GM-CSF as a systemic adjuvant in a phase II prostate cancer vaccine trial

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.

Comparisons of therapeutic efficacy and safety of ipilimumab plus GM-CSF versus ipilimumab alone in patients with cancer: a meta-analysis of outcomes

Background

Recent clinical studies have shown that initial therapy with combined cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4) blockade and granulocyte-macrophage colony-stimulating factor (GM-CSF)-based immunotherapies can enhance the antitumor efficacy of this approach. A key unanswered question is whether systemic GM-CSF enhances CTLA-4 blockade. Thus, the objective of this study was taking a meta-analysis of randomized controlled trials to compare the effect of ipilimumab plus GM-CSF versus ipilimumab alone on overall response, overall survival, and progression-free survival, as well as the risk of adverse events (AEs) in patients with cancer.

Materials and methods

Searches were made in electronic databases PubMed and Embase, and conference abstracts published by the American Society of Clinical Oncology from 2000 to 2017. Statistical analyses were carried out using either random-effects or fixed-effects models according to the heterogeneity of eligible studies.

Results

Six trials comprising of 445 patients were included in the meta-analysis. Combination group was superior to the ipilimumab alone in overall response rate, progression-free survival, and overall survival rate (combined relative risk [RR]=1.34, 95% CI: 1.24–1.45, P=0.09; combined hazard ratio [HR]=0.57, 95% CI: 0.32–1.02, P=0.06; combined HR=0.70, 95% CI: 0.60–0.82, P<0.001). Patients with combination therapies had a lower incidence of AEs including high-grade diarrhea (combined RR=0.27, 95% CI: 0.11–0.70, P=0.007), nausea (combined RR=0.25, 95% CI: 0.07–0.89, P=0.03), colitis (combined RR=0.34, 95% CI: 0.13–0.86, P=0.02), and fatigue (combined RR=0.91, 95% CI: 0.37–2.2.3, P=0.84) compared to the group having ipilimumab alone.

Conclusion

These data suggested that the combination of ipilimumab and GM-CSF was associated with a significant improvement in overall survival and lower high-grade toxicities, but there is no difference in overall response rate and progression-free survival among the cancer patients. Therefore, large-scale and well-designed studies are needed to summarize and analyze the data to draw a more convincing conclusion.

Stable incorporation of GM-CSF into dissolvable microneedle patch improves skin vaccination against influenza

The widely used influenza subunit vaccine would benefit from increased protection rates in vulnerable populations. Skin immunization by microneedle (MN) patch can increase vaccine immunogenicity, as well as increase vaccination coverage due to simplified administration. To further increase immunogenicity, we used granulocyte-macrophage colony stimulating factor (GM-CSF), an immunomodulatory cytokine already approved for skin cancer therapy and cancer support treatment. GM-CSF has been shown to be upregulated in skin following MN insertion. The GM-CSF-adjuvanted vaccine induced robust and long-lived antibody responses cross-reactive to homosubtypic and heterosubtypic influenza viruses. Addition of GM-CSF resulted in increased memory B cell persistence relative to groups given influenza vaccine alone and led to rapid lung viral clearance following lethal infection with homologous virus in the mouse model. Here we demonstrate that successful incorporation of the thermolabile cytokine GM-CSF into MN resulted in improved vaccine-induced protective immunity holding promise as a novel approach to improved influenza vaccination. To our knowledge, this is the first successful incorporation of a cytokine adjuvant into dissolvable MNs, thus advancing and diversifying the rapidly developing field of MN vaccination technology.

Prime-boost immunization by both DNA vaccine and oncolytic adenovirus expressing GM-CSF and shRNA of TGF-β2 induces anti-tumor immune activation

A successful DNA vaccine for the treatment of tumors should break established immune tolerance to tumor antigen. However, due to the relatively low immunogenicity of DNA vaccines, compared to other kinds of vaccines using live virus or protein, a recombinant viral vector was used to enhance humoral and cellular immunity. In the current study, we sought to develop a novel anti-cancer agent as a complex of DNA and oncolytic adenovirus for the treatment of malignant melanoma in the C57BL/6 mouse model. MART1, a human melanoma-specific tumor antigen, was used to induce an increased immune reaction, since a MART1-protective response is required to overcome immune tolerance to the melanoma antigen MelanA. Because GM-CSF is a potent inducer of anti-tumor immunity and TGF-β2 is involved in tumor survival and host immune suppression, mouse GM-CSF (mGM-CSF) and shRNA of mouse TGF-β2 (shmTGF-β2) genes were delivered together with MART1 via oncolytic adenovirus. MART1 plasmid was also used for antigen-priming. To compare the anti-tumor effect of oncolytic adenovirus expressing both mGM-CSF and shmTGF-β2 (Ad^GshT) with that of oncolytic adenovirus expressing mGM-CSF only (Ad^G), each virus was intratumorally injected into melanoma-bearing C57BL/6 mice. As a result, mice that received Ad^GshT showed delayed tumor growth than those that received Ad^G. Heterologous prime-boost immunization was combined with oncolytic Ad^GshT and MART1 expression to result in further delayed tumor growth. This regression is likely due to the following 4 combinations: MART1-derived mouse melanoma antigen-specific immune reaction, immune stimulation by mGM-CSF/shmTGF-β2, tumor growth inhibition by shmTGF-β2, and tumor cell-specific lysis via an oncolytic adenovirus. Immune activation was mainly induced by mature tumor-infiltrating dendritic cell (TIDC) and lowered regulatory T cells in tumor-infiltrating lymphocytes (TIL). Taken together, these findings demonstrate that human MART1 induces a mouse melanoma antigen-specific immune reaction. In addition, the results also indicate that combination therapy of MART1 plasmid, together with an oncolytic adenovirus expressing MART1, mGM-CSF, and shmTGF-β2, is a promising candidate for the treatment of malignant melanoma.

