Quantitation of antigen-reactive T cells in peripheral blood by IFNgamma-ELISPOT assay and chromium-release assay: a four-centre comparative trial

A novel multicolor fluorescent spot assay for the functional assessment of chimeric antigen receptor (CAR) T-cell products

BACKGROUND AIMS

Chimeric antigen receptor (CAR) T-cell (CAR-T) therapies have revolutionized the treatment of B-cell lymphomas. Unfortunately, relapses after CD19-targeted CAR-T are relatively common and, therefore, there is a critical need for assays able to assess the function and potency of CAR-T products pre-infusion, which will hopefully help to optimize CAR-T therapies. We developed a novel multicolor fluorescent spot assay (MFSA) for the functional assessment of CAR-T products on a single-cell level, combining the numerical assessment of CAR-T products with their functional characterization.

METHODS

We first used a standard single-cell interferon (IFN)-γ enzyme-linked immune absorbent spot assay to measure CD19-targeted CAR-T responses to CD19-coated beads. We then developed, optimized and validated an MFSA that simultaneously measures the secretion of combinations of different cytokines on a single CAR-T level.

RESULTS

We identified IFN-γ/tumor necrosis factor-α/granzyme B as the most relevant cytokine combination, and we used our novel MFSA to functionally and numerically characterize two clinical-grade CAR-T products.

CONCLUSIONS

In conclusion, we have developed a novel assay for the quantitative and functional potency assessment of CAR-T products. Our optimized MFSA is cost-effective, easy to perform, reliable, can be performed overnight, allowing for a fast delivery of the product to the patient, and requires relatively minimal maintenance and training. The clinical value of our novel assay will be assessed in studies correlating the pre-infusion assessment of CAR-T products with the patients' outcome in a prospective fashion.

Correlation of Immunomodulatory Cytokine Expression with Histopathological Changes and Viral Antigen in a Hamster Model of Equine Herpesvirus-9 Encephalitis

A group of hamsters (n = 25) was intranasally infected with equine herpesvirus-9 (EHV-9) and mRNA transcription levels of several proinflammatory (IFN-γ, TNF-α and IL-6) and anti-inflammatory (IL-4, IL-10 and TGF-β) cytokines were investigated in brain tissue using RT-qPCR. These levels were correlated with the severity of sequential histopathological changes and intensity of immunohistochemical labelling of virus antigen in brain. Early and progressive upregulation of all the proinflammatory and anti-inflammatory cytokines investigated (P < 0.05) was correlated with increasing severity of encephalitis and viral antigen expression from 2 days post infection (dpi) with a peak at 4-5 dpi (P <0.05).

Reader-free ELISPOT assay for immuno-monitoring in peptide-based cancer vaccine immunotherapy

Cancer vaccine immunotherapy is a therapy that induces cellular immune responses against a target molecule to elicit clinical anti-tumor effects. These cellular immune responses against the target molecule are monitored to evaluate whether the antigen-specific cellular immune responses are induced and maintained during the vaccination period. Enzyme-linked immunospot (ELISPOT) assay is widely performed to analyze not only the frequency of immune cells, but also their effector functions as determined by their cytokine production/secretion. The present study aimed to develop a reader-free ELISPOT assay using a handy membrane-punching device termed ELI 8. With the assistance of particle analysis by ImageJ software, the results of spot counting were reproducible with high inter-assay and inter-examiner concordance. Immune cells that produce and secrete Th1 cytokines without antigen-peptide stimulation of peripheral blood mononuclear cells (PBMCs) were detected, and their frequencies in patients with cancer were significantly higher compared with those in healthy individuals. These frequencies varied between individuals, as well as between time points during the course of cancer vaccine immunotherapy in each patient. Due to the variability in spontaneous cytokine production/secretion by PBMCs, an antigen-specific immune response (IR) index is proposed, which is a ratio of the number of spot-forming cells (SFCs) subjected to antigen-stimulation to that of SFCs with spontaneous cytokine secretion without antigen-stimulation. This index may be used as a marker for antigen-specific cellular immune responses in patients treated with cancer immunotherapy. The IR index successfully detected the induction of Wilms' tumor 1-specific cellular immune responses in patients with cancer treated with cancer vaccine immunotherapy.

Recent advances in the understanding of severe cutaneous adverse reactions

Severe cutaneous adverse reactions (SCARs) encompass a heterogeneous group of delayed hypersensitivity reactions, which are most frequently caused by drugs. Our understanding of several aspects of SCAR syndromes has evolved considerably over the last decade. This review explores evolving knowledge of the immunopathogenic mechanisms, pharmacogenomic associations, in vivo and ex vivo diagnostics for causality assessment, and medication cross-reactivity data related to SCAR syndromes. Given the rarity and severity of these diseases, multidisciplinary collaboration through large international, national and/or multicentre networks to collect prospective data on patients with SCAR syndromes should be prioritized. This will further enhance a systematized framework for translating epidemiological, clinical and immunopathogenetic advances into preventive efforts and improved outcomes for patients.

The Ex Vivo IFN-γ Enzyme-Linked Immunospot (ELISpot) Assay

The quantification of single cell interferon-gamma (IFN-γ) release for assessing cellular immune responses using the Enzyme-linked immunospot (ELISPOT) assay is an invaluable technique in immunology. Peripheral blood mononuclear cells (PBMC) are stimulated in vitro with recombinant proteins, peptides and recently whole malaria organisms. Stimulation may be short term (20-36 h) or long term (cultured ELISpot, up to 7 days). ELISpot is also able to quantify other cytokines secreted by antigen-specific T-cells, such as interleukin-2, interleukin-5, and other interleukins. ELISpot is playing an important role especially in vaccine research studies.

Combined IL-21-primed polyclonal CTL plus CTLA4 blockade controls refractory metastatic melanoma in a patient

Chapuis et al. demonstrate that the combination of adoptive cellular therapy with CTLA4 blockade induces long-term remission in a melanoma patient resistant to both modalities administered serially and individually.

Adoptive transfer of peripheral blood–derived, melanoma-reactive CD8⁺ cytotoxic T lymphocytes (CTLs) alone is generally insufficient to eliminate bulky tumors. Similarly, monotherapy with anti-CTLA4 infrequently yields sustained remissions in patients with metastatic melanoma. We postulated that a bolus of enhanced IL-21–primed polyclonal antigen-specific CTL combined with CTLA4 blockade might boost antitumor efficacy. In this first-in-human case study, the combination successfully led to a durable complete remission (CR) in a patient whose disease was refractory to both monoclonal CTL and anti-CTLA4. Long-term persistence and sustained anti-tumor activity of transferred CTL, as well as responses to nontargeted antigens, confirmed mutually beneficial effects of the combined treatment. In this first-in-human study, Chapuis et al. demonstrate that the combination of adoptive cellular therapy with CTLA4 blockade induces long-term remission in a melanoma patient resistant to both modalities administered serially and individually.

Dendritic cells primed with HPV positive cervical tumor lysate are superior to unprimed DCs in migratory capacity and induce a potent Th1 response

In this study, we assessed the efficacy of tumor lysate primed and unprimed monocyte derived mature dendritic cells (DCs) to trigger an effective anti-tumor immune response in cervical cancer patients who tested positive for human papilloma virus (HPV) DNA. Lysate primed and unprimed DCs were assessed for the expression of CD80, CD86, CD40, HLADR and CD83. The ability of DCs to migrate in response to the chemokines CCL19 and 21 as well as their ability to secrete IL12p40 was investigated. Mixed lymphocyte proliferation assays were used to assess DC stimulatory capacity and their ability to generate a Th1 response. Our results showed no difference in phenotypic expression between primed and unprimed DCs but both had significantly increased expression of the activation marker CD83 when compared to immature DCs. Importantly, the primed DCs showed significant (P value=0.03) IL-12p40 secretion and a superior migratory capacity towards CC19 and CCL21 (P value=0.04) compared to unprimed DCs even after cytokine withdrawal. Primed DCs showed superior stimulation of T cell proliferation (allogeneic and autologous) and secretion of IFN gamma (IFN-γ) than the unprimed DCs. Hence whole tumor lysate primed mature DCs could be potent immunotherapeutic adjuvants to standard treatment for cervical cancer.

