CTLA4 and melanoma: In this context, co-administration for a period of 14 days of a cocktail of antibiotics (ampicillin + colistin + streptomycin) to mice housed in pathogen-free conditions and harboring experimentally-induced tumors (sarcoma/melanoma), resulted in significant attenuation of the anti-tumor efficacy of PD-1-MAbs administered alone or in combination with anti-CTLA-4 (84).