Abstract P2-09-10: Epigenetic modulation—unlocking the potential of checkpoint inhibition in breast cancer

Immune checkpoint inhibition (ICI) has revolutionized treatment in cancers that are naturally immunogenic by enabling infiltration of T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. Tumors possessing complex immunosuppressive TME's such as breast cancer present unique therapeutic obstacles as response rates to ICI remain low. Such tumors often recruit myeloid-derived suppressor cells (MDSCs) whose functioning prohibits both T cell activation and infiltration. To date, most studies focus on use of ICI in triple negative disease. Our work aims to uncover the efficacy of ICI in both early and advanced HER2 positive (HER2+) disease and to advance our understanding of how to improve response rates to these new promising therapies.

We are using a HER-2/neu transgenic mouse model with tumor challenge of syngeneic cell lines to test the efficacy of different combinations of an epigenetic agent, the histone deacetylase inhibitor entinostat (ENT), checkpoint inhibitors anti-PD-1 and anti- CTLA-4, on primary and metastatic disease. We are examining treatment effects on primary tumor growth, metastatic burden, and survival. Characterization of tumor infiltrating lymphocytes and their functional capabilities are being investigated using fluorescence-activated cell sorting, gene expression profiling, and ex vivo suppression assays. Western blots, qPCR and other in vitro assays will be performed on MDSCs to investigate mechanisms behind response.

In the HER2+ mouse model of early stage disease, we show that combining ENT, with ICis significantly improves survival and delays tumor growth. Preliminary data in models of advanced disease, show only ENT + a-PD-1 improves survival and metastatic burden. Conversely, in the metastatic model, ENT + a-CTLA-4 negatively effects survival and metastatic burden. In primary tumors, ENT + ICIs leads to significantly decreased suppression by granulocytic-MDSCs. However, MDSC infiltration and function is not affected in lungs containing macrometastatic disease. Interestingly, we found an increase in activated granzyme-B-producing CD8+ T effector cells in mice treated with combination therapy in both primary and metastatic tumors. Finally, gene expression profiling of MDSCs from primary tumors identified significant changes in immune-related pathways, and identified a common downstream regulator –STAT3. Studies are ongoing to evaluate the mechanistic role of STAT3 in the response observed in primary tumors and to determine if STAT3 is involved in response in the metastatic setting.

In summary, addition of ENT to ICIs significantly affects overall survival in early stage models of HER2+ breast cancer however, only addition of a-PD-1 to ENT is beneficial in models of advanced disease. Additionally, the mechanism of action in early stage disease involves altered infiltration and function of MDSCs, allowing for a more robust adaptive immune response. However, a different mechanism of action is likely responsible for the responses seen in advanced stage disease. These novel findings provide a rationale for combination therapy in patients with HER2+ breast cancer and suggest responses to this combination therapy are linked to stage of disease likely due to different mechanisms of action.

Citation Format: Roussos Torres ET, Rafie C, Armstrong T, Jaffee EM. Epigenetic modulation—unlocking the potential of checkpoint inhibition in breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-09-10.

Abstract OT3-02-03: IMMUNe mOdulation in early stage estrogen receptor positive breast cancer treated with neoADjuvant Avelumab, Palbociclib, and Tamoxifen: The ImmunoADAPT study (NCT03573648)

Background:

While some patients with early stage endocrine receptor positive (ER+) breast cancer experience excellent prognosis, a subset of patients with more aggressive phenotypes still have a high rate of recurrence despite optimal adjuvant endocrine therapy and chemotherapy, thus novel therapies are needed for patients with high risk disease.

Although immune checkpoint blockade has shown significant benefit in numerous types of cancer, initial reports demonstrate low response rates to single agent programmed cell death ligand 1 (PD-L1) inhibition in ER+ breast cancer. Inhibitors of cyclin dependent kinases (CDK) 4 and 6 in combination with endocrine therapy are highly active in breast cancer, and recently have been demonstrated to recruit immune cells, and increase PD-L1 on tumor cells in preclinical models. Increased tumor infiltrating lymphocytes (TILs) has been observed with neoadjuvant treatment with CDK4/6 inhibitors in patients with ER+ breast cancer. We thus hypothesize that the addition of palbociclib (CDK4/6 inhibitor) will improve responses to avelumab (PD-L1) inhibitor in patients with high risk ER+ breast cancer.

Trial Design:

Eligible participants are those stage II or III ER+HER2- breast cancer (T2N0 must have ≥grade 2, T1N+ must have at least a 1.5cm breast primary). Patients will undergo a baseline MRI and biopsy, start tamoxifen +/- palbociclib for 1 cycle (1 cycle =28 days), and then undergo a repeat MRI and biopsy. Avelumab will be added to both arms in cycle 2. Patients will be treated for 3 cycles of avelumab with tamoxifen +/- palbociclib (thus 4 cycles total, including run-in without avelumab). Patients will be treated as long as there is no evidence of progression and therapy is tolerated, and then undergo MRI and surgery. The primary objective is to determine the clinical complete response (cCR) rate by MRI. Secondary objectives include evaluation of TILs (H&E), CD8 and FOXP3 by immunohistochemistry (IHC), T cell receptor (TCR) repertoire (TCR sequencing), multiplex gene expression panel (Nanostring), and multiplex IHC. Changes in these immune biomarkers will be assessed to determine differential immunophenotypic effects of palbociclib, and correlated to cCR in each arm.

The sample size of this pilot study is determined by primary analysis on the cCR rate. We hypothesize that the addition of palbociclib to tamoxifen will result in an increase rate of cCR in patients receiving avelumab. We hypothesize that the addition of avelumab will increase the response rate to palbociclib and tamoxifen by 30%. We thus estimate that a total of 40 evaluable patients (20 to each arm) will provide close to 80% power to detect a difference on cCR rates of 10% vs 40% at two-sided alpha level 10%. We will evaluate and compare cCR rates between arms by conducting Fisher's Exact test and reporting the estimated proportions together with their exact confidence intervals. Logistic regression analysis will also be conducted to explore the association between cCR and immune biomarkers.

This study has received IRB approval and is open as of Summer 2018.

Citation Format: Santa-Maria CA, Wang C, Cimino-Mathews A, Roussos-Torres E, Connolly RM, Wolff AC, Jaffee EM, Stearns V. IMMUNe mOdulation in early stage estrogen receptor positive breast cancer treated with neoADjuvant Avelumab, Palbociclib, and Tamoxifen: The ImmunoADAPT study (NCT03573648) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT3-02-03.

Development of tumor mutation burden as an immunotherapy biomarker: utility for the oncology clinic

Background

Treatment with immune checkpoint blockade (ICB) with agents such as anti-programmed cell death protein 1 (PD-1), anti-programmed death-ligand 1 (PD-L1), and/or anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) can result in impressive response rates and durable disease remission but only in a subset of patients with cancer. Expression of PD-L1 has demonstrated utility in selecting patients for response to ICB and has proven to be an important biomarker for patient selection. Tumor mutation burden (TMB) is emerging as a potential biomarker. However, refinement of interpretation and contextualization is required.

Materials and methods

In this review, we outline the evolution of TMB as a biomarker in oncology, delineate how TMB can be applied in the clinic, discuss current limitations as a diagnostic test, and highlight mechanistic insights unveiled by the study of TMB. We review available data to date studying TMB as a biomarker for response to ICB by tumor type, focusing on studies proposing a threshold for TMB as a predictive biomarker for ICB activity.

