The age of immunotherapy—Celebrating STEM CELLS' contribution to understanding mechanisms of immune system development and modulation

The exciting successes and commercialization of immunotherapy this year have led us into a new age. Cell-based immunotherapy, which utilizes gene-modified cells from a cancer patient's immune system, can offer another chance at life after relapse. Gene-modified chimeric antigen receptor (CAR-T) cells can seek out and eliminate cancer cells throughout the body. Other cells of the immune system (NK cells and B cells) can also be modified to recognize and mount an attack on cancer cells. Immunotherapy using genetically modified cells is a relatively new and hugely exciting field with much potential, and one in which STEM CELLS has played an important role over the past 36 years by publishing mechanisms of development and regulation of the immune system. During the past year, we published some truly excellent basic science manuscripts in STEM CELLS that will help move the field forward. Key manuscripts covered, among other topics, immune evasion, tolllike receptors affecting proper innate immune response signaling, immunomodulation triggered by phagocytosis, and repolarization of tumor-associated macrophages to suppress cancer cell proliferation in vivo. Concise reviews are from respected experts and help to move their respective fields forward in a reliable manner. New concise reviews in the fields of immunology and immunotherapy covered the topics of “Modulating cancer immunity with hematopoietic stem and progenitor cells,” “Targeting cancer stem cells and their supporting niche,” “Exploring immunomodulatory features of mesenchymal stromal cells in humanized mouse models,” and a new interesting report on “Metabolism and gut microbiota in cancer immuno-editing, CD8/Treg ratios, immune cell homeostasis, and cancer (immuno) therapy. ” In addition to the topic of regulation and development of the immune system, some of our top cited and most read/downloaded papers in 2019 are mentioned below. The most downloaded stem/progenitor cell biology manuscript in 2019 was “Highly purified human extracellular vesicles produced by stem cells alleviate aging cellular phenotypes of senescent human cells” by Linzhao Cheng's lab. Also on the topic of extracellular vesicles, the second most downloaded manuscript of 2019 was, “Extracellular vesicle-educated macrophages promote early Achilles tendon healing. ” The third most downloaded manuscript was “CRX expression in pluripotent stem cell-derived photoreceptors marks a transplantable subpopulation of early cones,” from Associate Editor Dr Lako's group. For more information on this key topic, please see the STEM CELLS Special Series: Transplantation of stem cells into the eye, available through the STEM CELLS Portal: https://stemcellsjournals. onlinelibrary.wiley. com/hub/journal/15494918/pages/virtual-issues/ stem-cell-eye-series. Among our most downloaded and cited manuscripts for 2019 were several concise reviews that are an excellent way to get up to speed in a specific field. The topics include mesenchymal stem cells, humananimal neural chimeras, development of microglia, and regulation of cardiac differentiation. We thank the authors of these important reviews for helping to inform our readers on these hot topics. Our Sister journals, STEM CELLS (www.StemCells.com, @StemCellsJournal) and STEM CELLS Translational Medicine (www. StemCellsTM.com, @StemCellsTM), have continued to publish important manuscripts in the field, submitted by talented authors and research teams who are pushing forward the frontiers of basic, mechanistic stem cell biology, cell and gene therapy, immunotherapy, and regenerative medicine. STEM CELLS will continue to focus primarily on the functional and mechanistic aspects of stem cell biology and well-controlled advances in stem cell clinical trials. Manuscripts should have definitive conclusions and be mechanism-based to be considered for potential publication in STEM CELLS. Received: 5 December 2019 Accepted: 5 December 2019