Direct visualization of antigen-specific T cells: HTLV-1 Tax11-19- specific CD8(+) T cells are activated in peripheral blood and accumulate in cerebrospinal fluid from HAM/TSP patients

Effect of Human Papillomavirus-16 Infection on CD8+ T-Cell Recognition of a Wild-Type Sequence p53264–272 Peptide in Patients with Squamous Cell Carcinoma of the Head and Neck

PURPOSE

Wild-type sequence (wt) p53 peptides are attractive candidates for broadly applicable cancer vaccines, currently considered primarily for patients whose tumors overexpress p53. Circumstances exist, however, where increased p53 degradation may result in appreciable presentation of p53-derived peptides, despite low p53 expression. Squamous cell carcinoma of the head and neck is associated with oncogenic human papillomavirus (HPV) subtypes, which inactivate p53 through proteasomal degradation. The criterion of p53 overexpression would exclude these individuals from wt p53-based immunotherapy.

EXPERIMENTAL DESIGN

We tested the correlation of HPV infection with enhanced antigenicity of the p53 protein and postulated that removal of HPV-16(+) tumors with enhanced p53(264)-(272) peptide presentation might lead to a drop in T cells specific for this peptide in vivo. Circulating frequencies of T cells specific for the HLA A*0201:p53(264)-(272) complex were measured ex vivo using dimeric HLA:peptide complexes in 15 head and neck cancer patients before and 6 months after tumor excision.

RESULTS

CD8+ T-cell recognition of HLA A*0201 restricted wt p53(264)-(272) peptide presented by HPV-16(-) squamous cell carcinoma of the head and neck lines was enhanced by HPV-16 E6 expression, sometimes exceeding that of a naturally transformed, HPV-16(+) wt p53 expressing squamous cell carcinoma of the head and neck cell line. In patients with HPV-16(-) tumors, the frequency of wt p53(264-272)-specific T cells remained largely unchanged after tumor removal. However, a significant decline in frequency of anti-p53(264-272) T cells was observed postoperatively in HPV-16(+) patients (P < 0.005).

CONCLUSIONS

Recognition of HPV-associated squamous cell carcinoma of the head and neck appears associated with levels of wt p53-specific T cells and inversely with p53 expression. p53 peptides may be useful tumor antigens for squamous cell carcinoma of the head and neck immunotherapy in addition to viral gene products.

Evaluation of melanoma vaccines with molecularly defined antigens by ex vivo monitoring of tumor-specific T cells

Immunotherapy of melanoma is aimed to mobilize cytolytic CD8+ T cells playing a central role in protective immunity. Despite numerous clinical vaccine trials, only few patients exhibited strong antigen-specific T-cell activation, stressing the need to improve vaccine strategies. For a rational development, we propose to focus on molecularly defined vaccine components, and evaluate their immunogenicity with highly reproducible and standardized methods for ex vivo immune monitoring. Careful immunogenicity comparison of vaccine formulations in phase I/II studies allow to select optimized vaccines for subsequent clinical efficacy testing in large scale phase III trials.

Identification of novel hepatitis C virus-specific cytotoxic T lymphocyte epitopes by ELISpot assay using peptides with human leukocyte antigen-A*2402-binding motifs

The human leukocyte antigen (HLA)-A*2402 is common in Asians. The authors attempted to identify epitopes for HLA-A*2402-restricted, hepatitis C virus (HCV)-specific CD8+ T cells by an enzyme-linked immunospot (ELISpot) assay using peripheral blood CD8+ T cells from HLA-A*2402-positive hepatitis C patients and synthetic HCV peptides based on HLA-A*2402-binding motifs and the amino acid sequence of type 1b HCV. Ten novel epitopes were identified in five of seven HLA-A*2402-positive patients with acute or short-term chronic HCV infection (<3 years), but in none of four with longer-term chronic infection (>10 years). Only one of the ten epitopes proved to be definitely HLA-A*2402-restricted. Another epitope was identified in one of two HLA-A*2402-negative acute hepatitis C patients. In two of the six patients with positive CD8+ T cell responses, the targeted epitopes were multiple. The same epitope was targeted in two patients. When patients with unresolved acute HCV infection were treated with alpha interferon, peripheral blood HCV-specific CD8+ T cells decreased with resolution of the hepatitis. In conclusion, CD8+ T cell responses to HCV infection are heterogeneous. One definite HLA-A*2402-restricted and ten probably non-HLA-A*2402-restricted epitopes were identified. Patients with short-term HCV infection are suitable for searching for novel HCV epitopes, but peripheral blood HCV-specific CD8+ T cells decrease markedly after loss of antigenic stimulation.

Increased expression of human T lymphocyte virus type I (HTLV-I) Tax11-19 peptide-human histocompatibility leukocyte antigen A*201 complexes on CD4+ CD25+ T Cells detected by peptide-specific, major histocompatibility complex-restricted antibodies in patients with HTLV-I-associated neurologic disease

Human T lymphocyte virus type I (HTLV-I)–associated chronic inflammatory neurological disease (HTLV-I–associated myelopathy/tropical spastic paraparesis [HAM/TSP]) is suggested to be an immunopathologically mediated disorder characterized by large numbers of HTLV-I Tax–specific CD8⁺ T cells. The frequency of these cells in the peripheral blood and cerebrospinal fluid is proportional to the amount of HTLV-I proviral load and the levels of HTLV-I tax mRNA expression. As the stimulus for these virus-specific T cells are immunodominant peptide–human histocompatibility leukocyte antigen (HLA) complexes expressed on antigen-presenting cells, it was of interest to determine which cells express these complexes and at what frequency. However, until now, it has not been possible to identify and/or quantify these peptide–HLA complexes. Using a recently developed antibody that specifically recognizes Tax11-19 peptide–HLA-A*201 complexes, the level of Tax11-19–HLA-A*201 expression on T cells was demonstrated to be increased in HAM/TSP and correlated with HTLV-I proviral DNA load, HTLV-I tax mRNA load, and HTLV-I Tax–specific CD8⁺ T cell frequencies. Furthermore, CD4⁺ CD25⁺ T cells were demonstrated to be the major reservoir of HTLV-I provirus as well as Tax11-19 peptide–HLA-A*201 complexes. These results indicate that the increased detection and visualization of peptide–HLA complexes in HAM/TSP CD4⁺ CD25⁺ T cell subsets that are shown to stimulate and expand HTLV-I Tax–specific CD8⁺ T cells may play an important role in the pathogenesis of HTLV-I–associated neurological disease.