Results

High TMB consistently selects for benefit with ICB therapy. In lung, bladder and head and neck cancers, the current predictive TMB thresholds proposed approximate 200 non-synonymous somatic mutations by whole exome sequencing (WES). PD-L1 expression influences response to ICB in high TMB tumors with single agent PD-(L)1 antibodies; however, response may not be dependent on PD-L1 expression in the setting of anti-CTLA4 or anti-PD-1/CTLA-4 combination therapy. Disease-specific TMB thresholds for effective prediction of response in various other malignancies are not well established.

Conclusions

TMB, in concert with PD-L1 expression, has been demonstrated to be a useful biomarker for ICB selection across some cancer types; however, further prospective validation studies are required. TMB determination by selected targeted panels has been correlated with WES. Calibration and harmonization will be required for optimal utility and alignment across all platforms currently used internationally. Key challenges will need to be addressed before broader use in different tumor types.

Histopathological and immunophenotypic features of ipilimumab-associated colitis compared to ulcerative colitis

BACKGROUND

Use of the immune checkpoint inhibitor ipilimumab is sometimes complicated by ipilimumab-associated colitis (Ipi-AC), an immune-mediated colitis that mimics inflammatory bowel disease.

OBJECTIVE

We sought to characterize the histopathologic and immunophenotypic features of Ipi-AC and to directly compare these features to ulcerative colitis (UC).

METHODS

This is a retrospective cohort study of 22 patients with Ipi-AC, 12 patients with treatment-naïve UC and five controls with diarrhoea but normal endoscopic findings. Immunohistopathologic features were described, and quantitative immunohistochemistry (IHC) was performed for CD4, CD8, CD20, CD138 and FOXP3.

RESULTS

Endoscopic findings in both the Ipi-AC and UC groups included ulcerated, oedematous and erythematous mucosa. Involvement of the GI tract was more diffuse in Ipi-AC. As compared to UC, a smaller proportion of Ipi-AC biopsies had basal plasmacytosis (14% for Ipi-AC vs. 92% for UC, P < 0.0001) and crypt distortion (23% for Ipi-AC vs. 75% for UC, P = 0.003), whereas Ipi-AC biopsies had more apoptotic bodies in the left colon (17.6 ± 15.3 for Ipi-AC vs. 8.2 ± 4.2 for UC, P = 0.011). Cryptitis, ulcerations and crypt abscesses were common in both groups. Biopsy specimens from Ipi-AC had a lower density of CD20-positive lymphocytes than UC (275.8 ± 253.3 cells mm^-2 for Ipi-AC vs. 1173.3 ± 1158.2 cells mm^-2 for UC, P = 0.022) but had a similar density of CD4, CD8, CD138 and FOXP3-positive cells.

CONCLUSIONS

Ipi-AC is a distinct pathologic entity with notable clinical and histopathological differences compared to UC. These findings provide insights into the pathophysiology of immune-related adverse events (iAEs) from ipilimumab therapy.

Abstract P1-08-01: Combination checkpoint inhibition and epigenetic modulation promotes tumor suppression and improves survival in Her2+ models of breast cancer

Background: Checkpoint inhibition is a very successful treatment strategy in cancers that are naturally immunogenic by attracting T cells into the tumor microenvironment (TME) and promoting cytotoxic signaling pathways. While this strategy has shown some efficacy in metastatic breast cancer, most breast cancers are not highly immunogenic likely due to an immunosuppressive microenvironment and a lack of tumor antigen expression and recognition. One strategy to transform the breast TME is to use epigenetic modulation to affect activation and trafficking of myeloid derived suppressor cells (MDSCs), known to alter the immunogenicity of the TME and sensitize tumors to checkpoint modulation. We hypothesize that combinatorial therapy primes the TME by altering infiltration and function of MDSCs leading to a more robust T cell response. Methods: We are using a HER-2/neu transgenic mouse model with tumor challenge of syngeneic cell lines to test the efficacy of different combinations of an epigenetic agent, the histone deacetylase inhibitor entinostat (ENT), checkpoint inhibitors anti -programmed cell death protein (a-PD-1) and anti-cytotoxic T-lymphocyte-associated protein 4 (a-CTLA-4) antibodies, with and without anti-HER2 antibodies. We will examine treatment effects on tumor growth, and hope to identify co-stimulatory and inhibitory factors regulating T cell and MDSC responses. Characterization of tumor infiltrating lymphocytes and their functional capabilities are being investigated in primary tumors using fluorescence-activated cell sorting, nanostring gene expression profiling, and immunohistochemistry. Results: We found significant improvement in survival and delay in tumor growth in mice treated with ENT in combination with a-PD-1 and/or a-CTLA-4. Addition of anti-HER2 therapy to ENT and a-CTLA4 or a-PD1 also significantly improves survival and delay in tumor growth. We also found addition of ENT to checkpoint inhibition leads to significantly increased infiltration of granulocytic-MDSCs into the TME. We demonstrate an increase in CD8+ T effector cells in mice treated with combination therapy. Flow cytometric evaluation of markers of T cell activation, exhaustion, and MDSC function demonstrate significantly increased T cell activation, exhaustion, and myeloid function however it is unclear how this directly effects the phenotype we have observed in these mice. Gene expression profiling of both MDSCs and lymphocytes infiltrating tumors is underway to help determine significant changes in immune related pathways that lead to our observed outcomes. Conclusions: Addition of ENT to checkpoint inhibition significantly increases infiltration of innate and adaptive immune cells into the highly tolerant neu-N breast tumors and leads to improved survival and decreased tumor burden. Functional assays are underway and future studies will further delineate changes in immune infiltration as well as genetic alterations responsible for these observations. It is our hope that these novel findings will provide further rationale for combination therapy and improve the response rate of these immune therapies in patients with breast cancer.

Citation Format: Roussos Torres ET, Ma H, Christmas B, Armstrong T, Jaffee EM. Combination checkpoint inhibition and epigenetic modulation promotes tumor suppression and improves survival in Her2+ models of breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-08-01.

Abstract P2-04-11: Promotion of immunogenicity using epigenetic modulation and immune checkpoint inhibition in mouse models of breast cancer

This abstract was not presented at the symposium.

Synergistic effects of A1896, T1653 and T1762/A1764 mutations in genotype c2 hepatitis B virus on development of hepatocellular carcinoma

The effects of genomic changes in hepatitis B virus (HBV) on the occurrence of hepatocellular carcinoma (HCC) are still unclear, especially in relation to the genotype of HBV. In this study, we examined the effects of genomic changes in HBV of genotype C2 on the development of HCC. A total of 318 patients with HBV-associated HCC and 234 patients with chronic hepatitis B (CHB) were studied. All of HCC cases were diagnosed histologically and treated with surgical resection. The whole of the X, S, basal core promoter (BCP) and precore regions of the viral genome from sera or liver tissues were sequenced. All subjects had HBV of genotype C2. The prevalence of the T1653 mutation in the X region and the A1896 mutation in the precore region of HBV was significantly higher in the HCC group than in the control CHB group (22% vs 11%, P = 0.003; 50% vs 23%, P < 0.001, respectively). Moreover, the T1762/A1764 mutations in the BCP region in combination with either T1653 or A1896 were more common in the HCC compared with the CHB group (BCP+X1653: 18% vs 11%, P = 0.05; BCP+PC, 40% vs 15%, P < 0.001, respectively). In multivariate analysis, T1653 and A1896 were revealed to be independent risk factors for HCC development. G1896A in the precore region and C1653T mutation in the X region of genotype C2 HBV are important risk factors for HCC development. Also, the A1762T/G1764A double mutation may act in synergy with C1653T to increase the risk of HCC in patients chronically infected with HBV genotype C2.

