Effective depletion of regulatory T cells allows the recruitment of mesothelin-specific CD8 T cells to the antitumor immune response against a mesothelin-expressing mouse pancreatic adenocarcinoma

A Phase I vaccine trial using dendritic cells pulsed with autologous oxidized lysate for recurrent ovarian cancer

PURPOSE

Ovarian cancer, like most solid tumors, is in dire need of effective therapies. The significance of this trial lies in its promise to spearhead the development of combination immunotherapy and to introduce novel approaches to therapeutic immunomodulation, which could enable otherwise ineffective vaccines to achieve clinical efficacy.

RATIONALE

Tumor-infiltrating T cells have been associated with improved outcome in ovarian cancer, suggesting that activation of antitumor immunity will improve survival. However, molecularly defined vaccines have been generally disappointing. Cancer vaccines elicit a modest frequency of low-to-moderate avidity tumor-specific T-cells, but powerful tumor barriers dampen the engraftment, expansion and function of these effector T-cells in the tumor, thus preventing them from reaching their full therapeutic potential. Our work has identified two important barriers in the tumor microenvironment: the blood-tumor barrier, which prevents homing of effector T cells, and T regulatory cells, which inactivate effector T cells. We hypothesize that cancer vaccine therapy will benefit from combinations that attenuate these two barrier mechanisms.

DESIGN

We propose a three-cohort sequential study to investigate a combinatorial approach of a new dendritic cell (DC) vaccine pulsed with autologous whole tumor oxidized lysate, in combination with antiangiogenesis therapy (bevacizumab) and metronomic cyclophosphamide, which impacts Treg cells.

INNOVATION

This study uses a novel autologous tumor vaccine developed with 4-day DCs pulsed with oxidized lysate to elicit antitumor response. Furthermore, the combination of bevacizumab with a whole tumor antigen vaccine has not been tested in the clinic. Finally the combination of bevacizumab and metronomic cyclophosphamide in immunotherapy is novel.

Inflammatory networks and immune surveillance of pancreatic carcinoma

Cancer-associated inflammation plays an important role in restraining anti-tumor immunity, particularly in pancreatic ductal adenocarcinoma (PDA) for which a massive infiltration of immunosuppressive leukocytes into the tumor stroma is an early and consistent event in oncogenesis. Intratumoral effector T cells are rare. This pathophysiology is in contrast to many other solid tumors for which infiltration of effector T cells is often prominent, associated with improved clinical outcomes, and mechanistically contributes to tumor immunoediting that ultimately can mediate immune escape. In PDA, increasing evidence suggests that the ras oncogene drives an inflammatory program that establishes immune privilege in the tumor microenvironment. Indeed, PDA cells might remain intrinsically sensitive to T cell killing because they have never been exposed to T cell selective pressure in vivo. In support of this hypothesis, recent studies demonstrate that derailing immune suppressive pathways in the PDA microenvironment, such as tumor derived GM-CSF, facilitates T-cell mediated tumor rejection. These findings carry major implications for the development of novel, combination immunotherapies for pancreatic cancer.

Dendritic cells fused with different pancreatic carcinoma cells induce different T-cell responses

Background

It is unclear whether there are any differences in the induction of cytotoxic T lymphocytes (CTL) and CD4⁺CD25^high regulatory T-cells (Tregs) among dendritic cells (DCs) fused with different pancreatic carcinomas. The aim of this study was to compare the ability to induce cytotoxicity by human DCs fused with different human pancreatic carcinoma cell lines and to elucidate the causes of variable cytotoxicity among cell lines.

Methods

Monocyte-derived DCs, which were generated from peripheral blood mononuclear cells (PBMCs), were fused with carcinoma cells such as Panc-1, KP-1NL, QGP-1, and KP-3L. The induction of CTL and Tregs, and cytokine profile of PBMCs stimulated by fused DCs were evaluated.

Results

The cytotoxicity against tumor targets induced by PBMCs cocultured with DCs fused with QGP-1 (DC/QGP-1) was very low, even though PBMCs cocultured with DCs fused with other cell lines induced significant cytotoxicity against the respective tumor target. The factors causing this low cytotoxicity were subsequently investigated. DC/QGP-1 induced a significant expansion of Tregs in cocultured PBMCs compared with DC/KP-3L. The level of interleukin-10 secreted in the supernatants of PBMCs cocultured with DC/QGP-1 was increased significantly compared with that in DC/KP-3L. Downregulation of major histocompatibility complex class I expression and increased secretion of vascular endothelial growth factor were observed with QGP-1, as well as in the other cell lines.

Conclusion

The present study demonstrated that the cytotoxicity induced by DCs fused with pancreatic cancer cell lines was different between each cell line, and that the reduced cytotoxicity of DC/QGP-1 might be related to the increased secretion of interleukin-10 and the extensive induction of Tregs.

