Follow-up evaluation of prostate cancer patients infused with autologous dendritic cells pulsed with PSMA peptides

Oncolytic Adenovirus Type 3 Coding for CD40L Facilitates Dendritic Cell Therapy of Prostate Cancer in Humanized Mice and Patient Samples

Dendritic cell (DC)-based vaccines have shown some degree of success for the treatment of prostate cancer (PC). However, the highly immunosuppressive tumor microenvironment leads to DC dysfunction, which has limited the effectiveness of these vaccines. We hypothesized that use of a fully serotype 3 oncolytic adenovirus (Ad3-hTERT-CMV-hCD40L; TILT-234) could stimulate DCs in the prostate tumor microenvironment by expressing CD40L. Activated DCs would then activate cytotoxic T cells against the tumor, resulting in therapeutic immune responses. Oncolytic cell killing due to cancer cell-specific virus replication adds to antitumor effects but also enhances the immunological effect by releasing tumor epitopes for sampling by DC, in the presence of danger signals. In this study, we evaluated the companion effect of Ad3-hTERT-CMV-hCD40L and DC-therapy in a humanized mouse model and PC histocultures. Treatment with Ad3-hTERT-CMV-hCD40L and DC resulted in enhanced antitumor responses in vivo. Treatment of established histocultures with Ad3-hTERT-CMV-hCD40L induced DC maturation and notable increase in proinflammatory cytokines. In conclusion, Ad3-hTERT-CMV-hCD40L is able to modulate an immunosuppressive prostate tumor microenvironment and improve the effectiveness of DC vaccination in PC models and patient histocultures, setting the stage for clinical translation.

Dendritic cells pulsed with prostate-specific membrane antigen in metastatic castration-resistant prostate cancer patients: a systematic review and meta-analysis

BACKGROUND

Dendritic cells (DCs) are used in many malignancies as vaccines to induce immunity against specific cancer antigens. The role of DCs in metastatic castration-resistant prostate cancer (mCRPC) is not determined. In this study, the proportion of mCRPC patients with clinically significant response to targeted therapy by DCs pulsed with prostate-specific membrane antigen was evaluated, and the possible adverse effects of this modality were investigated.

METHODS

Major databases were searched up to Feb 2017, to identify studies in which the antitumor efficacy of DCs pulsed with the extracellular portion of PSMA was studied for the treatment of mCRPC. Data were collected by two reviewers and analyzed using Comprehensive Meta-Analysis software, version 2.0.

FINDINGS

Our study consisted of 6 nonrandomized prospective (cohort) trials, overall reporting on 153 mCRPC patients. The event rate that is the representative of fraction of patients showing antitumor response was 0.43 (95% confidence interval = 0.355-0.512; P = 0.097). No significant between-study heterogeneity or inconsistency was detected (I2 = 5.47; Q = 5; P = 0.382). Our study failed to demonstrate a significant therapeutic efficacy for DCs in mCRPC. However, no significant adverse effects were seen.

Targeting prostate cancer: Prostate-specific membrane antigen based diagnosis and therapy

The high incidence rates of prostate cancer (PCa) raise demand for improved therapeutic strategies. Prostate tumors specifically express the prostate-specific membrane antigen (PSMA), a membrane-bound protease. As PSMA is highly overexpressed on malignant prostate tumor cells and as its expression rate correlates with the aggressiveness of the disease, this tumor-associated biomarker provides the possibility to develop new strategies for diagnostics and therapy of PCa. Major advances have been made in PSMA targeting, ranging from immunotherapeutic approaches to therapeutic small molecules. This review elaborates the diversity of PSMA targeting agents while focusing on the radioactively labeled tracers for diagnosis and endoradiotherapy. A variety of radionuclides have been shown to either enable precise diagnosis or efficiently treat the tumor with minimal effects to nontargeted organs. Most small molecules with affinity for PSMA are based on either a phosphonate or a urea-based binding motif. Based on these pharmacophores, major effort has been made to identify modifications to achieve ideal pharmacokinetics while retaining the specific targeting of the PSMA binding pocket. Several tracers have now shown excellent clinical usability in particular for molecular imaging and therapy as proven by the efficiency of theranostic approaches in current studies. The archetypal expression profile of PSMA may be exploited for the treatment with alpha emitters to break radioresistance and thus to bring the power of systemic therapy to higher levels.

EpCAM peptide-primed dendritic cell vaccination confers significant anti-tumor immunity in hepatocellular carcinoma cells

Cancer stem-like cells (CSCs) may play a key role in tumor initiation, self-renewal, differentiation, and resistance to current treatments. Dendritic cells (DCs) play a vital role in host immune reactions as well as antigen presentation. In this study, we explored the suitability of using CSC peptides as antigen sources for DC vaccination against human breast cancer and hepatocellular carcinoma (HCC) with the aim of achieving CSC targeting and enhancing anti-tumor immunity. CD44 is used as a CSC marker for breast cancer and EpCAM is used as a CSC marker for HCC. We selected CD44 and EpCAM peptides that bind to HLA-A2 molecules on the basis of their binding affinity, as determined by a peptide-T2 binding assay. Our data showed that CSCs express high levels of tumor-associated antigens (TAAs) as well as major histocompatibility complex (MHC) molecules. Pulsing DCs with CD44 and EpCAM peptides resulted in the efficient generation of mature DCs (mDCs), thus enhancing T cell stimulation and generating potent cytotoxic T lymphocytes (CTLs). The activation of CSC peptide-specific immune responses by the DC vaccine in combination with standard chemotherapy may provide better clinical outcomes in advanced carcinomas.

