SCFAs have also been implicated in anti-PD-1 efficacy, with patients with higher concentrations of acetic acid, propionic acid, butyric acid, and valeric acid having longer progression-free survival.129 The reasons why previous studies have shown that SCFAs are associated with different outcomes in anti-PD-1 immunotherapies and anti-CTLA-4 immunotherapies remain to be understood, but could be due to the different T cells that express these receptors or that SCFAs have different effects based on the SCFA and cancer type, as we have previously reviewed.130. The gene discussed is CTLA4; the disease is cancer.