Malignant glioma modulation of immune function: relative contribution of different soluble factors

We analyzed a series of human glioma cell lines with regard to establishing what variables may contribute to their overall functional immunomodulating capability. We observed that supernatants derived from the gliomas, but not those from non-malignant human astrocyte cultures, suppressed lymphocyte proliferation. The extent of suppression elicited differed between tumors and for the same tumor depending upon its growth phase. For individual gliomas, supernatants from cultures approaching or at confluency elicited maximal lymphocyte suppression. For the series of tumors, levels of production of the immunosuppressive molecules transforming growth factor beta 2 and prostanoids (prostaglandin E2) did not correlate with the levels of functional suppression observed at any of the different growth phases. In some cases, glioma cultures grown in the presence of indomethacin to abolish prostanoid synthesis resulted in supernatants with net stimulatory activity. Our results indicate that malignant transformation of astrocytes is associated with acquisition of immunosuppressive capability which is determined by the combined effect of multiple immunomodulatory soluble factors, inhibitory or enhancing, and is dependent on the growth phase of the tumor.