Autologous dendritic cells pulsed with allogeneic tumour cell lysate induce tumour-reactive T-cell responses in patients with pancreatic cancer: A phase I study

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is notorious for its poor prognosis even after curative resection. Responses to immunotherapy are rare and related to inadequate T-cell priming. We previously demonstrated the potency of allogeneic lysate-dendritic cell (DC) vaccination in a preclinical model. Here we translate this concept to patients.

METHODS

In this phase I study, patients with resected PDAC were included when they demonstrated no radiologic signs of recurrence after standard-of-care treatment. Allogeneic tumour lysate-loaded autologous monocyte-derived DCs were injected at weeks 0, 2, 4 and at months 3 and 6. Objectives are feasibility, safety and immunogenicity of allogeneic tumour-DCs. The presence of tumour antigens shared between the vaccine and patient tumours was investigated. Immunological analyses were performed on peripheral blood, skin and tumour.

RESULTS

Ten patients were included. DC production and administration were successful. All patients experienced a grade 1 injection-site and infusion-related reaction. Two patients experienced a grade 2 fever and 1 patient experienced a grade 3 dyspnoea. No vaccine-related serious adverse events were observed. Shared tumour antigens were found between the vaccine and patient tumours. All evaluated patients displayed a vaccine-induced response indicated by increased frequencies of Ki67+ and activated PD-1+ circulating T-cells. In addition, treatment-induced T-cell reactivity to autologous tumour of study patients was detected. Seven out of ten patients have not experienced disease recurrence or progression at a median follow-up of 25 months (15-32 months).

CONCLUSION

Allogeneic tumour lysate-DC treatment is feasible, safe and induces immune reactivity to PDAC expressed antigens.

Melanoma cells can be eliminated by sialylated CD43 × CD3 bispecific T cell engager formats in vitro and in vivo

Targeted cancer therapy with monoclonal antibodies has proven successful for different cancer types but is limited by the availability of suitable antibody targets. CD43s, a unique sialylated form of CD43 expressed by hematologic malignancies, is a recently identified target and antibodies interacting with CD43s may have therapeutic potential against acute myeloid leukemia (AML) and myelodysplastic syndrome. CD43s is recognized by the human antibody AT1413, that was derived from a high-risk AML patient who successfully cleared leukemia after allogeneic stem cell transplantation. Here we observed that AT1413 binds also to certain non-hematopoietic tumor cells, particularly melanoma and breast cancer. AT1413 immune precipitated CD43s from melanoma cells confirming that it recognizes the same target on melanoma as on AML. AT1413 induced antibody-dependent cellular cytotoxicity against short-term cultured patient-derived melanoma samples. However, AT1413 was unable to affect the growth of melanoma cells in vivo. To increase the efficacy of AT1413 as a therapeutic antibody, we generated two different formats of bispecific T-cell engaging antibodies (TCEs): one binding bivalently (bTCE) and the other monovalently (knob-in-hole; KiH) to both CD43s and CD3ε. In vitro, these TCEs redirected T-cell cytotoxicity against melanoma cells with differences in potencies. To investigate their effects in vivo, we grafted mice that harbor a human immune system with the melanoma cell line A375. Treatment with both AT1413 bTCE and AT1413 KiH significantly reduced tumor outgrowth in these mice. These data indicate a broad therapeutic potential of AT1413 that includes AML and CD43s-expressing solid tumors that originate from CD43-negative tissues.

Tbet-positive regulatory T cells accumulate in oropharyngeal cancers with ongoing tumor-specific type 1 T cell responses

Regulatory T cells (Tregs) may comprise different subsets allowing them to efficiently suppress different types of effector T cells. In this study, we show that high numbers of both conventional and Tbet co-expressing Foxp3^hi Tregs accumulate in human papilloma virus (HPV)-driven oropharyngeal squamous cell carcinoma (OPSCC). The infiltration of Tbet+ Foxp3+ Tregs was strongly correlated with a concomitant tumor-specific and conventional type 1-oriented intratumoral T cell infiltrate. Both conventional CD4+CD25+CD127–Foxp3^hi Tregs and their Tbet^hi counterparts exhibited an activated phenotype, co-expressed high levels of CTLA4 and Helios and exhibited a maximally demethylated Foxp3 gene locus TSDR, indicating their full capacity to impede a type 1 effector T cell response. Interestingly, while the prognostic value of conventional Tregs was neutral, a high intratumoral frequency of Tbet+ Tregs was associated with prolonged disease-specific survival, most likely because their presence reflected high numbers of effector T cells. The presence of these Tbet+ Tregs may in part explain why a dense type 1-oriented immune infiltrate in OPSCC is not enough to fully control tumor growth.

The blood mMDSC to DC ratio is a sensitive and easy to assess independent predictive factor for epithelial ovarian cancer survival

Epithelial ovarian cancer (EOC) may cause abnormal blood levels of leukocytes. This paraneoplastic manifestation is associated with a worse response to therapy and shorter survival. To understand the complexity and nature of these leukocytes, we dissected the different populations of myeloid cells and analyzed their relation to clinical outcome. Therefore, baseline blood samples of 36 EOC patients treated either with carboplatin/doxorubucin or with gemcitabine were analyzed for different subsets of monocytes/macrophages, myeloid derived suppressor cells (MDSC) and dendritic cells (DC) using multiparameter flow cytometry as well as functional assays for myeloid cell mediated suppression of antigen-specific T cell reactivity. Healthy donor blood served as control. EOC patients displayed an increase in monocytes/macrophages, monocytic MDSC (mMDSC) and CD33-CD11b+CD14-CD15- double-negative MDSC (CD33- dnMDSC) and a decrease in the frequency of DC, across all EOC subtypes. A low frequency of DC and high frequencies of monocytes/macrophages and mMDSC, but not CD33- dnMDSC, were associated with poor overall survival. Patient's monocytes/macrophages and mMDSC, but not CD33- dnMDSC, were shown to suppress T cell reactivity in vitro. The mMDSC and DC frequencies were not altered upon treatment. Importantly, the mMDSC to DC ratio was the strongest independent, highly sensitive and specific, predictive factor for survival. This was irrespective of the type of chemotherapy or disease stage and outperformed classical parameters as WHO status or time from last chemotherapy. Thus, the baseline blood mMDSC to DC ratio is a robust, independent and easy to analyze predictive factor for EOC survival, and may assist patient selection for immunotherapy.

