Enhancing efficacy of therapeutic vaccinations by combination with other modalities

Clinical Response of Live-Attenuated, Listeria monocytogenes Expressing Mesothelin (CRS-207) with Chemotherapy in Patients with Malignant Pleural Mesothelioma

PURPOSE

Malignant pleural mesothelioma (MPM) is an aggressive cancer associated with poor prognosis. CRS-207 is a live-attenuated Listeria monocytogenes engineered to express mesothelin, a tumor-associated antigen highly expressed in MPM. CRS-207 induces antitumor immune responses and increases susceptibility of neoplastic cells to immune-mediated killing.

PATIENTS AND METHODS

Patients with unresectable MPM, ECOG 0 or 1, and adequate organ and pulmonary function were enrolled in this multicenter, open-label phase Ib study. They received two priming infusions of 1 × 109 CFU CRS-207, followed by pemetrexed/cisplatin chemotherapy, and CRS-207 booster infusions. Primary objectives were safety and induction of immune response. Secondary/exploratory objectives included tumor response, progression-free survival (PFS), overall survival (OS), immune subset analysis, and gene-expression profiling of tumor.

RESULTS

Of 35 evaluable patients, 89% (31/35) had disease control with one complete response (3%), 19 partial responses (54%), and 10 stable disease (29%). The estimated median duration of response was 5.0 months (95% CI, 3.9-11.5). The median PFS and OS were 7.5 (95% CI, 7.0-9.9) and 14.7 (95% CI, 11.2-21.9) months, respectively. Tumor size reduction was observed post-CRS-207 infusion prior to chemotherapy in 11 of 35 (31%) patients. No unexpected treatment-related serious adverse events or deaths were observed. IHC analysis of pre- and post-CRS-207 treatment tumor biopsies revealed possible reinvigoration and proliferation of T cells, increased infiltration of dendritic and natural killer cells, increased CD8:Treg ratio, and a shift from immunosuppressive M2-like to proinflammatory M1-like macrophages following CRS-207 administration.

CONCLUSIONS

Combination of CRS-207 and chemotherapy induced significant changes in the local tumor microenvironment and objective tumor responses in a majority of treated patients.

The evolving role of immunotherapy in prostate cancer

PURPOSE OF REVIEW

In recent clinical trials, immunotherapeutic agents have demonstrated promising results for the treatment of prostate cancer. This review discusses emerging immunotherapies for prostate cancer and their evolving role in sequencing and combination therapy.

RECENT FINDINGS

Therapeutic vaccines including PROSTVAC and DCVAC/PCa have completed promising phase 2 trials for the treatment of prostate cancer and phase 3 trials are underway. Recent evidence supports a synergistic relationship between immunotherapy agents themselves, antiandrogens and with cytotoxic chemotherapy. Prostate cancer patients with good prognostic factors, such as minimal disease burden, appear to achieve the optimal benefit from immunotherapy.

SUMMARY

Therapeutic cancer vaccines and immunomodulating agents have demonstrated activity in the treatment of prostate cancer. Immunotherapies may alter the prostate tumor microenvironment and ongoing studies aim to provide guidance on effective sequencing and combination strategies.

A multi-antigen vaccine in combination with an immunotoxin targeting tumor-associated fibroblast for treating murine melanoma

A therapeutically effective cancer vaccine must generate potent antitumor immune responses and be able to overcome tolerance mechanisms mediated by the progressing tumor itself. Previous studies showed that glycoprotein 100 (gp100), tyrosinase-related protein 1 (TRP1), and tyrosinase-related protein 2 (TRP2) are promising immunogens for melanoma immunotherapy. In this study, we administered these three melanoma-associated antigens via lentiviral vectors (termed LV-3Ag) and found that this multi-antigen vaccine strategy markedly increased functional T-cell infiltration into tumors and generated protective and therapeutic antitumor immunity. We also engineered a novel immunotoxin, αFAP-PE38, capable of targeting fibroblast activation protein (FAP)-expressing fibroblasts within the tumor stroma. When combined with αFAP-PE38, LV-3Ag exhibited greatly enhanced antitumor effects on tumor growth in an established B16 melanoma model. The mechanism of action underlying this combination treatment likely modulates the immune suppressive tumor microenvironment and, consequently, activates cytotoxic CD8⁺ T cells capable of specifically recognizing and destroying tumor cells. Taken together, these results provide a strong rationale for combining an immunotoxin with cancer vaccines for the treatment of patients with advanced cancer.

Autologous melanoma cell vaccine using monocyte-derived dendritic cells (NBS20/eltrapuldencel-T)

Targeted therapy and immunotherapy have revolutionized the treatment of advanced melanoma. Despite recent advances, lack of long-term efficacy from targeted therapy and serious immune-related toxicity are major concerns. There is unmet need for 'durable' and 'safe' treatment options for advanced melanoma. Cancer vaccine therapy in melanoma has been investigated for many years with modest clinical efficacy. More recently, dendritic cell-based vaccine products have become available for clinical use and have been the focus of investigation. CLBS20 (NBS20/eltrapuldencel-T) is a novel dendritic cell-based vaccine product that has shown promising results in early phase trials in advanced melanoma. This cancer vaccine approach could play an important role in providing a sustainable survival benefit, targeting cancer cells themselves and avoiding off-target immune-related toxicity.

Therapeutic cancer vaccines: a long and winding road to success

Harnessing the immune system to achieve therapeutic efficacy in cancer has been a milestone in immuno-oncology. Tumor-induced suppression works as an obstacle for the effectiveness of immunotherapies. Advances in our understanding of the interrelationship between cancer immunoediting and immunotherapy led to successful manipulation of anticancer immunity; this provided the platform for combining cancer vaccines with chemotherapies counteracting, to some extent, tumor-induced suppressive entities and demonstrating clinical efficacy. Targeting co-inhibitory and co-stimulatory receptors with immunostimulatory antibodies has also shown clinical promise and its combined use with vaccines is a promising new approach of immunotherapy for cancer. Recent evidence supporting vaccine administration in patients with early and less aggressive disease should be additionally placed to select the appropriate patient population and to identify earlier markers of clinical benefit and immunological parameters that correlate with survival. This review focuses on promising vaccination platforms and essential perspectives in the treatment of cancer.

