Association of Cold Ischemia Time With Acute Renal Transplant Rejection

Guidelines From the French-Speaking Society of Histocompatibility and Immunogenetics for Virtual Crossmatching for Deceased Donor Kidney Transplantation and the Use of Wet Crossmatch in the Decision-Making Process

The systematic use of Single Antigen Flow Beads assays and the implementation of high-resolution HLA typing for donors and kidney transplant recipients allow a precise identification of anti-HLA donor-specific antibodies. In France, the availability of detailed molecular biology HLA typing for deceased donors in the national organ allocation software enables anticipation of wet crossmatch results and estimation of the immunological risk for a recipient/donor pair. This key process, named virtual crossmatching, involves a thorough analysis of the recipient's anti-HLA sensitisation records. Its main goal is to reduce cold ischaemia time in order to extend graft survival. In this article, we present the guidelines for virtual crossmatching developed by a working group from the French-speaking Society of Histocompatibility and Immunogenetics. The guidelines address several considerations regarding HLA typing, anti-HLA antibody testing, and sensitisation event history, which are required to perform virtual crossmatching. We also propose a decision-making process, which situates prospective or retrospective wet crossmatch depending on virtual crossmatch results. The guidelines specifically emphasise the need for a strong clinical-biological agreement to standardise practices and provide a framework for omission of wet crossmatch for both non-sensitised and sensitised recipients.

Effects of perioperative dexmedetomidine on delayed graft function following renal transplant: a systematic review and meta-analysis

BACKGROUND

Dexmedetomidine, a highly selective alpha-2 adrenoceptor agonist with sedative and analgesic effects, has been suggested in recent studies to possess renoprotective properties. Dexmedetomidine may reduce the incidence of delayed graft function and contribute to effective pain control post-renal transplantation. The primary objective of this systematic review was to assess whether dexmedetomidine decreases the occurrence of delayed graft function in renal transplant patients.

METHODS

Databases including MEDLINE, EMBASE, and CENTRAL were comprehensively searched from their inception until March 2023. The inclusion criteria covered all Randomized Clinical Trials (RCTs) and observational studies comparing dexmedetomidine to control in adult patients undergoing renal transplant surgery. Exclusions comprised case series and case reports.

RESULTS

Ten RCTs involving a total of 1358 patients met the eligibility criteria for data synthesis. Compared to the control group, the dexmedetomidine group demonstrated a significantly lower incidence of delayed graft function (OR = 0.71, 95% CI 0.52-0.97, p = 0.03, GRADE: Very low, I2 = 0%). Dexmedetomidine also significantly prolonged time to initiation of rescue analgesia (MD = 6.73, 95% CI 2.32-11.14, p = 0.003, GRADE: Very low, I2 = 93%) and reduced overall morphine consumption after renal transplant (MD = -5.43, 95% CI -7.95 to -2.91, p < 0.0001, GRADE: Very low, I2 = 0%). The dexmedetomidine group exhibited a significant decrease in heart rate (MD = -8.15, 95% CI -11.45 to -4.86, p < 0.00001, GRADE: Very low, I2 = 84%) and mean arterial pressure compared to the control group (MD = -6.66, 95% CI -11.27 to -2.04, p = 0.005, GRADE: Very low, I2 = 87%).

CONCLUSIONS

This meta-analysis suggests that dexmedetomidine may potentially reduce the incidence of delayed graft function and offers a superior analgesia profile as compared to control in adults undergoing renal transplants. However, the high degree of heterogeneity and inadequate sample size underscore the need for future adequately powered trials to confirm these findings.

Basiliximab induction alone vs a dual ATG-basiliximab approach in first live-donor non-sensitized kidney transplant recipients with low HLA matching

Background

Individualizing induction therapy based on immunological risk is crucial for optimizing outcomes in kidney transplantation.

Methods

A retrospective analysis included 157 first live-donor non-sensitized kidney transplant recipients (KTRs). Within this cohort, 96 individuals exhibited low human leukocyte antigen (HLA) matching (5-6 HLA mismatches). The low HLA match subgroup was categorized into 52 KTRs receiving basiliximab alone and 44 recipients treated with a combined single ATG dose of 1.5 mg/kg and basiliximab. The primary endpoint was early acute cellular rejection (ACR) within 6 months post-transplant while secondary outcomes encompassed infection rates, renal allograft function, length of stay (LOS) and readmissions post-transplant.

Results

The incidence of early ACR was decreased for low HLA match KTRs, who received ATG-basiliximab, when compared with low HLA-matched KTRs who received basiliximab alone (9.1% vs 23.9%, P = .067). Age was a predictor for rejection, and subgroup analysis showed consistent rejection reduction across age groups. No significant differences were observed in admission for transplant LOS or in peri-operative complications, nor in infections rate including BK and cytomegalovirus viremia, allograft function and number of readmissions post-transplant up to 6 months post-transplant.

Conclusion

In non-sensitized first live-donor KTRs with low HLA matching, a dual ATG-basiliximab induction approach significantly reduced early ACR without compromising safety.