The presence of human papillomavirus (HPV) in placenta and/or cord blood might result in Th2 polarization

The purpose of this study was to evaluate if an early exposure to human papillomavirus (HPV) during the prenatal period or infancy could result in HPV16-specific T helper (Th) responses resembling those of adults with HPV-induced lesions. We tested HPV16-specific cell-mediated immunity (CMI) in children born with HPV-positive umbilical cord blood and/or placenta or having persistent oral HPV infection and in constantly oral HPV-negative controls. Peripheral blood mononuclear cells from 33 children from the Finnish HPV Family Study cohort (mean age 14.7 years) were stimulated with peptide pools covering the amino acid sequence of the HPV16 E2, E6, and E7 proteins. Lymphocyte proliferation, secretion of cytokines (IFN-γ, TNF-α, IL-2, IL-4, IL-5, IL-10, IL-17A), and the frequency of Foxp3+ regulatory T-cells were determined in relation to the HPV DNA status during a 14-year follow-up. 73.6% of cases and 85.7% of controls responded against HPV16 E2, while reactivity against E6 was found in 10.5 and 35.7%, respectively. The proliferative response against E6 and E7 was more frequent in controls than in cases (p = 0.047). No HPV16-specific CMI response or antibodies were detected in two children with persistent oral HPV16. The profiles of induced cytokines indicated higher levels of IL-5, IL-10, and IL-17A in children with HPV DNA in placenta and/or cord blood than in other children. HPV16-specific CMI is common in HPV DNA-negative children. The cytokine profile in children infected with HPV16 during early life suggests that the viral dose and/or specific environment created by the placenta may have significant impact on the type of HPV-specific immunity.

The identification of patients at high risk for recurrent disease after treatment for early-stage cervical cancer

OBJECTIVE

To investigate prognostic factors in patients with recurrent cervical cancer after treatment of early-stage disease in order to identify high-risk patients who might benefit from alternative treatment strategies.

STUDY DESIGN

The authors retrospectively analyzed clinical and pathology data from 130 recurrent cervical cancer patients after surgical treatment for early-stage disease. Patients were compared with a recurrence-free control group matched for age, FIGO Stage, and adjuvant treatment. Univariate and multivariate Cox regression analyses were performed to determine prognostic factors for recurrence and survival.

RESULTS

Of 889 patients, 130 (14.6%) developed recurrent disease after primary treatment for early-stage cervical cancer. Local or loco-regional metastasis was observed in 45%, distant metastasis in 31%, and combined pelvic and distant metastasis in 24%. Median survival after recurrence was 12 months (range 1-107 months). Median five-year survival was 96% in the control group and 29% in the recurrence group. Tumor size ≥ 40 mm and lymph node metastasis were independent unfavorable prognostic factors for overall survival (OS) and disease-free survival (DFS). The number of positive lymph nodes (≥ one) and bilateral occurrence of pelvic lymph node metastasis were associated with adverse clinical outcome.

CONCLUSIONS

Tumor size ≥ 40 mm and lymph node metastasis were independent unfavorable prognostic factors in surgically treated, early-stage cervical cancer patients. The combination of these factors was particularly associated with recurrence. Future trials should focus on the role of alternative adjuvant treatment strategies in patients at high risk of recurrent disease (e.g., by chemotherapy, immunotherapy or combinations thereof).

Impact of (chemo)radiotherapy on immune cell composition and function in cervical cancer patients

New treatments based on combinations of standard therapeutic modalities and immunotherapy are of potential use, but require a profound understanding of immune modulatory properties of standard therapies. Here, the impact of standard (chemo)radiotherapy on the immune system of cervical cancer patients was evaluated. Thirty patients with cervical cancer were treated with external beam radiation therapy (EBRT), using conventional three-dimensional or intensity modulated radiation therapy without constraints for bone marrow sparing. Serial blood sampling for immunomonitoring was performed before, midway and at 3, 6 and 9 weeks after EBRT to analyze the composition of lymphocyte and myeloid-cell populations, the expression of co-stimulatory molecules, T-cell reactivity and antigen presenting cell (APC) function. Therapy significantly decreased the absolute numbers of circulating leukocytes and lymphocytes. Furthermore, the capacity of the remaining T cells to respond to antigenic or mitogenic stimulation was impaired. During treatment the frequency of both CD4⁺ and CD8⁺ T cells dropped and CD4⁺ T cells displayed an increased expression of programmed cell death-1 (PD-1). In vitro blocking of PD-1 successfully increased T-cell reactivity in all five samples isolated before radiotherapy but was less successful in restoring reactivity in samples isolated at later time points. Moreover, (chemo)radiotherapy was associated with an increase in both circulating monocytes and myeloid-derived suppressor cells (MDSCs) and an impaired capacity of APCs to stimulate allogeneic T cells. T-cell reactivity was slowly restored at 6–9 weeks after cessation of therapy. We conclude that conventional (chemo)radiotherapy profoundly suppresses the immune system in cervical cancer patients, and may restrict its combination with immunotherapy.

A phase I trial combining carboplatin/doxorubicin with tocilizumab, an anti-IL-6R monoclonal antibody, and interferon-α2b in patients with recurrent epithelial ovarian cancer

BACKGROUND

The immune system is important in epithelial ovarian cancer (EOC). Interleukin-6 is associated with chemoresistance and an immune-suppressive tumor microenvironment. We investigated whether a combination of chemotherapeutics, blockade of interleukin 6 (IL-6) receptor (IL-6R; tocilizumab), and immune enhancer interferon-α (Peg-Intron) is feasible, safe, and able to enhance immunity in patients with recurrent EOC.

PATIENTS AND METHODS

In this dose-escalation study, patients received tocilizumab 1, 2, 4, or 8 mg/kg i.v., q4 weeks during the first three cycles of carboplatin (AUC5) plus doxorubicin [pegylated liposomal doxorubicin (PLD) 30 mg/m(2) or doxorubicin 50 mg/m(2) i.v., day 1, q4 weeks, for six cycles]. At the highest tocilizumab dose (8 mg/kg), Peg-Intron (1 µg/kg s.c.) was added. Peripheral blood mononuclear cells were collected for immunomonitoring at baseline, after three and six cycles. Dose-limiting toxicity (DLT), CA-125, and radiologic response were evaluated.

RESULTS

In the 23 patients enrolled, no DLT was established. The most frequent grade 3/4 adverse events (CTCAE v4.03) were neutropenia (23%), febrile neutropenia (19%), and ileus (19%). No treatment-related deaths occurred. Using CT evaluation, 11 of 21 assessable patients responded, 6 had stable disease and 3 progressive disease. Patients receiving highest dose tocilizumab showed a functional blockade of IL-6R with increased levels of serum IL-6 (P = 0.02) and soluble IL-6R (P = 0.008). Consequently, immune cells displayed decreased levels of pSTAT3, myeloid cells produced more IL-12 and IL-1β while T cells were more activated and secreted higher amounts of effector cytokines interferon-γ and tumor necrosis factor-α. An increase in sIL-6R was potentially associated with a survival benefit (P = 0.03).

CONCLUSIONS

Functional IL-6R blocking is feasible and safe in EOC patients treated with carboplatin/(pegylated liposomal)doxorubicin, using 8 mg/kg tocilizumab. This combination is recommended for phase II evaluation based on immune parameters.

CLINICAL TRIAL REGISTER

NCT01637532.

