Current status of antigen-specific T-cell immunotherapy for advanced renal-cell carcinoma

In renal-cell carcinoma (RCC), tumor-reactive T-cell responses can occur spontaneously or in response to systemic immunotherapy with cytokines and immune checkpoint inhibitors. Cancer vaccines and engineered T-cell therapies are designed to selectively augment tumor antigen-specific CD8⁺ T-cell responses with the goal to elicit tumor regression and avoid toxicities associated with nonspecific immunotherapies. In this review, we provide an overview of the central role of T-cell immunity in the treatment of advanced RCC. Clinical outcomes for antigen-targeted vaccines or other T-cell-engaging therapies for RCC are summarized and evaluated, and emerging new strategies to enhance the effectiveness of antigen-specific therapy for RCC are discussed.

An efficient T-cell epitope discovery strategy using in silico prediction and the iTopia assay platform

Functional T-cell epitope discovery is a key process for the development of novel immunotherapies, particularly for cancer immunology. In silico epitope prediction is a common strategy to try to achieve this objective. However, this approach suffers from a significant rate of false-negative results and epitope ranking lists that often are not validated by practical experience. A high-throughput platform for the identification and prioritization of potential T-cell epitopes is the iTopia(TM) Epitope Discovery System(TM), which allows measuring binding and stability of selected peptides to MHC Class I molecules. So far, the value of iTopia combined with in silico epitope prediction has not been investigated systematically. In this study, we have developed a novel in silico selection strategy based on three criteria: (1) predicted binding to one out of five common MHC Class I alleles; (2) uniqueness to the antigen of interest; and (3) increased likelihood of natural processing. We predicted in silico and characterized by iTopia 225 candidate T-cell epitopes and fixed-anchor analogs from three human tumor-associated antigens: CEA, HER2 and TERT. HLA-A2-restricted fragments were further screened for their ability to induce cell-mediated responses in HLA-A2 transgenic mice. The iTopia binding assay was only marginally informative while the stability assay proved to be a valuable experimental screening method complementary to in silico prediction. Thirteen novel T-cell epitopes and analogs were characterized and additional potential epitopes identified, providing the basis for novel anticancer immunotherapies. In conclusion, we show that combination of in silico prediction and an iTopia-based assay may be an accurate and efficient method for MHC Class I epitope discovery among tumor-associated antigens.

Therapeutic applications of the selective high affinity ligand drug SH7139 extend beyond non-Hodgkin's lymphoma to many other types of solid cancers

SH7139, the first of a series of selective high affinity ligand (SHAL) oncology drug candidates designed to target and bind to the HLA-DR proteins overexpressed by B-cell lymphomas, has demonstrated exceptional efficacy in the treatment of Burkitt lymphoma xenografts in mice and a safety profile that may prove to be unprecedented for an oncology drug. The aim of this study was to determine how frequently the HLA-DRs targeted by SH7139 are expressed by different subtypes of non-Hodgkin’s lymphoma and by other solid cancers that have been reported to express HLA-DR. Binding studies conducted with SH7129, a biotinylated analog of SH7139, reveal that more than half of the biopsy sections obtained from patients with different types of non-Hodgkin’s lymphoma express the HLA-DRs targeted by SH7139. Similar analyses of tumor biopsy tissue obtained from patients diagnosed with eighteen other solid cancers show the majority of these tumors also express the HLA-DRs targeted by SH7139. Cervical, ovarian, colorectal and prostate cancers expressed the most HLA-DR. Only a few esophageal and head and neck tumors bound the diagnostic. Within an individual’s tumor, cell to cell differences in HLA-DR target expression varied by only 2 to 3-fold while the expression levels in tumors obtained from different patients varied as much as 10 to 100-fold. The high frequency with which SH7129 was observed to bind to these cancers suggests that many patients diagnosed with B-cell lymphomas, myelomas, and other non-hematological cancers should be considered potential candidates for new therapies such as SH7139 that target HLA-DR-expressing tumors.

