Complete Withdrawal Of Immunosuppression Research Articles

HLA molecular mismatches and induced donor-specific tolerance in combined living donor kidney and hematopoietic stem cell transplantation.

We investigated the potential role of HLA molecular mismatches (MM) in achieving stable chimerism, allowing for donor-specific tolerance in patients undergoing combined living donor kidney and hematopoietic stem cell transplantation (HSCT). All patients with available DNA samples (N=32) who participated in a phase 2 clinical trial (NCT00498160) where they received an HLA mismatched co-transplantation of living donor kidney and facilitating cell-enriched HSCT were included in this study. High-resolution HLA genotyping data were used to calculate HLA amino acid mismatches (AAMM), Eplet MM, three-dimensional electrostatic mismatch scores (EMS-3D), PIRCHE scores, HLA-DPB1 T-cell epitope group MM, HLA-B leader sequence MM, and KIR ligands MM between the donor and recipient in both directions. HLA MM were analyzed to test for correlation with the development of chimerism, graft vs. host disease (GvHD), de novo DSA, and graft rejection. Follow-up time of this cohort was 6-13.5 years. Of the 32 patients, 26 developed high-level donor or mixed stable chimerism, followed by complete withdrawal of immunosuppression (IS) in 25 patients. The remaining six of the 32 patients had transient chimerism or no engraftment and were maintained on IS (On-IS). In host versus graft direction, a trend toward higher median number of HLA-DRB1 MM scores was seen in patients On-IS compared to patients with high-level donor/mixed chimerism, using any of the HLA MM modalities; however, initial statistical significance was observed only for the EMS-3D score (0.45 [IQR, 0.30-0.61] vs. 0.24 [IQR, 0.18-0.36], respectively; p=0.036), which was lost when applying the Bonferroni correction. No statistically significant differences between the two groups were observed for AAMM, EMS-3D, Eplet MM, and PIRCHE-II scores calculated in graft versus host direction. No associations were found between development of chimerism and GvHD and non-permissive HLA-DPB1 T-cell epitope group MM, HLA-B leader sequence, and KIR ligands MM. Our results suggest an association between HLA-DRB1 molecular mismatches and achieving stable chimerism, particularly when electrostatic quality of the mismatch is considered. The non-permissive HLA-DPB1 T-cell epitope group, HLA-B leader sequence, and KIR ligands MM do not predict chimerism and GvHD in this combined kidney/HSCT transplant patient cohort. Further work is needed to validate our findings. https://clinicaltrials.gov/study/NCT00498160, identifier NCT00498160.

Outcomes of liver transplantation patients infected with COVID-19: pandemic hospital experience from Turkey

Aims: There are conflicting results for the course of the disease and mortality rates for liver transplantation patients infected with COVID-19. In this study, we aimed to present the outcomes of our liver transplant patients who were hospitalized and followed up in our tertiary hospital, which served as a pandemic hospital for COVID-19.
 Methods: Patients hospitalized with the diagnosis of COVID-19 between March 1, 2020 and March 1, 2022 in Sancaktepe Şehit Prof. Dr. İlhan Varank Training and Research Hospital and Prof. Dr. Feriha Öz Pandemic Hospital were included. In this retrospective observational study, the clinical data of the patients, the need for intensive care hospitalization, and mortality rates were recorded by hospital computer system. The relationships were analyzed with SPSS v20.0.
 Results: There were 25996 patients who were hospitalized with the diagnosis of COVID-19 and 28 of them were with the history of liver transplantation. Ages of the liver transplant patients ranged from 18 to 73, with a median age of 52. 82.1% of the patients were male and 17.9% were female. Intensive care unit hospitalization rate was 25% and mortality rate was 14.3%. The relationships according to the age groups revealed that all of the women were under the age of 50 (p=0.008) and the patients who deceased were male patients over the age of 50 (p=0.044).
 Conclusion: Mortality rates and intensive care unit requirements of chronically immunosuppressed liver transplant patients with COVID-19 infection were similar with general population. Complete immunosuppression withdrawal should not be urged in this population.

Refining Auxiliary Orthotopic Liver Transplantation (AOLT) Improves Outcomes in Adult Patients With Acute Liver Failure.