Humoral response to a viral glycan correlates with survival on PROSTVAC-VF

Therapeutic cancer vaccines can be effective for treating patients, but clinical responses vary considerably from patient to patient. Early indicators of a favorable response are crucial for making individualized treatment decisions and advancing vaccine design, but no validated biomarkers are currently available. In this study, we used glycan microarrays to profile antiglycan antibody responses induced by PROSTVAC-VF, a poxvirus-based cancer vaccine currently in phase III clinical trials. Although the vaccine is designed to induce T-cell responses to prostate-specific antigen, we demonstrate that this vaccine also induces humoral responses to a carbohydrate on the poxvirus, the Forssman disaccharide (GalNAcα1-3GalNAcβ). These responses had a statistically significant correlation with overall survival in two independent sample sets (P = 0.015 and 0.008) comprising more than 100 patients. Additionally, anti-Forssman humoral responses correlated with clinical outcome in a separate study of PROSTVAC-VF combined with a radiopharmaceutical (Quadramet). Studies on control subjects demonstrated that the survival correlation was specific to the vaccine. The results provide evidence that antiglycan antibody responses may serve as early biomarkers of a favorable response to PROSTVAC-VF and offer unique insights for improving vaccine design.

Combination therapy with a second-generation androgen receptor antagonist and a metastasis vaccine improves survival in a spontaneous prostate cancer model

PURPOSE

Enzalutamide, a second-generation androgen antagonist, was approved by the U.S. Food and Drug Administration (FDA) for castration-resistant prostate cancer (CRPC) treatment. Immunotherapy has been shown to be a promising strategy for prostate cancer. This study was performed to provide data to support the combination of enzalutamide and immunotherapy for CRPC treatment.

EXPERIMENTAL DESIGN

Male C57BL/6 or TRAMP (transgenic adenocarcinoma of the mouse prostate) prostate cancer model mice were exposed to enzalutamide and/or a therapeutic vaccine targeting Twist, an antigen involved in epithelial-to-mesenchymal transition and metastasis. The physiologic and immunologic effects of enzalutamide were characterized. The generation of Twist-specific immunity by Twist-vaccine was assessed. Finally, the combination of enzalutamide and Twist-vaccine to improve TRAMP mice overall survival was evaluated.

RESULTS

Enzalutamide mediated immunogenic modulation in TRAMP-C2 cells. In vivo, enzalutamide mediated reduced genitourinary tissue weight, enlargement of the thymus, and increased levels of T-cell excision circles. Because no changes were seen in T-cell function, as determined by CD4(+) T-cell proliferation and regulatory T cell (Treg) functional assays, enzalutamide was determined to be immune inert. Enzalutamide did not diminish the ability of Twist-vaccine to generate Twist-specific immunity. Twist was confirmed as a valid tumor antigen in TRAMP mice by immunohistochemistry. The combination of enzalutamide and Twist-vaccine resulted in significantly increased overall survival of TRAMP mice compared with other treatment groups (27.5 vs. 10.3 weeks). Notably, the effectiveness of the combination therapy increased with disease stage, i.e., the greatest survival benefit was seen in mice with advanced-stage prostate tumors.

CONCLUSIONS

These data support the combination of enzalutamide and immunotherapy as a promising treatment strategy for CRPC. Clin Cancer Res; 19(22); 6205-18. ©2013 AACR.

Challenges and opportunities for cancer vaccines in the current NSCLC clinical scenario

This review is aimed to focus on NSCLC as an emerging and promising model for active immunotherapy and the challenges for its inclusion in the current clinical scenario. Cancer vaccines for NSCLC have been focused as a therapeutic option based on the identification of a tumor hallmark and the active immunization with the related molecules that triggers cellular and/or humoral responses that consequently destroy or delay the rate of malignant progression. This therapeutic intervention in an established disease state has been aimed to impact into prolonging patient´s survival with ethically accepted quality of life. Understanding of relationship between structure and function in cancer vaccines is essential to interpret their opportunities to impact into prolonging survival and increasing quality of life in cancer patients. It is widely accepted that the failure of the cancer vaccines in the NSCLC scenario is related with its introduction in the advanced disease stages and poor performance status of the patients due to the combination of the tumor induced immunosuppression with the immune senescence. Despite first, second and emerging third line of onco-specific treatments the life expectancy for NSCLC patients diagnosed at advanced stages is surrounding the 12 months of median survival and in facts the today real circumstances are extremely demanding for the success inclusion of cancer vaccines as therapeutic choice in the clinical scenario. The kinetics of the active immunizations encompasses a sequential cascade of clinical endpoints: starting by the activation of the immune system, followed by the antitumor response and finalizing with the consequential impact on patients’ overall survival. Today this cascade of clinical endpoints is the backbone for active immunization assessment and moreover the concept of cancer vaccines, applied in the NSCLC setting, is just evolving as a complex therapeutic strategy, in which the opportunities for cancer vaccines start from the selection of the target cancer hallmark, followed by the vaccine formulation and its platforms for immune potentiating, also cover the successful insertion in the standard of care, the chronic administration beyond progression disease, the personalization based on predictors of response and the potential combination with other targeted therapies.

Vaccination for the prevention and treatment of breast cancer with special focus on Her-2/neu peptide vaccines

Immunologic interventions in a subset of breast cancer patients represent a well-established therapeutic approach reflecting individualized treatment modalities. Thus, the therapeutic administration of monoclonal antibodies targeting tumor-associated antigens (TAA), such as Her-2/neu, represents a milestone in cancer treatment. However, passive antibody administration suffers from several drawbacks, including frequency and long duration of treatment. These undesirables may be avoidable in an approach based on generating active immune responses against these same targets. Only recently has the significance of tumors in relation to their microenvironments been understood as essential for creating an effective cancer vaccine. In particular, the immune system plays an important role in suppressing or promoting tumor formation and growth. Therefore, activation of appropriate triggers (such as induction of Th1 cells, CD8+ T cells, and suppression of regulatory cells in combination with generation of antibodies with anti-tumor activity) is a desirable goal. Current vaccination approaches have concentrated on therapeutic vaccines using certain TAA. Many cancer antigens, including breast cancer antigens, have been described and also given priority ranking for use as vaccine antigens by the US National Cancer Institute. One of the TAA antigens which has been thoroughly examined in numerous trials is Her-2/neu. This review will discuss delivery systems for this antigen with special focus on T and B cell peptide vaccines. Attention will be given to their advantages and limitations, as well as the use of certain adjuvants to improve anti-cancer responses.

