Abstract: 【Abstract】 Objective To investigate immune effects of aminolevulinic acid-based photodynamic therapy （ALA-PDT） on mouse models of cutaneous squamous cell carcinoma （cSCC）. Methods Ultraviolet-induced SKH-1 hairless mouse models of cSCC were established, and 40 tumor- bearing mice were randomly and equally divided into several groups: control group receiving no treatment, and 7 treatment groups treated with ALA-PDT for 1, 3, 6, 12 and 24 hours, as well as 3 and 7 days respectively. After treatment, these mice were sacrificed at different time points, and skin tissues measuring 5 mm3 in size were resected. Immunohistochemical study and flow cytometry were performed to detect local infiltration of immune cells in cSCC tissues at different time points, including neutrophils, macrophages, T cells, B cells, natural killer cells and dendritic cells. Statistical analysis was done by the two-sample t test using SPSS 16.0 software. Results The number and proportion of local neutrophils and macrophages showed the most significant increase in mouse cSCC tumors 1 hour after ALA-PDT compared with those before treatment （immunohistochemical results ［number of cells per 400 × field］: 61.22 ± 6.65 vs. 22.56 ± 4.13, 59.67 ± 4.30 vs. 21.89 ± 3.26, respectively, both P < 0.05; flow cytometry results: 35.64% ± 15.33% vs. 5.46% ± 2.44%, 12.15% ± 4.86% vs. 1.98% ± 1.49%, respectively, both P < 0.05）. Both immunohistochemical study and flow cytometry showed that the expression of T cells, B cells, natural killer cells and dendritic cells significantly increased in cSCC tissues 6 hours after treatment （all P < 0.05）. After reaching the peak, the number and proportion of the above-mentioned cells decreased in cSCC tissues, but were still higher than those before treatment, and the increase continued until the end of this study, that is, day 7 after treatment. Conclusion ALA-PDT may exert anti-tumor effects by recruiting immune cells, especially neutrophils and macrophages.

Key words: Photochemotherapy, Carcinoma, squamous cell, Immunity, cellular, Aminolevulinic acid photodynamic therapy