Granzyme B ELISPOT assay for ex vivo measurements of T cell immunity

High-Throughput GLP-Capable Target Cell Visualization Assay for Measuring Cell-Mediated Cytotoxicity

One of the primary effector functions of immune cells is the killing of virus-infected or malignant cells in the body. Natural killer (NK) and CD8 effector T cells are specialized for this function. The gold standard for measuring such cell-mediated cytolysis has been the chromium release assay, in which the leakage of the radioactive isotope from damaged target cells is being detected. Flow cytometry-based single cell analysis of target cells has recently been established as a non-radioactive alternative. Here we introduce a target cell visualization assay (TVA) that applies similar target cell staining approaches as used in flow cytometry but based on single cell computer image analysis. Two versions of TVA are described here. In one, the decrease in numbers of calcein-stained, i.e., viable, target cells is assessed. In the other, the CFSE/PI TVA, the increase in numbers of dead target cells is established in addition. TVA assays are shown to operate with the same sensitivity as standard chromium release assays, and, leaving data audit trails in form of scanned (raw), analyzed, and quality-controlled images, thus meeting requirements for measuring cell-mediated cytolysis in a regulated environment.

HIV-Specific Granzyme B-Secreting but Not Gamma Interferon-Secreting T Cells Are Associated with Reduced Viral Reservoirs in Early HIV Infection

A major barrier to a human immunodeficiency virus type 1 (HIV-1) infection cure is the establishment of a viral reservoir in spite of combined antiretroviral therapy (cART). It is unclear how HIV-specific cytotoxic T lymphocytes (CTLs) influence the size of the reservoir in early HIV infection. Twenty-eight subjects with early HIV infection were recruited to receive cART and followed for 48 weeks. HIV reservoirs in peripheral CD4⁺ T cells measured by cell-associated proviral DNA and viral outgrowth cultures were determined at baseline and after 48 weeks of cART. At baseline, granzyme B and gamma interferon (IFN-γ) enzyme-linked immunosorbent spot (ELISpot) assays were performed with peptides spanning the HIV proteome. All subjects had detectable HIV-specific granzyme B and IFN-γ responses at baseline. The quantity and specificity of granzyme B responses did not correlate with IFN-γ responses. For granzyme B, Tat/Rev was the most dominant whereas for IFN-γ, Gag predominated. HIV-specific granzyme B T cell responses negatively correlated with HIV proviral loads at baseline and at 48 weeks and with replication-competent viral infectious units per million (IUPM) CD4⁺ T cells at baseline but not significantly at 48 weeks. Tat/Rev-, Env-, Gag-, and Vif-specific granzyme B responses correlated most strongly with reservoir control. There was no correlation of HIV-specific IFN-γ responses with reservoir size at baseline or at 48 weeks. The majority of granzyme B responses were contributed by CD8⁺ T cells. Thus, our findings suggest that the induction of potent granzyme B-producing CTLs to Tat, Rev, Env, Gag, and Vif during early infection may be able to prevent the establishment of a large viral reservoir, thereby facilitating a reduced HIV burden.IMPORTANCE A major barrier to the cure of human immunodeficiency virus type 1 (HIV-1) infection is the establishment of a viral reservoir that must be significantly reduced or eradicated entirely to enable a cure. Combined antiretroviral therapy (cART) alone is unable to clear this viral reservoir. It has been shown that CD8⁺ cytotoxic T lymphocytes (CTLs) are important in controlling early HIV infection by reducing plasma viremia. However, it is not known if these HIV-specific CTLs influence the establishment of the viral reservoir in early HIV infection. We show that HIV-specific granzyme B responses targeting HIV Tat/Rev, Env, Gag, and Vif, but not IFN-γ responses, are associated with reduced virus reservoirs at baseline and at 48 weeks of cART. These findings shed light on the nature of the effector CTL response that might limit reservoir size with implications for cure research and HIV vaccines.

Tumor antigen-specific T cells for immune monitoring of dendritic cell-treated glioblastoma patients

BACKGROUND AIMS

CD8(+) T cells are part of the adaptive immune system and, as such, are responsible for the elimination of tumor cells. Dendritic cells (DC) are professional antigen-presenting cells (APC) that activate CD8(+) T cells. Effector CD8(+) T cells in turn mediate the active immunotherapeutic response of DC vaccination against the aggressive glioblastoma (GBM). The lack of tumor response assays complicates the assessment of treatment success in GBM patients.

METHODS

A novel assay to identify specific cytotoxicity of activated T cells by APC was evaluated. Tumor antigen-pulsed DCs from HLA-A*02-positive GBM patients were cultivated to stimulate autologous cytotoxic T lymphocytes (CTL) over a 12-day culture period. To directly correlate antigen specificity and cytotoxic capacity, intracellular interferon (IFN)-γ fluorescence flow cytometry-based measurements were combined with anti-GBM tumor peptide dextramer staining. IFN-γ response was quantified by real-time polymerase chain reaction (PCR), and selected GBM genes were compared with healthy human brain cDNA by single specific primer PCR characterization.

RESULTS

Using CTL of GBM patients stimulated with GBM lysate-pulsed DCs increased IFN-γ messenger RNA levels, and intracellular IFN-γ protein expression was positively correlated with specificity against GBM antigens. Moreover, the GBM peptide-specific CD8(+) T-cell response correlated with specific GBM gene expression. Following DC vaccination, GBM patients showed 10-fold higher tumor-specific signals compared with unvaccinated GBM patients.

DISCUSSION

These data indicate that GBM tumor peptide-dextramer staining of CTL in combination with intracellular IFN-γ staining may be a useful tool to acquire information on whether a specific tumor antigen has the potential to induce an immune response in vivo.

Extended evaluation of a phase 1/2 trial on dosing, safety, immunogenicity, and overall survival after immunizations with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine in late-stage colorectal cancer

A phase 1/2 clinical trial evaluating dosing, safety, immunogenicity, and overall survival on metastatic colorectal cancer (mCRC) patients after immunotherapy with an advanced-generation Ad5 [E1-, E2b-]-CEA(6D) vaccine was performed. We report our extended observations on long-term overall survival and further immune analyses on a subset of treated patients including assessment of cytolytic T cell responses, T regulatory (Treg) to T effector (Teff) cell ratios, flow cytometry on peripheral blood mononuclear cells (PBMCs), and determination of HLA-A2 status. An overall survival of 20 % (median survival 11 months) was observed during long-term follow-up, and no long-term adverse effects were reported. Cytolytic T cell responses increased after immunizations, and cell-mediated immune (CMI) responses were induced whether or not patients were HLA-A2 positive or Ad5 immune. PBMC samples from a small subset of patients were available for follow-up immune analyses. It was observed that the levels of carcinoembryonic antigen (CEA)-specific CMI activity decreased from their peak values during follow-up in five patients analyzed. Preliminary results revealed that activated CD4+ and CD8+ T cells were detected in a post-immunization sample exhibiting high CMI activity. Treg to Teff cell ratios were assessed, and samples from three of five patients exhibited a decrease in Treg to Teff cell ratio during the treatment protocol. Based upon the favorable safety and immunogenicity data obtained, we plan to perform an extensive immunologic and survival analysis on mCRC patients to be enrolled in a randomized/controlled clinical trial that investigates Ad5 [E1-, E2b-]-CEA(6D) as a single agent with booster immunizations.

Granzyme B secretion by human memory CD4 T cells is less strictly regulated compared to memory CD8 T cells

Background

Granzyme B (GrzB) is a serine proteinase expressed by memory T cells and NK cells. Methods to measure GrzB protein usually involve intracellular (flow cytometry) and extracellular (ELISA and ELISpot) assays. CD8 T cells are the main source of GrzB during immunological reactions, but activated CD4 T cells deploy GrzB as well. Because GrzB is an important mediator of cell death, tissue pathology and disease, clarification of differences of GrzB expression and secretion between CD4 and CD8 T cells is important for understanding effector functions of these cells.