Cancer vaccines

This unit describes the use of retroviral vectors that can be successfully employed for gene transfer into both primary tumor cultures and established cell lines. The unit includes procedures for assaying the stability of the vaccine following gene transfer. Techniques for maintaining the retroviral producer lines and titering the retroviral vectors are also described. A protocol for frozen storage of the vaccine (transduced tumor cells) is provided. In addition, methods are described for characterizing the vaccine cells following gene transfer. Directions for testing the expression of the transferred gene in the transfected tumor line are also given. The final protocol provides suggestions for designing in vivo animal experiments and discusses what has to be observed in a clinical setting.

Molecular cytogenetic characterization of pancreas cancer cell lines reveals high complexity chromosomal alterations

Karyotype analysis can provide clues to significant genes involved in the genesis and growth of pancreas cancer. The genome of pancreas cancer is complex, and G-band analysis cannot resolve many of the karyotypic abnormalities seen. We studied the karyotypes of 15 recently established cell lines using molecular cytogenetic tools. Comparative genomic hybridization (CGH) analysis of all 15 lines identified genomic gains of 3q, 8q, 11q, 17q, and chromosome 20 in nine or more cell lines. CGH confirmed frequent loss of chromosome 18, 17p, 6q, and 8p. 14/15 cell lines demonstrated loss of chromosome 18q, either by loss of a copy of chromosome 18 (n = 5), all of 18q (n = 7) or portions of 18q (n = 2). Multicolor FISH (Spectral Karyotyping, or SKY) of 11 lines identified many complex structural chromosomal aberrations. 93 structurally abnormal chromosomes were evaluated, for which SKY added new information to 67. Several potentially site-specific recurrent rearrangements were observed. Chromosome region 18q11.2 was recurrently involved in nine cell lines, including formation of derivative chromosomes 18 from a t(18;22) (three cell lines), t(17;18) (two cell lines), and t(12;18), t(15;18), t(18;20), and ins(6;18) (one cell line each). To further define the breakpoints involved on chromosome 18, YACs from the 18q11.2 region, spanning approximately 8 Mb, were used to perform targeted FISH analyses of these lines. We found significant heterogeneity in the breakpoints despite their G-band similarity, including multiple independent regions of loss proximal to the already identified loss of DPC4 at 18q21.

Bone marrow-derived cells present MHC class I-restricted tumour antigens in priming of antitumour immune responses

Many tumours express tumour-specific antigens capable of being presented to CD8+ T cells by major histocompatibility complex (MHC) class I molecules. Current models of antigen presentation predict that the tumour cell itself should present its own MHC class I-restricted antigens to T cells. Earlier cross-priming experiments have demonstrated that at least some MHC class I-restricted antigens may also be presented by bystander cells. There is no detectable presentation of MHC class I-restricted tumour antigens by the tumour itself during priming of tumour-specific responses. The tumour antigens are presented exclusively by host bone marrow-derived cells. These results imply that an efficient mechanism exists in vivo for transfer of MHC I-restricted antigens to bone marrow-derived antigen presenting cells. They also suggest that HLA matching may not be critical in the clinical application of allogeneic tumour vaccines.

A safety and efficacy trial of lethally irradiated allogeneic pancreatic tumor cells transfected with the GM-CSF gene in combination with adjuvant chemoradiotherapy for the treatment of adenocarcinoma of the pancreas

3010

Background: Pancreatic cancer remains the fourth leading cause of cancer related deaths in the US in 2006. Surgical resection provides the only possibility of cure. A standard adjuvant treatment approach for patients with resected disease has not yet been determined. We have developed an irradiated GM-CSF transfected allogeneic whole cell line pancreas adenocarcinoma vaccine. We have previously reported a follow-up 60 patient study in this same population using the highest bioactive vaccine dose identified in the initial phase I study. Methods: Single institution phase II study of 60 patients with resected pancreatic adenocarcinoma administered a total of 5 vaccines using two pancreatic cancer cell lines each delivering 2.5 X 10 8 cells ID. Vaccine one was administered 8–10 weeks following surgical resection. Patients subsequently were treated with 5-FU CI based chemotherapy integrated with radiotherapy. Patients who were disease-free one month after completion of chemoradiotherapy received vaccines 2–4, each 1 month apart. A fifth and final booster vaccine was administered 6 months after vaccine 4. The objectives of the study were: 1. To estimate overall survival and disease-free survival in patients with minimal residual disease treated with adjuvant chemoradiotherapy in sequence with the irradiated allogeneic GM-CSF transfected pancreatic tumor cell lines. 2. To characterize toxicities associated with intradermal injections of the vaccine. Results/Conclusions: The study completed enrollment of new patients in January 2005. Median follow-up for these patients is approximately 36 months. 1) The administration of a GM-CSF allogeneic pancreas cancer vaccine is safe and well tolerated; 2) The median survival is approximately 26 months. These results compare favorably with published data for resected pancreas cancer; 3) A matched cohort analysis comparing patients enrolled on this adjuvant vaccine study to the Johns Hopkins Surgery database of patients receiving surgery followed by chemoradiotherapy alone will be presented at this meeting; 4) Immune correlates will be presented at this meeting.

No significant financial relationships to disclose.

Cost-effective manufacture of an allogeneic GM-CSF-secreting breast tumor vaccine in an academic cGMP facility

BACKGROUND

GM-CSF-secreting, allogeneic cell-based cancer vaccines have shown promise for the treatment of a variety of solid tumors. We have now applied this approach to breast cancer. The aim of these studies was to optimize expansion parameters, qualify the manufacturing process, and establish expected outcomes for cGMP-compliant manufacturing of two GM-CSF-secreting breast tumor cell lines.

METHODS

The variables affecting the efficiency of expanding and formulating two allogeneic GM-CSF-secreting cell lines, 2T47D-V and 3SKBR3-7, were systematically evaluated. Production criteria investigated included alternative cell culture vessels (flasks vs. cell factories), centrifugation time and speed variables for large volume cell concentration, cell seeding density, the minimal concentration of FBS required for maximal cell expansion, and the dose and timing of irradiation in relation to cryopreservation.

RESULTS

These studies demonstrate that, in comparison with standard 150-cm2 tissue culture flasks, Nunc 10-Stack Cell Factories are a more efficient and practical cell culture vessel for vaccine cell line manufacture. Centrifugation optimization studies using the COBE 2991 Cell Processor established that a speed of 2000 r.p.m. (450 g) for 2 min reliably concentrated the cells while maintaining acceptable viability and bioactivity. Radiation studies established that lethal irradiation prior to cryopreservation does not compromise the quality of the product, as measured by post-thaw cell viability and GM-CSF cell line-specific secretion levels. Finally, studies aimed at optimizing the production of one vaccine cell line, 3SKBR3-7, demonstrated that seeding the cells at a higher density and maintaining them in half the initial concentration of FBS maximized the yield of bioactive cells, resulting in significant cost savings.

DISCUSSION

A manufacturing process that simultaneously maximizes cell yield, minimizes cell manipulation and maintains vaccine cell potency is critical for producing cell-based cancer vaccines in an academic setting. These studies define a feasible, reproducible and cost-effective methodology for production of a GM-CSF-secreting breast cancer vaccine that is cGMP compliant.

