Cardiac allograft vasculopathy: The achilles’ heel of long-term survival after cardiac transplantation

Platelet-to-Albumin Ratio: The Prognostic Utility in the Prediction of 2-Month Postoperative Heart Transplant Complications

BACKGROUND

The platelet-to-albumin ratio (PAR), leucocyte-to-albumin ratio (LAR), neutrophil percentage-to-albumin ratio (NPAR), and monocyte-to-albumin ratio (MAR) represent easily reproducible markers, which may predict the outcomes in various diseases. Early postoperative complications might appear after heart transplantation, such as infections, diabetes mellitus type 2 (DM2), acute graft rejection, and atrial fibrillation (AFib).

OBJECTIVE

The aim of our study was to investigate the PAR, LAR, NPAR, and MAR values before and after heart transplantation, and the associations of the preoperative levels of these markers with the presence of postoperative complications in first two months after surgery.

METHODS

Our retrospective research was directed from May 2014 to January 2021, with a total number of 38 patients being included. We used cut-off values for the ratios from previously published studies, as well as our own determination of these levels by using a receiver operating characteristic (ROC) curve.

RESULTS

By ROC analysis, the optimal preoperative PAR cut-off value was 38.84 (AUC: 0.771, p = 0.0039), with 83.3% sensitivity, and 75.0% specificity. Applying a Chi square (χ²) test, PAR > 38.84 represented an independent risk factor for complications, regardless of cause, and postoperative infections.

CONCLUSIONS

Preoperative PAR > 38.84 was a risk factor of developing complications of any cause, and postoperative infections in the first two months after heart transplantation.

Interleukin-5 (IL-5) Therapy Prevents Allograft Rejection by Promoting CD4+CD25+ Ts2 Regulatory Cells That Are Antigen-Specific and Express IL-5 Receptor

CD4⁺CD25⁺Foxp3⁺T cell population is heterogenous and contains three major sub-groups. First, thymus derived T regulatory cells (tTreg) that are naïve/resting. Second, activated/memory Treg that are produced by activation of tTreg by antigen and cytokines. Third, effector lineage CD4⁺CD25⁺T cells generated from CD4⁺CD25^- T cells' activation by antigen to transiently express CD25 and Foxp3. We have shown that freshly isolated CD4⁺CD25⁺T cells are activated by specific alloantigen and IL-4, not IL-2, to Ts2 cells that express the IL-5 receptor alpha. Ts2 cells are more potent than naïve/resting tTreg in suppressing specific alloimmunity. Here, we showed rIL-5 promoted further activation of Ts2 cells to Th2-like Treg, that expressed foxp3, irf4, gata3 and il5. In vivo, we studied the effects of rIL-5 treatment on Lewis heart allograft survival in F344 rats. Host CD4⁺CD25⁺T cells were assessed by FACS, in mixed lymphocyte culture and by RT-PCR to examine mRNA of Ts2 or Th2-like Treg markers. rIL-5 treatment given 7 days after transplantation reduced the severity of rejection and all grafts survived ≥60d whereas sham treated rats fully rejected by day 31 (p<0.01). Treatment with anti-CD25 or anti-IL-4 monoclonal antibody abolished the benefits of treatment with rIL-5 and accelerated rejection. After 10d treatment with rIL-5, hosts' CD4⁺CD25⁺ cells expressed more Il5ra and responded to specific donor Lewis but not self. Enriched CD4⁺CD25⁺ cells from rIL-5 treated rats with allografts surviving >60 days proliferated to specific donor only when rIL-5 was present and did not proliferate to self or third party. These cells had more mRNA for molecules expressed by Th2-like Treg including Irf4, gata3 and Il5. These findings were consistent with IL-5 treatment preventing rejection by activation of Ts2 cells and Th2-like Treg.