Interleukin-6 receptor and its ligand interleukin-6 are opposite markers for survival and infiltration with mature myeloid cells in ovarian cancer

An increased level of interleukin-6 (IL-6) in epithelial ovarian cancer (EOC) is correlated with a worse prognosis. IL-6 stimulates tumor-growth and inflammation. We investigated the intricate interaction between the IL-6 signaling pathway and tumor-infiltrating myeloid cells (TIMs) to determine their prognostic impact in EOC. 160 EOC samples were analyzed for the expression of IL-6, its receptor (IL-6R) and downstream signaling via pSTAT3 by immunohistochemistry. Triple color immunofluorescence confocal microscopy was used to identify myeloid cell populations by CD14, CD33, and CD163. The relationship between these markers, tumor-infiltrating immune cells, clinical-pathological characteristics and survival was investigated. EOC displayed a dense infiltration with myeloid cells, in particular of the CD163⁺ type. The distribution pattern of all myeloid subtypes was comparable among the different histological subtypes. Analysis of the tumor cells revealed a high expression of IL-6R in 15% and of IL-6 in 23% of patients. Interestingly, tumors expressing IL-6 or IL-6R formed two different groups. Tumors with a high expression of IL-6R displayed low mature myeloid cell infiltration and a longer disease-specific survival (DSS), especially in late stage tumors. High expression of IL-6R was an independent prognostic factor for survival by multivariate analyses (hazard ratio = 0.474, p = 0.011). In contrast, tumors with high epithelial IL-6 expression displayed a dense infiltration of mature myeloid cells and were correlated with a shorter DSS. Furthermore, in densely CD8⁺ T-cell infiltrated tumors, the ratio between these lymphoid cells and CD163⁺ myeloid cells was predictive for survival. Thus, IL-6 and IL-6R are opposite markers for myeloid cell infiltration and survival.

Alterations in classical and nonclassical HLA expression in recurrent and progressive HPV-induced usual vulvar intraepithelial neoplasia and implications for immunotherapy

Immunotherapy of usual vulvar intraepithelial neoplasia (uVIN) is promising; however, many patients still fail to show clinical responses, which could be explained by an immune escape through alterations in human leukocyte antigen (HLA) expression. Therefore, we analyzed a cohort of patients with a primary (n = 43) and subsequent recurrent uVIN lesion (n = 20), vaccine-treated uVIN patients (n = 12), patients with human papillomavirus (HPV)-induced vulvar carcinoma (n = 21) and healthy controls (n = 26) for the expression of classical HLA-class I/II and nonclassical HLA-E/-G and MHC class I chain-related molecule A (MICA). HLA-class I was downregulated in 70% of uVIN patients, including patients with a clinical response to immunotherapy. Downregulation of HLA-class I is probably reversible, as only 15% of the uVIN cases displayed loss of heterozygosity (LOH) and HLA-class I could be upregulated in uVIN keratinocyte cultures by interferon γ. HLA-class I downregulation is more frequently associated with LOH in vulvar carcinomas (25-55.5%). HLA-class II was found to be focally expressed in 65% of uVIN patients. Of the nonclassical molecules, MICA was downregulated in 80% of uVIN whereas HLA-E and -G were expressed in a minority of cases. Their expression was more prominent in vulvar carcinoma. No differences were found between the alterations observed in paired primary and recurrent uVIN. Importantly, downregulation of HLA-B/C in primary uVIN lesions was associated with the development of recurrences and progression to cancer. We conclude that downregulation of HLA is frequently observed in premalignant HPV-induced lesions, including clinical responders to immunotherapy, and is associated with worse clinical outcome. However, in the majority of cases downregulation may still be reversible.

Tumor-infiltrating CD14-positive myeloid cells and CD8-positive T-cells prolong survival in patients with cervical carcinoma

One of the hallmarks of cancer is the influx of myeloid cells. In our study, we investigated the constitution of tumor-infiltrating myeloid cells and their relationship to other tumor-infiltrating immune cells, tumor characteristics and the disease-specific survival of patients with cervical cancer (CxCa). Triple-color immunofluorescence confocal microscopy was used to locate, identify and quantify macrophages (CD14), their maturation status (CD33) and their polarization (CD163) in a cohort of 86 patients with cervical carcinoma. Quantification of the numbers of myeloid cells revealed that a strong intraepithelial infiltration of CD14+ cells, and more specifically the population of CD14+CD33-CD163- matured M1 macrophages, is associated with a large influx of intraepithelial T lymphocytes (p = 0.008), improved disease-specific survival (p = 0.007) and forms an independent prognostic factor for survival (p = 0.033). The intraepithelial CD8+ T-cell and regulatory T-cell (Treg) ratio also forms an independent prognostic factor (p = 0.010) and combination of these two factors reveals a further increased benefit in survival for patients whose tumor displays a dense infiltration with intraepithelial matured M1 macrophages and a high CD8 T-cell/Treg ratio, indicating that both populations of immune cells simultaneously improve survival. Subsequently, we made a heatmap including all known immune parameters for these patients, whereby we were able to identify different immune signatures in CxCa. These results indicate that reinforcement and activation of the intratumoral M1 macrophages may form an attractive immunotherapeutic option in CxCa.

CXCR7 expression is associated with disease-free and disease-specific survival in cervical cancer patients

BACKGROUND

The CXC chemokine receptor (CXCR)7 is involved in tumour development and metastases formation. The aim of the present study was to determine protein expression of CXCR7, its putative co-receptors epidermal growth factor receptor (EGFR) and CXCR4, its predominant ligand CXCL12, their co-dependency and their association with survival in cervical cancer patients.

METHODS

CXC chemokine receptor 7, EGFR, CXCR4 and CXCL12 expression were determined immunohistochemically in 103 paraffin-embedded, cervical cancers. Subsequently, associations with patient characteristics were assessed and survival analyses were performed.

RESULTS

CXC chemokine receptor 7 was expressed by 43% of tumour specimens, in a large majority of cases together with either EGFR or CXCR4 (double positive), or both (triple positive). The CXCR7 expression was associated with tumour size (P=0.013), lymph node metastasis (P=0.001) and EGFR expression (P=0.009). CXC chemokine receptor 7 was independently associated with disease-free survival (hazard ratio (HR)=4.3, 95% confidence intervals (CI) 1.7-11.0, P=0.002), and strongly associated with disease-specific survival (HR=3.9, 95% CI 1.5-10.2, P=0.005).

CONCLUSION

CXC chemokine receptor 7 expression predicts poor disease-free and disease-specific survival in cervical cancer patients, and might be a promising new therapeutic marker. In a large majority of cases, CXCR7 is co-expressed with CXCR4 and/or EGFR, supporting the hypothesis that these receptors assist in CXCR7 signal transduction.