Results

Memory CD4 and memory CD8 T cells were purified from human peripheral blood of healthy donors, and production of GrzB was directly compared between memory CD4 and memory CD8 T cells from the same donors using parallel measurements of flow cytometry (intracellular GrzB), ELISpot (single cell secretion of GrzB), and ELISA (bulk extracellular GrzB). Memory CD8 T cells constitutively stored significantly more GrzB protein (~25%) compared to memory CD4 T cells as determined by flow cytometry (~3%), and this difference remained stable after 24 hrs of activation. However, measurement of extracellular GrzB by ELISA revealed that activated memory CD4 T cells secrete similar amounts of GrzB (~1,000 pg/ml by 1x10⁵ cells/200 μl medium) compared to memory CD8 T cells (~600 pg/ml). Measurement of individual GrzB-secreting cells by ELISpot also indicated that similar numbers of activated memory CD4 (~170/1x10⁵) and memory CD8 (~200/1x10⁵) T cells secreted GrzB. Expression of CD107a further indicated that Grzb is secreted similarly by activated CD4 and CD8 T cells, consistent with the ELISA and ELISpot results. However, memory CD8 T cells expressed and secreted more perforin compared to memory CD4 T cells, suggesting that perforin may be less associated with GrzB function for memory CD4 T cells.

Conclusions

Although measurement of intracellular GrzB by flow cytometry suggests that a larger proportion of CD8 T cells have higher capacity for GrzB production compared to CD4 T cells, ELISpot and ELISA show that similar numbers of activated CD4 and CD8 T cells secrete similar amounts of GrzB. Secretion of GrzB by activated CD8 T cells may be more tightly controlled compared to CD4 T cells.

Approaches for the design and evaluation of HIV-1 DNA vaccines

Although it is not clear what arm of the immune response correlates with protection from HIV-1 infection or disease, a robust broad cellular and humoral immune response will likely be needed to control this infection. Accordingly, it is crucial to characterize which HIV-1 gene products are potential targets to elicit these responses. DNA vaccination has been shown to be effective for induction of both humoral and cellular immune responses in animal models. Most DNA vaccine strategies studied to date have been based on targeting structural HIV-1 proteins, but others have focused on the regulatory/accessory HIV-1 proteins as an approach to induce immune responses able to recognize early infected cells. It has also become clear that HIV-DNA vaccine efficacy in humans requires improvement. Combinations of HIV-1 genes, improvement of the DNA vector itself, or addition of genetic adjuvants (cytokines or costimulatory molecules) as part of the DNA vaccine itself, have been evaluated by several groups as approaches for enhancing DNA vaccine-induced immune responses. Encouraging results have been obtained in primate models, supporting that these strategies should be further evaluated in humans, for either prophylaxis or immune therapy of HIV-1.

Cytotoxic response persists in subjects treated for tuberculosis decades ago

BACKGROUND

Data exploring the potential use of effector molecules produced by cytotoxic T lymphocytes (CTLs) in the immunodiagnostics of tuberculosis (TB) are scarce. The present study focused a) to gain an insight into the discriminatory power of CTLs in patients with acute pulmonary or extra-pulmonary TB, or latent tuberculosis infection (LTBI); and b) to evaluate the influence of various anti-TB therapeutic schemes on the immunological profiles of residual CTLs.

METHODS

Immunological signatures of antigen-specific CTLs were explored in patients with active pulmonary and extra-pulmonary TB, LTBI and in those treated for TB decades ago by using ELISPOT, intracellular flow cytometry and extracellular CD107a detection.

RESULTS

No difference was seen between active TB, LTBI or any of those treated for TB in the ELISPOT analysis of antigen-specific Granzyme B (GrB), Perforin (Prf) and interferon-gamma (IFN-γ) producing lymphocytes, the FACS analysis of the intracellular expression of IFN-γ, or the surface expression of CD107a degranulation factor of both CD8+ and CD4+ antigen-specific T cell subsets. The effector memory (TEM) phenotype proved predominant in the surface marker profiling both in active TB and LTBI. The proportion of the CD107a degranulation factor proved higher in the central memory (TCM) than in the other cell subsets in all the study groups. Interestingly, functionally and phenotypically similar CTLs profiles were observed in active TB, LTBI and in all the three groups treated for TB.

CONCLUSION

The phenotypic and functional profiling of CTLs has a limited potential in the immunodiagnostics of active TB. Antigen-specific CTLs persist in patients treated for TB decades ago regardless of the efficacy of implemented and completed anti-TB therapy.

Granzyme B ELISPOT assay to measure influenza-specific cellular immunity

The immunogenicity and efficacy of influenza vaccination are markedly lower in the elderly. Granzyme B (GrzB), quantified in fresh cell lysates, has been suggested to be a marker of cytotoxic T lymphocyte (CTL) response and a predictor of influenza illness among vaccinated older individuals. We have developed an influenza-specific GrzB ELISPOT assay using cryopreserved PBMCs. This method was tested on 106 healthy older subjects (ages 50-74) at baseline (Day 0) and three additional time points post-vaccination (Day 3, Day 28, Day 75) with influenza A/H1N1-containing vaccine. No significant difference was seen in GrzB response between any of the time points, although influenza-specific GrzB response appears to be elevated at all post-vaccination time points. There was no correlation between GrzB response and hemagglutination inhibition (HAI) titers, indicating no relationship between the cytolytic activity and humoral antibody levels in this cohort. Additionally, a significant negative correlation between GrzB response and age was observed. These results reveal a reduction in influenza-specific GrzB response as one ages. In conclusion, we have developed and optimized an influenza-specific ELISPOT assay for use with frozen cells to quantify the CTL-specific serine protease GrzB, as a measure of cellular immunity after influenza vaccination.

Monitoring of pathogen-specific T-cell immune reconstitution after allogeneic hematopoietic stem cell transplantation

The clinical outcome after allogeneic hematopoietic stem cell transplantation (HSCT) has been significantly improved during the last decades with regard to the reduction in organ failure, infection, and severe acute graft-versus-host disease. However, severe complications due to infectious diseases are still one of the major causes of morbidity and mortality after allogeneic HSCT, in particular in patients receiving haploidentical HSCT or cord blood transplant due to a slow and often incomplete immune reconstitution. In order to improve the immune control of pathogens without an increased risk of alloreactivity, adoptive immunotherapy using highly enriched pathogen-specific T cells offers a promising approach. In order to identify patients who are at high risk for infectious diseases, several monitoring assays have been developed with potential for the guidance of immunosuppressive drugs and adoptive immunotherapy in clinical practice. In this article, we aim to give a comprehensive overview regarding current developments of T-cell monitoring techniques focusing on T cells against viruses and fungi. In particular, we will focus on rather simple, fast, non-labor-intensive, cellular assays which could be integrated in routine clinical screening approaches.

Resting of Cryopreserved PBMC Does Not Generally Benefit the Performance of Antigen-Specific T Cell ELISPOT Assays

T cell monitoring is increasingly performed using cryopreserved PBMC. It has been suggested that resting of PBMC after thawing, that is, culturing them overnight in test medium, produces higher antigen-induced spot counts in ELISPOT assays. To evaluate the importance of overnight resting, we systematically tested cryopreserved PBMC from 25 healthy donors. CEF peptides (comprising CMV, EBV and flu antigens) were used to stimulate CD8 cells and mumps antigen to stimulate CD4 cells. The data show that resting significantly increased antigen-elicited T cell responses only for CEF high responder PBMC. The maximal gain observed was doubling of spot counts. For CEF low responders, and for mumps responders of either low- or high reactivity levels, resting had no statistically significant effect on the observed spot counts. Therefore, resting is not a generally applicable approach to improve ELISPOT assay performance, but can be recommended only for clinical subject cohorts and antigens for which it has a proven benefit. Because resting invariably leads to losing about half of the PBMC available for testing, and because doubling the PBMC numbers plated into the assay reliably doubles the antigen-induced spot counts, we suggest the latter approach as a simple and reliable alternative to resting for enhancing the performance of ELISPOT assays. Our data imply that resting is not required if PBMC were cryopreserved and thawed under conditions that minimize apoptosis of the cells. Therefore, this study should draw attention to the need to optimize freezing and thawing conditions for successful T cell work.

