To investigate the hypothesis blood was collected from patients with invasive ESCC before PDT and 7 and 14 days after treatment. Treg levels in the blood were quantified by FACS and Treg function by co culture proliferation assays with T effector cells (CD4 Our results indicate that PDT significantly diminishes by approximately 50 the suppressive capacity of peripheral Tregs from ESCC patients whereas their Treg levels seem to be unaffected. This is important since FoxP3 immunohistochemical stai