Then, we assessed the immune response of bilateral orthotopic tumor-bearing mice. First, the primary tumor slices were stained with immunofluorescence to detect exposure and release of the specific DAMPs. As shown in Fig. S23 (Supporting information), Losartan+D-HCuS@HA+L remarkably promoted CRT and HMGB-1 expression in primary tumor tissue, which improved the immunogenicity of primary tumors. Then mature DCs in lymph nodes and spleen were detected by flow cytometry. Consistent with the capacity to induce ICD, there was the highest percentage of CD80
+CD86
+ DCs in Losartan+D-HCuS@HA+L treated mice (Fig. S24 in Supporting information). The proportion of CD80
+ DCs and CD86
+ DCs in the lymph nodes of Losartan+D-HCuS@HA+L treated mice were 1.91-fold and 2.38-fold of the control group (
Figs. 3F and
G), and similar results were also observed in the spleen (Fig. S25 in Supporting information), suggesting that losartan combined with D-HCuS@HA upon irradiation could effectively promote the maturation of DCs. Mature DCs could further stimulate and activate T cells in lymph nodes to induce anti-tumor immune responses, so we then tested the levels of activated T cells in lymph nodes. The proportions of CD3
+CD8
+ T cells and CD3
+CD4
+ T cells in Losartan+D-HCuS@HA+L group were the highest in all groups (Figs. S26 and S27 in Supporting information), and the proportions of activated CD4
+ or CD8
+ cells in CD3
+ T cells were also significantly increased (
Figs. 3H and
I), suggesting that losartan combined with D-HCuS@HA upon irradiation could stimulate T cell activation and increase the ratio of helper T cells and effector T cells, thereby amplify the immune response. Then we detected the infiltration of activated T cells in bilateral tumors. As shown in the immunofluorescence staining of bilateral tumors (
Fig. 3J), CD8
α signals were significantly enhanced in the primary and contralateral tumor sections in Losartan+D-HCuS@HA+L group, indicating an increase of effector T cells in the tumor. To quantitatively detect T cell infiltration, flow cytometry was used to measure the proportions of CD3
+CD8
+ T cells and CD3
+CD4
+ T cells in bilateral tumors. In primary tumors, the proportions of CD3
+CD8
+ T cells and CD3
+CD4
+ T cells increased in all irradiation groups (
Figs. 3K and
L), suggesting that PTT could induce anti-tumor immune response in primary tumors. Notably, Losartan+D-HCuS@HA+L group showed a significant increase in the proportion of activated T cells in primary tumors. Compared with D-HCuS@HA+L group, the proportion of CD3
+CD8
+ T cells increased from 2.78% to 4.87%, CD3
+CD4
+ T cells increased from 2.18% to 4.61% in the primary tumor of Losartan+D-HCuS@HA+L group. The increasing proportions of activated T cells were also observed in the contralateral tumor of Losartan+D-HCuS@HA+L group (
Figs. 3M and
N). The proportion of CD3
+CD8
+ T cells and CD3
+CD4
+ T cells increased to 3.56-fold and 5.49-fold in Losartan+D-HCuS@HA+L group compared with the control group. However, no obvious increase of infiltrating T cells was observed in the contralateral tumor of D-HCuS@HA+L group. As a distant metastatic tumor that did not receive direct PTT, the therapeutic efficacy of the contralateral tumor mainly depended on the anti-tumor immune response induced by
in situ therapy. In the Losartan+D-HCuS@HA+L group, losartan could decrease the expression of tumor collagen, and improve T cell infiltrating, thus causing anti-tumor effect on the distant metastatic tumor and inhibiting their growth. Although the D-HCuS@HA+L group greatly inhibited the growth of the primary tumor and activated anti-tumor immune response in the host, the activated T cells could not infiltrate into the distant metastatic tumor due to the dense tumor matrix, thus producing ignorable contralateral tumor suppression.