Role of integrin CD103 in promoting destruction of renal allografts by CD8 T cells

Cytolytic CD4+ and CD8+ Regulatory T-Cells and Implications for Developing Immunotherapies to Combat Graft-Versus-Host Disease

Regulatory T-cells (Treg) are critical for the maintenance of immune homeostasis and tolerance induction. While the immunosuppressive mechanisms of Treg have been extensively investigated for decades, the mechanisms responsible for Treg cytotoxicity and their therapeutic potential in regulating immune responses have been incompletely explored and exploited. Conventional cytotoxic T effector cells (Teffs) are known to be important for adaptive immune responses, particularly in the settings of viral infections and cancer. CD4+ and CD8+ Treg subsets may also share similar cytotoxic properties with conventional Teffs. Cytotoxic effector Treg (cyTreg) are a heterogeneous population in the periphery that retain the capacity to suppress T-cell proliferation and activation, induce cellular apoptosis, and migrate to tissues to ensure immune homeostasis. The latter can occur through several cytolytic mechanisms, including the Granzyme/Perforin and Fas/FasL signaling pathways. This review focuses on the current knowledge and recent advances in our understanding of cyTreg and their potential application in the treatment of human disease, particularly Graft-versus-Host Disease (GVHD).

Urinary Cell mRNA Profiles Predictive of Human Kidney Allograft Status

Immune monitoring of kidney allograft recipients and personalized therapeutics may help reach the aspirational goal of "one transplant for life." The invasive kidney biopsy procedure, the diagnostic tool of choice, has become safer and the biopsy classification more refined. Nevertheless, biopsy-associated complications, interobserver variability in biopsy specimen scoring, and costs continue to be significant concerns. The dynamics of the immune repertoire make frequent assessments of allograft status necessary, but repeat biopsies of the kidney are neither practical nor safe. To address the existing challenges, we developed urinary cell mRNA profiling and investigated the diagnostic, prognostic, and predictive accuracy of absolute levels of a hypothesis-based panel of mRNAs encoding immunoregulatory proteins. Enabled by our refinements of the PCR assay and by investigating mechanistic hypotheses, our single-center studies identified urinary cell mRNAs associated with T cell-mediated rejection, antibody-mediated rejection, interstitial fibrosis and tubular atrophy, and BK virus nephropathy. In the multicenter National Institutes of Health Clinical Trials in Organ Transplantation-04, we discovered and validated a urinary cell three-gene signature of T-cell CD3 ε chain mRNA, interferon gamma inducible protein 10 (IP-10) mRNA, and 18s ribosomal RNA that is diagnostic of subclinical acute cellular rejection and acute cellular rejection and prognostic of acute cellular rejection and graft function. The trajectory of the signature score remained flat and below the diagnostic threshold for acute cellular rejection in the patients with no rejection biopsy specimens, whereas a sharp rise was observed during the weeks before the biopsy specimen that showed acute cellular rejection. Our RNA sequencing and bioinformatics identified kidney allograft biopsy specimen gene signatures of acute rejection to be enriched in urinary cells matched to acute rejection biopsy specimens. The urinary cellular landscape was more diverse and more enriched for immune cell types compared with kidney allograft biopsy specimens. Urinary cell mRNA profile-guided clinical trials are needed to evaluate their value compared with current standard of care.

Environmental cues orchestrate regional immune surveillance and protection by pulmonary CTLs

Tissue-resident memory CD8 T cells (T_RM) provide preemptive immunity against infections that begin in peripheral tissues by guarding the site of initial pathogen exposure. Their role in immunity to respiratory virus infection is particularly important because severe damage to the alveoli can be avoided when local populations of T_RM cells reduce viral burdens and dampen the responses of effector CD8 T cells in the lungs. Although a connection between rapid immune activation and early viral control is well established, the signals that keep T_RM cells poised for action in the local tissues remain poorly defined. Recent studies have shown that environmental cues influence the fate decisions of activated CTLs during memory formation. Manipulation of these signaling pathways could provide new ways to capitalize on protection from T_RM cells in mucosal tissues, while reducing collateral damage and pathology during vaccination.