Abstract CN01-03: Immunotherapy of established lesions caused by high-risk HPV

Therapeutic vaccination with a synthetic long peptide (SLP@) vaccine mediated the eradication of established human papillomavirus type 16 (HPV16)-positive tumors in mice and controlled wart growth and latent virus infection in rabbits persistently infected with cottontail rabbit papillomavirus. Subsequent phase I/II studies with an HPV16 SLP@ vaccine, consisting of 13 long peptides covering the HPV16 E6 and E7 antigens, in patients with advanced HPV16-positive cervical cancer, revealed that this vaccine was safe and highly immunogenic. The purpose of the current study was to test the clinical efficacy of this HPV16 SLP@ vaccine in HPV16-induced high-grade vulvar intraepithelial neoplasia (VIN3), a premalignant epithelial disorder, spontaneous regression of which occurs in less than 2% of patients and in which recurrence after standard treatment is high.

In a phase 2 trial, 20 women with VIN3 were vaccinated three times sc in the limbs with a mix of the HPV16 E6 and E7 synthetic long peptides formulated in Montanide ISA-51. The endpoints were objective clinical responses, defined as reduction of at least 50% in lesion size (partial response) or complete regressions, and HPV16-specific T-cell responses, determined before and after vaccination.

The vaccine was safe, as no side effects exceeding CTC grade 2 were observed. At 3 and 12 months after the last vaccination an objective response was observed in 12/20 (60%) and 15/19 (79%) patients respectively. Nine of them showed a complete and durable regression of the lesions at 12 months and at 24 months. The strength of the vaccine-induced HPV16-specific T-cell response was significantly higher in the group of patients with a complete regression of their lesions as compared to nonresponders.

This study shows that in women with VIN3 objective clinical responses can be achieved by therapeutic vaccination with synthetic long peptides that is able to induce effective HVP16-specific T-cell responses.

Literature:

1. Kenter GG, Welters MJ, Valentijn AR, Lowik MJ, Berends-van der Meer DM, Vloon AP, Essahsah F, Fathers LM, Drijfhout JW, Offringa R,Wafelman AR, Oostendorp J, Fleuren GJ, Burg van der SH, Melief CJ. Vaccination against Human Papillomavirus 16 oncoproteins for vulvar intraepithelial neoplasia. N Engl J Med. 2009 Nov 5;361(19):1838-47.

2. Melief CJ, van der Burg SH. Immunotherapy of established (pre)malignant disease by synthetic long peptide vaccines. Nat Rev Cancer. 2008 May;8(5):351-60.

Citation Information: Cancer Prev Res 2010;3(12 Suppl):CN01-03.

Minimal information about T cell assays: the process of reaching the community of T cell immunologists in cancer and beyond

Many assays to evaluate the nature, breadth, and quality of antigen-specific T cell responses are currently applied in human medicine. In most cases, assay-related protocols are developed on an individual laboratory basis, resulting in a large number of different protocols being applied worldwide. Together with the inherent complexity of cellular assays, this leads to unnecessary limitations in the ability to compare results generated across institutions. Over the past few years a number of critical assay parameters have been identified which influence test performance irrespective of protocol, material, and reagents used. Describing these critical factors as an integral part of any published report will both facilitate the comparison of data generated across institutions and lead to improvements in the assays themselves. To this end, the Minimal Information About T Cell Assays (MIATA) project was initiated. The objective of MIATA is to achieve a broad consensus on which T cell assay parameters should be reported in scientific publications and to propose a mechanism for reporting these in a systematic manner. To add maximum value for the scientific community, a step-wise, open, and field-spanning approach has been taken to achieve technical precision, user-friendliness, adequate incorporation of concerns, and high acceptance among peers. Here, we describe the past, present, and future perspectives of the MIATA project. We suggest that the approach taken can be generically applied to projects in which a broad consensus has to be reached among scientists working in fragmented fields, such as immunology. An additional objective of this undertaking is to engage the broader scientific community to comment on MIATA and to become an active participant in the project.

Response definition criteria for ELISPOT assays revisited

No consensus has been reached on how to determine if an immune response has been detected based on raw data from an ELISPOT assay. The goal of this paper is to enable investigators to understand and readily implement currently available methods for response determination. We describe empirical and statistical approaches, identifying the strengths and limitations of each approach to allow readers to rationally select and apply a scientifically sound method appropriate to their specific laboratory setting. Five representative approaches were applied to data sets from the CIMT Immunoguiding Program and the response detection and false positive rates were compared. Simulation studies were also performed to compare empirical and statistical approaches. Based on these, we recommend the use of a non-parametric statistical test. Further, we recommend that six medium control wells or four wells each for both medium control and experimental conditions be performed to increase the sensitivity in detecting a response, that replicates with large variation in spot counts be filtered out, and that positive responses arising from experimental spot counts below the estimated limit of detection be interpreted with caution. Moreover, a web-based user interface was developed to allow easy access to the recommended statistical methods. This interface allows the user to upload data from an ELISPOT assay and obtain an output file of the binary responses.

Performance of serum-supplemented and serum-free media in IFNgamma Elispot Assays for human T cells

The choice of serum for supplementation of media for T cell assays and in particular, Elispot has been a major challenge for assay performance, standardization, optimization, and reproducibility. The Assay Working Group of the Cancer Vaccine Consortium (CVC-CRI) has recently identified the choice of serum to be the leading cause for variability and suboptimal performance in large international Elispot proficiency panels. Therefore, a serum task force was initiated to compare the performance of commercially available serum-free media to laboratories' own medium/serum combinations. The objective of this project was to investigate whether a serum-free medium exists that performs as well as lab-own serum/media combinations with regard to antigen-specific responses and background reactivity in Elispot. In this way, a straightforward solution could be provided to address the serum challenge. Eleven laboratories tested peripheral blood mononuclear cells (PBMC) from four donors for their reactivity against two peptide pools, following their own Standard Operating Procedure (SOP). Each laboratory performed five simultaneous experiments with the same SOP, the only difference between the experiments was the medium used. The five media were lab-own serum-supplemented medium, AIM-V, CTL, Optmizer, and X-Vivo. The serum task force results demonstrate compellingly that serum-free media perform as well as qualified medium/serum combinations, independent of the applied SOP. Recovery and viability of cells are largely unaffected by serum-free conditions even after overnight resting. Furthermore, one serum-free medium was identified that appears to enhance antigen-specific IFNgamma-secretion.

Serum is not required for ex vivo IFN-gamma ELISPOT: a collaborative study of different protocols from the European CIMT Immunoguiding Program

The Cancer Immunotherapy Immunoguiding Program has conducted an IFN-γ ELISPOT proficiency panel to examine the influence of serum supplementation of test media on assay performance. Sixteen European laboratories analyzed the same PBMC samples using different locally established protocols. Participants generated two simultaneous data sets—one using medium supplemented with serum and one without serum. Performances of the two test conditions were compared by quantifying: (1) the number of viable cells, (2) background spot formation induced in the medium only control and (3) the ability to detect antigen-specific T cell responses. The study demonstrated that the number of viable cells recovered and the overall background spot production were not significantly different between the two conditions. Furthermore, overall laboratory performance was equivalent for the two test conditions; 11 out of 16 laboratories reported equal or greater detection rates using serum-free medium, while 5 laboratories reported decreased detections rates under serum-free conditions. These results show that good performance of the IFN-γ ELISPOT assay can be achieved under serum-free conditions. Optimization of the protocol for serum-free conditions should result in excellent detection rates and eliminate the requirement of serum batch and stability testing, allowing further harmonization of the assay.