Breast cancer vaccines: maximizing cancer treatment by tapping into host immunity

Optimizing standard treatment modalities for breast cancer has improved the outlook for women afflicted with it, but the fact that 40% still ultimately die from the disease highlights the need for new therapies. Remarkable advances in molecular immunology and biotechnology have created a unique opportunity for developing active vaccination strategies that engage the patient's own immune system in the fight against breast cancer. Early clinical trials have established the safety and bioactivity of some breast cancer vaccine approaches, with a hint of clinical response. They have also highlighted the importance of elucidating the pharmacodynamic interactions between established therapies for breast cancer, such as tamoxifen, aromatase inhibitors, chemotherapy, the HER-2/neu-specific monoclonal antibody trastuzumab (Herceptin), and breast cancer vaccines. Preclinical studies have simultaneously defined the importance of developing targeted approaches for circumventing established immune tolerance to breast cancer during the vaccination process. The first strategies targeting the negative influence of CD4(+)CD25(+)T regulatory cells and the CTLA-4 signaling pathway are just entering clinical testing in combination with tumor vaccines. Developing the most potent approach for activating antitumor immunity while maintaining the efficacy of standard approaches to breast cancer management will ensure that active immunotherapy is successfully integrated into the standard of care.

Mesothelin is overexpressed in the vast majority of ductal adenocarcinomas of the pancreas: identification of a new pancreatic cancer marker by serial analysis of gene expression (SAGE)

PURPOSE

Effective new markers of pancreatic carcinoma are urgently needed. In a previous analysis of gene expression in pancreatic adenocarcinoma using serial analysis of gene expression (SAGE), we found that the tag for the mesothelin mRNA transcript was present in seven of eight SAGE libraries derived from pancreatic carcinomas but not in the two SAGE libraries derived from normal pancreatic duct epithelial cells. In this study, we evaluate the potential utility of mesothelin as a tumor marker for pancreatic adenocarcinoma.

EXPERIMENTAL DESIGN

Mesothelin mRNA expression was evaluated in pancreatic adenocarcinomas using reverse-transcription PCR (RT-PCR) and in situ hybridization, whereas mesothelin protein expression was evaluated by immunohistochemistry.

RESULTS

Using an online SAGE database (http://www.ncbi.nlm.gov/SAGE), we found the tag for mesothelin to be consistently present in the mesothelioma, ovarian cancer, and pancreatic cancer libraries but not in normal pancreas libraries. Mesothelin mRNA expression was confirmed by in situ hybridization in 4 of 4 resected primary pancreatic adenocarcinomas and by RT-PCR in 18 of 20 pancreatic cancer cell lines, whereas mesothelin protein expression was confirmed by immunohistochemistry in all 60 resected primary pancreatic adenocarcinomas studied. The adjacent normal pancreas in these 60 cases did not label, or at most only rare benign pancreatic ducts showed weak labeling for mesothelin.

CONCLUSIONS

Mesothelin is a new marker for pancreatic adenocarcinoma identified by gene expression analysis. Mesothelin overexpression in pancreatic adenocarcinoma has potential diagnostic, imaging, and therapeutic implications.

Immunologic approaches to the management of pancreatic cancer

Pancreatic cancer remains one of the most difficult cancers to treat; very few effective therapies are available, with surgery being the sole chance for cure-yet surgery is not a viable option for most pancreatic cancer patients. Immunotherapy has the potential to provide a non-cross-resistant mechanism of antitumor activity that can be integrated with surgery, radiation therapy, and chemotherapy. However, the inherent instability of the tumorgenome as well as tumor tolerance mechanisms are significant practical obstacles that must be overcome if immune-based approaches for pancreatic cancer can achieve its promise. Recent advances in both tumor immunology and vaccine design have already resulted in promising preliminary data from phase I studies, and additional trials are already in progress. This article summarizes some of the progress and challenges in immunotherapy research.

Improved gene transfer efficiency to primary and established human pancreatic carcinoma target cells via epidermal growth factor receptor and integrin-targeted adenoviral vectors

In this study we analyzed two ways of retargeting of Ad-vectors to human pancreatic carcinoma with the aim of enhancing the gene transfer efficiency. First, we analyzed the expression of the epidermal growth factor receptor (EGFR) on primary, as well as established pancreatic carcinoma cells by flow cytometry which revealed high expression levels of EGFR on the surface of these cells. We showed that EGFR-retargeted entry pathway using a bispecific fusion protein formed by a recombinant soluble form of truncated Coxsackie and Adenovirus Receptor (sCAR) genetically fused with human EGF (sCAR-EGF) redirects them to the EGFR leading to an enhanced gene transfer efficiency to pancreatic carcinoma cells. Since flow cytometry revealed absence of CAR expression, but the presence of at least one of both alphav integrins on the pancreatic carcinoma cells, a second way of targeting was investigated using a genetically modified Ad vector which has an RGD (Arg-Gly-Asp)-containing peptide inserted into the HI-loop of the fiber knob. This RGD targeted Ad (AdlucRGD) revealed efficient CAR-independent infection by allowing binding to cellular integrins resulting in a dramatic enhancement of gene transfer. These findings have direct relevance for Ad-vector based gene therapy strategies for pancreatic carcinoma.

An immunodominant MHC class II-restricted tumor antigen is conformation dependent and binds to the endoplasmic reticulum chaperone, calreticulin

There is accumulating evidence that CD4(+) T cell responses are important in antitumor immunity. Accordingly, we generated CD4(+) T cells against the murine CT26 colon cancer. Three of three independent CT26-specific CD4(+) hybridomas were found to recognize the high m.w. precursor of the env gene product gp90. The CD4(+) response was completely tumor specific in that the same glycoprotein expressed by other tumors was not recognized by the CT26-specific hybridomas. The recognition of gp90 by the hybridomas was strictly dependent on the conformation of gp90. Different procedures that disrupted the conformation of the glycoprotein, such as disulfide bond reduction and thermal denaturation, completely abrogated recognition of gp90 by all three hybridomas. In CT26 cells, but not in other tumor cells tested, a large proportion of gp90 was retained in the endoplasmic reticulum, mostly bound to the endoplasmic reticulum chaperone, calreticulin. Although calreticulin was not essential for the stimulation of the gp90-specific hybridomas, most of the antigenic form of gp90 was bound to it. The antigenicity of gp90 correlated well with calreticulin binding, reflecting the fact that specificity of binding of calreticulin to its substrate required posttranslational modifications that were also necessary for the generation of this tumor-specific CD4(+) epitope.

Discovery of new markers of cancer through serial analysis of gene expression: prostate stem cell antigen is overexpressed in pancreatic adenocarcinoma

Serial analysis of gene expression (SAGE) can be used to quantify gene expression in human tissues. Comparison of gene expression levels in neoplastic tissues with those seen in nonneoplastic tissues can, in turn, identify novel tumor markers. Such markers are urgently needed for highly lethal cancers like pancreatic adenocarcinoma, which typically presents at an incurable, advanced stage. The results of SAGE analyses of a large number of neoplastic and nonneoplastic tissues are now available online, facilitating the rapid identification of novel tumor markers. We searched an online SAGE database to identify genes preferentially expressed in pancreatic cancers as compared with normal tissues. SAGE libraries derived from pancreatic adenocarcinomas were compared with SAGE libraries derived from nonneoplastic tissues. Three promising tags were identified. Two of these tags corresponded to genes (lipocalin and trefoil factor 2) previously shown to be overexpressed in pancreatic carcinoma, whereas the third tag corresponded to prostate stem cell antigen (PSCA), a recently discovered gene thought to be largely restricted to prostatic basal cells and prostatic adenocarcinomas. PSCA was expressed in four of the six pancreatic cancer SAGE libraries, but not in the libraries derived from normal pancreatic ductal cells. We confirmed the overexpression of the PSCA mRNA transcript in 14 of 19 pancreatic cancer cell lines by reverse transcription-PCR, and using immunohistochemistry, we demonstrated PSCA protein overexpression in 36 of 60 (60%) primary pancreatic adenocarcinomas. In 59 of 60 cases, the adjacent nonneoplastic pancreas did not label for PSCA. PSCA is a novel tumor marker for pancreatic carcinoma that has potential diagnostic and therapeutic implications. These results establish the validity of analyses of SAGE databases to identify novel tumor markers.