Biomarker and surrogate development in vascularised composite allograft transplantation: Current progress and future challenges

Vascularised composite allograft (VCA) transplantation is now a feasible reconstructive option for patients who have suffered significant soft tissue injuries. However, despite numerous technical advances in the field over two decades, a number of challenges remain, not least the management of transplant rejection. Part of the difficulty faced by clinicians is the early recognition and prevention of acute rejection episodes. Whilst this is potentially easier in VCAs than solid organ transplants, due to their visible skin component, at present the only validated method for the diagnosis of acute rejection is histological examination of a tissue biopsy. The aim of this review article is to provide an evidence-based overview of progress in the field of VCA biomarker discovery, including immune cell subsets, immune cell effector pathways, and circulating markers of allograft damage, and to discuss future challenges in the field.

Prolonged Cold Ischemia Time Results in Local and Remote Organ Dysfunction in a Murine Model of Vascularized Composite Transplantation

Vascularized composite allotransplantation (VCA) is a viable reconstructive option for complex tissue defects. Although grafts with a large muscular component may be uniquely susceptible to ischemia-reperfusion (I/R) syndrome, the safe cold ischemia time in VCA has not been established. We investigated the effects of cold ischemia on innate immune response and recipient survival in a murine orthotopic hindlimb transplantation model. Surprisingly, mice receiving grafts exposed to 6 h or longer of cold storage demonstrated reduced survival and massive elevations in serum creatinine, blood urea nitrogen, and creatine kinase, compared with 1 h of cold storage recipients. This was accompanied by progressive increase in macrophage and neutrophil cell infiltration in muscle biopsy specimens, altered platelet endothelial cell adhesion molecule-1 expression, and ultimate renal injury. Multiplex immunoassay analysis identified 21 cytokines in serum and 18 cytokines in muscle biopsy specimens that are likely essential in the complex response to I/R-triggered injury in VCA. In conclusion, this study, in a mouse model of orthotopic hindlimb transplantation, is the first to document that prolonged cold ischemia triggers progressive I/R injury with vascular endothelial damage and may lead to irrecoverable local and remote organ damage. These experimental findings are important in guiding future therapies for human VCA recipients.

Could Sentinel Skin Transplants Have Some Utility in Solid Organ Transplantation?

Accurate diagnosis of allograft rejection can be hazardous and challenging. A strategy that has emerged from experience with vascularized composite allografts (VCAs) is the use of sentinel skin transplants (SSTs)-portions of donor skin transplanted synchronously to an allograft. Work in nonhuman animal models and experience with VCAs suggest concordance between rejection occurring in the primary allograft and the SST, and that appearance of rejection in the SST may precede rejection in the primary allograft, permitting early therapeutic intervention that may improve outcomes with lower rates of chronic rejection. The encouraging findings reported in VCA transplantation raise the possibility that SST may also be useful in solid organ transplantation. Some evidence is provided by experience with abdominal wall transplantation in some intestinal and multivisceral transplant recipients. Results from those reports raise the possibility that rejection may manifest in the skin component before emergence in the intestinal allograft, providing a "lead time" during which treatment of rejection of the abdominal wall could prevent the emergence of intestinal rejection. It is plausible that these findings may be extrapolated to other solid organ allografts, especially those for which obtaining an accurate diagnosis of acute rejection can be hazardous and challenging, such as the lung or pancreas. However, more data are required to support widespread adoption of this technique.

A20 Haploinsufficiency Aggravates Transplant Arteriosclerosis in Mouse Vascular Allografts: Implications for Clinical Transplantation

BACKGROUND

Inflammation is central to the pathogenesis of transplant arteriosclerosis (TA). We questioned whether physiologic levels of anti-inflammatory A20 influence TA severity.

METHODS

We performed major histocompatibility complex mismatched aorta to carotid artery interposition grafts, using wild type (WT) or A20 heterozygote (HET) C57BL/6 (H-2) donors and BALB/c (H-2) recipients, and conversely BALB/c donors and WT/HET recipients. We analyzed aortic allografts by histology, immunohistochemistry, immunofluorescence, and gene profiling (quantitative real-time reverse-transcriptase polymerase chain reaction). We validated select in vivo A20 targets in human and mouse smooth muscle cell (SMC) cultures.

