Characterization of CD4- CD8- CD3+ T-cell receptor-alphabeta+ T cells in murine cytomegalovirus infection

Dynamic changes to tissue-resident immunity after MHC-matched and MHC-mismatched solid organ transplantation

The heterogeneous pool of tissue-resident lymphocytes in solid organs mediates infection responses and supports tissue integrity and repair. Their vital functions in normal physiology suggest an important role in solid organ transplantation; however, their detailed examination in this context has not been performed. Here, we report the fate of multiple lymphocyte subsets, including T, B, and innate lymphoid cells, after murine liver and heart transplantation. In major histocompatibility complex (MHC)-matched transplantation, donor lymphocytes are retained in liver grafts and peripheral lymphoid organs of heart and liver transplant recipients. In MHC-mismatched transplantation, increased infiltration of the graft by recipient cells and depletion of donor lymphocytes occur, which can be prevented by removal of recipient T and B cells. Recipient lymphocytes fail to recreate the native organs' phenotypically diverse tissue-resident lymphocyte composition, even in MHC-matched models. These post-transplant changes may leave grafts vulnerable to infection and impair long-term graft function.

Resolution of herpes simplex virus reactivation in vivo results in neuronal destruction

A fundamental question in herpes simplex virus (HSV) pathogenesis is the consequence of viral reactivation to the neuron. Evidence supporting both post-reactivation survival and demise is published. The exceedingly rare nature of this event at the neuronal level in the sensory ganglion has limited direct examination of this important question. In this study, an in-depth in vivo analysis of the resolution of reactivation was undertaken. Latently infected C57BL/6 mice were induced to reactivate in vivo by hyperthermic stress. Infectious virus was detected in a high percentage (60-80%) of the trigeminal ganglia from these mice at 20 hours post-reactivation stimulus, but declined by 48 hours post-stimulus (0-13%). With increasing time post-reactivation stimulus, the percentage of reactivating neurons surrounded by a cellular cuff increased, which correlated with a decrease in detectable infectious virus and number of viral protein positive neurons. Importantly, in addition to intact viral protein positive neurons, fragmented viral protein positive neurons morphologically consistent with apoptotic bodies and containing cleaved caspase-3 were detected. The frequency of this phenotype increased through time post-reactivation. These fragmented neurons were surrounded by Iba1+ cells, consistent with phagocytic removal of dead neurons. Evidence of neuronal destruction post-reactivation prompted re-examination of the previously reported non-cytolytic role of T cells in controlling reactivation. Latently infected mice were treated with anti-CD4/CD8 antibodies prior to induced reactivation. Neither infectious virus titers nor neuronal fragmentation were altered. In contrast, when viral DNA replication was blocked during reactivation, fragmentation was not observed even though viral proteins were expressed. Our data demonstrate that at least a portion of reactivating neurons are destroyed. Although no evidence for direct T cell mediated antigen recognition in this process was apparent, inhibition of viral DNA replication blocked neuronal fragmentation. These unexpected findings raise new questions about the resolution of HSV reactivation in the host nervous system.

Combination of mAb-AR20.5, anti-PD-L1 and PolyICLC inhibits tumor progression and prolongs survival of MUC1.Tg mice challenged with pancreatic tumors

A substantial body of evidence suggests the existence of MUC1-specific antibodies and cytotoxic T cell activities in pancreatic cancer patients. However, tumor-induced immunosuppression renders these responses ineffective. The current study explores a novel therapeutic combination wherein tumor-bearing hosts can be immunologically primed with their own antigen, through opsonization with a tumor antigen-targeted antibody, mAb-AR20.5. We evaluated the efficacy of immunization with this antibody in combination with PolyICLC and anti-PD-L1. The therapeutic combination of mAb-AR20.5 + anti-PD-L1 + PolyICLC induced rejection of human MUC1 expressing tumors and provided a long-lasting, MUC1-specific cellular immune response, which could be adoptively transferred and shown to provide protection against tumor challenge in human MUC1 transgenic (MUC.Tg) mice. Furthermore, antibody depletion studies revealed that CD8 cells were effectors for the MUC1-specific immune response generated by the mAb-AR20.5 + anti-PD-L1 + PolyICLC combination. Multichromatic flow cytometry data analysis demonstrated a significant increase over time in circulating, activated CD8 T cells, CD3⁺CD4^-CD8^-(DN) T cells, and mature dendritic cells in mAb-AR20.5 + anti-PD-L1 + PolyICLC combination-treated, tumor-bearing mice, as compared to saline-treated control counterparts. Our study provides a proof of principle that an effective and long-lasting anti-tumor cellular immunity can be achieved in pancreatic tumor-bearing hosts against their own antigen (MUC1), which can be further potentiated using a vaccine adjuvant and an immune checkpoint inhibitor.

