Lymphocyte subset reconstitution in pediatric liver recipients induced with steroid-free rabbit anti-human thymocyte globulin

Recurrent Primary Sclerosing Cholangitis: Current Understanding, Management, and Future Directions

Patients with primary sclerosing cholangitis (PSC) constitute 5 to 15% of patients listed for liver transplantation worldwide. Although post-transplant outcomes are favorable, recurrent PSC (rPSC) occurs in an important subset of patients, with higher prevalence rates reported with increasing time from transplant. Given its association with poor graft outcomes and risk of retransplant, effort has been made to understand rPSC, its pathophysiology, and risk factors. This review covers these facets of rPSC and focuses on implicated risk factors including pretransplant recipient characteristics, inflammatory bowel-disease-related factors, and donor-specific and transplant-specific factors. Confirming a diagnosis of rPSC requires thoughtful consideration of alternative etiologies so as to ensure confidence in diagnosis, management, subsequent risk assessment, and counseling for patients. Unfortunately, no cure exists for rPSC; however, future large-scale efforts are underway to better characterize the natural history of rPSC and its associated risk factors with hopes of identifying potential key targets for novel therapies.

Analysis of rabbit anti-thymocyte globulin vs basiliximab induction in pediatric liver transplant recipients

Literature is limited comparing induction immunosuppression in pediatric liver transplant (LTx) recipients. This is a single-center, retrospective cohort study of primary pediatric liver transplants at our center between 2005 and 2016 who received either basiliximab (BSX) or rabbit anti-thymocyte globulin (rATG) induction. Maintenance immunosuppression consisted of tacrolimus ± a corticosteroid taper. Exclusions included receipt of an ABO-incompatible graft, retransplantation, and multi-organ transplantation. Primary outcomes were incidence of treated biopsy-proven acute rejection (tBPAR) and PTLD within the first year and infections within 90 days of LTx. Secondary outcomes included graft and patient survival, time to first tBPAR, and incidence of steroid-resistant rejection (SRR) within the first year post-LTx. A total of 136 patients were included in the final analysis of which 57 patients (42%) received BSX induction. Patients who received rATG induction with or without a 2-week corticosteroid taper experienced significantly more tBPAR compared to those who received BSX induction with a 6-month corticosteroid taper (55.7% vs 33.3%, P = .01). There were no differences in the incidence of PTLD, infections, SRR, graft or patient survival, or time to first tBPAR between the two groups. Induction with rATG either with or without a short corticosteroid taper was associated with significantly more tBPAR in primary pediatric LTx recipients when compared to BSX induction with a prolonged corticosteroid taper in the setting of maintenance immunosuppression with tacrolimus.

Enhanced B Cell Alloantigen Presentation and Its Epigenetic Dysregulation in Liver Transplant Rejection

T cell suppression prevents acute cellular rejection but causes life-threatening infections and malignancies. Previously, liver transplant (LTx) rejection in children was associated with the single-nucleotide polymorphism (SNP) rs9296068 upstream of the HLA-DOA gene. HLA-DOA inhibits B cell presentation of antigen, a potentially novel antirejection drug target. Using archived samples from 122 white pediatric LTx patients (including 77 described previously), we confirmed the association between rs9296068 and LTx rejection (p = 0.001, odds ratio [OR] 2.55). Next-generation sequencing revealed that the putative transcription factor (CCCTC binding factor [CTCF]) binding SNP locus rs2395304, in linkage disequilibrium with rs9296068 (D' 0.578, r(2) = 0.4), is also associated with LTx rejection (p = 0.008, OR 2.34). Furthermore, LTx rejection is associated with enhanced B cell presentation of donor antigen relative to HLA-nonidentical antigen in a novel cell-based assay and with a downregulated HLA-DOA gene in a subset of these children. In lymphoblastoid B (Raji) cells, rs2395304 coimmunoprecipitates with CTCF, and CTCF knockdown with morpholino antisense oligonucleotides enhances alloantigen presentation and downregulates the HLA-DOA gene, reproducing observations made with HLA-DOA knockdown and clinical rejection. Alloantigen presentation is suppressed by inhibitors of methylation and histone deacetylation, reproducing observations made during resolution of rejection. Enhanced donor antigen presentation by B cells and its epigenetic dysregulation via the HLA-DOA gene represent novel opportunities for surveillance and treatment of transplant rejection.