Identification of a naturally processed HLA-A*02:01-restricted CTL epitope from the human tumor-associated antigen Nectin-4

Nectin-4 is a tumor antigen present on the surface of breast, ovarian and lung carcinoma cells. It is rarely present in normal adult tissues and is therefore a candidate target for cancer immunotherapy. Here, we identified a Nectin-4 antigenic peptide that is naturally presented to T cells by HLA-A2 molecules. We first screened the 502 nonamer peptides of Nectin-4 (510 amino acids) for binding to and off-rate from eight different HLA class I molecules. We then combined biochemical, cellular and algorithmic assays to select 5 Nectin-4 peptides that bound to HLA-A*02:01 molecules. Cytolytic T lymphocytes were obtained from healthy donors, that specifically lyzed HLA-A2(+) cells pulsed with 2 out of the 5 peptides, indicating the presence of anti-Nectin-4 CD8(+) T lymphocytes in the human T cell repertoire. Finally, an HLA-A2-restricted cytolytic T cell clone derived from a breast cancer patient recognized peptide Nectin-4145-153 (VLVPPLPSL) and lyzed HLA-A2(+) Nectin-4(+) breast carcinoma cells. These results indicate that peptide Nectin-4145-153 is naturally processed for recognition by T cells on HLA-A2 molecules. It could be used to monitor antitumor T cell responses or to immunize breast cancer patients.

High-throughput identification and dendritic cell-based functional validation of MHC class I-restricted Mycobacterium tuberculosis epitopes

Emergence of drug-resistant strains of the pathogen Mycobacterium tuberculosis (Mtb) and the ineffectiveness of BCG in curtailing Mtb infection makes vaccine development for tuberculosis an important objective. Identifying immunogenic CD8+ T cell peptide epitopes is necessary for peptide-based vaccine strategies. We present a three-tiered strategy for identifying and validating immunogenic peptides: first, identify peptides that form stable complexes with class I MHC molecules; second, determine whether cytotoxic T lymphocytes (CTLs) raised against the whole protein antigen recognize and lyse target cells pulsed with peptides that passed step 1; third, determine whether peptides that passed step 2, when administered in vivo as a vaccine in HLA-A2 transgenic mice, elicit CTLs that lyse target cells expressing the whole protein antigen. Our innovative approach uses dendritic cells transfected with Mtb antigen-encoding mRNA to drive antigen expression. Using this strategy, we have identified five novel peptide epitopes from the Mtb proteins Apa, Mtb8.4 and Mtb19.

Enhancement of T cell responses as a result of synergy between lower doses of radiation and T cell stimulation

As a side effect of cancer radiotherapy, immune cells receive varying doses of radiation. Whereas high doses of radiation (>10 Gy) can lead to lymphopenia, lower radiation doses (2-4 Gy) represent a valid treatment option in some hematological cancers, triggering clinically relevant immunological changes. Based on our earlier observations, we hypothesized that lower radiation doses have a direct positive effect on T cells. In this study, we show that 0.6-2.4 Gy radiation enhances proliferation and IFN-γ production of PBMC or purified T cells induced by stimulation via the TCR. Radiation with 1.2 Gy also lowered T cell activation threshold and broadened the Th1 cytokine profile. Although radiation alone did not activate T cells, when followed by TCR stimulation, ERK1/2 and Akt phosphorylation increased above that induced by stimulation alone. These changes were followed by an early increase in glucose uptake. Naive (CD45RA(+)) or memory (CD45RA(-)) T cell responses to stimulation were boosted at similar rates by radiation. Whereas increased Ag-specific cytotoxic activity of a CD8(+) T cell line manifested in a 4-h assay (10-20% increase), highly significant (5- to 10-fold) differences in cytokine production were detected in 6-d Ag-stimulation assays of PBMC, probably as a net outcome of death of nonstimulated and enhanced response of Ag-stimulated T cells. T cells from patients receiving pelvic radiation (2.2-2.75 Gy) also displayed increased cytokine production when stimulated in vitro. We report in this study enhanced T cell function induced by synergistic radiation treatment, with potential physiological significance in a wide range of T cell responses.

