Original Article
The abscopal effect induced by in situ-irradiated peripheral tumor cells in a murine GL261 brain tumor model
Abstract
Background: Localized radiotherapy is considered to act as an adjuvant for systemic anti-tumor immunity. We examined whether in situ-irradiated peripheral tumor cells can evoke an abscopal effect in the brain inhibiting malignant tumor growth.
Methods: Syngeneic albino C57BL/6 mice were inoculated with mouse glioma cells (GL261) transfected with the Kusabira Orange fluorescent gene (GL261-mKO) for monitoring the tumor growth with in vivo imaging system. GL261-mKO cells were subcutaneously implanted in the thigh and irradiated by X-rays (20 Gy) for in situ vaccination. Ex vivo-irradiated GL261-mKO cells were used as a conventional whole-cell vaccine for comparison. Following these treatments, the brain was challenged with the same GL261-mKO cells, and survival analyses were performed by Kaplan-Meier analysis. In addition, IFN-γ release from splenocytes and CD8+ cells infiltration into the brain were analyzed.
Results: Both in situ- and ex vivo-irradiated vaccines significantly prolonged the survival of the mice compared to the control group bearing an intracerebral tumor. Although there was no significant difference in survival between the two vaccination methods, in situ-vaccinated mice with local control by irradiation completely rejected the implanted tumor cells in the brain. In contrast, mice with local failure demonstrated a rapid growth of both subcutaneous and challenged intracerebral tumors. The cured mice demonstrated an accumulation of CD8+ cells surrounding the inoculation site, as well as increased release of IFN-γ via an ELISPOT assay.
Conclusions: Our results indicate that the X-ray irradiation to peripheral tumors evoked a protective, tumor-specific immune response in the brain when the peripheral tumors were successfully cured by irradiation.
Methods: Syngeneic albino C57BL/6 mice were inoculated with mouse glioma cells (GL261) transfected with the Kusabira Orange fluorescent gene (GL261-mKO) for monitoring the tumor growth with in vivo imaging system. GL261-mKO cells were subcutaneously implanted in the thigh and irradiated by X-rays (20 Gy) for in situ vaccination. Ex vivo-irradiated GL261-mKO cells were used as a conventional whole-cell vaccine for comparison. Following these treatments, the brain was challenged with the same GL261-mKO cells, and survival analyses were performed by Kaplan-Meier analysis. In addition, IFN-γ release from splenocytes and CD8+ cells infiltration into the brain were analyzed.
Results: Both in situ- and ex vivo-irradiated vaccines significantly prolonged the survival of the mice compared to the control group bearing an intracerebral tumor. Although there was no significant difference in survival between the two vaccination methods, in situ-vaccinated mice with local control by irradiation completely rejected the implanted tumor cells in the brain. In contrast, mice with local failure demonstrated a rapid growth of both subcutaneous and challenged intracerebral tumors. The cured mice demonstrated an accumulation of CD8+ cells surrounding the inoculation site, as well as increased release of IFN-γ via an ELISPOT assay.
Conclusions: Our results indicate that the X-ray irradiation to peripheral tumors evoked a protective, tumor-specific immune response in the brain when the peripheral tumors were successfully cured by irradiation.