ELISPOT Assay for Monitoring Cytotoxic T Lymphocytes (CTL) Activity in Cancer Vaccine Clinical Trials

The profiling and monitoring of immune responses are key elements in the evaluation of the efficacy and development of new biotherapies, and a number of assays have been introduced for analyzing various immune parameters before, during, and after immunotherapy. The choice of immune assays for a given clinical trial depends on the known or suggested immunomodulating mechanisms associated with the tested therapeutic modality. Cell-mediated cytotoxicity represents a key mechanism in the immune response to various pathogens and tumors. Therefore, the selection of monitoring methods for the appropriate assessment of cell-mediated cytotoxicity is thought to be crucial. Assays that can detect both cytotoxic T lymphocytes (CTL) frequency and function, such as the IFN-γ enzyme-linked immunospot assay (ELISPOT) have gained increasing popularity for monitoring clinical trials and in basic research. Results from various clinical trials, including peptide and whole tumor cell vaccination and cytokine treatment, have shown the suitability of the IFN-γ ELISPOT assay for monitoring T cell responses. However, the Granzyme B ELISPOT assay and Perforin ELISPOT assay may represent a more direct analysis of cell-mediated cytotoxicity as compared to the IFN-γ ELISPOT, since Granzyme B and perforin are the key mediators of target cell death via the granule-mediated pathway. In this review we analyze our own data and the data reported by others with regard to the application of various modifications of ELISPOT assays for monitoring CTL activity in clinical vaccine trials.

Immunological monitoring of the tumor immunoenvironment for clinical trials

Monitoring of immunotherapeutic clinical trials has undergone a considerable change in the last decade resulting in a general agreement that immune monitoring should guide the development of cancer vaccines. The emphasis on immune cell functions and quantitation of antigen-specific T cells have been playing a major role in the attempts to establish meaningful correlations between therapy-induced alterations in immune responses and clinical endpoints. However, one significant unresolved issue in modern immunotherapy is that when a tumor-specific cellular immune response is observed following the course of immunotherapy, it does not always lead to clinically proven cancer regression. This disappointing lack of a correlation between the tumor-specific cytotoxic immune responses and the clinical efficacy of immunotherapy may be explained, among other reasons, by the notion that the analysis of any single immunological parameter is not sufficient to provide clinically feasible information about the complex interactions between different cell subsets in the peripheral blood and immune, tumor, and stromal cells in the tumor milieu. By contrast, a systemic approach is required for improving the quality of a serial monitoring to ensure that it adequately and reliably measures potential changes induced in patients by administered vaccines or immunomodulators. Comprehensive evaluation of the balance between the immunostimulatory and immunosuppressive compartments of the immune system could be critical for a better understanding of how a given immunotherapy works or does not work in a particular clinical trial. New approaches to characterize tumor-infiltrating leukocytes, their phenotypic, biochemical, and genetic characteristics within the tumor microenvironment need to be developed and validated and should complement current monitoring techniques. These immune-monitoring assays for the local tumor immunoenvironment should be developed, validated, and standardized for reliability and consistency in order to establish the overall performance standards.

Unique strengths of ELISPOT for T cell diagnostics

The T cell system plays an essential role in infections, allergic reactions, tumor and transplant rejection, as well as autoimmune diseases. It does so by the selective engagement of different antigen-specific effector cell lineages that differentially secrete cytokines and other effector molecules. These T cell subsets may or may not have cytolytic activity, can preferentially migrate to different tissues, and display variable capabilities to expand clonally. The quest of T cell immune diagnostics is to understand which specific effector function and T cell lineage is associated with a given clinical outcome, be it positive or adverse. No single assay can measure all of the relevant parameters. In this chapter, we review the unique contributions that ELISPOT assays can make toward understanding T cell-mediated immunity. ELISPOT assays have an unsurpassed sensitivity in detecting low frequency antigen-specific T cells that secrete effector molecules, including granzyme and perforin. They provide robust, highly reproducible data - even by first time users. Because ELISPOT assays require roughly tenfold less cell material than flow cytometry, ELISPOT is ideally suited for all measurements requiring parallel testing under multiple conditions. These include defining (a) T cell reactivity to individual peptides of extensive libraries, thereby establishing the fine-specificity of the response, and determinant mapping; (b) reactivity to different concentrations of the antigen in serial dilutions to measure the avidity of the T cell response; or (c) different secretory products released by T cells which define their respective effector lineage/functions. Further, because T cells survive ELISPOT assays unaffected, they can be retested for the acquisition of additional information in follow-up assays. These strengths of ELISPOT assays the weaknesses of flow cytometry-based measurements. Thus, the two assays systems compliment each other in the quest to understand T cell-mediated immunity in vivo.

Recommendations from the iSBTc-SITC/FDA/NCI Workshop on Immunotherapy Biomarkers

PURPOSE

To facilitate development of innovative immunotherapy approaches, especially for treatment concepts exploiting the potential benefits of personalized therapy, there is a need to develop and validate tools to identify patients who can benefit from immunotherapy. Despite substantial effort, we do not yet know which parameters of antitumor immunity to measure and which assays are optimal for those measurements.

EXPERIMENTAL DESIGN

The iSBTc-SITC (International Society for Biological Therapy of Cancer-Society for Immunotherapy of Cancer), FDA (Food and Drug Administration), and NCI (National Cancer Institute) partnered to address these issues for immunotherapy of cancer. Here, we review the major challenges, give examples of approaches and solutions, and present our recommendations.

RESULTS AND CONCLUSIONS

Although specific immune parameters and assays are not yet validated, we recommend following standardized (accurate, precise, and reproducible) protocols and use of functional assays for the primary immunologic readouts of a trial; consideration of central laboratories for immune monitoring of large, multi-institutional trials; and standardized testing of several phenotypic and functional potential potency assays specific to any cellular product. When reporting results, the full QA (quality assessment)/QC (quality control) should be conducted and selected examples of truly representative raw data and assay performance characteristics should be included. Finally, to promote broader analysis of multiple aspects of immunity, and gather data on variability, we recommend that in addition to cells and serum, RNA and DNA samples be banked (under standardized conditions) for later testing. We also recommend that sufficient blood be drawn to allow for planned testing of the primary hypothesis being addressed in the trial, and that additional baseline and posttreatment blood is banked for testing novel hypotheses (or generating new hypotheses) that arise in the field.

Contemporary diagnostic methods for hemophagocytic lymphohistiocytic disorders

Hemophagocytic lymphohistiocytosis is a life-threatening multi-system hyperinflammatory disorder characterized by dysfunctional cytolytic lymphocyte responses, hypercytokinemia, and widespread lymphohistiocytic tissue infiltration and destruction. Diagnosis and definitive therapy are often delayed as clinical efforts are directed toward treatment of presumed overwhelming infection. Sporadic cases occur in association with underlying immune dysfunction related to autoimmune disease, malignancy, or severe infection. However, familial cases predominate with remarkable associations between underlying genetic defects and dysregulation of immune responses. Here, we review the genetic and immunologic basis of contemporary diagnostic methods for hemophagocytic lymphohistiocytosis.

