Radiation sterilisation of cultured human brain tumour cells for clinical immune tumour therapy

The aim is to investigate the radiosensitivity of noninfected cultured human glioma cells to ascertain that intracutaneously administered cells are viable enough to produce interferon-γ but not able to proliferate. Cell cultures were established from five patients undergoing brain tumour surgery. By karyotyping, we found four malignant (three glioblastoma multiforme (GBM), one giant cell glioma) and one normal. The cells were irradiated with 137Cs-γ rays at absorbed dose levels of 0, 20, 40, 60, 80, 100 and 120 Gy. The fraction of viable cells was examined by MTT incorporation assay. The average of the data obtained from three GBM cell cultures was fitted to an exponential model. The parameters were: extrapolation number n=0.85±0.10, mean lethal dose D0=12.4±3.2 Gy and an additional uncertainty parameter δS=0.14±0.03. By setting δS=0, the corresponding values of the parameters were n=0.86±0.16 and D0=30.0±8.1 Gy. The rate of proliferation was examined by 3H-thymidine incorporation. The average of the proliferation data obtained from three GBM cell cultures was fitted to an exponential model yielding n=0.943±0.005 and D0=5.8±0.5 Gy for δS=0.057±0.005, and by setting δS=0, n=1.00±0.02 and D0=8.4±1.6 Gy. No outgrowth of plated cells was observed after 4 weeks at an absorbed dose of 100 Gy. This absorbed dose is recommended for irradiation of 2 × 106 glioma cells used for clinical immunisation.