Policheni, AntoniaHorikawa, KeisukeMilla, LizKofler, JenniferBouillet, PhilippeBelz, GabrielleO'Reilly, Lorraine A.Goodnow, Christopher C.Strasser, AndreasGray, Daniel H. D.2020-07-170818-9641http://hdl.handle.net/1885/206322FOXP3+ regulatory T (Treg) cells are essential for immunological tolerance and immune homeostasis. Despite a great deal of interest in modulating their number and function for the treatment of autoimmune disease or cancer, the precise mechanisms that control the homeostasis of Treg cells remain unclear. We report a new ENU-induced mutant mouse, lack of costimulation (loco), with atopic dermatitis and Treg cell deficiency typical of Card11 loss-of-function mutants. Three distinct single nucleotide variants were found in the Card11 introns 2, 10 and 20 that cause the loss of CARD11 expression in these mutant mice. These mutations caused the loss of thymic-derived, Neuropilin-1+ (NRP1+) Treg cells in neonatal and adult loco mice; however, residual peripherally induced NRP1− Treg cells remained. These peripherally generated Treg cells could be expanded in vivo by the administration of IL-2:anti-IL-2 complexes, indicating that this key homeostatic signaling axis remained intact in CARD11-deficient Treg cells. Furthermore, these expanded Treg cells could mediate near-normal suppression of activated, conventional CD4+ T cells, suggesting that CARD11 is dispensable for Treg cell function. In addition to shedding light on the requirements for CARD11 in Treg cell homeostasis and function, these data reveal novel noncoding Card11 loss-of-function mutations that impair the expression of this critical immune-regulatory protein.Antonia N Policheni was supported by a Cancer Council Victoria Postdoctoral Fellowship. This work was also supported by a Cancer Council of Victoria Grants-in-Aid to Daniel H.D. Gray (1146518 and 1102104), Australian NHRMC Project Grants (1145888 and 1121325) to Daniel HD Gray, NHMRC Program grant #1016701 Andreas Strasser and Leukemia and Lymphoma Society of America Specialized Center of Research (SCOR) grant #7001-13 to Andreas Strasser, Cancer Australia and Cancer Council New South Wales Project grant #1047672 to LA O’Reilly. Gabrielle T Belz is supported by an Australian NHMRC Senior Principal Research Fellowship (1135898). Daniel HD Gray is supported by an Australian NHMRC RD Wright Fellowship (1090236). Andreas Strasser is supported by an Australian NHMRC Senior Principal Research Fellowship (1020363). This work was made possible through Victorian State Government Operational Infrastructure Support and Australian Government NHMRC IRIISS. Liz Milla’s work was supported by Melbourne Bioinformatics (VLSCI), The University of Melbourne.application/pdfen-AU© 2019 Australian and New Zealand Society for Immunology Inc.Card11homeostasismutantregulatory T cells2019-05-1410.1111/imcb.122682020-04-05