Alloreactive CD154-expressing T-cell subsets with differential sensitivity to the immunosuppressant, belatacept: potential targets of novel belatacept-based regimens

Belatacept blocks CD28-mediated T-cell costimulation and prevents renal transplant rejection. Understanding T-cell subset sensitivity to belatacept may identify cellular markers for immunosuppression failure to better guide treatment selection. Here, we evaluate the belatacept sensitivity of allo-antigen-specific CD154-expressing-T-cells, whose T-cytotoxic memory (TcM) subset predicts rejection with high sensitivity after non-renal transplantation. The belatacept concentration associated with half-maximal reduction (EC50) of CD154 expression was calculated for 36 T-cell subsets defined by combinations of T-helper (Th), Tc, T-memory and CD28 receptors, following allostimulation of peripheral blood leukocytes from 20 normal healthy subjects. Subsets were ranked by median EC50, and by whether subset EC50 was correlated with and therefore could be represented by the frequency of other subsets. No single subset frequency emerged as the significant correlate of EC50 for a given subset. Most (n = 25) T-cell subsets were sensitive to belatacept. Less sensitive subsets demonstrated a memory phenotype and absence of CD28 receptor. Potential drug-resistance markers for future validation include the low frequency highly differentiated, Th-memory-CD28-negative T-cells with the highest median EC50, and the least differentiated, high-frequency Tc subset, with the most CD28-negative T-cells, the third highest median EC50, and significant correlations with frequencies of the highest number of CD28-negative and memory subsets.

Antithymocyte globulin facilitates alloreactive T-cell apoptosis by means of caspase-3: potential implications for monitoring rejection-free outcomes

BACKGROUND

Alloreactive T-cell apoptosis may explain reduced immunosuppression requirements with proapoptotic immunosuppression and among rejection-free recipients. This possibility remains unproven.

METHODS

Apoptotic (caspase-3+, cathepsin B+) and inflammatory (CD154+) T-cell subsets were evaluated before and after adding rabbit antithymocyte globulin (rATG) to mixed lymphocyte co-cultures between human leukocyte antigen-mismatched peripheral blood lymphocytes from healthy adults. In random samples from children with liver (LTx-20) and intestine (ITx-13) transplantation, apoptotic T cells were evaluated for association with rejection-free outcomes using the caspase-3 substrate, phiphilux.

RESULTS

In mixed lymphocyte co-cultures between normal human peripheral blood lymphocytes, (1) frequencies of memory (M) and naive (N) Th and Tc, which expressed activated caspase-3, were enhanced most by the combination of allostimulation and rATG, than either stimulus alone. These findings were confirmed with antibody to activated caspase-3, phiphilux, and terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) assay; (2) frequencies of Th subsets, which expressed activated cathepsin B, were similarly increased with combined stimulation. Tc seemed resistant to cathepsin B activation; (3) with increasing rATG concentrations, proportionately more allospecific CD154+T-cytotoxic memory cells (TcM) survived than TcM, resulting in relative enrichment of allospecific CD154+TcM. In random blood samples, phiphilux+T-cell subset frequencies were higher among 14 rejection-free LTx and ITx recipients and demonstrated a greater increase with ex vivo rATG pretreatment than 19 rejectors. In logistic regression analysis, phiphilux+TcM associated best with rejection-free outcomes with a sensitivity of 57% and a specificity of 89%.

CONCLUSION

Rabbit antithymocyte globulin facilitates apoptosis of alloreactive T cells by means of caspase-3 activation, which may explain its steroid-sparing effect in pediatric liver and intestine recipients. Apoptotic susceptibility of T-cytotoxic memory cells, which resist cathepsin B activation, may distinguish rejection-free and rejection-prone liver recipients.