Harmonisation of short-term in vitro culture for the expansion of antigen-specific CD8(+) T cells with detection by ELISPOT and HLA-multimer staining

Ex vivo ELISPOT and multimer staining are well-established tests for the assessment of antigen-specific T cells. Many laboratories are now using a period of in vitro stimulation (IVS) to enhance detection. Here, we report the findings of a multi-centre panel organised by the Association for Cancer Immunotherapy Immunoguiding Program to investigate the impact of IVS protocols on the detection of antigen-specific T cells of varying ex vivo frequency. Five centres performed ELISPOT and multimer staining on centrally prepared PBMCs from 3 donors, both ex vivo and following IVS. A harmonised IVS protocol was designed based on the best-performing protocol(s), which was then evaluated in a second phase on 2 donors by 6 centres. All centres were able to reliably detect antigen-specific T cells of high/intermediate frequency both ex vivo (Phase I) and post-IVS (Phase I and II). The highest frequencies of antigen-specific T cells ex vivo were mirrored in the frequencies following IVS and in the detection rates. However, antigen-specific T cells of a low/undetectable frequency ex vivo were not reproducibly detected post-IVS. Harmonisation of the IVS protocol reduced the inter-laboratory variation observed for ELISPOT and multimer analyses by approximately 20 %. We further demonstrate that results from ELISPOT and multimer staining correlated after (P < 0.0001 and R (2) = 0.5113), but not before IVS. In summary, IVS was shown to be a reproducible method that benefitted from method harmonisation.

Immunological assessment of influenza vaccines and immune correlates of protection

Influenza vaccines remain the primary public health tool in reducing the ever-present burden of influenza and its complications. In seeking more immunogenic, more effective and more broadly cross-protective influenza vaccines, the landscape of influenza vaccines is rapidly expanding, both in near-term advances and next-generation vaccine design. Although the first influenza vaccines were licensed over 60 years ago, the hemagglutination-inhibition antibody titer is currently the only universally accepted immune correlate of protection against influenza. However, hemagglutination-inhibition titers appear to be less effective at predicting protection in populations at high risk for severe influenza disease; older adults, young children and those with certain medical conditions. The lack of knowledge and validated methods to measure alternate immune markers of protection against influenza remain a substantial barrier to the development of more immunogenic, broadly cross-reactive and effective influenza vaccines. Here, the authors review the knowledge of immune effectors of protection against influenza and discuss assessment methods for a broader range of immunological parameters that could be considered in the evaluation of traditional or new-generation influenza vaccines.

Differential regulatory T cell activity in HIV type 1-exposed seronegative individuals

The potential role of conventional and regulatory T cells (Tregs) in protection from HIV-1 infection remains unclear. To address this question, we analyzed samples from 129 HIV-1-exposed seronegative individuals (HESN) from an HIV-1-serodiscordant couples cohort. To assess the presence of HIV-specific T cell responses and Treg function, we measured the proliferation of T cells in response to HIV-1 peptide pools in peripheral blood mononuclear cells (PBMCs) and PBMCs depleted of Tregs. We identified HIV-specific CD4(+) and CD8(+) T cell responses and, surprisingly, the overall CD4(+) and CD8(+) T cell response rate was not increased when Tregs were removed from cell preparations. Of the 20 individuals that had HIV-1-specific CD4(+) T cell responses, only eight had Tregs that could suppress this proliferation. When compared with individuals whose Tregs could suppress HIV-1-specific CD4(+) T cell proliferation, individuals with Tregs unable to suppress showed a trend toward increased T cell activation and Treg frequency and a significant increase in HIV-1-specific production of microphage inflammatory protein-1β (MIP-1β) by CD4(+) T cells, autocrine production of which has been shown to be protective in terms of HIV-1 infection of CD4(+) T cells.

Immunological Monitoring to Rationally Guide AAV Gene Therapy

Recent successes with adeno-associated virus (AAV)-based gene therapies fuel the hope for new treatments for hereditary diseases. Pre-existing as well as therapy-induced immune responses against both AAV and the encoded transgenes have been described and may impact on safety and efficacy of gene therapy approaches. Consequently, monitoring of vector- and transgene-specific immunity is mandated and may rationally guide clinical development. Next to the humoral immune response, the cellular response is central in our understanding of the host reaction in gene therapy. But in contrast to the monitoring of antibodies, which has matured over many decades, sensitive and robust monitoring of T cells is a relatively new development. To make cellular immune assessments fit for purpose, investigators need to know, control and report the critical assay variables that influence the results. In addition, the quality of immune assays needs to be continuously adjusted to allow for exploratory hypothesis generation in early stages and confirmatory hypothesis validation in later stages of clinical development. The concept of immune assay harmonization which includes use of field-wide benchmarks, harmonization guidelines, and external quality control can support the context-specific evolution of immune assays. Multi-center studies pose particular challenges to sample logistics and quality control of sample specimens. Cooperative groups need to define if immune assessments should be performed in one central facility, in peripheral labs or including a combination of both. Finally, engineered reference samples that contain a defined number of antigen-specific T cells may become broadly applicable tools to control assay performance over time or across institutions.

Minor histocompatibility antigen UTY as target for graft-versus-leukemia and graft-versus-haematopoiesis in the canine model

Male patients with female-stem-cell donors have better prognosis compared to female-to-male combinations due to Y-encoded minor histocompatibility antigens recognized by female-alloimmune-effector lymphocytes in the context of a graft-versus-leukemia (GvL) effect. We provide data in a dog-model that the minor histocompatibility antigen UTY might be a promising target to further improve GvL-immune reactions after allogeneic-stem-cell transplantations. Female-canine-UTY-specific T cells (CTLs) were stimulated in vitro using autologous-DCs loaded with three HLA-A2-restricted-UTY-derived peptides (3-fold-expansion), and specific T cell responses were determined in 3/6 female dogs. CTLs specifically recognized/lysed autologous-female-peptide-loaded DCs, but not naïve-autologous-female DCs and monocytes. They mainly recognized bone-marrow (BM) and to a lower extent DCs, monocytes, PBMCs and B-cells from DLA-identical-male littermates and peptide-loaded T2-cells in an MHC-I-restricted manner. A UTY-/male-specific reactivity was also obtained in vivo after stimulation of a female dog with DLA-identical-male PBMCs. In summary, we demonstrated natural UTY processing and presentation in dogs. We showed that female-dog CTLs were specifically stimulated by HLA-A2-restricted-UTY peptides, thereby enabling recognition of DLA-identical-male cells, mainly BM cells. These observations suggest UTY as a promising candidate-antigen to improve GvL-reactions in the course of immunotherapy.

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.

Detection and characterisation of alloreactive T cells

T cell alloreactivity is responsible for much of the morbidity and mortality associated with tissue transplantation and graft versus host disease. Immunoassays for ex vivo monitoring and quantitation of alloreactive T cells are being increasingly utilised to provide valuable information for individualised clinical management of transplant recipients. Here we describe detailed methodologies for both traditional and novel assays utilised for the detection, quantitation, and functional characterisation of alloreactive T cells and highlight the key advantages and disadvantages of each system.