To investigate whether and how experience accumulation and technical refinements simultaneously implemented in auxiliary orthotopic liver transplantation (AOLT) may impact on outcomes. AOLT for acute liver failure (ALF) provides the unique chance of complete immunosuppression withdrawal after adequate native liver remnant regeneration but is a technically demanding procedure. Our department is a reference center for ALF and an early adopter of AOLT. This is a single-center retrospective before/after study of a prospectively maintained cohort of 48 patients with ALF who underwent AOLT between 1993 and 2019. In 2012, technical refinements were implemented to improve outcomes: (i) favoring the volume of the graft rather than that of the native liver, (ii) direct anastomosis of graft hepatic artery with recipient right hepatic artery instead of the use of large size vessels, (iii) end-to-side hepaticocholedocostomy instead of bilioenteric anastomosis. Early experience (1993-2011) group (n=26) and recent experience (2012-2019) group (n=22) were compared. Primary endpoint was 90-day severe morbidity rate (Clavien-Dindo≥IIIa) and secondary endpoints were overall patient survival and complete immunosuppression withdrawal rates. Compared with the earlier experience group, the recent experience group was associated with a lower severe complication rate (27% vs 65%, P <0.001), as well as less biliary (18% vs 54%, P =0.017) and arterial (0% vs 15%, P =0.115) complications. The 1-, 3-, and 5-year patient survival was significantly improved (91%, 91%, 91% vs 76%, 61%, 60%, P =0.045). The rate of complete immunosuppression withdrawal increased to 94% vs 70%, ( P =0.091) with no need of long-term graft explant. These technical refinements favoring the liver graft and reducing morbidity may promote AOLT implementation among LT centers.

215.9: Achievement of Persistent Mixed Chimerism in Recipients of Matched and Mismatched Living Donor Kidney Transplants in a Tolerance Induction Protocol

Purpose: The induction of tolerance to kidney transplants after development of specific unresponsiveness of recipient immune cells to donor alloantigens allows elimination of maintenance immunosuppressive (IS) drugs while preventing graft loss due to rejection. We have previously reported successful induction of mixed chimerism and tolerance in recipients of fully HLA-matched living donor kidney and hematopoietic cell (HCT) transplants. This work continues in HLA-mismatched transplants, wherein achieving persistent mixed chimerism is more challenging. Methods: Living donors underwent hematopoietic stem cell mobilization and leukopheresis 6 weeks before kidney donation. The recipient conditioning regimen for the HCT consisted of 10 doses of total lymphoid irradiation (TLI) and 5 doses of anti-thymocyte globulin (ATG) following kidney transplant, with HCT on day 11. The HCT consisted of CD34+ hematopoietic progenitor cells and CD3+ cells. Twenty-nine patients received fully HLA-matched living donor transplants. Twenty-five patients received HLA-mismatched (1-haplotype matched) living donor transplants with an escalating dose of CD3+ cells to enhance HCT engraftment. Six patients recently received HLA-mismatched living donor transplants with substitution of a dose of total body irradiation (TBI) for the final dose of TLI. Results: Of the 29 fully HLA-matched living donor transplants, complete IS drug withdrawal was achieved in 24, all of whom had at least 6 months of persistent mixed chimerism. Of the 24, 17 are alive, well and have been off IS drugs from 4 to 14 years without evidence of rejection. Two off IS drugs died due to cardiovascular events at 2 and 3 years. Two returned to IS drugs after loss of chimerism at 1 year followed by acute rejection at 4 years off IS drugs, and 3 after relapse of kidney disease at 1, 5 and 6 years off IS drugs. In the 25 1-haplotype matched living donor transplants, mixed whole blood chimerism persisted in 10 (mean 20% chimerism) at the end of the 1st year posttransplant while immunosuppression was reduced to tacrolimus monotherapy. Chimerism was lost during the 2nd year in the 5 who were withdrawn from monotherapy; they returned to IS drug(s). Mixed chimerism without rejection has persisted in 3 maintained on IS monotherapy, for up to 5 years. The recent addition of a dose of TBI markedly increased levels and stability of mixed chimerism during the 1st year posttransplant. Conclusions: The loss of chimerism during withdrawal of IS drug monotherapy in the HLA-mismatched transplants may have been due to the low level of whole blood chimerism, a contrast to the HLA-matched. A very low single dose of TBI added to the TLI/ATG conditioning regimen increased early chimerism. The stability of high levels of mixed chimerism after complete IS drug withdrawal during the 2nd year posttransplant is the subject of continuing investigation.

Revisiting transplant immunology through the lens of single-cell technologies.