Engineered drug resistant γδ T cells kill glioblastoma cell lines during a chemotherapy challenge: a strategy for combining chemo- and immunotherapy

Classical approaches to immunotherapy that show promise in some malignancies have generally been disappointing when applied to high-grade brain tumors such as glioblastoma multiforme (GBM). We recently showed that ex vivo expanded/activated γδ T cells recognize NKG2D ligands expressed on malignant glioma and are cytotoxic to glioma cell lines and primary GBM explants. In addition, γδ T cells extend survival and slow tumor progression when administered to immunodeficient mice with intracranial human glioma xenografts. We now show that temozolomide (TMZ), a principal chemotherapeutic agent used to treat GBM, increases the expression of stress-associated NKG2D ligands on TMZ-resistant glioma cells, potentially rendering them vulnerable to γδ T cell recognition and lysis. TMZ is also highly toxic to γδ T cells, however, and to overcome this cytotoxic effect γδ T cells were genetically modified using a lentiviral vector encoding the DNA repair enzyme O(6)-alkylguanine DNA alkyltransferase (AGT) from the O(6)-methylguanine methyltransferase (MGMT) cDNA, which confers resistance to TMZ. Genetic modification of γδ T cells did not alter their phenotype or their cytotoxicity against GBM target cells. Importantly, gene modified γδ T cells showed greater cytotoxicity to two TMZ resistant GBM cell lines, U373(TMZ-R) and SNB-19(TMZ-R) cells, in the presence of TMZ than unmodified cells, suggesting that TMZ exposed more receptors for γδ T cell-targeted lysis. Therefore, TMZ resistant γδ T cells can be generated without impairing their anti-tumor functions in the presence of high concentrations of TMZ. These results provide a mechanistic basis for combining chemotherapy and γδ T cell-based drug resistant cellular immunotherapy to treat GBM.

Therapeutic vaccines and immunotherapy in castration-resistant prostate cancer: current progress and clinical applications

Results of recent clinical trials have intensified interest in immunotherapy for cancer. Among the most promising candidates for immunotherapy are patients with prostate cancer. Results of therapeutic vaccine clinical trials in this population have suggested statistically significant and clinically meaningful improvements in overall survival, with substantially fewer side effects than with chemotherapy. Of particular interest are sipuleucel-T, the first U.S. Food and Drug Administration-approved therapeutic cancer vaccine, and PSA-TRICOM (PROSTVAC), a therapeutic cancer vaccine in phase III testing. The immune checkpoint inhibitor ipilimumab is also stirring considerable interest, with two phase III trials ongoing in prostate cancer. This article highlights data emerging from these trials and addresses remaining questions and practical clinical implications of this therapeutic strategy.

Therapeutic vaccines and immunotherapy in castration-resistant prostate cancer: current progress and clinical applications

Results of recent clinical trials have intensified interest in immunotherapy for cancer. Among the most promising candidates for immunotherapy are patients with prostate cancer. Results of therapeutic vaccine clinical trials in this population have suggested statistically significant and clinically meaningful improvements in overall survival, with substantially fewer side effects than with chemotherapy. Of particular interest are sipuleucel-T, the first U.S. Food and Drug Administration-approved therapeutic cancer vaccine, and PSA-TRICOM (PROSTVAC), a therapeutic cancer vaccine in phase III testing. The immune checkpoint inhibitor ipilimumab is also stirring considerable interest, with two phase III trials ongoing in prostate cancer. This article highlights data emerging from these trials and addresses remaining questions and practical clinical implications of this therapeutic strategy.

Therapeutic cancer vaccines: the latest advancement in targeted therapy

Therapeutic cancer vaccines represent an emerging therapeutic modality that may play a more prominent role in cancer treatment in the future. Therapeutic cancer vaccines are designed to generate a targeted, immune-mediated antitumor response. There are 2 main types of therapeutic vaccines: patient-specific (generated either from a patient's own cells or tumor) and patient- nonspecific, where a peptide- or vector-based vaccine induces an immune response in vivo against specific tumor-associated antigens. Studies are currently underway to investigate methods to enhance vaccine strategies, including combinations with standard anticancer therapies or immune-modulating agents. Cancer vaccines are usually well tolerated, with minimal toxicity compared with chemotherapy. This review summarizes selected therapeutic cancer vaccines in late clinical development.

Impact of tumour volume on the potential efficacy of therapeutic vaccines

With the recent approval by the U.S. Food and Drug Administration of the first therapeutic vaccine for cancer, the long-awaited goal of harnessing a patient's immune system to attack cancer through this modality is finally realized. However, as researchers in the field of cancer immunotherapy continue to perform randomized definitive studies, much remains to be learned about potential surrogate endpoints and appropriate patient populations for therapeutic vaccines. The present review addresses available data from clinical trials of immunotherapeutic agents relevant to the selection of appropriate patient populations. We believe that the weight of evidence supports the use of immunotherapy earlier in the disease course and in patients with less aggressive disease, and that the relevant findings have important implications for the design of clinical trials with therapeutic vaccines.

Sipuleucel-T: a therapeutic cancer vaccine for the treatment of castration- or hormone-refractory prostate cancer

Sipuleucel-T is a therapeutic cancer vaccine approved for the treatment of castration- or hormone-refractory prostate cancer. Through a novel process, it activates the body's own antigen-presenting cells to induce an immune response to prostatic acid phosphatase, a protein found on prostate cancer cells. A treatment course consists of three total infusions spread 2 weeks apart. Throughout all phases of clinical trials, sipuleucel-T has been shown to be safe and well tolerated. Sipuleucel-T has demonstrated an ability to increase overall survival by approximately 4 months when compared with placebo. However, sipuleucel-T has not shown any improvement in affecting patients' time to disease progression.

Cancer therapy and vaccination

Cancer remains one of the leading causes of death worldwide, both in developed and in developing nations. It may affect people at all ages, even fetuses, but the risk for most varieties increases with age. Current therapeutic approaches which include surgery, chemotherapy and radiotherapy are associated with adverse side effects arising from lack of specificity for tumors. The goal of any therapeutic strategy is to impact on the target tumor cells with limited detrimental effect to normal cell function. Immunotherapy is cancer specific and can target the disease with minimal impact on normal tissues. Cancer vaccines are capable of generating an active tumor-specific immune response and serve as an ideal treatment due to their specificity for tumor cells and long lasting immunological memory that may safeguard against recurrences. Cancer vaccines are designed to either prevent (prophylactic) or treat established cancer (therapeutic). Identification of tumor-associated antigens (TAAs) and tumor-specific antigens (TSAs) has led to increased efforts to develop vaccination strategies. Vaccines may be composed of whole cells or cell extracts, genetically modified tumor cells to express costimulatory molecules, dendritic cells (DCs) loaded with TAAs, immunization with soluble proteins or synthetic peptides, recombinant viruses or bacteria encoding tumor-associated antigens, and plasmid DNA encoding TSAs or TAAs in conjunction with appropriate immunomodulators. All of these antitumor vaccination approaches aim to induce specific immunological responses and localized to TAAs, destroying tumor cells alone and leaving the vast majority of other healthy cells of the body untouched.