Intravenously usable fully serotype 3 oncolytic adenovirus coding for CD40L as an enabler of dendritic cell therapy

Vaccination with dendritic cells (DCs), the most potent professional antigen-presenting cells in the body, is a promising approach in cancer immunotherapy. However, tumors induce immunosuppression in their microenvironment that suppresses and impairs the function of DCs. Therefore, human clinical trials with DC therapy have often been disappointing. To improve the therapeutic efficacy and to overcome the major obstacles of DC therapy, we generated a novel adenovirus, Ad3-hTERT-CMV-hCD40L, which is fully serotype 3 and expresses hCD40L for induction of antitumor immune response. The specific aim is to enhance DCs function. Data from a human cancer patient indicated that this capsid allows effective transduction of distant tumors through the intravenous route. Moreover, patient data suggested that virally produced hCD40L can activate DCs in situ. The virus was efficient in vitro and had potent antitumor activity in vivo. In a syngeneic model, tumors treated with Ad5/3-CMV-mCD40L virus plus DCs elicited greater antitumor effect as compared with either treatment alone. Moreover, virally coded CD40L induced activation of DCs, which in turn, lead to the induction of a Th1 immune response and increased tumor-specific T cells. In conclusion, Ad3-hTERT-CMV-hCD40L is promising for translation into human trials. In particular, this virus could enable successful dendritic cell therapy in cancer patients.

Clinical use of dendritic cells for cancer therapy

Since the mid-1990s, dendritic cells have been used in clinical trials as cellular mediators for therapeutic vaccination of patients with cancer. Dendritic cell-based immunotherapy is safe and can induce antitumour immunity, even in patients with advanced disease. However, clinical responses have been disappointing, with classic objective tumour response rates rarely exceeding 15%. Paradoxically, findings from emerging research indicate that dendritic cell-based vaccination might improve survival, advocating implementation of alternative endpoints to assess the true clinical potency of dendritic cell-based vaccination. We review the clinical effectiveness of dendritic cell-based vaccine therapy in melanoma, prostate cancer, malignant glioma, and renal cell carcinoma, and summarise the most important lessons from almost two decades of clinical studies of dendritic cell-based immunotherapy in these malignant disorders. We also address how the specialty is evolving, and which new therapeutic concepts are being translated into clinical trials to leverage the clinical effectiveness of dendritic cell-based cancer immunotherapy. Specifically, we discuss two main trends: the implementation of the next-generation dendritic cell vaccines that have improved immunogenicity, and the emerging paradigm of combination of dendritic cell vaccination with other cancer therapies.

Perspectives on immunotherapy in prostate cancer and solid tumors: where is the future?

The goals of any cancer therapy are to improve disease control, palliate pain and improve overall survival. We are fortunate to have in our cancer armamentarium two new immune-directed therapies which not only impact on disease control but also on overall survival. The first, sipuleucel-T, a cellular-based vaccine, was approved for prostate cancer and was shown to be safe with minimal toxicity. The second, ipilimumab, a monoclonal antibody directed to an immunologic checkpoint molecule, showed a survival benefit in patients with advanced melanoma. Benefit appeared to correlate in some cases with the development of autoimmune events, signaling that the immune system is in overdrive against the cancer. Where we are and where we will likely go are the topics to be discussed in this review.

Proof of Concept to Clinical Confirmation: Evolving Clinical Trial Designs for Targeted Agents

No single therapy benefits the majority of patients in the practice of oncology as responses differ even among patients with similar tumor types. The variety of response to therapy witnessed while treating our patients supports the concept of personalized medicine using patients' genomic and biologic information and their clinical characteristics to make informed decisions about their treatment. Personalized medicine relies on identification and confirmation of biologic targets and development of agents to target them. These targeted agents tend to focus on subsets of patients and provide improved clinical outcomes. The continued success of personalized medicine will depend on the expedited development of new agents from proof of concept to confirmation of clinical efficacy.

Optimizing DC vaccination by combination with oncolytic adenovirus coexpressing IL-12 and GM-CSF

Dendritic cell (DC)-based vaccination is a promising strategy for cancer immunotherapy. However, clinical trials have indicated that immunosuppressive microenvironments induced by tumors profoundly suppress antitumor immunity and inhibit vaccine efficacy, resulting in insufficient reduction of tumor burdens. To overcome these obstacles and enhance the efficiency of DC vaccination, we generated interleukin (IL)-12- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-coexpressing oncolytic adenovirus (Ad-ΔB7/IL12/GMCSF) as suitable therapeutic adjuvant to eliminate immune suppression and promote DC function. By treating tumors with Ad-ΔB7/IL12/GMCSF prior to DC vaccination, DCs elicited greater antitumor effects than in response to either treatment alone. DC migration to draining lymph nodes (DLNs) dramatically increased in mice treated with the combination therapy. This result was associated with upregulation of CC-chemokine ligand 21 (CCL21⁺) lymphatics in tumors treated with Ad-ΔB7/IL12/GMCSF. Moreover, the proportion of CD4⁺CD25⁺ T-cells and vascular endothelial growth factor (VEGF) expression was decreased in mice treated with the combination therapy. Furthermore, combination therapy using immature DCs also showed effective antitumor effects when combined with Ad-ΔB7/IL12/GMCSF. The combination therapy had a remarkable therapeutic efficacy on large tumors. Taken together, oncolytic adenovirus coexpressing IL-12 and GM-CSF in combination with DC vaccination has synergistic antitumor effects and can act as a potent adjuvant for promoting and optimizing DC vaccination.

Dendritic cell-based immunotherapy for prostate cancer

Dendritic cells (DCs) are professional antigen-presenting cells (APCs), which display an extraordinary capacity to induce, sustain, and regulate T-cell responses providing the opportunity of DC-based cancer vaccination strategies. Thus, clinical trials enrolling prostate cancer patients were conducted, which were based on the administration of DCs loaded with tumor-associated antigens. These clinical trials revealed that DC-based immunotherapeutic strategies represent safe and feasible concepts for the induction of immunological and clinical responses in prostate cancer patients. In this context, the administration of the vaccine sipuleucel-T consisting of autologous peripheral blood mononuclear cells including APCs, which were pre-exposed in vitro to the fusion protein PA2024, resulted in a prolonged overall survival among patients with metastatic castration-resistent prostate cancer. In April 2010, sipuleucel-T was approved by the United States Food and Drug Administration for prostate cancer therapy.