Trial watch: Naked and vectored DNA-based anticancer vaccines

One type of anticancer vaccine relies on the administration of DNA constructs encoding one or multiple tumor-associated antigens (TAAs). The ultimate objective of these preparations, which can be naked or vectored by non-pathogenic viruses, bacteria or yeast cells, is to drive the synthesis of TAAs in the context of an immunostimulatory milieu, resulting in the (re-)elicitation of a tumor-targeting immune response. In spite of encouraging preclinical results, the clinical efficacy of DNA-based vaccines employed as standalone immunotherapeutic interventions in cancer patients appears to be limited. Thus, efforts are currently being devoted to the development of combinatorial regimens that allow DNA-based anticancer vaccines to elicit clinically relevant immune responses. Here, we discuss recent advances in the preclinical and clinical development of this therapeutic paradigm.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Immunotherapeutic strategies for the treatment of renal cell carcinoma: where are we now?

Immunotherapy with cytokines was the first effective treatment in metastatic renal cell carcinoma (mRCC). Long-term responders and complete remissions were observed, but efficacy in the overall population was limited with the consequence that targeted agents replaced cytokines. The discovery of tumor associated antigens as direct targets paved the way from theses rather unspecific to specific immunotherapeutic strategies, which are discussed in this review. Autologous or dendritic cell (DC) based tumor vaccination with vitespen or AGS-003, adoptive T-cell transfer and synthetic peptide vaccination with IMA901 are new and promising approaches. Besides that the more passive strategies of antibody dependent cytotoxicity with the VEGF antibody bevacizumab or the carbonic anhydrase IX antibody girentuximab are discussed. Immunomodulation by cyclophosphamide, tyrosine kinase inhibitors or nivolumab, which targets the PD-1 axis, further promote T-cell activation and combinatory strategies with these agents are outlined.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a privileged position at the interface between innate and adaptive immunity, orchestrating a large panel of responses to both physiological and pathological cues. In particular, whereas the presentation of antigens by immature DCs generally results in the development of immunological tolerance, mature DCs are capable of priming robust, and hence therapeutically relevant, adaptive immune responses. In line with this notion, functional defects in the DC compartment have been shown to etiologically contribute to pathological conditions including (but perhaps not limited to) infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. Thus, the possibility of harnessing the elevated immunological potential of DCs for anticancer therapy has attracted considerable interest from both researchers and clinicians over the last decade. Alongside, several methods have been developed not only to isolate DCs from cancer patients, expand them, load them with tumor-associated antigens and hence generate highly immunogenic clinical grade infusion products, but also to directly target DCs in vivo. This intense experimental effort has culminated in 2010 with the approval by the US FDA of a DC-based preparation (sipuleucel-T, Provenge®) for the treatment of asymptomatic or minimally symptomatic metastatic castration-refractory prostate cancer. As an update to the latest Trial Watch dealing with this exciting field of research (October 2012), here we summarize recent advances in DC-based anticancer regimens, covering both high-impact studies that have been published during the last 13 mo and clinical trials that have been launched in the same period to assess the antineoplastic potential of this variant of cellular immunotherapy.

Cryopreservation of adenovirus-transfected dendritic cells (DCs) for clinical use

In this study, we examined the effects of cryoprotectant, freezing and thawing, and adenovirus (Adv) transduction on the viability, transgene expression, phenotype, and function of human dendritic cells (DCs). DCs were differentiated from cultured peripheral blood (PB) monocytes following Elutra isolation using granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for 6 days and then transduced using an Adv vector with an IL-12 transgene. Fresh, cryopreserved, and thawed transduced immature DCs were examined for their: 1) cellular concentration and viability; 2) antigenicity using an allogeneic mixed lymphocyte reaction (MLR); 3) phenotype (HLA-DR and CD11c) and activation (CD83); and 4) transgene expression based on IL-12 secretion. Stability studies revealed that transduced DCs could be held in cryoprotectant for as long as 75 min at 2-8°C prior to freezing with little effect on their viability and cellularity. Further, cryopreservation, storage, and thawing reduced the viability of the transduced DCs by an average of 7.7%; and had no significant impact on DC phenotype and activation. In summary, cryopreservation, storage, and thawing had no significant effect on DC viability, function, and transgene expression by Adv-transduced DCs.

Cytokine adjuvants for vaccine therapy of neoplastic and infectious disease

Vaccination, the revolutionary prophylactic immunotherapy developed in the eighteenth century, has become the most successful and cost-effective of medical remedies available to modern society. Due to the remarkable accomplishments of the past century, the number of diseases and pathogens for which a traditional vaccine approach might reasonably be employed has dwindled to unprecedented levels. While this happy scenario bodes well for the future of public health, modern immunologists and vaccinologists face significant challenges if we are to address the scourge of recalcitrant pathogens like HIV and HCV and well as the significant obstacles to immunotherapy imposed by neoplastic self. Here, the authors review the clinical and preclinical literature to highlight the manner by which the host immune system can be successfully manipulated by cytokine adjuvants, thereby significantly enhancing the efficacy of a wide variety of vaccination platforms.

Therapeutic cancer vaccines: are we there yet?

Enthusiasm for therapeutic cancer vaccines has been rejuvenated with the recent completion of several large, randomized phase III clinical trials that in some cases have reported an improvement in progression free or overall survival. However, an honest appraisal of their efficacy reveals modest clinical benefit and a frequent requirement for patients with relatively indolent cancers and minimal or no measurable disease. Experience with adoptive cell transfer-based immunotherapies unequivocally establishes that T cells can mediate durable complete responses, even in the setting of advanced metastatic disease. Further, these findings reveal that the successful vaccines of the future must confront: (i) a corrupted tumor microenvironment containing regulatory T cells and aberrantly matured myeloid cells, (ii) a tumor-specific T-cell repertoire that is prone to immunologic exhaustion and senescence, and (iii) highly mutable tumor targets capable of antigen loss and immune evasion. Future progress may come from innovations in the development of selective preparative regimens that eliminate or neutralize suppressive cellular populations, more effective immunologic adjuvants, and further refinement of agents capable of antagonizing immune check-point blockade pathways.