Low-dose cyclophosphamide administered as daily or single dose enhances the antitumor effects of a therapeutic HPV vaccine

Although therapeutic HPV vaccines are able to elicit systemic HPV-specific immunity, clinical responses have not always correlated with levels of vaccine-induced CD8(+) T cells in human clinical trials. This observed discrepancy may be attributable to an immunosuppressive tumor microenvironment in which the CD8(+) T cells are recruited. Regulatory T cells (Tregs) are cells that can dampen cytotoxic CD8(+) T-cell function. Cyclophosphamide (CTX) is a systemic chemotherapeutic agent, which can eradicate immune cells, including inhibitory Tregs. The optimal dose and schedule of CTX administration in combination with immunotherapy to eliminate the Treg population without adversely affecting vaccine-induced T-cell responses is unknown. Therefore, we investigated various dosing and administration schedules of CTX in combination with a therapeutic HPV vaccine in a preclinical tumor model. HPV tumor-bearing mice received either a single preconditioning dose or a daily dose of CTX in combination with the pNGVL4a-CRT/E7(detox) DNA vaccine. Both single and daily dosing of CTX in combination with vaccine had a synergistic antitumor effect as compared to monotherapy alone. The potent antitumor responses were attributed to the reduction in Treg frequency and increased infiltration of HPV16 E7-specific CD8(+) T cells, which led to higher ratios of CD8(+)/Treg and CD8(+)/CD11b(+)Gr-1(+) myeloid-derived suppressor cells (MDSCs). There was an observed trend toward decreased vaccine-induced CD8(+) T-cell frequency with daily dosing of CTX. We recommend a single, preconditioning dose of CTX prior to vaccination due to its efficacy, ease of administration, and reduced cumulative adverse effect on vaccine-induced T cells.

The tipping point for combination therapy: cancer vaccines with radiation, chemotherapy, or targeted small molecule inhibitors

Therapeutic cancer vaccines are a unique treatment modality in that they initiate a dynamic process of activating the host immune system, which can then be exploited by concurrent or subsequent therapies. The addition of immunotherapy to standard-of-care cancer therapies has shown evidence of efficacy in preclinical models and in the clinical setting. This review examines the preclinical and clinical interactions between vaccine-mediated tumor-specific immune responses and local radiation, systemic chemotherapy, or select small molecule inhibitors, as well as the potential synergy between these modalities.

A novel survival-based tissue microarray of pancreatic cancer validates MUC1 and mesothelin as biomarkers

BACKGROUND

One-fifth of patients with seemingly 'curable' pancreatic ductal adenocarcinoma (PDA) experience an early recurrence and death, receiving no definable benefit from a major operation. Some patients with advanced stage tumors are deemed 'unresectable' by conventional staging criteria (e.g. liver metastasis), yet progress slowly. Effective biomarkers that stratify PDA based on biologic behavior are needed. To help researchers sort through the maze of biomarker data, a compendium of ∼2500 published candidate biomarkers in PDA was compiled (PLoS Med, 2009. 6(4) p. e1000046).

METHODS AND FINDINGS

Building on this compendium, we constructed a survival tissue microarray (termed s-TMA) comprised of short-term (cancer-specific death <12 months, n = 58) and long-term survivors (>30 months, n = 79) who underwent resection for PDA (total, n = 137). The s-TMA functions as a biological filter to identify bona fide prognostic markers associated with survival group extremes (at least 18 months separate survival groups). Based on a stringent selection process, 13 putative PDA biomarkers were identified from the public biomarker repository. Candidates were tested against the s-TMA by immunohistochemistry to identify the best markers of tumor biology. In a multivariate model, MUC1 (odds ratio, OR = 28.95, 3+ vs. negative expression, p = 0.004) and MSLN (OR = 12.47, 3+ vs. negative expression, p = 0.01) were highly predictive of early cancer-specific death. By comparison, pathologic factors (size, lymph node metastases, resection margin status, and grade) had ORs below three, and none reached statistical significance. ROC curves were used to compare the four pathologic prognostic features (ROC area = 0.70) to three univariate molecular predictors (MUC1, MSLN, MUC2) of survival group (ROC area = 0.80, p = 0.07).

CONCLUSIONS

MUC1 and MSLN were superior to pathologic features and other putative biomarkers as predicting survival group. Molecular assays comparing cancers from short and long survivors are an effective strategy to screen biomarkers and prioritize candidate cancer genes for diagnostic and therapeutic studies.