Quality and quantity: new strategies to improve immunotherapy of cancer

Adoptive immunotherapy is a promising approach for the treatment of infectious diseases and cancer. Several lines of research are currently focusing on the development of different technologies to facilitate the induction and expansion of antigen-specific T cells. Here, we discuss two current articles that affect the field of adoptive immunotherapy. One article describes the engineering of artificial antigen-presenting cells, which promise to replace the cumbersome dendritic-cell approach for the in vitro generation of large numbers of antigen-specific T cells. The second development is a description of a new technique for the detection of functionally active antigen-specific T cells, which will enhance the ability to control the quality of the T cells to be used in adoptive immunotherapy. Together, these exciting findings will advance the field of immunotherapy.

Immune responses to HTLV-I(ACH) during acute infection of pig-tailed macaques

Human T cell lymphotropic virus type 1 (HTLV-I) is causally linked to adult T cell leukemia/lymphoma (ATL) and a chronic progressive neurological disease, HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). A nonhuman primate model that reproduces disease symptoms seen in HTLV-I-infected humans might facilitate identification of initial immune responses to the virus and an understanding of pathogenic mechanisms in HTLV-I-related disease. Previously, we showed that infection of pig-tailed macaques with HTLV-I(ACH) is associated with multiple signs of disease characteristic of both HAM/TSP and ATL. We report here that within the first few weeks after HTLV-I(ACH) infection of pig-tailed macaques, serum concentrations of interferon (IFN)-alpha increased and interleukin-12 decreased transiently, levels of nitric oxide were elevated, and activation of CD4(+) and CD8(+) lymphocytes and CD16(+) natural killer cells in peripheral blood were observed. HTLV-I(ACH) infection elicited virus-specific antibodies in all four animals within 4 to 6 weeks; however, Tax-specific lymphoproliferative responses were not detected until 25-29 weeks after infection in all four macaques. IFN-gamma production by peripheral blood cells stimulated with a Tax or Gag peptide was detected to varying degrees in all four animals by ELISPOT assay. Peripheral blood lymphocytes from one animal that developed only a marginal antigen-specific cellular response were unresponsive to mitogen stimulation during the last few weeks preceding its death from a rapidly progressive disease syndrome associated with HTLV-I(ACH) infection of pig-tailed macaques. The results show that during the first few months after HTLV-I(ACH) infection, activation of both innate and adaptive immunity, limited virus-specific cellular responses, sustained immune system activation, and, in some cases, immunodeficiency were evident. Thus, this animal model might be valuable for understanding early stages of infection and causes of immune system dysregulation in HTLV-I-infected humans.

Increased mortality associated with HTLV-II infection in blood donors: a prospective cohort study

Background

HTLV-I is associated with adult T-cell leukemia, and both HTLV-I and -II are associated with HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Several published reports suggest that HTLV-I may lead to decreased survival, but HTLV-II has not previously been associated with mortality.

Results

We examined deaths among 138 HTLV-I, 358 HTLV-II, and 759 uninfected controls enrolled in a prospective cohort study of U.S. blood donors followed biannually since 1992. Proportional hazards models yielded hazard ratios (HRs) for the association between mortality and HTLV infection, controlling for sex, race/ethnicity, age, income, educational level, blood center, smoking, injection drug use history, alcohol intake, hepatitis C status and autologous donation. After a median follow-up of 8.6 years, there were 45 confirmed subject deaths. HTLV-I infection did not convey a statistically significant excess risk of mortality (unadjusted HR 1.9, 95%CI 0.8–4.4; adjusted HR 1.9, 95%CI 0.8–4.6). HTLV-II was associated with death in both the unadjusted model (HR 2.8, 95%CI 1.5–5.5) and in the adjusted model (HR 2.3, 95%CI 1.1–4.9). No single cause of death appeared responsible for the HTLV-II effect.

Conclusions

After adjusting for known and potential confounders, HTLV-II infection is associated with increased mortality among healthy blood donors. If replicated in other cohorts, this finding has implications for both HTLV pathogenesis and counseling of infected persons.

HLA-Ig-based artificial antigen-presenting cells: setting the terms of engagement

Recent advances in molecular medicine have shown that soluble MHC-multimers can be valuable tools for both the stimulation of as well as the analysis of antigen-specific T cells in vitro. In this review, we describe the use of dimeric major histocompatibility complexes, HLA-Ig, to visualize antigen-specific T cells as well as their potential to stimulate immune responses as part of an artificial antigen-presenting cell (aAPC). The use of HLA-Ig-based aAPC represents an exciting new approach to generate antigen-specific CTL for adoptive immunotherapy that helps to overcome many of the obstacles associated with limitations in current approaches to adoptive immunotherapy.

Comprehensive Early and Lasting Loss of Memory CD8 T Cells and Functional Memory during Acute and Persistent Viral Infections

Viral infections have been shown to induce lymphopenias that lower memory CD8 T cell frequencies, and they also have been shown to cause a permanent loss of memory cells specific to previously encountered pathogens. In this study, the patterns and significance of virus-induced memory CD8 T cell depletion were examined in mice immune to heterologous (Pichinde, vesicular stomatitis, vaccinia) viruses and subsequently challenged with acute or persistent lymphocytic choriomeningitis virus infections. Memory CD8 T cell loss was comprehensive and occurred in both lymphoid and peripheral tissues of the immune host. The impact of the loss of memory T cells was reflected by in vivo cytotoxicity assays, which showed decreased clearance of epitope-expressing targets. Memory CD8 T cell loss occurred very early (day 2) after infection, and was thereafter sustained, consistent more with an active deletion model than with a competition model. Cross-reactive T cells, in contrast, increased in number, but memory cells were reduced whether or not there was competition from cross-reactive T cells. Memory T cell loss was more profound during persistent infection than after acute infection. Adoptive transfer studies showed that, unlike the resolved acute infection, in which the reduced memory frequencies became stable, memory T cell loss was a continuously ongoing process during persistent infection. This study therefore links an early virus-induced lymphopenia to a subsequent long-term loss of CD8 T cell memory and offers a new mechanism for immune deficiency during persistent viral infections.

Telomerase pulsed dendritic cells for immunotherapy for renal cell carcinoma

PURPOSE

Renal cell carcinoma (RCC) is known for its immunological susceptibility. Unfortunately RCC lacks specific tumor antigens for the induction of specific immunotherapy. We investigated the role of telomerase as a tumor antigen and pulsed dendritic cells (DCs) as antigen presenting cells with an immunogenic peptide from telomerase.

MATERIAL AND METHODS

DCs and immunological effector cells, that is cytokine induced killer (CIK) cells, from patients with RCC or healthy donors were generated. CIK cells were co-cultured with telomerase peptide pulsed DCs. CIK cells were tested for cytotoxic activity against primary cultures. Using the dimer technique we determined the percent of telomerase specific T cells. Activation status was identified using interferon-gamma secretion assay.