Solid organ transplantation (SOT) is the standard of care for end-stage organ disease. The most frequent complication of SOT involves allograft rejection, which may occur via T cell– and/or antibody-mediated mechanisms. Diagnosis of rejection in the clinical setting requires an invasive biopsy as there are currently no reliable biomarkers to detect rejection episodes. Likewise, it is virtually impossible to identify patients who exhibit operational tolerance and may be candidates for reduced or complete withdrawal of immunosuppression. Emerging single-cell technologies, including cytometry by time-of-flight (CyTOF), imaging mass cytometry, and single-cell RNA sequencing, represent a new opportunity for deep characterization of pathogenic immune populations involved in both allograft rejection and tolerance in clinical samples. These techniques enable examination of both individual cellular phenotypes and cell-to-cell interactions, ultimately providing new insights into the complex pathophysiology of allograft rejection. However, working with these large, highly dimensional datasets requires expertise in advanced data processing and analysis using computational biology techniques. Machine learning algorithms represent an optimal strategy to analyze and create predictive models using these complex datasets and will likely be essential for future clinical application of patient level results based on single-cell data. Herein, we review the existing literature on single-cell techniques in the context of SOT.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00281-022-00958-0.

Autoimmune hepatitis in patients aged 70 years or older: Disease characteristics, treatment response and outcome

Autoimmune hepatitis (AIH) affects both sexes and all age groups. However, very few studies have focused specifically on the characteristics and outcome of AIH in patients aged 70y or older. 25/234 patients with well-established AIH and disease onset at ≥70-y (median: 73-y) were analysed and compared to the rest patients (median: 47y). Treatment response was assessed in all patients from both groups who were eligible for treatment (n=202). Disease presentation was mainly insidious in both groups (19/25, 76% vs. 134/209, 64.1%; P=.313). At diagnosis, older patients had lower alaninoaminotrasferase (101[433] vs. 199[441] IU/L, P<.05) but were more frequently cirrhotic (12/25, 48% vs. 57/209, 27.3%; P=.03). Importantly, similar rates of on-treatment response (16/18, 89% vs. 154/184, 84%; P=.565), corticosteroid withdrawal (10/16, 62.5% vs. 113/154, 73.4%; P=.355) and complete withdrawal of immunosuppression (1/16, 6.3% vs. 40/154, 26%; P=.122) were achieved in both groups. Treatment-related adverse events were evenly observed between groups (6/18, 33% vs. 54/184, 29%; P=.724). In treated patients, the age ≥70y was only associated with the overall mortality (HR 8.3 [95% CI: 2.1-36.4], P=.003), but not with the liver-related mortality (HR 3.4 [95% CI: 0.4-30.0], P=.268). AIH should be seriously considered in patients ≥70y with unexplained impaired liver function tests as the disease is not infrequent in this group and seems to bear an increased risk for advanced disease stage at diagnosis. However, if immunosuppression is started promptly, it seems as safe and effective as in younger patients.

High mortality associated with gram-negative bacterial bloodstream infection in liver transplant recipients undergoing immunosuppression reduction.

BACKGROUNDImmunosuppression is an important factor in the incidence of infections in transplant recipient. Few studies are available on the management of immunosuppression (IS) treatment in the liver transplant (LT) recipients complicated with infection. The aim of this study is to describe our experience in the management of IS treatment during bacterial bloodstream infection (BSI) in LT recipients and assess the effect of temporary IS withdrawal on 30 d mortality of recipients presenting with severe infection.AIMTo assess the effect of temporary IS withdrawal on 30 d mortality of LT recipients presenting with severe infection.METHODSA retrospective study was conducted with patients diagnosed with BSI after LT in the Department of Liver Surgery, Renji Hospital from January 1, 2016 through December 31, 2017. All recipients diagnosed with BSI after LT were included. Univariate and multivariate Cox regression analysis of risk factors for 30 d mortality was conducted in the LT recipients with Gram-negative bacterial (GNB) infection.RESULTSSeventy-four episodes of BSI were identified in 70 LT recipients, including 45 episodes of Gram-positive bacterial (GPB) infections in 42 patients and 29 episodes of GNB infections in 28 patients. Overall, IS reduction (at least 50% dose reduction or cessation of one or more immunosuppressive agent) was made in 28 (41.2%) cases, specifically, in 5 (11.9%) cases with GPB infections and 23 (82.1%) cases with GNB infections. The 180 d all-cause mortality rate was 18.5% (13/70). The mortality rate in GNB group (39.3%, 11/28) was significantly higher than that in GPB group (4.8%, 2/42) (P = 0.001). All the deaths in GNB group were attributed to worsening infection secondary to IS withdrawal, but the deaths in GPB group were all due to graft-versus-host disease. GNB group was associated with significantly higher incidence of intra-abdominal infection, IS reduction, and complete IS withdrawal than GPB group (P < 0.05). Cox regression showed that rejection (adjusted hazard ratio 7.021, P = 0.001) and complete IS withdrawal (adjusted hazard ratio 12.65, P = 0.019) were independent risk factors for 30 d mortality in patients with GNB infections after LT. CONCLUSIONIS reduction is more frequently associated with GNB infection than GPB infection in LT recipients. Complete IS withdrawal should be cautious due to increased risk of mortality in LT recipients complicated with BSI.IS

