Synergistic CD40 signaling on APCs and CD8 T cells drives efficient CD8 response and memory differentiation

Lessons from transmissible cancers for immunotherapy and transplant

The emergence of horizontal transmission of cancer between vertebrates is an issue that interests scientists and medical society. Transmission requires: (i) a mechanism by which cancer cells can transfer to another organism and (ii) a repressed immune response on the part of the recipient. Transmissible tumors are unique models to comprehend the responses and mechanisms mediated by the major histocompatibility complex (MHC), which can be transposed for transplant biology. Here, we discuss the mechanisms involved in immune-mediated tissue rejection, making a parallel with transmissible cancers. We also discuss cellular and molecular mechanisms involved in cancer immunotherapy and anti-rejection therapies.

A High Preoperative Platelet-Lymphocyte Ratio Is a Negative Predictor of Survival After Liver Resection for Hepatitis B Virus-Related Hepatocellular Carcinoma: A Retrospective Study

Objective: To evaluate the importance of preoperative blood platelet to lymphocyte ratio (PLR) in patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) after liver surgery and to examine the connection with CD8⁺ lymph cell infiltration.

Methods: Between 2009 and 2014, consecutive HCC patients who received curative liver surgery were included into this retrospective study. Baseline clinicopathological characteristics were analyzed to identify predictors of recurrence-free and overall patient survival rate after liver resection. The samples of all patients were under Tissue Microarray (TMA) construction and immunohistochemical staining for CD8+.The association of the number of CD8+T-cells in the cancer nests and peritumoral stroma with PLR level was analyzed.

Results: A total of 1,174 HBV-related HCC patients who received a liver resection without any peri-operative adjuvant therapy were enrolled into this retrospective study. Univariate and Multivariate analysis using Cox regression model showed that PLR was an independent factor affecting recurrence and overall survivals. The optimal cutoff of PLR using the receiver operating characteristic curve was 150. There were 236 patients (20.1%) who had a PLR of 150 or more. The 5-year survival rate after liver resection was 71.8% in patients with a PLR of < 150 and it was 57.2% in those with a PLR of 150 or more (P < 0.001). Both 5-year recurrence-free and overall survival rates in liver cancer stage A patients at Barcelona Clinic with different PLR group were also significantly different (P = 0.007 for recurrence and P = 0.001 for overall survival). Similar results were also observed in stage B patients (P < 0.001 for recurrence and P = 0.033 for overall survival). To determine the association between PLR and the severity of liver inflammation, an immuno-histological examination using CD8⁺ staining was performed on the liver specimens of 1,174 patients. Compared with low PLR (<150) group, more CD8⁺T-cells were found in the peritumoral tissue in high PLR (≥ 150) group.

Conclusions: PLR played as an independent factor for predicting the survival after hepatectomy for HCC patients. A high PLR was associated with an accumulation of CD8⁺ T-cells in the peritumoral stroma.

Rationale for CD40 pathway blockade in autoimmune rheumatic disorders

CD40 and its ligand CD40L (CD154) belong to the tumor necrosis factor receptor superfamily and are expressed by a variety of immune and non-immune cells. CD40L plays a central role in co-stimulation and regulation of the immune response via activation of cells expressing CD40. Imbalance of the CD40-CD40L co-stimulatory pathway has been reported in many autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, and Sjögren's syndrome, thus supporting its role in the breach of immune tolerance that is typical of these diseases. Targeting CD40-CD40L signalling might represent a novel therapeutic option for several autoimmune disorders.

Pulmonary Dendritic Cell Subsets Shape the Respiratory Syncytial Virus-Specific CD8+ T Cell Immunodominance Hierarchy in Neonates

Young infants are generally more susceptible to viral infections and experience more severe disease than do adults. CD8⁺ T cells are important for viral clearance, and although often ineffective in neonates they can be protective when adequately stimulated. Using a murine CB6F1/J hybrid model of respiratory syncytial virus (RSV) infection, we previously demonstrated that the CD8⁺ T cell immunodominance hierarchy to two RSV-derived epitopes, K^dM2_82-90 and D^bM_187-195, was determined by the age at infection. To determine whether age-dependent RSV-specific CD8⁺ T cell responses could be modified through enhanced innate signaling, we used TLR4 or TLR9 agonist treatment at the time of infection, which remarkably changed the neonatal codominant response to an adult-like K^dM2_82-90 CD8⁺ T cell immunodominant response. This shift was associated with an increase in the number of conventional dendritic cells, CD11b⁺ and CD103⁺ dendritic cells, in the lung-draining lymph node, as well as increased expression of the costimulatory molecule CD86. The magnitude of the K^dM2_82-90 CD8⁺ T cell response in TLR agonist-treated neonates could be blocked with Abs against CD80 and CD86. These studies demonstrate the age-dependent function of conventional dendritic cells, their role in determining immunodominance hierarchy, and epitope-specific CD8⁺ T cell requirements for costimulation, all of which influence the immune response magnitude. The unique impact of TLR agonists on neonatal T cell responses is important to consider for RSV vaccines designed for young infants.

