Role of regulatory T cells in psoriasis pathogenesis and treatment

Psoriasis is a chronic inflammatory disease with a strong genetic component that can be triggered by environmental factors. Disease pathogenesis is mainly driven by type 1 and type 17 cytokine-producing cells which, in healthy individuals, are modulated by regulatory T cells (Tregs). Tregs play a fundamental role in immune homeostasis and contribute to the prevention of autoimmune disease by suppressing immune responses. In psoriasis, Tregs are impaired in their suppressive function leading to an altered T-helper 17/Treg balance. Although Treg dysfunction in patients with psoriasis is associated with disease exacerbation, it is unknown how they are functionally regulated. In this review, we discuss recent insights into Tregs in the setting of psoriasis with an emphasis on the effect of current treatments on Tregs and how already available therapeutics that modulate Treg frequency or functionality could be exploited for treatment of psoriasis.

Emerging roles of innate lymphoid cells in inflammatory diseases: Clinical implications

Innate lymphoid cells (ILC) represent a group of lymphocytes that lack specific antigen receptors and are relatively rare as compared to adaptive lymphocytes. ILCs play important roles in allergic and nonallergic inflammatory diseases due to their location at barrier surfaces within the airways, gut, and skin, and they respond to cytokines produced by activated cells in their local environment. Innate lymphoid cells contribute to the immune response by the release of cytokines and other mediators, forming a link between innate and adaptive immunity. In recent years, these cells have been extensively characterized and their role in animal models of disease has been investigated. Data to translate the relevance of ILCs in human pathology, and the potential role of ILCs in diagnosis, as biomarkers and/or as future treatment targets are also emerging. This review, produced by a task force of the Immunology Section of the European Academy of Allergy and Clinical Immunology (EAACI), encompassing clinicians and researchers, highlights the role of ILCs in human allergic and nonallergic diseases in the airways, gastrointestinal tract, and skin, with a focus on new insights into clinical implications, therapeutic options, and future research opportunities.

Expansion of highly activated invariant natural killer T cells with altered phenotype in acute dengue infection

Invariant natural killer T (iNKT) cells are capable of rapid activation and production of cytokines upon recognition of antigenic lipids presented by CD1d molecules. They have been shown to play a significant role in many viral infections and were observed to be highly activated in patients with acute dengue infection. In order to characterize further their role in dengue infection, we investigated the proportion of iNKT cells and their phenotype in adult patients with acute dengue infection. The functionality of iNKT cells in patients was investigated by both interferon (IFN)-γ and interleukin (IL)-4 ex-vivo enzyme-linked immunospot (ELISPOT) assays following stimulation with alpha-galactosyl-ceramide (αGalCer). We found that circulating iNKT cell proportions were significantly higher (P = 0·03) in patients with acute dengue when compared to healthy individuals and were predominantly of the CD4(+) subset. iNKT cells of patients with acute dengue had reduced proportions expressing CD8α and CD161 when compared to healthy individuals. The iNKT cells of patients were highly activated and iNKT activation correlated significantly with dengue virus-specific immunoglobulin (Ig)G antibody levels. iNKT cells expressing Bcl-6 (P = 0·0003) and both Bcl-6 and inducible T cell co-stimulator (ICOS) (P = 0·006) were increased significantly in patients when compared to healthy individuals. Therefore, our data suggest that in acute dengue infection there is an expansion of highly activated CD4(+) iNKT cells, with reduced expression of CD161 markers.

Dengue NS1 antigen contributes to disease severity by inducing interleukin (IL)-10 by monocytes

Both dengue NS1 antigen and serum interleukin (IL)-10 levels have been shown to associate with severe clinical disease in acute dengue infection, and IL-10 has also been shown to suppress dengue-specific T cell responses. Therefore, we proceeded to investigate the mechanisms by which dengue NS1 contributes to disease pathogenesis and if it is associated with altered IL-10 production. Serum IL-10 and dengue NS1 antigen levels were assessed serially in 36 adult Sri Lankan individuals with acute dengue infection. We found that the serum IL-10 levels correlated positively with dengue NS1 antigen levels (Spearman's r = 0·47, P < 0·0001), and NS1 also correlated with annexin V expression by T cells in acute dengue (Spearman's r = 0·63, P = 0·001). However, NS1 levels did not associate with the functionality of T cell responses or with expression of co-stimulatory molecules. Therefore, we further assessed the effect of dengue NS1 on monocytes and T cells by co-culturing primary monocytes and peripheral blood mononuclear cells (PBMC), with varying concentrations of NS1 for up to 96 h. Monocytes co-cultured with NS1 produced high levels of IL-10, with the highest levels seen at 24 h, and then declined gradually. Therefore, our data show that dengue NS1 appears to contribute to pathogenesis of dengue infection by inducing IL-10 production by monocytes.

Histamine enhances keratinocyte-mediated resolution of inflammation by promoting wound healing and response to infection

BACKGROUND

The role of the epidermis in the immune response is well known. While multiple cytokines are implicated in keratinocyte-mediated infection clearance and wound healing, little is known about the involvement of keratinocytes in promoting resolution of inflammation.

AIM

To assess effects of histamine stimulation on keratinocyte function.

METHODS

We performed a combined microarray/Gene Ontology analysis of histamine-stimulated keratinocytes. Functional changes were tested by apoptosis assessment and scratch assays. Histamine receptor involvement was also assessed by blocking wound closure with specific antagonists.

RESULTS

Histamine treatment had extensive effects on keratinocytes, including effects on proinflammatory responses and cellular functions promoting wound healing. At the functional level, there was reduced apoptosis and enhancement of wound healing in vitro. At the receptor level, we identified involvement of all keratinocyte-expressed histamine receptors (HRHs), with HRH1 blockage resulting in the most prominent effect.

CONCLUSIONS

Histamine activates wound healing and infection clearance-related functions of keratinocytes. While enhancement of histamine-mediated wound healing is mediated predominantly via the HRH1 receptor, other keratinocyte-expressed receptors are also involved. These effects could promote resolution of skin inflammation caused by infection or superficial injury.

Cytokine regulation of the epidermal barrier

Studies published in recent years have highlighted the role of epidermal barrier defects in both atopic skin disease and the development of broader allergic manifestations. While genetic determinants of barrier function are important, it is clear that local acquired effects are also involved in disease pathogenesis. In this review, we aimed to summarize the known influences of cytokines abundantly expressed during atopic skin disease on components of epidermal barrier integrity and function.

Histamine exerts multiple effects on expression of genes associated with epidermal barrier function

BACKGROUND

The role of epidermal barrier genes in the pathogenesis of atopic skin inflammation has recently been highlighted. Cytokines that are abundant in the skin during inflammation have been shown to exert various effects on the expression of barrier genes, although the role of histamine in this area of skin biology is not yet fully understood.

OBJECTIVE

To assess the effect of stimulation with histamine on keratinocytes by analysis of the pathways involved in epidermal barrier integrity.

MATERIAL AND METHODS

We performed a gene expression analysis of histamine-stimulated keratinocytes. Functional changes were tested using the dye penetration assay. Differential changes in filaggrin and the filaggrin-processing enzyme bleomycin hydrolase (BLMH) were validated at the protein level, and expression was also assessed in filaggrin knock-down keratinocytes.