GM-CSF plays a key role in zymosan-stimulated human dendritic cells for activation of Th1 and Th17 cells

In this study, we compared the effects of zymosan and LPS on human monocyte-derived dendritic cells. The specific effects of zymosan on the expression of several key cytokines, including granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukins (IL-1α, IL-1β and IL-12 p70) were quite distinct from the effects of LPS. Unlike activation with LPS, DCs activated by zymosan expressed little or no IL-12 p70 due to lack of expression of the p35 subunit. However, treatment with zymosan resulted in a substantial increase in Th1 and Th17 cell-polarizing capacity of DCs. Furthermore, the GM-CSF secreted by zymosan-activated DCs enhanced IL-23 production, resulting in activation of a Th17 response. GM-CSF and IL-27, rather than IL-12 p70, were both major direct contributors to the activation of a Th1 response. This signaling mechanism is distinct and yet complementary to LPS-mediated T-cell activation. We suggest that this novel zymosan-induced GM-CSF-mediated signaling network may play a key role in regulating specific immune cell type activities.

Use of GM-CSF as an adjuvant with cancer vaccines: beneficial or detrimental?

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been utilized in the clinical management of multiple disease processes. Most recently, GM-CSF has been incorporated into the treatment of malignancies as a sole therapy, as well as a vaccine adjuvant. While the benefits of GM-CSF in this arena have been promising, recent reports have suggested the potential for GM-CSF to induce immune suppression and, thus, negatively impact outcomes in the management of cancer patients. The purpose of this review is to critically evaluate these reports, while considering the most recent clinical data on immunotherapies. We aim to demonstrate the utility of this adjuvant, elucidate those instances in which GM-CSF may induce immune suppression and identify potential explanations for these recent findings.

Effect of granulocyte/macrophage colony-stimulating factor on vaccination with an allogeneic whole-cell melanoma vaccine

PURPOSE

The availability of a variety of immune response modifiers creates an opportunity for improved efficacy of immunotherapy, but it also leads to uncertainty in how to combine agents and how to assess those combinations. We sought to assess the effect of the addition of granulocyte/macrophage colony-stimulating factor (GM-CSF) to vaccination with a melanoma vaccine.

EXPERIMENTAL DESIGN

Ninety-seven patients with resected melanoma (stage II-IV) were enrolled, stratified by stage, and randomized to receive a cellular melanoma vaccine with or without GM-CSF. The primary endpoint was delayed-type hypersensitivity (DTH) response to melanoma cells. Antibody responses, peripheral leukocyte counts, and survival were also examined.

RESULTS

The GM-CSF arm showed enhanced antibody responses with an increase in IgM titer against the TA90 antigen and increased TA90 immune complexes. This arm also had diminished antimelanoma cell delayed-type hypersensitivity response. Peripheral blood leukocyte profiles showed increases in eosinophils and basophils with decreased monocytes in the GM-CSF arm. These immune changes were accompanied by an increase in early melanoma deaths and a trend toward worse survival with GM-CSF.

CONCLUSION

These data suggest that GM-CSF is not helpful as an immune adjuvant in this dose and schedule and raise concern that it may be harmful. Based on the discordant findings of an immune endpoint and clinical outcome, the use of such surrogate endpoints in selecting treatments for further evaluation must be done with a great deal of caution.

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.

Opposite immune functions of GM-CSF administered as vaccine adjuvant in cancer patients

Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been and is still widely used as an adjuvant in clinical trials of vaccination with autologous tumor cells, peptides and/or dendritic cells in a variety of human neoplasms. This cytokine was administered either as product of gene-transduced tumor cells or as recombinant protein together with the vaccine given subcutaneously or intradermally. Results of these trials were heterogeneous in terms of induction of vaccine-specific immune response and of clinical response. Though in some of these studies GM-CSF appeared to help in generating an immune response, in others no effect or even a suppressive effect was reported. Here, we review the literature dealing with the immune adjuvant activity of GM-CSF both in animal models and clinical trials. As a consequence of such analysis, we conclude that GM-CSF may increase the vaccine-induced immune response when administered repeatedly at relatively low doses (range 40-80 microg for 1-5 days) whereas an opposite effect was often reported at dosages of 100-500 microg. The potential mechanisms of the GM-CSF-mediated immune suppression are discussed at the light of studies describing the activation and expansion of myeloid suppressor cells by endogenous tumor-derived or exogenous GM-CSF.

Prostate Cancer Immunology: Biology, Therapeutics, and Challenges

A number of recently developed and promising approaches to antitumoral immunotherapy are being investigated as potential treatments for advanced prostate cancer. These approaches largely revolve around strategies to increase antigen-specific T-cell activation against prostate tumors as well as precise manipulations of critical co-regulatory receptors that help to maintain and prolong the activity of antigen-presenting cells and T cells that are capable of mediating tumor regression. Herein, we describe the experience with the most recent and promising approaches pertaining to prostate cancer immunotherapy. Additionally, we discuss the mechanistic basis for these approaches as well as current limitations that must still be addressed in order to propel immunotherapy into the forefront of prostate cancer treatment.

