Background: Triple-negative breast cancer (TNBC) represents the most aggressive breast cancer subtype, which recently attracts great interest for immune therapeutic development. In this context, in-depth understanding of TNBC immune landscape is highly demanded.Results: Here we report full-length single-cell RNA sequencing results of 9683 tumor-infiltrated immune cells isolated from 14 treatment naïve TNBC tumors, where 22 immune cell subsets, including T cells, macrophages, B cells, and DCs have been characterized. We identify a new T cell subset, CD8+CXCL8+ T cell, which associates with poor survival, and a subset of “pre-exhaustion” T cell cluster, which is predictive of favorable prognosis. A novel immune cell subset comprised of TCR+ macrophages, is found to be widely distributed in TNBC tumors. Further analyses reveal an up-regulation of molecules associated with TCR signaling and cytotoxicity in these immune cells.Conclusions: Altogether, our study provides a valuable resource to understand the immune ecosystem of TNBC. The novel immune cell subsets reported herein might be functionally important in cancer immunity. These data will be helpful for the immunotherapeutic strategy design of this disease.