Characterising the local immune responses in cervical intraepithelial neoplasia: a cross-sectional and longitudinal analysis

INTRODUCTION

Immunological competence influences the progression of cervical intraepithelial neoplasia (CIN) to invasive cancer. Information on the local immunological changes during the natural course of CIN is central for the development of new therapies.

OBJECTIVE

This study defines the populations of tissue-infiltrating immune cells in a cross-sectional cohort of different grades of CIN and also in a longitudinal cohort of regressing, persistent and progressing low-grade (LG)-CIN.

DESIGN

A cohort of 125 women with LG cytological atypia was recruited, of which 64/125 (51%) women with LG-CIN were followed prospectively for 1 year. Paraffin-embedded entry and exit cervical biopsies were used for immunohistochemistry analysis (CD4, CD8, CD56, FOXP3, CD1a and granzyme B).

RESULTS

At recruitment, 74/125 (59%), 39/125 (31%) and 12/125 (10%) women referred with LG smears had histologically proven LG-CIN, high-grade (HG) and normal biopsies, respectively. Seventeen of 64 (24.6%) women with LG-CIN progressed to HG-CIN within 1 year. In both LG-CIN and HG-CIN, the predominant intraepithelial cell population were cytotoxic T cells, while CD4+ and FOXP3+ T cells predominated the stromal compartment. Women with LG-CIN who later on regressed displayed a significantly higher number of cytotoxic (granzyme B+) cells in their entry samples. In addition, the ratio between CD8+ cells and granzyme B+ cells was close to 1, suggesting that all infiltrating CD8+ T cells were highly active. In contrast, this ratio was three-fold lower in women, in whom the lesions persisted or progressed.

CONCLUSIONS

This study suggests that the early infiltration of lesions by highly cytotoxic effector cells protects against progression.

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.

Therapeutic vaccination with papillomavirus E6 and E7 long peptides results in the control of both established virus-induced lesions and latently infected sites in a pre-clinical cottontail rabbit papillomavirus model

This study was performed to test the therapeutic efficacy of overlapping long E6 and E7 peptides, containing both CD4+ T-helper and CD8+ CTL epitopes, on CRPV-induced lesions, which is an appropriate pre-clinical model for HPV diseases, including recurrent respiratory papillomatosis (RRP). Therapeutic peptide vaccination was able to significantly control wart growth (p < 0.01) and abrogate latent CRPV infection (p = 0.0006) compared to controls. Vaccination was associated with a T(H)1 T cell response, as suggested by a strong DTH skin test, antigen-specific proliferation of PBMC and a minimal IgG antibody response. Thus, this study shows promise for treatment of RRP by vaccination with long peptides.

Dendritic cells in colorectal cancer correlate with other tumor-infiltrating immune cells

Dendritic cells (DCs) are the most efficient antigen-presenting cells and play a key role in a cellular antitumor immune response. In this study we investigated the exact localization of DCs within colorectal tumors and their relationship to tumor-infiltrating lymphocytes as well as clinical outcome of the patients. Primary tumor specimens of 104 patients with a diagnosis of colorectal cancer were identified retrospectively and analyzed with the dendritic cell markers S-100 protein and human leukocyte antigens (HLA) class II. The markers were individually combined with laminin as a second marker to facilitate the observation of the different tumor localizations. S-100 or HLA class II positive cells were found in the three different compartments of colorectal tumors: tumor epithelium, tumor stroma, and advancing tumor margin, but mainly present in tumor stroma and advancing tumor margin. S-100-positive tumor-infiltrating DCs in direct contact with tumor cells, i.e., in tumor epithelium, significantly correlated to the intraepithelial infiltration of CD4+ (p=0.02) and CD8+ (p=0.01) lymphocytes. High HLA class II+ cell infiltration in the tumor stroma correlated to a lower intraepithelial infiltration of CD8+ (p=0.02) lymphocytes. High intraepithelial infiltration of S-100-positive DCs suggested increased disease-free survival, but was not statistically significant, while high amounts of HLA class II+ cells in the tumor stroma correlated with an adverse survival outcome. Our results show that the infiltration of DCs in colorectal cancer, depending on both location and type of marker, is correlated with local immune interactions and patient prognosis, suggesting a central role for DCs in controlling local tumor immunity.

Interplay between human papillomaviruses and dendritic cells

The design of the human papillomavirus (HPV) infection cycle is tightly fitted to the differentiation program of its natural host, the keratinocyte. This has important consequences for the role of antigen-presenting cells in the priming of antiviral immunity. The confinement of HPV infection to epithelia puts the epithelial dendritic cell, the Langerhans cell (LC), in charge of the induction of T cell-dependent immunity. Because HPV-infected keratinocytes cannot reach the regional lymphoid organs, and HPV-infection of LCs does not result in viral gene expression, priming of antiviral T cells exclusively depends on cross-presentation of viral antigens by the LC. Sensitization of the immune system in the regional lymphoid organs elicits systemic anti-HPV immunity as well as intraepithelial immune surveillance by memory-type intraepithelial T cells and locally produced antibodies. The high rate of spontaneous rejections of high-risk HPV-infections and HPV-positive premalignant lesions indicates that in general the LC-driven antigen presentation machinery is capable of raising an effective immune defense against HPV. Epidemiological studies also reveal that a decrease in the vigilance of the immune system is readily exploited by HPV to escape immune destruction, resulting in persistent infections and development of HPV-positive cancers. In view of the inherent antigenicity of HPV, immune intervention strategies constitute a promising approach for both the prevention and the therapeutic treatment of HPV-induced diseases. Importantly, the mechanisms that govern the induction and effector phases of the intraepithelial immune surveillance against HPV must be taken into account when designing such strategies.

Enhancement of human papillomavirus (HPV) type 16 E6 and E7-specific T-cell immunity in healthy volunteers through vaccination with TA-CIN, an HPV16 L2E7E6 fusion protein vaccine

TA-CIN is a vaccine that comprises the human papillomavirus (HPV) type 16 L2, E6 and E7 as a single fusion protein. In a mouse model, TA-CIN effectively prevented outgrowth of HPV16-positive tumour cells. To assess the safety and immunogenicity of TA-CIN, a dose escalating (26, 128, 533 micro g), double blind and placebo-controlled phase I study was conducted in 40 healthy volunteers. TA-CIN was administered without adjuvant by intramuscular injection on weeks 0, 4 and 8. No serious adverse events of the vaccination were reported during the study. Both IgG antibodies and proliferative responses against TA-CIN were elicited at all three doses. More importantly, T-cell immunity against the HPV16 E6 and E7 oncoproteins was detected by IFN gamma ELISPOT in 8/11 evaluable subjects vaccinated with the 533 micro g dose.