The impact of harmonization on ELISPOT assay performance

During more than 25 years of application in immunological sciences, ELISPOT has been established as a routine, robust, versatile, and reliable assay. From basic research to clinical immune monitoring, ELISPOT is being used to address the quantification and (to a lesser extent) functional characterization of immune cells secreting different molecules in the context of health and disease, immune intervention, and therapy in humans and other species [Kalyuzhny (Ed.) (2005) Handbook of Elispot: methods and protocols, Vol. 302, Humana Press Inc., Totowa, NJ]. Over the last decade, ELISPOT assays have been increasingly implemented as an immune-monitoring tool in clinical trials [Schmittel et al. J Immunother 23:289-295, 2000; Whiteside Immunol Invest 29:149-162, 2000; Nagata et al. Ann N Y Acad Sci 1037:10-15, 2004; Cox et al. (2005) Cellular immune assays for evaluation of vaccine efficacy in developing countries., In Manual of Clinical Immunology Laboratory (Rose, N. R., Hamilton, R. G., and Detrick, B., Eds.), p 301, ASM Press, Washington, DC; Cox et al. Methods 38:274-282, 2006]. While the principles of the original protocol have changed little since its first introduction [Czerkinsky J Immunol Methods 110:29-36, 1988], individual laboratories have adapted assay procedures based on experimental needs, availability of reagents and equipment, obtained recommendations, and gained experience, leading to a wide disparity of applied ELISPOT protocols with inevitable consequences. This chapter addresses the resulting challenges for ELISPOT use in clinical trial settings, and discusses the influence of harmonization strategies as a tool for overcoming these challenges. Furthermore, harmonization is discussed in the context of assay standardization and validation strategies.

Response determination criteria for ELISPOT: toward a standard that can be applied across laboratories

ELISPOT assay readout is often dichomized as positive or negative responses according to prespecified criteria. However, these criteria can vary widely across institutions. The adoption of a common response criterion is a key step toward cross-laboratory comparability. This chapter describes the two main approaches to response determination, identifying the strengths and limitations of each. Nonparametric statistical tests and consideration of data quality are recommended and instructions provided for their ready implementation by nonstatisticians and statisticians alike.

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.

Determination of rubella virus-specific cell-mediated immunity using IFN gamma-ELISpot

Immunity to rubella virus (RV) is conventionally determined by measuring specific immunoglobulin G (IgG). However, several individuals may be considered immune despite undetectable antibody levels. In the present study RV-specific interferon-gamma (IFN gamma)-ELISpot and rubella-IgG-ELISA were compared in 75 young adults aged between 20 and 30 years. In a subgroup, not only rubella-like particles (RLP), but also HPV77 rubella vaccine derived antigen was used in IFN gamma-ELISpot. The results from both, ELISA and ELISpot were independent of previous encounter to RV (vaccination, exanthematous disease, or childhood infection). There was no difference between RLP and RV vaccine antigen in IFN gamma-ELISpot response, and there was no correlation between IFN gamma-ELISpot and RV-specific IgG levels. IFN gamma-producing cells were found in 78.7% of all tested persons, and 83.8% of them were positive in ELISA. In almost all individuals seronegative for RV antibody, IFN gamma-producing cells were detected. Considering both humoral and cell-mediated immune responses, a positive RV immune reaction was seen in 98.6%. The results indicate that the IFN gamma-ELISpot can provide valuable additional information in seronegative individuals.

CD28 down-regulation on circulating CD4 T-cells is associated with poor prognoses of patients with idiopathic pulmonary fibrosis

Background

Although the etiology of idiopathic pulmonary fibrosis (IPF) remains perplexing, adaptive immune activation is evident among many afflicted patients. Repeated cycles of antigen-induced proliferation cause T-cells to lose surface expression of CD28, and we hypothesized this process might also occur in IPF.

Methodology/Principal Findings

Peripheral blood CD4 T-cells from 89 IPF patients were analyzed by flow cytometry and cytokine multiplex assays, and correlated with clinical events. In comparison to autologous CD4⁺CD28⁺cells, the unusual CD4⁺CD28^null lymphocytes seen in many IPF patients had discordant expressions of activation markers, more frequently produced cytotoxic mediators perforin (2.4±0.8% vs. 60.0±7.4%, p<0.0001) and granzyme B (4.5±2.8% vs.74.9±6.5%, p<0.0001), produced greater amounts of many pro-inflammatory cytokines, and less frequently expressed the regulatory T-cell marker FoxP3 (12.9±1.1% vs. 3.3±0.6% p<0.0001). Infiltration of CD4⁺CD28^null T-cells in IPF lungs was confirmed by confocal microscopy. Interval changes of CD28 expression among subjects who had replicate studies were correlated with conterminous changes of their forced vital capacities (r_s = 0.49, p = 0.012). Most importantly, one-year freedom from major adverse clinical events (either death or lung transplantation) was 56±6% among 78 IPF patients with CD4⁺CD28⁺/CD4_total≥82%, compared to 9±9% among those with more extensive CD28 down-regulation (CD4⁺CD28⁺/CD4_total<82%) (p = 0.0004). The odds ratio for major adverse events among those with the most extensive CD28 down-regulation was 13.0, with 95% confidence intervals 1.6-111.1.

Conclusions/Significance

Marked down-regulation of CD28 on circulating CD4 T-cells, a result of repeated antigen-driven proliferations, is associated with poor outcomes in IPF patients. The CD4⁺CD28^null cells of these patients have potentially enhanced pathogenic characteristics, including increased productions of cytotoxic mediators and pro-inflammatory cytokines. These findings show proliferative T-cell responses to antigen(s) resulting in CD28 down-regulation are associated with progression and manifestations of IPF, and suggest assays of circulating CD4 T-cells may identify patients at greatest risk for clinical deterioration.

Dissociated induction of cytotoxicity and DTH by CFA and CpG

Vaccinations typically rely on immunization with live virus for eliciting protective CD8 T cell immunity. There is increasing interest to use subunit vaccination strategies to achieve such responses. Complete Freund's adjuvant (CFA) and unmethylated cytosine-guanine dinucleotide containing DNA are considered some of the most potent adjuvants for eliciting immunity. Whereas a wealth of information is available on how these adjuvants affect CD4 T cell responses, their effects on engaging CD8 T cell immunity are not completely understood. We immunized C57BL/6J mice with the class I restricted peptides Uty or SIINFEKL using these 2 adjuvants and tested for cytokine secretion, proliferation, in vivo cytotoxicity, and delayed-type hypersensitivity (DTH). Our data show that CFA-induced CD8 T cells to proliferate, mediate DTH, and to secrete interferon-gamma, interleukin (IL)-2 and IL-17. Despite these markers of CD8 T cell activation, CFA failed to induce an early cytotoxic CD8 T cell response. In contrast, unmethylated cytosine-guanine dinucleotide containing DNA promoted a vigorous cytolytic response without activating substantial cytokine production, proliferation or DTH. These data have implications for CD8 T cell subunit vaccine design in which cytotoxicity versus DTH plays a key role in host defense.

Identification of an immunogenic HLA-A*0201-binding T-cell epitope of the transcription factor PAX2

PAX2 is a transcription factor and member of the highly conserved family of paired box genes. PAX2 is aberrantly expressed in a variety of solid and hematologic malignancies. PAX2 regulates the transcription factor Wilms tumor gene 1, which is a promising target of cancer immunotherapy. The aim of this study was to apply a modified reverse immunology strategy to identify immunogenic epitopes of PAX2 which could be useful for cancer immunotherapy. Thirteen potential HLA-A*0201 epitopes were predicted by a major histocompatibility complex binding algorithm (SYFPEITHI) and a proteasome cleavage algorithm (PAProC) and screened for recognition by T cells from HLA-A*02-positive cancer patients using intracellular cytokine cytometry. Epitope-specific T cells were generated from CD4CD25 regulatory T-cell-depleted peripheral blood mononuclear cell. Nine of 20 colorectal cancer patients, 1 of 13 renal cell carcinoma patients, and 2 of 17 lymphoma patients had a spontaneous CD8 T-cell response toward at least 1 of 6 PAX2 peptide pools. None of the 20 healthy subjects showed reactivity toward PAX2. PAX2.337-345 (TLPGYPPHV)-specific T cells could repeatedly be generated, which specifically lysed the PAX2 expressing colorectal tumor cell line SW480. In this study, a modified reverse immunology strategy was employed to identify a first immunogenic HLA-A*0201 restricted T-cell epitope and natural ligand of the tumor antigen PAX2. Thus, PAX2 is another embryonic transcription factor, which is of potential interest as immunotherapy target antigen.

