A. Knoefel

Prevention of allograft rejection by use of regulatory T cells with a MHC-specific chimeric antigen receptor

CD4+CD25highFOXP3+ regulatory T cells (Tregs) are involved in graft‐specific tolerance after solid organ transplantation. However, adoptive transfer of polyspecific Tregs alone is insufficient to prevent graft rejection even in rodent models, indicating that graft‐specific Tregs are required. We developed a highly specific chimeric antigen receptor that recognizes the HLA molecule A*02 (referred to as A2‐CAR). Transduction into natural regulatory T cells (nTregs) changes the specificity of the nTregs without alteration of their regulatory phenotype and epigenetic stability. Activation of nTregs via the A2‐CAR induced proliferation and enhanced the suppressor function of modified nTregs. Compared with nTregs, A2‐CAR Tregs exhibited superior control of strong allospecific immune responses in vitro and in humanized mouse models. A2‐CAR Tregs completely prevented rejection of allogeneic target cells and tissues in immune reconstituted humanized mice in the absence of any immunosuppression. Therefore, these modified cells have great potential for incorporation into clinical trials of Treg‐supported weaning after allogeneic transplantation.

Isolation of human antigen-specific regulatory T cells with high suppressive function.

Adoptive transfer of regulatory T (Treg) cells could be an alternative to chronic immunosuppression for prevention of allogeneic graft rejection. While polyspecific Treg cells can prevent immune responses under lymphopenic conditions, Ag‐specific Treg cells are needed to treat autoimmunity and graft rejection. Yet, reliable markers for Ag‐specific Treg cells are missing. We report that latency‐associated peptide (LAP) and glycoprotein A repetitions predominant (GARP) can identify human Ag‐specific Treg cells. In addition, we show that the depletion of CD154+ cells from LAP+ or GARP+ Treg cells increases the Treg‐cell purity to over 90%, as assessed by epigenetic analysis. These Ag‐specific Treg cells can be isolated magnetically and might contribute to the development of GMP‐based protocols. In addition, Ag‐specific Treg cells are functionally far superior to CD4+CD25high or CD4+CD25highCD127low Treg cells in vitro and in preventing strong alloreactions in humanized mice. They could, therefore, have a high therapeutic potential for the control of alloimmune, autoimmune, and allergic immune responses in patients.

Augmentation of Transient Donor Cell Chimerism and Alloantigen‐Specific Regulation of Lung Transplants in Miniature Swine

Donor alloantigen infusion induces T cell regulation and transplant tolerance in small animals. Here, we study donor splenocyte infusion in a large animal model of pulmonary transplantation. Major histocompatibility complex–mismatched single lung transplantation was performed in 28 minipigs followed by a 28‐day course of methylprednisolone and tacrolimus. Some animals received a perioperative donor or third party splenocyte infusion, with or without low‐dose irradiation (IRR) before surgery. Graft survival was significantly prolonged in animals receiving both donor splenocytes and IRR compared with controls with either donor splenocytes or IRR only. In animals with donor splenocytes and IRR, increased donor cell chimerism and CD4+CD25high+ T cell frequencies were detected in peripheral blood associated with decreased interferon‐γ production of leukocytes. Secondary third‐party kidney transplants more than 2 years after pulmonary transplantation were acutely rejected despite maintained tolerance of the lung allografts. As a cellular control, additional animals received third‐party splenocytes or donor splenocyte protein extracts. While animals treated with third‐party splenocytes showed significant graft survival prolongation, the subcellular antigen infusion showed no such effect. In conclusion, minipigs conditioned with preoperative IRR and donor, or third‐party, splenocyte infusions may develop long‐term donor‐specific pulmonary allograft survival in the presence of high levels of circulating regulatory T cells.

Association of Higher CD4+CD25highCD127low, FoxP3+, and IL‐2+ T Cell Frequencies Early After Lung Transplantation With Less Chronic Lung Allograft Dysfunction at Two Years

Regulatory T cells (Treg) can regulate alloantigens and may counteract chronic lung allograft dysfunction (CLAD) in lung transplantation. We analyzed Treg in peripheral blood prospectively and correlated percentages of subpopulations with the incidence of CLAD at 2 years. Among lung-transplanted patients between January 2009 and July 2011, only patients with sufficient Treg measurements were included into the study. Tregs were measured immediately before lung transplantation, at 3 weeks and 3, 6, 12, and 24 months after transplantation and were defined as CD4+ CD25high T cells and further analyzed for CTLA4, CD127, FoxP3, and IL-2 expressions. Between January 2009 and July 2011, 264 patients were transplanted at our institution. Among the 138 (52%) patients included into the study, 31 (22%) developed CLAD within 2 years after transplantation. As soon as 3 weeks after lung transplantation, a statistically significant positive association was detected between Treg frequencies and later absence of CLAD. At the multivariate analysis, increasing frequencies of CD4+ CD25high CD127low , CD4+ CD25high FoxP3+ and CD4+ CD25high IL-2+ T cells at 3 weeks after lung transplantation emerged as protective factors against development of CLAD at 2 years. In conclusion, higher frequencies of specific Treg subpopulations early after lung transplantation are protective against CLAD development.

Donor-specific regulatory T cells generated on donor B cells are superior to CD4+CD25high cells in controlling alloimmune responses in humanized mice.