Pre-clinical safety and efficacy of TA-CIN, a recombinant HPV16 L2E6E7 fusion protein vaccine, in homologous and heterologous prime-boost regimens

Human papillomavirus (HPV) E6 and E7 oncoproteins are attractive targets for T-cell-based immunotherapy of cervical intraepithelial neoplasia (CIN) and cancer. A newly designed vaccine, comprising the HPV16 L2, E6 and E7 as a single fusion protein (TA-CIN), was shown to elicit HPV16-specific CTL, T-helper cells and antibodies in a pre-clinical mouse model. These immune responses effectively prevented outgrowth of HPV16-positive tumour cells in a prophylactic setting as well as in a minimal residual disease setting. CTL immunity was optimally induced when TA-CIN was employed in heterologous prime-boost regimens in combination with TA-HPV, a clinical grade vaccinia-based vaccine. These data provide a scientific basis for the use of TA-CIN, alone or in combination with TA-HPV in future human trials.

Natural T-helper immunity against human papillomavirus type 16 (HPV16) E7-derived peptide epitopes in patients with HPV16-positive cervical lesions: identification of 3 human leukocyte antigen class II-restricted epitopes

Tumor-specific T-helper (Th) immunity was found to play a pivotal role in the natural and vaccine-induced immune defense against tumors. Since the majority of cervical cancers express human papillomavirus type 16 (HPV16) E7 oncoprotein, it is important to investigate the Th response against this target antigen in detail. By means of PBMC cultures from HLA-typed healthy donors, we identified the central part of HPV16 E7 (E7(41-72)) as the major immunogenic region within this antigen. Furthermore, we mapped 3 distinct Th epitopes within this region (DR15/E7(50-62), DR3/E7(43-77), DQ2/E7(35-50)). In a parallel approach, employing IFN-gamma ELISPOT analysis, we detected Th immunity against HPV16 E7 in subjects with HPV16+ lesions. Several of these responses matched with the 3 Th epitopes defined in our study. A number of other HPV16+ subjects did not display any E7-specific type 1 cytokine-producing T-cell immunity, indicating failure of the immune response. Our combined data argue for more extensive as well as longitudinal analysis of HPV16-specific T-cell immunity using the ELISPOT assay described, as well as for HPV-specific vaccination of individuals with HPV+ lesions.

Identification of three non-VNTR MUC1-derived HLA-A*0201-restricted T-cell epitopes that induce protective anti-tumor immunity in HLA-A2/K(b)-transgenic mice

The human epithelial mucin MUC1 is over-expressed in more than 90% of carcinomas of the breast, ovary, and pancreas as well as in some other tumours, making it a potential target for tumour immunotherapy. We have identified several MUC1-derived peptides mapping outside the variable number tandem repeat region that comply with the peptide-binding motif for HLA-A*0201 and that become processed into stable major histocompatibility complex-peptide complexes as assessed by in vitro assays. In A2/K(b) transgenic mice, 3 peptides, namely MUC(79-87) (TLAPATEPA), MUC(167-175) (ALGSTAPPV) and MUC(264-272) (FLSFHISNL) elicit peptide-specific cytotoxic T lymphocyte (CTL) immunity, which protects these mice against a challenge with MUC1, A2/K(b)-expressing tumour cells. These peptides therefore represent naturally processed MUC1-derived CTL epitopes that could be used as components in peptide-based vaccines and for the analysis of anti-MUC1 CTL responses in A*0201-positive patients with MUC1-expressing tumours.

Long lasting p53-specific T cell memory responses in the absence of anti-p53 antibodies in patients with resected primary colorectal cancer

Colorectal carcinoma is commonly associated with mutation and overexpression of p53, making this antigen a potential target for immune intervention. We analyzed humoral and proliferative immunity against p53 in the blood of patients with resected primary colorectal cancer. The majority of these patients displayed anti-p53 T helper (Th) immunity in the absence of measurable p53 specific antibody levels. The Th responses were long-lasting since they could be detected up to several years after resection of the primary tumor. In a number of cases the Th responses were highly sensitive, reflected by the recognition of naturally processed p53 protein. Our data argue that boosting of these responses in patients with minimal residual disease through p53-specific vaccination, may be employed for improving the chance of disease-free survival of these patients.

Design and evaluation of antigen-specific vaccination strategies against cancer

After studies in preclinical mouse models, the efficacy and safety of tumor-specific vaccination strategies is currently being evaluated in cancer patients. The first wave of clinical trials has shown that in general such vaccination strategies are safe. However examples of clinical responses, especially in conjunction with vaccine-induced immune responses, are still scarce. The fact that most trials have so far been performed with end-stage cancer patients can largely account for this deficit. Greater efficacy of anticancer vaccines is expected in patients with less-progressed disease. In addition, the detection of both natural and vaccine-induced T cell immunity needs further improvement.

p53: a potential target antigen for immunotherapy of cancer

Approximately 50% of all human malignancies exhibit mutation and aberrant expression of p53, making this protein an interesting candidate target for immunotherapy of cancer. Mutations in p53 are highly diverse. Therefore, targeting of determinants within the wild-type p53 sequence appears most practical. Despite the fact that p53 is ubiquitously expressed, adoptive immunotherapy of tumor-bearing mice with p53-specific cytotoxic T lymphocytes (CTL) results in eradication of p53-overexpressing tumors in the absence of immunopathological damage to normal tissues. These CTL also eliminate tumors that do not show greatly enhanced expression of p53, indicating that the sensitivity of these tumors for p53-specific CTL is determined by the efficiency by which p53-derived peptides are processed into class I MHC, rather than by the steady state levels of p53. Of note, although p53-specific CTL can readily be isolated from p53-/- mice, tolerance for this self antigen may prevent induction of similarly effective CTL in p53+/+ subjects. The T helper (Th) branch of the p53-specific immune response does not seem to be profoundly affected by tolerance. In addition, more and more evidence is obtained for the pivotal role of tumor-specific Th cells in the induction and effector phases of the antitumor response, also against tumors that lack class II MHC expression. The efficacy of Th cells, specific for a recently identified class II MHC-restricted p53 peptide, against p53-overexpressing tumors is currently being investigated. In addition, natural and induced Th responses are analyzed both in a murine tumor model and in a phase I clinical trial involving p53-specific vaccination of colon cancer patients.

Identification of a conserved universal Th epitope in HIV-1 reverse transcriptase that is processed and presented to HIV-specific CD4+ T cells by at least four unrelated HLA-DR molecules

CD4+ Th cells play an important role in the induction and maintenance of specific T cell immunity. Indications for a protective role of CD4+ T cells against HIV-1 infection were found in subjects who were able to control HIV-1 viremia as well as in highly HIV-1-exposed, yet seronegative, individuals. This study describes the identification of an HIV-1-specific Th epitope that exhibits high affinity binding as well as high immunogenicity in the context of at least four different HLA-DR molecules that together cover 50-60% of the Caucasian, Oriental, and Negroid populations. This HIV-1 reverse transcriptase-derived peptide (RT171-190) is highly conserved among different HIV-1 isolates. Importantly, stimulation of PBL cultures from HIV-1 seronegative donors with this peptide resulted in Thl-type lymphocytes capable of efficient recognition of HIV-1-pulsed APCs. Taken together, these data indicate that peptide RT171-190 constitutes an attractive component of vaccines aiming at induction or enhancement of HIV-1-specific T cell immunity.

