The results showed that the population of CD4+ and CD8+ in the peripheral blood of carbon ion radiation-exposed B16 (Fig. 3A), MelanA (Fig. 3B) and S91 (Fig. 3C) melanoma-bearing mice were significantly higher than that of the X-ray irradiated and untreated melanoma-bearing animals, the same results were also observed in B16 (Fig. 3D), MelanA (Fig. 3E) and S91 (Fig. 3F) tumours, while the abundance of Treg was decreased remarkably after carbon ion exposure in peripheral blood in B16 (Fig. 3G), MelanA (Fig. 3H) and S91 (Fig. 3I) melanoma-bearing mice. Here, CD4 is linked to neoplasm.