CTLA4 and melanoma: Early reports from a group in the UK describe a predictive signature that has been developed based on the 9 gut bacteria found to be most significantly associated with response to ICI in melanoma, with 93% accuracy for differentiating patients who respond to those who have no response to PD-1 inhibitors, CTLA-4 inhibitors or combinations of both, based on shotgun metagenomic sequencing of stool samples [108, 109].