RESULTS

After pulsing DCs with telomerase peptide co-cultured CIK cells had a significant increase in cytotoxic activity against tumor cells compared with CIK cells without co-culture, that is 100% at an effector-to-target ratio of 60:1 vs 41.7% (p <0.05). Using a complete autologous model with immunological cells derived from patients with metastatic RCC we were able to induce cytotoxicity against autologous, telomerase positive primary cell cultures. We could detect 2.4% telomerase specific effector cells after co-culture with peptide pulsed DCs, which secreted interferon-gamma after re-stimulation.

CONCLUSIONS

Telomerase could serve as a specific tumor associated antigen for RCC. The presentation of telomerase peptide by DCs to lymphocytes allows the generation of antigen specific cytotoxic effector cells.

Immunological Monitoring of Patients with Melanoma After Peptide Vaccination Using Soluble Peptide/HLA-A2 Dimer Complexes

To facilitate the immunologic monitoring of a peptide vaccine trial, a novel, empty dimeric HLA-A2 molecule (A2 dimer) that could be loaded with peptides was produced. The dimer comprises the extracellular domain of HLA-A2 noncovalently linked to a fusion protein consisting of human beta2-microglobulin joined to the human IgG1 Fc domain. Peptide-loaded dimer complexes were used to assess the function of peptide-specific T cells. HLA-A2 gp100 peptide dimers stimulated interferon (IFN)-gamma production by the gp100-specific TIL-1520 cell line. Gp100/A2 dimer stimulation in combination with intracellular cytokine staining was used to analyze peptide-specific T-cell responses in patients with melanoma after vaccination with the modified gp100: 209-2M peptide in adjuvant. Titration analysis of the amount of peptide-loaded dimer required to stimulate gp100-specific T cells was used to estimate the functional avidity of effector/memory CD8+ T lymphocytes. The number of peptide-specific T cells detected in the peripheral blood of vaccinated patients using this assay was comparable to the number determined by staining with fluoresceinated gp100: 209-2M HLA-A2 tetramers. IFN-gamma production by T cells was comparable after stimulation with peptide-pulsed dimers, T2 cells, or autologous dendritic cells. Peptide-loaded A2 dimers could also be used directly to stimulate T cells in the ELISPOT assay.

The immune control and cell-to-cell spread of human T-lymphotropic virus type 1

Human T-lymphotropic virus type 1 (HTLV-1) varies little in sequence compared with human immunodeficiency virus type 1 (HIV) and it is difficult to detect HTLV-1 mRNA, proteins or virions in fresh blood. But the strong and chronically activated T cell response to the virus indicates that HTLV-1 proteins are expressed persistently. It now appears that the efficiency of an individual's cytotoxic T cell (CTL) response to HTLV-1 is the chief single determinant of that person's provirus load, which can differ between HTLV-1-infected people by more than 10 000-fold. Progress is now being made towards defining this CTL ‘efficiency’ in terms of host genetics, T cell function, T cell gene expression and mathematical dynamics. Lymphocytes that are naturally infected with HTLV-1 do not produce enveloped extracellular virions in short-term culture and this has reinforced the erroneous conclusion that the virus is latent. But recent evidence shows that HTLV-1 can spread directly between lymphocytes across a specialized, virus-induced cell–cell contact – a ‘viral synapse’. Instead of making extracellular virions, HTLV-1 uses the mobility of the host cell to spread within and between hosts. In this review the evidence is summarized on the persistent gene expression of HTLV-1 in vivo, the role of the immune system in protection and pathogenesis in HTLV-1 infection, and the mechanism of cell-to-cell spread of HTLV-1.

Detection and characterization of cellular immune responses using peptide-MHC microarrays

The detection and characterization of antigen-specific T cell populations is critical for understanding the development and physiology of the immune system and its responses in health and disease. We have developed and tested a method that uses arrays of peptide-MHC complexes for the rapid identification, isolation, activation, and characterization of multiple antigen-specific populations of T cells. CD4(+) or CD8(+) lymphocytes can be captured in accordance with their ligand specificity using an array of peptide-MHC complexes printed on a film-coated glass surface. We have characterized the specificity and sensitivity of a peptide-MHC array using labeled lymphocytes from T cell receptor transgenic mice. In addition, we were able to use the array to detect a rare population of antigen-specific T cells following vaccination of a normal mouse. This approach should be useful for epitope discovery, as well as for characterization and analysis of multiple epitope-specific T cell populations during immune responses associated with viral and bacterial infection, cancer, autoimmunity, and vaccination.

Antigen-specific T cells: analyses of the needles in the haystack

Antigen binding to T cell receptors is a critical step in an immune response. Detection and characterization of rare populations of T cells enhances our ability to understand and treat disease

Mediators of central nervous system damage during the progression of human T-cell leukemia type I-associated myelopathy/tropical spastic paraparesis

Human T-cell leukemia virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) represents one of the most devastating diseases associated with HTLV-I infection. Despite the delineation of clinical features associated with this neurologic disease, more progress needs to be made with respect to understanding the molecular mechanisms relating to the genesis of HAM/TSP. Several factors have been hypothesized to contribute to whether an HTLV-I-infected individual remains asymptomatic, develops adult T-cell leukemia (ATL), or progresses to HAM/TSP. Among the most intriguing of these factors is the immune response mounted by the host against HTLV-I. Several cell populations are crucial with respect to generating an efficient immune response against the virus. This includes CD4(+) T cells, CD8(+) T cells, dendritic cells (DCs), monocytes/macrophages, and HTLV-I-infected cells that interact with immune cells to stimulate their effector functions. Although all of these cell types likely play important roles in the etiology of HAM/TSP, this review focuses specifically on the potential function of the CD8(+) T-cell population during the progression of HTLV-I-induced neurologic disease. The immune response in HAM/TSP patients may transition from a beneficial response aimed at controlling the viral infection, to a detrimental response that ultimately participates in mediating the pathology observed in HAM/TSP. In this respect, the generation of a hyperactive CD8(+) cytotoxic T lymphocyte (CTL) response primarily targeting the HTLV-I Tax protein likely plays a key role in the genesis of pathologic abnormalities associated with HAM/TSP. The efficiency and activity of Tax-specific CD8(+) CTLs may be regulated at a number of levels, and deregulation of Tax-specific CTL activation may contribute to HAM/TSP. This review focuses on potential mechanisms of central nervous system (CNS) damage associated with the genesis of HAM/TSP following HTLV-I infection, focusing on the role of the Tax-specific CTL compartment.