RESULTS

Histamine altered expression of multiple barrier genes. Expression of filaggrin was downregulated, as was that of other markers, thus suggesting the presence of delayed/aberrant keratinocyte differentiation. Expression of genes involved in cellular adhesiveness and genes of protease expression was dysregulated, but expression of protease inhibitors was increased. BLMH was upregulated in keratinocytes subjected to histamine and filaggrin knockdown.

CONCLUSIONS

Histamine exerts a dual effect on epidermal barrier genes; it suppresses keratinocyte differentiation and dysregulates genes of cellular adhesiveness, although it induces genes contributing to stratum corneum function. Upregulation of BLMH and protease inhibitors could support maintenance of the permeability barrier by enhanced generation of moisturizing compounds and suppressed desquamation. In contrast, in the case of stratum corneum damage, histamine could enhance transcutaneous sensitization.

Human antimicrobial peptides LL-37 and human β-defensin-2 reduce viral replication in keratinocytes infected with varicella zoster virus

BACKGROUND

There is mounting evidence that antimicrobial peptides have an important role in cutaneous defence, but the expression of these antimicrobial peptides in atopic eczema (AE) is still unclear. There are several families of antimicrobial peptides, including cathelicidins and human β-defensins. Patients with AE are more susceptible to severe cutaneous viral infections, including varicella zoster virus (VZV).

AIM

To characterize the functional activity of the antimicrobial peptides LL-37 (human cathelicidin) and human β-defensin (hBD)-2 keratinocytes were infected with VZV, in a skin-infection model.

METHODS

Flow-cytometry analysis was used to investigate LL-37 expression in normal human keratinocytes, and quantitative PCR was used to determine viral loads in infected HaCaT keratinocytes and B cells, with and without exogenous LL-37 and hBD-2.

RESULTS

LL-37 expression was present in keratinocytes, and both exogenous LL-37 and hBD-2 significantly reduced VZV load in infected keratinocytes and B cells. Specific antibodies blocked the antiviral action exhibited by these antimicrobial peptides. Pre-incubation of VZV with LL-37, but not hBD-2, further reduced VZV load.

CONCLUSIONS

Both LL-37 and hBD-2 have an antiviral effect on VZV replication in the keratinocyte HaCaT cell line and in B cells, but their mechanism of action is different. Evidence of the relationship between antimicrobial peptide expression and higher susceptibility to infections in AE skin is still emerging. Developing novel antiviral therapies based on antimicrobial peptides may provide improved treatment options for patients with AE.

Identification of an immunodominant region of the major house dust mite allergen Der p 2 presented by common human leucocyte antigen alleles

BACKGROUND

Better understanding of the relevance of the immune response to common environmental allergens, such as the major house dust mite (HDM) allergen Der p 2, requires characterization of constituent T-cell epitopes.

AIM

To identify CD4(+) T-cell epitopes within Der p 2 recognized by commonly expressed human leucocyte antigen (HLA) alleles.

METHODS

HLA-blocking antibodies, peptide pools and truncations were used in ELISpot assays to establish restricted T-cell epitopes.

RESULTS

People with and without atopic dermatitis have detectable Der p 2-specific T cells in the peripheral blood, which can proliferate in response to Der p 2 peptides. Interleukin-4-specific responses, both ex vivo and cultured to Der p 2 peptides, had a significant positive correlation with HDM-specific serum IgE. Within one pool of Der p 2 peptides, the 20mer D11 was found to induce multiple responses restricted through several alleles, including HLA-DPB1*0401 and HLA-DRB1*01.

CONCLUSIONS

We have identified an immunogenic region of Der p 2 presented by common HLA class II alleles, including the most commonly expressed HLA allele DPB1*0401. Identification of such epitopes may be of future value in peptide immunotherapeutic approaches.

Interleukin-22 downregulates filaggrin expression and affects expression of profilaggrin processing enzymes

BACKGROUND

The identification of filaggrin mutations has contributed towards our understanding of hereditary factors associated with epidermal dysfunction observed in individuals with atopic eczema (AE). However, factors that predispose to acquired filaggrin modulation are not well understood. Interleukin (IL)-22 is upregulated in lesional AE tissue, but its effects on filaggrin expression and genes associated with epidermal function have not yet been comprehensively addressed.

OBJECTIVES

To investigate the effects of IL-22 on expression of filaggrin and genes encoding proteins relevant to epidermal function.

METHODS

Microarray analysis was performed on IL-22-stimulated HaCaT keratinocytes. Filaggrin protein level was assessed by an intracellular enzyme-linked immunosorbent assay (ELISA) and Western blot in HaCaT cells and the findings were validated in primary keratinocytes.

RESULTS

Exposure to IL-22 cytokine resulted in a downregulation of profilaggrin mRNA expression in HaCaT keratinocytes. The expression of genes involved in enzymatic processing of profilaggrin as well as the generation of natural moisturizing factor was also altered. Furthermore, there was an upregulation of many transcripts encoding proteins of the S100 family. Profilaggrin/filaggrin downregulation was detected by intracellular ELISA and Western blot in HaCaT cells. The relevance to the primary setting was confirmed in primary keratinocytes by Western blot.

CONCLUSIONS

IL-22 downregulates profilaggrin/filaggrin expression in keratinocytes at both mRNA and protein levels and affects genes relevant to epidermal function. This novel pathway may have relevance to the pathogenesis and treatment of atopic and other skin disease.

Phenotypic analysis of perennial airborne allergen-specific CD4+ T cells in atopic and non-atopic individuals

BACKGROUND

Accumulating evidence suggests that T cells play an important role in the pathogenesis of atopic dermatitis (AD); yet, little is known of the differentiation status of CD4+ T cells specific for common environmental allergens, such as the major cat allergen, Fel d 1.

OBJECTIVE

To determine the frequency, differentiation phenotype and function of circulating Fel d 1-specific CD4+ T cells in adult individuals with severe persistent AD in comparison with healthy controls.

METHODS

Using HLA class II tetrameric complexes based on a HLA-DPB1*0401-restricted Fel d 1 epitope, ex vivo and cultured T cell frequency and phenotype were analysed in individuals with AD and healthy controls. Cytokine secretion was measured by ex vivo and cultured IL-4 and IFN-γ ELISpots.

RESULTS

Ex vivo Fel d 1-specific DPB1*0401-restricted CD4+ T cells in both atopics and non-atopics express high levels of CCR7, CD62L, CD27 and CD28, placing the cells largely within the central memory subgroup. However, the functional phenotype was distinct, with greater IL-4 production from the cells derived from atopics, which correlated with disease severity.

CONCLUSIONS AND CLINICAL RELEVANCE

Circulating Fel d 1-specific DPB1*0401-restricted CD4+ T cells in both atopic and non-atopic donors maintain a central memory phenotype; however in atopics, the cells had greater Th2 effector function, compatible with a disease model of altered antigen delivery in atopic individuals.

Characteristics of Staphylococcus aureus colonization in patients with atopic dermatitis in Sri Lanka

BACKGROUND

Colonization of the skin of patients with atopic dermatitis (AD) by Staphylococcus aureus (SA) is associated with more severe disease.

AIM

To determine the association of SA colonization patterns and densities in lesional and nonlesional skin in patients with varying severities of AD, and to determine the antibiotic sensitivity patterns of SA isolates from Sri Lanka.