New flow cytometric assays for monitoring cell-mediated cytotoxicity

The exact immunologic responses after vaccination that result in effective antitumor immunity have not yet been fully elucidated and the data from ex vivo T-cell assays have not yet defined adequate surrogate markers for clinical efficacy. A more detailed knowledge of the specific immune responses that correlate with positive clinical outcomes should help to develop better or novel strategies to effectively activate the immune system against tumors. Furthermore, clinically relevant material is often limited and, thus, precludes the ability to perform multiple assays. The two main assays currently used to monitor lymphocyte-mediated cytoxicity in cancer patients are the (51)Cr-release assay and IFN-gamma ELISpot assay. The former has a number of disadvantages, including low sensitivity, poor labeling and high spontaneous release of isotope from some tumor target cells. Additional problems with the (51)Cr-release assay include difficulty in obtaining autologous tumor targets, and biohazard and disposal problems for the isotope. The ELISpot assays do not directly measure cytotoxic activity and are, therefore, a surrogate marker of cyotoxic capacity of effector T cells. Furthermore, they do not assess cytotoxicity mediated by the production of the TNF family of death ligands by the cytotoxic cells. Therefore, assays that allow for the simultaneous measurement of several parameters may be more advantageous for clinical monitoring. In this respect, multifactor flow cytometry-based assays are a valid addition to the currently available immunologic monitoring assays. Use of these assays will enable detection and enumeration of tumor-specific cytotoxic T lymphocytes and their specific effector functions and any correlations with clinical responses. Comprehensive, multifactor analysis of effector cell responses after vaccination may help to detect factors that determine the success or failure of a vaccine and its immunological potency.

Autocrine, not paracrine, interferon-gamma gene delivery enhances ex vivo antigen-specific cytotoxic T lymphocyte stimulation and killing

The adoptive transfer of antigen-specific cytotoxic T lymphocytes (CTL) shows promise in the treatment of cancer and infectious diseases. We utilize adeno-associated virus-(AAV-) based antigen gene-loaded dendritic cells (DCs) to stimulate such antigen-specific CTL. Yet further improvements in CTL stimulation and killing may result by gene delivery of various Th1-response interferons/cytokines, such as interferon gamma (IFN-gamma), as the delivered gene can continuously produce that interferon. However which immune cell type should optimally express IFN-gamma is unclear as the phenotypes of both DC and T cells are enhanced by it. Here, we used AAV to compare and contrast IFN-gamma gene delivery into DC or T cells, and versus the addition of exogenous IFN-gamma, for stimulating carcinoembryonic antigen-(CEA-) specific CTL. It was found that AAV/IFN-gamma delivery into T cells (autocrine) resulted in T cell populations with the highest CD8(+)/CD4(+) ratio, highest IFN-gamma(+)/IL-4(+) ratio, highest CD69(+),CD8(+) levels, and lowest CD4(+)/CD25(+) levels, all consistent with the strongest Th1 response. Most importantly, AAV/IFN-gamma transduction of T cells resulted in antigen-specific T cell populations with the highest killing capabilities, 49% above other treatments. These data strongly suggest that AAV/IFN-gamma autocrine gene delivery into T cells is worthy of further study towards maximizing the generation of antigen-specific anticancer CTL killers.

In vitro detection of cytotoxic T and NK cells in peripheral blood of patients with various drug-induced skin diseases

BACKGROUND

Cytotoxic cells are involved in most forms of drug-induced skin diseases. Till now, no in vitro test addressed this aspect of drug-allergic responses. Our report evaluates whether drug-induced cytotoxic cells can be detected in peripheral blood of nonacute patients with different forms of drug hypersensitivity, and also whether in vitro detection of these cells could be helpful in drug-allergy diagnosis.

METHODS

GranzymeB enzyme-linked immunosorbent spot-forming (ELISPOT) and cell surface expression of the degranulation marker CD107a were evaluated on peripheral blood mononuclear cells from 12 drug-allergic patients in remission state and 16 drug-exposed healthy controls.

RESULTS

In 10/12 allergic patients culprit but not irrelevant drug elicited granzymeB release after 48-72 h stimulation. It was clearly positive in patients with high proliferative response to the drug, measured in lymphocyte transformation tests. In patients, who showed moderate or low proliferation and low drug-response in granzymeB ELISPOT, overnight preincubation with interleukin (IL)-7/IL-15 enhanced drug-specific granzymeB release and allowed to clearly identify the offending agent. CD107a staining was positive on CD4+/CD3+, CD8+/CD3+ T cells as well as CD56+/CD3- natural killer cells. None of the drug-exposed healthy donors reacted to the tested drugs and allergic patients reacted only to the offending, but not to tolerated drugs.

CONCLUSION

GranzymeB ELISPOT is a highly specific in vitro method to detect drug-reacting cytotoxic cells in peripheral blood of drug-allergic patients even several years after disease manifestation. Together with IL-7/IL-15 preincubation, it may be helpful in indentifying the offending drug even in some patients with weak proliferative drug-response.

Evaluation of humoral and cellular immune responses against HSV-1 using genetic immunization by filamentous phage particles: a comparative approach to conventional DNA vaccine

Phage display is based on expressing peptides as a fusion to one of the phage coat proteins. To date, many vaccine researches have been conducted to display immunogenic peptides or mimotopes of various pathogens and tumors on the surface of filamentous bacteriophages. In recent years as a new approach to application of phages, recombinant bacteriophage lambda particles were used as DNA delivery vehicles to mammalian cells. In this study, recombinant filamentous phage whole particles were used for vaccination of mice. BALB/c mice were inoculated with filamentous phage particles containing expression cassette of Herpes simplex virus 1 (HSV-1) glycoprotein D that has essential roles in the virus attachment and entry. Both humoral and cellular immune responses were measured in the immunized mice and compared to conventional DNA vaccination. A dose-response relationship was observed in both arms of immune responses induced by recombinant filamentous phage inoculation. The results were similar to those from DNA vaccination. Filamentous phages can be considered as suitable alternative candidate vaccines because of easier and more cost-effective production and purification over plasmid DNA or bacteriophage lambda particles.

Methods for quantitating antigen-specific T cell responses using functional assays in rhesus macaques

Ex vivo enumeration of the absolute frequencies of antigen-specific T cells is key for evaluating the immunogenicity of T cell-based vaccines. Currently there are three methods that are widely used to quantify cellular immune responses: Enzyme-Linked Immuno Spot assay (ELISpot), Intracellular Cytokine Staining assay (ICS) and Tetramer assay. These three different assays offer different information. In this chapter, I discuss the two functional assays, ELISpot and ICS. The ELISpot and ICS assays use short term in vitro stimulation to assay the frequency and cytokine expression profiles of responding cells. The ELISpot assay scores spots of captured cytokine produced by individual cells whereas, ICS uses flow cytometry to profile individual cells for surface markers and the production of cytokines.

Chemotherapy targeted to cancer tissue potentiates antigen-specific immune response induced by vaccine for in vivo antigen loading and activation of dendritic cells

Our laboratory has created an Ad-sig-TAA/ecdCD40L vaccine platform designed to activate dendritic cells (DCs). Two subcutaneous (s.c.) injections of the TAA/ecdCD40L protein following the s.c. injection of the Ad-sig-TAA/ecdCD40L vector (TAA/ecdCD40L VPP vaccine) further increases the levels of the tumor-associated antigen (TAA)-specific CD8 effector T cells induced by the vector. We tested the combined effect of chemotherapy-induced destruction of tumor cells and TAA/ecdCD40L VPP vaccine which further increases the levels of TAA available to the DCs at the time of vaccination. The chemotherapy was delivered selectively to the tumor cells using intratumoral (i.t.) injection of the AdCDIRESE1A vector followed by intraperitoneal (i.p.) 5-fluorocytosine (5FC). The 5-fluorouracil (5FU) produced in the vector infected the tumor cells, destroys them and releases the TAA for processing and presentation by the DCs. This mode of delivery spares the TAA CD8 effector T cells from the destructive effect of the 5FU when their proliferation is induced by the vaccine. Test mice treated with both the s.c. administered TAA/ecdCD40L VPP vaccine and the AdCDIRESE1A/5FC chemosensitization vector had the smallest tumor volumes and survived longer than mice treated with either of these agents alone (P < 0.001).

Pre- and post-transplant monitoring of granzyme B enzyme-linked immunosorbent spot assay in pediatric liver recipients

This study aims to investigate potential role of granzyme B enzyme-linked immunosorbent spot (GrB ELISPOT) for immunological monitoring in pediatric liver transplantation.

