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Autologous hematopoietic stem cell transplantation (autoHSCT) is a treatment option for hematological disorders and pediatric solid tumors. After an autoHSCT, natural killer (NK) cells are the first lymphocyte subset returning to normal levels. To uncover global changes during NK cell reconstitution after autoHSCT, we performed RNA-sequencing on NK cells before and after autoHSCT. Results showed profound changes in the gene expression profile of NK cells immediately after autoHSCT. Several biological processes including cell cycle, DNA replication and the mevalonate pathway were enriched. Significantly, we observed that following autoHSCT, NK cells acquired a decidual-like gene expression profile, including the expression of CD9. By using multiparametric flow cytometry, we confirmed the expansion of NK cells expressing CD9 immediately after autoHSCT, which exhibited higher granzyme B and perforin expression levels than CD9 - NK cells. These results provide insights into the physiopathology of NK cells during their reconstitution after autoHSCT., Competing Interests: The authors declare no competing interests., (© 2022 The Author(s).)

Natural killer (NK) cells are usually identified by the absence of other lineage markers, due to the lack of cell-surface-specific receptors. CD56 neg NK cells, classically identified as CD56 neg CD16+, are very scarce in the peripheral blood of healthy people but they expand in some pathological conditions. However, studies on CD56 neg NK cells had revealed different results regarding the phenotype and functionality. This could be due to, among others, the unstable expression of CD16, which hinders CD56 neg NK cells' proper identification. Hence, we aim to determine an alternative surface marker to CD16 to better identify CD56 neg NK cells. We have found that NKp80 is superior to CD16. Furthermore, we found differences between the functionality of CD56 neg NKp80+ and CD56 neg CD16+, suggesting that the effector functions of CD56 neg NK cells are not as diminished as previously thought. We proposed NKp80 as a noteworthy marker to identify and accurately re-characterize human CD56 neg NK cells., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)