Immune responses against PSMA after gene-based vaccination for immunotherapy – A: results from immunizations in animals

Two plasmid DNA vaccines, encoding either products that are retained in the cytosol and degraded in the proteasome (tVacs; hPSMAt), or secreted proteins (sVacs; hPSMAs) were evaluated for stimulation of cytotoxic cell or antibody responses. Immunization with both vectors led to generation of cell cytotoxicity providing granulocyte-macrophage colony-stimulating factor was administered with the vaccine. Spleen cells from animals immunized with hPSMAt demonstrated stronger cytotoxicity to the target cells. Priming with a vector that encoded a xenogeneic protein (hPSMAt; 'xenogeneic' construct) and boosting with a vector that encoded an autologous protein (rPSMAt; 'autologous' construct) gave the best protection against tumor challenge. Immunization with tVacs did not lead to formation of antibodies to the target protein as detected by Western blot or ELISA, while immunization with sVacs or with the protein did. Antibodies were of mixed Th1-Th2 isotype. Priming with tVacs and boosting with protein also resulted in antibody formation, but in this case the antibodies were from the cytotoxic, Th1 isotype. The best strategy to obtain a strong cellular cytotoxic response, therefore, seems to be gene-based vaccinations with tVacs, priming with the 'xenogeneic' and boosting with the 'autologous' constructs. When cytotoxic antibody production is the goal, priming should be performed with the tVacs while boosting with the protein.

Abrogation of delayed type hypersensitivity response to Candida albicans produced by a molecular mimic of phosphorylated prolactin

The effects of two major forms of prolactin (PRL) were examined on delayed type hypersensitivity (DTH) responses to Candida albicans. Unmodified PRL (U-PRL) had no effect on the DTH response, whereas a molecular mimic of phosphorylated PRL (S179D PRL) significantly inhibited immune responses to this robust antigen. This effect of S179D PRL was not accompanied by gross alterations in splenic T cell numbers, CD4/CD8 ratios, or T and B cell activation markers, but did produce a decrease in splenocyte apoptosis. Using gld animals, Fas ligand (FasL) was implicated in the suppressive effects of S179D PRL. Circulating IgG1 and IgG2 antibody levels were increased in response to treatment with both forms of PRL, but the effects of S179D PRL were most pronounced. Cytokine changes in the popliteal lymph nodes specific to S179D PRL treatment showed an inhibition of pro-inflammatory cytokines. In conclusion, mice treated with a molecular mimic of phosphorylated prolactin showed a profound inhibition of DTH responses to Candida correlating with an absence of GM-CSF, IL-4, and IL-13 production and a marked reduction in IL-12p70 synthesis.

Immune-based therapies for prostate cancer

Prostate cancer is a leading cause of cancer morbidity and mortality in the United States. Animal and clinical studies performed four decades ago suggested that immunological approaches might be useful for the treatment of prostate cancer. The wealth of information that has been learned over the last two decades has suggested many new directions to the immune-based therapy of prostate cancer, including passive and active immunotherapy approaches. The findings from current trials, and the likely combination of current immunotherapy approaches with conventional therapies, portends a hopeful future for the treatment of prostate cancer.

Immunotherapy (APC8015, Provenge) targeting prostatic acid phosphatase can induce durable remission of metastatic androgen-independent prostate cancer: a Phase 2 trial

BACKGROUND

Prostate cancer is the most commonly diagnosed malignancy in American men, yet treatment of its metastatic androgen-independent form remains inadequate. This mandates development of new therapies such as immunotherapy. In this Phase 2 trial, we determined the efficacy of antigen presenting cells (APCs) loaded with PA2024, a recombinant fusion protein containing prostatic acid phosphatase (PAP) and GM-CSF.

METHODS

We enrolled 21 patients with histologically documented androgen-independent prostate carcinoma that could be evaluated by radionuclide bone scan or computed tomography scan. APC8015 was prepared from a leukapheresis product; it contained autologous CD54-positive PA2024-loaded APCs with admixtures of monocytes, macrophages, B and T cells. APC8015 was infused intravenously twice, 2 weeks apart. Two weeks after the second infusion, patients received three subcutaneous injections of 1.0 mg of PA2024 1 month apart. We monitored patients' physical condition, immune response, and laboratory parameters.

RESULTS

Nineteen patients could be evaluated for response to treatment. The median time to progression was 118 days. Treatment was tolerated reasonably well; most adverse effects were secondary to APC8015 and were NCI Common Toxicity Criteria Grade 1-2. Four of the 21 patients reported Grade 3-4 adverse events. Two patients exhibited a transient 25-50% decrease in prostate-specific antigen (PSA). For a third patient, PSA dropped from 221 ng/ml at baseline to undetectable levels by week 24 and has remained so for more than 4 years. In addition, this patient's metastatic retroperitoneal and pelvic adenopathy has resolved. PBMC collected from patients for at least 16 weeks proliferated upon in vitro stimulation by PA2024. For the patient with responsive disease, PBMC could be stimulated for 96 weeks.

CONCLUSIONS

This study demonstrates a definite clinical response of androgen-independent prostate cancer to APC immunotherapy. Currently we are studying this mode of therapy in Phase 3 trials.

Immunization of colorectal cancer patients with recombinant baculovirus-derived KSA (Ep-CAM) formulated with monophosphoryl lipid A in liposomal emulsion, with and without granulocyte-macrophage colony-stimulating factor

KSA (Ep-CAM) is highly expressed by colorectal cancers. The safety and immunologic effects of a vaccine consisting of recombinant baculovirus-derived KSA formulated with monophosphoryl lipid A (MPL) in liposomes and emulsified in mineral oil were evaluated, with and without co-administration of granulocyte-macrophage colony-stimulating factor (GM-CSF). Eleven patients with metastatic colorectal cancer received three subcutaneous (s.c.) injections of the vaccine at 4-week intervals. Six patients were randomized to also receive human recombinant GM-CSF (rGM-CSF) by subcutaneous injection daily for 4 days with each vaccination. Immunizations with and without rGM-CSF were well tolerated. Seven of the 11 patients developed significant KSA-specific cellular immune responses as assessed by lymphoproliferation and interferon-gamma (IFN-gamma) ELISPOT assays. All nine tested patients developed positive delayed type hypersensitivity reactions. Eight of the 11 patients developed KSA-specific antibody responses. The highest levels of cellular immune responses were observed in patients who received GM-CSF. Immunization with baculovirus-derived KSA formulated with monophosphoryl lipid A in liposomal emulsion is safe and can elicit KSA-specific immune responses. Co-administration of GM-CSF with this formulation is an effective method of generating KSA-specific T-helper (Th) 1-associated cellular immune responses.