Nanotechnology-based Strategies for Molecular Imaging, Diagnosis, and Therapy of Organ Transplantation

Organ transplantation is the preferred paradigm for patients with end-stage organ failures. Despite unprecedented successes, complications such as immune rejection, ischemia-reperfusion injury, and graft dysfunction remain significant barriers to long-term recipient survival after transplantation. Conventional immunosuppressive drugs have limited efficacy because of significant drug toxicities, high systemic immune burden, and emergence of transplant infectious disease, leading to poor quality of life for patients. Nanoparticle-based drug delivery has emerged as a promising medical technology and offers several advantages by enhancing the delivery of drug payloads to their target sites, reducing systemic toxicity, and facilitating patient compliance over free drug administration. In addition, nanotechnology-based imaging approaches provide exciting diagnostic methods for monitoring molecular and cellular changes in transplanted organs, visualizing immune responses, and assessing the severity of rejection. These noninvasive technologies are expected to help enhance the posttransplantation patient survival through real time and early diagnosis of disease progression. Here, we present a comprehensive review of nanotechnology-assisted strategies in various aspects of organ transplantation, including organ protection before transplantation, mitigation of ischemia-reperfusion injury, counteraction of immune rejection, early detection of organ dysfunction posttransplantation, and molecular imaging and diagnosis of immune rejection.

Rescue Allocation Modes in Eurotransplant Kidney Transplantation: Recipient Oriented Extended Allocation Versus Competitive Rescue Allocation-A Retrospective Multicenter Outcome Analysis

BACKGROUND

Whenever the kidney standard allocation (SA) algorithms according to the Eurotransplant (ET) Kidney Allocation System or the Eurotransplant Senior Program fail, rescue allocation (RA) is initiated. There are 2 procedurally different modes of RA: recipient oriented extended allocation (REAL) and competitive rescue allocation (CRA). The objective of this study was to evaluate the association of patient survival and graft failure with RA mode and whether or not it varied across the different ET countries.

METHODS

The ET database was retrospectively analyzed for donor and recipient clinical and demographic characteristics in association with graft outcomes of deceased donor renal transplantation (DDRT) across all ET countries and centers from 2014 to 2021 using Cox proportional hazards methods.

RESULTS

Seventeen thousand six hundred seventy-nine renal transplantations were included (SA 15 658 [89%], REAL 860 [4.9%], and CRA 1161 [6.6%]). In CRA, donors were older, cold ischemia times were longer, and HLA matches were worse in comparison with REAL and especially SA. Multivariable analyses showed comparable graft and recipient survival between SA and REAL; however, CRA was associated with shorter graft survival. Germany performed 76% of all DDRTs after REAL and CRA and the latter mode reduced waiting times by up to 2.9 y.

CONCLUSIONS

REAL and CRA are used differently in the ET countries according to national donor rates. Both RA schemes optimize graft utilization, lead to acceptable outcomes, and help to stabilize national DDRT programs, especially in Germany.

Preventing Rejection of the Kidney Transplant

With increasing knowledge of immunologic factors and with the advent of potent immunosuppressive agents, the last several decades have seen significantly improved kidney allograft survival. However, despite overall improved short to medium-term allograft survival, long-term allograft outcomes remain unsatisfactory. A large body of literature implicates acute and chronic rejection as independent risk factors for graft loss. In this article, we review measures taken at various stages in the kidney transplant process to minimize the risk of rejection. In the pre-transplant phase, it is imperative to minimize the risk of sensitization, aim for better HLA matching including eplet matching and use desensitization in carefully selected high-risk patients. The peri-transplant phase involves strategies to minimize cold ischemia times, individualize induction immunosuppression and make all efforts for better HLA matching. In the post-transplant phase, the focus should move towards individualizing maintenance immunosuppression and using innovative strategies to increase compliance. Acute rejection episodes are risk factors for significant graft injury and development of chronic rejection thus one should strive for early detection and aggressive treatment. Monitoring for DSA development, especially in high-risk populations, should be made part of transplant follow-up protocols. A host of new biomarkers are now commercially available, and these should be used for early detection of rejection, immunosuppression modulation, prevention of unnecessary biopsies and monitoring response to rejection treatment. There is a strong push needed for the development of new drugs, especially for the management of chronic or resistant rejections, to prolong graft survival. Prevention of rejection is key for the longevity of kidney allografts. This requires a multipronged approach and significant effort on the part of the recipients and transplant centers.

Clinical Impact of Ischemic Time of the Pancreas or Kidney Graft on Simultaneous Pancreas-Kidney Transplantation: A Single-Institution Study in Japan

BACKGROUND

Total ischemic time (TIT) potentially affects graft survival in organ transplantation. However, in simultaneous pancreas-kidney (SPK) transplantation, the impact of TIT of the pancreas (P-TIT) and kidney graft (K-TIT) on posttransplant outcomes remains unclear. This study investigated the impact of P-TIT and K-TIT on postoperative outcomes in patients after SPK at our institution in Japan.

PATIENTS AND METHODS

This study included 52 patients who underwent SPK at our hospital from April 2000 to March 2022. Of this patient group, the 52 patients were divided into a short P-TIT group (n = 25), long P-TIT group (n = 27), short K-TIT group (n = 42), and long K-TIT group (n = 10). Short- and long-term postoperative outcomes were compared between the groups.

RESULTS

The long K-TIT group had a significantly higher rate of patients who did not urinate intraoperatively (50% vs 7%; P = .0007) and those requiring postoperative hemodialysis (80% vs 38%; P = .0169), as well as a significant longer duration of postoperative hemodialysis (97 ± 147 days vs 6 ± 9 days; P = .0016). These were not significantly different between the short and long P-TIT groups. Kidney or pancreas graft survival was not significantly different between the short and long P-TIT or K-TIT groups.

