Cytotoxic CD8+T cells can effectively kill target cells by producing cytokines, chemokines, and granzymes. Expression of these effector molecules is however highly divergent, and tools that identify and preselect CD8+T cells with a cytotoxic expression profile are lacking. Human CD8+T cells can be divided into IFN-γ– and IL-2–producing cells. Unbiased transcriptomics and proteomics analysis on cytokine-producing fixed CD8+T cells revealed that IL-2+cells produce helper cytokines, and that IFN-γ+cells produce cytotoxic molecules. IFN-γ+T cells expressed the surface marker CD29 already prior to stimulation. CD29 also marked T cells with cytotoxic gene expression from different tissues in single-cell RNA-sequencing data. Notably, CD29+T cells maintained the cytotoxic phenotype during cell culture, suggesting a stable phenotype. Preselecting CD29-expressing MART1 TCR-engineered T cells potentiated the killing of target cells. We therefore propose that CD29 expression can help evaluate and select for potent therapeutic T cell products.

Hematopoietic stem cells differentiate into a broad range of specialized blood cells. This process is tightly regulated and depends on transcription factors, micro-RNAs, and long non-coding RNAs. Recently, also circular RNA (circRNA) were found to regulate cellular processes. Their expression pattern and their identity is however less well defined. Here, we provide the first comprehensive analysis of circRNA expression in human hematopoietic progenitors, and in differentiated lymphoid and myeloid cells. We here show that the expression of circRNA is cell-type specific, and increases upon maturation. CircRNA splicing variants can also be cell-type specific. Furthermore, nucleated hematopoietic cells contain circRNA that have higher expression levels than the corresponding linear RNA. Enucleated blood cells, i.e. platelets and erythrocytes, were suggested to use RNA to maintain their function, respond to environmental factors or to transmit signals to other cells via microvesicles. Here we show that platelets and erythrocytes contain the highest number of circRNA of all hematopoietic cells, and that the type and numbers of circRNA changes during maturation. This cell-type specific expression pattern of circRNA in hematopoietic cells suggests a hithero unappreciated role in differentiation and cellular function.