**1. Introduction**

362 Advances in the Biology, Imaging and Therapies for Glioblastoma

Yousry, I., Naidich, T.P. & Yousry, T.A. (2001). Functional magnetic resonance imaging:

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factors odulating the corticalactivation pattern of the motor system. *Neuroimaging* 

(1997). Localization of the motor hand area to a knob on the precentral gyrus. A

Since Roentgens discovery of the X-rays 1895, radiation therapy (RT) has been one of the most successful modalities used to treat cancer (Rontgen 1995). The experimental radiation treatment of glioma, however, took place first in 1938 (Bailey & Brunschwig 1938). Since then advances in radiation technology have expanded the role and value of using ionizing radiation in diagnosis, imaging and therapy of glioma. But despite substantial technical improvements in the current treatment modalities the survival rate for glioma patients is still very low (Barnholtz-Sloan, et al. 2007 ). Although the recently addition of temozolomide to conventional fractionated radiotherapy for newly diagnosed glioblastoma has resulted in an increased time of survival (Stupp, et al. 2005).

Immunotherapy utilizes the fact that the immune system has a potential to react against tumour antigens and that this can result in immunological control of the tumour. There is an increasing body of evidence that the activation of cytotoxic T-lymphocytes (CTL) has a positive effect on the long-term survival of cancer patients receiving traditional therapies such as surgery, chemo- or radiation-therapy (Nakano 2001; Prall 2004; L. Zhang, et al. 2003). It has been clearly demonstrated that tumour immune reactivity is of importance in treatment of several types of tumours (Shankar & Salgaller 2000). The immune response to glioma is primarily a result of the cell-killing function by the activated cytotoxic T cells (CTL). The aim of vaccination regimes is to enhance the effectors functions of CTL and the number of lymphoid cells within the glioma. But even if immune therapy cause large populations of lymphocytes to enter CNS tumours, total eradication of the glioma do not occur. This is partly due to the immunosuppressive factors produced by the glioma, which result in non-functioning CTL (Roszman, et al. 1991).

Traditional fractionated radiation therapy decrease the number of radiation sensitive T cells and damping the immune response of immunotherapy. Thus the interest in combining radiation therapy and immunotherapy has so far been very sparse. The use of sterotactic techniques with single radiation exposure or hypo-fractionated radiation therapy, however, does modulate the immune response and increases the therapeutic outcome (Lee, et al. 2009; Wersäll, et al. 2006). This radioimmuno modulatory effect of radiation opens for a new approach in glioma therapy by the combination of radiation- and immune-therapy.

Currently, there is a growing interest in combining radiation with other kinds of therapy, of which some are immunotherapy, to treat a broad range of malignancies (Chakraborty, et al.

Radiation Immune Modulation Therapy of Glioma 365

Tumour infiltrating lymphocytes (TILs) of various subtypes represent the host-to-tumour reaction. Anti-tumour immune response is mediated by infiltrating CD8(+) T cells which have been shown to lyses tumour cells directly via recognition of the major histocompatibility complex class I (MHC-I) present on most tumour cells. But some tumours, which have low or none expression of MHC-I, are not affected by the CTL. Tumour infiltrating CD4() helper T cells seems to play a role in regulating and amplifying tumours response by priming tumour-specific cytotoxic CD8(+) T cells, as well as macrophages involved in clearance of dead tumour cells (Toes, et al. 1999; Vesalainen, et al.

In Fig. 1 is shown how tumour antigens are captured by antigen presenting cells such as dendritic cells, which migrate to regional lymph nodes. There they present the antigen to Tcells which differentiate into CD8(+) cytotoxic T-cells, CD4(+) helper T-cells, and memory Tcells. The cytotoxic CD8(+) T-cells (CTL) are transferred to the tumour in order to kill the tumour cells. The CD4(+) release IL2 which help the CD8(+) T-Cells to proliferate. But the CD4(+) can also form CD4(+)CD25(+) regulatory T-cells which excrete IL10 to suppress the

The number of tumour infiltrating lymphocytes can be used as prognostic factor for several types of cancer (Cho, et al. 2003; Rauser, et al. 2010; Schumacher, et al. 2001; Zingg, et al. 2010). But in malignant glioma the use of tumour infiltrating lymphocytes as a prognostic factor seems to be more complex. The overall reports on tumour-infiltrating CD8(+), CD4(+) T-cells and major histocompatibility complex class I (MHC-I) expression in malignant glioma do not yield consistent correlation with clinical outcome (Dunn, et al. 2007). There seems to be factors present in patients with glioma that suppress the action of tumour infiltrated lymphocytes, and it has been demonstrated that glioma cells can actively

Regulatory CD4(+)CD25(+)FoxP3(+) T cells (Treg) have been shown to play a major role in suppression of the immune response to malignant glioma. In human CNS tumor samples both CD4(+) and Treg infiltration have found to be significantly increased throughout the time of metastatic tumor progression. Thus immunotherapeutic strategies for treating metastatic CNS tumors must fight against Treg (Sugihara, et al. 2009). In an experimental GL261 intracranial tumor model, it was shown that depletion of CD25(+) regulatory T-cells (Treg) using anti-CD25 antibodies enhance the efficacy of DC immunotherapy (Maes, et al.

Infiltration of myeloid suppressor cells (MSC) is another factor inhibiting the function of the CD8(+) T cells, which results in tumour progression (Graf, et al. 2005). Other studies indicate that glioma seems to secrete factors such as TGF and prostaglandins (PGE2) that depress the cell-mediated immunity by down regulating the function of infiltrated CD8(+) T-cells and monocytes (Dix, et al. 1999; Farmer, et al. 1989). This might be one of the reasons why anti-tumour response of the immune system is decreased in patients with primary glioma

Recent studies have shown that local single fraction radiotherapy stimulates the immune response by enhancing the antigen presentation of MHC class I (Liao, et al. 2004). The mechanism underlying these effects is probably at the level of the proteasome in the cytoplasm of the tumour cell, which are essential for production of antigenic peptides for

paralyze T cell migration by the expression of Tenascin-C (Huang, et al. 2010).

**2.2 Radio-immune-modulating effects by local irradiation** 

1994).

2009).

(Brooks, et al. 1972).

activity of the CD8(+) cytotoxic T-cells.

2004; Gulley, et al. 2005; Sharp, et al. 2007). There is also an ongoing pre-clinical search for methods to enhance the therapeutic response of malignant glioma by combining immunotherapy with single fraction or hypo-fractionated radiation therapy (Demaria, et al. 2005a; Graf, et al. 2002; Lumniczky, et al. 2002; Newcomb, et al. 2006; B. R. R. Persson, et al. 2002; B. R. R. Persson, et al. 2003; B. R. R. Persson, et al. 2010; B. R. R. Persson, et al. 2008). The clinical trials using this approach, however, are still very sparse.

This chapter will summarize the aspects of the interaction of ionizing radiation with the immune system and its immunomodulatory effects and its implications for glioma therapy (Friedman 2002). Preclinical studies of the combinational approaches of radiation and immune therapies, which results in high fractions complete remissions of glioma in animal models, is reviewed. Various clinical studies towards combination of radiation- and immune-therapy for treatment of glioma are summarized in a final section.