CONCLUSIONS

Patients with prolonged K-TIT during SPK exhibited poor short-term outcomes, but no significant influence of K-TIT was identified on long-term outcomes. The P-TIT did not affect any significant outcomes. These results indicate that shortening K-TIT may improve short-term outcomes after SPK.

Sterile Pancreas Inflammation during Preservation and after Transplantation

The pancreas is very susceptible to ischemia-reperfusion injury. Early graft losses due to pancreatitis and thrombosis represent a major issue after pancreas transplantation. Sterile inflammation during organ procurement (during brain death and ischemia-reperfusion) and after transplantation affects organ outcomes. Sterile inflammation of the pancreas linked to ischemia-reperfusion injury involves the activation of innate immune cell subsets such as macrophages and neutrophils, following tissue damage and release of damage-associated molecular patterns and pro-inflammatory cytokines. Macrophages and neutrophils favor tissue invasion by other immune cells, have deleterious effects or functions, and promote tissue fibrosis. However, some innate cell subsets may promote tissue repair. This outburst of sterile inflammation promotes adaptive immunity activation via antigen exposure and activation of antigen-presenting cells. Better controlling sterile inflammation during pancreas preservation and after transplantation is of utmost interest in order to decrease early allograft loss (in particular thrombosis) and increase long-term allograft survival. In this regard, perfusion techniques that are currently being implemented represent a promising tool to decrease global inflammation and modulate the immune response.

Delayed Graft Function in Kidney Transplant: Risk Factors, Consequences and Prevention Strategies

Background. Delayed graft function is a frequent complication of kidney transplantation that requires dialysis in the first week posttransplant. Materials and Methods. We searched for the most relevant articles in the National Institutes of Health library of medicine, as well as in transplantation, pharmacologic, and nephrological journals. Results. The main factors that may influence the development of delayed graft function (DGF) are ischemia–reperfusion injury, the source and the quality of the donated kidney, and the clinical management of the recipient. The pathophysiology of ischemia–reperfusion injury is complex and involves kidney hypoxia related to the duration of warm and cold ischemia, as well as the harmful effects of blood reperfusion on tubular epithelial cells and endothelial cells. Ischemia–reperfusion injury is more frequent and severe in kidneys from deceased donors than in those from living donors. Of great importance is the quality and function of the donated kidney. Kidneys from living donors and those with normal function can provide better results. In the peri-operative management of the recipient, great attention should be paid to hemodynamic stability and blood pressure; nephrotoxic medicaments should be avoided. Over time, patients with DGF may present lower graft function and survival compared to transplant recipients without DGF. Maladaptation repair, mitochondrial dysfunction, and acute rejection may explain the worse long-term outcome in patients with DGF. Many different strategies meant to prevent DGF have been evaluated, but only prolonged perfusion of dopamine and hypothermic machine perfusion have proven to be of some benefit. Whenever possible, a preemptive transplant from living donor should be preferred.

Abdominal Wall Vascularized Composite Allotransplantation: A Scoping Review

BACKGROUND

 Abdominal wall vascularized composite allotransplantation (AW-VCA) is a novel reconstructive technique used for large abdominal wall defects in combination with intestinal transplantation (ITx) or multivisceral abdominal transplantation (MVTx). Since the introduction of this procedure, several studies have been published reporting their experience. This study aims to present a scoping review looking at all available evidence-based medicine information to understand the most current surgical techniques and clinical outcomes.

METHODS

 This scoping review followed the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) extension for scoping reviews checklist. A comprehensive research strategy of several databases was conducted.

RESULTS

 A total of 31 studies were included in this review, which comprised animal, cadaveric, and human studies. In human studies, four surgical techniques with high flap survival rates and low complication rates were found. In cadaveric studies, it was shown that the use of iliofemoral cuff-based flaps provided adequate tissue perfusion to the abdominal wall graft. Also, the use of thoracolumbar nerves have been described to provide functionality to the AW-VCA and prevent long-term muscle atrophy.

CONCLUSION

 AW-VCA is a safe and efficient alternative for patients with large and complex abdominal wall defects. The future holds a promising evolution of a functional AW-VCA, though surgeons must face and overcome the challenge of distorted anatomy frequently present in this population. Forthcoming studies with a better level of evidence are required to evaluate functionality and differences between surgical techniques.

Kidney Transplantation After Rescue Allocation-the Eurotransplant Experience: A Retrospective Multicenter Outcome Analysis

BACKGROUND

At Eurotransplant (ET), kidneys are transferred to "rescue allocation" (RA), whenever the standard allocation (SA) algorithms Eurotransplant Kidney Allocation System (ETKAS) and Eurotransplant Senior Program (ESP) fail. We analyzed the outcome of RA.

METHODS

Retrospective patient clinical and demographic characteristics association analyses were performed with graft outcomes for 2422 recipients of a deceased donor renal transplantation (DDRT) after RA versus 25 481 after SA from 71 centers across all ET countries from 2006 to 2018.