DC therapy for prostate cancer

The wide range of currently available treatments for metastatic prostate cancer have demonstrated a modest palliative effect, but none to date has shown an increase in overall survival. The immune system has evolved to protect against infection, however, the modulation of this system represents the possibility of allowing it to identify and destroy cancer cells. The immune system is capable of inciting a powerful immune response against tissues, in the form of transplant rejection, and the potential exists to harness these powers to fight against tumors. Modest clinical responses have been seen in patients with metastatic prostate cancer treated with DC therapies; however, no increase in overall survival has been demonstrated. The current state of DC immunotherapy for prostate cancer is reviewed.

Immunotherapy and prostate cancer

Prostate cancer is the second leading cause of cancer death in the US, largely because of the limitations of our current therapeutic options, especially once the cancer has metastasized. Investigators have long sought new therapeutic modalities such as angiogenesis inhibitors, vaccines, and gene therapy, among others. It appears that a combination approach will be required to cure the majority of malignancies. Immunotherapy for prostate cancer appears feasible and a likely therapeutic modality in the armamentarium. Unfortunately, further research in basic immunology and the interaction of the immune system with other forms of therapy is needed. Many obstacles exist in immunotherapy, including vector design, tumouricidal specificity, and tumor evasion, which will have to be overcome in order to realize the maximum therapeutic benefit from this treatment modality.

Cytokines as clinical adjuvants: how far are we?

In spite of the explosive growth in the discovery of cytokines and chemokines and in the understanding of their modes of action, clinical use of such agents as adjuvants has been primarily restricted to patients with cancer or chronic viral infections suffering from various levels of immune impairment and for whom the chemotherapeutic armamentarium, as well as other forms of immunotherapy, have been exhausted. This cautious approach has been justified by the difficulties inherent to the biological function and delivery of such pleiotropic agents, where doses needed to achieve the targeted immune enhancement often result in serious side effects, especially during systemic administration. In addition, optimization of dosages, administration schedules and biological effects in humans often do not correlate well with preclinical data derived from animal models. Nevertheless, novel preventive immunization strategies that target a precise type of immune response in immunocompetent individuals are expected to greatly benefit from the incorporation of cytokines and chemokines. This review provides an overview of current clinical administration of cytokines as well as a description of select Phase I testing of new agents designed to enhance immune defenses in vivo.

Modulation of antitumor immune responses by hematopoietic cytokines

BACKGROUND

Advances in immunotherapy for the treatment of patients with malignant disease have led to increasingly successful use of these methods in the clinical setting. This review presents findings from recent studies that have explored improved methods for the presentation of tumor-associated antigens and for the restoration of tumor specific immune responses using cytokine therapy.

METHODS

A review of human clinical trial research on immune cytokines from 1995 (MEDLINE) to the present was conducted. Particular attention was focused on articles that reported results from Phase II or later clinical studies in patients with malignant disease.

RESULTS

The defects in cellular immunity commonly seen in patients with malignancies often are expressed as tumor specific anergy. Reversing patient tolerance to tumor antigens may be accomplished by treatment with immunoregulatory cytokines, such as Flt-3 and granulocyte-macrophage-colony stimulating factor, that mature and activate dendritic cells. Published clinical studies indicate that granulocyte-macrophage-colony stimulating factor stimulates antigen-presenting cells and has promising antitumor activity as an adjunct or as stand-alone therapy for patients with malignant disease, including leukemia, melanoma, breast carcinoma, prostate carcinoma, and renal cell carcinoma.

CONCLUSIONS

Immune-modulating cytokines may be used alone or in combination with other treatments to help restore immune function, improve response to tumor-associated antigens, and reduce the toxic effects of standard antitumor therapies. The evolving understanding of how dendritic cells regulate immune responses and promising results from published studies of immune-enhancing cytokines in the treatment of patients with malignant disease support the conduct of randomized clinical trials to confirm the clinical benefit of these immunotherapeutic strategies.

Immunization by particle-mediated transfer of the granulocyte-macrophage colony-stimulating factor gene into autologous tumor cells in melanoma or sarcoma patients: report of a phase I/IB study

The primary objective of this phase I study was to determine the safety of an autologous tumor vaccine given by intradermal injection of lethally irradiated granulocyte-macrophage colony-stimulating factor (GM-CSF) gene-transfected autologous melanoma and sarcoma cells. Secondary objectives included validation of the gene delivery technology (particle-mediated gene transfer), determining the host immune response to the tumor after vaccination, and monitoring patients for evidence of antitumor response. Sixteen patients were treated with either of two different doses of GM-CSF-treated tumor cells. One patient received treatment with both doses of tumor cells. No treatment-related local or systemic toxicity was noted in any patient. Patients administered 100% treated cells (i.e., with a preparation of tumor cells that had all been exposed to GM-CSF DNA transfection) had a more extensive lymphocytic infiltrate at the vaccine site than did patients given 10% treated cells (a preparation of tumor cells in which 10% had been exposed to GM-CSF transfection) or nontreated tumor. The generation of a systemic immune response to autologous tumor by a delayed-type hypersensitivity response to the intradermal placement of nontransfected tumor cells was noted in one patient. One patient had a transient partial response of metastatic tumor sites. The entire procedure, from tumor removal to vaccine placement, was accomplished in less than 6 hr in all patients. Four of 17 patient tumor preparations produced greater than 3.0 ng of GM-CSF per 10(6) cells per 24 hr in vitro. The one patient with greater than 30 ng of GM-CSF per 10(6) cells per 24 hr in vitro had positive DTH, a significant histologic inflammatory response, and clinically stable disease. This technique of gene transfer was safe and feasible, but resulted in clinically relevant levels of gene expression in only a minority of patients.