Cyclophosphamide, doxorubicin, and paclitaxel enhance the antitumor immune response of granulocyte/macrophage-colony stimulating factor-secreting whole-cell vaccines in HER-2/neu tolerized mice

Tumor-specific immune tolerance limits the effectiveness of cancer vaccines. In addition, tumor vaccines alone have a limited potential for the treatment of measurable tumor burdens. This highlights the importance of identifying more potent cancer vaccine strategies for clinical testing. We tested immune-modulating doses of chemotherapy in combination with a granulocyte/macrophage-colony stimulating factor (GM-CSF)-secreting, HER-2/neu (neu)-expressing whole-cell vaccine as a means to treat existing mammary tumors in antigen-specific tolerized neu transgenic mice. Earlier studies have shown that neu transgenic mice exhibit immune tolerance to the neu-expressing tumors similar to what is observed in patients with cancer. We found that cyclophosphamide, paclitaxel, and doxorubicin, when given in a defined sequence with a GM-CSF-secreting, neu-expressing whole-cell vaccine, enhanced the vaccine's potential to delay tumor growth in neu transgenic mice. In addition, we showed that these drugs mediate their effects by enhancing the efficacy of the vaccine rather than via a direct cytolytic effect on cancer cells. Furthermore, paclitaxel and cyclophosphamide appear to amplify the T helper 1 neu-specific T-cell response. These findings suggest that the combined treatment with immune-modulating doses of chemotherapy and the GM-CSF-secreting neu vaccine can overcome immune tolerance and induce an antigen-specific antitumor immune response. These data provide the immunological rationale for testing immune-modulating doses of chemotherapy in combination with tumor vaccines in patients with cancer.

Chemotherapy: friend or foe to cancer vaccines?

Cancer vaccines are on the threshold of taking their place alongside the more traditional cancer treatment modalities of surgery, radiation therapy and chemotherapy. The toxicology and immunopharmacology of therapeutic cancer vaccines, particularly those that secrete granulocyte macrophage colony stimulating factor (GM-CSF), are currently under active clinical investigation. Interestingly, drugs traditionally used for tumor cytoreduction can have both positive and negative effects on host immunity. Exploration of the potential pharmacodynamic interactions of antineoplastic drugs with GM-CSF-secreting vaccines has revealed that low doses of some chemotherapeutics can augment the antitumor immunity induced by GM-CSF-secreting vaccines. These interactions will require thorough preclinical evaluation to maximize the clinical impact of this type of therapeutic cancer vaccine.

The collaboration of both humoral and cellular HER-2/neu-targeted immune responses is required for the complete eradication of HER-2/neu-expressing tumors

HER-2/neu (neu) transgenic mice (neu-N mice), which express the nontransforming rat proto-oncogene, demonstrate immunological tolerance to neu that is similar to what is encountered in patients with neu-expressing breast cancer. We have shown previously that a significant increase in neu-specific T cells, but no induction of neu-specific antibody, is seen after neu-specific vaccination in neu-N mice. In contrast, a significant induction of both neu-specific T-cell and antibody responses is found in nontoleragenic FVB/N mice after vaccination. These mice are fully protected from a s.c. challenge with NT cells, a mammary tumor cell line derived from a spontaneous tumor that arose in a neu-N mouse, whereas neu-N mice are not. In this study, we demonstrate that CD4+ T cell-depleted FVB/N mice show no induction of neu-specific IgG after vaccination and are unable to reject an NT challenge (0 of 10 mice were tumor free). Conversely, the depletion of natural killer cells has no effect on vaccine-mediated tumor rejection (100% of mice were tumor free). In CD8+ T cell-depleted animals, where vaccine-induced neu-specific IgG titers were normal, NT growth was delayed, but only 10% of mice remained tumor free, demonstrating that neu-specific IgG alone is insufficient for protection from NT challenge. To directly assess the necessity for the combination of neu-specific cellular and humoral immune responses, severe combined immunodeficient mice were given an adoptive transfer of CTLs plus IgG derived from FVB/N mice. Animals that were given CTLs that recognized an irrelevant antigen plus neu-specific IgG developed tumors at a rate similar to CD8+ T cell-depleted FVB/N mice. Animals receiving an adoptive transfer of neu-specific CTLs plus control IgG derived from naive FVB/N mice were only partially protected from NT challenge (50% of animals were tumor free). However, only animals receiving the combination of neu-specific CTLs and neu-specific IgG were fully protected from NT challenge (100% of animals were tumor free). These studies specifically define the immunological requirements for the eradication of neu-expressing tumors in this model system, demonstrating that both cellular and humoral neu-specific responses are necessary for protection from an NT challenge. These data suggest that vaccines optimized to induce maximal T- and B-cell immunity to neu, and possibly to similar putative tumor-rejection antigens, may lead to more potent in vivo antitumor immunity.

Humoral and cellular immune responses: independent forces or collaborators in the fight against cancer?

Recent advances in our understanding of immune function with regard to the generation of a potent antitumor response have resulted in a renewed interest in cancer vaccines and point to a role for immunotherapy in the treatment of cancer. Currently, the majority of vaccine strategies for the treatment of solid malignancies focus on the generation of cytotoxic T lymphocytes (CTL) that destroy tumor cells that express a given target protein, or antigen. However, antibody therapies have already been successful against some cancers. Current humoral immunotherapy typically involves the passive infusion of monoclonal antibodies, which usually target a specific tumor-encoded antigen. However, vaccines can be engineered to induce humoral immunity. By focusing on the cellular arm of the immune response at the expense of humoral immunity (or the converse), we may have inadvertently limited the potential efficacy of our anticancer vaccines. This article seeks to explore the notion that a vaccine designed to optimally activate both arms of the immune system may well generate an antitumor immune response greater than the sum of the two individual effector mechanisms alone.

Novel allogeneic granulocyte-macrophage colony-stimulating factor-secreting tumor vaccine for pancreatic cancer: a phase I trial of safety and immune activation

PURPOSE

Allogeneic granulocyte-macrophage colony-stimulating factor (GM-CSF)-secreting tumor vaccines can cure established tumors in the mouse, but their efficacy against human tumors is uncertain. We have developed a novel GM-CSF-secreting pancreatic tumor vaccine. To determine its safety and ability to induce antitumor immune responses, we conducted a phase I trial in patients with surgically resected adenocarcinoma of the pancreas.

PATIENTS AND METHODS

Fourteen patients with stage 1, 2, or 3 pancreatic adenocarcinoma were enrolled. Eight weeks after pancreaticoduodenectomy, three patients received 1 x 10(7) vaccine cells, three patients received 5 x 10(7) vaccine cells, three patients received 10 x 10(7) vaccine cells, and five patients received 50 x 10(7) vaccine cells. Twelve of 14 patients then went on to receive a 6-month course of adjuvant radiation and chemotherapy. One month after completing adjuvant treatment, six patients still in remission received up to three additional monthly vaccinations with the same vaccine dose that they had received originally.

RESULTS

No dose-limiting toxicities were encountered. Vaccination induced increased delayed-type hypersensitivity (DTH) responses to autologous tumor cells in three patients who had received >or= 10 x 10(7) vaccine cells. These three patients also seemed to have had an increased disease-free survival time, remaining disease-free at least 25 months after diagnosis.