A novel multivalent human CTL peptide construct elicits robust cellular immune responses in HLA-A*0201 transgenic mice: implications for HTLV-1 vaccine design

Cytotoxic T-lymphocytes are critical in the clearance of chronic viral infections such as HTLV-1. Peptide-based vaccines may have potential application in invoking antiviral CTL responses. In the development of vaccination strategies, it is becoming increasingly important to elicit a broad immune response against several epitopes simultaneously that may provide large population coverage. In the present study, we addressed this issue, namely the processing and presentation of multiple CTL epitopes simultaneously for the generation of multispecific CTL responses. We designed a novel multivalent peptide consisting of three HLA-A(*)0201 restricted CTL epitopes, with intervening double arginine residues in tandem. These epitopes were derived from the HTLV-1 regulatory protein Tax, which is an attractive target for vaccine development against HTLV-1. Arginine residues were included to provide cleavage sites for proteasomes, to generate the intended MHC Class I ligands. Proteasomal digestion studies and mass spectrometry analysis showed cleavage of the multivalent construct to generate the individual epitopes. Immunization of HLA-A(*)0201 transgenic mice with this construct efficiently elicited cellular responses to each intended epitope in vivo, further validating the applicability of this approach. These data may have potential in the development of immunotherapeutic strategies for the treatment of HTLV-1 disease and in the future design of multivalent subunit peptide vaccines.

Tumors as elusive targets of T-cell-based active immunotherapy

The understanding of tumor-host interactions remains elusive despite significant progress in the identification of tumor antigens (TAs) recognized by autologous T cells. In particular, most human tumors do not regress and continue to grow in spite of spontaneous or immunization-induced immune responses demonstrated in circulating lymphocytes. Indeed, systemic immune responses might insufficiently address the complexity of tumor-host interactions because of factors, such as (1) the lack of productive T-cell receptor (TCR) engagement with epitope owing to qualitative and/or quantitative defects in the generation and maintenance of the immune response, (2) insufficient costimulation provided by the host, (3) the lack of localization of the immune response in target tissues and (4) the complexity of tumor-host interactions within the tumor microenvironment caused by temporal changes in tumor phenotypes and an array of immune mediators expressed in the tumor microenvironment. Here, we will review current knowledge of the different 'levels' of immune response that might be necessary for immunotherapy to be effective in the treatment of cancer. Furthermore, we will discuss the information still required in order to understand the mechanism(s) governing tumor rejection by the immune system in response to TA-specific immunization.

The dynamics of T-cell fratricide: application of a robust approach to mathematical modelling in immunology

Fratricide between CD8(+) T lymphocytes is known to occur in HTLV-I and possibly HSV-1 and HIV-1 infection. However it is not known what effect, if any, T-cell fratricide has on the course of infection. Here we present simple mathematical techniques to investigate T-cell fratricide with particular reference to HTLV-I infection. Using a general model we predict the qualitative and quantitative effect of fratricide on HTLV-I equilibrium proviral load. We also investigate the effect of fratricide on the probability of viral clearance. We show that, surprisingly, fratricide can lead either to an increase or a decrease in equilibrium proviral load. We derive the conditions necessary for fratricide to cause a decrease in load and deduce that, for the five HTLV-I-positive patients considered here, fratricide has probably caused an increase in equilibrium load. We also estimate the percentage increase in load that is attributable to fratricide and determine the parameters that should be measured in order to improve this estimate. Finally, we show that fratricide reduces the probability of viral clearance. Mathematical modelling of HTLV-I infection, as is often the case in biology, is severely hampered by a lack of experimental data. Consequently it is difficult to know what functional form a model should take. The behaviour of complex nonlinear systems is highly model-dependent. Predictions based on theoretical models are therefore sensitive to the choice of model; this is a very severe problem that undermines and limits the success of the application of mathematics to immunology. In this paper we reduce the model dependency of the results in two ways-by considering (analytically) a general model with a minimal number of assumptions and, where this is not possible, by checking (numerically) that a wide range of models yield the same results. We therefore begin to develop two practical methods for dealing with the problem of robustness in mathematical models of the immune system.

Ex vivo induction and expansion of antigen-specific cytotoxic T cells by HLA-Ig-coated artificial antigen-presenting cells

Adoptive immunotherapy holds promise as a treatment for cancer and infectious diseases, but its development has been impeded by the lack of reproducible methods for generating therapeutic numbers of antigen-specific CD8(+) cytotoxic T lymphocytes (CTLs). As a result, there are only limited reports of expansion of antigen-specific CTLs to the levels required for clinical therapy. To address this issue, artificial antigen-presenting cells (aAPCs) were made by coupling a soluble human leukocyte antigen-immunoglobulin fusion protein (HLA-Ig) and CD28-specific antibody to beads. HLA-Ig-based aAPCs were used to induce and expand CTLs specific for cytomegalovirus (CMV) or melanoma. aAPC-induced cultures showed robust antigen-specific CTL expansion over successive rounds of stimulation, resulting in the generation of clinically relevant antigen-specific CTLs that recognized endogenous antigen-major histocompatibility complex complexes presented on melanoma cells. These studies show the value of HLA-Ig-based aAPCs for reproducible expansion of disease-specific CTLs for clinical approaches to adoptive immunotherapy.

A novel single chain I-A(b) molecule can stimulate and stain antigen-specific T cells

Multimers of soluble major histocompatibility complex class I and II molecules have proven to be useful reagents in quantifying and following specific T cell populations. This study describes the design, generation, and characterization of a novel, single chain I-A(b) molecule which utilizes a unique linker derived from the murine invariant chain. A fragment of the invariant chain, residues 58-85, binds to a region proximal to the class II peptide binding groove and stabilizes occupancy of the class II invariant chain-associated peptide. We have utilized this fragment, replacing CLIP with the Ealpha peptide sequence, to lock the attached peptide into the class II binding groove. The single chain I-A(b) molecule was recognized by a panel of conformation-sensitive, I-A(b)-specific, monoclonal antibodies. Membrane-bound and soluble forms of the single chain I-A(b) stimulated an antigen-specific T cell hybridoma, and tetramers made from soluble monomers stained these cells. The unique features of this molecule may be useful in the design of recombinant T cell receptor ligands containing peptides with low affinity for MHC.

