Immunological Low-dose Radiation Modulates the Pediatric Medulloblastoma Antigens and Enhances Antibody-dependent Cellular Cytotoxicity

Background: Immunotherapy can be an effective treatment for pediatric medulloblastoma (MB) patients. However, major subpopulations do not respond to immunotherapy, due to the lack of antigenic mutations or the immune-evasive properties of MB cells. Clinical observations suggest that radiation therapy (RT) may expand the therapeutic reach of immunotherapy. The aim of the present investigation is to study the effect of low-dose X-ray radiation (LDXR, 1 Gy) on the functional immunological responses of MB cells (DAOY, D283, and D341).

Methods: Induction of MB cell death was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Production of reactive oxygen species (ROS) was measured by fluorescent probes. Changes in the expression of  human leukocyte antigen (HLA) molecules and caspase-3 activities during treatment were analyzed using Western blotting and caspase-3 assay.

Results: Western blot analysis demonstrated that LDXR upregulated the expression of HLA class I and HLA II molecules by more than 20% compared with control and high-dose (12 Gy) groups in vitro. Several of these HLA subtypes, such as MAGE C1, CD137, and ICAM-1, have demonstrated upregulation. In addition, LDXR increases ROS production in association with phosphorylation of NF-κB and cell surface expression of mAb target molecules (HER2 and VEGF). These data suggest that a combined LDXR and mAb therapy can create a synergistic effect in vitro.

Conclusion: These results suggest that LDXR modulates HLA molecules, leading to alterations in T-cell/tumor-cell interaction and enhancement of T-cell-mediated MB cell death. Also, low-dose radiotherapy combined with monoclonal antibody therapy may one day augment the standard treatment for MB, but more investigation is needed to prove its utility as a new therapeutic combination for MB patients.