A changing world for DCvax: a PSMA loaded autologous dendritic cell vaccine for prostate cancer

BACKGROUND

Northwest Therapeutics' DCvax-prostate consists of autologous dendritic cells (DCs) loaded with prostate-specific membrane antigen (PSMA) peptides, administered intravenously. Phase I-II testing, a decade ago, showed clinical benefit and immunological response in some patients. More recently DCvax brain, a product using a similar DC platform showed encouraging Phase I-II results and sipleucel-T, a prostatic acid phosphatase (PAP)-directed DC immunotherapy had positive Phase III results.

OBJECTIVE

Features of the clinical setting into which a new immunotherapy could be introduced are discussed, to refine a perspective on DCvax-prostate in the context of evolving prostate cancer therapeutics. PSMA-directed therapeutics and immune anticancer technologies are reviewed, and the clinical and immunological correlative testing of DCvax-prostate is discussed.

METHODS

Clinical and preclinical data from peer-reviewed literature, meetings proceedings and manufacturer-provided information are considered.

CONCLUSION

DCvax-prostate had encouraging early-phase trial results, but development and testing had stalled. As a more detailed understanding of patient-selection for capacity for anticancer immune response, the quantitation of immunological correlates, and the changing marketplace develop, it is appealing to consider a well tolerated, PSMA-directed autologous dendritic cell therapeutic product. Further clinical trial development of DCvax-prostate is warranted, and required if it is to find a relevant clinical application.

Phase I clinical trial of an adenovirus/prostate-specific antigen vaccine for prostate cancer: safety and immunologic results

PURPOSE

We performed a phase I clinical trial of adenovirus/prostate-specific antigen (PSA) vaccine in men with measurable metastatic hormone-refractory disease.

EXPERIMENTAL DESIGN

Men with measurable metastatic disease received one vaccine injection. Toxicity, immune responses, changes in PSA doubling times, and patient survival were assessed. Thirty-two patients with hormone-refractory metastatic prostate cancer were treated with a single s.c. vaccine injection at one of three dose levels, either as an aqueous solution or suspended in a Gelfoam matrix. All patients returned for physical and clinical chemistry examinations at regular intervals up to 12 months after injections.

RESULTS

The vaccine was deemed safe at all doses in both administration forms. There were no serious vaccine-related adverse events; the most prevalent were localized erythema/ecchymoses and cold/flu-like symptoms. Anti-PSA antibodies were produced by 34% of patients and anti-PSA T-cell responses were produced by 68%. PSA doubling time was increased in 48%, whereas 55% survived longer than predicted by the Halabi nomogram.

CONCLUSIONS

The adenovirus/PSA vaccine was proven safe with no serious vaccine-related adverse events. The majority of vaccinated patients produced anti-PSA T-cell responses and over half survived longer than predicted by nomogram. Although the latter data are only derived from a small number of patients in this phase I trial, they are encouraging enough to pursue further studies.

CpG oligonucleotide as an adjuvant for the treatment of prostate cancer

The use of an adenovirus transduced to express a prostate cancer antigen (PSA) as a vaccine for the treatment of prostate cancer has been shown to be active in the destruction of antigen-expressing prostate tumor cells in a pre-clinical model, using Balb/C or PSA transgenic mice. The destruction of PSA-secreting mouse prostate tumors was observed in Ad/PSA immunized mice in a prophylaxis study with 70% of the mice surviving long term tumor free. This successful immunotherapy was not observed in therapeutic studies in which tumors were established before vaccination and the development of anti-PSA immune response was not as easily generated in PSA transgenic mice. Immunization of conventional and transgenic animals was enhanced by incorporating a collagen matrix into the immunizing injection. Therefore the need to strengthen anti-PSA and anti-prostate cancer immunity was an obvious next step in developing a successful prostate cancer immunotherapy. Because the use of immunostimulatory CpG motifs was shown to enhance immune responses to a wide variety of antigens, our studies incorporated CpG into the Ad/PSA vaccine experimental plans. The results of the subsequent studies demonstrated a dichotomy where Ad/PSA plus CpG enhanced the in vivo destruction of PSA-secreting tumors and the survival of experimental animals, but revealed that the number and in vitro activities of antigen specific CD8+ T cells was decreased as compared to the values observed when the vaccine alone was used for immunization. The dichotomous observations were confirmed using another antigen system, OVA also incorporated into a replication defective adenovirus. Despite the reduction in antigen-specific CD8+ cells after vaccine plus CpG immunization the enhanced destruction of sc and systemic tumors was shown to be mediated entirely by CD8+ T cells. Finally, the reduction of the CD8+ T cells was the result of an observed decrease in the proliferation of the antigen specific cell population.

Advances in specific immunotherapy for prostate cancer

OBJECTIVES

The absence of effective therapies for advanced prostate cancer has entailed an intensive search for novel treatments. This review presents an overview of specific immunotherapeutic strategies for prostate cancer.

METHODS

Current literature was reviewed regarding the identification of tumor antigens and the design of T-cell- and antibody-based immunotherapy for prostate cancer. The PubMed database was searched using the key words antibodies, clinical trials, dendritic cells, immunotherapy, prostate cancer, and T cells.

RESULTS

T cells and antibodies are powerful components of the specific antitumor immune response. CD8+ cytotoxic T lymphocytes (CTLs) efficiently destroy tumor cells. CD4+ T cells improve the antigen-presenting capacity of dendritic cells (DCs) and support the stimulation of tumor-reactive CTLs. Monoclonal antibodies exhibit their antitumor effects via antibody-dependent cellular cytotoxicity and complement activation. Consequently, much attention has been given to the identification of tumor antigens that represent attractive targets for specific immunotherapy. Several prostate cancer-related antigens were described and used in clinical trials. Such studies were based on the administration of peptides, proteins, or DNA. Furthermore, men with prostate cancer were vaccinated with peptide-, protein-, or RNA-loaded DCs, which display an extraordinary capacity to induce tumor-reactive T cells. Monoclonal antibodies directed against surface antigens were also used. Clinical trials revealed that immunotherapeutic strategies represent safe and feasible concepts for the induction of immunologic and clinical responses in men with prostate cancer.