Prostate-specific antigen vaccines for prostate cancer

Prostate cancer is the most common malignant tumour in men and there are few treatment options available once the tumour becomes refractory to hormonal manipulation. Prostate-specific antigen (PSA) is a secretory glycoprotein that is commonly expressed by prostatic epithelial cells and is found in elevated levels in the serum of men with prostate cancer. The identification of T cell specific epitopes within the coding sequence of PSA has led to the development of various vaccine strategies that target PSA in an attempt to treat established prostate cancer. These strategies have included human leukocyte antigen-restricted PSA peptides, dendritic cells pulsed with PSA, recombinant viruses expressing PSA and combinations of different vectors. In addition to PSA, several other antigens have been described that may be useful for targeting prostate tumours by vaccines. Animal studies have established the feasibility and safety for many of these agents and clinical trials are now in progress to evaluate the immunological and clinical responses of PSA vaccines. Further research in manipulating anti-PSA immunity with cytokines, costimulatory molecules and other immune modulating agents will likely improve the therapeutic effectiveness of PSA vaccines. Clinical trials designed to evaluate the effects of vaccination in different stages of disease and through different routes of administration need to be performed to define the optimal schedule for PSA vaccines in patients with prostate cancer, or for those at high risk of developing the disease.

Gene therapy for urologic cancer

Advances in molecular technology and the completion of the human genome project have ushered in a new era of medicine, that of gene therapy. In every field of medicine, investigators are developing gene therapeutics in an attempt to cure diseases. Urologic oncology is no exception. Herein, we review the current status of gene therapy for urologic malignancy. Included is an overview of advances in gene delivery systems and immunology, which are driving forces for gene therapy research. Finally, we review the current gene therapy trials and experimental approaches for urologic malignancy.

Cytokines as adjuvants for the induction of anti-human immunodeficiency virus peptide immunoglobulin G (IgG) and IgA antibodies in serum and mucosal secretions after nasal immunization

Safe and potent new adjuvants are needed for vaccines that are administered to mucosal surfaces. This study was performed to determine if interleukin-1alpha (IL-1alpha) combined with other proinflammatory cytokines provided mucosal adjuvant activity for induction of systemic and mucosal anti-human immunodeficiency virus (HIV) peptide antibody when intranasally administered with an HIV peptide immunogen. Nasal immunization of BALB/c mice with 10 microg of an HIV env peptide immunogen with IL-1alpha, IL-12, and IL-18 on days 0, 7, 14, and 28 induced peak serum anti-HIV peptide immunoglobulin G1 (IgG1) and IgA titers of 1:131,072 and 1:7,131, respectively (P = 0.05 versus no adjuvant). The use of cholera toxin (CT) as a mucosal adjuvant induced serum IgG1 and IgA titers of 1:32,768 and 1:776, respectively. The adjuvant combination of IL-1alpha, IL-12, and IL-18 induced anti-HIV peptide IgA titers of 1:1,176, 1:7,131, and 1:4,705 in saliva, fecal extracts and vaginal lavage, respectively. Titers induced by the use of CT as an adjuvant were 1:223, 1:1,176, and 1:675, respectively. These results indicate that the proinflammatory cytokines IL-1alpha, IL-12, and IL-18 can replace CT as a mucosal adjuvant for antibody induction and are important candidates for use as mucosal adjuvants with HIV and other vaccines.

Oral cytokine gene therapy against murine tumor using attenuated Salmonella typhimurium

An attenuated strain of Salmonella typhimurium was used as a vehicle for oral gene therapy against murine tumor. Eukaryotic expression vectors containing genes of human interleukin-12 (hIL-12), human granulocyte/macrophage colony-stimulating factor (hGM-CSF), mouse (m)IL-12, mGM-CSF and green fluorescent protein (GFP) were used to transform attenuated Salmonella (SL3261), and such transformants were administered orally to BALB/c and C57BL/6 mice. As a reporter gene, GFP expression in murine liver, spleen, tumor, intestine and kidney was confirmed by confocal and flow cytometry. Soluble cytokines were detected in murine sera, and the concentrations were much higher than those of the control, which contributed to the increased number of cytotoxic T cells and prolongation of survival. Oral cytokine gene therapy using live attenuated Salmonella demonstrated a significant protection against the development of two unrelated murine tumors. These results suggest that such gene therapy has the potential to be simple, effective and (above all) safe against tumor.

Gene therapy for prostate cancer: current status and future prospects

PURPOSE

Locally advanced, relapsed and metastatic prostate cancer has a dismal prognosis with conventional therapies offering no more than palliation. In recent years advances achieved in understanding the molecular biology of cancer have afforded clinicians and scientists the opportunity to develop a range of novel genetic therapies for this disease.

MATERIALS AND METHODS

We performed a detailed review of published reports of gene therapy for prostate cancer. Particular emphasis was placed on recent developments in the arena of nonviral (plasmid DNA, DNA coated gold particles, liposomes and polymer DNA complexes) and viral (adenovirus, retrovirus, adeno-associated virus, herpes virus and pox virus) vectors. Therapeutic strategies were categorized as corrective, cytoreductive and immunomodulatory gene therapy for the purpose of data analysis and comparison.

RESULTS

Locoregional administration of nonviral and viral vectors can yield impressive local gene expression and therapeutic effects but to our knowledge no efficient systemically delivered vector is available to date. Corrective gene therapy to restore normal patterns of tumor suppressor gene (p53, Rb, p21 and p16) expression or negate the effect of mutated tumor promoting oncogenes (ras, myc, erbB2 and bcl-2) have efficacy in animal models but this approach suffers from the fact that each cancer cell must be targeted. A wide variety of cytoreductive strategies are under development, including suicide, anti-angiogenic, radioisotopic and pro-apoptotic gene therapies. Each approach has strengths and weaknesses, and may best be suited for use in combination. Immunomodulatory gene therapy seeks to generate an effective local immune response that translates to systemic antitumor activity. Currently most studies involve immunostimulatory cytokine genes, such as granulocyte-macrophage colony-stimulating factor, or interleukin-2 or 12.

