Yu, Xiatong

Abstract The immune responses to anti-PD-1 therapy in cancer patients are not completely defined due to lack of reliable biomarkers that identifies responsive and functional T cells. Bim, a molecule of the Bcl-2 family, was recently identified as a downstream signaling molecule of PD-1 pathway in CD8+ T cells and has both pro-apoptotic and effective roles in CD8 T cells. Our clinical data shown that high level of Bim in CD8+ T cells (before checkpoint blockade) was predictive of response in metastatic melanoma whereas in colorectal cancer, low level of Bim was associated with treatment response. Using co-immunoprecipitation, high resolution microscopy and FRET we identified ANT2 (Adenine Nucleotide Translocase 2, an inner membrane protein of mitochondria) as a protein interacting with Bim. Accordingly, we found CD8+ T cells with low and high mitochondrial potential demonstrated different ANT2/Bim ratio, and high ANT2/Bim ratio fall in effector T cells with low mitochondrial potential but high cytotoxic activity. Given the pro-survival of ANT2, our results indicate that ANT2 may function to balance the pro-apoptotic and effective role of Bim in mitochondria in order to preserve effector T cells before contraction. Understanding the molecular mechanism of Bim and ANT2 interaction in CD8+ T cells may provide a novel marker to identify resilient CD8+ T cells responsive to anti-PD-1 therapy, and predict clinical response to the therapy.

Abstract The immune response to anti-PD-1 therapy in cancer patients is not completely defined due to lack of reliable biomarkers that can determine T cell function. Bim, a member of the Bcl-2 family, was recently identified as a downstream signaling molecule in the PD-1 pathway. Within CD8 T cells, Bim appears to have a dual function, and can be pro-apoptotic or promote effector activity. Our clinical data has shown that high levels of Bim in CD8 T cells are predictive of response to anti-PD-1 therapy in metastatic melanoma whereas in colorectal cancer, a low level of Bim is associated with treatment response. Thus, we sought to determine what molecular partners might influence the role of Bim. Using co-immunoprecipitation, high resolution microscopy and FRET we identified ANT2 (Adenine Nucleotide Translocase 2), an inner membrane protein of mitochondria, as a protein that interacts with Bim. Accordingly, we found CD8 T cells with low and high mitochondrial potential demonstrated different ANT2/Bim ratios, and a low ANT2/Bim ratio was present in effector T cells with low mitochondrial potential but high cytotoxic activity. Given the pro-survival function of ANT2, our results indicate that ANT2 may balance the pro-apoptotic and effector roles of Bim in mitochondria in order to preserve effector T cells before contraction. Understanding the molecular mechanism of Bim and ANT2 interactions in CD8 T cells may provide a novel marker to predict clinical response to anti-PD-1 therapy.