The checkpoint for agonist selection precedes conventional selection in human thymus

The thymus plays a central role in self-tolerance, partly by eliminating precursors with a T cell receptor (TCR) that binds strongly to self-antigens. However, the generation of self-agonist-selected lineages also relies on strong TCR signaling. How thymocytes discriminate between these opposite outcomes remains elusive. Here, we identified a human agonist-selected PD-1⁺ CD8αα⁺ subset of mature CD8αβ⁺ T cells that displays an effector phenotype associated with agonist selection. TCR stimulation of immature post-β-selection thymocyte blasts specifically gives rise to this innate subset and fixes early T cell receptor alpha variable (TRAV) and T cell receptor alpha joining (TRAJ) rearrangements in the TCR repertoire. These findings suggest that the checkpoint for agonist selection precedes conventional selection in the human thymus.

Tumour suppressor Fus1 provides a molecular link between inflammatory response and mitochondrial homeostasis

Fus1, encoded by a 3p21.3 tumour suppressor gene, is down-regulated, mutated or lost in the majority of inflammatory thoracic malignancies. The mitochondrial localization of Fus1 stimulated us to investigate how Fus1 modulates inflammatory response and mitochondrial function in a mouse model of asbestos-induced peritoneal inflammation. Asbestos treatment resulted in a decreased Fus1 expression in wild-type (WT) peritoneal immune cells, suggesting that asbestos exposure may compromise the Fus1-mediated inflammatory response. Untreated Fus1(-/-) mice had an ~eight-fold higher proportion of peritoneal granulocytes than Fus1(+/+) mice, pointing at ongoing chronic inflammation. Fus1(-/-) mice exhibited a perturbed inflammatory response to asbestos, reflected in decreased immune organ weight and peritoneal fluid protein concentration, along with an increased proportion of peritoneal macrophages. Fus1(-/-) immune cells showed augmented asbestos-induced activation of key inflammatory, anti-oxidant and genotoxic stress response proteins ERK1/2, NFκB, SOD2, γH2AX, etc. Moreover, Fus1(-/-) mice demonstrated altered dynamics of pro- and anti-inflammatory cytokine expression, such as IFNγ, TNFα, IL-1A, IL-1B and IL-10. 'Late' response cytokine Ccl5 was persistently under-expressed in Fus1(-/-) immune cells at both basal and asbestos-activated states. We observed an asbestos-related difference in the size of CD3(+) CD4(-) CD8(-) DN T cell subset that was expanded four-fold in Fus1(-/-) mice. Finally, we demonstrated Fus1-dependent basal and asbestos-induced changes in major mitochondrial parameters (ROS production, mitochondrial potential and UCP2 expression) in Fus1(-/-) immune cells and in Fus1-depleted cancer cells, thus supporting our hypothesis that Fus1 establishes its immune- and tumour-suppressive activities via regulation of mitochondrial homeostasis.

Flagellin, a TLR5 agonist, reduces graft-versus-host disease in allogeneic hematopoietic stem cell transplantation recipients while enhancing antiviral immunity

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality in patients treated with allogeneic hematopoietic stem cell transplantation (HSCT). Posttransplant immunosuppressive drugs incompletely control GVHD and increase susceptibility to opportunistic infections. In this study, we used flagellin, a TLR5 agonist protein (∼50 kDa) extracted from bacterial flagella, as a novel experimental treatment strategy to reduce both acute and chronic GVHD in allogeneic HSCT recipients. On the basis of the radioprotective effects of flagellin, we hypothesized that flagellin could ameliorate GVHD in lethally irradiated murine models of allogeneic HSCT. Two doses of highly purified flagellin (administered 3 h before irradiation and 24 h after HSCT) reduced GVHD and led to better survival in both H-2(b) → CB6F1 and H-2(K) → B6 allogeneic HSCT models while preserving >99% donor T cell chimerism. Flagellin treatment preserved long-term posttransplant immune reconstitution characterized by more donor thymic-derived CD4(+)CD25(+)Foxp3(+) regulatory T cells and significantly enhanced antiviral immunity after murine CMV infection. The proliferation index and activation status of donor spleen-derived T cells and serum concentration of proinflammatory cytokines in flagellin-treated recipients were reduced significantly within 4 d posttransplant compared with those of the PBS-treated control recipients. Allogeneic transplantation of radiation chimeras previously engrafted with TLR5 knockout hematopoietic cells showed that interactions between flagellin and TLR5 expressed on both donor hematopoietic and host nonhematopoietic cells were required to reduce GVHD. Thus, the peritransplant administration of flagellin is a novel therapeutic approach to control GVHD while preserving posttransplant donor immunity.

