Abstract
It is well established that interactions between tumor cells and the host tissue stroma play a key role in tumor progression. However, the contribution of the different stromal cell components to tumor growth remains to be clarified after radiation therapy. We report here the antitumor characteristics of tumor-infiltrating neutrophils (CD11b+Gr-1+high cells), which were recruited to irradiated tumor in LLC-OVA (OVA-transfected LLC)-bearing mice. We observed that the number of them peaked at 36 h after 11 Gy irradiation. Surprisingly, the therapeutic effect of irradiation was attenuated in the mice depleted of both CD11b+Gr-1+high cells and CD8+ cells before irradiation compared to in the mice depleted only CD8+ cells. Although CD11b+Gr-1+high cells isolated from tumors both 36 h post-irradiated mice and un-irradiated mice had a neutrophil-like morphology, most of them in irradiated tumors were more hyper-segmented. Coinjection of LLC-OVA with radiation-induced CD11b+Gr-1+high cells resulted in a dramatic decrease in tumor growth. They expressed higher levels of pro-inflammatory cytokines and lower levels of VEGF and MMP9 than control cells. Thus, our findings strongly suggest that radiation-induced CD11b+Gr-1+high cells may have the antitumor activity.
