**Entering a New Era – Prostate Cancer Immuno-Therapy After the FDA Approval for Sipuleucel-T**

Thomas H. Brill *Technische Universität München (TUM) Germany* 

### **1. Introduction**

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> As cancer is estimated to cause 1,500,000 deaths in Europe and more than 500,000 alone in the US each year (Ferlay et al., 2007; Jemal et al., 2010) newer strategies are needed to improve current treatment success rates. The role of the immune system is designated cancer immunosurveillance as it limits tumor growth (Dunn et al., 2002). This biological principle has been deduced from clinical observations in human as if veterinary cancer patients and has also been proved experimentally in immunodeficient mice characterized by a high incidence of tumors (Shankanan et al., 2001). The evidence on the role of the immune system found in limiting tumor growth and progression is linked to observations showing a positive correlation between the presence of tumor infiltrating lymphocytes (TILs) and improved outcome in most – but not all – tumor entities studied so far; e.g. in colorectal cancer significantly higher levels of memory CD8+T-cell infiltrates are positively correlated with clinical benefit, defined as less advanced pathological stage, absence of metastatic invasion, and increased survival (Pages et al., 2005; Galon et al., 2006). Similarly, the presence of TILs has been associated with decreased tumor cells in the draining lymph nodes of cervical cancer patients limiting the risk of metastatic progression (Piersma et al., 2007). In lung carcinoma patients, increasing numbers of TILs have also been shown to significantly improve disease-specific survival (Al-Shibli et al., 2008). PCa glands are also frequent diffusely infiltrated (CD4+T-cells as if CD8+T-cells) so suggesting that PCa may be immunogenic but the correlation of these findings to clinical data is not that clear as in other tumor entities (McArdle et al., 2004; Zhang et al., 2006). Altogether, these observations support the immunosurveillance hypothesis and form the rationale to use the immune system to control tumor burden by vaccine-based interventions against cancer relying on the stimulation of an effective antitumor immune response in the cancer patient and resulted recently in labelling "avoiding immune destruction" as an emerging hallmark of cancer by the scientific community (Hanahan & Weinberg, 2011). The therapeutic cancer vaccine definition as given by the National Cancer Institute (NCI) is: vaccines, which are intended to treat already existing cancers by strengthening the body´s natural defences against cancer. But it is of great importance to notice the two paradoxical roles the immune system has in

> cancer: while at the one hand various components of the immune response – innate as if adaptive – are able to mediate cancer cell destruction, at the other hand specific types of

Entering a New Era – Prostate Cancer

Ref. (e.g.)

(Mu et al.,

(Pandha et al., 2004)

(Simons et al., 2006; Small et al., 2007; Higano et al., 2008; Higano et al., 2009b)

(Brill et al.,

(Simons et al., 1999)

PSA in VV and FV (e.g.

1. Immunisation against multiple (not specified) antigens

1.1.1 DCs pulsed ex vivo with allogeneic whole-tumor cell

1.1.2 DCs pulsed ex

autologous wholetumor cell lysates

e.g. GVAX

LNCaP/IL2/IFNγ

Cell modification via viral vectors e.g.

AdV-IL2

1.1.3 Allogeneic whole-tumor cells

e.g. OnyP (Michael

1.1.4 whole tumor cells (modified

mRNA

vivo with

e.g.

Immuno-Therapy After the FDA Approval for Sipuleucel-T 295

1.1 Cell-based 2.1 Cell-based

2. Immunisation against specified antigen(s)

human PAP as target (e.g. sipuleucel-T) xenogeneic

PSA as target

et al., 2005) PSCA as target (Thomas-Kaskel et al.,

2007, 2009) Telomerase as target (Vonderheide et al.,

PAP as target

(modified ex vivo) PSMA as target (Tjoa et al., 1999;

in situ – "in situ vaccination") 2.1.2 DCs pulsed ex vivo with multiple peptides

 PSA in AdV (Lubaroff et al., 2009) MUC1 in MVA (Dreicer et al., 2009)

 PSMA (Low et al., 2009) human PAP (McNeel et al., 2009)

2.2 Viral vector-based

2.3 DNA based

DCs pulsed "peptide cocktail" diff. epitopes from prostate TAAs

Prostvac-VF)

2005) 2.1.1 DCs pulsed ex vivo with a single peptide

Ref. (e.g.)