METHODS

Skin and nasal swabs collected from 100 patients with AD and 120 controls were used to investigate the presence of SA. Severity of AD was graded using the Nottingham Eczema Severity Score. Colony counts were obtained for skin samples, and antibiotic sensitivity testing was performed in cases positive for SA.

RESULTS

Skin colonization was seen in 57 patients (57%) but in only 10 controls (8%). Lesional skin of most patients (52/57; 91%) had SA densities of > 300 colony-forming units/cm(2) . Colonization rates with SA significantly increased with increasing age (Spearman correlation coefficient R = 0.9, P < 0.05) and increasing duration of lesions in patients with AD (Spearman R = 0.87, P < 0.05). Isolates from eight patients (13.5%) were found to be methicillin-resistant S. aureus (MRSA). Only 6 isolates (10%) were susceptible to penicillin and 22 (37%) to erythromycin, while 28 (47%) isolates had erythromycin-induced resistance to clindamycin.

CONCLUSIONS

SA colonization rates were significantly associated with increasing age and severity of AD, and particularly with duration of lesions. Patients with severe disease were also more likely to be colonized with SA strains resistant to conventional antibiotics.

Common filaggrin null alleles are not associated with hymenoptera venom allergy in Europeans

The association of filaggrin mutations with atopic eczema (atopic dermatitis, AD) is well established and it is thought that filaggrin dysfunction impairs the skin's barrier function allowing allergen penetration and subsequent cutaneous sensitisation and inflammation. However, as most forms of barrier dysfunction are not associated with allergic sensitisation to common allergens, the possibility that filaggrin itself is involved in Th1/Th2 polarisation remains. We tested the hypothesis that allergen delivered to the skin independently of the stratum corneum is not associated with filaggrin mutations. Wasp stings bypass the stratum corneum and deliver antigen to the dermis. We found that European individuals with AD (n = 32) have an increased frequency of the 2 commonest filaggrin null mutations (R501X and 2282del4) compared to those with vespid allergy (n = 56) and healthy controls (n = 30). Thus, filaggrin does not appear to have a downstream effect on the development of allergic disease, and it is indeed filaggrin's role in the epithelial function that is likely to determine the link between filaggrin mutations and allergic sensitisation.

IE63-specific T-cell responses associate with control of subclinical varicella zoster virus reactivation in individuals with malignancies

Background:

Reactivation of the varicella zoster virus (VZV) is more common in patients with malignancies; however, the molecular and cellular mechanisms underlying this susceptibility are unclear.

Methods:

Using ex vivo interferon-γ ELISpot assays, we set out to analyse VZV-specific immune responses in a large cohort of patients with malignancies.

Results:

We observed that patients with malignancies had impaired VZV-specific T-cell responses, particularly in those with haematological malignancies and breast carcinoma. Immediate-early protein 63 (IE63)-specific T-cell responses were significantly impaired in those with subclinical VZV re-activation.

Conclusions:

Our results suggest that T-cell responses to IE63 are important in controlling VZV replication.

Identification of an immunodominant region of Fel d 1 and characterization of constituent epitopes

BACKGROUND

Characterization of T cell epitopes restricted by common HLA alleles is a powerful tool in the understanding of the immune responses to allergens and for the identification of potential peptides for future peptide immunotherapy (PIT). One important requirement is the identification and use of peptides that will bind to HLA molecules covering a large proportion of the population.

OBJECTIVE

To identify commonly recognized CD4(+) T cell epitopes in Fel d 1, restricted through frequently expressed HLA molecules for potential future use in PIT.

METHODS

HLA matched antigen presenting cells, HLA blocking antibodies, and peptide truncations were used in ELISpot assays to establish HLA-restricted T cell epitopes. Cytokine responses were measured by ex vivo and cultured IFN-gamma, IL-4, and IL-10 ELISpots.

RESULTS

Responses to an immunodominant region of chain 2 were identified in the majority of atopic individuals and epitopes restricted by HLA-DQB1(*)06 and -DPB1(*)0401 were characterized in detail. Significantly higher ex vivo IL-4 and lower IFN-gamma responses were observed to both epitopes in individuals with atopic dermatitis (AD) compared with those without disease. IL-10 responses were significantly lower in those with AD in the individuals with HLA-DPB1(*)0401.

CONCLUSIONS

We have identified an immunodominant region of Fel d 1 which is frequently recognized by CD4(+) T cells from atopic individuals and contains epitopes that are restricted by very common HLA alleles.

Varicella zoster virus glycoprotein E-specific CD4+ T cells show evidence of recent activation and effector differentiation, consistent with frequent exposure to replicative cycle antigens in healthy immune donors

Varicella zoster viru (VZV)-specific T cell responses are believed to be vital in recovery from primary VZV infection and also in the prevention of viral reactivation. While glycoprotein E (gE) is the most abundant and one of the most immunogenic proteins of the virus, there are no data addressing potential T cell epitopes within gE, nor the phenotype of specific T cells. Using interferon gamma enzyme-linked immunospot assays and intracellular cytokine assays, we identified gE-specific immune responses in 20 adult healthy immune donors which were found to be dominated by the CD4+ subset of T cells. We characterized three immune dominant epitopes within gE restricted through DRB1*1501, DRB1*07 and DRB4*01, and used DRB1*1501 class II tetrameric complexes to determine the ex vivo frequency and phenotype of specific T cells. In healthy immune donors, the cells were largely positive for CCR7, CD28 and CD27, but expressed variable CD62L and low levels of cutaneous lymphocyte associated antigen with evidence of recent activation. In summary, we show that circulating gE-specific CD4+ T cells are detected at a relatively high frequency in healthy immune donors and show evidence of recent activation and mixed central and effector memory phenotype. These data would be compatible with frequent exposure to replicative cycle antigens in healthy donors and are consistent with a role for gE-specific CD4+ T cells in the control of viral replication.

Anti-lymphocyte function associated antigen-1 inhibits T-helper 2 function of human allergen-specific CD4+ T cells

BACKGROUND

Blockade of lymphocyte function associated antigen-1 (LFA-1) is proving successful in the management of psoriasis and other inflammatory skin conditions including atopic dermatitis (AD), but the dependence of allergen-specific CD4+ T-cell function on LFA-1 has not been studied extensively.

OBJECTIVES

We sought to investigate the potential ability of LFA-1 inhibition to influence keratinocyte presentation of allergen to specific T-helper (Th) 2 cell clones.

METHODS

Using human leucocyte antigen class II tetrameric complexes, we generated Der p 1-specific DRB1*1501-restricted CD4+ T-cell lines (n=5) and clones (n=4) from the peripheral blood of five adults with AD.

RESULTS

Using doses of anti-LFA-1 present in vivo, we observed significant inhibition (P<0.05) of allergen-specific CD4+ T-cell production of interleukin-4 with such inhibition occurring during presentation of allergen by keratinocytes.

CONCLUSIONS

These data show that at doses present in vivo, LFA-1 blockade inhibits keratinocyte presentation to allergen-specific Th2 cells, suggesting one mechanism through which anti-LFA-1 may be beneficial therapeutically.

HLA analysis of Sri Lankan Sinhalese predicts North Indian origin

The origin of the Sinhalese population of Sri Lanka is debated. We subtyped HLA-A*02 in 101 Sinhalese and observed a preponderance of the rare allele HLA-A*0211 which was similar to reported frequencies in northern India. Taken with low-resolution typing for the remaining A, B, C, DR and DQ alleles, these data suggest a North Indian origin for the Sri Lankan Sinhalese.