RESULTS

Numbers of DDRTs after RA increased over the time, especially in Germany. RA played a minor role in ESP versus ETKAS (2.7% versus 10.4%). RA recipients and donors were older compared with SA recipients and donors, cold ischemia times were longer, waiting times were shorter, and the incidence of primary nonfunction was comparable. Among ETKAS recipients, HLA matching was more favorable in SA (mean 3.7 versus 2.5). In multivariate modeling, the incidence of graft loss in ETKAS recipients was reduced in RA compared with SA (subdistribution hazard ratio, 0.80; 95% confidence interval [0.70-0.91], P < 0.001), whereas other outcomes (mortality, death with functioning graft (DwFG)) were not significantly different. None of the 3 outcomes were significantly different when comparing RA with SA within the ESP program.

CONCLUSIONS

Facing increased waiting times and mortality on dialysis due to donor shortage, this study reveals encouragingly positive DDRT outcomes following RA. This supports the extension of RA to more patients and as an alternative tool to enable transplantation in patients in countries with prohibitively long waiting times or at risk of deterioration.

The role of bypass filters in deceased donor kidney allocation in the United States

Kidney transplant centers set organ offer filters enabling all candidates at their center to be bypassed during allocation of deceased donor kidneys from the UNOS Organ Center. These filters aim to increase allocation efficiency by preemptively screening out offers unlikely to be accepted. National data were used to compare filter settings of 175 centers in 2007 and in 2019. We examined characteristics of centers whose settings became increasingly restrictive over time, and associations between filter settings and organ offer acceptance. Overall, centers became more open to receiving offers over time, from a median 62% of filters open to receiving national offers in 2007 to 73% in 2019. Intravenous drug use filter settings changed most, from 63 to 153 willing centers. Centers with more open filter settings had higher transplant volume and offer acceptance ratios across all risk categories despite preemptively screening out fewer offers compared to centers with less open settings, but similar transplant rates. There was significant geographic heterogeneity in the distribution of centers with more open filter settings. Current center bypass filters may impact patients' access to transplantation without achieving their full potential for improving allocation efficiency.

Deceased donor kidneys allocated out of sequence by organ procurement organizations

Deceased donor kidney allocation follows a ranked match-run of potential recipients. Organ procurement organizations (OPOs) are permitted to deviate from the mandated match-run in exceptional circumstances. Using match-run data for all deceased donor kidney transplants (Ktx) in the US between 2015 and 2019, we identified 1544 kidneys transplanted from 933 donors with an OPO-initiated allocation exception. Most OPOs (55/58) used this process at least once, but 3 OPOs performed 64% of the exceptions and just 2 transplant centers received 25% of allocation exception Ktx. At 2 of 3 outlier OPOs these transplants increased 136% and 141% between 2015 and 2019 compared to only a 35% increase in all Ktx. Allocation exception donors had less favorable characteristics (median KDPI 70, 41% with history of hypertension), but only 29% had KDPI ≥ 85% and the majority did not meet the traditional threshold for marginal kidneys. Allocation exception kidneys went to larger centers with higher offer acceptance ratios and to recipients with 2 fewer priority points-equivalent to 2 less years of waiting time. OPO-initiated exceptions for kidney allocation are growing increasingly frequent and more concentrated at a few outlier centers. Increasing pressure to improve organ utilization risks increasing out-of-sequence allocations, potentially exacerbating disparities in access to transplantation.

Trends in Survival for Pediatric Transplantation

OBJECTIVES

Progress in pediatric transplantation measured in the context of waitlist and posttransplant survival is well documented but falls short of providing a complete perspective for children and their families. An intent-to-treat analysis, in which we measure survival from listing to death regardless of whether a transplant is received, provides a more comprehensive perspective through which progress can be examined.

METHODS

Univariable and multivariable Cox regression was used to analyze factors impacting intent-to-treat survival in 12 984 children listed for heart transplant, 17 519 children listed for liver transplant, and 16 699 children listed for kidney transplant. The Kaplan-Meier method and log-rank test were used to assess change in waitlist, posttransplant, and intent-to-treat survival. Wait times and transplant rates were compared by using χ2 tests.

RESULTS

Intent-to-treat survival steadily improved from 1987 to 2017 in children listed for heart (hazard ratio [HR] 0.96, 95% confidence interval [CI] 0.96-0.97), liver (HR 0.95, 95% CI 0.94-0.97), and kidney (HR 0.97, 95% CI 0.95-0.99) transplant. Waitlist and posttransplant survival also improved steadily for all 3 organs. For heart transplant, the percentage of patients transplanted within 1 year significantly increased from 1987 to 2017 (60.8% vs 68.7%); however, no significant increase was observed in liver (68.9% vs 72.5%) or kidney (59.2% vs 62.7%) transplant.

CONCLUSIONS

Intent-to-treat survival, which is more representative of the patient perspective than individual metrics alone, steadily improved for heart, liver, and kidney transplant over the study period. Further efforts to maximize the donor pool, improve posttransplant outcomes, and optimize patient care while on the waitlist may contribute to future progress.

Donor Death Category Is an Effect Modifier Between Cold Ischemia Time and Post-transplant Graft Function in Deceased-Donor Kidney Transplant Recipients

Objectives: We aimed to analyze the effect of cold ischemia time (CIT) on post-transplant graft function through mixed-effect model analysis to reduce the bias caused by paired mate kidneys.

Methods: We reviewed all kidney transplantation records from 2015 to 2019 at our center. After applying the exclusion criteria, 561 cases were included for analysis. All donor characteristics, preservation and matching information, and recipient characteristics were collected. Transplant outcomes included delayed graft function (DGF) and estimated glomerular filtration rate (eGFR). Generalized linear mixed models were applied for analysis. We also explored potential effect modifiers, namely, donor death category, expanded criteria donors, and donor death causes.