(Higano et al., 2009a; Kantoff et al., 2010a) (Fong et al., 2001)

Fishman, 2009)

(Barrou et al., 2004) (Hildenbrand et al., 2007)

2004; Su et al., 2005)

(Fuessel et al., 2006; Waeckerle-Men et al., 2006)

(Kaufman et al., 2004; Kantoff et al., 2010b; Gulley et al., 2010)

2006)

immune cells can also induce an environment that favours tumor growth as also the development of metastasis (DeNardo et al., 2008). Among the latter are, for example, tumor associated macrophages (TAM) (Mantovani et al., 2002; Luo et al., 2006), type 2 helper CD4+(TH2) T-cells (DeNardo et al., 2009; Ziegler et al., 2009), and last not least regulatory T(Treg)-cells (Curiel et al., 2004; Yamaguchi & Sakaguchi, 2006). These various immune cells have been shown to accumulate at tumor sites, negatively impacting the establishment of antitumor T-cell responses, and so creating an immunosuppressive tumor environment. Cancer cells themselves can also evolve mechanisms that allow them to evade immunosurveillance and to negatively affect the functionality of effector T-cells. These so called tumor-escape-mechanisms are: i) down regulation of antigen expression, components of the antigen-processing and presentation machinery, and expression of Major Histocompatibility Complex (MHC) molecules (Marincola et al., 2000), ii) decreased expression of co-stimulatory cytokines which are of crucial importance to T-cell activation (Sica et al., 2003), iii) enhanced surface expression of molecules that negatively regulate Tcell activation, so called "co-inhibitory signals", such as PDL1/B7-H1 and B7-H4 (Dong et al., 2002; Driessens et al., 2009), and iv) secreting a milieu of soluble factors that ultimately inhibit the activation, proliferation, and differentiation of the various components of the immune response; e.g. TGF-β (Thomas & Massague, 2005), IL-10 (Kurte et al., 2004), IL-13 (Terabe et al., 2000), and VEGF (Gabrilovich et al., 1996). And it was shown that the differential genetic and proteomic alterations of cancer cells accumulate in the course of disease from the localised tumor to lymph node positive state to end stage metastatic disease (Taylor et al., 2006). In order to design a successful anti-cancer immunostimulative strategy, it is important not to ignore the discoveries made by scientists working in the areas of immunity, infection and especially autoimmunity. For example, successful immunological clearance of viral as if bacterial infections are naturally accompanied by tremendous expansions of pathogen-reactive cytotoxic T-lymphocytes (CTLs), with up to 50 % of all circulating CD8+T-cells being antigen specific CTLs, which only subside after the infection has been defeated. On the other hand, most cancer vaccines which are in the field today generate poor T-cell responses with antigen-specific CTL rates beneath 1 % that often disappear soon after vaccination. Thus, one should not be surprised that insufficient tumor responses or regressions are observed (Cho & Celis, 2010).

The goal of vaccine-based cancer immunotherapy approaches is to induce a tumor-specific immune response that will reduce tumor burden by tipping the balance from a protumor to an antitumor immune environment – and from a clinicians point of view it is a success if tumor progression is stopped or if the tumor does not even metastasizes. So achieving cure is a high goal, which the so called therapeutic cancer vaccines might never reach, but we would save millions if we could force cancer into a chronic disease patients learn to live with but don't succumb from it. This chapter discusses strategies employed in the field of PCa vaccines aiming to enhance activation of an immune response that has shown impact in clinical trials.