CONCLUSIONS

Specific immunotherapy represents a promising treatment modality for prostate cancer. Further improvement of the current approaches is required and may be achieved by combining T-cell- and antibody-based vaccination strategies with radio-, hormone-, chemo-, or antiangiogenic therapy.

Immunology and immunotherapy approaches for prostate cancer

Several mechanisms that impair the immune response to promote tumour progression are reported. These mechanisms aim to reduce the ability of antigen-presenting cells to present antigen and activate naïve T cells to support an active immune response or to create a suppressive environment that induce non-functional tumour-associated antigen-specific T cells. Prostate cancer (PC) alone accounts for 33% of incident cancer cases and about 9% of all cancer-related deaths among men in the USA during 2006. Whereas androgen deprivation has remained the first line of therapy for advanced PC, other therapies are still required due to progression to an androgen-resistant state and eventually loss of control in patients receiving hormonal therapy. Immunotherapy seems to be a promising approach to enhance tumour-specific T-cell responses in different cancers including prostate. More importantly, clinical trials in advanced PC patients have shown that immunotherapy may generate significant clinical responses. Immunology and immunotherapy aspects of PC with focus on prostate-specific antigen will be presented.

Results of a phase I clinical study using dendritic cell vaccinations for thyroid cancer

OBJECTIVE

We assessed the feasibility and efficacy of dendritic cell (DC) therapy for advanced thyroid papillary and follicular cancer.

DESIGN

Six Japanese patients (2 men and 4 women; aged 46-72 years, mean 60 years), who were diagnosed as advanced thyroid cancer with refractory distant metastases (papillary, n=5; follicular, n=1), were enrolled. Patients were first vaccinated weekly for 4 weeks with 10(7) autologous tumor lysate-pulsed monocyte-derived mature DCs followed by fortnightly vaccinations for 8 weeks (total=8 vaccinations). Lowdose (350 KIU) interleukin-2 was also administered for 3 days at each vaccination. Clinical response, adverse effects, delayed-type hypersensitivity skin testing (DTH), and IFN-( ) production by peripheral CD3(+) lymphocytes were evaluated.

MAIN OUTCOME

Of the 6 patients, disease was assessed as stable in 2 and as progressive in 4. No adverse events were observed. Results of DTH and IFN-( ) production in peripheral lymphocytes did not correlate to the clinical response.

CONCLUSIONS

DC immunotherapy could be administered to patients with thyroid papillary or follicular cancer without substantial side effects.

Advances in Prostate Cancer Immunotherapies

Prostate cancer is a major cause of mortality in men in the Western world. Although treatment of early stage prostate cancer with radiation therapy or prostatectomy is efficient in most cases, some patients develop a fatal hormone-refractory disease. Treatments in this case are limited to aggressive chemotherapies, which can reduce serum prostate-specific antigen (PSA) levels in some patients. Taxane- and platinum-compound-based chemotherapies produce a survival benefit of only a few months. Therefore, it is crucial to develop novel, well tolerated treatment strategies. Over the past years, immunotherapy of hormone-refractory prostate cancer has been studied in numerous clinical trials. The fact that the prostate is a non-essential organ makes prostate cancer an excellent target for immunotherapy. Administration of antibodies targeting the human epidermal growth factor receptor-2 or the prostate-specific membrane antigen led to stabilisation of PSA levels in several patients. Vaccination of prostate cancer patients with irradiated allogeneic prostate cell lines has demonstrated that whole cell-based vaccines can significantly attenuate increases in PSA. Two different recombinant viral expression vectors have been applied in prostate cancer treatment: poxvirus and adenovirus vectors. Both vaccines have the advantages of using a natural method to induce immune responses and achieving high levels of transgene expression. Vaccinia viruses in combination with recombinant fowlpox or canarypox virus have been used to express recombinant PSA. Several studies demonstrated that this approach is safe and can lead to stabilisation of PSA values. A very promising approach in prostate cancer immunotherapy is vaccination of patients with dendritic cells. Thereby, peptides, recombinant proteins, tumour lysates or messenger RNA have been used to deliver antigens to autologous dendritic cells. Loading of dendritic cells with up to five different peptides derived from multiple proteins expressed in prostate cancer demonstrated that cytotoxic T-cell responses could be elicited in prostate cancer patients. Sipuleucel-T (APC8015), an immunotherapy product consisting of antigen-presenting cells, loaded ex vivo with a recombinant fusion protein consisting of prostatic acid phosphatase linked to granulocyte-macrophage colony-stimulating factor, demonstrated in a phase III, placebo-controlled trial an improvement in median time to disease progression. The improvement in overall survival was 4.5 months for sipuleucel-T-treated patients compared with the placebo group. Although there is a minor increase in overall survival of metastatic prostate cancer patients with some approaches, more effective therapeutic strategies need to be developed.

Immunotherapy for prostate cancer using prostatic acid phosphatase loaded antigen presenting cells

Dendritic cells from patients with cancer are deficient in number and functional activity, leading to inadequate tumor immunosurveillance as a result of poor induction of T-cell antitumor responses. Loaded dendritic cell therapy is a vaccination strategy aimed at eliciting tumor antigen-specific, T-cell immune responses. Loaded dendritic cell therapy using prostatic acid phosphatase (APC8015; Provenge, Dendreon Corp., Seattle, WA) as an immunogen has shown a survival benefit in patients with metastatic hormone-refractory prostate cancer in a randomized phase III trial. This review will summarize the prostate cancer clinical trials using APC8015 and discuss the potential future role of APC8015 in prostate cancer treatment.

