CTLA4 and melanoma: It is also possible that changing the source of mice (Jackson Laboratories vs. Charles River Laboratories) could explain the change in overall survival of the mice, as other groups have shown that differences in gut microbiome between sources of C57BL/6 has been linked to a difference in the growth kinetics and severity of B16 melanoma tumor progression with anti-PD-L1 therapy [51] or anti-CTLA-4 therapy [52], suggesting that the gut microbiome may one day be used as a predictor of responsiveness to immune checkpoint inhibitors [53].