Provided is a marker that determines effectiveness prior to or in an early stage of disease treatment with a PD-1 signal inhibitor. A biomarker that can serve as an indicator of metabolic change related to T-cell mitochondrial activity and/or T-cell activation in a subject is used as a biomarker for predicting or determining the effectiveness of treatment with a PD-1 signal inhibitor. The following can be used as the indicator: intestinal flora-related metabolites in serum or plasma energy metabolism-related metabolites in serum or plasma amino acid metabolism-related metabolites and/or derivatives thereof in serum or plasma oxygen consumption level and/or ATP turnover rate in peripheral CD8+ cells amino acids in T-cells and T-bet in peripheral CD8+ cells.本發明提供一種於利用PD-1訊息抑制劑之疾病治療之前或早期階段判定有效性的標記。作為用以預測或判定利用PD-1訊息抑制劑之治療之有效性之生物學標記,使用成為與受驗者之T細胞之線粒體活性及/或T細胞之活化相關之代謝變化之指標者。作為指標,可使用血清或血漿中之腸內菌叢相關代謝物、血清或血漿中之能量代謝相關代謝物、血清或血漿中之胺基酸代謝相關代謝物及/或其衍生物、末梢血液CD8+細胞中之耗氧量及/或ATP轉換率、T細胞中之胺基酸、末梢血液CD8+細胞中之T-bet。