PATIENTS AND METHODS

Peripheral blood mononuclear cells from 28 pediatric recipients were serially tested for GrB-producing donor-reactive cells at day 0 pre-transplantation (baseline) and days 7, 14, and 28 post-transplantation.

RESULTS

At baseline, no difference of GrB value was found in acute rejection (14/28) compared to normal graft function patients (day 0: 4(3.9) spots versus 5(2.9) spots, respectively: p=0.65). At day 7 post-transplantation, acute rejection patients showed frequencies of GrB ELISPOT higher than those with normal graft function, but the differences observed were not statistically significant (day 7: 15(4.9) spots versus 10(4.0) spots, respectively: p=0.55). GrB increased significantly at day 7 from baseline in the rejection group (15(4.9) spots versus 4(3.9), respectively p=0.04), whereas corresponding changes were not significant in the group without rejection (10(4.0) versus 5(2.9), respectively: p=0.15).

CONCLUSION

GrB ELISPOT pre-transplantation could not predict the occurrence of early post-transplant acute rejection; similarly frequencies at days 7, 14 and 28 could not be correlated with acute rejection in pediatric liver recipients. However, a kinetic study of GrB ELISPOT could be helpful to predict or confirm early rejection in the small group of liver allograft recipients analyzed in this study.

Measuring cell death mediated by cytotoxic lymphocytes or their granule effector molecules

Cytotoxic lymphocytes (CL) are highly motile cells that utilize granule exocytosis to kill virus-infected or transformed targets. Isolated CL and purified granule proteins have been used to investigate the molecular processes that CL use to kill their targets and to investigate the basis of human disease. We have set out various methods that are routinely used to isolate CL and characterize the cell death pathways they induce. As cell death mediated through TNF-superfamily members and their respective receptors is covered elsewhere, this manuscript will deal specifically with cytotoxic granule-mediated cell death.

Characterization of a single peptide derived from cytochrome P450 1B1 that elicits spontaneous human leukocyte antigen (HLA)-A1 as well as HLA-B35 restricted CD8 T-cell responses in cancer patients

Cytochrome P450 1B1 (CYP1B1) is widely expressed in human malignancies, but silent in most normal tissues. Importantly, the protein is believed to play an important role in the survival and growth of cancer cells in a stressed environment, e.g., as a result of hypoxia or chemotherapy. Thus, targeting of CYP1B1 represents a potentially successful strategy in the treatment of metastatic cancer, e.g., by therapeutic vaccination. Herein, we describe the characterization of a novel peptide from the CYP1B1 protein (CYP240), which is spontaneously recognized by CD8 T cells in cancer patients. Interestingly, the peptide binds to both human leukocyte antigen (HLA)-A1 and HLA-B35. Hence, peripheral blood lymphocytes from a total of 49 cancer patients (25 melanoma, 13 RCC, and 11 breast cancer; 41 HLA-A1 positive, 8 HLA-B35 positive) were analyzed for reactivity taking advantage of the EliSpot assay. Rare but strong responses were detected in HLA-A1-positive patients, and more frequent responses were detected in HLA-B35-positive patients. No reactivity against the peptide could be detected in healthy donors. Furthermore, we demonstrated that peptide-specific T cells were able to lyze target cells presenting the peptide on the surface. The characterized CYP240 peptide presented herein opens the avenue for more broader recruitment of patients in vaccination trials targeting CYB1B1.

Dissociated production of perforin, granzyme B, and IFN-gamma by HIV-specific CD8(+) cells in HIV infection

CD8(+) T cells play a crucial role in the control of viral infections such as HIV. The functional characterization of HIV-specific CD8(+) T cells has so far been largely restricted to studies of IFN-gamma. The TCR-triggered release of the effector molecules perforin (PFN) and granzyme B (GzB), however, is thought to be a central pathway for the destruction of virus-infected target cells by CD8(+) effector T cells. Here we would like to address two major findings. On the one hand we propose that ex vivo measurements of PFN and GzB secretion via ELISPOT may permit the distinction between in vivo resting versus activated CD8(+) memory T cells in healthy and HIV-infected individuals. Therefore, extending the present standard of IFN-gamma measurements to the analysis of PFN and GzB release in functional T cell assays will provide new insights into CD8(+) effector T cell functions. It should enable the evaluation of therapeutic vaccination efficacy by its ability to reactivate and convert IFN-gamma-positive, but GzB- and PFN-negative memory CD8(+) T cells into PFN/GzB-secreting effector cells. On the other hand, we report on a frequent ex vivo dissociation of the HIV peptide-induced secretion of PFN and GzB in chronic HIV infection underlining CD8(+) effector T cell diversity in this disease--an aspect that also has to be accounted for in immune monitoring approaches.

New approaches for monitoring CTL activity in clinical trials

We have developed a modification of the ELISPOT assay that measures Granzyme B (GrB) release from cytotoxic T lymphocytes (CTLs). The GrB ELISPOT assay is a superior alternative to the 51Cr-release assay since it is significantly more sensitive and provides an estimation of cytotoxic effector cell frequency. Additionally, unlike the IFN-gamma ELISPOT assay, the GrB ELISPOT directly measures the release of a cytolytic protein. We report that the GrB ELISPOT can be utilized to measure ex vivo antigen-specific cytotoxicity of peripheral blood mononuclear cells (PBMCs) from cancer patients vaccinated with a peptide-based cancer vaccine. We compare the reactivity of patients' PBMCs in the GrB ELISPOT, with reactivity in the tetramer, IFN-gamma ELISPOT and chromium (51Cr)-release assays. Differences in immune response over all assays tested were found between patients, and four response patterns were observed. Reactivity in the GrB ELISPOT was more closely associated with cytotoxicity in the 51Cr-release assay than the tetramer or IFN-gamma ELISPOT assays. We also optimized the GrB ELISPOT assay to directly measure immune responses against autologous primary tumor cells in vaccinated cancer patients. A perforin ELISPOT assay was also adapted to evaluate peptide-stimulated reactivity of PMBCs from vaccinated melanoma patients. Modifications of the ELISPOT assay described in this chapter allow a more comprehensive evaluation of low-frequency tumor-specific CTLs and their specific effector functions and can provide a valuable insight into immune responses in cancer vaccine trials.

Granzyme B production distinguishes recently activated CD8(+) memory cells from resting memory cells

For immune diagnostic purposes it would be critical to be able to distinguish between ongoing immune processes, such as active infections, and long-term immune memory, for example imprinted by infections that have been cleared a long time ago or by vaccinations. We tested the hypothesis that the secretion of granzyme B, as detected in ex vivo ELISPOT assays, permits this distinction. We studied EBV-, flu- and CMV-specific CD8(+) cells in healthy individuals, Vaccinia virus-reactive CD8(+) cells in the course of vaccination, and HIV-specific CD8(+) cells in HIV-infected individuals. Antigen-specific ex vivo GzB production was detected only transiently after Vaccinia immunization, and in HIV-infected individuals. Our data suggest that ex vivo ELISPOT measurements of granzyme B permit the identification of actively ongoing CD8(+) cell responses-a notion that is pertinent to the immune diagnostic of infections, transplantation, allergies, autoimmune diseases, tumors and vaccine development.

Identification and characterization of equine granzyme B

In the present study we describe the isolation and characterization of putative equine granzyme B for which we propose the designation 'eqGrzmB'. Sequence analysis revealed characteristic features of a GrzmB protease such as the presence of a signal (leader-) peptide and an activation di-peptide. The isolated eqGrzmB is functionally active when expressed in human or in insect cells. Furthermore, exchange of any of three putative active site amino acids, which are highly conserved along granzyme B enzymes, led to a complete loss of enzymatic activity in the newly identified eqGrzmB. Phylogenetic analysis places eqGrzmB in the chymase-locus within the large family of granzymes in close proximity to putative equine mast cell protease and to granzyme B from mouse, rat, and human. eqGrzmB proteolytic activity has been kinetically characterized and can be specifically inhibited by granzyme B inhibitors. Taken together, we conclude that we have isolated a new member of the granzyme B family, the first granzyme identified in Equidae. The description of equine granzyme B might facilitate the development of immunological assays for the activity of equine lymphocytes.