Immunogenicity of sequences around HIV-1 protease cleavage sites: potential targets and population coverage analysis for a HIV vaccine targeting protease cleavage sites

Developing an effective preventative vaccine against HIV-1 has proved to be a great challenge. The classical and proven vaccine approach has failed so far or produced a modest effect, new approaches are needed. In this study we evaluated the immunogenicity of the sequences around the protease cleavage sites (PCS) and the population coverage of a vaccine targeting HIV-1 PCS. The sequence conservation was evaluated by comparing entropy score of sequences around PCS with Gag and Pol. The immunogenicity of sequences around the 12 PCS (+10/-10 amino acids) was analyzed by identifying epitopes of HLA class I alleles in PCS region using four approaches: (1) identification of previously reported HLA class I allele epitopes around PCS region; (2) screening and validating epitopes of 8 HLA class I alleles common to most world populations using iTopia Epitope Discovery system and IFN-γ ELISpot assays; (3) screening of 151 patients of Pumwani cohort for PBMC IFN-γ ELISPOT responses to the subtype A and D consensus around PCS region; and (4) prediction of HLA alleles with epitopes around the PCS using NetMHCpan. Population coverage was calculated using the web-based analysis tool of the Immune Epitope Database based on HLA class I genotype frequencies from dbMHC database. The results showed that many HLA class I alleles have multiple epitopes in the 12 PCS regions, indicating sequence immunogenicity around PCS. Multiple epitopes of many HLA class I alleles common to >95% world populations have been identified around the 12 PCS region. Targeting these sites is a feasible vaccine approach.

A broad profile of co-dominant epitopes shapes the peripheral Mycobacterium tuberculosis specific CD8+ T-cell immune response in South African patients with active tuberculosis

We studied major histocompatibility complex (MHC) class I peptide-presentation and nature of the antigen-specific CD8+ T-cell response from South African tuberculosis (TB) patients with active TB. 361 MHC class I binding epitopes were identified from three immunogenic TB proteins (ESAT-6 [Rv3875], Ag85B [Rv1886c], and TB10.4 [Rv0288], including amino acid variations for Rv0288, i.e., A10T, G13D, S27N, and A71S for MHC allotypes common in a South African population (e.g., human leukocyte antigen [HLA]-A*30, B*58, and C*07). Inter-allelic differences were identified regarding the broadness of the peptide-binding capacity. Mapping of frequencies of Mycobacterium tuberculosis (M. tb) antigen-specific CD8+ T-cells using 48 different multimers, including the newly constructed recombinant MHC class I alleles HLA-B*58:01 and C*0701, revealed a low frequency of CD8+ T-cell responses directed against a broad panel of co-dominant M. tb epitopes in the peripheral circulation of most patients. The antigen-specific responses were dominated by CD8+ T-cells with a precursor-like phenotype (CD45RA+CCR7+). The data show that the CD8+ T-cell response from patients with pulmonary TB (prior to treatment) is directed against subdominant epitopes derived from secreted and non-secreted M. tb antigens and that variant, natural occurring M. tb Rv0288 ligands, have a profound impact on T-cell recognition.

CD8+ T-cell clones specific for the 5T4 antigen target renal cell carcinoma tumor-initiating cells in a murine xenograft model

The tumor antigen 5T4 is frequently expressed at high levels on renal cell carcinoma (RCC) and other epithelial carcinomas. Surveys of normal tissues demonstrate abundant 5T4 expression on placental trophoblast cells with limited expression elsewhere. 5T4 is the target for a therapeutic cancer vaccine (MVA-5T4) that elicits 5T4-specific serological, proliferative, and cytotoxic T lymphocyte (CTL) responses. However, the antitumor activity of 5T4-specific CTL has not been extensively characterized. CD8 T cells from HLA-A2 healthy donors (n=4) or RCC patients (n=2) were stimulated in vitro with the HLA-A2-binding nonamer peptides 5T417-25 or 5T497-105 and screened by flow cytometry with specific tetramers (TET). CD8/TET T-cell clones specific for 5T417-25 or 5T497-105 peptide were isolated from 4/6 and 1/4 donors, respectively. A subset of clones specific for 5T417-25 was cytolytic for MVA-5T4-infected HLA-A2 EBV-transformed lymphoblastoid cell line target cells and for constitutively HLA-A2-expressing and 5T4-expressing RCC tumor cell lines (including A498 RCC). In a xenoengraftment assay, the coinoculation of a representative 5T417-25-specific CTL clone with A498 RCC tumors cells into immune-deficient mice completely prevented growth of A498 tumors. Taken together, these data demonstrate high-avidity CD8 CTL able to recognize the naturally processed 5T417-25 epitope on RCC tumor cells including putative tumor-initiating cells are present in peripheral blood of both healthy donors and RCC patients. CD8T-cell immunity targeting 5T417-25 is therefore of substantial interest both as a potential target for further development of vaccination or adoptive cellular immunotherapy and for immune monitoring studies in association with nonspecific immunotherapies.

