A global prospective study involving 39 melanoma patients receiving CTLA-4 (Ipilimumab) in combination with anti-PD-1 therapy (Nivolumab) or PD-1 therapy only, identified enrichment of filamentous bacilli of the genus Bacterium hordemannii, anaplastic bacilli of the species Polyporus, and Clostridium pumilus in responders to the combination therapy. The gene discussed is PDCD1; the disease is melanoma.