RESULTS

We noted significantly greater intimal hyperplasia in HET versus WT allografts, indicating aggravated TA. Inadequate upregulation of A20 in HET allografts after transplantation was associated with excessive NF-кB activation, gauged by higher levels of IkBα, p65, VCAM-1, ICAM-1, CXCL10, CCL2, TNF, and IL-6 (mostly localized to SMC). Correspondingly, cytokine-induced upregulation of TNF and IL-6 in human and mouse SMC cultures inversely correlated with A20 expression. Aggravated TA in HET versus WT allografts correlated with increased intimal SMC proliferation, and a higher number of infiltrating IFNγ and Granzyme B CD4 T cells and natural killer cells, and lower number of FoxP3 regulatory T cells. A20 haploinsufficiency in allograft recipients did not influence TA.

CONCLUSIONS

A20 haploinsufficiency in vascular allografts aggravates lesions of TA by exacerbating inflammation, SMC proliferation, and infiltration of pathogenic T cells. A20 single nucleotide polymorphisms associating with lower A20 expression or function in donors of vascularized allografts may inform risk and severity of TA, highlighting the clinical implications of our findings.

Early inflammatory markers are independent predictors of cardiac allograft vasculopathy in heart-transplant recipients

BACKGROUND

Identification of risk is essential to prevent cardiac allograft vasculopathy (CAV) and graft failure due to CAV (GFDCAV) in heart transplant patients, which account for 30% of all deaths. Early CAV detection involves invasive, risky, and expensive monitoring approaches. We determined whether prediction of CAV and GFDCAV improves by adding inflammatory markers to a previously validated atherothrombotic (AT) model.

METHODS AND FINDINGS

AT and inflammatory markers interleukin-6 (IL-6) and C-reactive protein (CRP) were measured in heart biopsies and sera of 172 patients followed prospectively for 8.9±5.0 years. Models were estimated for 5- and 10-year risk using (1) the first post-transplant biopsy only, or (2) all biopsies obtained within 3 months. Multivariate models were adjusted for other covariates and cross-validated by bootstrapping. After adding IL-6 and CRP to the AT models, we evaluated the significance of odds ratios (ORs) associated with the additional inflammatory variables and the degree of improvement in the area under the receiver operating characteristic curve (AUROC). When inflammatory markers were tested alone in prediction models, CRP (not IL-6) was a significant predictor of CAV and GFDCAV at 5 (CAV: p<0.0001; GFDCAV: p = 0.005) and 10 years (CAV: p<0.0001; GFDCAV: p = 0.003). Adding CRP (not IL-6) to the best AT models improved discriminatory power to identify patients destined to develop CAV (using 1st biopsy: p<0.001 and p = 0.001; using all 3-month biopsies: p<0.04 and p = 0.008 at 5- and 10-years, respectively) and GFDCAV (using 1st biopsy: 0.92 vs. 0.95 and 0.86 vs. 0.89; using all 3-month biopsies: 0.94 vs. 0.96 and 0.88 vs. 0.89 at 5- and 10-years, respectively), as indicated by an increase in AUROC.

CONCLUSIONS

Early inflammatory status, measured by a patient's CRP level (a non-invasive, safe and inexpensive test), independently predicts CAV and GFDCAV. Adding CRP to a previously established AT model improves its predictive power.

Impaired selectin-dependent leukocyte recruitment induces T-cell exhaustion and prevents chronic allograft vasculopathy and rejection