A novel HLA-A*0201 restricted peptide derived from cathepsin G is an effective immunotherapeutic target in acute myeloid leukemia

PURPOSE

Immunotherapy targeting aberrantly expressed leukemia-associated antigens has shown promise in the management of acute myeloid leukemia (AML). However, because of the heterogeneity and clonal evolution that is a feature of myeloid leukemia, targeting single peptide epitopes has had limited success, highlighting the need for novel antigen discovery. In this study, we characterize the role of the myeloid azurophil granule protease cathepsin G (CG) as a novel target for AML immunotherapy.

EXPERIMENTAL DESIGN

We used Immune Epitope Database and in vitro binding assays to identify immunogenic epitopes derived from CG. Flow cytometry, immunoblotting, and confocal microscopy were used to characterize the expression and processing of CG in AML patient samples, leukemia stem cells, and normal neutrophils. Cytotoxicity assays determined the susceptibility of AML to CG-specific cytotoxic T lymphocytes (CTL). Dextramer staining and cytokine flow cytometry were conducted to characterize the immune response to CG in patients.

RESULTS

CG was highly expressed and ubiquitinated in AML blasts, and was localized outside granules in compartments that facilitate antigen presentation. We identified five HLA-A*0201 binding nonameric peptides (CG1-CG5) derived from CG, and showed immunogenicity of the highest HLA-A*0201 binding peptide, CG1. We showed killing of primary AML by CG1-CTL, but not normal bone marrow. Blocking HLA-A*0201 abrogated CG1-CTL-mediated cytotoxicity, further confirming HLA-A*0201-dependent killing. Finally, we showed functional CG1-CTLs in peripheral blood from AML patients following allogeneic stem cell transplantation.

CONCLUSION

CG is aberrantly expressed and processed in AML and is a novel immunotherapeutic target that warrants further development.

T cell subsets and colorectal cancer: discerning the good from the bad

Tumor-specific T cells must overcome a multitude of suppressive mechanisms to destroy cancerous cells effectively. Furthermore, it appears that the tumor microenvironment facilitates the development of highly immunosuppressive T cells, which may also allow subsequent tumor progression. In colorectal cancer, the relationship between regulatory T cells (e.g. FoxP3(+) Tregs) and tumor prognosis and progression is less clear, despite their well-documented ability to impinge on anti-tumor immune responses. Here we explore our current knowledge of colorectal TIL heterogeneity, deciphering subsets which may be of benefit or detriment.

IGKV3 proteins as candidate "off-the-shelf" vaccines for kappa-light chain-restricted B-cell non-Hodgkin lymphomas

PURPOSE

An increasing set of B-cell non-Hodgkin lymphomas (B-NHL) show a biased usage of IGKV3-20 and IGKV3-15 immunoglobulin genes, a feature that could be exploited for the development of ready-to-use, broadly applicable cancer vaccines.

EXPERIMENTAL DESIGN

The immunogenic properties of clonal IGKV3-20 and IGKV3-15 proteins were analyzed with particular focus on their ability to elicit cross-reactive responses against molecularly related IGKV proteins expressed by different B-cell lymphoproliferative disorders.