Epidemiological pattern, incidence, and outcomes of COVID-19 in liver transplant patients

Background & AimsThe incidence and outcomes of coronavirus disease 2019 (COVID-19) in immunocompromised patients are a matter of debate.MethodsWe performed a prospective nationwide study including a consecutive cohort of liver transplant patients with COVID-19 recruited during the Spanish outbreak from 28 February to 7 April, 2020. The primary outcome was severe COVID-19, defined as the need for mechanical ventilation, intensive care, and/or death. Age- and gender-standardised incidence and mortality ratios (SIR and SMR) were calculated using data from the Ministry of Health and the Spanish liver transplant registry. Independent predictors of severe COVID-19 among hospitalised patients were analysed using multivariate Cox regression.ResultsA total of 111 liver transplant patients were diagnosed with COVID-19 (SIR = 191.2 [95% CI 190.3–192.2]). The epidemiological curve and geographic distribution overlapped widely between the liver transplant and general populations. After a median follow-up of 23 days, 96 patients (86.5%) were admitted to hospital and 22 patients (19.8%) required respiratory support. A total of 12 patients were admitted to the ICU (10.8%). The mortality rate was 18%, which was lower than in the matched general population (SMR = 95.5 [95% CI 94.2–96.8]). Overall, 35 patients (31.5%) met criteria of severe COVID-19. Baseline immunosuppression containing mycophenolate was an independent predictor of severe COVID-19 (relative risk = 3.94; 95% CI 1.59–9.74; p = 0.003), particularly at doses higher than 1,000 mg/day (p = 0.003). This deleterious effect was not observed with calcineurin inhibitors or everolimus and complete immunosuppression withdrawal showed no benefit.ConclusionsBeing chronically immunosuppressed, liver transplant patients have an increased risk of acquiring COVID-19 but their mortality rates are lower than the matched general population. Upon hospital admission, mycophenolate dose reduction or withdrawal could help in preventing severe COVID-19. However, complete immunosuppression withdrawal should be discouraged.Lay summaryIn liver transplant patients, chronic immunosuppression increases the risk of acquiring COVID-19 but it could reduce disease severity. Complete immunosuppression withdrawal may not be justified. However, mycophenolate withdrawal or temporary conversion to calcineurin inhibitors or everolimus until disease resolution could be beneficial in hospitalised patients.

Research Highlights

Research Highlights

Immunosuppression-induced clonal T-cell lymphoproliferative disease causing severe diarrhoea mimicking coeliac disease following renal transplantation: a case report

BackgroundPost-transplant lymphoproliferative disease is a recognized complication following solid organ transplantation. This is usually a B cell disease and frequently associated with Epstein Barr virus infection, although T cell PTLD can occur. T cell PTLD is usually a monomorphic, lymphomatous disease associated with an adverse prognosis.Case reportWe report a 52 year old male pre-emptive renal transplant recipient who developed severe diarrhea with weight loss following intensification of his immunosuppression due to antibody mediated rejection 3 years after transplantation. Duodenal biopsy demonstrated monoclonal CD8+ T cell duodenitis leading to increased intraepithlieal lymphocytes and sub-total villous atrophy mimicking coeliac disease. Coeliac disease was excluded by negative anti-tissue transglutaminase antibody, HLA-DQ2 and HLA-DQ8 testing. There was no evidence of lymphoma either on biopsy or CT enterography and no FDG avid disease on PET. Symptoms did not improve with reduction of immunosuppression, but resolved fully on complete withdrawal of treatment. The transplant failed and he was established on dialysis. The diagnosis was early PTLD.ConclusionsOesophagogastroduodenoscopy with small bowel biopsies is a useful investigation for determining the cause of diarrhoea in renal transplant patients when more common causes have been excluded. This is the first report that we are aware of clonal T cell PTLD mimicking coeliac disease which only resolved after complete withdrawal of immunosuppression. As treatments for lymphoma are aggressive they are only initiated in the malignant phase and management of early stage PTLD is to minimise risk of progression by reducing immunosuppression. Any plans to retransplant will have to take into consideration the possibility that PTLD will recur.