Identification of EGFRvIII-derived CTL epitopes restricted by HLA A0201 for dendritic cell based immunotherapy of gliomas

The type III variant of the epidermal growth factor receptor (EGFRvIII) mutation is present in 20-25% of patients with glioblastoma multiforme (GBM). EGFRvIII is not expressed in normal tissue and is therefore a suitable candidate antigen for dendritic cell (DC) based immunotherapy of GBM. To identify the antigenic epitope(s) that may serve as targets for EGFRvIII-specific cytotoxic T lymphocytes (CTLs), the peptide sequence of EGFRvIII was screened with two software programs to predict candidate epitopes restricted by the major histocompatibility complex class I subtype HLA-A0201, which is the predominant subtype in most ethnic groups. Three predicted peptides were constructed and loaded to mature human DCs generated from peripheral blood monocytes. Autologous CD8+ T cells were stimulated in vitro with the EGFRvIII peptide-pulsed DCs. One of the three peptides was found to induce EGFRvIII-specific CTLs as demonstrated by IFN-gamma production and cytotoxicity against HLA-A0201+ EGFRvIII transfected U87 glioma cells. These results suggest that vaccination with EGFRvIII peptide-pulsed DCs or adoptive transfer of in vitro elicited EGFRvIII-specific CTLs by EGFRvIII peptide-pulsed DCs are potential approaches to the treatment of glioma patients.

The immunotherapy of prostate and bladder cancer

The role of the immune system in controlling the growth of tumour cells is highly complex and has been extensively debated. It is well documented that the immune system controls virally induced cancers, and there is evidence for a role of specific immunity in other types of tumours. The greater understanding of the regulation and optimization of adoptive, specific immune responses, and the better characterization of tumour-associated antigens indicate the way for active specific vaccination and cell therapy in urological tumours. Currently, bacille Calmette Guerin immunotherapy is established for localized bladder cancer and many experimental immunotherapies are under evaluation. Here we review some timely aspects of tumour immunology, and describe the current status and development of immunotherapy in prostate and bladder cancer.

Induction of autoantibodies to syngeneic prostate-specific membrane antigen by xenogeneic vaccination

Prostate-specific membrane antigen (PSMA) is a prototypical differentiation antigen expressed on normal and neoplastic prostate epithelial cells, and on the neovasculature of many solid tumors. Monoclonal antibodies specific for PSMA are in development as therapeutic agents. Methodologies to actively immunize against PSMA may be limited by immunologic ignorance and/or tolerance that restrict the response to self-antigens. Our studies have previously shown that xenogeneic immunization with DNA vaccines encoding melanosomal differentiation antigens induces immunity in a mouse melanoma model. Here we apply this approach to PSMA to establish proof of principle in a mouse model. Immunization with xenogeneic human PSMA protein or DNA induced antibodies to both human and mouse PSMA in mice. Monoclonal antibodies specific for mouse PSMA were generated to analyze antibody isotypes and specificity for native and denatured PSMA at the clonal level. Most antibodies recognized denatured PSMA, but C57BL/6 mice immunized with xenogeneic PSMA DNA followed by a final boost with xenogeneic PSMA protein yielded autoantibodies that reacted with native folded mouse PSMA. Monoclonal antibodies were used to confirm the expression of PSMA protein in normal mouse kidney. These results establish the basis for clinical trials to test PSMA DNA vaccines in patients with solid tumors that either express PSMA directly or that depend on normal endothelial cells expressing PSMA for their continued growth.

A dendritic cell based hybrid cell vaccine generated by electrofusion for immunotherapy strategies in HNSCC

OBJECTIVE

Hybrid cells generated from dendritic cells (DC) and tumor cells provide tumor-associated antigens (TAA) in a polyvalent mode and therefore they have aroused interest in cancer immunotherapy. The present study was designed to investigate the hybrid cell generation and optimize its implementation for a TAA-target treatment of head and neck squamous cell carcinoma (HNSCC).

METHODS

Hybrid cells from mature DC and laryngeal carcinoma cell line UTSCC-19A were generated by electrofusion. Fusion efficiency and viability were determined by flow cytometry, light and fluorescence microscopy analyses.

RESULTS

The gradual electrofusion process constituted real human tumor and dendritic cell hybrids characterized by polynuclear cells and double staining as a result of overlay of red (HLA-DR:R-PE) and green (HEA:FITC) fluorescence. Furthermore, analyses have proven viability of fusion results, and factors influencing fusion yield were determined.

CONCLUSION

Physical fusion of mature dendritic cells with laryngeal carcinoma cells provides a dendritic cell based hybrid cell vaccine as a quantitative prerequisite for anti-cancer vaccination. Specific cytotoxic T-lymphocytes need to be induced before hybrid cell application in clinical studies.

Correlation between PSMA and VEGF expression as markers for LNCaP tumor angiogenesis

Our aim is the identification and correlation of changes in tumor-associated protein expression which results from therapy. LNCaP tumors, excised from nude mice treated either by orchiectomy or with the chemotherapeutic agent paclitaxel, were evaluated for the expression of proteins and receptors associated with growth, differentiation, and angiogenesis using immunohistologic procedures. Compared to untreated control tumors, both treatments reduced the expression of vascular endothelial growth factor (VEGF), prostate-specific membrane antigen (PSMA), prostate-specific antigen (PSA), androgen receptor (AR), and epidermal growth factor receptor (EGFR). The effect of paclitaxel treatment on AR expression was the most significant (P = .005). Of particular interest was identifying a significant correlation (P < .000801) between PSMA and VEGF expression regardless of treatment modality. These altered expressions suggest that PSMA may also be a marker for angiogenesis and could represent a target for deliverable agents recognizing either prostatic tumors or endothelial development. Cell surface PSMA would then present a unique target for treatment of patients early in their development of prostatic metastases.

In vitro and preclinical targeted alpha therapy of human prostate cancer with Bi-213 labeled J591 antibody against the prostate specific membrane antigen