Virus-specific CD8 T cells in peripheral tissues are more resistant to apoptosis than those in lymphoid organs

CD8 T cells persist at high frequencies in peripheral organs after resolution of an immune response, and their presence in the periphery is important for resistance to secondary challenge. We show here that LCMV-specific T cells in peripheral tissue (peritoneal cavity, lung, fat pads) reacted much less with the apoptotic marker Annexin-V than those in spleen and lymph nodes. This was not due to a TCR-based selection. In comparison to lymphoid tissue, T cells in the periphery expressed lower levels of Fas and Fas ligand and were resistant to activation-induced cell death in vitro. This may contribute to the survival of nondividing peripheral memory T cells, enabling them to efficiently function without being driven into apoptosis.

Degenerate specificity of HTLV-1-specific CD8+ T cells during viral replication in patients with HTLV-1-associated myelopathy (HAM/TSP)

Human T-lymphotropic virus type 1 (HTLV-1)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is an inflammatory neurologic disease caused by HTLV-1 infection, in which HTLV-1-infected CD4(+) T cells and HTLV-1-specific CD8(+) T cells may play a role in the disease pathogenesis. Patients with HAM/TSP have high proviral loads despite vigorous virus-specific CD8(+) T-cell responses; however, it is unknown whether the T cells are efficient in eliminating the virus in vivo. To define the dynamics of HTLV-1-specific CD8(+) T-cell responses, we investigated longitudinal alterations in HTLV-1 proviral load, amino acid changes in an immunodominant viral epitope, frequency of HTLV-1-specific T cells, and degeneracy of T-cell recognition in patients with HAM/TSP. We showed that the frequency and the degeneracy of the HTLV-1-specific CD8(+) T cells correlated well with proviral load in the longitudinal study. The proviral load was much higher in a patient with low degeneracy of HTLV-1-specific T cells compared to that in a patient with comparable frequency but higher degeneracy of the T cells. Furthermore, in a larger number of patients divided into 2 groups by the proviral load, those with high proviral load had lower degeneracy of T-cell recognition than those with low proviral load. Sequencing analysis revealed that epitope mutations were remarkably increased in a patient when the frequency and the degeneracy were at the lowest. These data suggest that HTLV-1-specific CD8(+) T cells with degenerate specificity are increased during viral replication and control the viral infection.

Real-time monitoring of immune responses

With the advent of cellular immunotherapy, the ability to monitor immune responses during treatment will be essential to evaluate the effectiveness of the new therapies. While the ultimate determinate of the success of immunotherapy trials will be clinical outcome, methods of monitoring immunity in real-time have become available that will assist in the development of immunotherapy strategies and in the prediction of individual patient prognosis during the course of treatment. The essentials of existing immune assays are described here with examples of how these techniques have been used previously. A perspective on which approaches will likely prove the most useful for monitoring immune responses in real-time during immunotherapy is also presented.

Human T-cell lymphotropic virus type I and neurological diseases

Human T-cell lymphotropic virus type I (HTLV-I) infection is associated with a variety of human diseases. In particular, there are two major diseases caused by HTLV-I infection. One is an aggressive neoplastic disease called adult T-cell leukemia (ATL), and another is a chronic progressive inflammatory neurological disease called HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is still unknown why one virus causes these different diseases. With regard to HAM/TSP, virus-host immunological interactions are an considered to be important cause of this disease. Coexisting high HTLV-I proviral load and HTLV-I-specific T cells (CD4+ T cells and CD8+ T cells) is an important feature of HAM/TSP. Histopathological studies indicate the existence of an inflammatory reaction and HTLV-I-infected cells in the affected lesions of HAM/TSP. Therefore, the immune response to HTLV-I probably contributes to the inflammatory process of the central nervous system lesions in HAM/TSP patients.

Viral persistence alters CD8 T-cell immunodominance and tissue distribution and results in distinct stages of functional impairment

Chronic viral infections often result in ineffective CD8 T-cell responses due to functional exhaustion or physical deletion of virus-specific T cells. However, how persisting virus impacts various CD8 T-cell effector functions and influences other aspects of CD8 T-cell dynamics, such as immunodominance and tissue distribution, remains largely unknown. Using different strains of lymphocytic choriomeningitis virus (LCMV), we compared responses to the same CD8 T-cell epitopes during acute or chronic infection. Persistent infection led to a disruption of the normal immunodominance hierarchy of CD8 T-cell responses seen following acute infection and dramatically altered the tissue distribution of LCMV-specific CD8 T cells in lymphoid and nonlymphoid tissues. Most importantly, CD8 T-cell functional impairment occurred in a hierarchical fashion in chronically infected mice. Production of interleukin 2 and the ability to lyse target cells in vitro were the first functions compromised, followed by the ability to make tumor necrosis factor alpha, while gamma interferon production was most resistant to functional exhaustion. Antigen appeared to be the driving force for this loss of function, since a strong correlation existed between the viral load and the level of exhaustion. Further, epitopes presented at higher levels in vivo resulted in physical deletion, while those presented at lower levels induced functional exhaustion. A model is proposed in which antigen levels drive the hierarchical loss of different CD8 T-cell effector functions during chronic infection, leading to distinct stages of functional impairment and eventually to physical deletion of virus-specific T cells. These results have implications for the study of human chronic infections, where similar T-cell deletion and functional dysregulation has been observed.

Human T cell leukemia virus type I-induced disease: pathways to cancer and neurodegeneration

Retroviral infection is associated with a number of pathologic abnormalities, including a variety of cancers, immunologic diseases, and neurologic disorders. Shortly after its discovery in 1980, human T cell leukemia virus type I (HTLV-I) was found to be the etiologic agent of both adult T cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a neurologic disease characterized by demyelinating lesions in both the brain and the spinal cord. Approximately 5-10% of HTLV-I-infected individuals develop either ATL or HAM/TSP. Interestingly, the two diseases have vastly different pathologies and have rarely been found to occur within the same individual. While a number of host and viral factors including virus strain, viral load, and HLA haplotype have been hypothesized to influence disease outcome associated with HTLV-I infection, the relative contributions of such factors to disease pathogenesis have not been fully established. Recent research has suggested that the route of primary viral infection may dictate the course of disease pathogenesis associated with HTLV-I infection. Specifically, mucosal exposure to HTLV-I has been associated with cases of ATL, while primary viral infection based in the peripheral blood has been correlated with progression to HAM/TSP. However, the cellular and molecular mechanisms regulating disease progression resulting from primary viral invasion remain to be elucidated. Although a variety of factors likely influence these mechanisms, the differential immune response mounted by the host against the incoming virus initiated in either the peripheral blood or the mucosal compartments likely plays a key role in determining the outcome of HTLV-I infection. It has been proposed that the route of infection and size of the initial viral inoculum allows HTLV-I to infect different target cell populations, in turn influencing the breadth of the immune response mounted against HTLV-I and affecting disease pathogenesis. A model of HTLV-I-induced disease progression is presented, integrating information regarding the role of several host and viral factors in the genesis of both neoplasia and neurologic disease induced following HTLV-I infection, focusing specifically on differential viral invasion into the bone marrow (BM) and the influence of this event on the virus-specific CD8(+) cytotoxic T lymphocyte (CTL) response that is initiated following HTLV-I infection.