Host and donor immune responses contribute to antiviral effects of amotosalen-treated donor lymphocytes following early posttransplant cytomegalovirus infection

We have previously shown that amotosalen-treated splenocytes rescued allorecipients from a lethal dose of mouse CMV (MCMV) administered on day 0 in experimental parent C57BL/6-->CB6F1 allogeneic bone marrow transplant. In this study, we investigated the mechanism of antiviral activity of amotosalen-treated donor splenocytes when sublethal MCMV infections were administered 7 days posttransplant. Recipients of 3 x 10(6) untreated splenocytes were used as control. Following MCMV infection, recipients of untreated splenocytes had 40% early mortality due to acute graft-vs-host disease compared with no deaths among recipients of 10 x 10(6) treated splenocytes. However, recipients of both types of donor splenocytes effectively cleared MCMV from their liver. Like the untreated CD8(+) T cells, amotosalen-treated CD8(+) T cells equally retained their in vivo CTL activity against MCMV early peptide-pulsed targets and expressed similar levels of granzyme B within 11 days of infection. In contrast to full donor chimerism in recipients of untreated splenocytes, recipients of amotosalen-treated splenocytes showed mixed chimerism with both donor spleen- and host-derived anti-MCMV CD8(+) T cells in their blood and lymphoid organs, with significantly higher numbers of host-derived CD4(-)CD8(-) (double negative) T cells in the spleens of recipients of treated splenocytes compared with the recipients of untreated splenocytes. Additionally, recipients of amotosalen-treated splenocytes had lower levels of serum IFN-gamma and TNF-alpha in response to MCMV infection compared with untreated recipients. Thus, adoptive immunotherapy with treated T cells is a novel therapeutic approach that facilitates hematopoietic engraftment and permits antiviral immunity of both donor and host T cells without graft-vs-host disease.

Cytokine-mediated disruption of lymphocyte trafficking, hemopoiesis, and induction of lymphopenia, anemia, and thrombocytopenia in anti-CD137-treated mice

CD137-mediated signals costimulate T cells and protect them from activation-induced apoptosis; they induce curative antitumor immunity and enhance antiviral immune responses in mice. In contrast, anti-CD137 agonistic mAbs can suppress T-dependent humoral immunity and reverse the course of established autoimmune disease. These results have provided a rationale for assessing the therapeutic potential of CD137 ligands in human clinical trials. In this study, we report that a single 200-mug injection of anti-CD137 given to otherwise naive BALB/c or C57BL/6 mice led to the development of a series of immunological anomalies. These included splenomegaly, lymphadenopathy, hepatomegaly, multifocal hepatitis, anemia, altered trafficking of B cells and CD8 T cells, loss of NK cells, and a 10-fold increase in bone marrow (BM) cells bearing the phenotype of hemopoietic stem cells. These events were dependent on CD8 T cells, TNF-alpha, IFN-gamma, and type I IFNs. BM cells up-regulated Fas, and there was a significant increase in the number of CD8+ T cells that correlated with a loss of CD19+ and Ab-secreting cells in the BM. TCR Valphabeta usage was random and polyclonal among liver-infiltrating CD8 T cells, and multifocal CD8+ T cell infiltrates were resolved upon termination of anti-CD137 treatment. Anti-CD137-treated mice developed lymphopenia, thrombocytopenia, and anemia, and had lowered levels of hemoglobin and increased numbers of reticulocytes.