CONCLUSION

Allogeneic GM-CSF-secreting tumor vaccines are safe in patients with pancreatic adenocarcinoma. This vaccine approach seems to induce dose-dependent systemic antitumor immunity as measured by increased postvaccination DTH responses against autologous tumors. Further clinical evaluation of this approach in patients with pancreatic cancer is warranted.

Intensified adjuvant combined modality therapy for resected periampullary adenocarcinoma: acceptable toxicity and suggestion of improved 1-year disease-free survival

PURPOSE

(1) To determine the toxicity of an intensified postoperative adjuvant regimen for periampullary adenocarcinoma (pancreatic and nonpancreatic) utilizing concurrent 5-fluorouracil (5-FU), leucovorin (LV), dipyridamole (DPM), and mitomycin-C (MMC) combined with split-course locoregional external beam radiotherapy (EBRT) to 50 Gy. This was followed by 4 cycles of the same chemotherapy as adjuvant therapy. (2) To determine preliminary estimates of the overall and disease-free survival associated with the use of this regimen. (3) To compare the toxicities and early survival results of patients treated with the current regimen to those of patients who completed our prior trial of concurrent chemoradiation infusion with 5-FU/LV chemotherapy and regional nodal and prophylactic hepatic irradiation.

METHODS

Postpancreaticoduodenectomy, patients received every 4 weeks bolus administration of 5-FU, (400 mg/m(2)), and LV, (20 mg/m(2), Days l-3), DPM (75 mg p.o., 4 times per day, Days 0-3, and every 8 weeks), MMC, (10 mg/m(2); maximum of 20 mg, Day l during EBRT). This was followed by 4 months of the same chemotherapy, beginning 1 month following the completion of EBRT. EBRT consisted of split-course 5000 cGy/20 fractions with a 2-week planned rest after the first 10 fractions (2500 cGy).

RESULTS

From 4/96 to 6/99, 45 patients were enrolled and treated. Their experience constitutes the basis of this analysis. There were 29 patients with pancreatic cancer and 16 with nonpancreatic periampullary cancer. Seventeen patients had tumors of 3 cm or more, and 39 patients had at least 1 histologically involved lymph node. Thirteen patients had a histologically positive margin of resection. The mean time to start of treatment was 63 days following surgery. During chemoradiation therapy there were no Grade 3 or worse nonhematologic toxicities and 47% Grade 3 or Grade 4 hematologic toxicities of short duration. Following chemoradiation, during chemotherapy treatment only, there was one Grade 3 hepatic and one Grade 3 pulmonary toxicity which was nondebilitating (2% each case) and 42% Grade 3 or 4 hematologic toxicity. There were 2 episodes of neutropenic fever requiring admission and no treatment-related mortalities. One patient developed a mild case of HUS, which responded to standard management. One patient developed persistent shortness of breath (nondebilitating), and another patient had occasional dyspnea on exertion, both occurring after all therapy. The majority of patients complained of increased fatigue (Grade 1-2), greatest during the combined therapy and improving post all treatment. As of 6/23/99, 20 of 45 patients have relapsed, 13 in the liver. Twelve patients have died. Median follow-up for surviving patients is 14.3 months. Disease-free survival at 12 months following surgery is 66% (as compared to 25% in our prior study), and the median disease-free survival is 17 months (as compared to 8. 3 months in our prior study). Median survival has not yet been reached, but will be greater than 17 months.

CONCLUSION

With a 14.3-month median follow-up, acute toxicity has been acceptable and manageable. Observed relapses were seen 9-13 months following surgical resection. Early survival analysis suggests a trend toward increased median disease-free survival (8.3 vs. 17 months), especially for patients with nonpancreatic periampullary adenocarcinoma.

Enhanced antigen-specific antitumor immunity with altered peptide ligands that stabilize the MHC-peptide-TCR complex

T cell responsiveness to an epitope is affected both by its affinity for the presenting MHC molecule and the affinity of the MHC-peptide complex for TCR. One limitation of cancer immunotherapy is that natural tumor antigens elicit relatively weak T cell responses, in part because high-affinity T cells are rendered tolerant to these antigens. We report here that amino acid substitutions in a natural MHC class I-restricted tumor antigen that increase the stability of the MHC-peptide-TCR complex are significantly more potent as tumor vaccines. The improved immunity results from enhanced in vivo expansion of T cells specific for the natural tumor epitope. These results indicate peptides that stabilize the MHC-peptide-TCR complex may provide superior antitumor immunity through enhanced stimulation of specific T cells.

Intracranial paracrine interleukin-2 therapy stimulates prolonged antitumor immunity that extends outside the central nervous system

To explore the potential efficacy of local cytokine delivery against tumors in the central nervous system (CNS), C57BL6 mice were simultaneously given intracranial injections of tumor challenge and of irradiated B16F10 melanoma cells transduced to secrete interleukin-2 (IL-2). Intracranial IL-2 therapy generated antitumor responses capable of extending the survival of animals that received simultaneous intracranial tumor challenge either locally or at distant sites in the brain. Nontransduced melanoma cells had little effect. Animals that survived intracranial IL-2 therapy and tumor challenge showed prolonged survival compared with controls when challenged with a second tumor dose 70 days after initial treatment. In addition, animals that rejected intracranial tumors were also protected from tumor growth upon rechallenge at sites outside the CNS (i.e., subcutaneous tumor challenge). Conversely, identical or 10-fold larger doses of IL-2-transduced cells administered by subcutaneous injection failed to generate protection against intracranial tumor challenges. Elimination of T-cell and natural killer (NK) subsets using gene knockout mice and antibody-depletion techniques demonstrated that NK cells were most important for the initial antitumor response, whereas CD4+ T-cells were not necessary. These studies demonstrate that local IL-2 therapy in the brain not only generates an immediate local antitumor immune response, but also establishes long-term immunologic memory capable of eliminating subsequent tumor challenges within and outside of the CNS. Furthermore, the antitumor response to paracrine IL-2 in the brain differed significantly from that in the flank, suggesting that the intrinsic CNS cells involved in initiating immunity within the brain have different cytokine requirements from their peripheral counterparts.

HER-2/neu is a tumor rejection target in tolerized HER-2/neu transgenic mice

HER-2/neu (neu-N) transgenic mice, which express the nontransforming rat proto-oncogene, develop spontaneous focal mammary adenocarcinomas beginning at 5-6 months of age. The development and histology of these tumors bears a striking resemblance to what is seen in patients with breast cancer. We have characterized the immunological responses to HER-2/neu (neu) in this animal model. neu-positive tumor lines, which were derived from spontaneous tumors that formed in neu-N animals, are highly immunogenic in parental, FVB/N mice. In contrast, a 100-fold lower tumor challenge is sufficient for growth in 100% of transgenic animals. Despite significant tolerance to the transgene, neu-specific immune responses similar to those observed in breast cancer patients can be demonstrated in neu-N mice prior to vaccination. Both cellular and humoral neu-specific responses in transgenic mice can be boosted with neu-specific vaccination, although to a significantly lesser degree than what is observed in FVB/N mice, indicating that the T cells involved are less responsive than in the nontoleragenic parental strain. Using irradiated whole-cell and recombinant vaccinia virus vaccinations we are able to protect neu-N mice from a neu-expressing tumor challenge. T-cell depletion experiments demonstrated that the observed protection is T cell dependent. The vaccine-dependent neu-specific immune response is also sufficient to delay the onset of spontaneous tumor formation in these mice. These data suggest that, despite tolerance to neu in this transgenic model, it is possible to immunize neu-specific T cells to achieve neu-specific tumor rejection in vivo. These transgenic mice provide a spontaneous tumor model for identifying vaccine approaches potent enough to overcome mechanisms of immune tolerance that are likely to exist in patients with cancer.