Location, location, location: CD103 demarcates intraepithelial, prognostically favorable CD8+ tumor-infiltrating lymphocytes in ovarian cancer

Although high levels of tumor-infiltrating lymphocytes (TILs) generally correlate with good prognosis in high-grade serous ovarian cancer (HGSC) patients, little is known about the phenotype or specificity of these cells. We have recently demonstrated that TIL expressing the intra-epithelial lymphocyte marker CD103 (official name, integrin α_E, ITGAE) abundantly infiltrate HGSCs, strongly correlating with increased disease-specific survival.

Guarding the perimeter: protection of the mucosa by tissue-resident memory T cells

Mucosal tissues are continually bombarded with infectious agents seeking to gain entry into the body. The absence of a tough physical exterior layer surrounding these tissues creates a unique challenge for the immune system, which manages to provide broad protection against a plethora of different organisms with the aid of special adaptations that augment immunity at these vulnerable sites. For example, specialized populations of memory T lymphocytes reside at initial sites of pathogen entry into the body, where they provide an important protective barrier. Similar anatomically-confined populations of pathogen-specific CD8 T cells can be found near the outer margins of the body following recovery from a variety of local infections, where they share very similar phenotypic characteristics. How these tissue-resident T cells are retained in a single anatomic location where they can promote immunity is beginning to be defined. Here, we will review current knowledge of the mechanisms that help establish and maintain these regional lymphocytes in the mucosal tissues and discuss relevant data that enhance our understanding of the contribution of these lymphocyte populations to protective immunity against infectious diseases.

A novel approach to the assessment of lymphocytic bronchiolitis after lung transplantation--transbronchial brush

BACKGROUND

Lymphocytic bronchiolitis (LB) is the strongest risk factor for subsequent allograft loss due to bronchiolitis obliterative syndrome (BOS); however, it is poorly assessed by transbronchial biopsy (TBBx) because of sampling error, interpretation error and the presence of non-alloimmune airway inflammation. We hypothesized that flow cytometric evaluation of bronchiolar brushings (transbronchial brush, TBBr) may be a better approach.

METHODS

Transbronchial brushings (2 to 3 cm from the pleural surface under radiologic guidance) were obtained prior to TBBx in 32 patients and analyzed by flow cytometry. We assessed the proportion of nucleated cells that were CD3(+)CD103(+) (epithelial-specific T cells).

RESULTS

No adverse events occurred; 0.5% (0.27 to 0.84) of the cells were epithelial-specific T cells and numbers increased with episodes of Grade A1 rejection (p < 0.01) and in patients with BOS (p = 0.02). Viral and invasive fungal infection were associated with marked infiltration with CD103(-) T cells (p < 0.01).

CONCLUSION

TBBr is simple to obtain, low risk, quantitative, and can discriminate between infective and alloimmune LB. It may be a valuable addition to current lung allograft assessment.

Matrilysin (Matrix Metalloproteinase-7) regulates anti-inflammatory and antifibrotic pulmonary dendritic cells that express CD103 (alpha(E)beta(7)-integrin)