Selectin-selectin ligand interactions mediate the initial steps in leukocyte migration, an integral part of immune responses. Fucosyltransferase-VII (FucT-VII), encoded by Fut7, is essential for biosynthesis of selectin ligands. In an established model of cardiac allograft vasculopathy and chronic rejection, Fut7(-/-) recipients exhibited long-term graft survival with minimal vasculopathy compared with WT controls. Graft survival was associated with CD4 T-cell exhaustion in the periphery, characterized by impaired effector cytokine production, defective proliferation, increased expression of inhibitory receptors programmed death-1 (PD-1) and T cell Ig- and mucin-domain-containing molecule-3 (Tim-3), low levels of IL-7Rα on CD4 T cells, and reduced migration of polyfunctional CD4 memory T cells to the allograft. Blocking PD-1 triggered rejection only in Fut7(-/-) recipients, whereas depleting regulatory T cells had no effect in either Fut7(-/-) or WT recipients. Adoptive transfer experiments confirmed that this CD4 T cell-exhausted phenotype is seen primarily in Fut7(-/-) CD4 T cells. These data suggest that impaired leukocyte recruitment is a novel mechanism leading to CD4 T-cell exhaustion. Our experimental system serves as an excellent model to study CD4 T-cell exhaustion as a dominant mechanism of transplant tolerance. Further, targeting FucT-VII may serve as a promising strategy to prevent chronic allograft rejection and promote tolerance.

Efficacy and Safety of Low-Dose Cyclosporine with Everolimus and Steroids in de novo Heart Transplant Patients: A Multicentre, Randomized Trial

A six-month, multicenter, randomized, open-label study was undertaken to determine whether renal function is improved using reduced-exposure cyclosporine (CsA) versus standard-exposure CsA in 199 de novo heart transplant patients receiving everolimus and steroids ± induction therapy. Mean C(2) levels were at the low end of the target range in standard-exposure patients (n = 100) and exceeded target range in reduced-exposure patients (n = 99) throughout the study. Mean serum creatinine at Month 6 (the primary endpoint) was 141.0 ± 53.1 μmol/L in standard-exposure patients versus 130.1 ± 53.7 μmol/L in reduced-exposure patients (P = 0.093). The incidence of biopsy-proven acute rejection ≥3A at Month 6 was 21.0% (21/100) in the standard-exposure group and 16.2% (16/99) in the reduced-exposure group (n.s.). Adverse events and infections were similar between treatment groups. Thus, everolimus with reduced-exposure CsA resulted in comparable efficacy compared to standard-exposure CsA. No renal function benefits were demonstrated; that is possibly related to poor adherence to reduced CsA exposure.

Donor-specific antibodies to human leukocyte antigens are associated with and precede antibodies to major histocompatibility complex class I-related chain A in antibody-mediated rejection and cardiac allograft vasculopathy after human cardiac transplantation

Humoral immune responses to mismatched donor human leukocyte antigen (HLA) and major histocompatibility complex (MHC) class I-related chain A (MICA) have been reported to contribute to immunopathogenesis of antibody-mediated rejection (AMR) in the early period and cardiac allograft vasculopathy (CAV) in the late period after cardiac transplantation (HTx). The goal of this study is to define the roles of donor-specific antibodies (DSA) and anti-MICA in AMR and CAV. A total of 95 post-HTx recipients were enrolled; 43 patients in the early period (≤ 12 months post-HTx) and 52 patients in the late period (>12 months post-HTx). Development of DSA and anti-MICA were serially monitored using Luminex. Development of DSA (AMR+: n = 6/8.75%, AMR-: n = 4/35.11%, p = 0.009) and anti-MICA (AMR+: n = 5/8.63%, AMR-: n = 4/35.11%, p = 0.002) was significantly associated with AMR. AMR+DSA+ patients demonstrated increased anti-MICA levels compared with AMR+DSA- patients (p=0.01). Serial monitoring revealed DSA (2.7 ± 1.4 months) preceded development of anti-MICA (6.5 ± 2.1 months) in recipients diagnosed with AMR at 8.3 ± 2.5 months post-HTx. Development of DSA (CAV+: n = 8/12.67%, CAV-: n = 5/40.13%, p = 0.004) and anti-MICA (CAV+: n = 9/12.75%, CAV-: n = 5/40.13%, p = 0.001) was significantly associated with CAV. CAV+DSA+ patients demonstrated increased anti-MICA levels compared with CAV+DSA- patients (p = 0.01). Antibodies to HLA are associated with and precede development of anti-MICA in AMR and CAV. Therefore, DSA and anti-MICA can be used as noninvasive markers for monitoring AMR and CAV.

