Combining carbon ion radiotherapy and local injection of α-galactosylceramide-pulsed dendritic cells inhibits lung metastases in an in vivo murine model.

Our previous report indicated that carbon ion beam irradiation upregulated membrane-associated immunogenic molecules, underlining the potential clinical application of radioimmunotherapy. The antimetastatic efficacy of local combination therapy of carbon ion radiotherapy and immunotherapy was examined by use of an in vivo murine model.Tumors of mouse squamous cell carcinoma (NR-S1) cells inoculated in the legs of C3H/HeSlc mice were locally irradiated with a single 6-Gy dose of carbon ions (290 MeV/nucleon, 6-cm spread-out Bragg peak). Thirty-six hours after irradiation, α-galactosylceramide-pulsed dendritic cells (DCs) were injected into the leg tumor. We investigated the effects on distant lung metastases by counting the numbers of lung tumor colonies, making pathologic observations, and assessing immunohistochemistry.The mice with no treatment (control) presented with 168 ± 53.8 metastatic nodules in the lungs, whereas the mice that received the combination therapy of carbon ion irradiation and DCs presented with 2.6 ± 1.9 (P = 0.009) at 2 weeks after irradiation. Immunohistochemistry showed that intracellular adhesion molecule 1, which activates DCs, increased from 6 h to 36 h after irradiation in the local tumors of the carbon ion-irradiated group. The expression of S100A8 in lung tissue, a marker of the lung pre-metastatic phase, was decreased only in the group with a combination of carbon ions and DCs.The combination of carbon ion radiotherapy with the injection of α-galactosylceramide-pulsed DCs into the primary tumor effectively inhibited distant lung metastases.