Combined kidney and hematopoeitic cell transplantation to induce mixed chimerism and tolerance.

Based on preclinical studies, combined kidney and hematopoietic cell transplantation was performed on fully HLA matched and haplotype matched patients at the Stanford University Medical Center. The object of the studies was to induce mixed chimerism, immune tolerance, and complete immunosuppressive drug withdrawal. Tolerance, persistent mixed chimerism, and complete withdrawal was achieved in the majority of fully matched patients. Persistent mixed chimerism and partial withdrawal has been achieved in the haplotype matched patients at present.

Summary of the Third International Workshop on Clinical Tolerance.

The Third International Workshop on Clinical Tolerance was held in Stanford, California, September 8-9, 2017. This is a summary of Workshop presentations of clinical trials designed to withdraw or minimize immunosuppressive (IS) drugs in kidney and liver transplant patients without subsequent evidence of rejection. All clinical protocols had in common the use of donor or recipient cell therapy combined with organ transplantation. Tolerance to HLA matched and mismatched living donor kidney transplants with complete withdrawal of IS drugs without subsequent rejection for up to 14 years of observation was achieved in more than 50 patients enrolled in trials in four medical centers after the establishment of transient or persistent chimerism. Complete IS drug withdrawal without chimerism was reported in a prospective trial of liver transplantation combined with injection of regulatory T cells. IS drug minimization without rejection was reported in recipients of living donor kidney transplants enrolled in the One Study consortium after injection of recipient regulatory T cells, or injection of donor regulatory monocytes or dendritic cells. In conclusion, considerable progress has been made in achieving IS drug withdrawal after cell therapy in recipients of organ transplants.

Induction of Tolerance for Long-Term Liver Allograft Survival Without Immunosuppression in Cynomolgus Monkeys

Background Spontaneous liver tolerance occurs only in highly selected patients with stable liver function for several years. There is an unmet need for a safe and reliable regimen allowing rapid immunosuppression (IS) withdrawal. Herein, we investigated if tolerance to liver allografts can be achieved in cynomolgus macaques using four different non-myeloablative preparative regimens. Methods Nine combined liver and bone marrow cell transplants were performed in cynomolgus monkeys, using three various conditioning regimens (group A, B, C). All animals received total body irradiation (1.5 Gy), thymic irradiation (7 Gy), and ATGAM (50 mg/kg) prior to the transplant. Rituximab (20 mg/kg), anti-CD40 (50 mg/kg), and anti-CD2 (1-2 mg/kg) monoclonal antibodies were given according to Table 1. Four additional livers (group D) were transplanted with the same protocol as in group C, but BMT was omitted. All IS was completely discontinued by day 55. Results All recipients developed multilineage mixed chimerism. Group A showed severe rejection with CD8+ T effector memory (Tmem) cell expansion. Improved pretransplant host Tmem depletion using anti-CD2 in group B resulted in prolonged multlineage MC and graft acceptance. Animal B(2), however, developed grade 1 GVHD in skin and rectum. The addition of post-transplant anti-CD2 in group C depleted donor Tmem, prevented GVHD, while permitting prolonged MC and extended IS-free graft survival. With the exclusion of BMT (group D), passenger leukocytes in the liver promoted transient MC. Even when chimerism was lost and memory T cells recovered, group D maintained normal graft function without any inflammation seen in protocol biopsies beyond six months. The percentage of Tregs in total CD4 were elevated over baseline during the period of stable graft function in Groups C and D animals.Conclusions This is the first proof of concept study demonstrating long-term stable liver allograft function in nonhuman primates using a non-myeloablative treatment regimen to facilitate rapid IS withdrawal. The results demonstrate the ability of anti-CD2 to control Tmem responses, and that liver transplantation alone (without infusion of DBM cells) generates MC and is associated with long-term graft survival after complete IS withdrawal. NIAID R56AI122332-01A1. AASLD Career Development Award in the Memory of the University of Michigan Transplant Team. Columbia University Irving Institute for Clinical Research.