Blood donor derived dendritic cells and cytotoxic T cells for specific fusion-gene adoptive immunotherapy

BACKGROUND AND OBJECTIVES

Therapeutic immunological reagents tailored to individual patients have been shown to be a viable treatment strategy for some forms of leukaemia. This work investigates the possibility of using blood donations as a source of leukaemia-specific immune therapeutics.

MATERIALS AND METHODS

The acute promyelocytic cell line NB4 carrying the PML-RAR alpha fusion was used as a target for cytotoxic T lymphocytes (CTL) stimulated to recognize the fusion. Stimulation of CTL was by production of dendritic cells pulsed with plasmid vectors containing polymerase chain reaction (PCR)-generated sequences of PML-RAR alpha derived from NB4 cells. PCR primer design included a Kozak consensus sequence to allow correct translation of the nucleic acid into protein. Identification of specific cytotoxicity was by both Granzyme B ELISPOT and by (51)Cr-release assays.

RESULTS

Specific CTL activity targeting NB4 cells can be generated from donor-derived peripheral blood mononuclear cells. However, individual donors appear to respond differently to the length of stimulatory sequence encoded in the vector. Use of an internal methionine in the PML gene, which also satisfies the Kozak rules, allows translation in vitro and, thus, might provide a suitable start site for stimulation using acute promyelocytic leukaemia-specific sequence.

CONCLUSION

The work presented here suggests that blood donor derived dendritic cells can be used to stimulate leukaemia-specific CTL from the same donation ex vivo. This would enable the generation of patient-specific therapeutics from major histocompatibility (MHC)-matched allogeneic donors. However, different MHC-matched donors might vary in their response depending on the length of the antigenic sequence.

Tumor Antigen–Specific T-Cell Expansion Is Greatly Facilitated by In vivo Priming

PURPOSE

Adoptive T-cell therapy is a promising strategy for the treatment of patients with established tumors but is often limited to specific cancers where tumor-infiltrating lymphocytes, the source of T cells for ex vivo culture, can be obtained. In this study, we evaluated the feasibility of expanding HER-2/neu-specific T cells derived from peripheral blood ex vivo following in vivo priming with a HER-2/neu peptide vaccine.

EXPERIMENTAL DESIGN

Peripheral blood mononuclear cells from cytomegalovirus (CMV)-seronegative and CMV-seropositive donors as well as HER-2/neu-positive cancer patients who had or had not been vaccinated with a HER-2/neu peptide-based vaccine was used as a source of T lymphocytes. Antigen-specific T-cell lines were generated by in vitro stimulation with antigen followed by nonspecific expansion on CD3/CD28 beads. The ability to expand antigen-specific T cells was assessed using IFN-gamma and granzyme B enzyme-linked immunosorbent spot. The phenotype of the resultant T-cell lines was evaluated by flow cytometry, including the presence of FOXP3-expressing CD4(+) T cells.

RESULTS

The frequencies of CMV-specific T cells generated from CMV(+) donors were >11-fold higher than the frequencies from CMV(-) donors (P = 0.001), with 22-fold increase of total number of CD3(+) T cells. The frequencies of HER-2/neu-specific T cells generated from the primed patients were >25-fold higher than the frequencies from unvaccinated patients (P = 0.006), with an average of a 19-fold increase of total number of CD3(+) T cells. Using peripheral blood as the source of T cells did not result in concurrent expansion of FOXP3(+)CD4(+) regulatory T cells despite the use of interleukin-2 in in vitro culture. Both CD4(+) and CD8(+) HER-2/neu-specific T cells could be expanded. The extent of ex vivo expansion correlated with the magnitude of immunity achieved during immunization (P = 0.008).

CONCLUSION

Tumor-specific T cells can be efficiently expanded from the peripheral blood ex vivo following in vivo priming with a vaccine. This approach provides an effective method to generate tumor-specific polyclonal T cells for therapeutic use that could be applied to cancer patients with any tumor type.

An altered peptide ligand for naïve cytotoxic T lymphocyte epitope of TRP-2(180-188) enhanced immunogenicity

Tyrosinase-related protein-2 (TRP-2) is a non-mutated melanocyte differentiation antigen. The TRP-2-recognizing CD8(+) T cells can evoke immune responses to melanoma in both humans and mice. Developing epitopes with amino acid replacements in their sequences might improve the low immunogenicity against this 'self' tumor antigen. We designed altered peptide ligands (APLs) of TRP-2((180-188)) (SVYDFFVWL) with preferred primary and auxiliary HLA-A*0201 molecule anchor residue replacement. These APLs were screened for MHC-affinity by affinity prediction plots and molecular dynamics simulation, and analyzed in vitro for stability and binding-affinity to molecular HLA-A*0201. We also investigated the CTLs activities induced by TRP-2 wild-type epitope and the APLs both in vitro in human PBMCs and HLA-A2.1/K(b) transgenic mice. The results indicate that TRP-2 2M analog simultaneously had stronger binding-affinity and a lower dissociation rate to HLA-A*0201, than wild-type peptide. In addition, the analog 2M was superior to other APLs and wild-type epitope in terms of immunological efficacy ex vivo as measured by the ELISPOT assays of IFN-gamma and granzyme B. These results demonstrate that TRP-2 2M is an agonist epitope that can induce anti-tumor immunity superior to its wild-type epitope, and has potential application in peptide-mediated immunotherapy.

Bacillus Calmette Guerin vaccination of human newborns induces a specific, functional CD8+ T cell response

Mounting evidence points to CD8+ T cells playing an important role in protective immunity against Mycobacterium tuberculosis. The only available vaccine against tuberculosis, bacillus Calmette Guérin (BCG), has traditionally been viewed not to induce these cells optimally. In this study, we show that vaccination of human newborns with BCG does indeed induce a specific CD8+ T cell response. These cells degranulated or secreted IFN-gamma, but not both, when infant blood was incubated with BCG. This stimulation also resulted in proliferation and up-regulation of cytotoxic molecules. Overall, the specific CD8+ T cell response was quantitatively smaller than the BCG-induced CD4+ T cell response. Incubation of whole blood with M. tuberculosis also caused CD8+ T cell IFN-gamma expression. We conclude that BCG induces a robust CD8+ T cell response, which may contribute to vaccination-induced protection against tuberculosis.

Cell-mediated immune responses in humans after immunization with one or two doses of oral live attenuated typhoid vaccine CVD 909

CVD 909 is a novel live attenuated S. Typhi oral vaccine candidate derived from strain CVD 908-htrA which constitutively expresses Vi. Herein we investigated whether the genetic manipulations involved in modifying CVD 908-htrA altered its ability to induce potent T-cell immune responses (CMI) after a single dose (five subjects) and, in a separate trial, whether a second dose (eight subjects) further enhanced its immunogenicity. In these clinical trials we observed that CVD 909 immunization elicits a wide array of CMI, including cytotoxic T cells (CTL), IFN-gamma, TNF-alpha and IL-10 (but not IL-2, IL-4 or IL-5) production, and proliferation to S. Typhi antigens. However, the administration of a second dose did not result in increases in CMI. These results suggest that the genetic manipulations to constitutively express Vi did not adversely affect the ability of CVD 909 to elicit a wide array of CMI responses. These observations add impetus for the continuing evaluation of CVD 909 as a typhoid vaccine candidate.