CONCLUSIONS

Various therapeutic genes have proved activity against prostate cancer in vitro and in vivo. However, the chief challenge facing clinical gene therapy strategies is the lack of efficient gene delivery by local and systemic routes. For the foreseeable future vector development may remain a major focus of ongoing research. Despite this caveat it is anticipated that gene therapy approaches may significantly contribute to the management of prostate cancer in the future.

Immunotherapy for prostate cancer

The components of an effective immune response have been elucidated in recent years. An understanding of the dysfunction of the immune response in cancer in one or more of these components has led to a variety of immunotherapeutic approaches. These therapeutic strategies are designed to stimulate dendritic cell proliferation, promote antigen uptake and processing, stimulate an effector cell response via direct antigen presentation, or target tumor cells via antibody therapy. Many approaches in prostate cancer have demonstrated successful induction of the desired immune response. Limited clinical success has also been seen.

RNA as a tumor vaccine: a review of the literature

Many approaches have been attempted to harness the host immune system to act against malignant tumors. These have included animal and clinical trials with agents to non-specifically boost immunity, factors to augment specific immunity, transfer of lymphokine-activated killer cells and transfer of expanded populations of tumor-infiltrating lymphocytes. Therapeutic vaccination strategies have been employed using tumor extracts, purified tumor antigens, recombinant peptide tumor antigens and specific DNA sequences coding for a tumor antigen (genetic vaccination) both through direct administration to the host and by administration of antigen presenting cells exposed to these materials ex vivo. Recently, the use of RNA has been proposed for use in tumor vaccination protocols. The use of RNA has several potential advantages. Since total cellular RNA or mRNA can be utilized, it is not necessary to know the molecular nature of the putative tumor antigen(s). RNA can be effectively amplified; thus, unlike tumor-extract vaccines, only a small amount of tumor is needed to prepare the material for vaccination. Also, unlike DNA-based vaccines, there is little danger of incorporation of RNA sequences into the host genome. The possible utility of RNA-based vaccines for tumor immunotherapy should be further explored to determine whether such approaches are clinically useful.

A method for the production of cryopreserved aliquots of antigen-preloaded, mature dendritic cells ready for clinical use

Dendritic cells (DC) are increasingly used as a vaccine. Unfortunately, a satisfactory cryopreservation of DC in the absence of FCS is not yet available, so that laborious repeated generation of DC from fresh blood or frozen peripheral blood mononuclear cells for each vaccination has been required to date. We now aimed at developing an effective cryopreservation method, and by testing several variables found that it was crucial to combine the most advantageous maturation stimulus with an improved freezing procedure. We generated monocyte-derived DC from leukapheresis products by using GM-CSF and IL-4 and showed that amongst several known maturation stimuli the cocktail consisting of TNF-alpha+IL-1 beta+IL-6+PGE(2) achieved the highest survival of mature DC. We then systematically explored cryopreservation conditions, and found that freezing matured DC at 1 degrees C/min in pure autologous serum+10% DMSO+5% glucose at a cell density of 10x10(6) DC/ml gave the best results. Using this approach 85-100% of the frozen DC could be recovered in a viable state after thawing (Table 1). The morphology, phenotype, survival as well as functional properties (allogeneic mixed leukocyte reaction, induction of influenza matrix or melan A peptide-specific cytotoxic T cells) of these thawed DC were equivalent to freshly prepared ones. The addition of CD40L or TRANCE/RANKL further improved DC survival. Importantly, we demonstrate that DC can effectively be loaded with antigens (such as Tetanus Toxoid, influenza matrix and melan A peptides) before cryopreservation so that it is now possible to generate antigen-preloaded, frozen DC aliquots that after thawing can be used right away. This is an important advance as both the generation of a standardized DC vaccine under GMP conditions and the carrying out of clinical trials are greatly facilitated.

Development of dendritic-cell based prostate cancer vaccine

Available treatments for metastatic prostate cancer have failed to demonstrate significant curative potential. Current efforts are now directed towards developments of novel strategies for the treatment of metastatic prostate cancer. Cancer immunotherapeutic strategies utilize patient immune system components to kill cancer cells. This review discusses progress in active specific immunotherapeutic approaches as potential alternative methods in the treatment of metastatic prostate cancer. One of the newest advances in cancer immunotherapy is the use of dendritic cells as the vehicle to deliver cancer antigens for an effective in vivo T cell activation. The development of dendritic cell-based prostate cancer vaccine, as well as results of several clinical trials in prostate cancer involving the administration of peptide-pulsed autologous dendritic cell pulsed are discussed.

Endothelium-derived factors as paracrine mediators of prostate cancer progression

BACKGROUND

Vascular endothelium represents a complex network of cells producing a large number of active substrates affecting physiologic, metabolic, and immunologic properties of the whole organism, as well as particular organs or tissues. The potential influence of endothelium-derived paracrine factors on prostate cancer progression has only begun to be examined.

METHODS

This review summarizes recent literature on endothelium-derived factors, including vasoactive agents, peptide growth factors, cytokines, and colony-stimulating factors, involved in the development and progression of prostate cancer.

RESULTS

Endothelial cells produce an array of active substrates, many of which have been shown to influence prostate cancer growth. Available data demonstrate the positive impact of such molecules as endothelin-1, basic FGF, TGF-beta, IL-6, and IL-8 on prostate cancer progression. Many other endothelium-derived factors NO, IGF, PDGF, IL-1, G-CSF, and GM-CSF (Nitric Oxide, Insulin-Like Growth Factor, Platelet-Derived Growth Factor, Interleukin-1, Granulocyte Colony Stimulating Factor, and Granulocyte-Macrophage Colony Stimulating Factor) are, at best, implicated in prostate cancer growth, and in most cases support cancer progression.