Recurrence of primary sclerosing cholangitis in pediatric liver transplant recipients

There is little detailed clinical information on recurrent primary sclerosing cholangitis (rPSC) after liver transplantation in children. Our purpose was to describe the characteristics of children who had experienced rPSC after liver transplantation so that we could identify potential risk factors for recurrence. Clinical information for pediatric patients undergoing transplantation for primary sclerosing cholangitis (PSC) was retrospectively reviewed, and variables related to the pretransplant diagnosis of PSC and posttransplant variables were abstracted. The studied variables included the following: cytomegalovirus/Epstein-Barr virus status, early/late rejection, induction regimen, immunosuppression in the first year, steroid-resistant rejection, diagnosis of inflammatory bowel disease, and human leukocyte antigen markers commonly associated with PSC. A diagnosis of rPSC was made on the basis of radiographic features, histology, or both. Twelve patients underwent liver transplantation for PSC between 1993 and 2012. Patients received tacrolimus for maintenance immunosuppression after induction with steroids (n = 6) or thymoglobulin (n = 6). Three patients were diagnosed with rPSC 44, 60, and 62 months after transplantation. A fourth patient underwent retransplantation for graft failure with features of both hepatic artery stenosis and rPSC. This patient had distinct histological features of rPSC in the second graft. Three of the 4 patients were 7 years old or younger at the diagnosis of PSC. The patient and graft survival rates were similar for the steroid and thymoglobulin groups. All 4 children with rPSC received steroid-free thymoglobulin induction. In conclusion, our observation of an association between thymoglobulin, and age less than 10 years at the diagnosis of PSC, and rPSC adds to the existing suggestion of a link between the immune environment and the pathogenesis of rPSC. Defining the natural history of rPSC and searching for the etiology and risk factors of rPSC are important for the long-term outcomes of pediatric patients.

Peripheral blood biomarkers for the characterization of alloimmune reactivity after pediatric liver transplantation

Individualization of immunosuppressive medications is an important objective in transplantation medicine. Reliable biomarkers to distinguish between patients dependent from intensive immunosuppressive therapy and those where therapy can be minimized among pediatric transplant recipients receiving immunosuppressive medications are still not established. We evaluated the potential of cross-sectional quantification of regulatory T cells, lymphocyte subsets, and cytokine concentrations as biomarkers in 60 pediatric liver transplant recipients with AR, CR, or normal graft function and in 11 non-transplanted patients. Transplant recipients presenting with AR had significantly higher CD8+ T-cell counts, significantly higher concentrations of IL-2, and increased levels of IFN-γ compared with asymptomatic patients or controls. Regulatory T-cell numbers did not differ between children with rejection and children with good graft function. A tendency toward increased concentrations of IL-4 and TGF-β was detected in transplant recipients with good graft function. Cross-sectional parameters of peripheral regulatory T cells in pediatric liver transplant recipients do not seem to be valuable biomarkers for individualizing immunosuppressive therapy prior to the weaning process. Lymphocyte subsets, IL-2, IFN-γ, IL-4, and TGF-β serum concentrations may be helpful to identify children in whom immunosuppression can be reduced or discontinued.

Genetic variants in major histocompatibility complex-linked genes associate with pediatric liver transplant rejection

BACKGROUND & AIMS

Limited access to large samples precludes genome-wide association studies of rare but complex traits. To localize candidate genes with family-based genome-wide association, a novel exploratory analysis was first tested on 1774 major histocompatibility complex single nucleotide polymorphisms (SNPs) in 240 DNA samples from 80 children with primary liver transplantation and their biologic parents.

METHODS

Initially, 57 SNPs with large differences (P < .05) in minor allele frequencies were selected when parents of children with early rejection (rejectors) were compared with parents of nonrejectors.

RESULTS

In hypothesis testing of selected SNPs, the gamete competition statistic identified the minor allele G of the SNP rs9296068, near HLA-DOA, as being significantly different (P = .018) between outcome groups in parent-to-child transmission. Subsequent simple association testing confirmed over- and undertransmission of rs9296068 based on the most significant differences between outcome groups, of 1774 SNPs tested (P = .002), and allele (G) frequencies that were greater among rejectors (51.4% vs 36.8%, respectively, P = .015) and lower among nonrejectors (26.8% vs 36.8%, respectively, P = .074) compared with 400 normal control Caucasian children. In early functional validation, rejectors demonstrated significant repression of the first HLA-DOA exon closest to rs9296068. Also, intragraft B lymphocytes, whose antigen-presenting function is selectively inhibited by HLA-DOA were 3-fold more numerous during rejection among rejectors with the risk allele, than those without.

CONCLUSIONS

The minor allele of the SNP rs9296068 is significantly associated with liver transplantation rejection and with enhanced B-lymphocyte participation in rejection, likely because of a dysfunctional HLA-DOA gene product.