Anti-PD1 immunotherapy, as a single agent or in combination with standard chemotherapies, has significantly improved the outcome of many patients with cancers. However, resistance to anti-PD1 antibodies often decreases the long-term therapeutic benefits. Despite this observation in clinical practice, the molecular mechanisms associated with resistance to anti-PD1 antibody therapy have not yet been elucidated. To identify the mechanisms of resistance associated with anti-PD1 antibody therapy, we developed cellular models including purified T cells and different cancer cell lines from glioblastoma, lung adenocarcinoma, breast cancer and ovarian carcinoma. A murine model of lung cancer was also used. Longitudinal blood samples of patients treated with anti-PD1 therapy were also used to perform a proof-of-concept study of our findings. We found that anti-PD1 exposure of T-cell promotes an enrichment of exosomal miRNA-4315. We also noted that exosomal miRNA-4315 induced a phenomenon of apopto-resistance to conventional chemotherapies in cancer cells receiving exosomal miRNA-4315. At molecular level, we discern that the apopto-resistance phenomenon was associated with the miRNA-4315-mediated downregulation of Bim, a proapoptotic protein. In cellular and mice models, we observed that the BH3 mimetic agent ABT263 circumvented this resistance. A longitudinal study using patient blood showed that miRNA-4315 and cytochrome c can be used to define the time period during which the addition of ABT263 therapy may effectively increase cancer cell death and bypass anti-PD1 resistance.This work provides a blood biomarker (exosomal miRNA-4315) for patient stratification developing a phenomenon of resistance to anti-PD1 antibody therapy and also identifies a therapeutic alternative (the use of a BH3 mimetic drug) to limit this resistance phenomenon.