Molecular tracking of antigen-specific T cell clones in neurological immune-mediated disorders

T cells recognizing self or microbial antigens may trigger or reactivate immune-mediated diseases. Monitoring the frequency of specific T cell clonotypes to assess a possible link with the course of disease has been a difficult task with currently available technology. Our goal was to track individual candidate pathogenic T cell clones, selected on the basis of previous extensive studies from patients with immune-mediated disorders of the CNS, including multiple sclerosis, HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP) and chronic Lyme neuroborreliosis. We developed and applied a highly specific and sensitive technique to track single CD4(+) and CD8(+) T cell clones through the detection and quantification of T cell receptor (TCR) alpha or beta chain complementarity-determining region 3 transcripts by real-time reverse transcriptase (RT)-PCR. We examined the frequency of the candidate pathogenic T cell clones in the peripheral blood and CSF during the course of neurological disease. Using this approach, we detected variations of clonal frequencies that appeared to be related to clinical course, significant enrichment in the CSF, or both. By integrating clonotype tracking with direct visualization of antigen-specific staining, we showed that a single T cell clone contributed substantially to the overall recognition of the viral peptide/MHC complex in a patient with HAM/TSP. T cell clonotype tracking is a powerful new technology enabling further elucidation of the dynamics of expansion of autoreactive or pathogen-specific T cells that mediate pathological or protective immune responses in neurological disorders.

Peptide-beta2-microglobulin-MHC fusion molecules bind antigen-specific T cells and can be used for multivalent MHC-Ig complexes

Recombinant soluble MHC molecules are widely used for visualization, activation and inhibition of antigen-specific immune responses. Using a genetic approach, we have generated two novel peptide-beta2-microglobulin-MHC constructs. We have linked the MHC molecule with the peptide of interest, without limiting the recognition by the cognate TCR. This molecule can also be joined with the IgG heavy chain resulting in a dimeric MHC-Ig fusion protein. These molecules bind antigen-specific T cells with high specificity and sensitivity, therefore, providing a valuable tool for detection as well as enrichment of antigen-specific T cells.

Immunopathogenesis of human T cell lymphotropic virus type I-associated neurologic disease

This review focuses on current approaches to understanding the immunopathogenesis of human T cell lymphotropic virus (HTLV) type I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) based on newly developed molecular and immunologic techniques that have been adapted to studies of HTLV-I proviral load, HTLV-I mRNA, and HTLV-I tax-specific CD8 T cells. These methods enable researchers to study previously inaccessible aspects of this disease and allow a more detailed analysis of virus/host immune responses as they relate to disease specificity in this disorder. The role of HTLV-I-specific CD8 T cell immune responses is highlighted. The elucidation of the immunopathology of HAM/TSP will enhance our understanding of other HTLV-I-associated disorders plus other neurologic, hematologic, and inflammatory diseases for which viral etiologies have been suggested.

Generation and use of alternative multimers of peptide/MHC complexes

For many years, the detection of antigen-specific T cells has relied on indirect in vitro assays such as cytokine secretion, proliferation or chromium release assays. Things have dramatically changed during the past few years, thanks to the imagination of several investigators who have developed very elegant strategies to produce multivalent peptide/MHC complexes. One of these strategies has been to produce peptide-loaded monomeric biotinylated MHC molecules, which could be obtained as tetramers upon incubation with tetravalent streptavidin. Although this latter approach has been by far the most popular, this review focuses on other strategies which have also been successful.

Oligomeric MHC molecules and their homologues: state of the art

This special issue of the Journal of Immunological Methods brings together articles from some of the leaders in labelling antigen-specific T and NKT cells, describing recent technical advances and their impact on the study of immunology. Although tetramers, or tetrameric MHC class I/peptide complexes, are the best known reagents in the field, various forms of oligomeric complexes are now being successfully used to detect antigen-specific T cells, including cytotoxic T lymphocytes, MHC class II-restricted CD4+ T cells, and glycolipid-specific T cells restricted by CD1 isoforms. The articles presented here detail the breadth of the oligomeric structures being used to probe T, NK and NKT cell function, and cover both the technical and practical aspects of their use, as well as the new biology revealed. In addition to providing a summary of the current state of the art, these contributions also provide clear pointers to strategies likely to succeed in the future. In this introductory chapter, we summarise the work presented in the other articles of this issue, and provide an overarching view of this rapidly evolving field. We also provide a summary of the MHC class I molecules successfully refolded to date, and provide references to other relevant sources of technical information.

Major histocompatibility complex (MHC) tetramer technology: an evaluation

Single-cell assays are currently favored to quantitate T-cell responses. Staining antigen-specific T-cells with fluorescently labeled tetrameric major histocompatibility complex (MHC)/peptide complexes has greatly enhanced the ability to assess the cellular dynamics of an immune response at the single-cell level. This article reviews MHC tetramer technology, defining it, discussing how MHC tetramers are made, outlining the benefits of this technology, comparing and contrasting it to other methods for evaluating immune responses, and describing current applications.

Escaping high viral load exhaustion: CD8 cells with altered tetramer binding in chronic hepatitis B virus infection

Deletion, anergy, and a spectrum of functional impairments can affect virus-specific CD8 cells in chronic viral infections. Here we characterize a low frequency population of CD8 cells present in chronic hepatitis B virus (HBV) infection which survive in the face of a high quantity of viral antigen. Although they do not appear to exert immunological pressure in vivo, these CD8 cells are not classically "tolerant" since they proliferate, lyse, and produce antiviral cytokines in vitro. They are characterized by altered HLA/peptide tetramer reactivity, which is not explained by TCR down-regulation or reduced functional avidity and which can be reversed with repetitive stimulation. CD8 cells with altered tetramer binding appear to have a specificity restricted to envelope antigen and not to other HBV antigens, suggesting that mechanisms of CD8 cell dysfunction are differentially regulated according to the antigenic form and presentation of individual viral antigens.