A novel flow cytometric assay focusing on perforin release mechanisms of cytotoxic T lymphocytes

CD8(hi+) cytotoxic T lymphocytes (CTL) are major players in immune defense. In addition, they contribute to the maintenance of immune homeostasis. We now describe a hitherto unavailable, but simple assay to determine ex vivo lytic granule-based cytotoxic functions of human CD8(hi+) CTL subgroups in a clinical setting, under target cell free conditions. Ficoll-isolated peripheral blood lymphocytes from 17 healthy volunteers were stimulated either by phorbol 12-myristate 13-acetate (PMA) in combination with ionomycin or by antibody mediated crosslinking of the CD3 molecule on the T cell surface. Using perforin as a marker for lytic granules, the reduction of CTL granules over time intervals up to 120 min was quantified by FACScan flow cytometry. The kinetics of perforin reduction were compared to the kinetics of NA-CBZ-L-lysine-thiobenzyl ester hydrochloride (BLT)-esterase release and of CD63 upregulation. The reduction in the perforin(+) portion of CD8(hi+) CTLs was correlated inversely with BLT-esterase release and CD63 upregulation. At 30 and 120 min after PMA/ionomycin stimulation, 55 +/- 14% and 42 +/- 14%, respectively, of CD8(hi+) CTLs still stained perforin(+) (time point 0 min = 100%). Perforin-granule release induced by CD3-crosslinking occurred as fast within 30 min (55 +/- 17%), but over the 120 min time interval it was not as complete when compared to PMA/ionomycin-stimulated perforin-reduction. Thus, the combination of an established degranulation assay with the power of immuno flow cytometry allows one to investigate the cytotoxic capability of CTL-subtypes and the kinetics of perforin-granule release. In addition, the assay may prove useful in the elucidation of intracellular signaling cascades governing the perforin-granule release process.

Oral spray immunization may be an alternative to intranasal vaccine delivery to induce systemic antibodies but not nasal mucosal or cellular immunity

Sixty-five healthy adult volunteers were immunized four times at 1-week intervals with an inactivated whole-virus influenza vaccine based on the strain A/New Caledonia/20/99 (H1N1) without adjuvant. The vaccine was administered as nasal spray with a newly developed device to secure intranasal delivery (OptiMist, OptiNose AS, Oslo, Norway), as regular nasal spray, nasal drops or as an oral spray. Significant IgA-antibody responses in nasal secretions were induced in volunteers immunized intranasally but not after oral spray immunization. In saliva, IgA antibodies were only marginally amplified even after oral spray immunizations. At least 73% of the volunteers belonging to any group of vaccine delivery reached serum haemagglutination inhibition titres of 40 or higher, considered protective against influenza, after only two vaccine doses. Those who had the vaccine delivered intranasally also showed evidence from in vitro secretion of granzyme B that cytotoxic T cells had been stimulated. Although immunization with the breath-actuated OptiMist device and nasal drops were superior with respect to both mucosal and systemic immune responses, oral spray immunization might still be considered for studies of mucosal adjuvants that are not yet acceptable for intranasal use.

Interferon-gamma decreases replication of primary R5 HIV-1 isolates in thymocytes

As interferon-gamma (IFN-gamma) is produced at lower levels by neonatal than adult T cells, we determined whether IFN-gamma influences HIV-1 replication in thymocytes. IFN-gamma significantly decreased replication of R5 but not X4 viruses, and reduced depletion of CD3(hi)CD27 (mature) thymocytes, the preferential targets for R5 HIV-1. Thus infection and depletion of functionally mature thymocytes that can produce endogenous IFN-gamma may mutually contribute to HIV-1 replication in the thymus and to reduced T-cell output.

Evaluating antigen-specific cytotoxic T lymphocyte responses by a novel mouse granzyme B ELISPOT assay

We have established novel ELISA- and ELISPOT-based assays specific for the detection of a potent cytotoxic mediator, granzyme B (GrB), for the assessment of antigen-specific cytotoxic T lymphocyte responses in mice. The sensitivity and specificity of our assays was demonstrated by ELISA using purified mouse GrB and supernatants and cell lysates of cytotoxic lymphocytes derived from GrB-deficient mice. No reactivity was observed by the GrB ELISA in GrB-deficient cells. The mouse GrB ELISPOT was successfully employed to detect antigen-specific effector cell responses of two CTL clones, producing GrB ELISPOT results that correlated strongly with target cell lysis, as assessed by 51Cr-release. Furthermore, we were able to demonstrate direct correlations between GrB ELISPOT and killing by LCMV gp33-specific effector and memory T cells generated in vivo. Thus, the mouse GrB ELISPOT may be used to detect cytotoxic responses, at the single-cell level, for the functional assessment of antigen-specific CD8+ T cell responses in mouse models of infection.

Recipient-Specific Tolerance after HLA-Mismatched Umbilical Cord Blood Stem Cell Transplantation

BACKGROUND

Lower incidence and severity of acute graft versus host disease (GVHD) has been observed in leukemia patients receiving HLA-mismatched umbilical cord (UCB) transplants. However, despite the increased use of UCB in stem cell transplantation, the mechanisms underlying these favorable outcomes are not well delineated.

METHODS

We analyzed antigen specific lymphocyte responses after transplant to determine whether the decreased allogeneic responsiveness of UCB lymphocytes is attributable to pan-unresponsiveness, lymphocyte repressive or recipient-specific tolerance.

RESULTS

Circulating lymphocytes collected early (3 months) after UCB transplant demonstrate a less naïve phenotype compared with that in the infused graft. Additionally, after transplant, circulating peripheral blood UCB-derived lymphocytes produced normal levels of interferon-gamma and proliferated normally when stimulated with mitogen or third party alloantigen. In contrast, when stimulated with recipient antigen, circulating lymphocytes emerging posttransplant did not proliferate nor produce interferon-gamma. Moreover, analysis of interleukin-4 production revealed a Th2 response to recipient antigens. These data indicate early induction of immune tolerance of naïve UCB graft lymphocytes with skewing of transplant recipient-specific immune response towards Th2 cytokine profile.

CONCLUSIONS

UCB graft lymphocyte immune naivety and observed early tolerance induction may contribute to the observed favorable GVHD incidence, despite infusion of HLA mismatch grafts in the unrelated allogeneic setting.

Abnormal Natural Killer Cell Function in Systemic Sclerosis: Altered Cytokine Production and Defective Killing Activity

Natural killer (NK) cells are innate immune effectors that produce various immunoregulatory cytokines. Recent studies have shown that NK cells are involved in the initiation of autoimmunity. In this study, we determined abnormalities of NK cells in systemic sclerosis (SSc), an autoimmune connective tissue disease, by assessing the frequency and absolute number, activation marker expression, cytokine production, and killing activity. The frequency and absolute number of NK cells increased in diffuse cutaneous SSc (dcSSc), whereas they were normal in limited cutaneous SSc (lcSSc). NK cells from both dcSSc and lcSSc patients exhibited activated phenotypes characterized by up-regulated CD16 and CD69 expression and downregulated CD62L expression. Interferon (IFN)-gamma production by non-stimulated NK cells from both dcSSc and lcSSc patients was increased compared to the normal control, whereas on stimulation, a reduced amount of IFN-gamma was produced. Interleukin (IL)-5 and IL-10 production by non-stimulated NK cells and IL-6 production by stimulated NK cells were augmented in dcSSc patients, but not in lcSSc patients. Despite the augmented cytokine production by non-stimulated NK cells, natural cytotoxicity activity and granzyme B secretion was reduced in NK cells from dcSSc and lcSSc patients. These results suggested that altered NK cell function contributes to immunological abnormalities in SSc.

