Tissue-resident memory T cells in the urogenital tract.

Our understanding of T cell memory responses changed drastically with the discovery that specialized T cell memory populations reside within peripheral tissues at key pathogen entry sites. These tissue-resident memory T (TRM) cells can respond promptly to an infection without the need for migration, proliferation or differentiation. This rapid and local deployment of effector functions maximizes the ability of TRM cells to eliminate pathogens. TRM cells do not circulate through peripheral tissues but instead form isolated populations in the skin, gut, liver, kidneys, the reproductive tract and other organs. This long-term retention in the periphery might allow TRM cells to fully adapt to the local conditions of their environment and mount customized responses to counter infection and tumour growth in a tissue-specific manner. In the urogenital tract, TRM cells must adapt to a unique microenvironment to confer protection against potential threats, including cancer and infection, while preventing the onset of auto-inflammatory disease. In this Review, we discuss insights into the diversification of TRM cells from other memory T cell lineages, the adaptations of TRM cells to their local environment, and their enhanced capacity to counter infection and tumour growth compared with other memory T cell populations, especially in the urogenital tract.

How to Reliably Define Human CD8+ T-Cell Subsets: Markers Playing Tricks.

In recent years, our understanding about the functional complexity of CD8+ T-cell populations has increased tremendously. The immunology field is now facing challenges to translate these insights into phenotypic definitions that correlate reliably with distinct functional traits. This is key to adequately monitor and understand compound immune responses including vaccination and immunotherapy regimens. Here we will summarize our understanding of the current state in the human CD8+ T-cell subset characterization field. We will address how reliably the currently used cell surface markers are connected to differentiation status and function of particular subsets. By restricting ourselves to CD8+ αß T cells, we will focus mostly on major histocompatibility complex (MHC) class I-restricted virus- and tumor-specific T cells. This comes with a major advantage as fluorescently labeled peptide-loaded MHC class I multimers have been widely used to identify and characterize these cells.

CD8 and CD4 T Cell Populations in Human Kidneys.

BACKGROUND: At border sites, and in internal organs, tissue resident memory T cells (TRM) contribute to the immune barrier against pathogens like viruses, bacteria, fungi, and cancer. However, information on the presence and function of these cells in the human kidney is scant. In order to better understand the T cell-mediated immunological defense in this organ, we aimed to determine phenotypic and functional aspects of CD8 and CD4 T cells present in healthy and allograft kidney tissue. METHODS: Using multichannel flow cytometry, we assessed the phenotype and function of T cells in healthy renal tissue samples (n = 5) and kidney allograft tissue (n = 7) and compared these aspects to T cells in peripheral blood from healthy controls (n = 13). RESULTS: Kidney tissue samples contained substantial amounts of CD8 and CD4 T cells. In contrast to the circulating cells, kidney T cells frequently expressed CD69 and CD103, and were more often actively cycling. Furthermore, nearly all kidney T cells expressed CXCR3, and often expressed CXCR6 compared to T cells in the circulation. Markedly, kidney T cells produced greater quantities of IFNγ than circulating cells and were frequently polyfunctional. CONCLUSION: Functional T cells with the characteristic traits of TRM reside in human kidney tissues. These cells are more often actively cycling and frequently express CXCR3 and CXCR6.

Clinically Relevant Reactivation of Polyomavirus BK (BKPyV) in HLA-A02-Positive Renal Transplant Recipients Is Associated with Impaired Effector-Memory Differentiation of BKPyV-Specific CD8+ T Cells.

Polyomavirus BK (BKPyV) frequently reactivates in immunosuppressed renal transplant recipients (RTRs) and may lead to graft loss due to BKPyV-induced interstitial nephritis (BKVN). Little is known on the differentiation of CD8+ T cells targeting BKPyV in RTRs. Here we investigated whether BKPyV-specific CD8+ T cell differentiation differs in RTRs with varying degrees of BKPyV reactivation and/or BKVN. Using combinatorial encoding with tetramers carrying BKPyV major capsid protein (VP1) and large T antigen protein (LTAG) epitopes, we investigated CD8+ T cell responses to BKPyV in longitudinally obtained PBMC samples from 46 HLA-A02-positive RTRs and 20 healthy adults. We were also able to isolate BKPyV-specific CD8+ T cells from five renal allografts, two of which were affected by BKVN. Before transplantation, BKPyV-specific CD8+ T cells targeting VP1 and LTAG epitopes appeared predominantly as central-memory and CD27+/CD28+ effector-memory (TEM), and naïve-like PD-1-expressing cells, respectively. After viral reactivation, BKPyV-specific CD8+ T cells assumed CD28- TEM and TEMRA states in patients who were able to control BKPyV, whereas differentiation lagged behind in patients with severe viral reactivation or BKVN. Furthermore, VP1-specific CD69+/CD103+ tissue-resident memory (TRM) cells accumulated in BKVN-affected allografts but lacked signs of effector differentiation. In contrast, granzyme B-expressing effector cells were detected in allografts not affected by BKVN. In conclusion, effector-memory differentiation of BKPyV-specific CD8+ T cells in patients with high viral load or BKVN is impaired. Further characterization of the specific mechanisms behind this altered cellular differentiation is necessary to develop therapies that can prevent the emergence of BKVN.

Intragraft Blood Dendritic Cell Antigen-1-Positive Myeloid Dendritic Cells Increase during BK Polyomavirus-Associated Nephropathy.