Characterization of HLA-B57-restricted human immunodeficiency virus type 1 Gag- and RT-specific cytotoxic T lymphocyte responses

HLA-B57 has been shown to be strongly associated with slow disease progression in human immunodeficiency virus type 1 (HIV-1)-infected patients from the Amsterdam Cohort. Since HIV-1-specific CTL can control and eliminate virus-infected cells, we sought to characterize the dominant HLA-B57-restricted CTL responses at the epitope level. It was found that HLA-B57-restricted CTL responses were targeted at multiple proteins of HIV-1, with CTL specific for Gag and RT being the most pronounced. Gag-specific CTL recognized peptides ISPRTLNAW (aa 147-155) and STLQEQIGW (aa 241-249), which had previously been reported as HLA-B57-restricted. The RT-specific CTL response in one long-term survivor studied in great detail persisted for > 10 years and was dominated by HLA-B57-restricted CTL that recognized the newly defined epitope IVLPEKDSW (RT(LAI), aa 244-252). This epitope could be recognized in the context of both HLA-B*5701 and HLA-B*5801. Interestingly, three epitope variants of IVLPEKDSW were observed, which coincided with the strongest detectable CTL response to RT. One variant (T2E7) was not recognized by IVLPEKDSW-specific CTL despite the fact that this variant bound to HLA-B*5701 with a similar affinity as the index peptide. Finally, only viruses which contained the epitope index sequence were obtained suggesting efficient virus control by CTL. In conclusion, we report the characterization of dominant HIV-1 Gag- and RT-derived, HLA-B57-restricted CTL epitopes which are associated with longer time to AIDS. Further characterization of CTL responses restricted by HLA-B57 and other protective HLA alleles may contribute to the development of effective AIDS vaccines.

Targeting of cytotoxic T cells against leukemic B cells by bispecific antibody (aCD3 x aCD19) does not distract the T cell from its primary target

Bispecific Abs (BsAb) represent a novel format of immunotherapy, recognizing immune effector cells (e.g., T cells), on the one hand, and target cells (e.g., tumor cells), on the other hand. To be successful, cross-linking of the two cell types is necessary for effector cell activation and subsequent killing of the malignant target cells. We asked the question, whether CTL that were incubated with the BsAb aCD3 x aCD19 and malignant B cells and activated to kill the malignant B cells were still able to eliminate their natural target cells (e.g., virus-infected autologous body cells). To test this, HLA-A*0201-restricted, influenza-specific CTL were incubated with BsAb- and HLA-A*0201-positive B lymphoid tumor cells in combination with HLA-A*0201-positive, virus-infected non-B lymphoid cells as natural target cells. The results showed that even in the presence of BsAb and high amounts of tumor B cells, CTL were still capable of eliminating the virus-infected non-B lymphoid target cells; actually, CTL recognized and eliminated the homologous original target cells preferentially.

Targeting of cytotoxic T cells against leukemic B cells by bispecific antibody (aCD3 x aCD19) does not distract the T cell from its primary target

Bispecific Abs (BsAb) represent a novel format of immunotherapy, recognizing immune effector cells (e.g., T cells), on the one hand, and target cells (e.g., tumor cells), on the other hand. To be successful, cross-linking of the two cell types is necessary for effector cell activation and subsequent killing of the malignant target cells. We asked the question, whether CTL that were incubated with the BsAb aCD3 x aCD19 and malignant B cells and activated to kill the malignant B cells were still able to eliminate their natural target cells (e.g., virus-infected autologous body cells). To test this, HLA-A*0201-restricted, influenza-specific CTL were incubated with BsAb- and HLA-A*0201-positive B lymphoid tumor cells in combination with HLA-A*0201-positive, virus-infected non-B lymphoid cells as natural target cells. The results showed that even in the presence of BsAb and high amounts of tumor B cells, CTL were still capable of eliminating the virus-infected non-B lymphoid target cells; actually, CTL recognized and eliminated the homologous original target cells preferentially.

HIV-1 reverse transcriptase-specific CTL against conserved epitopes do not protect against progression to AIDS

A small group of HIV-1-infected subjects who either do not progress to AIDS or progress only slowly have sustained HIV-1-specific CTL responses. It has been suggested that the specificities of these responses differ from the CTL responses of rapid progressors due to recognition of epitopes that are under structural or functional constraints. We have, in this respect, studied the CTL response to reverse transcriptase (RT) in long term survivors (LTS) and in HIV-1-infected individuals who progressed to AIDS within 3 to 6 yr. Both LTS and progressors displayed vigorous RT-specific CTL responses of comparable magnitude during the asymptomatic phase. From each individual at least two CTL lines were obtained from blood samples drawn at different time points during follow-up. A total of 19 CTL lines recognized nine different RT-derived epitopes. CTL obtained from progressors recognized epitopes with a similar degree of amino acid conservation as epitopes targeted by CTL from LTS. Furthermore, five of seven epitopes were recognized by both LTS and progressors. Moreover, one of the epitopes recognized by progressors contained the highly conserved YMDD motif that is essential for RT activity. In conclusion, our data imply that neither the magnitude nor the specificity of HIV-1-specific CTL against RT is a major cause of a more protracted course of disease.

HIV-1 reverse transcriptase-specific CTL against conserved epitopes do not protect against progression to AIDS

A small group of HIV-1-infected subjects who either do not progress to AIDS or progress only slowly have sustained HIV-1-specific CTL responses. It has been suggested that the specificities of these responses differ from the CTL responses of rapid progressors due to recognition of epitopes that are under structural or functional constraints. We have, in this respect, studied the CTL response to reverse transcriptase (RT) in long term survivors (LTS) and in HIV-1-infected individuals who progressed to AIDS within 3 to 6 yr. Both LTS and progressors displayed vigorous RT-specific CTL responses of comparable magnitude during the asymptomatic phase. From each individual at least two CTL lines were obtained from blood samples drawn at different time points during follow-up. A total of 19 CTL lines recognized nine different RT-derived epitopes. CTL obtained from progressors recognized epitopes with a similar degree of amino acid conservation as epitopes targeted by CTL from LTS. Furthermore, five of seven epitopes were recognized by both LTS and progressors. Moreover, one of the epitopes recognized by progressors contained the highly conserved YMDD motif that is essential for RT activity. In conclusion, our data imply that neither the magnitude nor the specificity of HIV-1-specific CTL against RT is a major cause of a more protracted course of disease.