Immune response to sipuleucel-T in prostate cancer

Historically, chemotherapy has remained the most commonly utilized therapy in patients with metastatic cancers. In prostate cancer, chemotherapy has been reserved for patients whose metastatic disease becomes resistant to first line castration or androgen deprivation. While chemotherapy palliates, decreases serum prostate specific antigen and improves survival, it is associated with significant side effects and is only suitable for approximately 60% of patients with castrate-resistant prostate cancer. On that basis, exploration of other therapeutic options such as active secondary hormone therapy, bone targeted treatments and immunotherapy are important. Until recently, immunotherapy has had no role in the treatment of solid malignancies aside from renal cancer and melanoma. The FDA-approved autologous cellular immunotherapy sipuleucel-T has demonstrated efficacy in improving overall survival in patients with metastatic castrate-resistant prostate cancer in randomized clinical trials. The proposed mechanism of action is reliant on activating the patients' own antigen presenting cells (APCs) to prostatic acid phosphatase (PAP) fused with granulocyte-macrophage colony stimulating factor (GM-CSF) and subsequent triggered T-cell response to PAP on the surface of prostate cancer cells in the patients body. Despite significant prolongation of survival in Phase III trials, the challenge to health care providers remains the dissociation between objective changes in serum PSA or on imaging studies after sipleucel-T and survival benefit. On that basis there is an unmet need for markers of outcome and a quest to identify immunologic or clinical surrogates to fill this role. This review focuses on the impact of sipuleucel-T on the immune system, the T and B cells, and their responses to relevant antigens and prostate cancer. Other therapeutic modalities such as chemotherapy, corticosteroids and GM-CSF and host factors can also affect immune response. The optimal timing for immunotherapy, patient selection and best sequencing with other prostate cancer therapies remain to be determined. A better understanding of immune response may help address these issues.

Treatment of a solid tumor using engineered drug-resistant immunocompetent cells and cytotoxic chemotherapy

Multimodal therapy approaches, such as combining chemotherapy agents with cellular immunotherapy, suffers from potential drug-mediated toxicity to immune effector cells. Overcoming such toxic effects of anticancer cellular products is a potential critical barrier to the development of combined therapeutic approaches. We are evaluating an anticancer strategy that focuses on overcoming such a barrier by genetically engineering drug-resistant variants of immunocompetent cells, thereby allowing for the coadministration of cellular therapy with cytotoxic chemotherapy, a method we refer to as drug-resistant immunotherapy (DRI). The strategy relies on the use of cDNA sequences that confer drug resistance and recombinant lentiviral vectors to transfer nucleic acid sequences into immunocompetent cells. In the present study, we evaluated a DRI-based strategy that incorporates the immunocompetent cell line NK-92, which has intrinsic antitumor properties, genetically engineered to be resistant to both temozolomide and trimetrexate. These immune effector cells efficiently lysed neuroblastoma cell lines, which we show are also sensitive to both chemotherapy agents. The antitumor efficacy of the DRI strategy was demonstrated in vivo, whereby neuroblastoma-bearing NOD/SCID/γ-chain knockout (NSG) mice treated with dual drug-resistant NK-92 cell therapy followed by dual cytotoxic chemotherapy showed tumor regression and significantly enhanced survival compared with animals receiving either nonengineered cell-based therapy and chemotherapy, immunotherapy alone, or chemotherapy alone. These data show there is a benefit to using drug-resistant cellular therapy when combined with cytotoxic chemotherapy approaches.

Immune response to sipuleucel-T in prostate cancer

Historically, chemotherapy has remained the most commonly utilized therapy in patients with metastatic cancers. In prostate cancer, chemotherapy has been reserved for patients whose metastatic disease becomes resistant to first line castration or androgen deprivation. While chemotherapy palliates, decreases serum prostate specific antigen and improves survival, it is associated with significant side effects and is only suitable for approximately 60% of patients with castrate-resistant prostate cancer. On that basis, exploration of other therapeutic options such as active secondary hormone therapy, bone targeted treatments and immunotherapy are important. Until recently, immunotherapy has had no role in the treatment of solid malignancies aside from renal cancer and melanoma. The FDA-approved autologous cellular immunotherapy sipuleucel-T has demonstrated efficacy in improving overall survival in patients with metastatic castrate-resistant prostate cancer in randomized clinical trials. The proposed mechanism of action is reliant on activating the patients' own antigen presenting cells (APCs) to prostatic acid phosphatase (PAP) fused with granulocyte-macrophage colony stimulating factor (GM-CSF) and subsequent triggered T-cell response to PAP on the surface of prostate cancer cells in the patients body. Despite significant prolongation of survival in Phase III trials, the challenge to health care providers remains the dissociation between objective changes in serum PSA or on imaging studies after sipleucel-T and survival benefit. On that basis there is an unmet need for markers of outcome and a quest to identify immunologic or clinical surrogates to fill this role. This review focuses on the impact of sipuleucel-T on the immune system, the T and B cells, and their responses to relevant antigens and prostate cancer. Other therapeutic modalities such as chemotherapy, corticosteroids and GM-CSF and host factors can also affect immune response. The optimal timing for immunotherapy, patient selection and best sequencing with other prostate cancer therapies remain to be determined. A better understanding of immune response may help address these issues.

IL-13 receptor-directed cancer vaccines and immunotherapy

Many immunotherapy approaches including therapeutic cancer vaccines targeting specific tumor-associated antigens are at various stages of development. Although the significance of overexpression of (IL-13Rα2) in cancer is being actively investigated, we have reported that IL-13Rα2 is a novel tumor-associated antigen. The IL-13Rα2-directed cancer vaccine is one of the most promising approaches to tumor immunotherapy, because of the selective expression of IL-13Rα2 in various solid tumor types but not in normal tissues. In this article, we will summarize its present status and potential strategies to improve IL-13Rα2-directed cancer vaccines for an optimal therapy of cancer.