Limited options for the treatment of prostate cancer have spurred the search for new therapies. One innovative approach is the use of targeted alpha therapy (TAT) to inhibit cancer growth, using an alpha particle emitting radioisotope such as (213)Bi. Because of its short range and high linear energy transfer (LET), alpha-particles may be particularly effective in the treatment of cancer, especially in inhibiting the development of metastatic tumors from micro-metastases. Prostate-specific membrane antigen (PSMA) is expressed in prostate cancer cells and the neovasculature of a wide variety of malignant neoplasms including lung, colon, breast and others, but not in normal vascular endothelium. The expression is further increased in higher-grade cancers, metastatic disease and hormone-refractory prostate cancer (PCA). J591 is one of several monoclonal antibodies (mabs) to the extracellular domain of PSMA. Chelation of J591 mab with (213)Bi forms the alpha-radioimmunoconjugate (AIC). The objective of this preclinical study was to design an injectable AIC to treat human prostate tumors growing subcutaneously in mice. The anti-proliferative effects of AIC against prostate cancer were tested in vitro using the MTS assay and in vivo with the nude mice model. Apoptosis was documented using terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridinetriphosphate [dUTP] nick end-labeling (TUNEL) assay, while proliferative index was assessed using the Ki-67 marker. We show that a very high density of PSMA is expressed in an androgen-dependent human PCA cell line (LNCaP-LN3) and in tumor xenografts from nude mice. We also demonstrate that the AIC extensively inhibits the growth of LN3 cells in vitro in a concentration-dependent fashion, causing the cells to undergo apoptosis. Our in vivo studies showed that a local AIC injection of 50 microCi at 2 days post-cell inoculation gave complete inhibition of tumor growth, whereas results for a non-specific AIC were similar to those for untreated mice. Further, after 1 and 3 weeks post-tumor appearance, a single (100 microCi/100 microl) intra-lesional injection of AIC can inhibit the growth of LN3 tumor xenografts (volume<100 mm(3)) in nude mice. Tumors treated with AIC decreased in volume from a mean 46+/-14 mm(3) in the first week or 71+/-15 mm(3) in the third week to non-palpable, while in control mice treated with a non-specific AIC using the same dose, tumor volume increased from 42 to 590 mm(3). There were no observed side effects of the treatment. Because of its in vitro cytotoxicity and these anti-proliferative properties in vivo, the (213)Bi-J591 conjugate has considerable potential as a new therapeutic agent for the treatment of prostate cancer.

A prostate stem cell antigen-derived peptide immunogenic in HLA-A24- prostate cancer patients

BACKGROUND

We attempted to identify prostate stem cell antigen (PSCA)-derived peptides immunogenic in HLA-A24+ prostate cancer patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) were stimulated in vitro with each of three different PSCA-derived peptides, which were prepared based on the HLA-A24 binding motif, and their peptide-specific and HLA-A24-restricted anti-tumor responses were examined. Plasma levels of immunoglobulin G (IgG) against PSCA peptides were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Among three PSCA peptides, the PSCA 76-84 peptide most effectively induced peptide-specific cytotoxic T lymphocytes (CTLs) from PBMCs of HLA-A24+ prostate cancer patients. Cytotoxicity was dependent on peptide-specific and CD8+ T cells. The PSCA 76-84 peptide-stimulated PBMCs showed a significant level of cytotoxicity against prostate cancer cells in an HLA-A24-restricted manner. IgG reactive to the PSCA 76-84 peptide was detected in half of patients.

CONCLUSIONS

The PSCA 76-84 peptide should be considered for use in clinical trials of immunotherapy for HLA-A24+ patients.

Clinical applications of dendritic cell vaccination in the treatment of cancer

Dendritic cell (DC) immunotherapy has shown significant promise in animal studies as a potential treatment for cancer. Its application in the clinic depends on the results of human trials. Here, we review the published clinical trials of cancer immunotherapy using exogenously antigen-exposed DCs. We begin with a short review of general properties and considerations in the design of such vaccines. We then review trials by disease type. Despite great efforts on the part of individual investigative groups, most trials to date have not yielded data from which firm conclusions can be drawn. The reasons for this include nonstandard DC preparation and vaccination protocols, use of different antigen preparations, variable means of immune assessment, and nonrigorous criteria for defining clinical response. While extensive animal studies have been conducted using DCs, optimal parameters in humans remain to be established. Unanswered questions include optimal cell dose, use of mature versus immature DCs for vaccination, optimal antigen preparation, optimal route, and optimal means of assessing immune response. It is critical that these questions be answered, as DC therapy is labor- and resource-intensive. Cooperation is needed on the part of the many investigators in the field to address these issues. If such cooperation is not forthcoming, the critical studies that will be required to make DC therapy a clinically and commercially viable enterprise will not take place, and this therapy, so promising in preclinical studies, will not be able to compete with the many other new approaches to cancer therapy presently in development. Trials published in print through June 2003 are included. We exclude single case reports, except where relevant, and trials with so many variables as to prevent interpretation about DC therapy effects.

Induction of cellular and humoral immune responses to tumor cells and peptides in HLA-A24 positive hormone-refractory prostate cancer patients by peptide vaccination

BACKGROUND

To assess the safety and immune response of a peptide-based immunotherapy for patients with hormone-refractory prostate cancer, a phase I clinical trial was conducted.

METHODS

This study first investigated whether cytotoxic T-lymphocyte (CTL) precursors reacting to peptide with vaccine candidates (14 peptides for HLA-A24 positive patients) were detectable in the pre-vaccination peripheral blood mononuclear cells (PBMCs) of ten patients with hormone-refractory prostate cancer. Patients were then vaccinated subcutaneously with only those peptides to which pre-vaccination PBMCs reacted (CTL precursor-oriented peptide vaccine) for up to four kinds of peptides.

RESULTS

Overall vaccinations were generally well tolerated, but most patients (nine of ten) developed grade 1 local redness and swelling at the injection site. Increased CTL response to both peptides and cancer cells were observed in four of ten patients. Anti-peptide IgG antibodies were also detected in post-vaccination sera of seven of ten patients. One patient achieved a partial response with an 89% decrease in PSA. Stable disease was demonstrated in five of ten patients (50%) for the median duration of 2 months (range, 2-5 months). There were no objective responses of measurable lesions.

CONCLUSIONS

Increase in cellular and humoral immune responses, and decrease in PSA level in some patients support further development of peptide-based immunotherapy for hormone refractory prostate cancer.