Results: Among the 561 cases, 79 DGF recipients developed DGF, and 15 recipients who died after surgery were excluded from the eGFR estimation. The median stable eGFR of the 546 recipients was 60.39 (47.63, 76.97) ml/min/1.73 m². After adjusting for confounding covariates, CIT had a negative impact on DGF incidence [odds ratio = 1.149 (1.006, 1.313), P = 0.041]. In the evaluation of the impact on eGFR, the regression showed that CIT had no significant correlation with eGFR [β = −0.287 (−0.625, 0.051), P = 0.096]. When exploring potential effect modifiers, only the death category showed a significant interaction with CIT in the effect on eGFR (P_interaction = 0.027). In the donation after brain death (DBD) group, CIT had no significant effect on eGFR [β = 0.135 (−0.433, 0.702), P = 0.642]. In the donation after circulatory death/donation after brain death followed by circulatory death (DCD/DBCD) group, CIT had a significantly negative effect on eGFR [β= −0.700 (−1.196, −0.204), P = 0.006]. Compared to a CIT of 0–6 h, a CIT of 6–8 or 8–12 h did not decrease the post-transplant eGFR. CIT over 12 h (12–16 h or over 16 h) significantly decreased eGFR. With the increase in CIT, the regenerated eGFR worsened (P_trend = 0.011).

Conclusion: Considering the effect of paired mate kidneys, the risk of DGF increased with prolonged CIT. The donor death category was an effect modifier between CIT and eGFR. Prolonged CIT did not reduce the eGFR level in recipients from DBDs but significantly decreased the eGFR in recipients from DCDs/DBCDs. This result indicates the potential biological interaction between CIT and donor death category.

Intra-Organ Delivery of Nanotherapeutics for Organ Transplantation

Targeted delivery of therapeutics through the use of nanoparticles (NPs) has emerged as a promising method that increases their efficacy and reduces their side effects. NPs can be tailored to localize to selective tissues through conjugation to ligands that bind cell-specific receptors. Although the vast majority of nanodelivery platforms have focused on cancer therapy, efforts have begun to introduce nanotherapeutics to the fields of immunology as well as transplantation. In this review, we provide an overview from a clinician's perspective of current nanotherapeutic strategies to treat solid organ transplants with NPs during the time interval between organ harvest from the donor and placement into the recipient, an innovative technology that can provide major benefits to transplant patients. The use of ex vivo normothermic machine perfusion (NMP), which is associated with preserving the function of the organ following transplantation, also provides an ideal opportunity for a localized, sustained, and controlled delivery of nanotherapeutics to the organ during this critical time period. Here, we summarize previous endeavors to improve transplantation outcomes by treating the organ with NPs prior to placement in the recipient. Investigations in this burgeoning field of research are promising, but more extensive studies are needed to overcome the physiological challenges to achieving effective nanotherapeutic delivery to transplanted organs discussed in this review.

Effect of Long Cold Ischemia Time of Kidneys from Aged Donors on Prognosis of Kidney Transplantation

With the increasing incidence of end-stage renal disease (ESRD), patients' life span and life quality are significantly reduced. Kidney transplantation has gradually become the ideal method for treating ESRD, and the shortage of organ sources has become the main problem. In recent years, China has successfully realized the transformation of organ sources. Voluntary donation after the death of citizens has increased year by year, and the number of kidney transplantations has increased, which alleviates the organ shortage to a certain extent, but compared with the past, the increasing proportion of aged donors has also become an inevitable global problem. At the same time, due to the sudden and widespread distribution of voluntary donation, most donor kidneys have the problem of longer cold ischemic time (CIT). The probability of adverse events, such as delayed renal function recovery after transplantation, was also significantly increased. At present, there is little research on the effect of donor's aging and long CIT on the prognosis of renal transplantation. This paper reviews the literature in recent years and explore this problem from 2 aspects: the elderly donor and the long CIT.

The causes and frequency of kidney allograft failure in a low-resource setting: observational data from Iraqi Kurdistan

Background

In the developing world, transplantation is the most common long-term treatment for patients with end-stage renal disease, but rates and causes of graft failure are uncertain.

Methods

This was a retrospective outcomes study of renal transplant patients seen in Iraqi Kurdistan nephrology clinics in the year 2019. In 2019, 871 renal transplant patients were registered and outcomes followed through 12/31/2020. Indicated renal biopsies were obtained on 431 patients at 1 day to 18 years post-transplantation. Outcomes were compared with United States Renal Data System (USRDS) living donor reports.

Results

All donors were living. The recipient age was 38.5 ± 13.3 years, 98.2% were < 65 years old, 3.7% had previous transplants, and 2.8% had pretransplant donor-specific antibodies (DSA). Gehan-Breslow estimated failure rates for all-cause, return to HD, and death with functional graft were 6.0, 4.2, and 1.9% at 1 year and 18.1, 13.7, and 5.1% at 5 years post-engraftment (USRDS 2000; 1 year: 7.0, 5.0, 2.6%; 5 year: 22.3, 15.2, 10.6%. USRDS 2010; 1 year: 3.7, 2.4, 1.4%; 5 year: 15.3, 9.6, 7.3%). The median graft survival was 15 years. Acute tubular injury (ATI), infarction, and acute T cell-mediated rejection accounted for 22.2% of graft loss, with > 75% of these failures taking place in the first year. Most graft failures occurred late, at a median post-transplant time of 1125 (interquartile range, 365–2555) days, and consisted of interstitial fibrosis and tubular atrophy (IF/TA) (23.8%), transplant glomerulopathy (13.7%), and acquired active antibody-mediated rejection (12.0%). The significant predictors of graft loss were C4d + biopsies (P < 0.01) and advanced IF/TA (P < 0.001).