There are many attempts around to describe the different vaccine platforms systematically, but as for most approaches the molecular mode of action is not exactly known attempts to divide into active versus passive, specific versus unspecific vaccines are difficult. It is more practical to categorize each vaccine depending on the vaccine-delivery system used, and whether specific or multiple antigens are targeted (Palena & Schlom, 2010). In the multiantigen vaccine formulations often known and unknown antigens are included. A list of the various types of vaccine-delivery systems under investigation in the field of PCa in clinical stages is presented in Table 1.

immune cells can also induce an environment that favours tumor growth as also the development of metastasis (DeNardo et al., 2008). Among the latter are, for example, tumor associated macrophages (TAM) (Mantovani et al., 2002; Luo et al., 2006), type 2 helper CD4+(TH2) T-cells (DeNardo et al., 2009; Ziegler et al., 2009), and last not least regulatory T(Treg)-cells (Curiel et al., 2004; Yamaguchi & Sakaguchi, 2006). These various immune cells have been shown to accumulate at tumor sites, negatively impacting the establishment of antitumor T-cell responses, and so creating an immunosuppressive tumor environment. Cancer cells themselves can also evolve mechanisms that allow them to evade immunosurveillance and to negatively affect the functionality of effector T-cells. These so called tumor-escape-mechanisms are: i) down regulation of antigen expression, components of the antigen-processing and presentation machinery, and expression of Major Histocompatibility Complex (MHC) molecules (Marincola et al., 2000), ii) decreased expression of co-stimulatory cytokines which are of crucial importance to T-cell activation (Sica et al., 2003), iii) enhanced surface expression of molecules that negatively regulate Tcell activation, so called "co-inhibitory signals", such as PDL1/B7-H1 and B7-H4 (Dong et al., 2002; Driessens et al., 2009), and iv) secreting a milieu of soluble factors that ultimately inhibit the activation, proliferation, and differentiation of the various components of the immune response; e.g. TGF-β (Thomas & Massague, 2005), IL-10 (Kurte et al., 2004), IL-13 (Terabe et al., 2000), and VEGF (Gabrilovich et al., 1996). And it was shown that the differential genetic and proteomic alterations of cancer cells accumulate in the course of disease from the localised tumor to lymph node positive state to end stage metastatic disease (Taylor et al., 2006). In order to design a successful anti-cancer immunostimulative strategy, it is important not to ignore the discoveries made by scientists working in the areas of immunity, infection and especially autoimmunity. For example, successful immunological clearance of viral as if bacterial infections are naturally accompanied by tremendous expansions of pathogen-reactive cytotoxic T-lymphocytes (CTLs), with up to 50 % of all circulating CD8+T-cells being antigen specific CTLs, which only subside after the infection has been defeated. On the other hand, most cancer vaccines which are in the field today generate poor T-cell responses with antigen-specific CTL rates beneath 1 % that often disappear soon after vaccination. Thus, one should not be surprised that insufficient tumor

The goal of vaccine-based cancer immunotherapy approaches is to induce a tumor-specific immune response that will reduce tumor burden by tipping the balance from a protumor to an antitumor immune environment – and from a clinicians point of view it is a success if tumor progression is stopped or if the tumor does not even metastasizes. So achieving cure is a high goal, which the so called therapeutic cancer vaccines might never reach, but we would save millions if we could force cancer into a chronic disease patients learn to live with but don't succumb from it. This chapter discusses strategies employed in the field of PCa vaccines aiming to enhance activation of an immune response that has shown impact in

There are many attempts around to describe the different vaccine platforms systematically, but as for most approaches the molecular mode of action is not exactly known attempts to divide into active versus passive, specific versus unspecific vaccines are difficult. It is more practical to categorize each vaccine depending on the vaccine-delivery system used, and whether specific or multiple antigens are targeted (Palena & Schlom, 2010). In the multiantigen vaccine formulations often known and unknown antigens are included. A list of the various types of vaccine-delivery systems under investigation in the field of PCa in clinical

responses or regressions are observed (Cho & Celis, 2010).

clinical trials.

stages is presented in Table 1.


Entering a New Era – Prostate Cancer

recommendation (NCCN, 2010).

the immune response to PAP (Kanthoff et al., 2010a).

intravenously to the patient (FDA, 2010a; Kanthoff et al., 2010a).

verum and placebo patients and thus not meet statistical significance.