Characterization of immune responses to cardiac self-antigens myosin and vimentin in human cardiac allograft recipients with antibody-mediated rejection and cardiac allograft vasculopathy

BACKGROUND

Herein we study the role of donor-specific antibodies (DSA) to mismatched human leukocyte antigen (HLA) and antibodies (Abs) to the cardiac self-antigens myosin (MYO) and vimentin (VIM) in the pathogenesis of acute antibody-mediated rejection (AMR) in the early post-transplant period (EP, <12 months) and cardiac allograft vasculopathy (CAV) in the late post-transplant period (LP, >12 months) after heart transplantation (HTx).

METHODS

One hundred forty-eight HTx recipients (65 in EP, 83 in LP) were enrolled in the study. Development of DSA was determined by Luminex. Circulating Abs against MYO and VIM in sera were measured using enzyme-linked immunoassay (ELISA). Frequency of CD4+ T-helper cells (CD4+ Th) secreting interferon (IFN)-γ, interleukin (IL)-17, IL-10 or IL-5 specific to either MYO or VIM were analyzed in vitro using ELISpot assays.

RESULTS

AMR patients were more likely DSA positive (AMR-: 15%; AMR+: 70%; p = 0.03) and demonstrated increased Abs to MYO (AMR-: 144 ± 115 μg/ml; AMR+: 285 ± 70 μg/ml; p = 0.033) and VIM (AMR-: 37 ± 19 μg/ml; AMR+: 103 ± 43 μg/ml; p = 0.014). AMR patients demonstrated increased IL-5 CD4+ Th cells specific to MYO (5.2 ± 0.9 fold, p = 0.003) and VIM (7.3 ± 2.9-fold, p = 0.004) and decreased IL-10 CD4+ Th cells specific to MYO (2.2 ± 0.4-fold, p = 0.009) and VIM (1.7 ± 0.2-fold, p = 0.03). CAV patients were more likely DSA positive (CAV-): 25%; CAV+: 79%; p = 0.03) and demonstrated increased Abs to MYO (CAV-: 191 ± 120 μg/ml; CAV+: 550 ± 98 μg/ml; p = 0.025) and VIM (CAV-: 55 ± 25 μg/ml; CAV+: 255 ± 49 μg/ml; p = 0.001). CAV patients demonstrated increased IL-17 CD4+ Th cells specific to MYO (10.5 ± 7.3-fold, p = 0.002) and VIM (7.0 ± 3.9-fold, p = 0.003).

CONCLUSIONS

The presence of DSA in AMR and CAV is significantly associated with development of Abs to MYO and VIM in post-HTx patients. Induction of high CD4+ Th cells specific to cardiac self-antigens that secrete predominantly IL-5 and IL-17 plays a significant role in the development of Abs to self-antigens leading to AMR and CAV, respectively.

Therapeutic applications of bilirubin and biliverdin in transplantation

Bilirubin is the end product of heme catabolism by heme oxygenases. The inducible form of these enzymes is heme oxygenase-1 (HO-1), which is the rate-limiting enzyme that can degrade heme into equimolar quantities of carbon monoxide (CO), biliverdin, and free iron. Biliverdin is very rapidly converted to bilirubin by the enzyme biliverdin reductase, and free iron upregulates the expression of ferritin. HO-1 is a ubiquitous stress protein and is induced in many cell types by various stimuli. Induced HO-1 exerts antiinflammatory effects and modulates apoptosis. Expression of HO-1 in vivo suppresses the inflammatory responses in endotoxic shock, hyperoxia, acute pleurisy, and organ transplantation, as well as ischemia-reperfusion injury, and thereby provides salutary effects in these conditions. Accumulating evidence indicates that biliverdin/bilirubin can mediate the protective effects of HO-1 in many disease models, such as IRI and organ transplantation, via its antiinflammatory, antiapoptotic, antiproliferative, and antioxidant properties, as well as its effects on the immune response. This review attempts to summarize these protective roles as well as the molecular mechanisms by which biliverdin/bilirubin benefit IRI and solid-organ transplantation, including chronic rejection, and islet transplantation.