Phenotypic study of peripheral blood leucocytes in HTLV-I-infected individuals from Minas Gerais, Brazil

The human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) associated with the HTLV-I is a well-defined clinical-pathological entity in which the virus and host immune responses contribute to the pathological mechanism. In this study, flow cytometric analysis of whole peripheral blood leucocytes (PBL) was performed to evaluate the immunological status of HTLV-I-infected individuals in an effort to better understand the role of the immune system in the development of HAM/TSP. We have evaluated three groups of infected patients including asymptomatic (AS = 18), ambulatory/oligosymptomatic (AM = 14) and hospitalized HAM/TSP individuals (HO = 42). Noninfected healthy blood donors were used for the control group (NI = 32). Our results demonstrated that the HO group presents an increased percentage of circulating T cells and a decreased percentage of B and natural killer (NK) cells, leading to the highest T/B-cell ratio in comparison with the other groups. Interestingly, while an increased percentage of activated CD4+HLA-DR+ T lymphocytes was observed in both AM and HO, only HO presented higher percentage of activated CD8+HLA-DR+ in combination with the highest CD18 surface expression. This was true for all cell populations analysed, including T lymphocytes, monocytes and neutrophils. Moreover, the HO group was distinguished by a dramatic decrease in the percentage of CD8+CD28+ lymphocytes. Taken together, these findings demonstrate a potent cellular immune activation response involving primarily CD8+ T cells that is concomitant with disease progression in HAM/TSP. We also show that an upregulation of CD18 expression, a hallmark for increased cell migratory potential, might play a critical role in the development/maintenance of HAM/TSP.

Escaping high viral load exhaustion: CD8 cells with altered tetramer binding in chronic hepatitis B virus infection

Deletion, anergy, and a spectrum of functional impairments can affect virus-specific CD8 cells in chronic viral infections. Here we characterize a low frequency population of CD8 cells present in chronic hepatitis B virus (HBV) infection which survive in the face of a high quantity of viral antigen. Although they do not appear to exert immunological pressure in vivo, these CD8 cells are not classically "tolerant" since they proliferate, lyse, and produce antiviral cytokines in vitro. They are characterized by altered HLA/peptide tetramer reactivity, which is not explained by TCR down-regulation or reduced functional avidity and which can be reversed with repetitive stimulation. CD8 cells with altered tetramer binding appear to have a specificity restricted to envelope antigen and not to other HBV antigens, suggesting that mechanisms of CD8 cell dysfunction are differentially regulated according to the antigenic form and presentation of individual viral antigens.

Escaping high viral load exhaustion: CD8 cells with altered tetramer binding in chronic hepatitis B virus infection

Deletion, anergy, and a spectrum of functional impairments can affect virus-specific CD8 cells in chronic viral infections. Here we characterize a low frequency population of CD8 cells present in chronic hepatitis B virus (HBV) infection which survive in the face of a high quantity of viral antigen. Although they do not appear to exert immunological pressure in vivo, these CD8 cells are not classically "tolerant" since they proliferate, lyse, and produce antiviral cytokines in vitro. They are characterized by altered HLA/peptide tetramer reactivity, which is not explained by TCR down-regulation or reduced functional avidity and which can be reversed with repetitive stimulation. CD8 cells with altered tetramer binding appear to have a specificity restricted to envelope antigen and not to other HBV antigens, suggesting that mechanisms of CD8 cell dysfunction are differentially regulated according to the antigenic form and presentation of individual viral antigens.

Selected cytotoxic T lymphocytes with high specificity for HTLV-I in cerebrospinal fluid from a HAM/TSP patient

Human T lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic inflammatory disease of the spinal cord in which HTLV-I Tax-specific cytotoxic T lymphocytes (CTL) have been suggested to be immunopathogenic. However, it is unknown whether the HTLV-I-specific CTL in the central nervous system differ from those in the periphery. We investigated functional T-cell receptor diversity in HTLV-I Tax11-19-specific CTL clones derived from peripheral blood and cerebrospinal fluid (CSF) of a HAM/TSP patient using analogue peptides of the viral antigen. CTL responses to the analogue peptides varied between T-cell clones, however, CTL clones from CSF showed limited recognition of the peptides when compared to those from peripheral blood. This suggests that CTL with highly focused specificity for HTLV-I Tax accumulate in the CSF and may contribute to the pathogenesis of HAM/TSP. Furthermore, this study provides a rationale for analogue peptide-based immunotherapeutic strategies focusing on the immunopathogenic T-cells in HTLV-I-associated neurologic disease.

Human T cell leukemia virus type I and neurologic disease: events in bone marrow, peripheral blood, and central nervous system during normal immune surveillance and neuroinflammation

Human T cell lymphotropic/leukemia virus type I (HTLV-I) has been identified as the causative agent of both adult T cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Although the exact sequence of events that occur during the early stages of infection are not known in detail, the initial route of infection may predetermine, along with host, environmental, and viral factors, the subset of target cells and/or the primary immune response encountered by HTLV-I, and whether an HTLV-I-infected individual will remain asymptomatic, develop ATL, or progress to the neuroinflammatory disease, HAM/TSP. Although a large number of studies have indicated that CD4(+) T cells represent an important target for HTLV-I infection in the peripheral blood (PB), additional evidence has accumulated over the past several years demonstrating that HTLV-I can infect several additional cellular compartments in vivo, including CD8(+) T lymphocytes, PB monocytes, dendritic cells, B lymphocytes, and resident central nervous system (CNS) astrocytes. More importantly, extensive latent viral infection of the bone marrow, including cells likely to be hematopoietic progenitor cells, has been observed in individuals with HAM/TSP as well as some asymptomatic carriers, but to a much lesser extent in individuals with ATL. Furthermore, HTLV-I(+) CD34(+) hematopoietic progenitor cells can maintain the intact proviral genome and initiate viral gene expression during the differentiation process. Introduction of HTLV-I-infected bone marrow progenitor cells into the PB, followed by genomic activation and low level viral gene expression may lead to an increase in proviral DNA load in the PB, resulting in a progressive state of immune dysregulation including the generation of a detrimental cytotoxic Tax-specific CD8(+) T cell population, anti-HTLV-I antibodies, and neurotoxic cytokines involved in disruption of myelin-producing cells and neuronal degradation characteristic of HAM/TSP.

Increased HTLV-I proviral load and preferential expansion of HTLV-I Tax-specific CD8+ T cells in cerebrospinal fluid from patients with HAM/TSP

To date, high human T-cell lymphotropic virus type I proviral load in patients with human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis has been reported and is thought to be related to the pathogenesis of human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis. However, the proviral load in cerebrospinal fluid has not been well investigated. We measured human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells from human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis patients using real-time quantitative polymerase chain reaction (TaqMan). Human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells were significantly higher than that of the matched peripheral blood mononuclear cells, and a high ratio of human T-cell lymphotropic virus type I proviral load in cerebrospinal fluid cells to peripheral blood mononuclear cells were observed in patients with short duration of illness. Human T-cell lymphotropic virus type I Tax-specific CD8+ T cells, as detected by peptide-loaded HLA tetramers, accumulated in cerebrospinal fluid compared with that in peripheral blood mononuclear cells, while the frequency of cytomegalovirus-specific CD8+ T cells in cerebrospinal fluid was reduced. These observations suggest that accumulation of both human T-cell lymphotropic virus type I-infected cells and preferential expansion of human T-cell lymphotropic virus type I-specific CD8+ cells in cerebrospinal fluid may play a role in the pathogenesis of human T-cell lymphotropic virus type I-associated myelopathy/tropical spastic paraparesis.