Although both polyomavirus infection and T cell-mediated rejection (TCMR) are characterized by tubulointerstitial inflammation in the renal allograft, these conditions are treated with opposing therapeutic regimens. To gain more insight into the differences between antiviral and alloimmune responses, we performed a case-control study, in which we immunophenotyped the inflammatory infiltrates in renal biopsy specimens with BK polyomavirus-associated nephropathy (BKPyVAN) and specimens with TCMR. Compared with TCMR, BKPyVAN was diagnosed later after transplantation; therefore, BKPyVAN specimens showed more chronic damage than TCMR specimens showed. However, TCMR and BKPyVAN specimens had comparable levels of tubulointerstitial inflammation. Adjustment for confounders in various multivariable models revealed more blood dendritic cell antigen-1(+) (BDCA-1(+)) myeloid dendritic cells (mDCs) present during BKPyVAN (odds ratio, 2.31; 95% confidence interval, 1.03 to 5.16; P=0.04) than during TCMR. Double immunostaining for SV40 and BDCA-1 showed that, during BKPyVAN, BDCA-1(+) mDCs localized in proximity to the polyomavirus-infected tubular epithelial cells. We ensured that time of biopsy after transplantation was not a confounding factor by including additional specimens with late TCMR and protocol biopsy specimens matched for biopsy time. These additional specimens showed amounts of BDCA-1(+) mDCs comparable with amounts in the early TCMR specimens. These results suggest that BDCA-1(+) mDCs, known to be involved in the antiviral immune response during various viral infections, might have a pivotal role during BKPyVAN infection in the grafted kidney.

Blood and beyond: properties of circulating and tissue-resident human virus-specific αß CD8(+) T cells.

CD8(+) αß T-cell responses form an essential line of defence against viral infections. An important part of the mechanisms that control the generation and maintenance of these responses have been elucidated in experimental mouse models. In recent years it has become clear that CD8(+) T-cell responses in humans not only show similarities, but also display differences to those occurring in mice. Furthermore, while several viral infections occur primarily in specialised organ systems, for obvious reasons, most human CD8(+) T-cell investigations were performed on cells deriving from the circulation. Indeed, several lines of evidence now point to essential functional differences between virus-specific CD8(+) memory T cells found in the circulation and those providing protection in organ systems, such as the lungs. In this review, we will focus on summarising recent insights into human CD8(+) T-cell differentiation in response to several viruses and emphasise that for a complete understanding of anti-viral immunity, it is pivotal to scrutinize such responses in both blood and tissue.

Phenotypic and functional characterization of circulating polyomavirus BK VP1-specific CD8+ T cells in healthy adults.

The human polyomavirus BK virus (BKV) establishes a latent and asymptomatic infection in the majority of the population. In immunocompromised individuals, the virus frequently (re)activates and may cause severe disease such as interstitial nephritis and hemorrhagic cystitis. Currently, the therapeutic options are limited to reconstitution of the antiviral immune response. T cells are particularly important for controlling this virus, and T cell therapies may provide a highly specific and effective mode of treatment. However, little is known about the phenotype and function of BKV-specific T cells in healthy individuals. Using tetrameric BKV peptide-HLA-A02 complexes, we determined the presence, phenotype, and functional characteristics of circulating BKV VP1-specific CD8(+) T cells in 5 healthy individuals. We show that these cells are present in low frequencies in the circulation and that they have a resting CD45RA(-) CD27(+) memory and predominantly CCR7(-) CD127(+) KLRG1(+) CD49d(hi) CXCR3(hi) T-bet(int) Eomesodermin(lo) phenotype. Furthermore, their direct cytotoxic capacity seems to be limited, since they do not readily express granzyme B and express only little granzyme K. We compared these cells to circulating CD8(+) T cells specific for cytomegalovirus (CMV), Epstein-Barr virus (EBV), and influenza virus (Flu) in the same donors and show that BKV-specific T cells have a phenotype that is distinct from that of CMV- and EBV-specific T cells. Lastly, we show that BKV-specific T cells are polyfunctional since they are able to rapidly express interleukin-2 (IL-2), gamma interferon (IFN-γ), tumor necrosis factor α, and also, to a much lower extent, MIP-1ß and CD107a.

Elevated numbers and altered subsets of procoagulant microparticles in breast cancer patients using endocrine therapy.

INTRODUCTION: Microparticles (MP) can be elevated in cancer and thromboembolic disease. We hypothesized a role for MP in the hypercoagulable state in breast cancer patients using endocrine therapy, in whom both cancer and the use of endocrine therapy are independent risk factors for the development of thrombosis. DESIGN AND METHODS: Plasma samples were collected from 40 breast cancer patients using endocrine therapy (20 patients without metastases receiving adjuvant therapy and 20 patients with metastatic disease treated in a palliative setting) and from 20 female healthy controls. The endocrine therapy used was either an anti-estrogen or an aromatase inhibitor. Numbers and cellular origin of MP subsets were analyzed by flowcytometry. MP-associated procoagulant activity was measured using a thrombin generation assay using conditions that allow analysis of MP induced thrombin generation. RESULTS: Breast cancer patients using endocrine therapy had higher levels of MP positive for Annexin V (median 10000 vs 6500×10E6/l), P-selectin (330 vs 200×10E6/l), tissue factor (33 vs 15×10E6/l), and of MP derived from platelets (CD41) and leukocytes (CD45). Thrombin generation in plasma was dependent on the presence of MP and thrombin generation performed after addition of isolated MP to normal plasma showed a higher endogenous thrombin potential (1105 vs 1029 nM.min) in breast cancer patients. No differences were observed in MP levels and thrombin generation parameters between the metastatic and adjuvant group. CONCLUSION: Breast cancer patients using endocrine therapy have an increased MP number and a higher MP-dependent thrombin generation, irrespective of the presence of metastatic disease. Altered MP subset characteristics in these patients, especially the higher number of (activated) platelet derived MP and leukocyte derived MP, may in part explain a heightened procoagulant state in breast cancer patients using endocrine therapy.