The role of skin-homing T cells in extrinsic atopic dermatitis

BACKGROUND

T cells that express Cutaneous Lymphocyte-Associated antigen (CLA) have the potential of migrating to the skin, and are hypothesized to play a role in cutaneous atopic disease.

AIM

To investigate the immune phenotype and cytokine responses to Der p 1 stimulation of CLA+ T cells in extrinsic atopic dermatitis (EAD).

DESIGN

In vitro testing, with controls.

METHODS

Peripheral blood mononuclear cells (PBMC) were obtained from EAD patients (n=27) and non-atopic healthy individuals (n=22). Phenotypic analysis of naive, CLA+ and non-CLA+ memory/effector CD4+ and CD8+ T cells used markers of cell activation, differentiation, adhesion, apoptosis and chemokine receptor expression. Cytokine responses in these cells were studied following Der p 1 stimulation.

RESULTS

CLA+ T cells from EAD patients expressed significantly higher levels of CD25, HLA-DR, CD38, CD71, CXCR1, CXCR2 and lower levels of bcl2, CCR5, CCR7, CXCR3, and CD62L (p<0.05).

DISCUSSION

In EAD patients, CLA+ T cells express increased levels of markers associated with activation, adhesion and apoptosis, show differences in the level of expression of differentiation markers and display a distinct chemokine receptor preference, compared with cells from healthy controls. These data suggest a significant role for CLA+ T cells in the pathogenesis of cutaneous atopic disease.

Severe atopic dermatitis is associated with a reduced frequency of IL-10 producing allergen-specific CD4+ T cells

BACKGROUND

Several studies have investigated levels of T-cell-derived interleukin (IL)-10 in individuals with atopic dermatitis, with conflicting results.

AIMS/HYPOTHESIS

In order to address whether stratification of disease severity may help resolve the different findings, the hypothesis was tested that individuals with severe atopic dermatitis have a lower frequency of circulating IL-10-producing, allergen-specific CD4+ T cells than do individuals with mild disease.

METHODS

Using peripheral blood mononuclear cells derived from individuals with severe (n=12) and mild atopic dermatitis (n=10) and from nonatopic controls (n=10), we investigated production by CD4+ T cells of tumour necrosis factor (TNF)-alpha, IL-4, IL-5, IL-13 and IL-10 in response to phorbol myristate acetate/ionomycin and Der p1 allergen.

RESULTS

It was observed that there were significantly higher frequencies of allergen-specific circulating CD4+ T cells producing TNF-alpha- IL-4-, IL-5- and IL-13, and lower frequencies of these cells producing IL-10 in individuals with severe atopic dermatitis compared with mildly affected individuals and nonatopic controls (P<0.01 for all comparisons). Furthermore, the Der p1-specific CD4+ T cells were enriched within the subset of cells positive for cutaneous lymphocyte-associated antigen.

CONCLUSIONS

Analysis of levels of allergen-specific CD4+ T-cell production of IL-10 in relation to disease severity argues in favour of a role for IL-10 in the control of atopic dermatitis.

p53-specific CD8+ T-cell responses in individuals with cutaneous squamous cell carcinoma

BACKGROUND

Systemic immunosuppression is a significant risk factor for cutaneous squamous cell carcinoma (SCC). p53 is mutated and overexpressed in up to 90% of cutaneous SCC lesions. Despite considerable evidence that the immune response is important in the control of cutaneous SCC, there are no studies documenting potential tumour-associated antigens.

OBJECTIVES

We tested the hypothesis that individuals with cutaneous SCC have functional circulating CD8+ T cells specific for p53.

METHODS

Interferon-gamma immunosorbent assays were used to screen peripheral blood mononuclear cells for reactivity to six p53-derived HLA-A*0201-restricted epitopes from HLA-A*0201-positive patients and controls.

RESULTS

We observed significantly elevated frequencies of p53-specific CD8+ T cells in seven of 26 individuals with cutaneous SCC and in one of 10 controls. The degree of lymphocytic infiltrate significantly correlated with the frequency of CD8+ T cells specific for p53 epitopes, but not with control epitopes.

CONCLUSIONS

Overall, these data suggest that p53 may represent a target for CD8+ T cells in a proportion of individuals with cutaneous SCC.

Interleukin-4 induced down-regulation of skin homing receptor expression by human viral-specific CD8 T cells may contribute to atopic risk of cutaneous infection

Factors controlling the expression of cutaneous lymphocyte-associated antigen (CLA) by T cells are poorly understood, but data from murine and human CD4(+) T cell systems have suggested that cytokines play an important role. However, there are no data examining the influence of cytokines on the expression of CLA by human antigen-specific CD8(+) T cells. Peripheral blood mononuclear cells (PBMC) were isolated from 10 HLA-A*0201-positive healthy individuals. Using HLA-peptide tetrameric complexes refolded with immunodominant peptides from Epstein-Barr virus (EBV), cytomegalovirus (CMV) and influenza A virus, we investigated the temporal associations of CLA expression by viral-specific CD8(+) T cells following stimulation with antigen. Ex vivo influenza matrix-specific CD8(+) T cells expressed significantly (P < 0.05) greater levels of CLA than EBV BMLF1 and CMV pp65-specific CD8(+) T cells (mean 9.7% influenza matrix versus 1.4% BMLF1 versus 1.1% pp65) and these differences were sustained on culture. However, regardless of viral specificity, interleukin (IL)-12 and IL-4 induced significant (P < 0.05) dose-dependent up-regulation and down-regulation of CLA expression, respectively, with IL-4 showing a dominant negative effect. In many cases, IL-4 resulted in complete abrogation of detectable CLA expression by the viral-specific CD8(+) T cells. Overall these data demonstrate that CLA expression by human viral-specific CD8(+) T cells is highly dynamic and that IL-4 causes significant down-regulation. Disorders associated with a type 2 cytokine shift may reduce the efficiency of skin homing by viral-specific CD8(+) T cells. Furthermore, the ability to modify the local and systemic microenvironment may offer novel therapeutic strategies that influence tissue-specific T cell homing.

Rapid effector function of circulating NC16A-specific T cells in individuals with mucous membrane pemphigoid

BACKGROUND

Mucous membrane pemphigoid (MMP) is a chronic blistering skin disease frequently associated with circulating autoantibodies directed to a number of antigens including the NC16A region of BP180. NC16A domain-specific T cells have been identified in the blood of individuals with bullous pemphigoid (BP), pemphigoid gestationis and linear IgA disease, but there are no data investigating the potential role for such T cells in the pathogenesis of MMP.

OBJECTIVES

To test the hypothesis that NC16A-specific T cells exist in the peripheral blood of individuals with MMP.

METHODS

We isolated peripheral blood mononuclear cells from 10 patients with MMP, 17 with BP and 10 healthy controls and examined the immunogenicity of overlapping peptides spanning the NC16A domain using interferon (IFN)-gamma enzyme-linked immunospot assay.

RESULTS

Significant IFN-gamma production was observed in response to the NC16A peptides in two of the patients with MMP and two of the patients with BP but in none of the normal controls. These data suggest that in a minority of individuals with MMP, NC16A domain-specific T cells circulate at sufficiently high frequency to be detectable directly ex vivo and to show rapid effector function.