Association of allograft rejection with reduction of immunosuppression for post-transplant lymphoproliferative disorder: Analysis of a 20-year single-institutional experience.

e19047 Background: Post transplant lymphoproliferative disorder (PTLD) is a rare, but potentially fatal complication of transplantation and therapeutic immunosuppression (IS). The cornerstone of PTLD management is reduction of IS, which carries the risk of allograft rejection. Methods: Retrospective analysis of patients diagnosed with PTLD after solid organ (SOT) or allogeneic stem cell transplant (HSCT) at the University of Florida were identified through a review of individual EMR charts. This analysis focused on rates of allograft rejection and graft failure with RI. Results: Of 138 patients diagnosed with PTLD between 1994 and 2016, 15% (n = 20) experienced allograft rejection during PTLD treatment. The primary organ of transplant and rejection included liver (35%), lung (25%), heart (10%), HSCT (15%) and kidney (15%). Median age at PTLD diagnosis was 14.5 years (range 2-59), males (50%) and median time from transplant to PTLD diagnosis was 25 months (range 0-173). RI was a documented as a component of initial PTLD treatment in 19/20 (95%) patients, with 2/20 (10%) undergoing complete withdrawal of immunosuppression, 13/20 (65%) partial RI (withdraw of one or more drugs) and 3/20 (10%) dose reductions of their established IS regimen. One lung recipient (5%) was transitioned to an alternative agent, and one patient had no documented records of IS adjustment. Treatment for acute rejection included observation 2/20 (10%), pulse steroids 11/29 (55%) or IS increase 12/20 (60%). 7/20 (35%) received combination steroids and increased IS. Allograft failure developed in 5/20 (25%) (1 kidney, 1 lung, 1 heart, 1 liver, 1 BMT). Allograft failure was not shown to correlate with RPI score at diagnosis, organ transplanted, induction therapy at transplant or 3-year OS. Of note 5/5 (100%) of patients received Rituximab as part of initial treatment, versus 5/15 patients whose grafts survived. Conclusions: RI for PTLD is associated with moderate rates of response, however acute graft rejection is common and is associated with high rates of graft failure. PTLD may still have favorable outcomes when combining partial RI with chemotherapy and Rituximab.

Five-year histological and serological follow-up of operationally tolerant pediatric liver transplant recipients enrolled in WISP-R.

Operationally tolerant pediatric liver transplant recipients maintain generally stable allograft histology in spite of apparently active humoral allo-immune responses. The absence of increased inflammation or progressive fibrosis suggests that a subset of liver allografts seem resistant to the chronic injury that is characteristic of antibody-mediated damage. (Hepatology 2017;65:647-660).