Cancer immunotherapy: sipuleucel-T and beyond

In April 2010, sipuleucel-T became the first anticancer vaccine approved by the United States Food and Drug Administration. Different from the traditional chemotherapy agents that produce widespread cytotoxicity to kill tumor cells, anticancer vaccines and immunotherapies focus on empowering the immune system to overcome the tumor. The immune system consists of innate and adaptive components. The CD4(+) and CD8(+) T cells are the most crucial components of the adaptive arm of the immune system that act to mediate antitumor responses. However, T-cell responses are regulated by intrinsic and extrinsic mechanisms, which may interfere with effective antitumor responses. Many anticancer immunotherapies use tumor-associated antigens as vaccines in order to stimulate an immune response against tumor cells. Sipuleucel-T is composed of autologous mononuclear cells incubated with a fusion protein consisting of a common prostate cancer antigen (prostatic acid phosphatase) linked to an adjuvant (granulocyte-macrophage colony-stimulating factor). It is postulated that when the vaccine is infused into the patient, the activated antigen-presenting cells displaying the fusion protein will induce an immune response against the tumor antigen. In a recent randomized, double-blind, placebo-controlled, phase III clinical trial, sipuleucel-T significantly improved median overall survival by 4.1 months in men with metastatic castration-resistant prostate cancer compared with placebo. Although overall survival was improved, none of the three phase III clinical trials found a significant difference in time to disease progression. This, along with cost and logistic issues, has led to an active discussion. Although sipuleucel-T was studied in the metastatic setting, its ideal place in therapy is unknown, and clinical trials are being conducted in patients at different stages of disease and in combination with radiation therapy, antiandrogen therapy, and chemotherapy. Various other anticancer vaccines and immunotherapies for other tumor types are currently under investigation and in clinical trials. These immunotherapies were formulated to incorporate tumor-associated antigens aimed at stimulating effector T-cell responses or to block regulatory mechanisms that suppress the function of effector T cells. Additional studies will determine how these therapies can best improve clinical outcomes in patients with cancer.

Endpoints, patient selection, and biomarkers in the design of clinical trials for cancer vaccines

Therapeutic cancer vaccines are an emerging and potentially effective treatment modality. Cancer vaccines are usually very well tolerated, with minimal toxicity compared with chemotherapy. Unlike conventional cytotoxic therapies, immunotherapy does not result in immediate tumor shrinkage but may alter growth rate and thus prolong survival. Multiple randomized controlled trials of various immunotherapeutic agents have shown a delayed separation in Kaplan-Meier survival curves, with no evidence of clinical benefit within the first 6-12 months of vaccine treatment. Overall survival benefit is seen in patients with lower disease burden who are not expected to die within those initial 6-12 months. The concept of improved overall survival without marked initial tumor reduction represents a significant shift from the current paradigms established by standard cytotoxic therapies. Future clinical studies of therapeutic vaccines should enroll patients with either lower tumor burden, more indolent disease or both, and must seek to identify early markers of clinical benefit that may correlate with survival. Until then, improved overall survival is the only clear, discriminatory endpoint for therapeutic vaccines as monotherapies.

A novel combination immunotherapy for cancer by IL-13Rα2-targeted DNA vaccine and immunotoxin in murine tumor models

Optimum efficacy of therapeutic cancer vaccines may require combinations that generate effective antitumor immune responses, as well as overcome immune evasion and tolerance mechanisms mediated by progressing tumor. Previous studies showed that IL-13Rα2, a unique tumor-associated Ag, is a promising target for cancer immunotherapy. A targeted cytotoxin composed of IL-13 and mutated Pseudomonas exotoxin induced specific killing of IL-13Rα2(+) tumor cells. When combined with IL-13Rα2 DNA cancer vaccine, surprisingly, it mediated synergistic antitumor effects on tumor growth and metastasis in established murine breast carcinoma and sarcoma tumor models. The mechanism of synergistic activity involved direct killing of tumor cells and cell-mediated immune responses, as well as elimination of myeloid-derived suppressor cells and, consequently, regulatory T cells. These novel results provide a strong rationale for combining immunotoxins with cancer vaccines for the treatment of patients with advanced cancer.

Immunotherapy in prostate cancer: emerging strategies against a formidable foe

Recent clinical trials have shown therapeutic vaccines to be promising treatment modalities against prostate cancer. Unlike preventive vaccines that teach the immune system to fight off specific microorganisms, therapeutic vaccines stimulate the immune system to recognize and attack certain cancer-associated proteins. Additional strategies are being investigated that combine vaccines and standard therapeutics, including radiation, chemotherapy, targeted therapies, and hormonal therapy, to optimize the vaccines' effects. Recent vaccine late-phase clinical trials have reported evidence of clinical benefit while maintaining excellent quality of life. One such vaccine, sipuleucel-T, was recently FDA-approved for the treatment of metastatic prostate cancer. Another vaccine, PSA-TRICOM, is also showing promise in completed and ongoing randomized multicenter clinical trials in both early- and late-stage prostate cancer. Clinical results available to date indicate that immune-based therapies could play a significant role in the treatment of prostate and other malignancies.

Dendritic cell-based vaccination of patients with advanced pancreatic carcinoma: results of a pilot study

BACKGROUND AND AIMS

Dendritic cell (DC)-based vaccination can induce antitumor T cell responses in vivo. This clinical pilot study examined feasibility and outcome of DC-based tumor vaccination for patients with advanced pancreatic adenocarcinoma.

METHODS

Tumor lysate of patients with pancreatic carcinoma was generated by repeated freeze-thaw cycles of surgically obtained tissue specimens. Patients were eligible for DC vaccination after recurrence of pancreatic carcinoma or in a primarily palliative situation. DC were generated from peripheral blood mononuclear cells (PBMC), loaded with autologous tumor lysate, stimulated with TNF-α and PGE(2) and injected intradermally. All patients received concomitant chemotherapy with gemcitabine. Disease response was the primary endpoint. Individual immunological responses to DC vaccination were analyzed by T cell-based immunoassays using pre- and post-vaccination samples of non-adherent PBMC.

RESULTS

Twelve patients received DC vaccination and concomitant chemotherapy. One patient developed a partial remission, and two patients remained in stable disease. Median survival was 10.5 months. No severe side effects were observed. Tumor-reactive T cells could be detected prior to vaccination. DC vaccination increased the frequency of tumor-reactive cells in all patients tested; however, the degree of this increase varied. To quantify the presence of tumor-reactive T cells, stimulatory indices (SI) were calculated as the ratio of proliferation-inducing capacity of lysate-loaded versus -unloaded DC. The patient with longest overall survival of 56 months had a high SI of 6.49, indicating that the presence of a pre-vaccination antitumor T cell response might be associated with prolonged survival. Five patients survived 1 year or more.

CONCLUSION

DC-based vaccination can stimulate an antitumoral T cell response in patients with advanced or recurrent pancreatic carcinoma receiving concomitant gemcitabine treatment.

