Cytokine secretion in glioblastoma patients

Abstract

Gliomas are the most common primary tumours of the central nervous system with a lethality rate approaching 80% in the first year of glioblastoma diagnosis. Their highly invasive nature renders local therapies such as surgery and radiation ineffective; whereas novel approaches such as immunotherapy are being actively studied as possible adjuncts in
the treatment of patients with malignant gliomas.
A number of factors have been proposed to play a role in glioma immune escape, including their poor immunogenicity since they do not express specific glioma antigens; their location within the CNS, which is considered to be an immune-privileged organ and some indications that glioma cells are capable of releasing various immunosuppressive cytokines, which inhibit the cytotoxic function of T cells. Cytokines are multifunctional pleiotropic proteins, which are involved in intercellular communication and cellular activation, and they may exert their effects in the CNS both directly and indirectly. Since they may originate either from peripheral immune organs, and cross the blood-brain barrier or they may be produced by the neuronal cells within the CNS, their properties are both immunoregulatory and neuromodulatory.
This thesis investigated gliomas for the expression of cytokines and implicated their expression in the malignancy and the angiogenesis of the tumours.
Cytokine secretion was evaluated from isolated peripheral blood mononuclear cells (PBMCs) of 33 patients with malignant gliomas (grade IV) immediately before surgery, in parallel with a control group of 23 age-matched individuals, and in 5 primary glioma cell cultures using the sensitive ELISPOT methodology.
Thi cytokines tumour necrosis factor (TNF-a) and interferon (IFN7) were markedly reduced compared to control levels (P=0.01 and P<0.001, respectively). In contrast, Th2 interleukins IL-(4) and IL-(10) were strongly expressed in both peripheral lymphocytes and glioma cell cultures (P<0.05 and P<0.001 respectively).
Immunohistochemical localisation of IL-6, IL-8, COX, IL-lO, VEGF (vascular endothelial growth factor) and CD34 expression levels was performed in formalin-fixed paraffin-embedded tissue sections taken from 23 patients. Microvessels highlighted by
means of anti-CD34 irnmunohistochemistry were enumerated with computer assisted image analysis.
IL-6 was identified immunohistochemically in all specimens and showed an elevation in expression as necrosis grade increased (p=O.00S). IL-6 was also increased as the histological grade of the tumour increased (p0.020). IL-S expression was detected in all cases of gliomas with a mean of 19.5% of the cells. Expression was not related to either necrosis grade or increase in tumour grade. COX immunoreactivity was detected in all cases with an average of 29.1% positive cells. However, COX immunoreactivity was not significantly correlated with either necrosis or tumour grade. VEGF immunoreactivity
occurred in 58.3% of cells and demonstrated a positive correlation with tumour grade (pzr0.035). The expression level of IL-10 was low both in terms of staining intensity and percentage of positive cells, and did not correlate with either necrosis or histological grade.
CD34 immunoreactivity indicated that vascular volumetric parameters were not affected by either tumour or by necrosis grade. The expression of soluble CD95 as measured using a specific ELISA was not significantly (p>0.05) reduced in the serum of 43 glioma patients compared to normal levels.
In conclusion, these results indicate that patients harbouring malignant gliomas exhibit a broad suppression of cell-mediated immunity possibly due to the marked dysregulation in their cytokinetic profile. Glial tumours seem to induce a Thi (stimulatory) to Th2-type (inhibitory) cytokine shift which further supports humoral immunity at the expense of cell-mediated immune responses, contributing to the inefficient anti-tumour responses generated in these patients.