CONCLUSIONS

Overall, these findings are the first to examine the potential role for antigen-specific autoreactive T cells in the pathogenesis of MMP, and confirm that in some individuals the NC16A domain may be an important target antigen.

The role of p53 in the immunobiology of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma is typically characterized by the over-expression of the tumour suppressor protein p53. Considerable evidence suggests that immune competence is important in the control of cutaneous SCC. We discuss the immunobiology of p53 and its relevance to cutaneous SCC, including the potential interaction with human papillomavirus.

Comparison between HIV- and CMV-specific T cell responses in long-term HIV infected donors

The mechanisms underlying non-progression in HIV-1 infection are not well understood; however, this state has been associated previously with strong HIV-1-specific CD8+ T cell responses and the preservation of proliferative CD4+ T cell responses to HIV-1 antigens. Using a combination of interferon-gamma (IFN-gamma) ELISpot assays and tetramer staining, the HIV-1-specific CD8+ T cell populations were quantified and characterized in untreated long-term HIV-1-infected non-progressors and individuals with slowly progressive disease, both in relation to CD4+ T cell responses, and in comparison with responses to cytomegalovirus (CMV) antigens. High levels of CD8+ T cell responses specific for HIV-1 or CMV were observed, but neither their frequency nor their phenotype seemed to differ between the two patient groups. Moreover, while CMV-specific CD4+ T cell responses were preserved in these donors, IFN-gamma release by HIV-1-specific CD4+ T cells was generally low. These data raise questions with regard to the role played by CD8+ T cells in the establishment and maintenance of long-term non-progression.

Cytotoxic T-cell abundance and virus load in human immunodeficiency virus type 1 and human T-cell leukaemia virus type 1

The correlation between virus load and specific cytotoxic T-lymphocyte (CTL) frequency during the chronic phase in human immunodeficiency virus type 1 (HIV-1) infection has been found to be negative in cross-sectional studies. We report here that, in infection with the related retrovirus human T-cell leukaemia virus type 1 (HTLV-1), the correlation is positive in asymptomatic carriers and zero in patients with the associated inflammatory disease HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). We demonstrate that the direction of the correlation may depend on the efficacy of the CTL response using mathematical models. We conclude that the CTL response is effective in asymptomatic carriers of HTLV-1, but ineffective in patients with HAM/TSP. Virus-mediated impairment of specific CTL production in HIV-1 infection can account for the negative correlation observed.

Lamivudine treatment can overcome cytotoxic T-cell hyporesponsiveness in chronic hepatitis B: new perspectives for immune therapy

The hepatitis B virus (HBV) cytotoxic T lymphocyte (CTL) response in patients with chronic HBV infection is generally weak or totally undetectable. This inability to mount protective CTL responses is believed to be a crucial determinant of viral persistence, and its correction represents an important objective of immune therapies for chronic hepatitis B. However, amplification of CTL responses in vivo may be ineffective if HBV-specific CD8 cells are either absent or nonresponsive to exogenous stimulation. In this study, we asked whether antiviral treatments able to inhibit viral replication and to reduce viral and antigen load can successfully reconstitute CTL responses creating the appropriate conditions for their therapeutic stimulation. For this purpose, the HBV-specific CTL response before and during lamivudine therapy was studied longitudinally in 6 HLA-A2-positive patients with HBeAg+ chronic hepatitis B. Both HBV-specific cytotoxic T cell activity measured by chromium release assay on peptide stimulation in vitro and CD8+ T cell frequency measured ex vivo by HLA-A2/peptide tetramer staining were significantly augmented by lamivudine therapy. This enhancement followed the reconstitution of CD4 reactivity and the decline of viral load induced by therapy. Our study shows that lamivudine treatment in chronic hepatitis B can restore CTL reactivity, making CTL susceptible to exogenous stimulation. This effect may enhance the probability that T cell-based immune therapies delivered after lamivudine treatment can successfully reconstitute a protective CTL response able to cure chronic HBV infection.

HLA-B*35-restricted CD8 T cell epitopes in the antigen 85 complex of Mycobacterium tuberculosis

Few target epitopes have been described for human CD8 T lymphocytes in antigens of Mycobacterium tuberculosis. By use of a reverse immunogenetics approach, 23 motif-bearing peptides of the Ag85 complex were tested for binding to HLA-B*35, one of the common B-types in West Africa. Three 9-mer peptides bound with high affinity to HLA-B*3501 and displayed low dissociation rates of peptide-major histocompatibility complexes (MHCs). IC(50) and half-life values of peptide-MHC class I complexes were in the same range as reported earlier for other immunogenic peptides. Immune responses against peptide Ag85C (aa 204-212) WPTLIGLAM were characterized in detail. Peptide-stimulated effector cells were able to kill macrophages infected with M. tuberculosis or bacille Calmette-Guérin. Peptide-specific CD8 T cells could be visualized by using HLA-B*3501 tetramers and were shown to produce interferon-gamma and tumor necrosis factor-alpha. Together with other published epitopes, these peptides can be used to study more closely the role of CD8 T cells in mycobacterial infection and tuberculosis.

Skewed maturation of memory HIV-specific CD8 T lymphocytes

Understanding the lineage differentiation of memory T cells is a central question in immunology. We investigated this issue by analysing the expression of the chemokine receptor CCR7, which defines distinct subsets of naive and memory T lymphocytes with different homing and effector capacities and antiviral immune responses to HIV and cytomegalovirus. Ex vivo analysis of the expression of CD45RA and CCR7 antigens, together with in vitro analysis of the cell-division capacity of different memory CD8+ T-cell populations, identified four subsets of HIV- and CMV-specific CD8+ T lymphocytes, and indicated the following lineage differentiation pattern: CD45RA+ CCR7+ --> CD45RA- CCR7+ --> CD45RA- CCR7- --> CD45RA+ CCR7-. Here we demonstrate through analysis of cell division (predominantly restricted to the CCR7+ CD8+ T-cell subsets) that the differentiation of antigen-specific CD8+ T cells is a two-step process characterized initially by a phase of proliferation largely restricted to the CCR7+ CD8+ cell subsets, followed by a phase of functional maturation encompassing the CCR7- CD8+ cell subsets. The distribution of these populations in HIV- and CMV-specific CD8+ T cells showed that the HIV-specific cell pool was predominantly (70%) composed of pre-terminally differentiated CD45RA- CCR7- cells, whereas the CMV-specific cell pool consisted mainly (50%) of the terminally differentiated CD45RA+ CCR7- cells. These results demonstrate a skewed maturation of HIV-specific memory CD8+ T cells during HIV infection.

High viral burden in the presence of major HIV-specific CD8(+) T cell expansions: evidence for impaired CTL effector function

To investigate the effect of HIV-specific CD8(+) T cells on viral plasma load and disease progression, we enumerated HLA-A2-, B8- and B57-restricted CD8(+) T cells directed against several HIV epitopes in a total of 54 patients by the use of tetrameric HLA-peptide complexes. In patients with high CD4(+) T cell numbers, HIV-specific tetramer(+) cells inversely correlated with viral load. Patients with CD4(+) T cell numbers below 400/microl blood, however, carried high viral load despite frequently having high tetramer(+) T cell numbers. This lack of correlation between viral load and tetramer(+) cells did not result from viral escape variants, as in only 4 of 13 patients, low frequencies of viruses with mutated epitopes were observed. In 15 patients we measured CD8(+) T cell antigen responsiveness to HIV peptide stimulation in vitro. FACS analyses showed differential IFN-gamma production of the tetramer(+) cells, and this proportion of IFN-gamma-producing tetramer(+) cells correlated with AIDS-free survival and with T cell maturation to the CD27(-) effector stage. These data show that most HIV-infected patients have sustained HIV-specific T cell expansions but many of these cells seem not to be functional, leaving the patient with high numbers of non-functional virus-specific CD8(+) T cells in the face of high viral burden.