Immunotherapy for prostate cancer: recent advances, lessons learned, and areas for further research

A surge of interest in therapeutic cancer vaccines has arisen in the wake of recent clinical trials suggesting that such vaccines can result in statistically significant and clinically meaningful improvements in overall survival-with substantially limited side effects compared with chemotherapy-in patients with metastatic castration-resistant prostate cancer. One of these trials led to the registration of sipuleucel-T, the first therapeutic vaccine to be approved for cancer patients. In this review we highlight emerging patterns from clinical trials that suggest a need for more-appropriate patient populations (i.e., with lower tumor volume and less-aggressive disease) and endpoints (i.e., overall survival) for studies of immunotherapy alone, as well as biologically plausible explanations for these findings. We also explore the rationale for ongoing and planned studies combining therapeutic vaccines with other modalities. Finally, we attempt to put these findings into a practical clinical context and suggest fertile areas for future study. Although our discussion focuses on prostate cancer, the concepts we address most likely have broad applicability to immunotherapy for other cancers as well.

Tumor regression and growth rates determined in five intramural NCI prostate cancer trials: the growth rate constant as an indicator of therapeutic efficacy

PURPOSE

In solid tumors such as prostate cancer, novel paradigms are needed to assess therapeutic efficacy. We utilized a method estimating tumor growth and regression rate constants from serial PSA measurements, and assessed its potential in patients with metastatic castration resistant prostate carcinoma (mCRPC).

EXPERIMENTAL DESIGN

Patients were enrolled in five phase II studies, including an experimental vaccine trial, representing the evolution of therapy in mCRPC. PSA measurements obtained before, and during, therapy were used. Data analysis using a two-phase mathematical equation yielded concomitant PSA growth and regression rate constants.

RESULTS

Growth rate constants (g) can be estimated while patients receive therapy and in such patients g is superior to PSA-DT in predicting OS. Incremental reductions in growth rate constants were recorded in successive trials with a 10-fold slower g in the most recent combination therapy trial (log g = 10(-3.17)) relative to single-agent thalidomide (log g = 10(-2.08)) more than a decade earlier. Growth rate constants correlated with survival, except in patients receiving vaccine-based therapy where the evidence demonstrates prolonged survival presumably due to immunity developing subsequent to vaccine administration.

CONCLUSION

Incremental reductions in tumor growth rate constants suggest increased efficacy in successive chemotherapy trials. The derived growth rate constant correlates with survival, and may be used to assess efficacy. The PSA-TRICOM vaccine appears to have provided marked benefit not apparent during vaccination, but consistent with subsequent development of a beneficial immune response. If validated as a surrogate for survival, growth rate constants would offer an important new efficacy endpoint for clinical trials.

Immunotherapy for lung cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. Although treatment methods in surgery, irradiation, and chemotherapy have improved, prognosis remains unsatisfactory and developing new therapeutic strategies is still an urgent demand. Immunotherapy is a novel therapeutic approach wherein activated immune cells can specifically kill tumor cells by recognition of tumor-associated antigens without damage to normal cells. Several lung cancer vaccines have demonstrated prolonged survival time in phase II and phase III trials, and several clinical trials are under investigation. However, many clinical trials involving cancer vaccination with defined tumor antigens work in only a small number of patients. Cancer immunotherapy is not completely effective in eradicating tumor cells because tumor cells escape from host immune scrutiny. Understanding of the mechanism of immune evasion regulated by tumor cells is required for the development of more effective immunotherapeutic approaches against lung cancer. This paper discusses the identification of tumor antigens in lung cancer, tumor immune escape mechanisms, and clinical vaccine trials in lung cancer.

Novel targeted agents on the horizon for castration-resistant prostate cancer

Androgen deprivation treatment in prostate cancer patients is well established; however, resistance to such treatment manifests itself by progression to castration-resistant prostate cancer (CRPC). Despite significant advances in treatment options for patients with CRPC, their prognosis remains poor. Resistance results from multiple processes that facilitate cancer cell growth and survival. Mechanisms underlying the shift to castrate resistance have been attributed to a complex interplay of clonal selection, reactivation of the androgen receptor axis despite castrate levels of serum testosterone, stress-induced prosurvival genes and cytoprotective chaperone networks and alternative mitogenic growth factor pathways. This article discusses several pathways involved in the development of CRPC, with a particular focus on those mechanisms that have led to the development of new targeted therapies.

Chemotherapy delivered after viral immunogene therapy augments antitumor efficacy via multiple immune-mediated mechanisms

The most widely used approach to cancer immunotherapy is vaccines. Unfortunately, the need for multiple administrations of antigens often limits the use of one of the most effective vaccine approaches, immunogene therapy using viral vectors, because neutralizing antibodies are rapidly produced. We hypothesized that after viral immunogene therapy "primed" an initial strong antitumor immune response, subsequent "boosts" could be provided by sequential courses of chemotherapy. Three adenoviral (Ad)-based immunogene therapy regimens were administered to animals with large malignant mesothelioma and lung cancer tumors followed by three weekly administrations of a drug regimen commonly used to treat these tumors (Cisplatin/Gemcitabine). Immunogene therapy followed by chemotherapy resulted in markedly increased antitumor efficacy associated with increased numbers of antigen-specific, activated CD8(+) T-cells systemically and within the tumors. Possible mechanisms included: (i) decreases in immunosuppressive cells such as myeloid-derived suppressor cells (MDSC), T-regulatory cells (T-regs), and B-cells, (ii) stimulation of memory cells by intratumoral antigen release leading to efficient cross-priming, (iii) alteration of the tumor microenvironment with production of "danger signals" and immunostimulatory cytokines, and (iv) augmented trafficking of T-cells into the tumors. This approach is currently being tested in a clinical trial and could be applied to other trials of viral immunogene therapy.

The state of antibody therapy

Therapeutic antibodies are widely used in the treatment of various diseases and disease conditions, including cardiovascular diseases, autoimmune disorders, malignancies, and infections. With at least 23 therapeutic agents currently in clinical use and a successful business generating large revenues, major technological advances are now in place to improve the specificity and efficacy of those antibodies already in the market and also generate new, safe and effective macromolecules for the treatment of other ailments. This review provides a summary of the current state of antibody therapy, highlights and discusses recent developments in the field of antibody-based therapeutics production, combination therapy and shows the status of some of the agents that are in clinical trial.