Conclusions

Kurdistan transplant patients had graft failure rates similar to living donors reported by the USRDS for the year 2000 but higher than reported for 2010. Compared to USRDS 2010, Kurdistan patients had a moderate excess of HD failures at one and 5 years post-engraftment. Nevertheless, prolonged survival is the norm, with chronic disorders and acquired DSA being the leading causes of graft loss.

Endogenous memory T cells with donor-reactivity: early post-transplant mediators of acute graft injury in unsensitized recipients

The pretransplant presence of endogenous donor-reactive memory T cells is an established risk factor for acute rejection and poorer transplant outcomes. A major source of these memory T cells in unsensitized recipients is heterologously generated memory T cells expressing reactivity to donor allogeneic MHC molecules. Multiple clinical studies have shown that the pretransplant presence of high numbers of circulating endogenous donor-reactive memory T cells correlates with higher incidence of acute rejection and decreased graft function during the first-year post-transplant. These findings have spurred investigation in preclinical models to better understand mechanisms underlying endogenous donor-reactive memory T-cell-mediated allograft injury in unsensitized graft recipients. These studies have led to the identification of unique mechanisms underlying the activation of these memory T cells within allografts at early times after transplant. In particular, optimal activation to mediate acute allograft injury is dependent on the intensity of ischaemia-reperfusion injury. Therapeutic strategies directed at the recruitment and activation of endogenous donor-reactive memory T cells are effective in attenuating acute injury in allografts experiencing increased ischaemia-reperfusion injury in preclinical models and should be translatable to clinical transplantation.

Multiplex gene analysis reveals T-cell and antibody-mediated rejection-specific upregulation of complement in renal transplants

In renal transplantation, complement is involved in ischemia reperfusion injury, graft rejection and dysfunction. However, it is still unclear how induction of complement and its activation are initiated. Using allograft biopsies of a well-characterized cohort of 28 renal transplant patients with no rejection (Ctrl), delayed graft function (DGF), acute T-cell-mediated (TCMR) or antibody-mediated rejection (ABMR) we analyzed differences in complement reaction. For that mRNA was isolated from FFPE sections, quantified with a multiplex gene expression panel and correlated with transplant conditions and follow-up of patients. Additionally, inflammatory cells were quantified by multiplex immunohistochemistry. In allograft biopsies with TCMR and ABMR gene expression of C1QB was 2-4 fold elevated compared to Ctrl. In TCMR biopsies, mRNA counts of several complement-related genes including C1S, C3, CFB and complement regulators CFH, CR1 and SERPING1 were significantly increased compared to Ctrl. Interestingly, expression levels of about 75% of the analyzed complement related genes correlated with cold ischemia time (CIT) and markers of inflammation. In conclusion, this study suggest an important role of complement in transplant pathology which seems to be at least in part triggered by CIT. Multiplex mRNA analysis might be a useful method to refine diagnosis and explore new pathways involved in rejection.

Allograft nephrectomy versus nonallograft nephrectomy after failed renal transplantation: a systematic review by updated meta-analysis

There is limited evidence regarding the impact of allograft nephrectomy (AN) on the long-term outcome of subsequent kidney re-transplantation compared with no prior allograft nephrectomy. The aim of the present study was to conduct a systematic review and meta-analysis to estimate the accumulation of evidence over time. Primary outcomes were 5-year graft and patient survival. Cochrane library, Google scholar, PubMed, Medline and Embase were systematically searched. Meta-analysis was conducted using both fixed- and random-effects models. Study quality was assessed in duplicate using the Newcastle-Ottawa scale. Sixteen studies were included, with a total of 2256 patients. All included studies were retrospective and comparative. There was no significant difference in 5-year graft survival (GS) [Hazard Ratio (HR) = 1.11, 95% Confidence Intervals (CI): 0.89, 1.38, P = 0.37, I²  = 10%) or in 5-year patient survival (PS; HR = 0.70, 95% CI: 0.45, 1.10, P = 0.12, I²  = 0%]. Patients in the AN cohort were significantly younger than patients in the nonallograft nephrectomy (NAN) cohort by one year. Prior allograft nephrectomy was associated with a significantly higher risk of delayed graft function (DGF), acute rejection, primary nonfunction (PNF), per cent of panel reactive antibodies (% PRA) and allograft loss of the subsequent transplant. Although, DGF, % PRA, acute rejection and primary nonfunction rates were significantly higher in the AN cohort, allograft nephrectomy prior to re-transplantation had no significant association with five-year graft and patient survival.

Kidney transplantation after rescue allocation-meticulous selection yields the chance for excellent outcome

BACKGROUND

The small number of organ donors forces transplant centres to consider potentially suboptimal kidneys for transplantation. Eurotransplant established an algorithm for rescue allocation (RA) of kidneys repeatedly declined or not allocated within 5 h after procurement. Data on the outcomes and benefits of RA are scarce to date.