RESULTS

IGK+ lymphoma patients show humoral and T-cell responses to IGKV3-20 and IGKV3-15 proteins and IGKV3-specific cytotoxic T lymphocytes (CTL) can be easily induced ex vivo. IGKV3-20-specific CTLs cross-react against different IGKV3 proteins, an effect mediated by the presence of 21 shared, sometimes promiscuous, T-cell epitopes, presented by common HLA class I allele products, thus assuring a broad HLA coverage of IGKV3-based vaccines. Many natural epitope variants are carried by IGK light chains expressed by a broad spectrum of B-NHLs and we show that IGKV3-20-specific CTLs cross-react also against several of these variant epitopes. Both humoral and CTL-specific responses were induced by KLH-conjugated IGKV3-20 protein in HLA-A2-transgenic mice and coinjection of IGKV3-20-specific CTLs with IGKV3-20+ or IGKV3-15+ lymphoma cells into SCID mice totally prevented tumor growth, thus confirming the ability of these effectors to mediate efficient and cross-reactive cytotoxic responses also in vivo.

CONCLUSIONS

These results provide the rationale to exploit IGKV3 proteins as "off-the-shelf" vaccines for a large fraction of lymphoma patients.

Overexpression and potential targeting of the oncofoetal antigen 5T4 in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is resistant to conventional treatments. Novel, targeted treatments are hampered by the relative lack of MPM-associated tumour antigens. The aim of this study was to evaluate the level of expression and the relevance of 5T4 as a tumour-associated antigen in MPM. 5T4 expression was assessed by Western blotting, flow cytometry, immuno-cytochemistry and -histochemistry in 11 mesothelioma cell lines, 21 tumour biopsies, and ex vivo tumour cells obtained from the pleural fluid (PF) of 10 patients. 5T4 antibody levels were also determined in the plasma of patients and healthy donors. The susceptibility of MPM cells to 5T4-specific T-cell-mediated killing was determined using an HLA-A2(+), CD8(+) T-cell line, developed against the 5T4(17-25) peptide. We report here that cell surface 5T4 expression was detected in all mesothelioma cell lines and PF cell samples. Mesothelin and CD200, a suggested mesothelioma marker, were co-expressed with 5T4 on tumour cells in PF. Immunohistochemistry confirmed overexpression of 5T4, similar to mesothelin, on tumour cells but not on reactive stroma in all tissue sections tested. Median 5T4 antibody levels were 46% higher in patient than in healthy donor plasma, indicating immune recognition. Importantly, 5T4-specific CD8(+) T-cells were able to kill four out of six HLA-A2(+) MPM cell lines but not an HLA-A2(-) cell line, demonstrating immune recognition of MPM-associated 5T4 antigen at the effector T-cell level. We conclude that 5T4 is a potential new antigen for targeted therapies such as immunotherapy in MPM, as it is overexpressed on mesothelioma cells and recognised by 5T4-specific cytotoxic T-cells. Our findings have been translated into a Phase II clinical trial applying 5T4-targeted therapies in MPM patients.

TroVax® vaccine therapy for renal cell carcinoma

Renal cell carcinoma (RCC) is the most common primary malignancy affecting the kidney. In the past decade, several well-designed clinical trials have shifted the treatment paradigm for RCC to favor targeted therapies as first-line agents. Recognition of the immunogenic nature of RCC has also resulted in the development of immunotherapy approaches with high-dose IL-2 treatment being the best established and associated with durable disease control. The lack of defined antigens in RCC has hindered more specific vaccine development. TroVax® is a novel vaccine based on a modified vaccinia virus Ankara vector engineered to express the 5T4 tumor-associated antigen, found on over 95% of clear cell and papillary RCC tumors. The safety and efficacy of TroVax has been evaluated in several Phase I/II clinical trials and in a multicenter Phase III trial. This article will discuss the clinical background of RCC, the rationale for TroVax development, results of several TroVax clinical trials and future directions for optimizing TroVax therapy in patients with RCC and other cancers.

For protection from HIV-1 infection, more might not be better: a systematic analysis of HIV Gag epitopes of two alleles associated with different outcomes of HIV-1 infection