Immuno-Therapy After the FDA Approval for Sipuleucel-T 297

Adenocarcinoma Treatment (IMPACT) study, were presented to the community at an AUA national conference and to the FDA (Schellhammer et al., 2009). After re-analysis of these facts the FDA finally permitted sipuleucel-T end of April 2010, so it is worth to have a closer look into the prescription information (FDA, 2010a) and the approval letter (FDA, 2010b) as this product is not just another in a row of existing PCa vaccines but – as the first active immune therapy granted with approval for use in human subjects – opens an entire new entity for curative intervention. Finally in July 2010 the IMPACT trial data were presented in a peer reviewed journal (Kanthoff et al., 2010b) and as a result the prostate panel of the National Comprehensive Cancer Network (NCCN) has changed its guidelines how to treat mCRPC patients by adding sipuleucel-T as a category 1 treatment

Sipuleucel-T is an antigen specific cellular immunotherapy based on autologoues DCs (see Tab. 1) and indicated in metastatic but asymptomatic or minimally symptomatic patients who are in a hormone refractory and disease progressive stage. Sipuleucel-T consists of APCs and other cells of the peripheral blood mononuclear cells (PBMC) compartment, that have been activated during a defined ex vivo period with a recombinant human fusion protein combining PAP and GM-CSF. To obtain patient's PBMCs a standard leukapheresis procedure approximately 72 hours prior to the infusion date has to be performed. During ex vivo culture period the PAP protein can bind to and be processed by APCs into smaller TAA fragments, so the recombinant antigen should target the DCs, and is thought to direct

Due to the autologoues nature of sipuleucel-T and the individuality of this approach its final cellular composition (T-, B-, NK-, and other cells) depends on the cells obtained from the patient's leukapheresis and will vary from patient to patient and from dose to dose, but the ex vivo procedure is regulated in that a minimum of 50 million PAP-GM-CSF activated CD54+ cells are included, suspended in 250 mL of Lactated Ringer's solution, and reinfused

The IMPACT trial was randomized, placebo-controlled, double-blind, multicentered. A total of 512 patients were randomized (2:1 ratio) to receive sipuleucel-T (n = 341) or control (n = 171). The placebo material used in control subjects was peripheral blood mononuclear cells that had not been PAP-activated, but given back to the patients under equal clinical conditions. In case of disease progression control subjects were allowed to cross over to an open-label use of the vaccine. The effectiveness of sipuleucel-T showed an increase in OS of 4.1 months in the pivotal phase III trial (25.8 vs 21.7 months) and OS benefit (3-year OS of 31.7 % vs 23.0 %). Sipuleucel-T successfully reached the prespecified level of statistical significance and reduced the overall risk of death by 22 % compared to control (p < 0.05) (Kanthoff et al., 2010b). Analyses of time to disease progression did not differ between

As sipuleucel-T is intended and produced solely for personalized use in a central laboratory there is no routine testing for transmissible infectious diseases so general precautions for handling blood products has to be employed. Due to the expiration time being as short as 18 h the product safety testing is challenging and sipuleucel-T has to be released for use based on the sterility and microbial results from a number of tests. If the sterility results show positive for microbial contamination after the use of sipuleucel-T, the manufacturer will inform the treating doctor. As, due to the character of the product, no cell filter can be used during the i.v. re-infusion of the ex vivo stimulated blood compounds, acute infusion reactions are the most common solely adverse event (AE) in patients receiving sipuleucel-T but also in control


AdV = Adenovirus; DCs = dendritic cells; diff. = different; FV = Fowl pox virus; mRNA = messenger RNA; PAP = prostatic acid phosphatase; PSMA = prostate-specific membrane antigen; PSCA = prostate stem cell antigen; TAA = tumor associated antigen; VV = Vaccinia virus

Table 1. Systematic list of vaccine-delivering systems in PCa vaccine approaches

Novel therapeutic options for patients of this stage of disease have been stated as an urgent medical need. Thus besides vaccine therapies a number of agents (e. g. endothelin receptor antagonists, receptor activator of nuclear factor κB ligand inhibitors, anti-angiogenic drugs, cytochrome P17 enzyme inhibitors, vitamin D analogues) are now tested in phase III registration trials either alone or in combination with docetaxel for first- or second-line use in mCRPC patients (Antonarakis & Drake, 2010; Antonarakis & Eisenberger, 2011).

Clinical trails that have engrossed most interest include i) Dendritic Cell (DC)-based vaccines (with clinically meaningful outcome for sipuleucel-T), ii) DNA vaccines (e.g. viral vector-based Prostvac-VF) together with recombinant peptide vaccines, and iii) wholetumor cell vaccines (e.g. GVAX).