METHODS

We conducted a retrospective 8-year analysis of transplant outcomes of RA offers based on our in-house criteria catalogue for acceptance and decline of organs and potential recipients.

RESULTS

RA donors and recipients were both older compared with standard allocation (SA). RA donors more frequently had a history of hypertension, diabetes or fulfilled expanded criteria donor key parameters. RA recipients had poorer human leucocyte antigen (HLA) matches and longer cold ischaemia times (CITs). However, waiting time was shorter and delayed graft function, primary non-function and biopsy-proven rejections were comparable to SA. Five-year graft and patient survival after RA were similar to SA. In multivariate models accounting for confounding factors, graft survival and mortality after RA and SA were comparable as well.

CONCLUSIONS

Facing relevant comorbidities and rapid deterioration with the risk of being removed from the waiting list, kidney transplantation after RA was identified to allow for earlier transplantation with excellent outcome. Data from this survey propose not to reject categorically organs from multimorbid donors with older age and a history of hypertension or diabetes to aim for the best possible HLA matching and to carefully calculate overall expected CIT.

Low Pre-Transplant Caveolin-1 Serum Concentrations Are Associated with Acute Cellular Tubulointerstitial Rejection in Kidney Transplantation

Acute and chronic transplant rejections due to alloreactivity are essential contributors to graft loss. However, the strength of alloreactivity is biased by non-immunological factors such as ischemia reperfusion injury (IRI). Accordingly, protection from IRI could be favorable in terms of limiting graft rejection. Caveolin-1 (Cav-1) is part of the cell membrane and an important regulator of intracellular signaling. Cav-1 has been demonstrated to limit IRI and to promote the survival of a variety of cell types including renal cells under stress conditions. Accordingly, Cav-1 could also play a role in limiting anti-graft immune responses. Here, we evaluated a possible association between pre-transplant serum concentrations of Cav-1 and the occurrence of rejection during follow-up in a pilot study. Therefore, Cav-1-serum concentrations were analyzed in 91 patients at the time of kidney transplantation and compared to the incidence of acute and chronic rejection. Higher Cav-1 levels were associated with lower occurrence of acute cellular tubulointerstitial rejection episodes.

Kidney transplantation in children with CAKUT and non-CAKUT causes of chronic kidney disease: Do they have the same outcomes?

Almost half the children who undergo kidney transplantation (KTx) have congenital abnormalities of the kidney and urinary tract (CAKUT). We compared patient, graft survival, and kidney function at last follow-up between CAKUT and non-CAKUT patients after KTx. We divided the analysis into two eras: 1988-2000 and 2001-2019. Of 923 patients, 52% had CAKUT and 48% non-CAKUT chronic kidney disease (CKD). Of the latter, 341 (77%) had glomerular disease, most frequently typical HUS (32%) and primary FSGS (27%); 102 had non-glomerular disease. CAKUT patients were more often boys, younger at KTx, transplanted more frequently preemptively, but with longer time on chronic dialysis. They had less delayed graft function (DGF) and better eGFR, but higher incidence of urinary tract infection (1 year post-KTx). In both eras, 1-, 5-, and 10-year patient survival was similar in the groups, but graft survival was better in CAKUT recipients vs those with primary glomerular and primary recurrent glomerular disease: Era 1, 92.3%, 80.7%, and 63.6% vs 86.9%, 70.6%, and 49.5% (P = .02), and 76.7%, 56.6%, and 34% (P = .0003); Era 2, 96.2%, 88%, and 73.5% vs 90.3%, 76.1%, and 61% (P = .0075) and 75.4%, 54%, and 25.2% (P < .0001), respectively. Main predictors of graft loss were DGF, late acute rejection (AR), and age at KTx in CAKUT group and disease relapse, DGF, early AR, and number of HLA mismatches in recipients with glomerular disease. Graft survival was better in CAKUT patients. DGF was the main predictor of graft loss in all groups. Disease recurrence and early AR predicted graft failure in patients with glomerular disease.

The Histological Picture of Indication Biopsies in the First 2 Weeks after Kidney Transplantation

BACKGROUND AND OBJECTIVES

In preclinical studies, ischemia-reperfusion injury and older donor age are associated with graft inflammation in the early phase after transplantation. In human kidney transplantation, impaired allograft function in the first days after transplantation is often adjudicated to donor- and procedure-related characteristics, such as donor age, donor type, and ischemia times.

DESIGN

, setting, participants, & measurementsIn a cohort of 984 kidney recipients, 329 indication biopsies were performed within the first 14 days after transplantation. The histologic picture of these biopsies and its relationship with alloimmune risk factors and donor- and procedure-related characteristics were studied, as well as the association with graft failure. Multivariable Cox models were applied to quantify the cause-specific hazard ratios for early rejection and early inflammatory scores, adjusted for potential confounders. For quantification of hazard ratios of early events for death-censored graft failure, landmark analyses starting from day 15 were used.

RESULTS

Early indication biopsy specimens displayed microvascular inflammation score ≥2 in 30% and tubulointerstitial inflammation score ≥2 in 49%. Rejection was diagnosed in 186 of 329 (57%) biopsies and associated with the presence of pretransplant donor-specific HLA antibodies and the number of HLA mismatches, but not nonimmune risk factors in multivariable Cox proportional hazards analysis. In multivariable Cox proportional hazards analysis, delayed graft function, the graft dysfunction that prompted an early indication biopsy, HLA mismatches, and pretransplant donor-specific HLA antibodies were significantly associated with a higher risk for death-censored graft failure, whereas early acute rejection was not.