Effect of a small molecule BCL-2 inhibitor on immune function and use with a recombinant vaccine

Small molecule BCL-2 inhibitors are being examined as monotherapy in phase I/II clinical trials for several types of tumors. However, few data are available about the effect of BCL-2 inhibitors on immune function. The aims of our study were to investigate the effect of a small molecule BCL-2 inhibitor on immune function and determine the most effective way of combining this inhibitor with a recombinant vaccine to treat tumors. The in vitro effect of the pan-BCL-2 inhibitor GX15-070 was assessed in mouse CD8 T lymphocytes at 2 different stages of activation as well as regulatory T lymphocytes (Treg). The in vivo effect of GX15-070 after recombinant vaccinia/fowlpox CEA-TRICOM vaccination was analyzed in tumor-infiltrating lymphocytes, and in splenocytes of mice bearing subcutaneous tumors. The therapeutic efficacy of such sequential therapy was measured as a reduction of pulmonary tumor nodules. Activated mature CD8 T lymphocytes were more resistant to GX15-070 as compared to early-activated cells. Treg function was significantly decreased after treatment with the BCL-2 inhibitor. In vivo, GX15-070 was given after vaccination so as to not negatively impact the induction of vaccine-mediated immunity, resulting in increased intratumoral activated CD8:Treg ratio and significant reduction of pulmonary tumor nodules. Our study is the first to show the effect of a small molecule BCL-2 inhibitor on the immune system and following a vaccine. It is also the first to demonstrate the efficacy of this sequence in reducing tumors in mouse models, providing a rationale for the design of combinational clinical studies.

Vaccine-induced antibody responses in patients with carcinoma

Cancer vaccines based on defined antigens are capable of inducing antibodies that recognize and kill tumor cells. Antibodies are ideally suited to address minimal residual disease, and vaccination in an adjuvant setting may favorably influence the outcome of a disease. The present article gives a short summary of antibody production by B cells, and the mechanism of action of antibodies, as well as a description of the current methods for measuring antibody responses and for assessing their antitumor efficacy in the context of clinical trials. It concludes with an overview of antibody responses induced by vaccines based on structurally defined tumor-associated antigens tested in patients with carcinomas. Correlation between antibody responses, T-cell responses and clinical outcome has been noted in a few studies, signaling the importance of vaccine design and adjuvants to exploit the interactions of the innate and adaptive immune system. However, humoral responses, which may provide a surrogate marker for T-helper responses and simplify monitoring of large Phase III trials, are still not or incompletely explored in many vaccination trials.

Therapeutic cancer vaccines in prostate cancer: the paradox of improved survival without changes in time to progression

Therapeutic cancer vaccines represent a new class of agents in the treatment of cancer. Sipuleucel-T is an antigen-presenting cell-based vaccine that recently demonstrated a significant 4.8-month improvement in overall survival in advanced prostate cancer patients and was well tolerated. The findings of that study have been met with skepticism, primarily because the agent did not change initial disease progression and yet led to longer survival. Although the commonly accepted treatment paradigm suggests that treatments should initially decrease tumor volume, perhaps vaccines work differently. Vaccines may induce delayed responses not seen in the first few months of therapy or they may initiate a dynamic immune response that ultimately slows the tumor growth rate, resulting in longer survival. Subsequent therapies may also combine with the induced immune response, resulting in a combination that is more effective than conventional treatments alone. Also, other treatments may alter tumor-associated antigen expression, enhancing the immune response. Future trials are currently planned to investigate these hypotheses; however, the results of the sipuleucel-T vaccine in prostate cancer should not be dismissed. Results with another vaccine in prostate cancer are similar, perhaps suggesting a class effect. In a broader context, clinicians may need to reconsider how they measure success. Several agents have been approved that produce superior disease progression results, but do not affect overall survival. Given the toxicity and costs of cancer therapies, perhaps studies should put more weight on long-term survival endpoints than on short-term endpoints that may be less consequential.

Prostate cancer as a model for tumour immunotherapy

Advances in basic immunology have led to an improved understanding of the interactions between the immune system and tumours, generating renewed interest in approaches that aim to treat cancer immunologically. As clinical and preclinical studies of tumour immunotherapy illustrate several immunological principles, a review of these data is broadly instructive and is particularly timely now that several agents are beginning to show evidence of efficacy. This is especially relevant in the case of prostate cancer, as recent approval of sipuleucel-T by the US Food and Drug Administration marks the first antigen-specific immunotherapy approved for cancer treatment. Although this Review focuses on immunotherapy for prostate cancer, the principles discussed are applicable to many tumour types, and the approaches discussed are highlighted in that context.

INGN-225: a dendritic cell-based p53 vaccine (Ad.p53-DC) in small cell lung cancer: observed association between immune response and enhanced chemotherapy effect

IMPORTANCE OF THE FIELD

Novel approaches are needed for patients with small cell lung cancer (SCLC), as response after relapse is poor with standard therapies. p53 gene mutations often occur, resulting in tumoral protein overexpression and allowing for their recognition by p53-specific cytotoxic T cells.

AREAS COVERED IN THIS REVIEW

We describe the characteristics and manufacturing of INGN-225, a p53-modified adenovirus-tranduced dendritic cell vaccine, and review available data, to understand INGN-225's role in SCLC treatment. We discuss our pre-clinical, early Phase I/II, and ongoing randomized Phase II studies.

WHAT THE READER WILL GAIN

INGN-225 was well tolerated (all toxicities

TAKE HOME MESSAGE

INGN-225 is safe, induces a significant immune response, and appears to sensitize SCLC to subsequent chemotherapy. Improvements in immune response induction and understanding the chemotherapy-immunotherapy synergism will determine INGN-225's future role as an anticancer therapy.

Collapse

Key Words

• adenovirus
• dendritic cells
• ingn-225
• p53 gene
• small cell lung cancer

Collapse

MESH Headings

• Animals
• Cancer Vaccines/administration & dosage
• Cancer Vaccines/adverse effects
• Cancer Vaccines/therapeutic use
• Clinical Trials, Phase I as Topic
• Clinical Trials, Phase II as Topic
• Dendritic Cells/immunology
• Humans
• Immunotherapy
• Lung Neoplasms/immunology
• Lung Neoplasms/therapy
• Randomized Controlled Trials as Topic
• Small Cell Lung Carcinoma/immunology
• Small Cell Lung Carcinoma/therapy
• Tumor Suppressor Protein p53/immunology

Collapse

Grants

• K24 CA128953 NCI NIH HHS
• P50 CA119997 NCI NIH HHS
• 5P50- CA- 119997 NCI NIH HHS

Collapse

Affiliation(s)

Alberto A Chiappori Department of Thoracic Oncology, H Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, FL 33612, USA.
Hatem Soliman
William E Janssen
Scott J Antonia
Dmitry I Gabrilovich

Collapse

Collaborators Collapse

Immunotherapy for prostate cancer: an emerging treatment modality

This article examines prostate cancer as a target for immunotherapy and investigates active immunotherapy for prostate cancer, combining conventional therapy with active immunotherapy, immune modulators (brakes and accelerators), and monoclonal antibodies.