Novel Cell-Penetrating Peptide-Based Vaccine Induces Robust CD4+ and CD8+ T Cell-Mediated Antitumor Immunity

Vaccines that can coordinately induce multi-epitope T cell-mediated immunity, T helper functions, and immunologic memory may offer effective tools for cancer immunotherapy. Here, we report the development of a new class of recombinant protein cancer vaccines that deliver different CD8(+) and CD4(+) T-cell epitopes presented by MHC class I and class II alleles, respectively. In these vaccines, the recombinant protein is fused with Z12, a novel cell-penetrating peptide that promotes efficient protein loading into the antigen-processing machinery of dendritic cells. Z12 elicited an integrated and multi-epitopic immune response with persistent effector T cells. Therapy with Z12-formulated vaccines prolonged survival in three robust tumor models, with the longest survival in an orthotopic model of aggressive brain cancer. Analysis of the tumor sites showed antigen-specific T-cell accumulation with favorable modulation of the balance of the immune infiltrate. Taken together, the results offered a preclinical proof of concept for the use of Z12-formulated vaccines as a versatile platform for the development of effective cancer vaccines.

CD40 is required for protective immunity against liver stage Plasmodium infection

The costimulatory molecule CD40 enhances immunity through several distinct roles in T cell activation and T cell interaction with other immune cells. In a mouse model of immunity to liver stage Plasmodium infection, CD40 was critical for the full maturation of liver dendritic cells, accumulation of CD8(+) T cells in the liver, and protective immunity induced by immunization with the Plasmodium yoelii fabb/f(-) genetically attenuated parasite. Using mixed adoptive transfers of polyclonal wild-type and CD40-deficient CD8(+) T cells into wild-type and CD40-deficient hosts, we evaluated the contributions to CD8(+) T cell immunity of CD40 expressed on host tissues including APC, compared with CD40 expressed on the CD8(+) T cells themselves. Most of the effects of CD40 could be accounted for by expression in the T cells' environment, including the accumulation of large numbers of CD8(+) T cells in the livers of immunized mice. Thus, protective immunity generated during immunization with fabb/f(-) was largely dependent on effective APC licensing via CD40 signaling.

CD40 signaling to the rescue: A CD8 exhaustion perspective in chronic infectious diseases

Chronic infectious diseases such as HIV, HBV, and HCV, among others, cause severe morbidity and mortality globally. Progressive decline in CD8 functionality, survival, and proliferative potential-a phenomenon referred to as CD8 exhaustion-is believed to be responsible for poor pathogen control in chronic infectious diseases. While the role of negative inhibitory receptors such as PD-1 in augmenting CD8 exhaustion has been extensively studied, the role of positive costimulatory receptors remains poorly understood. In this review, we discuss how one such costimulatory pathway, CD40-CD40L, regulates CD8 dysfunction and rescue. While the significance of this pathway has been extensively investigated in models of autoimmunity, acute infectious diseases, and tumor models, the role played by CD40-CD40L in regulating CD8 exhaustion in chronic infectious diseases is just beginning to be understood. Considering that monotherapy with blocking antibodies targeting inhibitory PD-1-PD-L1 pathway is only partially effective at ameliorating CD8 exhaustion and that humanized CD40 agonist antibodies are currently available, a better understanding of the role of the CD40-CD40L pathway in chronic infectious diseases will pave the way for the development of more robust immunotherapeutic and prophylactic vaccination strategies.

Inhibition of CD8+ T cell-derived CD40 signals is necessary but not sufficient for Foxp3+ induced regulatory T cell generation in vivo

Current models of CD4(+) T cell help suggest a major role for CD154 binding to CD40 expressed on dendritic cells, with a lesser role for direct T:T interactions via CD40 expressed on CD8(+) T cells. However, the contribution of CD8(+) T cell-derived CD40 signals during the donor-reactive T cell response to a transplant has never been studied. In this study, we examined the graft-rejection kinetics and CD4(+) and CD8(+) donor-reactive T cell responses under conditions in which CD40 was genetically ablated only on APC, as well as under conditions in which CD40 was genetically ablated only on donor-reactive CD8(+) T cells. Our results revealed a significant role for CD8(+) T cell-expressed CD40 in the augmentation of donor-reactive CD8(+) T cell responses following transplantation and showed that CD40 expressed on CD8(+) T cells must be inhibited to allow conversion of CD4(+) T cells into induced regulatory T cells. Thus, this study identifies a major role for CD8(+) T cell-derived CD40 signals as a critical switch factor that both promotes optimal differentiation of cytokine-producing CD8(+) effector T cell responses and inhibits the differentiation of Ag-specific Foxp3(+) induced regulatory T cells in vivo.

