Group 2 Innate lymphoid cells promote allograft survival by constraining and inducing anergy in  alloreactive CD4+ T cells
Despite significant improvements in solid organ transplant outcomes over the past several decades, our limited understanding of the immune interface between donor organs and recipient immune systems has hindered the development of strategies to expand immunoregulatory cell populations and induce immune tolerance in transplant recipients. Given that group 2 innate lymphoid cells (ILC2s) are resident in transplanted solid organs, play a role in wound healing, and coordinate immunoregulatory cell populations, we sought to investigate their function in the alloimmune response. Using a murine heterotopic cardiac transplant model, we demonstrate that recipient ILC2s replace donor ILC2s and upregulate MHC class II (MHCII) without expressing costimulatory molecules. These recipient-derived ILC2s process and present alloantigens, inducing CD4+ T cell anergy through the Caspase-3-dependent pathway. In the absence of recipient-derived ILC2s, we observed a marked increase in infiltrating donor-reactive CD4+ T cells and significantly reduced allograft survival. Furthermore, in vivo expansion of ILC2s via IL-33 administration prolonged murine heart allograft survival. Collectively, these findings reveal a critical and previously unrecognized immunoregulatory role of host-derived ILC2s in solid organ transplantation, where they promote alloimmune tolerance by inducing anergy in alloreactive CD4+ T cells. Overall design: The study aims to compare the transcriptomic profiles of naive and graft-infiltrating ILC2 populations in cardiac transplantation. The overall design of this study includes SmartSeq sequencing of ILC2s isolated from mouse hearts. The dataset comprises 3 biological replicates of naive heart ILC2s and 4 biological replicates of graft-infiltrating ILC2s. Each sequencing replicate represents a pool of ILC2s isolated from 4-7 mouse hearts. Balb/C to C57BL/6 (B6) mouse heart transplant model, which develops acute rejection, was employed in this study. At 7 days post-transplantation, cardiac allografts were harvested and subjected to mechanical dissociation and enzymatic digestion. Single-cell suspensions were obtained, and CD45+ Lineage-ST2+ ILC2s were isolated using fluorescence-activated cell sorting (FACS) for RNA extraction.