Spontaneous Immunity against Bcl-xL in Cancer Patients

It is well-established that peptide epitopes derived from human tumor-associated Ags can be recognized by CTL in the context of the MHC molecule. However, the vast majority of Ags described are not vital for survival and growth of the tumor cells, and immunoselection of Ag-loss variants during immunotherapy has been demonstrated in several cases. Malfunctions in death pathways observed in human cancers are often due to overexpression of antiapoptotic proteins in the Bcl-2 protein family, i.e., Bcl-2, Mcl-1, and Bcl-xL. These antiapoptotic proteins are implicated in cancer development, tumor progression, and drug resistance. The general overexpression of the antiapoptotic members of the Bcl-2 family in cancer and the fact that down-regulation or loss of expression of these proteins as a means of immune escape would impair sustained tumor growth makes them very attractive targets for anticancer immunotherapy. Recently, we identified spontaneous T cell responses against Bcl-2- and Mcl-1-derived peptides in patients suffering from cancers of different origin. In this study, we demonstrate that Bcl-xL is a target for T cell recognition in cancer patients. Thus, we describe spontaneous HLA-A2-restricted cytotoxic T cell responses against peptide epitopes derived from Bcl-xL by means of ELISPOT and flow cytometry stainings, whereas no responses were detected against any of the Bcl-xL epitopes in any healthy controls. Moreover, Bcl-xL-specific T cells are cytotoxic against HLA-matched cancer cells of different origin. Thus, cellular immune responses against apoptosis inhibitors like the Bcl-2 family proteins appear to represent a general feature in cancer.

A novel flow cytometric assay for evaluating cell-mediated cytotoxicity

Comprehensive evaluation of cell-mediated cytotoxicity is very important, especially in the clinical setting, when a surrogate immunologic endpoint that correlates with a clinical outcome needs to be defined. With the objective of simultaneously evaluating target cell death and effector cell frequency, the authors combined the measuring of the expression of the degranulation marker CD107a by effector cells with the apoptosis marker annexin V binding to target cells. Using human cytotoxic T lymphocytes, the authors found a significant incubation time-dependent increase of surface CD107a expression on effector cells due to degranulation. A parallel increase of annexin V binding to target cells due to target cell apoptosis was also found. These two parameters have shown excellent correlation in all effector/target cell systems studied. To find possible connections between effector cell degranulation (CD107a expression), granzyme B secretion, and target cell death (annexin V binding), the GrB ELISPOT assay and flow cytometric assay were performed and excellent cross-correlation was found between all three parameters. The specificity of the assay was also shown. These data show that this novel assay allows measurement of cytolytic cell activation and frequency as well as target cell death in the same sample.

Phenotypic and functional analysis of EBV-specific memory CD8 cells in SLE

T cell dysfunction has been described in systemic lupus erythematosus (SLE). However, the specific phenotype and function of antigen-specific CD8 cells is less clear. Here we determined phenotype and function of Epstein-Barr virus (EBV)-specific CD8 cells at the single-cell level in SLE. HLA-A2-restricted EBV-BMLF-1-specific CD8 cells were enumerated by flow cytometry using tetramers in SLE and healthy control subjects. Antigen-specific CD8 cells were analyzed for expression of differentiation, activation, proliferation, and anti-apoptotic markers. EBV-specific, other virus-specific (specific against a viral peptide pool consisting of cytomegalovirus, EBV and influenza virus peptides), and mitogen-induced CD8 cell function was assessed by INF-gamma ELISPOT assay. Frequencies of EBV-specific CD8 cells tended to be greater in SLE subjects than in healthy control subjects (p=0.07). While over 10% of EBV-specific CD8 cells were capable of producing IFN-gamma in four out of five healthy control subjects, such proportions of EBV-specific CD8 cells capable of IFN-gamma production were observed in only one out of six SLE subjects (p=0.04). In contrast, viral peptide pool-specific and mitogen-induced IFN-gamma-producing T cell function was intact in SLE subjects. Phenotypic analysis revealed EBV-specific CD8 cells to be in an early to intermediate differentiation and resting memory state in both groups. While EBV-specific CD8 cells are similar in phenotype, their frequency tends to be increased, and function appears to be decreased in SLE. Therefore, an impaired EBV-specific CD8 immune response may exist in SLE, potentially contributing to disease pathogenesis.

The Granzyme B and Interferon-?? Enzyme-Linked Immunospot Assay as Alternatives for Cytotoxic T-Lymphocyte Precursor Frequency after Renal Transplantation

BACKGROUND

The interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) assay has gained increased popularity as a surrogate marker of cytotoxic T-lymphocyte (CTL) activity. However, the functional activity of CTL might be a more relevant surrogate marker of CTL. Therefore, the authors wondered whether the granzyme B (GrB) ELISPOT assay is a better marker for determining the number of CTL than the IFN-gamma ELISPOT assay. METHOD.: Peripheral blood mononuclear cells (PBMC) from 19 kidney transplant patients were stimulated with donor cells or third-party cells. The authors determined the CTL precursor frequency (CTLpf) and simultaneously measured the number of IFN-gamma- and GrB-producing cells (pc) by ELISPOT assay.

RESULTS

In all three different assays, the reactivity to donor cells was significant lower than the reactivity to third-party cells: CTLpf, median: 9 versus 60/10(6) PBMC (P=0.0002); number of IFN-gamma pc: 10 versus 90/10(6) PBMC (P=0.0001); number of GrB pc: 60 versus 205/10(6) PBMC (P=0.05). When the authors compared the CTLpf after third-party stimulation with the corresponding ELISPOT results, they found a positive correlation between the CTLpf and the number of IFN-gamma pc (r(s)=0.47, P=0.05). No correlation was found between the CTLpf and the number of GrB pc (r(s)=0.23, P=0.36). However, when they compared the donor-specific CTLpf with the corresponding ELISPOT results, no correlation with the ELISPOT for IFN-gamma (r(s)=0.10, P=0.69) or GrB (r(s)=-0.24, P=0.34) was found.

CONCLUSIONS

The authors feel that the CTLpf, as a measure of the actual endpoint of cytolytic activity and independent of the pathway of killing, remains the "gold standard" for determining donor-specific cytolytic activity after clinical organ transplantation.

Isolation and characterization of novel single-chain Fv specific for human granzyme B

Granzyme B, a neutral serine protease, has been demonstrated to be a pivotal molecule for protective immunity against viral infection and cellular malignant transformation. To facilitate monitoring of granzyme B levels, we have recently applied phage display technology to produce single-chain Fv antibodies specific for granzyme B, as versatile alternatives and complementary reagents to currently available monoclonal antibodies. Through four rounds of panning on purified human granzyme B-coated on solid phase, three unique clones were isolated. Expressed soluble scFv antibodies demonstrated specific immunological applications including ELISA, Western blotting, immunoprecipitation and intracellular staining. Based on sequence analyses and structural modeling, one scFv, Fv17, may have overlapping antigen binding specificity with monoclonal antibodies 2C5/F5 and GB11. Owing to the availability of its DNA sequence and large scale production capability, Fv17 should be a superior reagent for monitoring granzyme B expression in natural killer cells and antigen specific CD8+ T cell immunity.

Granzyme B ELISPOT Assay Determines the Cytotoxic T Lymphocyte Precursor Frequency After HLA-Identical Living-Related Kidney Transplantation

A major goal in organ transplantation is to define the optimal immunosuppressive dose. Recently, we demonstrated that the frequency of cytotoxic T lymphocytes (CTLpf) identifies patients in whom the immunosuppressive load can be safely reduced. However, in peripheral blood mononuclear cells (PBMC) from HLA-identical living-related kidney transplant patients, no donor-specific CTLpf can be measured. The determination of the functional activity of cytotoxic T lymphocytes (CTLs) could be an alternative method for the CTLpf. Granzyme B (GrB) is present in the granules of CTLs and is involved in the direct lethal hit of donor target cells. Therefore, we wondered whether the GrB ELISPOT assay is an alternative method to determine the activity of CTLs after HLA-identical living-related kidney transplantation. We measured the number of GrB producing cells (pc) against donor PBMC and third-party PBMC in PBMC from HLA-identical patients who were reduced in their immunosuppression from 100% to 50% azathioprine with 5 to 10 mg/day prednisone. We found low numbers of GrB pc before reduction of immunosuppression, as only 20% of the patients' PBMC responded to donor cells, whereas 57% of the patients' PBMC responded to donor cells after reduction of immunosuppression. After third-party stimulation, the number of GrB pc increased after tapering the immunosuppressive load (P = .03). Our results demonstrate that the GrB ELISPOT assay might be used as an alternative for the CTLpf after HLA-identical living-related kidney transplantation.