IntroductionHuman hematopoietic tissue and cell transplantation into immunodeficient mice, such as mice with the severe combined immunodeficiency (SCID) 1,2 mutation and their derivatives, including NOD/SCID, 3 NOD/SCID/␤2m null , 4 and NOD/SCID/ ␥c null mice, 5 has been widely used to study the function of human immune cells. However, only a few studies have shown the ability to achieve systemic in vivo immune responses in humanized mice. 6 In general, immunodeficient mice that received a transplant of human hematopoietic stem cells (HSCs) have poor human T-cell development. Although some human T-cell reconstitution was seen in NOD/SCID/␥c null mice after human umbilical cord blood (UCB) stem-cell transplantation, human thymopoiesis in the recipient thymus appeared inefficient, and the mouse thymus remained underdeveloped in these mice. 5 Recently, Traggiai et al 6 reported that intrahepatic injection of human CD34 ϩ UCB cells into newborn Rag2 Ϫ/ Ϫ␥c Ϫ/Ϫ mice results in improved human T-cell development in the mouse thymus. An important advancement in this model compared with UCB transplantation in adult mice was the ability of grafted mice to mediate in vivo antiviral immune responses. 6 However, a long period of time (16 weeks) was required to achieve significant peripheral human T-cell repopulation in these mice, and the levels of human T cells in the spleen of long-term surviving mice were relatively low. Furthermore, the MHC restriction and tolerance status of human T cells that were selected in the mouse thymus in these mice still remains undefined.A commonly used mouse model for the study of human For personal use only. on June 19, 2019. by guest www.bloodjournal.org From Materials and methods Animals and human fetal tissuesImmunodeficient nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice were housed in a specific pathogen-free microisolator environment and used at 6 to 10 weeks of age. Human fetal thymus and liver tissues of gestational age of 17 to 20 weeks were obtained from Advanced Bioscience Resource (Alameda, CA). Inbred Massachusetts General Hospital miniature swine (kindly provided by David H. Sachs) 10 were used as porcine skin donors. Protocols involving the use of human tissues and animals were approved by the Massachusetts General Hospital Human Research Committee and Subcommittee on Research Animal Care, and all of the experiments were performed in accordance with the protocols. Human tissue implantationMice were conditioned with sublethal (2-3 Gy) whole-body irradiation. Human fetal Thy and Liv fragments measuring about 1 mm 3 were implanted under the recipient kidney capsule within 3 days after irradiation. Some mice also received CD34 ϩ FLCs (1-5 ϫ 10 5 /mouse, intravenously) purified from the same donor on the day of human Thy/Liv transplantation. CD34 ϩ FLCs were isolated by the magnetic-activated cell sorter (MACS) separation system using anti-CD34 microbeads (Miltenyi Biotec, Auburn, CA). Levels of human hematopoietic cells in the mice that underwent transplantation ...

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Plants utilize extracellular vesicles (EVs) to transport small RNAs (sRNAs) into their fungal pathogens and silence fungal virulence-related genes through a phenomenon called “cross-kingdom RNAi.” It remains unknown, however, how sRNAs are selectively loaded into EVs. Here, we identified several RNA-binding proteins (RBPs) in Arabidopsis , including Argonaute 1 (AGO1), RNA helicases (RHs) and Annexins (ANN), which are secreted by exosome-like EVs. AGO1, RH11 and RH37 selectively bind to EV-enriched sRNAs but not non-EV enriched sRNAs, suggesting that they contribute to the selective loading of sRNAs into EVs. Conversely, ANN1 and ANN2 bind to sRNAs non-specifically. The ago1, rh11rh37 and ann1ann2 mutants showed reduced secretion of sRNAs in EVs, demonstrating that these RBPs play an important role in sRNA loading and/or stabilization in EVs. Furthermore, rh11rh37 and ann1ann2 showed increased susceptibility to Botrytis cinerea , supporting that RH11, RH37, ANN1 and ANN2 positively regulate plant immunity against B. cinerea .

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