Research Highlights

Apoptosis Inhibitor of Macrophage Protein Enhances Intraluminal Debris Clearance and Ameliorates Acute Kidney Injury in Mice Arai S, Kitada K, Yamazaki T, Takai R, Zhang X, Tsugawa Y, Sugisawa R, Matsumoto A, Mori M, Yoshihara Y, Doi K, Maehara N, Kusunoki S, Takahata A, Noiri E, Suzuki Y, Yahagi N, Nishiyama A, Gunaratnam L, Takano T, and Miyazaki T Nature Medicine, 2016;2:183–193. Acute kidney injury (AKI) has a high prevalence among hospitalized patients and is thought to be a precipitating factor for chronic kidney disease and subsequent end-stage organ failure. Acute kidney injury in a transplanted kidney may also occur posttransplantation as a result of the ischemia-reperfusion injury, infection and nephrotoxic immunosuppression.1 Acute kidney injury is therefore both a cause and consequence of transplantation. Cell death during early stages of AKI can result in renal tubular obstruction, causing a further insult to kidney function and thus a vicious circle of renal damage. There are currently no clear treatment strategies for AKI, and our comprehension of the complex pathophysiology remains limited. However, harnessing physiological clearance mechanisms is a useful strategy for tackling AKI. Injured epithelial cells within tubules may act to help clear dead cells and debris, through a mechanism which requires the use of Kidney Injury Molecule-1 (KIM-1), inducing the dedifferentiation of epithelial cells into phagocytes.2 In the study by Arai and coinvestigators, apoptosis inhibitor of macrophage (AIM; CD5L) was identified as a KIM-1 ligand, involved in the clearance of debris from renal tubules by epithelial cells. In an AIM-deficient mouse model, AIM was shown to be associated with impaired recovery from AKI in mice due to reduced cell debris clearance. More importantly, the interaction of AIM with KIM-1 was shown to accelerate cell debris removal. This pathway is therefore amenable to therapeutic intervention. Promoting dead cell and debris clearance from transplanted kidneys with the use of a recombinant AIM therapy (for example) may thus ameliorate the consequences of ischemia-reperfusion injury and other immediately traumatic events improving overall long-term graft survival. REFERENCES Nehus EJ, Devarajan P. Acute kidney injury: AKI in kidney transplant recipients—here to stay. Nat Rev Nephrol. 2012;8:198–199. Yang L, Brooks CR, Xiao S, et al. KIM-1-mediated phagocytosis reduces acute injury to the kidney. J Clin Invest. 2015;125:1620–1636. Cell-Free DNA Comprises an In Vivo Nucleosome Footprint That Informs Its Tissues-of-Origin Snyder MW, Kircher M, Hill AJ, Daza RM, and Shendure J Cell, 2016;164:57–68. Biomarkers of immune status and graft function are critical in directing current clinical decision making, particularly after transplantation when the aim is to determine the correct immunosuppressive balance without compromising graft function and survival.1 Similarly, there is an interest in understanding when patients are displaying evidence of immune tolerance that might facilitate complete withdrawal of immunosuppression.2 Currently, graft rejection can only reliably be detected based on biopsies that are invasive and possibly further damaging to an already rejecting organ. Other less invasive biomarkers are therefore likely to be useful. Cell-free DNA (cfDNA) is present in blood plasma and urine and is thought to derive from the apoptosis of normal cells. As cfDNA has a short half-life, its baseline presence ongoing release under physiological conditions. Importantly, cfDNA carries a signature related to its size which may help identify its tissue of origin. In the study by Snyder and colleagues, the cfDNA signature is further refined to be able to identify the tissue of origin with more accuracy while assessing whether the tissue producing the cfDNA is normal. Using deep sequencing of cfDNA, the authors identify that in vivo occupancies of transcription factors are directly footprinted by cfDNA and that nucleosome spacing in regulatory elements and gene bodies correlates with gene expression in hematopoeitic cell types. Previously, it has been shown that allograft rejection may be correlated with cfDNA levels.3 The authors' method in the current study is likely to help identify whether the tissue of origin is of donor or recipient origin. In the future, it will be interesting to investigate whether cfDNA is useful for the identification of graft rejection biomarkers before organ damage occurs, and whether cfDNA may help to identify patients who could be amenable to tapering or even withdrawal of immunosuppression. REFERENCES Heidt S, San Segundo D, Shankar S, et al. Peripheral blood sampling for the detection of allograft rejection: biomarker identification and validation. Transplantation. 2011;92:1–9. Heidt S, Wood KJ. Biomarkers of operational tolerance in solid organ transplantation. Expert Opin Med Diagn. 2012;6:281–93. Snyder TM, Khush KK, Valantine HA, et al. Universal noninvasive detection of solid organ transplant rejection. Proc Natl Acad Sci U S A. 2011;108:6229–34.

Memory T Cells in Vascularized Composite Allotransplantation

Memory T cells are generated as part of the body's primary immune response to infection and environmental exposure so that a primed and more rapid response can be mounted in subsequent encounters. While beneficial in response to subsequent pathogen exposures, the unique characteristics of memory T cells such as their longevity, distinct trafficking patterns to multiple body sites, and cross-reactivity with donor antigens, have been demonstrated to represent a formidable barrier to successful transplantation and tolerance induction in both animal research models and clinical studies. In the context of vascularized composite allotransplantation (VCA) where acute rejection episodes are frequent despite chronic immunosuppression, current research efforts are directed toward immunosuppression minimization or complete withdrawal of immunosuppression through the attainment of transplantation tolerance. This review focuses on the potential roles of memory T cells on the rejection process at the level of the skin ...