Compromised HOXA5 function can limit p53 expression in human breast tumours

Expression of the p53 gene protects cells against malignant transformation. Whereas control of p53 degradation has been a subject of intense scrutiny, little is known about the factors that regulate p53 synthesis. Here we show that p53 messenger RNA levels are low in a large proportion of breast tumours. Seeking potential regulators of p53 transcription, we found consensus HOX binding sites in the p53 promoterS. Transient transfection of Hox/HOXA5 activated the p53 promoter. Expression of HOXA5 in epithelial cancer cells expressing wild-type p53, but not in isogenic variants lacking the p53 gene, led to apoptotic cell death. Moreover, breast cancer cell lines and patient tumours display a coordinate loss of p53 and HOXA5 mRNA and protein expression. The HOXA5 promoter region was methylated in 16 out of 20 p53-negative breast tumour specimens. We conclude that loss of expression of p53 in human breast cancer may be primarily due to lack of expression of HOXA5.

Immunotherapy of cancer

The goal of cancer treatment is to develop modalities that specifically target tumor cells, thereby avoiding unnecessary side effects to normal tissue. Vaccine strategies that result in the activation of the immune system specifically against proteins expressed by a cancer have the potential to be effective treatment for this purpose. An early vaccine approach that was developed by our group involves the insertion of the granulocyte-macrophage colony stimulating factor (GM-CSF) gene into cancer cells that are then used to immunize patients. These genetically modified tumor cells produce the immune activating protein GM-CSF in the local environment of the tumor cells, specifically activating the patient's T cells to eradicate cancer at metastatic sites. We have performed many studies that demonstrate that this vaccine can cure mice of cancer. We recently demonstrated that this approach can activate an immune response in patients with renal cell carcinoma. We are currently testing a similar approach in patients with pancreatic cancer. Until recently, whole tumor cells were used to produce the vaccine because the proteins expressed by the tumor cells that can be recognized by the immune system were unknown. However, recent advances have allowed the identification of many of the proteins expressed by some cancers. In addition, significant attention has been focused on the mechanisms by which antitumor immunity can be modulated. These active areas of research will undoubtably lead to the development of more specific and more potent vaccine strategies in the near future. The first part of this paper focuses on data from two recent clinical trials that evaluated the whole tumor cell approach. The second part of this paper discusses some of the more exciting antigen-specific vaccine approaches that are under development for the treatment of cancer.

Potential role of tumor vaccines in GI malignancies

Although surgery remains the only curative option for patients with gastrointestinal (GI) malignancies, the use of adjuvant chemotherapy and/or localized radiation is considered standard therapy for patients who present with locoregional disease. Even with adjuvant therapy, however, the 5-year survival rate for such patients ranges from 2% to 50%, depending on the specific cancer type and stage. As a result, more effective interventions are necessary for all but the earliest stages of GI malignancies. Colon cancer represents the paradigm for the management of GI malignancies, not only because it is, by far, the most common cancer in this group, but also because the biological progression to disease is well characterized. Immunotherapy is an alternative approach for treating GI malignancies that can either: (1) activate tumor-specific T-cells; or (2) use monoclonal antibodies derived from tumor-specific antigens. Monoclonal antibodies act by a mechanism that is distinct from that of chemotherapy and, thus, represent a non-cross-resistant treatment with an entirely different spectrum of toxicities. Thanks to an improved understanding of tumor immunology, as well as the events needed to generate an optimal immune response, the possibility of designing an effective colon cancer vaccine approach that induces both humoral and cellular responses has become even more realistic.

Cancer vaccines

It has been more than 100 years since the first reported attempts to activate a patient's immune system to eradicate developing cancers. Although a few of the subsequent vaccine studies demonstrated clinically significant treatment effects, active immunotherapy has not yet become an established cancer treatment modality. Two recent advances have allowed the design of more specific cancer vaccine approaches: improved molecular biology techniques and a greater understanding of the mechanisms involved in the activation of T cells. These advances have resulted in improved systemic antitumor immune responses in animal models. Because most tumor antigens recognized by T cells are still not known, the tumor cell itself is the best source of immunizing antigens. For this reason, most vaccine approaches currently being tested in the clinics use whole cancer cells that have been genetically modified to express genes that are now known to be critical mediators of immune system activation. In the future, the molecular definition of tumor-specific antigens that are recognized by activated T cells will allow the development of targeted antigen-specific vaccines for the treatment of patients with cancer.

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

Human T lymphotropic virus type 1 (HTLV-1) -associated myelopathy/tropic spastic paraparesis is a demyelinating inflammatory neurologic disease associated with HTLV-1 infection. HTLV-1 Tax11-19-specific cytotoxic T cells have been isolated from HLA-A2-positive patients. We have used a peptide-loaded soluble HLA-A2-Ig complex to directly visualize HTLV-1 Tax11-19-specific T cells from peripheral blood and cerebrospinal fluid without in vitro stimulation. Five of six HTLV-1-associated myelopathy/tropic spastic paraparesis patients carried a significant number (up to 13.87%) of CD8(+) lymphocytes specific for the HTLV-1 Tax11-19 peptide in their peripheral blood, which were not found in healthy controls. Simultaneous comparison of peripheral blood and cerebrospinal fluid from one patient revealed 2.5-fold more Tax11-19-specific T cells in the cerebrospinal fluid (23.7% vs. 9.4% in peripheral blood lymphocyte). Tax11-19-specific T cells were seen consistently over a 9-yr time course in one patient as far as 19 yrs after the onset of clinical symptoms. Further analysis of HTLV-1 Tax11-19-specific CD8(+) T lymphocytes in HAM/TSP patients showed different expression patterns of activation markers, intracellular TNF-alpha and gamma-interferon depending on the severity of the disease. Thus, visualization of antigen-specific T cells demonstrates that HTLV-1 Tax11-19-specific CD8(+) T cells are activated, persist during the chronic phase of the disease, and accumulate in cerebrospinal fluid, showing their pivotal role in the pathogenesis of this neurologic disease.

Development and characterization of a cytokine-secreting pancreatic adenocarcinoma vaccine from primary tumors for use in clinical trials

Preclinical studies with murine tumor models have demonstrated that tumor cell vaccines engineered to secrete certain cytokines in a paracrine fashion elicit systemic immune responses capable of eliminating small amounts of established tumor. In particular, tumors that express the cytokine GM-CSF produce potent systemic antitumor immune responses against poorly immunogenic murine tumors. These results have encouraged the development of paracrine-cytokine secreting tumor vaccines for gene therapy of human cancer. GM-CSF recruits professional antigen-presenting cells, which in turn activate effector T cells. These findings suggest that allogeneic as well as autologous tumor cells can be used as the tumor source for developing cancer vaccines. A major obstacle to creating genetically modified human allogeneic tumor vaccines is the absence of stable cell lines required for efficient gene transfer, because most human tumors isolated from primary surgical specimens fail to proliferate in long-term culture. We have developed a method for the routine generation of in vitro cell lines from primary tumors of the pancreas. This method overcomes the common problem of stromal and fibroblast overgrowth that can inhibit the in vitro expansion of many histologic types of tumors. In addition, we have analyzed 12 of these cell lines for cytokeritin and mutated K-ras expression to demonstrate that they derive from the original epithelial tumor tissue. The lines can be genetically modified to stably express the cytokine GM-CSF. These methods should be helpful to investigators attempting to establish cell lines from other histologic tumor types for the development of allogeneic genetically modified tumor vaccines.