The E-cadherin receptor CD103 (alpha(E)beta(7)-integrin) is expressed on specific populations of pulmonary dendritic cells (DC) and T cells. However, CD103 function in the lung is not well understood. Matrilysin (MMP-7) expression is increased in lung injury and cleaves E-cadherin from injured lung epithelium. Thus, to assess matrilysin effects on CD103-E-cadherin interactions in lung injury, wild-type, CD103(-/-), and Mmp7(-/-) mice, in which E-cadherin isn't cleaved in the lung, were treated with bleomycin or bleomycin with nFMLP to reverse the defect in acute neutrophil influx seen in Mmp7(-/-) mice. Pulmonary CD103(+) DC were significantly increased in injured wild-type compared with Mmp7(-/-) mice, and CD103(+) leukocytes showed significantly enhanced interaction with E-cadherin on injured wild-type epithelium than with Mmp7(-/-) epithelium in vitro and in vivo. Bleomycin-treated CD103(-/-) mice had persistent neutrophilic inflammation, increased fibrosis, and increased mortality compared with wild-type mice, a phenotype that was partially recapitulated in bleomycin/nFMLP-treated Mmp7(-/-) mice. Soluble E-cadherin increased IL-12 and IL-10 and reduced IL-6 mRNA expression in wild-type bone marrow-derived DC but not in CD103(-/-) bone marrow-derived DC. Similar mRNA patterns were seen in lungs of bleomycin-injured wild-type, but not CD103(-/-) or Mmp7(-/-), mice. In conclusion, matrilysin regulates pulmonary localization of DC that express CD103, and E-cadherin cleavage may activate CD103(+) DC to limit inflammation and inhibit fibrosis.

Alloantigen-induced regulatory CD8+CD103+ T cells

Regulatory T cells (Tregs) appear of great importance in the balance between alloreactivity and tolerance and subsets of both CD4(+) and CD8(+) T cells have been recognized to function as regulatory T cells after allogenic transplantation. Among the CD8(+) T-cell subsets, the CD103(+) cells were most recently identified as regulatory. In this review, we describe their phenotypical and functional properties, as well as their relevance for the alloimmune response in vivo. These CD8(+)CD103(+) Tregs are generated within mixed lymphocyte cultures (MLCs) and are elevated by additional transforming growth factor-beta. Interestingly, myeloid dendritic cells are the responsible cell type for induction of CD103(+) Tregs. Allostimulated CD8(+)CD103(+) Tregs display an antigen-experienced effector phenotype with limited effector functions such as cytotoxicity and interferon-gamma production and show a reduced proliferation capacity after restimulation. Beside this anergic phenotype, CD8(+)CD103(+) Tregs are able to suppress alloreactive effector T cells. Through intracellular cytokine staining and transwell assays, we showed that the mechanism of suppression is cytokine independent, but close cell-cell contact is required for suppression.

Cell adhesion antagonists: therapeutic potential in asthma and chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) and asthma are inflammatory diseases of the lung where a hallmark feature is excessive leukocyte infiltration that leads to tissue injury. Cell adhesion molecules (e.g. selectins and integrins) play a key role in cell trafficking, and in the lung they regulate leukocyte extravasation, migration within the interstitium, cellular activation, and tissue retention. All selectin family members (including L-selectin, P-selectin, and E-selectin) and many of the beta1 and beta2 integrins appear to be important therapeutic targets, as numerous animal studies have demonstrated essential roles for these cell adhesion molecules in lung inflammation. Not surprisingly, these families of adhesion molecules have been under intense investigation by the pharmaceutical industry for the development of novel therapeutics. Integrins are validated drug targets, as drugs that antagonize integrin alphaIIbbeta3 (e.g. abciximab), integrin alphaLbeta2 (efalizumab), and integrin alpha4beta1 (natalizumab) are currently US FDA-approved for acute coronary syndromes, psoriasis, and multiple sclerosis, respectively. However, none has been approved for indications related to asthma or COPD. Here, we provide an overview of roles played by selectins and integrins in lung inflammation. We also describe recent clinical results (both failures and successes) in developing adhesion molecule antagonists, with specific emphasis on those targets that may have potential benefit in asthma and COPD. Early clinical trials using selectin and integrin antagonists have met with limited success. However, recent positive phase II clinical trials with a small-molecule selectin antagonist (bimosiamose) and a small-molecule integrin alpha4beta1 antagonist (valategrast [R411]), have generated enthusiastic anticipation that novel strategies to treat asthma and COPD may be forthcoming.

