It has been demonstrated by us as well as others that eosinophils may alter their phenotype and function based on the local environment (7, 9, 10). Since costimulation plays a critical role in T cell cytokine production and environmental polarization (11, 12), we examined the possibility that eosinophils may lose their tolerogenic properties in the absence of CSB immunosuppression. Cytokine expression was examined in BALB/c (H2 d) lung allografts transplanted into fully MHC-mismatched C57BL/6 (B6) (H2 b) recipient mice. In the absence of immunosuppression, lung allografts had higher levels of Th1-polarizing cytokines IFN-γ and TNF-α than did CSB-treated accepting lung grafts (Figure 1A). Limited amounts of Th2-polarizing cytokines IL-4, IL-13, IL-33, and GM-CSF were evident in lung allografts treated with or without CSB immunosuppression (Supplemental Figure 1A; supplemental material available online with this article; https://doi.org/10.1172/jci.insight.128241DS1). We next evaluated lung-resident eosinophils from both CSB-treated and nonimmunosuppressed grafts. Based on a previously identified eosinophil polarization phenotype (7), we noted higher levels of Th1-defining (or E1-defining) features, such as CXCL9, CXCL10, CXCL11, and iNOS in eosinophils isolated from rejecting compared with CSB-treated lung allografts (Figure 1A). In no group was Th2 (or E2) polarization of eosinophils detected (Supplemental Figure 1A). Flow cytometric characterization demonstrated an absence of MHC II and costimulatory molecules such as CD80, CD86, and CD40. However, there were high levels of recipient-derived MHC I (H2K b), PD-L1, and CD101 on lung-resident eosinophils in the absence of CSB (Figure 1B). Notably, we did not detect BALB/c-derived H2 d-MHC on graft-resident eosinophils, indicating a lack of "cross-dressing" or antigen swapping for donor derived-antigens (ref. 13 and Supplemental Figure 1B). Thus, while eosinophils from rejecting lungs resembled those from accepting lungs in some aspects, we did observe some differences. It is thus possible that in the absence of immunosuppression, eosinophils may contribute to graft rejection rather than acceptance, specifically because CD101 expression has been previously associated with an inflammatory eosinophil subtype (14). In order to evaluate this directly, we conditionally depleted eosinophils from B6 iPHIL mice, in which the diphtheria toxin (DT) receptor is expressed under the control of the eosinophil peroxidase promoter (Supplemental Figure 1C and ref. 15). DT-treated mice or saline-injected controls were challenged with a BALB/c lung allograft in the absence of immunosuppression. Surprisingly, mice depleted of eosinophils had higher grades of rejection (Figure 1C), increased numbers of lung-resident T lymphocytes, increased rates of T cell proliferation, and increased effector cell differentiation by day 4 after engraftment (Figure 1D). These patterns of T lymphocyte activation and infiltration were especially prominent for CD8 + T cells. CD4 + T cell proliferation did ...

Despite standardized postoperative care, some lung transplant patients suffer multiple episodes of acute and chronic rejection while others avoid graft problems for reasons that are poorly understood. Using an established model of C57BL/10 to C57BL/6 minor antigen mismatched single lung transplantation, we now demonstrate that the recipient microbiota contributes to variability in the alloimmune response. Specifically, mice from the Envigo facility in Frederick, Maryland contain nearly double the number of CD4 + Foxp3 + regulatory T cells (T regs ) than mice from the Jackson facility in Bar Harbor, Maine or the Envigo facility in Indianapolis, Indiana (18 vs 9 vs 7%). Lung graft recipients from the Maryland facility thus do not develop acute or chronic rejection. Treatment with broad-spectrum antibiotics decreases T regs and increases both acute and chronic graft rejection in otherwise tolerant strains of mice. Constitutive depletion of regulatory T cells, using Foxp3-driven expression of diphtheria toxin receptor, leads to the development of chronic rejection and supports the role of T regs in both acute and chronic alloimmunity. Taken together, our data demonstrate that the microbiota of certain individuals may contribute to tolerance through T reg -dependent mechanisms and challenges the practice of indiscriminate broad-spectrum antibiotic use in the perioperative period. K E Y W O R D Sanimal models: murine, basic (laboratory) research/science, bronchiolitis obliterans (BOS), immunosuppression/immune modulation, lung disease: immune/inflammatory, lung transplantation/pulmonology, rejection: acute, rejection: chronic

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Ex vivo expansion followed by reinfusion of tumor-infiltrating leukocytes (TILs) has been used successfully for the treatment of multiple malignancies. Most protocols rely on the use of the cytokine IL-2 to expand TILs prior to reinfusion. In addition, TIL administration relies on systemic administration of IL-2 after reinfusion to support transferred cell survival. The use of IL-2, however, can be problematic because of its preferential expansion of regulatory T and myeloid cells as well as its systemic side effects. In this study, we describe the use of a novel IL-2 mutant retargeted to NKG2D rather than the high-affinity IL-2R for TIL-mediated immunotherapy in a murine model of malignant melanoma. We demonstrate that the NKG2D-retargeted IL-2 (called OMCPmutIL-2) preferentially expands TIL-resident CTLs, such as CD8+ T cells, NK cells, and γδT cells, whereas wild-type IL-2 provides a growth advantage for CD4+Foxp3+ T cells as well as myeloid cells. OMCPmutIL-2–expanded CTLs express higher levels of tumor-homing receptors, such as LFA-1, CD49a, and CXCR3, which correlate with TIL localization to the tumor bed after i.v. injection. Consistent with this, OMCPmutIL-2–expanded TILs provided superior tumor control compared with those expanded in wild-type IL-2. Our data demonstrate that adoptive transfer immunotherapy can be improved by rational retargeting of cytokine signaling to NKG2D-expressing CTLs rather than indiscriminate expansion of all TILs.

Pathways regulating lung alloimmune responses differ from most other solid organs and remain poorly explored. Based on our recent work identifying the unique role of eosinophils in downregulating lung alloimmunity, we sought to define pathways contributing to eosinophil migration and homeostasis. Using a murine lung transplant model, we have uncovered that immunosuppression increases eosinophil infiltration into the allograft in an IL‐5‐dependent manner. IL‐5 production depends on immunosuppression‐mediated preservation of donor‐derived group 2 innate lymphoid cells (ILC2). We further describe that ischemia reperfusion injury upregulates the expression of IL‐33, which functions as the dominant and nonredundant mediator of IL‐5 production by graft‐resident ILC2. Our work thus identifies unique cellular mechanisms that contribute to lung allograft acceptance. Notably, ischemia reperfusion injury, widely considered to be solely deleterious to allograft survival, can also downregulate alloimmune responses by initiating unique pathways that promote IL‐33/IL‐5/eosinophil‐mediated tolerance.