Differentiation associated regulation of microRNA expression in vivo in human CD8+ T cell subsets

Background: The differentiation of CD8(+) T lymphocytes following priming of nave cells is central in the establishment of the adaptive immune response. Yet, the molecular events underlying this process are not fully understood. MicroRNAs have been recently shown to play a key role in the regulation of haematopoiesis in mouse, but their implication in peripheral lymphocyte differentiation in humans remains largely unknown. Methods: In order to explore the potential implication of microRNAs in CD8(+) T cell differentiation in humans, microRNA expression profiles were analysed using microarrays and quantitative PCR in several human CD8(+) T cell subsets defining the major steps of the T cell differentiation pathway. Results: We found expression of a limited set of microRNAs, including the miR-17 similar to 92 cluster. Moreover, we reveal the existence of differentiation-associated regulation of specific microRNAs. When compared to naive cells, miR-21 and miR-155 were indeed found upregulated upon differentiation to effector cells, while expression of the miR17 similar to 92 cluster tended to concomitantly decrease. Conclusions: This study establishes for the first time in a large panel of individuals the existence of differentiation associated regulation of microRNA expression in human CD8(+) T lymphocytes in vivo, which is likely to impact on specific cellular functions.