CD4(+)CD25highFOXP3(+) regulatory T cells (Tregs) can control allospecific immune responses in vitro and in titrated lymphopenic transplantation models. However, under non-lymphopenic conditions, as seen in patients with autoimmune diseases or after organ transplantation, polyspecific Tregs so far have been largely ineffective to control immune responses in animal models. Yet currently polyspecific CD4(+)CD25high Tregs are being tested in clinical trials. Donor materials are usually limited for the generation of donor-specific Tregs. Herein we have developed a method to produce large quantities of activated donor B cells by stimulation of donor peripheral blood mononuclear cells with 3T3 fibroblasts expressing CD40L. These activated donor B cells are potent stimulators of CD4(+)CD25high Tregs, which were expanded efficiently to inhibit an allo-MLR in donor-specific fashion. They were far more potent in inhibiting alloimmune responses in humanized mice compared with the polyspecific CD4(+)CD25high Tregs. Generation of donor-specific Tregs could be performed under good manufacturing practice conditions. Donor-reactive Tregs may be a valuable tool to control immune responses after transplantation a setting in which polyspecific Tregs have failed to date.

Role for primary immunosuppression with everolimus after pulmonary transplantation

Abstract Purpose Everolimus is a proliferation signal inhibitor used for triple immunosuppressive therapy following solid organ transplantation. Its positive benefits, such as reduction of acute rejection episodes and reduced nephrotoxicity have been shown in kidney- as well as heart transplantation. However the role of everolimus is less well defined in lung transplantation. We thus wished to study the effect of primary immunosuppression with everolimus in a preclinical large animal lung transplantation model. Methods Left-sided single lung transplantation from MHC-mismatched donors was performed in 11 adult minipigs. Intravenous pharmacologic immunosuppression was maintained for 28 days with 1.5 mg/kg/d methylprednisolone, 1.0 mg/kg/d azathioprine and cyclosporine A (blood levels 300-500 ng/ml; CsA group; n = 5). A further group (CsA + Ev; n = 6) received methylprednisolone, CsA (200–300 ng/ml) and Everolimus (5–10 ng/ml). Immunosuppression was discontinued on postoperative day (POD) 28. Graft survival was monitored by sequential chest X-rays, bronchoscopies and transbronchial biopsy histology. Results All animals survived the 28 day course of immunosuppressive therapy and showed healthy grafts on POD 28. Median allograft survival in the CsA group was 55 ± 15 days. CsA + Ev grafts showed median survival of 49 ± 86 days (p = 0.37). Conclusion Whereas everolimus might be advantageous as maintenance immunosuppressive agent, this data does not support an important role for everolimus in the immunosuppressive induction phase following lung transplantation.

Veno-Venous Extracorporeal Membrane Oxygenation in a Mouse

The use of extracorporeal membrane oxygenation (ECMO) has increased substantially in recent years. ECMO has become a reliable and effective therapy for acute as well as end-stage lung diseases. With the increase in clinical demand and prolonged use of ECMO, procedural optimization and prevention of multi-organ damage are of critical importance. The aim of this protocol is to present a detailed technique of veno-venous ECMO in a non-intubated, spontaneously breathing mouse. This protocol demonstrates the technical design of the ECMO and surgical steps. This murine ECMO model will facilitate the study of pathophysiology related to ECMO (e.g., inflammation,bleeding and thromboembolic events). Due to the abundance of genetically modified mice, the molecular mechanisms involved in ECMO-related complications can also be dissected.

Preemptive treatment of early donor-specific antibodies with IgA- and IgM-enriched intravenous human immunoglobulins in lung transplantation

This retrospective study presents our 4‐year experience of preemptive treatment of early anti‐HLA donor specific antibodies with IgA‐ and IgM‐enriched immunoglobulins. We compared outcomes between patients with antibodies and treatment (case patients) and patients without antibodies (control patients). Records of patients transplanted at our institution between March 2013 and November 2017 were reviewed. The treatment protocol included one single 2 g/kg immunoglobulin infusion followed by successive 0.5 g/kg infusions for a maximum of 6 months, usually combined with a single dose of anti‐CD20 antibody and, in case of clinical rejection or positive crossmatch, with plasmapheresis or immunoabsorption. Among the 598 transplanted patients, 128 (21%) patients formed the case group and 452 (76%) the control group. In 116 (91%) patients who completed treatment, 106 (91%) showed no antibodies at treatment end. Fourteen (13%) patients showed antibody recurrence thereafter. In case versus control patients and at 4‐year follow‐up, respectively, graft survival (%) was 79 versus 81 (P = .59), freedom (%) from biopsy‐confirmed rejection 57 versus 53 (P = .34), and from chronic lung allograft dysfunction 82 versus 78 (P = .83). After lung transplantation, patients with early donor‐specific antibodies and treated with IgA‐ and IgM‐enriched immunoglobulins had 4‐year graft survival similar to patients without antibodies and showed high antibody clearance.

Prediction of transplant outcome after 24-hour ex vivo lung perfusion using the Organ Care System in a porcine lung transplantation model

Ex vivo lung perfusion (EVLP) has become routine practice in lung transplantation. Still, running periods exceeding 12 hours have not been undertaken clinically to date, and it remains unclear how the perfusion solution for extended running periods should be composed and which parameters may predict outcomes. Twenty‐four porcine lungs underwent EVLP for 24 hours using the Organ Care System (OCS). Lungs were ventilated and perfused with STEENs solution enriched with erythrocytes (n = 8), acellular STEENs solution (n = 8), or low‐potassium dextran (LPD) solution enriched with erythrocytes (n = 8). After 24 hours, the left lungs were transplanted into recipient pigs. After clamping of the contralateral lung, the recipients were observed for 6 hours. The most favorable outcome was observed in organs utilizing STEEN solution enriched with erythrocytes as perfusate, whereas the least favorable outcome was seen with LPD solution enriched with erythrocytes for perfusion. Animals surviving the observation period showed lower peak airway pressure (PAWP) and pulmonary vascular resistance (PVR) during OCS preservation. The results suggest that transplantation of lungs following 24 hours of EVLP is feasible but dependent on the composition of the perfusate. PAWP and PVR during EVLP are early and late predictors of transplant outcome, respectively.