Fit for purpose? A case study: validation of immunological endpoint assays for the detection of cellular and humoral responses to anti-tumour DNA fusion vaccines

Clinical trials are governed by an increasingly stringent regulatory framework, which applies to all levels of trial conduct. Study critical immunological endpoints, which define success or failure in early phase clinical immunological trials, require formal pre-trial validation. In this case study, we describe the assay validation process, during which the sensitivity, and precision of immunological endpoint assays were defined. The purpose was the evaluation of two multicentre phase I/II clinical trials from our unit in Southampton, UK, which assess the effects of DNA fusion vaccines on immune responses in HLA-A2+ patients with carcinoembryonic antigen (CEA)-expressing malignancies and prostate cancer. Validated immunomonitoring is being performed using ELISA and IFNgamma ELISPOTs to assess humoral and cellular responses to the vaccines over time. The validated primary endpoint assay, a peptide-specific CD8+ IFNgamma ELISPOT, was tested in a pre-trial study and found to be suitable for the detection of low frequency naturally occurring CEA- and prostate-derived tumour-antigen-specific T cells in patients with CEA-expressing malignancies and prostate cancer.

Fludarabine modulates immune response and extends in vivo survival of adoptively transferred CD8 T cells in patients with metastatic melanoma

Background

Adoptive T cell therapy involving the use of ex vivo generated antigen-specific cytotoxic T lymphocytes provides a promising approach to immunotherapy. It has become increasingly apparent that anti-tumor efficacy using adoptively transferred T cells is linked to their duration of in vivo persistence and can only be achieved when combined with some form of pre-infusion patient conditioning regimen. An optimal conditioning regimen that provides a positive benefit without serious toxicities has yet to be defined. We have established a unique clinical model that allows for evaluation of a given conditioning regimen on adoptively transferred T cells in humans. In this first-in-human study (FHCRC #1796), we evaluate the use of fludarabine, an FDA-approved reagent with predictable lymphodepleting kinetics and duration of action, as a conditioning regimen that promotes homeostatic upregulation of cytokines and growth signals contributing to in vivo T cell persistence.

Methods/Findings

We conducted a phase I study in patients with refractory metastatic melanoma. Patients received two infusions of a single tumor-reactive antigen-specific CTL clone expanded to 10¹⁰/m²; the first infusion was given without fludarabine conditioning, and the second CTL infusion was given after a course of fludarabine (25 mg/m²/day×5 days). This design permits intra-patient comparison of in vivo T cell persistence pre- and post-fludarabine. Nineteen CTL infusions were administered to ten patients. No serious toxicities were observed. Three of nine evaluable patients experienced minor response or stable disease for periods of 5.8–11.0 months with two additional patients demonstrating delayed disease stabilization. The median overall survival in this heavily pre-treated population was 9.7 months. Fludarabine led to a 2.9 fold improvement in the in vivo persistence of transferred CTL clones from a median of 4.5 days (range 0–38+) to 13.0 days (range 2–63+) (p<0.05). Fludarabine lymphodepletion increased plasma levels of the homeostatic cytokines IL-7 and IL-15. Surprisingly, fludarabine also increased the relative percentage of CD4+ T cells expressing the regulatory protein Foxp3.

Conclusions/Significance

Lymphodepletion with fludarabine enhances transferred T cell persistence but suggest that additional improvements to optimize T cell survival and address regulatory T cells are critical in providing anti-tumor efficacy.

Trial Registration

ClinicalTrials.gov NCT00317759

Results and harmonization guidelines from two large-scale international Elispot proficiency panels conducted by the Cancer Vaccine Consortium (CVC/SVI)

The Cancer Vaccine Consortium of the Sabin Vaccine Institute (CVC/SVI) is conducting an ongoing large-scale immune monitoring harmonization program through its members and affiliated associations. This effort was brought to life as an external validation program by conducting an international Elispot proficiency panel with 36 laboratories in 2005, and was followed by a second panel with 29 participating laboratories in 2006 allowing for application of learnings from the first panel. Critical protocol choices, as well as standardization and validation practices among laboratories were assessed through detailed surveys. Although panel participants had to follow general guidelines in order to allow comparison of results, each laboratory was able to use its own protocols, materials and reagents. The second panel recorded an overall significantly improved performance, as measured by the ability to detect all predefined responses correctly. Protocol choices and laboratory practices, which can have a dramatic effect on the overall assay outcome, were identified and lead to the following recommendations: (A) Establish a laboratory SOP for Elispot testing procedures including (A1) a counting method for apoptotic cells for determining adequate cell dilution for plating, and (A2) overnight rest of cells prior to plating and incubation, (B) Use only pre-tested serum optimized for low background: high signal ratio, (C) Establish a laboratory SOP for plate reading including (C1) human auditing during the reading process and (C2) adequate adjustments for technical artifacts, and (D) Only allow trained personnel, which is certified per laboratory SOPs to conduct assays. Recommendations described under (A) were found to make a statistically significant difference in assay performance, while the remaining recommendations are based on practical experiences confirmed by the panel results, which could not be statistically tested. These results provide initial harmonization guidelines to optimize Elispot assay performance to the immunotherapy community. Further optimization is in process with ongoing panels.

The CIMT-monitoring panel: a two-step approach to harmonize the enumeration of antigen-specific CD8+ T lymphocytes by structural and functional assays

The interpretation of the results obtained from immunomonitoring of clinical trials is a difficult task due to the variety of methods and protocols available to detect vaccine-specific T-cell responses. This heterogeneity as well as the lack of standards has led to significant scepticism towards published results. In February 2005, a working group was therefore founded under the aegis of the Association for Immunotherapy of Cancer ("CIMT") in order to compare techniques and protocols applied for the enumeration of antigen-specific T-cell responses. Here we present the results from two consecutive phases of an international inter-laboratory testing project referred to as the "CIMT monitoring panel". A total of 13 centers from six European countries participated in the study in which pre-tested PBMC samples, synthetic peptides and PE-conjugated HLA-tetramers were prepared centrally and distributed to participants. All were asked to determine the number of antigen-specific T-cells in each sample using tetramer staining and one functional assay. The results of the first testing round revealed that the total number of cells analyzed was the most important determinant for the sensitive detection of antigen-specific CD8(+) T-cells by tetramer staining. Analysis by ELISPOT was influenced by a combination of cell number and a resting phase after thawing of peripheral blood mononuclear cells. Therefore, the experiments were repeated in a second phase but now the participants were asked to change their protocols according to the new guidelines distilled from the results of the first phase. The recommendations improved the number of antigen-specific T-cell responses that were detected and decreased the variability between the laboratories. We conclude that a two-step approach in inter-laboratory testing allows the identification of distinct variables that influence the sensitivity of different T-cell assays and to formally show that a defined correction to the protocols successfully increases the sensitivity and reduces the inter-center variability. Such "two-step" inter-laboratory projects could define rational bases for accepted international guidelines and thereby lead to the harmonization of the techniques used for immune monitoring.