Immunodeficiency and cancer: prospects for correction

Cellular immunodeficiency is associated with human cancer. Extensive reviews on cancer of the head and neck, lung, esophagus and breast convince the author that for these diseases the immunodeficiency is reasonably well established yet the mechanisms are poorly understood. Evidence indicates that other tumors are similarly associated with cellular immune deficiency. The advent of recombinant cytokines and of antitumor monoclonal antibodies has served to focus attention toward direct tumoricidal mechanisms. As tumor antigens relating to cellular and humoral immune mechanisms are being defined and vaccine strategies are increasingly being attempted, it is critical to confront issues of the mechanism of anergy and effective immunorestoration in order to maximize the potential of cellular immune response to address these tumor antigens. Intrinsic to this approach is the introduction of contrasuppressive therapy to alleviate the tumor-associated immune suppression. Encouraging attempts have been made with plasmapheresis, indomethacin, low-dose cyclophosphamide, anti CTLA-4, anti FAS ligand and, perhaps in the future, more judiciously applied chemotherapy. In contrast to the popular notion that thymic involution cannot be reversed in the adult, studies from the author's laboratory indicate that in aged hydrocortisone stressed mice, a natural Type 1-cytokine mixture (IRX-2) hastens the reversal of thymic involution and promotes T-cell responses to cytokines and mitogens. Recombinant IL-1 and IL-2 by themselves, and in combination, were inactive. Similar positive effects were observed with oral zinc, zinc-thymulin and thymosin alpha(1). The combination of a natural cytokine mixture (IRX-2) with thymosin alpha1 had a very large effect and increased the absolute number of peripheral T lymphocytes as measured in the spleen. In studies of combination immunotherapy in lymphocytopenic squamous cell head and neck cancer patients using IRX-2 (18 patients) and IRX-2 plus thymosin alpha(1) (IRX-3) in IRX-2-refractory patients (7 patients), marked increases in CD(45)RA(+) 'naïve' T cells (>250/mm(3)) were observed. These are among the first insights into how to generate T lymphocyte replacement in the adult. These and many other experimental efforts point to ways to achieve more effective immunotherapy of human cancer in the future, particularly if tumor-induced immune deficiency can be effectively addressed.

Clinical application of dendritic cells in cancer vaccination therapy

During the last decade use of dendritic cells (DC) has moved from murine and in vitro studies to clinical trials as adjuvant in cancer immunotherapy. Here they function as delivery vehicles for exogenous tumor antigens, promoting an efficient antigen presentation. The development of protocols for large-scale generation of dendritic cells for clinical applications has made possible phase I/II studies designed to analyze the toxicity, feasibility and efficacy of this approach. In clinical trials, DC-based vaccination of patients with advanced cancer has in many cases led to immunity and in selected patients to tumor regression. However, the majority of clinical trials are still in phase I, and interpretations are hampered by pronounced variation in study design related to technical aspects of DC preparation, treatment and schedule, monitoring of immune response, and clinically relevant endpoints, including toxicity and response evaluation. This paper aims to review the technical aspects and clinical impact of vaccination trials, focusing on the generation of DC-based vaccines, evaluation of immunologic parameters and design of clinical trials necessary to meet the need for good laboratory and clinical practice.

Rational approaches to human cancer immunotherapy

Over most of the 20th century, immunotherapy for cancer was based on empiricism. Interesting phenomena were observed in the areas of cancer, infectious diseases, or transplantation. Inferences were made and extrapolated into new approaches for the treatment of cancer. If tumors regressed, the treatment approaches could be refined further. However, until the appropriate tools and reagents were available, investigators were unable to understand the biology underlying these observations. In the early 1990s, the first human tumor T cell antigens were defined and dendritic cells were discovered to play a pivotal role in antigen presentation. The current era of cancer immunotherapy is one of translational research based on known biology and rationally designed interventions and has led to a rapid expansion of the field. The beginning of the 21st century brings the possibility of a new era of effective cancer immunotherapy, combining rational, immunological treatments with conventional therapies to improve the outcome for patients with cancer.

Immunotherapy for melanoma

BACKGROUND

Immunotherapy for cancers is based on the principle that the host's immune system is capable of generating immune responses against tumor cells. Currently available treatments for melanoma patients are limited by poor response rates. Interferon-a has been approved for adjuvant treatment of stage III melanoma with improved survival. New and more innovative approaches with improved efficacy are needed.

METHODS

We reviewed the various new approaches and strategies for immunotherapy for the treatment of melanoma.

RESULTS

Immunotherapy for melanoma includes a number of different strategies with vaccines utilizing whole cell tumors, peptides, cytokine-mediated dendritic cells, DNA and RNA, and antibodies.

CONCLUSIONS

A variety of approaches can be used to enhance immune reactivity in patients with melanoma. Preclinical studies and initial clinical trials have shown promising results. Additional clinical trials are currently ongoing to evaluate the clinical efficacy and the associated toxicities of these novel treatment strategies.

Generation in vitro of B-cell chronic lymphocytic leukaemia-proliferative and specific HLA class-II-restricted cytotoxic T-cell responses using autologous dendritic cells pulsed with tumour cell lysate

Immunotherapy using dendritic cells has shown encouraging results in both haematological and non-haematological malignancies. In this study, monocyte-derived dendritic cells from patients with B-CLL were cultured for 6 days in the presence of IL-4 and GM-CSF. Autologous B-CLL T-cells were cultured alone or with B-CLL lysate-pulsed and unpulsed autologous dendritic cells. IFN-gamma secretion was assessed using ELISA. Cytotoxicity was assessed, after 21 days in culture and re-stimulation, using flow cytometry with and without blockade by anti-HLA class I, anti-HLA class II, anti-CD4, anti-CD8 and anti-TCRalphabeta monoclonal antibodies. B-CLL T cells stimulated with B-CLL lysate-pulsed autologous dendritic cells showed a significant (P = 0.0004) increase in IFN-gamma secretion and a significant (P = 0.0008) increase in specific cytotoxicity to autologous B-cell targets, but none to autologous T cell or B cell targets from healthy individuals. B-CLL T cells cultured with (non-B-CLL) B-cell lysate-pulsed B-CLL dendritic cells showed no significant response. Pulsing dendritic cells from healthy volunteers with an autologous (non-B-CLL) B-cell lysate did not stimulate proliferation, cytokine production or cytotoxicity by autologous T cells. Pulsing B-CLL dendritic cells with allogeneic B-CLL lysates and culturing with autologous T-cells elicited cytotoxicity against autologous B-CLL targets in some cases, but not in others. Cytotoxicity was significantly reduced by blocking with anti-HLA class II (P = 0.001), anti-TCRalphabeta (P = 0.03) and anti-CD4 (P = 0.046) antibodies. Phenotyping of the responding T-cell population demonstrated the majority to be CD4 positive. Our data demonstrate that HLA class II-restricted proliferative and cytotoxic T-cell responses to B-CLL can be generated using autologous dendritic cells pulsed with tumour cell lysate.

