Alisa, A.A.H.I.; (2012) Alpha-fetoprotein and immunotherapy for hepatocellular carcinoma. Doctoral thesis , UCL (University College London).

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Abstract

Background and Aims: Hepatocellular carcinoma (HCC) often presents at a late stage which limits the use of curative therapy. Hence the pressing need for increasing research into newer therapies such as immunotherapy. Alpha-Fetoprotein (AFP) is an oncofetal antigen elaborated in most HCCs and is a tumour rejection antigen in animal models for HCC making it a target for the development of T cell based immunotherapy. The effect of AFP on antitumour immune responses in patients with HCC has not been explored in depth. We aimed to study the effects of AFP on the immune system cells including dendritic cells (DCs). In man, naturally occurring anti-AFP CD8 T cell responses have been detected in patients with HCC. One vital step for the design of epitope-based therapeutic vaccines is the identification and characterization of T-cell epitopes on AFP. Several AFPderived peptides have been identified and T cells recognizing these epitopes have been studied in patients with HCC. However, the role of anti-AFP CD4+ T cell responses (Th1 cells or regulatory T cells) in HCC patients has not been studied. Also, our aim was to study the role of Th1 cells in HCC patients and investigate any possible association between the expansion of these cells with clinical features of the disease such as stage of disease, serum AFP levels and tumour invasiveness. Results and Conclusions: In our first study, the treatment of monocyte-derived DCs with AFP led to DC dysfunction as detected by the down-regulation of surface molecules (CD40 and CD86) and inhibition of their T cell-stimulatory capacity. In addition, AFP treatment induced apoptosis of DCs and reduced their ability to produce TNF-alpha and IL-12. Our ex vivo results showed that the ability of monocytes, isolated from patients with elevated levels of serum AFP (>1,000 ng/ml), to produce TNF-alpha was impaired. In the second study we identified an AFP-derived T cell epitope that was recognized by circulating CD4+ T cells from patients with HCC and normal or mildly elevated AFP level in the early stage of the disease. This response was absent in healthy donors and in patients with chronic liver disease, which suggested that this response had been previously expanded in vivo in response to the tumour. The induction or activation of regulatory T cells (T-regs) by tumours or pathogens may suppress protective immunity. In the third study, we demonstrated that AFP contained an epitope which activated the expansion of inducible TGF-beta producing T-regs. In our fourth study we revealed that CD4 T-cell response expanded in the early stages of disease (Child–Pugh A score), which is usually associated with low concentrations of serum AFP. Furthermore, CD8 T cell response was largely detected in HCC patients with a Child–Pugh B or C score. Necrosis of tumour cells can activate both innate and adaptive antitumor immunity. In a further study by our group, development of higher frequencies of AFP-specific CD4+ T cells after embolisation therapy was noted. Necrosis produced by Transarterial Chemoembolization (TACE) or Chemoembolization (TAE) unmasks tumour rejection Antigen-specific T cell responses. This represented a method of in situ immune response induction that could be combined with immunotherapy to increase the frequency of AFP-specific T cells with the aim of controlling tumour growth and improving survival. Also, two further HLA-DR-restricted AFP-derived CD4+ T cell epitopes were detected. From our studies thus far, we concluded that predictive factors for detecting an AFP-specific Th1 response in patients with HCC included a serum AFP of <1000 ng/ml, Okuda stage 1 and treatment with TACE/TAE.

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