5. Transplantation tolerance

Immune tolerance is the Holy Grail of transplantation. Tolerance allows transplantation without need for lifelong immunosuppression, granting the transplant recipient freedom from rejection of the transplant organ, freedom from the complications of immunosuppression – primarily infection and cancer over time – and freedom from the side effects of the immunosuppressive drugs, which can be serious and compromise the life of the transplant organ and recipient. There are rare instances of spontaneous tolerance in kidney transplantation, in recipients who independently stopped their immunosuppressive medications. Usually withdrawal of these drugs results in rejection and organ loss. Tolerance induction in kidney transplantation today requires transplantation of both hematopoietic cells and kidney from donor to recipient. There are three centers in the United States actively pursuing tolerance induction in this manner. They are the Massachusetts General Hospital, Northwestern, and Stanford. The protocols at the three centers differ in the nature and timing of the hematopoietic cell transplant and in the nature of the conditioning regimen necessary to prepare for hematopoietic cell transplantation. The goal of this approach is the achievement of chimerism – transient, mixed or complete depending on the protocol – which can then allow complete immunosuppressive drug withdrawal. All three centers have attempted tolerance induction in HLA-matched and HLA-mismatched living donor transplantation, with success measured as at least 1 year free of immunosuppression with no rejection and normal transplant kidney function. Both the MGH and Northwestern have been successful in approximately 50% of their HLA-mismatched recipients, while Stanford has been successful in approximately 80% of their HLA-matched recipients. Work continues at all three centers to improve efficacy, safety and durability of this approach to tolerance induction. The Stanford protocol differs from the protocols at the other centers in that the conditioning regimen for the hematopoietic cell transplant begins after transplantation of the kidney, potentially allowing the protocol’s use in deceased donor transplantation. In the protocols employed by the other centers, the conditioning regimen begins several days prior to transplantation of the kidney, restricting these protocols to living donor transplantation. Living donor transplantation is scheduled; deceased donor transplantation occurs urgently, usually well within 24 h of organ availability. Enhanced organ viability and organ banking could expand the applicability of protocols employing the early conditioning regimen for the hematopoietic cell transplant and allow easier implementation of the Stanford protocol in deceased donor transplantation. Furthermore, improved organ viability should result in less delayed and impaired function of the transplant organ, improving its longevity particularly when coupled with a state of tolerance. The ultimate goal is one (transplant) kidney for life.

Chimerism, Graft Survival, and Withdrawal of Immunosuppressive Drugs in HLA Matched and Mismatched Patients After Living Donor Kidney and Hematopoietic Cell Transplantation

Thirty-eight HLA matched and mismatched patients given combined living donor kidney and enriched CD34(+) hematopoietic cell transplants were enrolled in tolerance protocols using posttransplant conditioning with total lymphoid irradiation and anti-thymocyte globulin. Persistent chimerism for at least 6 months was associated with successful complete withdrawal of immunosuppressive drugs in 16 of 22 matched patients without rejection episodes or kidney disease recurrence with up to 5 years follow up thereafter. One patient is in the midst of withdrawal and five are on maintenance drugs. Persistent mixed chimerism was achieved in some haplotype matched patients for at least 12 months by increasing the dose of T cells and CD34(+) cells infused as compared to matched recipients in a dose escalation study. Success of drug withdrawal in chimeric mismatched patients remains to be determined. None of the 38 patients had kidney graft loss or graft versus host disease with up to 14 years of observation. In conclusion, complete immunosuppressive drug withdrawal could be achieved thus far with the tolerance induction regimen in HLA matched patients with uniform long-term graft survival in all patients.

Posttransplant Metabolic Syndrome in the Withdrawal of Immunosuppression in Pediatric Liver Transplant Recipients (WISP-R) Pilot Trial

Posttransplant metabolic syndrome (PTMS)-obesity, hypertension, elevated triglycerides, low HDL and glucose intolerance-is a major contributor to morbidity after adult liver transplant. This analysis of the Withdrawal of Immunosuppression in Pediatric Liver Transplant Recipients (WISP-R) pilot trial is the first prospective study of PTMS after pediatric liver transplant. Twenty children were enrolled in WISP-R, at median age 8.5 years (IQR 6.4-10.8), and weaned from calcineurin-inhibitor monotherapy. The 12 children who tolerated complete immunosuppression withdrawal were compared to matched historical controls. At baseline, 45% of WISP-R subjects and 58% of controls had at least one component of PTMS. Calcineurin-inhibitor withdrawal in the WISP-R subjects did not impact the prevalence of PTMS components compared to controls. At 5 years, despite weaning off of immunosuppression, 92% of the 12 tolerant WISP-R subjects had at least one PTMS component and 58% had at least two; 33% were overweight or obese, 50% had dyslipidemia, 33% glucose intolerance and 42% systolic hypertension. Overweight/obesity increased the risk of hypertension in all children. Compared to controls, WISP-R tolerant subjects had similar GFR at baseline but did have higher GFR at 2, 3 and 4 years. Further study of PTMS and immunosuppression withdrawal after pediatric liver transplant is warranted.