Cytotoxic activity of immunotoxin SS1P is modulated by TACE-dependent mesothelin shedding

Mesothelin is a cell-surface tumor-associated antigen expressed in several human cancers. The limited expression of mesothelin on normal tissues and its high expression in many cancers make it an attractive candidate for targeted therapies using monoclonal antibodies, immunoconjugates, and immunotoxins. Mesothelin is actively shed from the cell surface and is present in the serum of patients with malignant mesothelioma, which could negatively affect the response to these therapies. We have found that mesothelin sheddase activity is mediated by a TNF-α converting enzyme (TACE), a member of the matrix metalloproteinase/a disintegrin and metalloprotease family. We showed that EGF and TIMP-3 act through TACE as endogenous regulators of mesothelin shedding. We also found that reducing shedding significantly improved the in vitro cytotoxicity of immunotoxin SS1P, which targets mesothelin and is currently in clinical trials for the treatment of patients with mesothelioma and lung cancer. Our findings provide a mechanistic understanding of mesothelin shedding and could help improve mesothelin-based targeted therapies.

Immune modulation by chemotherapy or immunotherapy to enhance cancer vaccines

Chemotherapy has been a mainstay in cancer treatment for many years. Despite some success, the cure rate with chemotherapy remains unsatisfactory in some types of cancers, and severe side effects from these treatments are a concern. Recently, understanding of the dynamic interplay between the tumor and immune system has led to the development of novel immunotherapies, including cancer vaccines. Cancer vaccines have many advantageous features, but their use has been hampered by poor immunogenicity. Many developments have increased their potency in pre-clinical models, but cancer vaccines continue to have a poor clinical track record. In part, this could be due to an inability to effectively overcome tumor-induced immune suppression. It had been generally assumed that immune-stimulatory cancer vaccines could not be used in combination with immunosuppressive chemotherapies, but recent evidence has challenged this dogma. Chemotherapies could be used to condition the immune system and tumor to create an environment where cancer vaccines have a better chance of success. Other types of immunotherapies could also be used to modulate the immune system. This review will discuss how immune modulation by chemotherapy or immunotherapy could be used to bolster the effects of cancer vaccines and discuss the advantages and disadvantages of these treatments.

Immunomodulatory effects of cyclophosphamide and implementations for vaccine design

Drug repositioning refers to the utilization of a known compound in a novel indication underscoring a new mode of action that predicts innovative therapeutic options. Since 1959, alkylating agents, such as the lead compound cyclophosphamide (CTX), have always been conceived, at high dosages, as potent cytotoxic and lymphoablative drugs, indispensable for dose intensity and immunosuppressive regimen in the oncological and internal medicine armamentarium. However, more recent work highlighted the immunostimulatory and/or antiangiogenic effects of low dosing CTX (also called "metronomic CTX") opening up novel indications in the field of cancer immunotherapy. CTX markedly influences dendritic cell homeostasis and promotes IFN type I secretion, contributing to the induction of antitumor cytotoxic T lymphocytes and/or the proliferation of adoptively transferred T cells, to the polarization of CD4(+) T cells into TH1 and/or TH17 lymphocytes eventually affecting the Treg/Teffector ratio in favor of tumor regression. Moreover, CTX has intrinsic "pro-immunogenic" activities on tumor cells, inducing the hallmarks of immunogenic cell death on a variety of tumor types. Fifty years after its Food and Drug Administration approval, CTX remains a safe and affordable compound endowed with multifaceted properties and plethora of clinical indications. Here we review its immunomodulatory effects and advocate why low dosing CTX could be successfully combined to new-generation cancer vaccines.

The human cancer antigen mesothelin is more efficiently presented to the mouse immune system when targeted to the DEC-205/CD205 receptor on dendritic cells

To develop a tumor vaccine directly targeting tumor antigen to dendritic cells in situ, we engineered human mesothelin (MSLN) into an antibody specific for mouse DEC-205, a receptor for antigen presentation. We then characterized both T cell and humoral responses to human MSLN and compared immunizing efficacy of DEC-205-targeted MSLN to nontargeted protein after a single-dose immunization. Targeting human MSLN to DEC-205 receptor induced stronger CD4(+) T-cell responses compared to high doses of mesothelin protein. Approximately 0.5% CD4(+) T cells were primed to produce IFN-gamma, tumor necrosis factor-alpha, and IL-2 via intracellular cytokine staining, and the T cells also could proliferate rapidly. The immune response exhibited breadth because the primed CD4(+) T cells responded to at least three epitopes in the H-2(b) background. Targeting MSLN protein to DEC-205 receptor also resulted in cross-presentation to CD8(+) T cells. Antibody responses against human MSLN were also detected in serum from primed mice by ELISA assays. In summary, targeting of MSLN to DEC-205 improves the induction of CD4(+) and CD8(+) T-cell immunity accompanied by an antibody response. DEC-205-targeting could be valuable for enhancing immunity to MSLN in cancers where this nonmutated protein is expressed.