Direct measurement of CD4+ and CD8+ T-cell responses to CMV in HIV-1-infected subjects

Data from murine models of chronic viral infection suggest that CD4+ T-cell responses to viral pathogens are important in sustaining the number and/or function of CD8+ cytotoxic T-cell (CTL) effectors. In this study, we used cytokine flow cytometry (CFC), staining with HLA-A*0201-peptide tetramers, and peptide stimulation with epitopic peptides to study functional CD4+ and CD8+ T-cell responses to cytomegalovirus (CMV) in human subjects coinfected with CMV and the human immunodeficiency virus, type 1 (HIV-1). We show that strong CD4+ and CD8+ T-cell responses to CMV antigens are sustained over time in HIV-1-infected individuals. Those who maintain a strong CD4+ T-cell response to CMV are also likely to maintain higher frequencies of CD8+ T cells capable of binding to HLA-A*0201-CMV pp65 (A2-pp65) tetramers as well as responses to pp65 peptide stimulation with effector cytokine production. These data support the hypothesis that declines in frequencies of CD4+ T-cell responses to CMV are associated with an inability to sustain high levels of CMV-specific CD8+ T-cell responses in HIV-1-infected subjects. These declines may precede the onset of CMV-associated end organ disease.

T cell receptor usage of virus-specific CD8 cells and recognition of viral mutations during acute and persistent hepatitis B virus infection

T cells specific for a single viral epitope, but using different T cell receptors, should have flexibility in their epitope recognition to protect the infected host against the emergence of viral escape mutants. Therefore, polyclonality of the hepatitis B virus (HBV)-specific cytotoxic T lymphocyte response has been hypothesized to be a major determinant in the control of infection. We analyzed the Vbeta chain composition of the core 18-27-specific CD8 cells in acute and persistently HBV-infected patients using HLA-A2 tetrameric complexes and a panel of Vbeta antibodies. Different T cell receptors were utilized by core 18-27-specific CD8 cells both in patients with acute and chronic infection. The functional ability of these epitope-specific T cells to respond to potential viral mutations was then tested. The polyclonal HBV-specific CD8 response present in patients with acute hepatitis displayed a limited efficiency to recognize mutations introduced within the epitope. The ability of core 18-27-specific CD8 to tolerate epitope mutations was found only during persistent HBV infection. The data suggest that although a clonally heterogeneous CD8 response can be largely inhibited by the occurrence of single epitope mutations in primary HBV infection, preferential selection of T cells able to counteract the emergence of viral mutations can occur during persistent infection.

Human CD8+ CTL specific for the mycobacterial major secreted antigen 85A

The role of CD8(+) CTL in protection against tuberculosis in human disease is unclear. In this study, we stimulated the peripheral blood mononuclear cells of bacillus Calmette-Guérin (BCG)-vaccinated individuals with live Mycobacterium bovis BCG bacilli to establish short-term cell lines and then purified the CD8(+) T cells. A highly sensitive enzyme-linked immunospot (ELISPOT) assay for single cell IFN-gamma release was used to screen CD8(+) T cells with overlapping peptides spanning the mycobacterial major secreted protein, Ag85A. Three peptides consistently induced a high frequency of IFN-gamma responsive CD8(+) T cells, and two HLA-A*0201 binding motifs, P(48-56) and P(242-250), were revealed within the core sequences. CD8(+) T cells responding to the 9-mer epitopes were visualized within fresh blood by ELISPOT using free peptide or by binding of HLA-A*0201 tetrameric complexes. The class I-restricted CD8(+) T cells were potent CTL effector cells that efficiently lysed an HLA-A2-matched monocyte cell line pulsed with peptide as well as autologous macrophages infected with Mycobacterium tuberculosis or recombinant vaccinia virus expressing the whole Ag85A protein. Tetramer assays revealed a 6-fold higher frequency of peptide-specific T cells than IFN-gamma ELISPOT assays, indicating functional heterogeneity within the CD8(+) T cell population. These results demonstrate a previously unrecognized, MHC class I-restricted, CD8(+) CTL response to a major secreted Ag of mycobacteria and supports the use of Ag85A as a candidate vaccine against tuberculosis.

T cell receptor usage of virus-specific CD8 cells and recognition of viral mutations during acute and persistent hepatitis B virus infection

T cells specific for a single viral epitope, but using different T cell receptors, should have flexibility in their epitope recognition to protect the infected host against the emergence of viral escape mutants. Therefore, polyclonality of the hepatitis B virus (HBV)-specific cytotoxic T lymphocyte response has been hypothesized to be a major determinant in the control of infection. We analyzed the Vbeta chain composition of the core 18-27-specific CD8 cells in acute and persistently HBV-infected patients using HLA-A2 tetrameric complexes and a panel of Vbeta antibodies. Different T cell receptors were utilized by core 18-27-specific CD8 cells both in patients with acute and chronic infection. The functional ability of these epitope-specific T cells to respond to potential viral mutations was then tested. The polyclonal HBV-specific CD8 response present in patients with acute hepatitis displayed a limited efficiency to recognize mutations introduced within the epitope. The ability of core 18-27-specific CD8 to tolerate epitope mutations was found only during persistent HBV infection. The data suggest that although a clonally heterogeneous CD8 response can be largely inhibited by the occurrence of single epitope mutations in primary HBV infection, preferential selection of T cells able to counteract the emergence of viral mutations can occur during persistent infection.

Incubation phase of acute hepatitis B in man: dynamic of cellular immune mechanisms

After hepatitis B virus (HBV) infection, liver injury and viral control have been thought to result from lysis of infected hepatocytes by virus-specific cytotoxic T cells. Patients are usually studied only after developing significant liver injury, and so the viral and immune events during the incubation phase of disease have not been defined. During a single-source outbreak of HBV infection, we identified patients before the onset of symptomatic hepatitis. The dynamics of HBV replication, liver injury, and HBV-specific CD8+ and CD4+ cell responses were investigated from incubation to recovery. Although a rise in alanine transaminase (ALT) levels was present at the time of the initial fall in HBV-DNA levels, maximal reduction in virus level occurred before significant liver injury. Direct ex vivo quantification of HBV-specific CD4+ and CD8+ cells, by using human leukocyte antigen (HLA) class I tetramers and intracellular cytokine staining, showed that adaptive immune mechanisms are present during the incubation phase, at least 4 weeks before symptoms. The results suggest that the pattern of reduction in HBV replication is not directly proportional to tissue injury during acute hepatitis B in humans. Furthermore, because virus-specific immune responses and significant reductions in viral replication are seen during the incubation phase, it is likely that the immune events central to viral control occur before symptomatic disease.

Detection of HLA-specific IGG antibodies using single recombinant HLA alleles: the MonoLISA assay

BACKGROUND

Because of the presence of confounding antigens, the assignment of HLA antibody specificity is difficult in highly sensitized patients, and the definition of an acceptable HLA mismatch requires a significant workload per patient. We describe a new ELISA method, monoLISA, for detection of immunoglobulin (Ig)G HLA antibody using single recombinant HLA class I monomers bound to microtiter plates.