CONCLUSIONS

A better understanding of endothelium-derived factors, as paracrine mediators of prostate carcinogenesis and progression, should aid in the development of novel therapeutic strategies.

An overview of cancer immunotherapy

The survival of patients with cancer has improved steadily but incrementally over the last century, with the advent of effective anticancer treatments such as chemotherapy and radiotherapy. However, the majority of patients with metastatic disease will not be cured by these measures and will eventually die of their disease. New and more effective methods of treating these patients are required urgently. The immune system is a potent force for rejecting transplanted organs or microbial pathogens, but effective spontaneous immunologically induced cancer remissions are very rare. In recent years, much has been discovered about the mechanisms by which the immune system recognizes and responds to cancers. The specific antigens involved have now been defined in many cases. Improved adjuvants are available. Means by which cancer cells overcome immunological attack can be exploited and overcome. Most importantly, the immunological control mechanisms responsible for initiating and maintaining an effective immune response are now much better understood. It is now possible to manipulate immunological effector cells or antigen-presenting cells ex vivo in order to induce an effective antitumour response. At the same time, it is possible to recruit other aspects of the immune system, both specific (e.g. antibody responses) and innate (natural killer cells and granulocytes).

Prostate cancer immunotherapy at the dawn of the new millennium

Standard treatments for adenocarcinoma of the prostate, such as surgery, hormones, radiation and chemotherapy, often achieve a clinical response, but this is usually short-lived. Prostate cancer frequently recurs and second-line therapies have a poor response rate. Many clinicians seem comfortable in limiting their philosophy of treating advanced recurrent disease merely to new regimens of failed therapies, such as combination chemotherapy. However, other medical researchers have chosen to pursue novel approaches, including immunotherapy, several of which are summarised in this review. Although ranging widely in antigen specificity, all attempt to exploit the body's natural antitumour immunity. Furthermore, all aim to stimulate immunity above a threshold level necessary for tumour regression or to induce stability in the face of progression. The goal of in vivo or ex vivo gene therapy is the modification of gene expression within an antigen-presented cell by the introduction of a vector, DNA, or RNA. Within that field, much progress has been made and is ongoing currently concerning gene delivery systems, target identification and characterisation. Comparatively, monoclonal antibodies are an established type of cancer immunotherapy. However, the more recent development of humanized or fully human antibodies, as well as novel moieties they can be coupled to, renews their prospects for clinical impact. Lastly, various cell-based therapies are the focus of several recent clinical studies demonstrating tumour regression or stabilisation. Immune cells, for example, T-lymphocytes and dendritic cells, have already demonstrated treatment benefit, as well as the ability to maintain an excellent quality of life for participants. Overall, there is a multitude of approaches being considered for the treatment of prostate cancer. The following review concentrates on those approaches that are currently in human or animal studies and have a specific emphasis on prostate cancer.

Uses of granulocyte-macrophage colony-stimulating factor in vaccine development

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a potent cytokine capable of inducing differentiation, proliferation, and activation of a variety of immunologically active cell populations. In addition to its effects on stimulating granulocytic hematopoiesis, it also facilitates development of both humoral and cellular mediated immunity. Accordingly, strategies involving the use of GM-CSF as a vaccine adjuvant have attracted considerable attention. These strategies include the systemic administration of soluble GM-CSF with an immunogen, and also its use as part of gene therapy approaches to immunization. Because of the potency of this cytokine as an immune adjuvant, particular interest has focused on its use to overcome poorly immunogenic antigens such as those associated with intracellular infections and cancer. This review focuses on recent advances in the use of GM-CSF as a vaccine adjuvant.

Higher-dose and less frequent dendritic cell infusions with PSMA peptides in hormone-refractory metastatic prostate cancer patients

BACKGROUND

Infusion of dendritic cells (DCs) pulsed with PSMA peptides was considered possible in hormone-refractory metastatic prostate cancer patients both with or without prior treatment with a greater number of DCs and for lesser infusions than previously administered.

METHODS

DCs + PSMA peptides in patients undergoing leukapheresis were administered monthly 1-4 times, at rates greater than 20 million DCs in 17 patients not previously treated, and in 11 patients previously treated.

RESULTS

Three partial responders and one complete responder were noted in the 17 previously untreated persons. DCs + PSMA peptides averaged 28.5 million cells (range in millions, 21.0-42.3). All responders received 3 or 4 infusions of greater than 22 million cells (3-4 times). In the previously treated group of 11 patients, DCs infused averaged 29.3 million cells (range in millions, 20-40.5). One new responder (bone scan) was noted. Two prior responders continued. Observation times were similar. Toxicity was minimal.

CONCLUSIONS

These results suggest that DCs + PSMA peptide infusions can be given with greater numbers of DCs with a lesser number of infusions (1-4 monthly) with no loss of response rates compared to those noted previously, and without increased side effects. In previously treated patients (both relapsing and nonrelapsing), adverse effects were not noted, and new responses can be anticipated to be without harmful side effects. However, the follow-up time, and number of patients in this group, were small.

Progress in active specific immunotherapy of prostate cancer

Treatments available for metastatic prostate cancer have failed to demonstrate significant curative potential. Current efforts are now directed towards developments of novel strategies for the treatment of metastatic prostate cancer. Cancer immunotherapeutic strategies utilize patient immune system components to kill cancer cells. This review discusses progress in active specific immunotherapeutic approaches as potential alternative methods in the treatment of metastatic prostate cancer. Various methods of augmenting the immune response against prostate cancer are discussed including systemic cytokine adjuvant therapy, cytokine gene transduced tumor vaccines, non-antigen specific immunization, DNA and peptide vaccines plus adjuvants, as well as dendritic cell-based cancer vaccines.