Activation of HTLV-I long terminal repeat by stress-inducing agents and protection of HTLV-I-infected T-cells from apoptosis by the viral tax protein

HTLV-I is etiologically implicated with tropical spastic paraparesis/HTLV-I associated myelopathy, adult T-cell leukemia and certain other diseases. However, after infection the virus enters into a dormant state, whereas the characteristics of the HTLV-I related diseases indicate that their genesis requires activation of the dormant virus by a Tax-independent mechanism. In the present study we demonstrate that a variety of stress-inducing agents (TPA, cisplatin, etoposide, taxol, and 3-methylcholanthrene) are capable of Tax-independent activation of HTLV-I LTR and that this activation is detected mainly in cells that are undergoing through the apoptotic process. Furthermore, it is demonstrated that both apoptosis induction and HTLV-I LTR activation are inhibited by Bcl-2 and by PKC, indicating that these two processes are mechanistically cross-linked. In addition, using an HTLV-I producing human T-cell line which permanently express the negatively transdominant tax mutant, Delta58tax, under the Tet-Off control system, we prove that the virally encoded Tax protein protects the host cells from apoptosis. Together, these data suggest that activation of the dormant virus in the carriers' infected T-cells by certain stress-inducing conditions and protecting these cells from the consequent apoptotic death by the viral Tax protein emerging after this activation, might be the basis for switching the virus from latency to a pathogenic phase.

An enhanced and scalable process for the purification of SIV Gag-specific MHC tetramer

A recently developed method for the identification and quantitation of antigen-specific T lymphocytes involves the use of complexes of biotinylated major histocompatibility complex (MHC) and avidin conjugated to a fluorescent reporter group. This complex, dubbed the "tetramer," binds to antigen-specific T lymphocytes in vitro, which can then be sorted and counted by fluorescence-activated flow cytometry to measure immune response. Our research has focused on developing the purification process for preparing tetramer reagent. Our goal was to reengineer a published lab-scale purification process to reduce the number of processing steps and to make the process scalable. In our reengineered process, recombinant MHC alpha chain is isolated from Escherichia coli as inclusion bodies by tangential flow filtration. The purified MHC alpha chain is refolded with beta-2-microglobulin and the target peptide antigen to form the class I MHC. The resulting MHC is purified by hydrophobic interaction chromatography (HIC) and biotinylated enzymatically, and the biotinylated MHC is purified by a second HIC step. The tetramer is prepared by mixing biotinylated MHC with an avidin-fluorophore conjugate. The tetramer is further purified to remove any excess MHC or avidin components. Analysis by flow cytometry confirmed that the tetramers generated by this new process gave bright staining and specific binding to CD3+/CD8+ cells of vaccinated monkeys and led to results that were equivalent to those generated with tetramer produced by the original process.

Memory CD8+ T cells in heterologous antiviral immunity and immunopathology in the lung

A potent role for memory CD8+ T cells in heterologous immunity was shown with a respiratory mucosal model of viral infection. Memory CD8+ T cells generated after lymphocytic choriomeningitis virus (LCMV) infection were functionally activated in vivo to produce interferon-gamma (IFN-gamma) during acute infection with vaccinia virus (VV). Some of these antigen-specific memory cells selectively expanded in number, which resulted in modulation of the original LCMV-specific T cell repertoire. In addition, there was an organ-selective compartmental redistribution of these LCMV-specific T cells during VV infection. The presence of these LCMV-specific memory T cells correlated with enhanced VV clearance, decreased mortality and marked changes in lung immunopathology. Thus, the participation of pre-existing memory T cells specific to unrelated agents can alter the dynamics of mucosal immunity and disease course in response to a pathogen.

Antigen-specific blockade of T cells in vivo using dimeric MHC peptide

Ag-specific immune tolerance in clinical organ transplantation is currently an unrealized but critical goal of transplant biology. The specificity and avidity of multimerized MHC-peptide complexes suggests their potential ability to modulate T cell sensitization and effector functions. In this study, we examined the ability of MHC-peptide dimers to modulate T cell function both in vitro and in vivo. Soluble MHC dimers induced modulation of surface TCR expression and inhibited T cell cytolytic activity at nanomolar concentrations in vitro. Furthermore, engagement of TCR by soluble dimers resulted in phosphorylation of the TCR zeta-chain and recruitment and phosphorylation of zeta-associated protein-70 to the signaling complex, the latter of which increased upon dimer cross-linking. Significantly, Ag-specific inhibition of an alloreactive TCR-transgenic T cell population in vivo resulted in consequent outgrowth of an allogeneic tumor. The prolonged Ag-specific suppression of expansion and/or effector function of cognate T cells in vivo suggests that soluble MHC dimers may be a means of inducing sustained Ag-specific T cell unresponsiveness in vivo.

In vitro spontaneous lymphoproliferation in patients with human T-cell lymphotropic virus type I-associated neurologic disease: predominant expansion of CD8+ T cells

Peripheral blood mononuclear cells (PBMCs) from patients with human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) proliferate spontaneously in vitro. This spontaneous lymphoproliferation (SP) is one of the immunologic hallmarks of HAM/TSP and is considered to be an important factor related to the pathogenesis of HAM/TSP. However, the cell populations involved in this phenomenon have not yet been definitively identified. To address this issue, the study directly evaluated proliferating cell subsets in SP with a flow cytometric method using bromodeoxyuridine and Ki-67. Although both CD4+ and CD8+ T cells proliferated spontaneously, the percentage of proliferating CD8+ T cells was 2 to 5 times higher than that of CD4+ T cells. In addition, more than 40% of HTLV-I Tax11-19-specific CD8+ T cells as detected by an HLA-A*0201/Tax11-19 tetramer proliferated in culture. In spite of this expansion of HTLV-I-specific CD8+ T cells, HTLV-I proviral load did not decrease. This finding will help elucidate the dynamics of in vivo virus-host immunologic interactions that permit the coexistence of high HTLV-I-specific CD8+ cytotoxic T-lymphocyte responses and high HTLV-I proviral load in HAM/TSP.