PDCD1 and metastatic melanoma: Based on the benefits of FMT in anti-PD-1 therapy in a mouse model [72], Baruch et al. designed a phase I clinical trial (NCT03353402) in which stool donors, including two melanoma patients who received anti-PD-1 antibody therapy and achieved complete remission, were recruited to evaluate the safety and feasibility of FMT combined with anti-PD-1 antibody immunotherapy in 10 patients with refractory metastatic melanoma.