Construction and functional test of a chicken MHC-I (BF2*15)/peptide tetramer

The major histocompatibility complex class I (MHC class I) peptide tetramer is a sensitive and valuable tool to evaluate antigen-specific cytotoxic T lymphocytes (CTLs) of many animal species. To date, no chicken MHC class I peptide tetramer has been reported. In this report, we describe construction and functional evaluation of a chicken MHC-I (BF2*15)/peptide tetramer. To construct the chicken MHC class I peptide tetramer, genes of the chicken MHC-I α chain (BF2*15) and β2 microglobulin (Chβ2m) were synthesized by RT-PCR from the total RNA of PBMCs and the signal sequences were deleted. The BF2*15 was then fused with the BirA substrate peptide (BSP) sequence at the C terminus. Next, the synthesized PCR products of BF2*15 and Chβ2m were cloned into the expression vector pET-28a (+) and expressed in Escherichia coli strain BL21 (DE3). Highly purified BF2*15-BSP heavy chain and Chβ2m were obtained by a Ni²⁺ NTA column affinity purification, yielding approximately 1.6 mg of BF2*15-BSP and 2.4 mg of Chβ2m per 1 g of the pelleted bacteria. The purified BF2*15-BSP heavy chain and Chβ2m were refolded with synthetic peptide originated from infectious bronchitis virus nucleoprotein (IBV N_71–78) in refolding buffer to generate the monomer of BF2*15/peptide complex. The monomer was then biotinylated and tetramerized using PE-labeled streptavidin. Upon functional evaluation of the construct by using flowcytometry, we observed that 3.65% of CTLs were specific to IBV nucleoprotein. This demonstrates that the CTL response of IBV-infected chicks could effectively be evaluated using the prepared MHC-I BF2*15/peptide tetramer.

Heterologous prime-boost immunotherapy of melanoma patients with Influenza virosomes, and recombinant Vaccinia virus encoding 5 melanoma epitopes and 3 co-stimulatory molecules. A multi-centre phase I/II open labeled clinical trial

To the exception of early stages of disease, the morbidity and mortality of melanoma is considerable, with no acknowledged therapeutic options beyond surgery. Immunotherapy of melanoma has achieved some success, but further refinements are urgently needed in order to realize its potential. This paper describes a multi-centre phase I/II open labeled, controlled clinical trial investigating 2 innovative immunotherapeutic reagents. Two successive groups of 20 resected AJCC stages IIb-IV melanoma patients will be treated, first with melanoma epitopes included into Influenza virosomes (group 1), and second with a heterologous prime-boost protocol priming with a recombinant Vaccinia virus, and boosting with Influenza virosomes (group 2). Five melanoma epitopes from three different melanoma differentiation antigens were included into Influenza virosomes, that cross-stimulate CD4+ T cells and are endowed with high adjuvant capacity in the generation of CTL. The same five melanoma epitopes, two co-stimulatory molecules CD80 and CD86, and the CD40 ligand, a marker known to play a crucial role in CTL generation and memory maintenance were encoded in a recombinant Vaccinia virus. GM-CSF will be administered as a supporting cytokine. Both Influenza virosomes and octo-recombinant Vaccinia virus are innovative and original constructs assessed for the first time in human. Immunotherapy foresees 12 weekly immunizations for each group. Toxicity and adverse events will be monitored clinically. Immunological efficacy will be assessed dynamically by ex-vivo multimer analysis, Elispot, and quantitative real-time PCR for up to 3 months following completion of immunotherapy schedule. Disease free survival will be assessed by 4-monthly serial clinic visits, including physical and FDG-PET examinations, for a follow-up time of 2 years. Quality of life will be assessed with a dedicated FACT-BRM 4 questionnaire.

Immune monitoring

A wide array of immunologic tests are available for immune monitoring in cancer vaccine trials, and the number of novel assays and technical modifications continues to burgeon. Because only a small fraction of all proposed vaccine trials tested in phase I-II trials, for practical reasons, will ultimately move forward to be tested in phase III trials, there must be a system of establishing the most promising immunization strategies. This evaluation of cancer vaccine will require standardization of the immune assays and statistical methods used in immunologic monitoring. Furthermore, the use of a systematic approach to evaluating and adopting novel technologies for immunologic assessment would likely lead to timely implementation of more reliable, practical and cost-effective methods of immune. It should be the goal and expectation that this rational approach to immune monitoring will allow the critical appraisal of the most promising vaccine candidates in the context of pivotal, multi-center trials.

Progesterone sensitive Interferon-? producing cells detected by ELISpot assay in autoimmune progesterone dermatitis

Autoimmune progesterone dermatitis (APD) is a rare cutaneous disorder, characterized by recurrent polymorphous cutaneous and mucosal manifestations. It is considered to be caused by a hypersensitive reaction to endogenous progesterone. However, in vitro T-cell activity to this hormone has been described in few patients. Here we report the case of a 30-year-old woman with recurrent pruritic erythematous, and erythema multiforme-like eruptions localized to the genital area. Positive cutaneous reaction to intradermal progesterone injection suggested the diagnosis of APD. The analysis of cellular immune response to progesterone, investigated by the ELISpot assay, showed a significantly higher level of Interferon-gamma (IFN-gamma) producing cells in this patient compared with a control group comprising five asymptomatic women in the luteal phase of the menstrual cycle. Our results suggest that the ELISpot technique, together with clinical evaluations and assessment of allergies, could be useful in the diagnosis of APD.

Immunological techniques in viral hepatitis

The need to quantitate and monitor immune responses of large patient cohorts with standardized techniques is increasing due to the growing range of treatment options for hepatitis B and hepatitis C, the development of combination therapies, and candidate experimental vaccines for HCV. In addition, advances in immunological techniques have provided new tools for detailed phenotypic and functional analysis of cellular immune responses. At present, there is substantial variation in laboratory protocols, reagents, controls and analysis and presentation of results. Standardization of immunological assays would therefore allow better comparison of results amongst individual laboratories and patient cohorts. The EASL-sponsored and AASLD-endorsed Monothematic Conference on Clinical Immunology in Viral Hepatitis was held at the University College London, United Kingdom, Oct 7-8, 2006 to bring together investigators with research experience in clinical immunology of hepatitis B virus (HBV) and hepatitis C virus (HCV) infections for in-depth discussion, critical evaluation and standardization of immunological assays. This report summarizes the information presented and discussed at the conference, but is not intended to represent a consensus statement. Our aim is to highlight topics and issues that were supported by general agreement and those that were controversial, as well as to provide suggestions for future work.

Defining blood processing parameters for optimal detection of cryopreserved antigen-specific responses for HIV vaccine trials

Interferon-gamma (IFN-gamma) ELISpot and intracellular cytokine staining (ICS) assays are routinely employed in clinical HIV vaccine trials to identify antigen-specific T cells in cryopreserved peripheral blood mononuclear cells (PBMC). Several parameters involved in blood collection, processing and shipping may influence immunological function of the resulting cells, including anticoagulant type, time from venipuncture to PBMC isolation/cryopreservation, method of PBMC isolation and procedure for sample shipping. We examined these parameters in single and multiple site studies, and found the length of time from venipuncture to cryopreservation is the most important parameter affecting performance of T cells in immunological assays. Comparing blood processed at 24 h after venipuncture with that processed within 8 h, we observed on average a modest reduction in PBMC viability ( approximately 8% decrease), a greater loss in cell recovery ( approximately 32%), and between 36-56% loss in IFN-gamma T cell frequencies by ELISpot assay. We also describe three cold shipping methods that maintain immunological function in appropriately cryopreserved PBMC. These data indicate that cryopreservation of PBMC should occur within 8 h of venipuncture for optimal performance. This narrow window for specimen processing has important implications in selecting and monitoring clinical sites with laboratory capacity to perform these procedures in future clinical trials.