Recipient Immune Repertoire and Engraftment Site Influence the Immune Pathway Effecting Acute Hepatocellular Allograft Rejection

As novel acute allograft rejection mechanisms are being discovered, determining the conditions that promote or subvert these distinct rejection pathways is important to interpret the clinical relevance of these pathways for specific recipient groups as well as specific tissue and organ transplants. We have employed a versatile hepatocellular allograft model to analyze how the host immune repertoire and immune locale influences the phenotype of the rejection pathway. In addition, we investigated how peripheral monitoring of cellular and humoral immune parameters correlates with the activity of a specific rejection pathway. Complete MHC mismatched hepatocellular allografts were transplanted into immune competent CD4-deficient, CD8-deficient, or C57BL/6 hosts to focus on CD8-dependent, CD4-dependent, or combined CD4 and CD8-dependent alloimmunity, respectively. Hepatocellular allografts were transplanted to the liver or kidney subcapsular space to investigate the influence of the immune locale on each rejection pathway. The generation of donor-reactive DTH, alloantibody, and allospecific cytotoxicity was measured to assess both cellular and humoral immunity. Graft-infiltrating lymphocytes were phenotyped and enumerated in each recipient group. In the presence of CD8+ T cells, cytolytic cellular activity is the dominant mechanism of graft destruction and is amplified in the presence of CD4+ T cells. The absence of CD8+ T cells (CD8 KO) results in potent humoral immunity as reflected by high levels of cytotoxic alloantibody and graft rejection with similar kinetics. Transplant to the liver compared to the kidney site is distinguished by more rapid kinetics of rejection and alloimmunity, which is predominately cell mediated rather than a mix of both humoral and cell-mediated immunity. These studies define several rejection mechanisms occurring in distinct immune conditions, highlighting the plasticity of acute allograft rejection responses and the need to design specific monitoring strategies for these pathways to allow dynamic immune assessment of clinical transplant recipients and targeted immunotherapies.

T regulatory cells in stable posttransplant bronchiolitis obliterans syndrome

BACKGROUND

Obliterative bronchiolitis (OB), mainly mediated by T cells, remains the major cause of morbidity and death in long-term lung transplant. Acute rejection (AR), also a T-cell mediated process, is strongly linked to OB. For unknown reasons, several patients with OB halt their pulmonary function decline and stabilize their obstructive defect for a long period. Our aim was to assess the T-cell activation in blood, induced sputum, and broncho-alveolar lavage during AR, stable OB (sOB), and evolving OB (eOB).

METHODS

T-cell phenotype and cytokine production were assessed by flow cytometry in these three compartments. Interleukin-4, interferon-gamma and transforming growth factor (TGF)-beta levels were measured by enzyme-linked immunosorbent assay in blood cell culture supernatants. Results were compared between healthy lung transplant recipients and AR (n=7), sOB (n=7), and eOB (n=13).

RESULTS

Stable and evolutive OB were characterized by a Treg, Th1, and Th2 activation, but compared to eOB, Treg and Th2 cells predominated in sOB. A clear Th1 activation was observed in AR. TGF-beta was increased in AR and evolving OB.

CONCLUSION

These preliminary results indicate a contrasted T-cell activation profile depending on the clinical conditions. We speculate that Treg cells could counterbalance the Th0 activation seen in evolving OB and participate in stabilization of airway obstruction.

Corneal integrins and their functions

Integrins were first described just over 20 years ago and have been studied in the cornea by many groups interested in how the cornea functions in health and disease. There are a minimum of 12 different integrin heterodimers reported to be expressed by the major resident cells of the cornea: the corneal and limbal epithelial cells, keratocytes/fibroblasts, and corneal endothelial cells. These different integrin heterodimers play important and varied roles in maintaining the cornea and organizing how its cells interact with their surrounding extracellular matrix to maintain corneal clarity. In this review, an overview of the discovery and functions of integrins is provided along with a description of the current state of our knowledge of this large family of important proteins. While we have learned a lot about corneal integrins over the past 20 years, there is still much to learn. Areas where gaps in our knowledge of integrin functions in the cornea are slowing our progress in understanding corneal diseases and dystrophies at a molecular level are highlighted.