Combination of all-trans retinoic acid and a human papillomavirus therapeutic vaccine suppresses the number and function of immature myeloid cells and enhances antitumor immunity

Despite advances in the development of human papillomavirus (HPV) prophylactic vaccines, little progress has been made in the field of therapeutic vaccines in recent years. In the present study, we found a significant accumulation of immature myeloid cells (ImC) in large TC-1 tumors and demonstrated that a HPV therapeutic vaccine restored antitumor immune responses with the correction of aberrant myeloid cell differentiation by all-trans retinoic acid (ATRA). Our study demonstrated that combining ATRA with vaccination not only decreased the number of Gr-1+ CD11b+ ImC, but for the first time also suppressed the function of Gr-1+ CD11b+ ImC with decreased expression of CD80. Furthermore, large numbers of CD11c+ CD80+, CD11c+ CD86+, and CD11c+ MHCII+ mature dendritic cells were recruited. The combination therapy generated significantly increased numbers of functional E7-specific T cells with elevated interferon- secretion and enhanced cytotoxic T-cell activity. These findings suggest potential clinical benefits for the combined use of ATRA and HPV therapeutic vaccines.

Principles of vaccination and possible development strategies for rational design

Historically, apart from hygiene, vaccination can be considered as one of the most successful accomplishments of public health in the 20th century. It has lead to some of the greater public health triumphs ever, including the eradication of naturally occurring smallpox and in the control of diseases such as polio. In addition there has been a significant reduction in disease burden imposed by measles, mumps, hepatitis, influenza, diphtheria, haemophilus influenza B and many other infections.

Dendritic cell-based cancer vaccination: quo vadis?

Dendritic cells (DCs) play a central role in the initiation and regulation of primary immune responses. DCs loaded with tumor-associated antigens induce anti-tumoral cytotoxic T cells in vitro and in vivo. However, clinical trials using ex vivo-generated DCs have failed to demonstrate clinical efficacy. This review summarizes recent advances in concepts and techniques that are providing new impulses to DC-based cancer vaccination. Improvements in protocols for ex vivo-generation of DCs, innovations in immunomonitoring, strategies to overcome tumor-induced immunosuppression and insights into the mutual beneficial effects of vaccines and chemotherapy are all considered. Furthermore, we highlight novel developments in cell-free vaccines targeting DCs in vivo.

Pilot study of vaccination with recombinant CEA-MUC-1-TRICOM poxviral-based vaccines in patients with metastatic carcinoma

PURPOSE

Poxviral vectors have a proven safety record and can be used to incorporate multiple transgenes. Prior clinical trials with poxviral vaccines have shown that immunologic tolerance to self-antigens can be broken. Carcinoembryonic antigen (CEA) and MUC-1 are overexpressed in a substantial proportion of common solid carcinomas. The primary end point of this study was vaccine safety, with immunologic and clinical responses as secondary end points.

EXPERIMENTAL DESIGN

We report here a pilot study of 25 patients treated with a poxviral vaccine regimen consisting of the genes for CEA and MUC-1, along with a triad of costimulatory molecules (TRICOM; composed of B7.1, intercellular adhesion molecule 1, and lymphocyte function-associated antigen 3) engineered into vaccinia (PANVAC-V) as a prime vaccination and into fowlpox (PANVAC-F) as a booster vaccination.

RESULTS

The vaccine was well tolerated. Apart from injection-site reaction, no grade > or =2 toxicity was seen in more than 2% of the cycles. Immune responses to MUC-1 and/or CEA were seen following vaccination in 9 of 16 patients tested. A patient with clear cell ovarian cancer and symptomatic ascites had a durable (18-month) clinical response radiographically and biochemically, and one breast cancer patient had a confirmed decrease of >20% in the size of large liver metastasis.

CONCLUSIONS

This vaccine strategy seems to be safe, is associated with both CD8 and CD4 immune responses, and has shown evidence of clinical activity. Further trials with this agent, either alone or in combination with immunopotentiating and other therapeutic agents, are warranted.

Anti-angiogenetic effects of immune-reconstituted influenza virosomes assembled with parathyroid hormone-related protein derived peptide vaccine

BACKGROUND

C-IRIV/PTR-4 is a novel anticancer vaccine construct composed of immune-reconstituted influenza virosomes (IRIV) assembled with the PTH-rP derived peptide (PTR)-4, a synthetic CTL epitope with HLA-A(*)02.01 amino acid binding motifs. This peptide is able to generate a human PTH-rP specific CTL response with anti-tumor activity in vitro and in mice.

MATERIALS AND METHODS

We have investigated the immunological and preventive anti-tumor activity of C-IRIV/PTR-4 compared with the soluble PTR-4 peptide, in HHD mice inoculated with autologous PTH-rP+ tumor cells.

RESULTS

Peptide vaccination with either a soluble and an IRIV formulation showed similar immunological activity and the ability to purge the tumor tissue of tumor cell clones able to produce the target antigen (PTR-rP). The most efficient protection from tumor growth was however observed in animals vaccinated with C-IRIV/PTR-4 in which an additional IRIV related anti-angiogenetic effect was detected in the tumor tissue.

CONCLUSIONS

These results confirm the immunological activity of PTR-4 vaccination and suggest a more efficacious therapeutic potential of C-IRIV/PTR-4 against bone metastases and malignancies like breast, prostate and lung which very often over-express PTH-rP.

Lessons from randomized phase III studies with active cancer immunotherapies--outcomes from the 2006 meeting of the Cancer Vaccine Consortium (CVC)

After years of effort to develop active cancer immunotherapies, seven candidate products achieved promising results in phase I/II studies that triggered phase III randomized studies. One candidate to date has received an approvable letter from the United States Food and Drug Administration (FDA), defining a clear path to licensure for sipuleucel-T (Provenge, Dendreon) within the next couple of years. The other phase III studies failed to achieve statistical criteria for some or all of the critical endpoints. Yet, there is widespread recognition that using a patient's own immune system to target and destroy cancer cells may offer an effective biological therapy with less toxicity than presently available anti-cancer therapies, and several candidates are still being evaluated in clinical studies. This review summarizes the lessons learned from these case studies, evaluates scientific, study design, and business factors that can affect study outcomes, identifies common challenges faced by sponsors developing these innovative therapies, and provides considerations for future study designs that may increase the likelihood of success.