Phenotypic and functional differences between lymphocytes from NALT and nasal passages of mice

Nasal-associated lymphoid tissue (NALT) and nasal passages (NP) are considered as inductive and effector sites, respectively. The differences among lymphocyte populations of these nasal compartments have not been clearly established. The aim of this work was to contribute to the characterization of NALT and NP lymphocytes in mice. We isolated lymphocytes from both compartments, determined the frequencies of B220(+) cells as well as CD8(+), CD4(+) T cells; and analysed the expression of CD69 and CD25. Besides we analysed the proportion of T cells producing IL-2, IL-4, IL-5, IL-10, IFN-gamma and TNF-alpha. We found differences between NALT and NP. Two populations of B cells, B220+(hi) and B220+(low) were clearly distinguished only in NP, but not in NALT. Both (hi) and (low) B220(+) cells expressed CD19, but only a fraction of the B220+(low) population, expressed the plasma cell marker CD138(+). More B than T lymphocytes, as well as higher frequencies of CD4(+) than CD8(+) T cells were found in both compartments. A small fraction of NK cells (CD3(-)DX5(+)) along with a significant proportion of double negative CD4(-)CD8(-)CD3(+)DX5(-) T cells was detected in both nasal tissues. Furthermore, as expected for a mucosal effector site, NP contained major proportions of B220(+), T CD4(+) and T CD8(+) cells expressing CD25 and CD69 in comparison to NALT. Likewise, the proportion of T cells spontaneously producing IL-2, IFN-gamma, and IL-4, was higher in NP than in NALT. These data provide further evidence indicating that distinctive phenotypic and functional features exist in the lymphocyte populations residing at NALT and NP.

Chronic GvHD decreases antiviral immune responses in allogeneic BMT

Chronic graft-versus-host disease (cGvHD) is associated with functional immunodeficiency and an increased risk of opportunistic infections in allogeneic bone marrow transplantation (BMT). We used a parent to F1 model of allogeneic BMT to test the hypothesis that cGvHD leads to impaired antigen-specific antiviral immunity and compared BM transplant recipients with cGvHD to control groups of allogeneic BM transplant recipients without GvHD. Mice with and without cGvHD received a nonlethal dose of murine cytomegalovirus (MCMV) +100 days after transplantation. Recipients with cGvHD had more weight loss and higher viral loads in the spleen and liver. MCMV infection led to greater than 25-fold expansion of donor spleen-derived MCMV peptide-specific tetramer-positive CD8(+) T cells in blood of transplant recipients with and without cGvHD, but mice with cGvHD had far fewer antigen-specific T cells in peripheral tissues and secondary lymphoid organs. The immunosuppression associated with cGvHD was confirmed by vaccinating transplant recipients with and without cGvHD using a recombinant Listeria expressing MCMV early protein (Lm-MCMV). Secondary adoptive transfer of lymphocytes from donor mice with or without cGvHD into lymphopenic congenic recipients showed that cGvHD impaired tissue-specific homing of antigen-specific T cells. These results indicate that cGvHD causes an intrinsic immunosuppression and explain, in part, the functional immunodeficiency in allogeneic transplant recipients.

Double-negative regulatory T cells: non-conventional regulators

The crucial role of regulatory T (Treg) cells in self-tolerance and downregulating immune responses has been clearly established. Numerous different Treg subsets have been identified that possess distinct phenotypes and functions in various disease models. Among these subsets, alphabeta-TCR+CD3+CD4-CD8- double-negative (DN) Treg cells have been shown to be able to inhibit a variety of immune responses in part via direct killing of effector T cells in an antigenspecific manner in both mice and humans. This was shown to occur at least partially by acquisition of MHC-peptide complexes from antigen-presenting cells (APCs) and subsequent Fas/Fas-ligand interactions. In addition, DN Treg cells have been shown to express several molecules uncommon to other Treg cell subsets, such as IFN-gamma, TNF-alpha, Ly6A, FcRgamma, and CXCR5, which may contribute to their unique regulatory ability. Understanding the development and regulatory functions of DN Treg cells may elucidate the etiology for loss of self-tolerance and serve as a therapeutic modality for various diseases. This review will summarize the characteristics, developmental pathways, and mechanisms of action of DN Treg cells, as well as their role in transplant tolerance, autoimmunity, and anticancer immunity.

Increased proportion of CD3+CD4-CD8- double-negative T cells in peripheral blood of children with Behcet's disease

INTRODUCTION

Behcet's disease (BD) is a multi-system inflammatory disorder of poorly understood pathogenesis, which is characterized by oral aphtosis, genital ulcers and uveitis.

OBJECTIVE

To assess the role of CD3+CD4-CD8- double negative (DN) T cells in pathogenesis of Behcet's disease.

PATIENTS

Ten BD patients (age 12.2+/-2.2 years, 7 in remission, 3 in exacerbation state) treated at the Pediatric Rheumatology unit of Soroka University Medical Center and 3 age-matched controls participated in the study.