Enhanced tumor protection by granulocyte-macrophage colony-stimulating factor expression at the site of an allogeneic vaccine

Murine tumor models have demonstrated that whole tumor cell vaccines engineered to secrete certain cytokines in a paracrine fashion elicit systemic immune responses capable of eliminating small amounts of established tumor. In particular, autologous tumors that express the cytokine GM-CSF induce potent systemic immune responses against poorly immunogenic murine tumors. However, phase I clinical trials have demonstrated the technical difficulty of routinely expanding primary autologous human tumor cells to the numbers required for vaccination, making the generalization of autologous vaccines impractical. Dissection of the mechanism by which antitumor immunity is generated has demonstrated that GM-CSF recruits professional antigen-presenting cells that act as intermediates in presenting tumor antigen to and activating effector T cells. Furthermore, the identification of commonly recognized murine and human tumor antigens indicates that many are shared rather than unique. These findings would suggest that allogeneic as well as autologous tumor cells can be used as the vaccinating cells for activating antitumor immunity. A major concern in the application of allogeneic vaccines relates to the potential interference of allogeneic MHC expression at the vaccine site with priming of tumor-specific T cell responses. Here we describe a series of experiments that directly examines the effects of allogeneic MHC molecules on the immune-priming capabilities of a whole cell tumor vaccine engineered to secrete GM-CSF. The results demonstrate that the expression of an allogeneic MHC molecule by a vaccine cell can actually enhance the induction of systemic antitumor immunity. In addition, allogeneic MHC expression has no inhibitory effect on the ability of GM-CSF-transduced vaccines to induce systemic antitumor immunity. These findings support the design of clinical trials for testing this more feasible and generalizable allogeneic whole tumor cell vaccine approach.

Considerations for the clinical development of cytokine gene-transduced tumor cell vaccines

In preclinical models, tumor cells genetically altered to secrete cytokines or express costimulatory molecules can generate systemic antitumor immunity. In some studies, these tumor vaccines have been shown to eradicate micrometastases. These results have led to the initiation of numerous phase I clinical trials employing either genetically modified or allogenic tumor vaccines. This article addresses a number of issues related to the clinical development of cytokine gene-transduced tumor cell vaccines including: (1) the production of cytokine-secreting tumor vaccines; and (2) the preclinical feasibility and toxicity studies required for testing these vaccines in patients with cancer.

Pancreatic carcinoma cell killing via adenoviral mediated delivery of the herpes simplex virus thymidine kinase gene

OBJECTIVE

Use of adenoviral mediated delivery of the herpes simplex virus thymidine kinase (HSV-TK) gene as a gene therapy strategy for carcinoma of the pancreas.

SUMMARY BACKGROUND DATA

Expression of HSV-TK selectively sensitizes cells to the nucleoside analog ganciclovir (GCV). This strategy has been used to treat other compartmentalized tumor models. Therefore, the containment of pancreatic carcinoma makes it amenable to this gene therapy approach.

METHODS

A recombinant adenoviral vector encoding the HSV-TK gene was used to induce GCV sensitivity and test the potential bystander effect in established pancreatic carcinoma cell lines and patient-derived tumor material. Additionally, Balb/C nude mice were injected intraperitoneally with human pancreatic carcinoma cells and treated with GCV (50 mg/kg per day) for 14 days.

RESULTS

Expression of the HSV-TK gene elicited a significant bystander effect in the presence of GCV. Pancreatic tumor cells injected intraperitoneally into nude mice resulted in significant tumor formation. Treatment of animals with AdCMVHSV/HSV-TK and GCV induced a dramatic decrease in overall tumor burden for up to 8 weeks post-GCV treatment.

CONCLUSIONS

Pancreatic carcinoma cells are highly susceptible to transduction with recombinant adenoviral vector and elicit a potent bystander effect on neighboring tumor cells. Additionally, in vivo treatment of tumor-bearing animals results in dramatic reduction of overall tumor burden, thus providing the rationale for molecular chemotherapy of pancreatic carcinoma.

Bioactivity of autologous irradiated renal cell carcinoma vaccines generated by ex vivo granulocyte-macrophage colony-stimulating factor gene transfer

Granulocyte-macrophage colony-stimulating factor (GM-CSF) gene-transduced, irradiated tumor vaccines induce potent, T-cell-mediated antitumor immune responses in preclinical models. We report the initial results of a Phase I trial evaluating this strategy for safety and the induction of immune responses in patients with metastatic renal cell carcinoma (RCC). Patients were treated in a randomized, double-blind dose-escalation study with equivalent doses of autologous, irradiated RCC vaccine cells with or without ex vivo human GM-CSF gene transfer. The replication-defective retroviral vector MFG was used for GM-CSF gene transfer. No dose-limiting toxicities were encountered in 16 fully evaluable patients. GM-CSF gene-transduced vaccines were equivalent in toxicity to nontransduced vaccines up to the feasible limits of autologous tumor vaccine yield. No evidence of autoimmune disease was observed. Biopsies of intradermal sites of injection with GM-CSF gene-transduced vaccines contained distinctive macrophage, dendritic cell, eosinophil, neutrophil, and T-cell infiltrates similar to those observed in preclinical models of efficacy. Histological analysis of delayed-type hypersensitivity responses in patients vaccinated with GM-CSF-transduced vaccines demonstrated an intense eosinophil infiltrate that was not observed in patients who received nontransduced vaccines. An objective partial response was observed in a patient treated with GM-CSF gene-transduced vaccine who displayed the largest delayed-type hypersensitivity conversion. No replication-competent retrovirus was detected in vaccinated patients. This Phase I study demonstrated the feasibility, safety, and bioactivity of an autologous GM-CSF gene-transduced tumor vaccine for RCC patients.

Systemic and local paracrine cytokine therapies using transduced tumor cells are synergistic in treating intracranial tumors

Development of an effective immunotherapeutic approach for treatment of CNS tumors must take into account the unique anatomic and immunologic features of the brain. We explored the antitumor immune response in the brain elicited by nonreplicating melanoma cells genetically engineered to produce either granulocyte-macrophage colony-stimulating factor (GM-CSF) or interleukin-2 (IL-2) in a paracrine fashion. Using a new model of intracranial melanoma in C57BL/6 mice, the cytokine-producing cells were given either as a subcutaneous vaccine to induce systemic antitumor immunity or as a direct injection into the brain as local immunotherapy. We found that GM-CSF-transduced cells, as a subcutaneous vaccine but not as an intracranial injection, afforded some protection from intracranial challenge with the wild-type tumor. In contrast, direct intracranial injection of tumor cells secreting IL-2 was protective whereas flank vaccination with IL-2 transductants was not. Combination therapy with both the subcutaneous GM-CSF-transductants as a vaccine and local administration of IL-2-transductants in the brain achieved a synergistic response. These findings provide a basis for the application of paracrine cytokine delivery to brain cancer therapy both as a systemic vaccine and via local administration. The demonstration of synergy between paracrine cytokine therapies holds promise as a novel therapy for brain tumors.

Murine tumor antigens: is it worth the search?

Standardized techniques that allow the direct identification of tumor antigens are now available. Several murine antigens recognized by T cells have already been identified. So far, the majority of these antigens derive from cellular proteins similar to those that give rise to human tumor antigens. While many of the known human tumor antigens are widely shared, most of the murine tumor antigens appear to be unique to the individual tumor from which they were isolated. Nonetheless, common features between murine and human tumor antigens are emerging, suggesting that these murine antigens will provide essential tools in the evaluation of antigen-based vaccines for the future treatment of cancer.