Identification of a Highly Immunogenic HLA-A*01-Binding T Cell Epitope of WT1

PURPOSE

The transcription factor Wilms tumor protein 1 (WT1) belongs to a new generation of tumor antigens, as it is essential for tumor cell proliferation and is highly expressed in various hematologic and solid malignancies. The aim of this study was to apply a modified reverse immunology strategy to identify immunogenic epitopes of WT1 which could be useful for immunotherapy.

EXPERIMENTAL DESIGN

Potential HLA-A*01 epitopes predicted by a MHC binding algorithm were screened for recognition by peripheral blood mononuclear cells (PBMC) from patients with spontaneous T cell responses using intracellular cytokine cytometry. Epitope processing was shown by proteasomal cleavage. Epitope-specific T cells were generated from CD4+CD25+ regulatory T cell-depleted PBMC.

RESULTS

One of five predicted HLA-A*01-binding candidate epitopes showed high immunogenicity as 5 of 14 patients with hematologic malignancies had WT1.317-327-reactive T cells ranging from 0.4% to 1.5% of CD3+CD8+ T cells. Proteasomal degradation assays indicated the cleavage of WT1.317-327. The depletion of regulatory T cells from PBMCs enabled the rapid expansion of WT1.317-327-specific CTL, whereas no CTL could be generated from unfractionated PBMC. WT1.317-327-specific CTL efficiently lysed an autologous WT1-expressing tumor cell line but not HLA-A*01-negative WT1-expressing tumor cells. Immunogenicity of the epitope across histologies was verified by the demonstration of spontaneous ex vivo WT1.317-327-specific T cell responses in two of six patients with HLA-A*01-positive melanoma or lung cancer.

CONCLUSION

In this study, a modified reverse immunology strategy was employed to identify a first immunogenic HLA-A*01-restricted T cell epitope of the tumor antigen WT1, which is of considerable interest for use in vaccination trials.

Construction of bioactive chimeric MHC class I tetramer by expression and purification of human–murine chimeric MHC heavy chain and β2m as a fusion protein in Escherichia coli

Major histocompatibility (MHC) class I tetramers are used in the quantitative analysis of epitope peptide-specific CD8+ T-cells. An MHC class I tetramer was composed of 4 MHC class I complexes and a fluorescently labeled streptavidin (SA) molecule. Each MHC class I complex consists of an MHC heavy chain, a beta(2)-microglobulin (beta(2)m) molecule and a synthetic epitope peptide. In most previous studies, an MHC class I complex was formed in the refolding buffer with an expressed MHC heavy chain molecule and beta(2)m, respectively. This procedure inevitably resulted in the disadvantages of forming unwanted multimers and self-refolding products, and the purification of each kind of monomer was time-consuming. In the present study, the genes of a human/murine chimeric MHC heavy chain (HLA-A2 alpha1, HLA-A2 alpha2 and MHC-H2D alpha3) and beta(2)m were tandem-cloned into plasmid pET17b and expressed as a fusion protein. The recombinant fusion protein was refolded with each of the three HLA-A2 restricted peptides (HBc18-27 FLPSDFFPSI, HBx52-60 HLSLRGLPV, and HBx92-100 VLHKRTLGL) and thus three chimeric MHC class I complexes were obtained. Biotinylation was performed, and its level of efficiency was observed via a band-shift assay in non-reducing polyacrylamide gel electrophoresis (PAGE). Such chimeric MHC class I tetramers showed a sensitive binding activity in monitoring HLA/A2 restrictive cytotoxic T lymphocytes (CTLs) in immunized HLA/A*0201 transgenic mice.

A comparison of standard immunogenicity assays for monitoring HIV type 1 gag-specific T cell responses in Ad5 HIV Type 1 gag vaccinated human subjects

Currently, there are numerous candidate HIV vaccines aimed at inducing T-cell mediated immune responses against HIV. To assess the immunogenicity of such vaccines, a reliable T cell assay must be utilized and typically one of the following assays is chosen for this purpose: bulk culture CTL, MHC I tetramer staining, IFN-gamma ELISPOT, or IFN-gamma intracellular cytokine staining. In this paper we report a comparison of the T cell responses detected by each assay in a large cohort of healthy normal volunteers vaccinated with adenovirus serotype 5 expressing HIV gag. Using stringently validated formats of each of these assays and pools of overlapping HIV gag peptides, we demonstrate that there is a high degree of correlation between all four of the common T cell assays, but inherent differences in the sensitivity of each assay to detect responders. In this study, the ELISPOT assay is shown to have the greatest sensitivity in detecting vaccine responses, while the ICS assay, although less sensitive, has the advantage of providing additional information on the phenotype of the responding cells.

Evaluation of the interlaboratory concordance in quantification of human immunodeficiency virus-specific T cells with a gamma interferon enzyme-linked immunospot assay

The gamma interferon (IFN-gamma) enzyme-linked immunospot (ELISPOT) assay is a reference method for the ex vivo monitoring of antigen-specific T cells and a primary tool for assessing clinical trials of human immunodeficiency virus (HIV) or cancer vaccines. Four experienced laboratories in Paris compared their results with this method by exchanging frozen blood samples from eight HIV-seronegative and eight HIV-seropositive subjects. Each laboratory measured the IFN-gamma-producing cells specific for HIV, Epstein-Barr virus, cytomegalovirus, and influenza using the same set of peptides and the same ELISPOT reader but its own ELISPOT technique. The cutoff values for positive responses (50 or 100 spot-forming cells/10(6) peripheral blood mononuclear cells over background) were consistent with the binomial statistic criterion. The global qualitative concordance, as assessed by the kappa index, ranged from 0.38 to 0.92, that is, moderate to excellent, and was better for non-HIV 9-mer peptide pools than for HIV 15-mer peptide pools. The interlaboratory coefficient of variation for the frequency of virus-specific T cells was 18.7% (data are expressed on a log scale). Clustering analysis of HIV-positive subjects showed qualitative agreement for ELISPOT results from all four laboratories. Overall, the good interlaboratory qualitative concordance of IFN-gamma ELISPOT assays with only the peptide source and ELISPOT reader in common suggests that a qualitative comparison of interlaboratory findings is feasible. Nonetheless, a single set of standard operating procedures should be used in multicenter trials to improve standardization.

A phase II trial of vaccination with autologous, tumor-derived heat-shock protein peptide complexes Gp96, in combination with GM-CSF and interferon-alpha in metastatic melanoma patients

The aim of this study was to determine the immunogenicity and antitumor activity of autologous, tumor-derived heat shock protein gp96-peptide complex vaccine (HSPPC-96; Oncophage given with GM-CSF and IFN-alpha in pre-treated metastatic (AJCC stage IV) melanoma patients. Patients underwent surgical resection of metastatic lesions for HSPPC-96 production. HSPPC-96 was administered subcutaneously (s.c.) in four weekly intervals (first cycle). Patients with more available vaccine and absence of progressive disease received four additional injections in 2-week intervals (second cycle) or more. GM-CSF was given s.c. at the same site at days -1, 0 and +1, while IFN-alpha (3 MU) was administered s.c. at a different site at days +4 and +6. Antigen-specific anti-melanoma T and NK lymphocyte response was assessed by enzyme-linked immunospot assay on peripheral blood mononuclear cells obtained before and after vaccination. Thirty-eight patients were enrolled, 20 received at least four injections (one cycle) of HSPPC-96 and were considered assessable. Toxicity was mild and most treatment-related adverse events were local erythema and induration at the injection site. Patients receiving at least four injections of HSPPC-96 were considered evaluable for clinical response: of the 18 patients with measurable disease post surgery, 11 showed stable disease (SD). The ELISPOT assay revealed an increased class I HLA-restricted T and NK cell-mediated post-vaccination response in 5 out of 17 and 12 out of the 18 patients tested, respectively. Four of the five class I HLA-restricted T cell responses fall in the group of SD patients. Vaccination with autologous HSPPC-96 together with GM-CSF and IFN-alpha is feasible and accompanied by mild local and systemic toxicity. Both tumor-specific T cell-mediated and NK cell responses were generated in a proportion of patients. Clinical activity was limited to SD. However, both immunological and clinical responses were not improved as compared with those recorded in a previous study investigating HSPPC-96 monotherapy.

