weaned from immunosuppression and are spontaneously accepted in some animal models. We review past and recent findings of liver transplantation and propose a unified model in which several mechanisms act in concert to induce and maintain tolerance in both naïve and effector T cell compartments. First, passenger leukocytes migrate to lymphoid tissues and induce apoptosis of alloreactive naïve T cells. Second, antigen-specific activation and subsequent deletion of naïve and effector cells within the liver itself purge the repertoire of alloreactive T cells. Other mechanisms such as microchimerism and migration of donor dendritic cells to the thymus may play a predominant role in maintaining tolerance, and soluble major histocompatibility complex molecules, donor peptides, and regulatory T cells may participate in the induction and maintenance phases. Thus, the major challenge in liver transplantation will be to favor these tolerogenic processes while developing strategies that specifically inhibit alloreactive memory T cells.

Naïve T cells activated in the liver by hepatocytes express a phenotype consistent with death by neglect (B69)

The liver has unique immunological properties. We have proposed that these properties are associated with the unique ability of the hepatic tissue to support primary activation of CD8+ T cells independently of lymphoid tissues. The fate of T cells activated in the liver however remains a matter of debate. Our results indicate that liver-activated cells die prematurely due to lower expression of cytokines and cell survival genes. In contrast, recent studies in a mouse liver transplantation model indicate that liver-activated T cells mature into full effector cells able to recirculate into lymph nodes (LN) and become tolerised at a latter stage through other mechanisms. In this latter model, it is not clear whether full effector T cells originate from recirculating T cells activated in LN or whether intrahepatic inflammation changes the phenotype of T cells activated locally. To address specifically the recirculation patterns, phenotype and fate of naïve CD8+ lymphocytes activated in the liver and LN in the absence of injury, we used transgenic mouse models in which the antigen is expressed at only one of these sites. Liver-activated cells down-regulated CD62L and thus, were unable to recirculate to LN during the first 3 days. Importantly, these cells were found to express lower levels of CD25 and CD54 than LN-activated cells. Simultaneously anti-apoptotic proteins were upregulated in liver-activated cells whereas this did not occur in LN-activated cells. Thus, liver-activated CD8+ T cells do not recirculate to the LN at early time points and are rather programmed to undergo premature death in vivo thus contributing to the liver tolerance effect.

Marked changes of the hepatic sinusoid in a transgenic mouse model of acute immune-mediated hepatitis

BACKGROUND/AIMS

The liver sinusoidal endothelial cell (LSEC) is increasingly recognized as having an important role in hepatic immunity. However, the responses of LSECs and the hepatic sinusoid in immune-mediated hepatitis are poorly described.

METHODS

We studied a transgenic mouse model of acute immune-mediated hepatitis: Met-Kb mice injected with T cells from Des-TCR mice.

RESULTS

Hepatitis was characterized by lymphocyte infiltrates causing severe but transient liver damage. There were marked changes in the ultrastructure of the LSEC five days after injection of the T cells that coincided with the peak of the hepatitis. The porosity of fenestrations in the LSEC decreased and the endothelium became thickened. LSECs appeared to be markedly activated. These changes were associated with narrowing of the space of Disse, loss of hepatocellular microvilli and deposition of basal lamina. Lymphocytes were seen passing through fenestrations. Loss of fenestration in the LSEC prevented hepatitis induced by a second injection of lymphocytes on day 5.

CONCLUSIONS

Structural changes in the LSEC occur during the peak of a mouse model of immune-mediated hepatitis. These changes were associated with attenuation of subsequent liver damage, suggesting that they may influence immunological responses mediated by LSECs or the passage of lymphocytes through LSEC fenestrations.