Identification of HLA-A*0201-restricted CTL epitopes encoded by the tumor-specific MAGE-2 gene product

MAGE-2 is expressed in many tumors, including melanoma, laryngeal tumors, lung tumors and sarcomas, but not in healthy tissue, with the exception of testis. Thus, MAGE-2-derived peptides that bind to HLA class I molecules and elicit cytotoxic T lymphocyte (CTL) responses could be of significant therapeutic importance. In this study, we show that several MAGE-2-derived peptides bind with high affinity to HLA-A*0201. Three of them form complexes with HLA-A*0201 that are stable at 37 degrees C and are immunogenic in HLA-A*0201Kb transgenic mice. Moreover, CTLs against 2 of them (M2 112-120, and M2 157-166) specifically recognize cells that express both the MAGE-2 protein and HLA-A*0201Kb. These 2 peptides are processed and presented in the context of HLA-A*0201. Therefore, these peptides are candidate components in peptide-based vaccines for the treatment and prevention of several types of MAGE-2-expressing cancers.

Affinity, specificity and T-cell-receptor diversity of melanoma-specific CTL generated in vitro against a single tyrosinase epitope

MHC-class-I-restricted cytotoxic T lymphocytes (CTL) specific for tumor-associated antigens expressed by malignant cells are important components of the immune response against cancer. Recently, tumor-specific CTL could be generated in vitro, with responding lymphocytes from the blood of healthy blood donors. In the present study, we confirm that peptide-specific stimulation in vitro can induce high-affinity CTL capable of recognizing tumor cells expressing the appropriate tumor antigen. These tyrosinase-specific CTL display a restricted usage of TCRAV and TCRBV gene segments but of diverse CDR3 regions, resulting in a distinct fine-specificity for each CTL clone. This suggests that, similar to in vivo priming, peptide-pulsed APC are capable of stimulating a T-cell response in vitro expressing a limited TCR repertoire against autologous tumors. The generated CTL can recognize their target structure with high affinity, and this correlates in part with tumor-cell lysis. This methodology may be used to treat melanoma patients with infusion of ex vivo-induced and -expanded CTL.

Identification of potential HLA-A *0201 restricted CTL epitopes derived from the epithelial cell adhesion molecule (Ep-CAM) and the carcinoembryonic antigen (CEA)

The altered expression pattern of the Epithelial Cell Adhesion Molecule (Ep-CAM) and the Carcinoembryonic Antigen (CEA) on tumor cells of epithelial origin as compared to normal epithelia may permit T cells to preferentially recognize and lyse these tumor cells. The binding affinity for human leucocyte antigen A2.1 (HLA-A*0201) and the capacity to form stable peptide-major histocompatibility complex (MHC) interactions with this molecule were tested for 410 Ep-CAM-derived sequences, including an overlapping set of 9 amino-acid-long peptides, and 73 CEA-derived peptides fulfilling the HLA-A*0201 motif. Peptides with a high binding affinity and a low peptide-MHC dissociation rate were subsequently tested for their immunogenicity in HLA-A*0201Kb transgenic mice. One Ep-CAM-derived peptide and 1 CEA-derived peptide were able to reproducibly induce peptide-specific cytotoxic T cells (CTL) in these mice. This indicates that EpCAM and CEA are potential target antigens for CTL-mediated immunotherapy of epithelial cancers.

Analogues of CTL epitopes with improved MHC class-I binding capacity elicit anti-melanoma CTL recognizing the wild-type epitope

The MHC class-I binding affinity of an epitope is an important parameter determining the immunogenicity of the peptide-MHC complex. In order to improve the immunogenicity of an epitope derived from melanocyte lineage-specific antigen gp100, we performed amino-acid substitutions within the epitope and assayed both HLA-A*0201 binding and CTL recognition. Anchor replacements towards the HLA-A*0201 peptide-binding motif gave rise to peptides with higher HLA-A*0201 binding capacity compared to the wild-type epitope. In addition, several of the gp100 154-162 epitope-analogues were more efficient at target-cell sensitization for lysis by anti-gp100 154-162 CTL compared to the wild-type epitope. These altered gp100 154-162 epitopes were subsequently tested for their capacity to induce CTL responses in vivo using HLA-A*0201/Kb transgenic mice, and in vitro using HLA-A*0201 + donor-derived lymphocytes. Interestingly, the peptide-specific CTL obtained, which were raised against the different gp100 154-162 epitope-analogues, displayed cross-reactivity with target cells endogenously processing and presenting the native epitope. These data demonstrate that altered epitopes can be exploited to elicit native epitope-reactive CTL. The use of epitope-analogues with improved immunogenicity may contribute to the development of CTL-epitope based vaccines in viral disease and cancer.

Peptide-pulsed dendritic cells induce tumoricidal cytotoxic T lymphocytes from healthy donors against stably HLA-A*0201-binding peptides from the Melan-A/MART-1 self antigen

The melanoma antigen Melan-A/MART-1 was screened for the presence of potential HLA-A*0201-binding cytotoxic T lymphocytes (CTL) epitopes. The immunodominant nonamer epitope AAGIGILTV demonstrated weak binding to T2 but a significant half-life of binding to HLA-A*0201 in contrast to the decamer EAAGIGILTV. In addition to the immunodominant CTL epitope, we describe two peptides, GILTVILGV and ALMDKSLHV, that display stable binding to HLA-A*0201. Using cultured autologous dendritic cells pulsed with these peptides, CTL lines were induced from peripheral blood lymphocytes that displayed reactivity with HLA-A2+, Melan-A/MART-1+ melanoma cells. CTL reactivity against the immunodominant epitope could be induced with the nonamer epitope alone, but not with the decamer variant. CTL clones generated from an (EAAGIGILTV + AAGIGILTV)-induced CTL line recognize the appropriate melanoma cells and normal melanocytes. Upon further characterization of one of these CTL clones, it was found to be of surprisingly high affinity considering that it is directed against a self antigen. This study demonstrates that immunogenic peptides can be selected based on stability (half-life) of peptide/HLA binding. In addition, cultured DC were found to efficiently induce CTL responses in vitro against such selected peptides, and some of these CTL were capable of recognizing endogenously processed antigen.

Immunogenicity of peptides bound to MHC class I molecules depends on the MHC-peptide complex stability

The impact of the MHC class I peptide binding stability on the immunogenicity of particular peptide Ags in class I-restricted cytotoxic T lymphocyte responses is not clearly established. Therefore, we have determined the dissociation rate of each peptide from MHC class I at 37 degrees C and compared this to that of a consensus CTL epitope. Newly defined immunogenic peptides formed relatively stable MHC-peptide complexes as shown by their low dissociation rates, whereas nonimmunogenic peptides displayed high dissociation rates. In addition virtually all previously described HLA-A*0201-restricted T cell epitopes showed low dissociation rates. Furthermore, we show that the immunogenicity of HIV-1-derived peptides can be predicted more accurately by their dissociation rate than by the MHC class I binding affinity. Selection of peptides based on affinity and their dissociation rate leads to a more precise identification of candidate CTL epitopes than selection based on affinity alone. These results help to understand why some peptides are recognized by CTL and, along with detailed knowledge of protein processing rules, therefore have important implications for the selection of peptides in peptide-based vaccines.