METHODS

HLA-A2 and -B8 monomers were synthesized and used as screening targets for 85 sera from renal patients. The sera contained various IgG and IgM HLA-specific antibodies, including anti-A2 and anti-B8,defined in a conventional complement-dependent cytotoxicity test (CDC). Investigations were performed to determine possible effects on antibody binding of differential monomer peptide presentation as well as lack of glycosylation.

RESULTS

A good correlation was found between CDC-defined specificities and the reactivity observed with HLA monomers. MonoLISA attained means of 100% sensitivity and 92.5% specificity compared with CDC. Neither the presence of different peptides, nor the absence of glycosylation of the monomer affected the ability of monoLISA to detect antibody.

CONCLUSION

This study demonstrates that the mono-LISA method for HLA antibody detection is valid. Because this has the potential to reduce the work involved in screening sensitized patients awaiting transplantation for HLA antibodies, resources aimed at increasing the number of constructed monomers would be well targeted.

Isolation of cytomegalovirus-specific cytotoxic T-lymphocytes from gut-associated lymphoid tissue (GALT) of HIV type 1-infected subjects

Cytomegalovirus (CMV) can be an important opportunistic infection in HIV-1-infected patients, particularly when the CD4+ T-cell count drops below 50 lymphocytes/mm3. CMV-associated disease, including retinitis, pneumonitis, gastroenteritis, and encephalitis, is estimated to affect up to 40% of AIDS patients. We have studied the cellular immune response to CMV in gut-associated lymphoid tissue (GALT) of HIV-1-infected patients. Two patients with chronic diarrhea of unknown etiology were examined by flexible sigmoidoscopy and upper endoscopy. Biopsy specimens were obtained from lymphoid-associated tissue sites in rectum and duodenum. Both patients were seropositive for CMV IgG, but had not been treated with ganciclovir, and neither had clinical signs of CMV disease. Mononuclear cell cultures were established from GALT and blood and assayed for the presence of CMV-specific CD8+ T cells. CD8+ T-cell phenotype and function were assessed by MHC Class I tetramer staining, using an HLA-A*0201 tetramer complex specific for peptide 495-503 (NLVPMVATV) of CMV lower matrix protein pp65, and by a standard 51Cr release assay. CMV pp65-specific cytotoxic lymphocytes (CTL) were detected in GALT and blood MNC from both patients. These results demonstrate that HIV-1-infected subjects seropositive for CMV, but without active CMV gastrointestinal disease, harbor CMV-specific CTL in intestinal lymphoid tissue. This is the first report of isolation of CMV-specific CTL in GALT and will lead to greater understanding of the pathogenesis of CMV disease in human mucosal tissue.

Detection of antigen-specific cytotoxic T lymphocytes: significance for investigative dermatology

Novel recombinant tetrameric complexes of HLA class I molecules allow the direct visualization of antigen-specific CD8+ T cells using flow cytometry. By facilitating the quantification, isolation and phenotypic analysis of CD8+ T cells, the use of HLA tetramers has extended our understanding of the role of cellular immunity in various disease settings. Recently the technique has also been applied to the study of cutaneous disease and provides insights into mechanisms of dermatopathology.

Differential narrow focusing of immunodominant human immunodeficiency virus gag-specific cytotoxic T-lymphocyte responses in infected African and caucasoid adults and children

Cytotoxic T-lymphocyte (CTL) activity plays a central role in control of viral replication and in determining outcome in cases of human immunodeficiency virus type 1 (HIV-1) infection. Incorporation of important CTL epitope sequences into candidate vaccines is, therefore, vital. Most CTL studies have focused upon small numbers of adult Caucasoid subjects infected with clade-B virus, whereas the global epidemic is most severe in sub-Saharan African populations and predominantly involves clade-C infection in both adults and children. In this study, sensitive enzyme-linked immunospot (elispot) assays have been utilized to identify the dominant Gag-specific CTL epitopes targeted by adults and children infected with clade-B or -C virus. Cohorts evaluated included 44 B-clade-infected Caucasoid American and African American adults and children and 37 C-clade-infected African adults and children from Durban, South Africa. The results show that 3 out of 46 peptides spanning p17(Gag) and p24(Gag) sequences tested contain two-thirds of the dominant Gag-specific epitopes, irrespective of the clade, ethnicity, or age group studied. However, there were distinctive differences between the dominant responses made by Caucasoids and Africans. Dominant responses in Caucasoids were more often within p17(Gag) peptide residues 16 to 30 (38 versus 12%; P < 0.01), while p24(Gag) peptide residues 41 to 60 contained the dominant Gag epitope more often in the African subjects tested (39 versus 4%; P < 0.005). Within this 20-mer p24(Gag), an epitope presented by both B42 and B81 is defined which represents the dominant Gag response in >30% of the total infected population in Durban. This epitope is closely homologous with dominant HIV-2 and simian immunodeficiency virus Gag-specific CTL epitopes. The fine focusing of dominant CTL responses to these few regions of high immunogenicity is of significance to vaccine design.

Characterization of HIV-1-specific cytotoxic T lymphocytes expressing the mucosal lymphocyte integrin CD103 in rectal and duodenal lymphoid tissue of HIV-1-infected subjects

Acute HIV-1 infection depletes CD4(+) T cells in gut-associated lymphoid tissue (GALT). The failure of containment of local viral replication, and consequent CD4(+) T cell depletion, might be due to delayed mobilization of effector CD8(+) T cells or absence of functioning HIV-1-specific CD8(+) T cell effectors within GALT. No studies have addressed human intestinal HIV-1-specific CD8(+) T cell functions. We sought to determine whether functional HIV-1-specific CTL were present in GALT and whether the repertoire differed from HIV-1-specific CTL isolated from peripheral blood mononuclear cells. From three HIV-1-infected subjects, we isolated HIV-1-specific CD8(+) T cells expressing the mucosal lymphocyte integrin CD103 from GALT. These antigen-specific effector cells could be expanded in vitro and lysed target cells in an MHC class I-restricted manner. HIV-1-specific CTL could be isolated from both duodenal and rectal GALT sites, indicating that CD8(+) effectors were widespread through GALT tissue. The breadth and antigenic specificities of GALT CTL appeared to differ from those in peripheral blood in some cases. In summary, we found HIV-1-specific CD8(+) effector T cells in GALT, despite HIV-1-induced CD4(+) T cell lymphopenia. This suggests that HIV-1-specific CTL in gut tissue can be maintained with limited CD4(+) T cell help.

The role of virus-specific CD8(+) cells in liver damage and viral control during persistent hepatitis B virus infection

Hepatitis B virus (HBV) is a noncytopathic virus, and the recognition of infected hepatocytes by HBV-specific CD8 cells has been assumed to be the central mechanism causing both liver damage and virus control. To understand the role of cytotoxic T cells in the pathogenesis of HBV infection, we used functional assays that require T cell expansion in vitro and human histocompatibility leukocyte antigen (HLA)-peptide tetramers that allow direct ex vivo quantification of circulating and liver-infiltrating HBV-specific CD8 cells. Two groups of patients with persistent HBV infection were studied: one without liver inflammation and HBV replication, the other with liver inflammation and a high level of HBV replication. Contrary to expectation, a high frequency of intrahepatic HBV-specific CD8 cells was found in the absence of hepatic immunopathology. In contrast, virus-specific T cells were more diluted among liver infiltrates in viremic patients, but their absolute number was similar because of the massive cellular infiltration. Furthermore, inhibition of HBV replication was associated with the presence of a circulating reservoir of CD8(+) cells able to expand after specific virus recognition that was not detectable in highly viremic patients with liver inflammation. These results show that in the presence of an effective HBV-specific CD8 response, inhibition of virus replication can be independent of liver damage. When the HBV-specific CD8 response is unable to control virus replication, it may contribute to liver pathology not only directly but by causing the recruitment of nonvirus-specific T cells.