Dynamic evolution of antibody populations in a rhesus macaque infected with attenuated simian immunodeficiency virus identified by surface plasmon resonance

BACKGROUND

Increasing evidence suggests that an effective AIDS vaccine will need to elicit broadly neutralizing antibody responses. However, the mechanisms of antibody-mediated neutralization have not been defined. Previous studies from our lab have identified significant differences in the rates of antibody binding to trimeric SIV envelope proteins that correlate with neutralization sensitivity. Importantly, these results demonstrate differences in monoclonal antibody (MAb) binding to neutralization-sensitive and neutralization-resistant envelope proteins, suggesting that one mechanism for virus neutralization may be related to the stability of antibody binding. To date, little has been done to evaluate the binding properties of polyclonal serum antibodies elicited by SIV infection or vaccination.

METHODS

In the current study, we translate these findings with MAbs to study antibody binding properties of polyclonal serum antibody responses generated in rhesus macaques infected with attenuated SIV. Quantitative and qualitative binding properties of well-characterized longitudinal serum samples to trimeric, recombinant SIV gp140 envelope proteins were analyzed using surface plasmon resonance (SPR) technology (Biacore).

RESULTS

Results from these studies identified two antibody populations in most of the samples analyzed; one antibody population exhibited fast association/dissociation rates (unstable) while the other population demonstrated slower association/dissociation rates (stable). Over time, the percentage of the total binding response of each antibody population evolved, demonstrating a dynamic evolution of the antibody response that was consistent with the maturation of antibody responses defined using our standard panel of serological assays. However, the current studies provided a higher resolution analysis of polyclonal antibody binding properties, particularly with respect to the early time-points post-infection (PI), that is not possible with standard serological assays. More importantly, the increased stability of the antibody population with time PI corresponded with potent neutralization of homologous SIV in vitro.

CONCLUSIONS

These results suggest that the stability of the antibody-envelope interaction may be an important mechanism of serum antibody virus neutralization. In addition, measurements of the 'apparent' rates of association and dissociation may offer unique numerical descriptors to characterize the level of antibody maturation achieved by candidate vaccine strategies capable of eliciting broadly neutralizing antibody responses.

HLA class I mono-specific APCs and target cells: A method to standardise in vitro CD8+ T cell expansion and functional assays

The introduction of in vitro T cell expansion and assay methods that are robust and easy to use would be welcome in cancer vaccine and infectious disease research. By coating HLA class I--ve B cells with recombinant HLA class I peptide complexes, we are able to produce antigen presenting cells and target cells expressing a single defined antigen in the context of costimulatory and adhesion molecules. HLA class I mono-specific cells promoted the in vitro expansion of CMV epitope specific CD8+ T cells from 0.03% to 30.6% in 2 weeks, which was comparable to using peptide-loaded dendritic cells. The HLA class I mono-specific cells were also shown to promote in vitro antigen specific T cell function in assays based on measuring cytokine production and cytolytic activity. HLA class I mono-specific cells are simple to prepare, can be used with any recombinant HLA class I allele/peptide combination and should provide a useful system for in vitro T cell expansion and functional analysis.

Predicting tumor outcome following cancer vaccination by monitoring quantitative and qualitative CD8+ T cell parameters

Identification of reliable surrogate predictors for evaluation of cancer vaccine efficacy is a critical issue in immunotherapy. We analyzed quantitative and qualitative CD8+ T cell parameters in a large pool of BALB/c mice that were DNA-vaccinated against P1A self tumor-specific Ag. After immunization, mice were splenectomized and kept alive for a subsequent tumor challenge to correlate results of immune monitoring assays with tumor regression or progression in each individual animal, and to assess the prognostic value of the assays. The parameters tested were 1) percentage of in vivo vaccine-induced tumor-specific CD8+ T cells; 2) results of ELISPOT tests from fresh splenocytes; 3) percentage of tumor-specific CD8+ T cells in culture after in vitro restimulation; 4) in vitro increase of tumor-specific CD8+ T cell population expressed as fold of expansion; and 5) antitumor lytic activity of restimulated cultures. Except for the ELISPOT assay, each parameter tested was shown by univariate statistical analysis to correlate with tumor regression. However, multivariate analysis revealed that only in vitro percentage of Ag-specific CD8+ T cells was an independent prognostic factor that predicted tumor outcome. These findings should be considered in the design of new immune monitoring systems used in cancer immunotherapy studies.

Neutrophil granule proteins as targets of leukemia-specific immune responses

PURPOSE OF REVIEW

Recent progress in the identification of leukemia antigens has stimulated the development of vaccines to treat hematological malignancies. Here we review the identification and characterization of the myeloid leukemia-specific antigens proteinase 3 and neutrophil elastase found in the primary (azurophil) granule proteins of granulocytes and their precursors. A peptide 'PR1' derived from these proteins induces powerful HLA-A0201-restricted CD8 T-cell proliferation. PR1-specific T cells are cytotoxic to leukemia and myelodysplastic syndrome progenitors, and occur at low frequencies in normal individuals. Frequencies are higher in patients with myeloid leukemias, and highest in patients with chronic myeloid leukemia entering molecular remission after allogeneic stem cell transplantation.

RECENT FINDINGS

These observations, together with the known association of autoimmunity to proteinase 3 and neutrophil elastase in Wegener's granulomatosis, support the concept that there is a natural immunity to primary granule proteins which can be boosted to enhance immunity to leukemia. Preliminary reports indicate that PR1 peptide vaccination induces significant increases in PR1-specific cytotoxic T cells with rapid and durable remissions in some patients with advanced myeloid leukemias.

SUMMARY

These promising developments in antileukemia vaccines have stimulated research to optimize vaccine delivery and modify regulation of natural T-cell immunity to primary granule proteins to improve treatment of otherwise refractory myeloid leukemias and myelodysplastic syndrome.

Immunological monitoring of cancer vaccine therapy

Immunological treatment of malignant diseases in humans aiming at the induction and proliferation of antigen-specific T cells has made rapid progress in recent years. A growing number of tumour-associated antigens, potentially synergistic combinations with adjuvants, and various routes of application provide new opportunities for cancer vaccination. Therefore, a highly accurate assessment of vaccine-induced T cell responses is required. Three T cell assays (tetramers, intracellular cytokine flow cytometry and ELISPOT assay) have emerged as first-line methods for monitoring T cell induction during vaccination. These assays are relatively easy to perform, reliable, sensitive and allow an ex vivo T cell analysis at the single cell level. Although at this stage assays are not a defined surrogate marker for clinical efficacy, they already provide information concerning the immunological potency of a given vaccine. In particular, comparing immune responses under various treatment conditions will help to develop more clinically efficient tumour vaccination. Novel assays, such as CD107 staining, human leukocyte antigen/green fluorescent protein-antigen-presenting cells or microarrays, and assays determining functions, such as proliferation assays, are beginning to complement first-line monitoring assays.