METHODS

Peripheral blood lymphocytes of study subjects were isolated and stained with fluorescein-labeled anti-CD45, CD3, CD4, CD8 antibodies and analyzed by FACS assay.

RESULTS

Proportion of CD4-CD8- DN T cells was significantly increased in BD patients (n=10) as compared to healthy controls (6.2+/-3.4% vs. 3.2+/-1.1% of total CD3+ cells, p<0.05), this cell group was additionally enhanced in BD exacerbation, compared to patients in remission (10+/-4.1% vs. 4.7+/-1.2%, p<0.05, respectively). DN T cells were significantly increased in BD patients in remission, compared to healthy controls (4.7+1.2% vs. 3.2+1.1% of total CD3+ cells, p<0.05, respectively).

CONCLUSIONS

Behcet's disease is characterized by increased proportion of CD3+CD4-CD8- double negative T cells in peripheral blood. Further studies, that include additional immunophenotyping and analysis of gene expression, aimed at characterization of these cells are currently underway.

CD4-CD8- T cells control intracellular bacterial infections both in vitro and in vivo

Memory T cells, including the well-known CD4⁺ and CD8⁺ T cells, are central components of the acquired immune system and are the basis for successful vaccination. After infection, CD4⁺ and CD8⁺ T cells expand into effector cells, and then differentiate into long-lived memory cells. We show that a rare population of CD4⁻CD8⁻CD3⁺αβ⁺γδ⁻NK1.1⁻ T cells has similar functions. These cells potently and specifically inhibit the growth of the intracellular bacteria Mycobacterium tuberculosis (M. tb.) or Francisella tularensis Live Vaccine Strain (LVS) in macrophages in vitro, promote survival of mice infected with these organisms in vivo, and adoptively transfer immunity to F. tularensis LVS. Furthermore, these cells expand in the spleens of mice infected with M. tb. or F. tularensis LVS, and then acquire a memory cell phenotype. Thus, CD4⁻CD8⁻ T cells have a role in the control of intracellular infection and may contribute to successful vaccination.

Expansion of TcRalphabeta+CD3+CD4-CD8- (CD4/CD8 double-negative) T lymphocytes in a case of staphylococcal toxic shock syndrome

A 55-year-old woman presented with staphylococcal toxic shock syndrome (TSS). During the course of the disease a significant lymphocytosis appeared, and a high number of TcRalphabeta+CD3+CD4-CD8- (double-negative, DN) lymphocytes was observed both in bone marrow and in peripheral blood samples. Correction of the altered lymphocyte immunophenotype was observed only 6 weeks after recovery from TSS. The immunophenotype of circulating and bone marrow lymphocytes was also studied during a phase of an aspecific febrile episode observed 2 months after recovery, but no subset of DN lymphocytes was found. A small subset of DN lymphocytes can be found in normal bone marrow, liver, thymus, and skin. These cells show peculiar immune regulatory properties and can increase in certain autoimmune diseases. Our findings may represent a specific effect of lymphocyte stimulation by the staphylococcal exotoxin, which is the effector agent of TSS.

Multiple T cell subsets control Francisella tularensis LVS intracellular growth without stimulation through macrophage interferon gamma receptors

A variety of data suggest that in vivo production of interferon (IFN)-gamma is necessary, but not sufficient, for expression of secondary protective immunity against intracellular pathogens. To discover specific IFN-gamma-independent T cell mediated mechanisms, we took advantage of an in vitro culture system that models in vivo immune responses to the intracellular bacterium Francisella tularensis live vaccine strain (LVS). LVS-immune lymphocytes specifically controlled 99% of the growth of LVS in wild-type murine bone marrow-derived macrophages. Surprisingly, LVS-immune lymphocytes also inhibited LVS intracellular growth by as much as 95% in macrophages derived from IFN-gamma receptor knockout (IFNgammaR KO) mice. CD8+ T cells, and to a lesser degree CD4+ T cells, controlled LVS intracellular growth in both wild-type and IFNgammaR KO macrophages. Further, a unique population of Thy1+alphabeta+CD4-CD8- cells that was previously suggested to operate during secondary immunity to LVS in vivo strongly controlled LVS intracellular growth in vitro. A large proportion of the inhibition of LVS intracellular growth in IFNgammaR KO macrophages by all three T cell subsets could be attributed to tumor necrosis factor (TNF) alpha. Thus, T cell mechanisms exist that control LVS intracellular growth without acting through the IFN-gamma receptor; such control is due in large part to TNF-alpha, and is partially mediated by a unique double negative T cell subpopulation.