Effector CD8 T cell trafficking within the liver

CD8 T cells play a critical role in several pathological conditions affecting the liver, most notably viral hepatitis. Accordingly, understanding the mechanisms that modulate the intrahepatic recruitment of CD8 T cells is of paramount importance. Some of the rules governing the behavior of these cells in the liver have been characterized at the population level, or have been inferred by studying the intrahepatic behavior of other leukocyte subpopulations. In contrast to most microvascular beds where leukocyte adhesion is restricted to the endothelium of post-capillary venules, it is now becoming clear that in the liver leukocytes, including CD8 T cells, can efficiently interact with the endothelium of hepatic capillaries (i.e. the sinusoids). While physical trapping has been proposed to play an important role in leukocyte adhesion to hepatic sinusoids, there is mounting evidence that T cell recruitment to the liver is highly regulated and depends on recruitment signals that are either constitutive or induced by inflammation. We review here several specific adhesive mechanisms that have been shown to regulate CD8 T cell trafficking within the liver, as well as highlight recent data that establish platelets as key cellular regulators of intrahepatic CD8 T cell accumulation.

Influenza-induced, helper-independent CD8+ T cell responses use CD40 costimulation at the late phase of the primary response

The helper-dependent pathway of priming CD8(+) T cells involves "licensing" of DCs by CD40L on CD4(+) T cells. The helper-independent ("helpless") pathways elicited by many viruses, including influenza, are less widely understood. We have postulated that CD40L can be up-regulated on DCs by such viruses, and this promotes priming of CD8(+) T cells via CD40. Most studies on costimulation have been performed in the presence of CD4(+) T cells, and so the role of CD40L costimulation under helpless circumstances has not been fully elucidated. Here, we investigated such a role for CD40L using CD40L KO mice. Although the number of influenza-specific CD8(+) T cells was unaffected by the absence of CD4(+) T cells, it was markedly decreased in the absence of CD40L. Proliferation (the number of CD44(+)BrdU(+) influenza-specific CD8(+) T cells) in the primary response was diminished in CD40L KO mice at Day 8 but not at Day 5 after infection. MLR studies indicated that CD40L expression on DCs was critical for CD8(+) T cell activation. Adoptive transfer of CD40 KO CD8(+) T cells compared with WT cells confirmed that CD40 on such cells was critical for the generation of primary anti-influenza CD8(+) T cell responses. The late effect also corresponded with the late expression of CD40 by influenza-specific CD8(+) T cells. We suggest that costimulation via CD40L on DCs and CD40 on CD8(+) T cells is important in optimizing primary CD8(+) T cell responses during influenza infection.

Antiplatelet therapy prevents hepatocellular carcinoma and improves survival in a mouse model of chronic hepatitis B

Chronic infection with hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). The pathogenesis of HBV-associated HCC involves both viral and host factors. The latter include a functionally inefficient CD8(+) T-cell response that fails to clear the infection from the liver but sustains a chronic necroinflammatory process that contributes to the development of HCC. According to this scenario, amelioration of immune-mediated chronic liver injury may prevent HCC. Because platelets facilitate immune-mediated liver injury by promoting the hepatic accumulation of virus-specific CD8(+) T cells, we evaluated the long-term consequences of antiplatelet therapy in an HBV transgenic mouse model of chronic immune-mediated necroinflammatory liver disease that progresses to HCC. Treatment with aspirin and clopidogrel during the chronic phase of the disease diminished the number of intrahepatic HBV-specific CD8(+) T cells and HBV-nonspecific inflammatory cells, the severity of liver fibrosis, and the development of HCC. Antiplatelet therapy improved overall survival without causing significant side effects. In contrast, the same antiplatelet regimen had no antitumor effect when HCC was induced nonimmunologically by chronic exposure to a hepatotoxic chemical. The unprecedented observation that antiplatelet therapy inhibits or delays immune-mediated hepatocarcinogenesis suggests that platelets may be key players in the pathogenesis of HBV-associated liver cancer and supports the notion that immune-mediated necroinflammatory reactions are an important cause of hepatocellular transformation during chronic hepatitis.