A novel dendritic cell vaccine for the treatment of prostate cancer

Abstract

Prostate cancer (PCa) is the most common cancer diagnosed in Australian males and the second most common cause of death (1). The mainstay of PCa treatment has been hormonal therapy, initially with androgen ablation by either chemical or surgical castration. In recent years, novel anti-androgens have led to improved overall survival (OS) (2-6) as has bringing these agents and docetaxel earlier in the time course of metastatic disease to before androgen resistance has occurred (7-9). However, ultimately treatment resistance still occurs, and new therapies are required for this common disease. Immunotherapy to date has had disappointing results in PCa with trials of CTLA-4 and PD-1 inhibitors failing to improve OS (10-12). In contrast Sipuleucel-T, a dendritic cell (DC) based vaccine, did improve OS (13). However, its uptake in practice has been limited, in part due to the cost and expertise required to deliver an autologous cellular based vaccine. In this body of work I first review progress in DC vaccine technology with particular focus on PCa. From this I propose that targeting DC with tumour antigen in situ is a promising strategy to optimise DC vaccine deliverability and enhance efficacy. I assess two methods of targeting DC in situ. Nanoparticles using polyhydroxybutyrate (PHB) beads gifted by our collaborators, Bernd Rehm at Griffith University (14) and antibody directed antigen uptake. The nanoparticles were quickly taken up by DC but did not induce an antigen specific immune response. I then identify a panel of antibodies that target DC for their ability to internalise, expression on DC and monocytes, lack of expression on human tissue and ability to produce an antigen specific immune response. From this panel I put forward Dendritic Cell Research mAb number 2 (DCR-2), a monoclonal antibody against human (h)CD300f as the best to target DC. This mouse antibody was then humanized and manipulated to express the prostate antigen PSMA in its fragment crystallizable (Fc) region. This antibody retained its ability to bind CD300f and internalise. In one experiment I show that hDCR-2 with PSMA produces an anti-PSMA T cell response. CD300f is an immune modulatory molecule that is part of the CD300 family. We know that DCR-2 leads to conformational change in CD300f and thus I hypothesised that DCR-2 may affect the phenotype and function of DC and monocytes. I show that DCR-2 leads to activation of DC, increases their ability to migrate and increases their ability to stimulate T cells in an MLR. In contrast, on monocytes DCR-2 increased PD-L1 expression and suppressed T cell proliferation in a monocyte suppressor assay. Lastly, I look at our DC vaccine in the context of PCa. Are the DC present in PCa, are they affected by treatment, and do they express our target CD300f? Monocyte and T cell phenotype and function can influence the efficacy of a DC vaccine. I determine the presence and phenotype of monocytes and T cells in PCa, I assess the impact of treatment with docetaxel chemotherapy and the novel therapy ribociclib on immune cells. Lastly, I look at the effect of patient serum on monocyte and DC function and determine whether macrophage inhibitory cytokine 1 (MIC-1) is contributing to immune evasion in PCa.

In this thesis I have made a novel DC vaccine for PCa. I show that this can produce an antigen specific immune response in vitro. I show that this DC vaccine skews DC towards a more active phenotype with improved chemotaxis and increased ability to stimulate T cells. I show that that those simulated T cells demonstrate increased IFNγ production suggesting, a Th1 response. I explore when to use this vaccine in PCa and show that there are more DC present in localized PCa (LPCa) with less myeloid derived suppressor cells (MDSC) suggesting a DC vaccine early in the course of PCa maybe more effective.