A subset of women in the Pumwani Sex Worker Cohort, established in 1985 in Nairobi, Kenya, remains uninfected despite repeated high-risk exposure (HIV-exposed, seronegative [HESN]) through active sex work. This HESN phenotype is associated with several alleles of human leukocyte antigens (HLAs) and specific CD8(+) and CD4(+) T cell responses to HIV-1. The associations of HLA alleles with differential HIV-1 infection are most likely due to their different abilities to present antigen and the different immune responses they induce. The characteristics of epitopes of HLA alleles associated with different outcomes of HIV-1 infection might therefore point to a vital clue for developing an effective vaccine. In this study, we systematically analyzed HIV-1 clade A and D Gag CD8(+) T cell epitopes of two HLA class I alleles associated with different outcomes of HIV-1 infection. Binding affinity and off-rates of the identified epitopes were determined. Gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) assays with patient peripheral blood mononuclear cells (PBMCs) validated the epitopes. Epitope-specific CD8(+) T cells were further phenotyped for memory markers with tetramer staining. Our study showed that the protective allele A*01:01 recognizes only three Gag epitopes. By contrast, B*07:02, the allele associated with susceptibility, binds 30 epitope variants. These two alleles differ most importantly in the spectrum of Gag epitopes they can present and not in affinity, off-rates, the location of the epitopes, or epitope-specific Tem/Tcm frequencies. The binding of more epitopes and strong IFN-gamma ELISpot responses are associated with susceptibility to HIV-1 infection, while more focused antigen recognition of multiple subtypes is protective. Rational vaccine design should take these observations into account.

Dana-Farber repository for machine learning in immunology

The immune system is characterized by high combinatorial complexity that necessitates the use of specialized computational tools for analysis of immunological data. Machine learning (ML) algorithms are used in combination with classical experimentation for the selection of vaccine targets and in computational simulations that reduce the number of necessary experiments. The development of ML algorithms requires standardized data sets, consistent measurement methods, and uniform scales. To bridge the gap between the immunology community and the ML community, we designed a repository for machine learning in immunology named Dana-Farber Repository for Machine Learning in Immunology (DFRMLI). This repository provides standardized data sets of HLA-binding peptides with all binding affinities mapped onto a common scale. It also provides a list of experimentally validated naturally processed T cell epitopes derived from tumor or virus antigens. The DFRMLI data were preprocessed and ensure consistency, comparability, detailed descriptions, and statistically meaningful sample sizes for peptides that bind to various HLA molecules. The repository is accessible at http://bio.dfci.harvard.edu/DFRMLI/.

MHC-based detection of antigen-specific CD8+ T cell responses

The hallmark of adaptive immunity is its ability to recognise a wide range of antigens and technologies that capture this diversity are therefore of substantial interest. New methods have recently been developed that allow the parallel analysis of T cell reactivity against vast numbers of different epitopes in limited biological material. These technologies are based on the joint binding of differentially labelled MHC multimers on the T cell surface, thereby providing each antigen-specific T cell population with a unique multicolour code. This strategy of 'combinatorial encoding' enables detection of many (at least 25) different T cell populations per sample and should be of broad value for both T cell epitope identification and immunomonitoring.

Extensive major histocompatibility complex class I binding promiscuity for Mycobacterium tuberculosis TB10.4 peptides and immune dominance of human leucocyte antigen (HLA)-B*0702 and HLA-B*0801 alleles in TB10.4 CD8 T-cell responses

The molecular definition of major histocompatibility complex (MHC) class I-presented CD8(+) T-cell epitopes from clinically relevant Mycobacterium tuberculosis (Mtb) target proteins will aid in the rational design of T-cell-based diagnostics of tuberculosis (TB) and the measurement of TB vaccine-take. We used an epitope discovery system, based on recombinant MHC class I molecules that cover the most frequent Caucasian alleles [human leucocyte antigen (HLA)-A*0101, A*0201, A*0301, A*1101, A*2402, B*0702, B*0801 and B*1501], to identify MHC class I-binding peptides from overlapping 9-mer peptides representing the Mtb protein TB10.4. A total of 33 MHC class I-binding epitopes were identified, spread across the entire amino acid sequence, with some clustering at the N- and C-termini of the protein. Binding of individual peptides or closely related peptide species to different MHC class I alleles was frequently observed. For instance, the common motif of xIMYNYPAMx bound to six of eight alleles. Affinity (50% effective dose) and off-rate (half life) analysis of candidate Mtb peptides will help to define the conditions for CD8(+) T-cell interaction with their nominal MHC class I-peptide ligands. Subsequent construction of tetramers allowed us to confirm the recognition of some of the epitopes by CD8(+) T cells from patients with active pulmonary TB. HLA-B alleles served as the dominant MHC class I restricting molecules for anti-Mtb TB10.4-specific CD8(+) T-cell responses measured in CD8(+) T cells from patients with pulmonary TB.