Cancer vaccines

Attempts to generate an anticancer immune response in vivo in patients with cancer have taken several forms. Although to date there have been relatively few published studies describing the effects of the approach in hematologic malignancy, that circumstance is expected to change rapidly during the next few years. In solid tumors, it is not known which, if any, of the approaches being explored will be able to produce responses of sufficient effectiveness and duration to be of general clinical value. Despite the documented increase in survival of patients developing an immune response to tumor immunization, no randomized clinical trial has been entirely convincing. As knowledge of the molecular basis of the immune response and of the immune defenses used by cancer cells improves, it is reasonable to expect to see increasing benefits from tumor vaccines, which are likely to complement, long before they replace, conventional therapies.

Dendritic cell vaccines for cancer therapy

Dendritic cells (DC) are professional antigen-presenting cells whose primary function is the initiation of immune response. Based on the finding that the immune system usually fails to identify and kill cancer cells, DC have been recently used as vaccines for stimulation of tumour-specific immunity. This review focuses on pitfalls related to DC-based vaccination against solid tumours and on improvement of this immunotherapeutic approach for routine treatment of cancer disease.

Dendritic cells: immunological features and utilisation for tumour immunotherapy

The prospect of developing 'magic bullets' to attack tumour cells has been a goal of biologists for decades. Abundant experimental and clinical observations demonstrating that an effective specific immune response may engender tumour regression has prompted efforts to find an immunotherapeutic approach to this problem. The most important arm of cellular immunity for such responses appears to be cytotoxic T-lymphocytes (CTL) which can recognise antigen on virtually all cell types and which are key to the elimination of virally-infected cells. The specific activation and maintenance of activity of these cells is therefore the major goal of designing a therapeutic cancer vaccine. Advances in our understanding of the role of dendritic cells (DC) in priming and modifying immune responses suggest that they should be potent adjuvants for vaccination. The use of antigens targeted to the major histocompatibility complex (MHC) molecules expressed on these cells as an approach to tumour immunotherapy has already been tested in the treatment of many malignancies, and recent findings shed light on additional directions through which their efficacy may be improved.

Immunotherapy of prostate cancer

The realization that prostate cancer is an immunogenic tumor, in conjunction with the discovery of novel methods for priming the immune system to generate an antitumor response, has resulted in several new approaches for prostate cancer immunotherapy. Based on these various approaches, several human clinical trials have begun using immune-based therapies for prostate cancer. These approaches can be divided into cytokine-based therapies, tumor-associated antigen-based therapies, tumor vaccines, and dendritic cell-based therapies. This review summarizes the latest findings from each of these approaches and gives results from the few completed human clinical trials.

The use of dendritic cells in cancer therapy

Although the immune system evolved to protect the host from infection, what fires the popular imagination is its potential to recognise and destroy cancer. The immune system can generate potent cytotoxicity (eg transplant rejection), but can these mechanisms be harnessed for therapeutic benefit in patients with cancer? The discovery of an ever-increasing array of tumour antigens shows clearly that the targets exist. The challenge lies in generating a sufficiently potent response towards them. Central to the processes of antigen recognition, processing, and presentation to the immune system are dendritic cells. Understanding of the relation between these and the cellular immune response is crucial to elucidation of how to manipulate immune responses. The past 20 years have witnessed a dramatic expansion in this understanding and led to the first early-phase clinical trials of dendritic cells for the treatment of cancer. These studies have established the safety and feasibility of this approach and have produced encouraging evidence of therapeutic efficacy. This paper reviews the biology of dendritic cells and their use in clinical trials, as well as highlighting issues for future trial design.

Genetic prodrug activation therapy (GPAT) in two rat prostate models generates an immune bystander effect and can be monitored by magnetic resonance techniques

Treatment of hormone refractory prostate cancer requires new treatment strategies. Genetic prodrug activation therapy (GPAT) may provide a new therapeutic avenue. In this study the antitumour efficacy of the gene encoding herpes simplex virus thymidine kinase (HSVtk) activating the prodrug ganciclovir (GCV) was compared in two models of ectopic (subcutaneous) rat prostate cancer. Both models, which differ in their characteristics, were previously shown to be weakly immunogenic but susceptible to immunotherapy. Tumour cell lines were stably transfected with HSVtk and were rendered highly sensitive to GCV. Little or no bystander killing effect was observed by tk-transfected cells on wild-type cells in vitro. However, a significant in vivo bystander effect was observed suggesting an immune-mediated response. Indeed, such an immune response was capable of slowing the growth of distant wild-type tumours and increased overall animal survival. A T helper 1 immune response was generated as a result of GCV activation and cell kill, demonstrated by the secretion of IFNgamma by cultured splenocytes in response to tumour cells. BrDU staining of tk-transfected cells treated with GCV in vitro suggested apoptotic cell death, but Annexin V staining was less marked for one of the cell lines. Serial in vivo monitoring by non-invasive magnetic resonance spectroscopy (MRS) of the tk-transfected MATLyLu tumours demonstrated a decreased ATP/Pi ratio (a measure of cell energy status) during growth and an increase in the ATP/Pi ratio during regression initiated by treatment with GCV. Further, significant differences were found in the phosphomonester (PME) to total phosphate (SigmaP) ratios in treated compared with untreated tumours, a result rarely seen in animal models, but commonly observed in patients. This study showed that a Th1-biased immune response generated by killing prostate tumour cells with tk/GCV can kill distant as well as local wild-type tumour cells. These findings suggest that GPAT may have a potential application in patients with both confined and metastatic prostate cancer and MRS may provide a method of monitoring response to treatment.