Differences in HCV-specific T cell responses between chronic HCV infection and HIV/HCV co-infection

Hepatitis C virus (HCV)-specific CD4+ and CD8+ T cell responses were investigated using a panel of 728 overlapping peptides spanning the whole HCV genome in 47 HCV mono-infected and 26 HIV/HCV co-infected individuals using the IFN-gamma ELISPOT assay and flow cytometry. The frequency of HCV-specific T cell responses was similar (approximately 40%) in both groups, but the breadth of the T cell responses tended to be reduced in HIV/HCV co-infected individuals. Of interest, 23 new HCV-derived epitopes were identified, and CD4+ HCV-specific T cell responses were detected overall in a proportion similar to CD8+ T cell responses. A tendency towards a dominant CD8+ T cell response was associated with HIV/HCV co-infection. HCV-specific CD8+ T cells secreted both IL-2 and IFN-gamma, although a reduction in the percentage of IL-2/IFN-gamma-secreting cells was observed in HIV/HCV co-infected individuals. The increase in CD4+ T cell counts after antiretroviral therapy in HIV/HCV co-infected individuals was not associated with restoration of HCV-specific T cell responses. Altogether, these results provide new insights into the characterization of HCV-specific T cell responses in HCV mono-infected and HIV/HCV co-infected individuals.

Equine interferon gamma synthesis in lymphocytes after in vivo infection and in vitro stimulation with EHV-1

Equine cytotoxic T lymphocyte (CTL) responses to equine herpesvirus-1 (EHV-1) are well characterised but little is known about the cytokine response after infection or vaccination. EHV-1 is common in horses and infects lymphocytes in vivo. This virus was used as a model to measure the synthesis of interferon gamma (IFN-gamma) by equine peripheral blood mononuclear cells (PBMC) after in vivo infection and/or in vitro stimulation with EHV-1. Both flow cytometry and ELISPOT assays were used to quantify equine IFN-gamma using a mouse anti-bovine IFN-gamma monoclonal antibody (clone CC302; shown to cross-react with recombinant equine IFN-gamma) and a rabbit anti-canine IFN-gamma polyclonal antibody. The percentage of PBMC synthesising IFN-gamma after in vitro stimulation with EHV-1 increased with age. In yearlings infected experimentally with EHV-1, PBMC showed two peaks of IFN-gamma synthesis, 11 and 56 days after infection. The IFN-gamma synthesis was principally associated with CD8(+) cells. The patterns of IFN-gamma synthesis detected by intracellular IFN-gamma staining or ELISPOT were compared with CTL data and shown to be similar. These methods were also applied successfully to frozen samples of PBMC. Measurement of equine IFN-gamma using these simple techniques can now be applied to future studies on protective cellular immune responses following virus infection and/or vaccination of horses.

Homing in on the cellular immune response to HSV-2 in humans

PROBLEM

Genital herpes simplex infections are generally limited to epithelia and neurons. Vaccines have had activity in herpes simplex virus (HSV)-seronegative women only. Understanding how HSV-specific T cells traffic to infected sites may assist in vaccine design.

METHOD OF STUDY

Herpes simplex virus epitopes recognized by HSV-specific CD8 T cells were identified and used to make fluorescent human leukocyte antigen (HLA)-peptide tetramers. Molecules related to lymphocyte rolling adhesion were studied by flow cytometry and cell binding. HSV-specific CD4 T cells identified ex vivo by cytokine accumulation or activation marker expression, or detected in vitro by 5-(and-6)-carboxyfluorescein diacetate, succinimidyl ester (CFSE) dilution, were similarly investigated.

RESULTS

Herpes simplex virus-specific T cells are 10- to 100-fold more prevalent in lesional skin compared with blood and greatly enriched in lesions compared with normal skin. Diverse viral antigens are recognized by HSV-specific T cells. Functionally active E-selectin ligand, and cutaneous lymphocyte antigen (CLA), are expressed by circulating HSV-2-specific CD8 cells. CD4 cells display lower levels of CLA that are dramatically up-regulated upon re-stimulation with antigen.

CONCLUSIONS

Herpes simplex virus-2-specific CD8 and CD4 T cells differ in constitutive expression of skin homing molecules. Vaccines designed to induce proper homing are postulated to have increased efficacy.

A vaccinia-based elispot assay for detection of CD8+ T cells from HIV-1 infected children

HIV-specific CD8+ T lymphocytes participate in the control of viral replication in infected patients. These responses are of low intensity in young infants and are decreased by antiretroviral therapy. In the present study, we report on a recombinant Vaccinia virus (rVV)-based Elispot assay for the detection of HIV-specific CD8+ T cells immediately after isolation of peripheral blood mononuclear cells (PBMC). The rVV-based assay was highly sensitive; 48 out of 50 children had a positive response against the rVV encoding HIV Env-Gag-Pol antigen. Interferon-gamma was produced by CD8+ T cells, and CD14+/15+ cells were the main cell subset presenting antigens expressed by rVV. We observed that the cell input per well had a critical influence on the sensitivity of the assay. Results from the ex vivo Elispot assay correlated poorly with those of the 51Cr release assay performed after expansion of PBMC in vitro; thus, both assays gave information on different subsets and/or functions of the HIV-specific T cell response.

Ex Vivo Characterization of Multiepitopic Tumor-Specific CD8 T Cells in Patients with Chronic Myeloid Leukemia: Implications for Vaccine Development and Adoptive Cellular Immunotherapy

Identification of tumor-associated Ags is a prerequisite for vaccine-based and adoptive immune therapies. Some tumor-associated Ags elicit specific CD8 T cells in patients with chronic myeloid leukemia (CML). Here, we characterized ex vivo responses of CD8 T cells from CML patients to extrajunction bcr-abl peptides and telomerase 540-548 hTert, PR1, and WT1 peptides. CML-specific CD8 T cells were present in most treated patients and were usually multiepitopic: WT1, hTert, PR1, and bcr74 tetramer(+) cells were detected in 85, 82, 67, and 61% of patients, respectively. The breadth and magnitude of these responses did not differ significantly according to treatment or disease status. CML-specific tetramer(+) CD8 T cells had a predominantly memory phenotype, an intermediate perforin content, and low intracellular IFN-gamma accumulation in the presence of the relevant peptide. However, in short-term culture with HLA-matched leukemia cells, the patients' memory T cells were specifically reactivated to become IFN-gamma-producing effector cells, suggesting that CD8 T cell precursors with lytic potential are present in vivo and can be activated by appropriate stimulation. In conclusion, this study shows that multiepitopic tumor-specific CD8 T cell responses occur naturally in most CML patients, opening the way to new strategies for enhancing anti-CML immunity, in particular in patients with minimal residual disease.

The duration of in vitro stimulation with recall antigens determines the subset distribution of interferon-γ-producing lymphoid cells: A kinetic analysis using the Interferon-γ Secretion Assay™

Analyses of cellular immune responses during natural infections and following vaccination with established or candidate vaccines are becoming increasingly important and so are the research tools used to achieve this goal. During a recent evaluation of the analytical performance characteristics of one of these techniques, the interferon-gamma secretion assay, we noticed that following overnight incubation of PBMC with recall antigens (varicella-zoster antigen, Candida albicans antigen or hepatitis B surface antigen) NK cells are frequently the most predominant interferon-gamma-producing cell population. In this study, we monitored the subset distribution of interferon-gamma-producing cells following more extended in vitro culture periods and found that, irrespective of the antigen applied, the contribution of NK cells decreased whereas the importance of T cells and NKT cells rose. Analysis of the subset distribution showed that HBsAg stimulated CD4 cells predominantly whereas Candida antigen and varicella-zoster antigen were better inducers of CD8 responses. No correlation was found between the kinetics of total number of interferon-gamma-producing cells and the changes of concentrations of interferon-gamma in the culture supernatants. Interferon-gamma levels in culture supernatants correlated strongly with the kinetics of T(H) lymphocytes (CD3+, CD4+), CTL (CD3+, CD8+), and NKT cells (CD3+, CD56+). These observations lead us to conclude that methods that enumerate cytokine-secreting cells without determining their phenotype should be interpreted with great care and that an 'elispot' should not be directly considered as the footprint of a T lymphocyte.