Identification and characterization of HLA-A*0301 epitopes in HIV-1 gag proteins using a novel approach

Identification of CTL epitopes correlated to immune protection is important for the development of vaccines that enhance T-cell mediated immune responses. The correlation of positively selected amino acids (PS) of HIV-1 with host HLA alleles can identify regions containing potential T-cell epitopes. However, the specific epitopes have to be identified and characterized using overlapping peptides through T-cell functional assays. In this study we used a new approach to identify and characterize potential epitopes in the gag region containing PS mutations that significantly correlated with HLA-A*0301. The iTopia Epitope Discovery System was used to rapidly screen a panel of peptides overlapping the regions containing PS mutations and the peptides identified were assessed for relative affinity and complex stability. The potential epitopes were then validated by interferon gamma (IFN-gamma) ELISpot assays with patient PBMCs. Using this approach we identified/confirmed the predicted HLA-A*0301 epitopes in two regions of gag containing PS mutations V7I and K403R, one previously reported and the other novel. Five of the seven peptides that bound to A*0301 contained the K403R mutation and corresponded to the documented LARNCRAPRK-A3 supertype epitope. Two epitope variants, RASVLSGGK and RASILSGGK containing the V7I mutation, were identified using the iTopia Epitope Discovery System, however only the consensus variant (RAK9C) was confirmed using the ELISpot assay and it represents a novel A*0301 epitope.

Kit K641E oncogene up-regulates Sprouty homolog 4 and trophoblast glycoprotein in interstitial cells of Cajal in a murine model of gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GIST) are thought to derive from the interstitial cells of Cajal (ICC) or an ICC precursor. Oncogenic mutations of the receptor tyrosine kinase KIT are present in most GIST. KIT K642E was originally identified in sporadic GIST and later found in the germ line of a familial GIST cohort. A mouse model harbouring a germline Kit K641E mutant was created to model familial GIST. The expression profile was investigated in the gastric antrum of the Kit(K641E) murine GIST model by microarray, quantitative PCR and immunofluorescence. Gja1/Cx43, Gpc6, Gpr133, Pacrg, Pde3a, Prkar2b, Prkcq/Pkce, Rasd2, Spry4 and Tpbg/5T4 were found to be up-regulated. The proteins encoded by Gja1/Cx43, Pde3a, Prkcq/Pkce were localized in Kit-ir ICC in wild-type and Kit(K641E) animals while Spry4 and Tpbg/5T4 were detected in Kit-ir cells only in Kit(K641E), but not in Kit(WT/WT) animals. Most up-regulated genes in this mouse model belong to the gene expression profile of human GIST but also to the profile of normal Kit(+) ICC in the mouse small intestine. Spry4 and Tpbg/5T4 may represent candidates for targeted therapeutic approaches in GIST with oncogenic KIT mutations.

Development of modified vaccinia Ankara-5T4 as specific immunotherapy for advanced human cancer

BACKGROUND

The tumor-associated antigen 5T4 is expressed on a high percentage of human carcinomas and has limited expression in normal tissues. A recombinant pox virus vector expressing this antigen, modified vaccinia Ankara (MVA)-5T4, has been tested as a cancer vaccine.

OBJECTIVE

Treatment with MVA-5T4 has been studied both as a single agent and in combination with standard chemo-, biologic- or targeted-therapies in patients with advanced colorectal cancer, renal cell carcinoma (RCC) or hormone-refractory prostate cancer.

METHODS

This review summarizes data from clinical studies with MVA-5T4 reported in published manuscripts, meeting abstracts or posted on websites relevant to clinical trials or MVA-5T4.

RESULTS/CONCLUSION

Vaccination with MVA-5T4 is well tolerated and elicits 5T4-specific humoral and/or cellular responses in most of the treated patients. Retrospective analyses of Phase II studies have suggested a positive association between immune responses to 5T4 and favorable clinical outcomes. A continuing Phase III, double-blind, placebo-controlled trial seeks to confirm a positive association between vaccination with MVA-5T4 and survival in patients with advanced RCC.