Sensitization of tumour cells to lysis by virus-specific CTL using antibody-targeted MHC class I/peptide complexes

A number of cell surface molecules with specificity to tumour cells have been identified and monoclonal antibodies (mAb) to some of these antigens have been used for targeting tumour cells in vivo. We have sought to link the powerful effector mechanisms of cytotoxic T-cells with the specificity of mAb, by targeting recombinant HLA class I molecules to tumour cells using an antibody delivery system. Soluble recombinant MHC class I/peptide complexes including HLA-A2.1 refolded around an immunodominant peptide from the HIV gag protein (HLA-A2/gag) were synthesized, and the stability of these complexes at 37 degrees C was confirmed by enzyme-linked immunosorbent assay using a conformation-specific antibody. MHC class I-negative lymphoma cells (Daudi) were labelled with a biotinylated mAb specific for a cell surface protein (anti-CD20) then linked to soluble biotinylated HLA-A2/gag complexes using an avidin bridge. Flow cytometry revealed strong labelling of lymphoma cells with HLA-A2/gag complexes (80-fold increase in mean channel fluorescence). CTL specific for HLA-A2/gag efficiently lysed complex-targeted cells, while control CTL (specific for an HLA-A2.1-restricted epitope of melan-A) did not. Similarly, SK-mel-29 melanoma cells were also efficiently lysed by HLA-A2/gag-specific CTL when HLA-A2/gag complexes were linked to their surface via the HMW-MAA specific anti-melanoma antibody 225.28s. With further consideration to the in vivo stability of the MHC class I/peptide complexes, this system could prove a new strategy for the immunological therapy of cancer.

Direct visualization of HIV-1-specific cytotoxic T lymphocytes during primary infection

OBJECTIVE

HIV-specific cytotoxic T lymphocytes (CTL) are believed to play an important role in containing viral replication throughout HIV-1 infection. Previous studies have attempted to quantify the HIV-1-specific CTL precursor frequency during primary HIV infection by using limiting dilution analysis, which almost certainly underestimates the true CTL frequency. Here we use a relatively new technique to quantify HIV-specific CD8 T cells in primary HIV infection.

METHODS

We have used soluble tetrameric complexes of HLA class I molecules complexed with HIV epitope peptides to study the dynamics and frequency of HIV-specific CD8 T cells in relation to plasma viral load in early HIV infection, in three patients with a highly focused HIV-specific CTL response.

RESULTS

We show that the frequencies of HIV-1-specific CD8 T cells in acute infection are significantly higher than previously documented and can be demonstrated well before full seroconversion. These studies also confirm the immunodominance of the B27-restricted response in HIV infection and demonstrate a close temporal relationship between the numbers of circulating HIV-specific CD8 T cells and viral load.

CONCLUSIONS

These findings strongly suggest that HIV-1-specific CD8 T cells are responding directly to the level of viral replication in early HIV infection and are a major factor in its control. In addition, the data indicate that immunodominance for CD8 T-cell responses is established in the acute phase of HIV infection.

High frequency of cytomegalovirus-specific cytotoxic T-effector cells in HLA-A*0201-positive subjects during multiple viral coinfections

How the cellular immune response copes with diverse antigenic competition is poorly understood. Responses of virus-specific cytotoxic T lymphocytes (CTL) were examined longitudinally in an individual coinfected with human immunodeficiency virus type 1 (HIV-1), Epstein-Barr virus (EBV), and cytomegalovirus (CMV). CTL responses to all 3 viruses were quantified by limiting dilution analysis and staining with HLA-A*0201 tetrameric complexes folded with HIV-1, EBV, and CMV peptides. A predominance of CMV-pp65-specific CTL was found, with a much lower frequency of CTL to HIV-1 Gag and Pol and to EBV-BMLF1 and LMP2. The high frequency of CMV-specific CTL, compared with HIV-1- and EBV-specific CTL, was confirmed in an additional 16 HLA-A*0201-positive virus-coinfected subjects. Therefore, the human immune system can mount CTL responses to multiple viral antigens simultaneously, albeit with different strengths.

Human immunodeficiency virus type 1- and cytomegalovirus-specific cytotoxic T lymphocytes can persist at high frequency for prolonged periods in the absence of circulating peripheral CD4(+) T cells

CD4(+) T cells are thought to be critical in the maintenance of virus-specific CD8(+) cytotoxic T-cell (CTL) responses. In human immunodeficiency virus type 1 (HIV-1) infection, a selective decline in HIV-1-specific CTL as the CD4(+) T-cell count decreases has been reported. Using HLA-peptide tetrameric complexes, we show the presence at high frequency of HIV-1- and cytomegalovirus-specific CD8(+) T cells when the peripheral CD4(+) T-cell count was low or zero in three HIV-1-infected patients. No direct virus-specific CD8(+)-mediated effector activity was seen in these subjects, suggesting antigen unresponsiveness, although tetramer-sorted cells could be expanded in vitro in the presence of interleukin-2 into responsive effector cells. Thus, virus-specific CD8(+) T cells can be maintained in the peripheral circulation at high frequency in the absence of circulating peripheral CD4(+) T cells, but these cells may lack direct effector activity. Strategies designed to overcome this antigen unresponsiveness may be of value in therapies for the treatment of AIDS.

Direct ex vivo analysis of hepatitis B virus-specific CD8(+) T cells associated with the control of infection

BACKGROUND & AIMS

Cytotoxic T cells have been suggested to be responsible for lysis of hepatitis B virus (HBV)-infected hepatocytes and control of virus infection. The frequency, kinetics, phenotype, and capacity for clonal expansion of circulating HBV-specific CD8 cells were analyzed directly in patients with acute HBV infection to clarify their pathogenetic role.

METHODS

Three HLA-A2 peptide tetramers able to visualize HBV core, envelope, and polymerase epitope-specific cytotoxic T lymphocytes were synthesized and used for flow cytometric analysis of antigen-specific populations.

RESULTS

Tetramer-positive cells specific for the core 18-27 epitope were found at a higher frequency than those specific for polymerase 575-583 and envelope 335-343 epitopes in most patients with acute HBV. The number of HBV-specific CD8 cells was highest during the clinically acute stage of infection and decreased after recovery. These cells expressed an activated phenotype and had an impaired capacity to expand in vitro and to display cytolytic activity in response to peptide stimulation. Recovery of these functions was observed when the frequency of specific CD8 cells decreased, coincident with a progressive decrease in their expression of activation markers.

CONCLUSIONS

This study provides the first ex vivo evidence that the highest frequency of circulating HBV-specific CD8 cells coincides with the clinically acute phase of hepatitis B. These cells exhibit an activated phenotype with limited further proliferative capacity that is restored during recovery.