CONCLUSIONS

Indication biopsies performed early after kidney transplantation display inflammatory changes related to alloimmune risk factors. Nonimmune risk factors for ischemia-reperfusion injury, such as cold and warm ischemia time, older donor age, and donor type, were not identified as strong risk factors for early inflammation after human kidney transplantation.

Cellular Mechanisms of Rejection of Optic and Sciatic Nerve Transplants: An Observational Study

Background.

Organ transplantation is a standard therapeutic strategy for irreversible organ damage, but the utility of nerve transplantation remains generally unexplored, despite its potential benefit to a large patient population. Here, we aimed to establish a feasible preclinical mouse model for understanding the cellular mechanisms behind the rejection of peripheral and optic nerves.

Methods.

We performed syngenic and allogenic transplantation of optic and sciatic nerves in mice by inserting the nerve grafts inside the kidney capsule, and we assessed the allografts for signs of rejection through 14 d following transplantation. Then, we assessed the efficacy of CTLA4 Ig, Rapamycin, and anti-CD3 antibody in suppressing immune cell infiltration of the nerve allografts.

Results.

By 3 d posttransplantation, both sciatic and optic nerves transplanted from BALB/c mice into C57BL/6J recipients contained immune cell infiltrates, which included more CD11b⁺ macrophages than CD3⁺ T cells or B220⁺ B cells. Ex vivo immunogenicity assays demonstrated that sciatic nerves demonstrated higher alloreactivity in comparison with optic nerves. Interestingly, optic nerves contained higher populations of anti-inflammatory PD-L1⁺ cells than sciatic nerves. Treatment with anti-CD3 antibody reduced immune cell infiltrates in the optic nerve allograft, but exerted no significant effect in the sciatic nerve allograft.

Conclusions.

These findings establish the feasibility of a preclinical allogenic nerve transplantation model and provide the basis for future testing of directed, high-intensity immunosuppression in these mice.

Lymph node fibroblastic reticular cells deposit fibrosis-associated collagen following organ transplantation

Although the immune response within draining lymph nodes (DLNs) has been studied for decades, how their stromal compartment contributes to this process remains to be fully explored. Here, we show that donor mast cells were prominent activators of collagen I deposition by fibroblastic reticular cells (FRCs) in DLNs shortly following transplantation. Serial analysis of the DLN indicated that the LN stroma did not return to its baseline microarchitecture following organ rejection and that the DLN contained significant fibrosis following repetitive organ transplants. Using several FRC conditional-knockout mice, we show that induction of senescence in the FRCs of the DLN resulted in massive production of collagen I and a proinflammatory milieu within the DLN. Stimulation of herpes virus entry mediator (HVEM) on FRCs by its ligand LIGHT contributed chiefly to the induction of senescence in FRCs and overproduction of collagen I. Systemic administration of ex vivo-expanded FRCs to mice decreased DLN fibrosis and strengthened the effect of anti-CD40L in prolonging heart allograft survival. These data demonstrate that the transformation of FRCs into proinflammatory myofibroblasts is critically important for the maintenance of a proinflammatory milieu within a fibrotic DLN.

Vascularized composite allotransplantation versus solid organ transplantation: innate-adaptive immune interphase

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA), a life-enhancing treatment for patients with complex tissue defects, trauma or illness, expounds upon the foundation of solid organ transplantation (SOT), the gold standard in end-stage organ failure. As innate and adaptive immunity remain the fundamental concern, this review highlights divergent immunobiology responses in VCA and SOT recipients.

RECENT FINDINGS

Host innate immune activation drives peritransplant tissue ischemia-reperfusion injury (IRI). Despite the direct relationship between ischemia-reperfusion (IR)-stress and cell-mediated acute rejection, the mechanism of how IRI may affect VCA loss needs investigation. With skin grafts being highly immunogenic, the incidence of cell-mediated rejection is higher in VCA than SOT; whereas ex-vivo perfusion may exert cytoprotection against IRI in VCA and SOT. New treatment concepts, such as topical immunosuppression or cell-based tolerogenic therapies, may avoid systemic immunosuppression in VCA. Although antibody-mediated rejection is relatively rare in VCA and its disease seems to be distinct from that in SOT, little is known as to whether and how IRI may influence humoral immune rejection cascade in VCA or SOT.

SUMMARY

Further understanding of the innate-adaptive immune crosstalk should contribute to much needed development of novel therapies to improve VCA outcomes, based on strategies established in SOT.

Outcomes of en bloc simultaneous liver-kidney transplantation compared to the traditional technique

Simultaneous liver-kidney transplantation (SLKT) is indicated for patients with end-stage liver disease (ESLD) and concurrent renal insufficiency. En bloc SLKT is an alternative to traditional separate implantations, but studies comparing the two techniques are limited. The en bloc technique maintains renal outflow via donor infrahepatic vena cava and inflow via anastomosis of donor renal artery to donor splenic artery. Comparison of recipients of en bloc (n = 17) vs traditional (n = 17) SLKT between 2013 and 2017 was performed. Recipient demographics and comorbidities were similar. More recipients of traditional SLKT were dialysis dependent (82.4% vs 41.2%, P = .01) with lower baseline pretransplant eGFR (14 vs 18, P = .01). En bloc SLKT was associated with shorter kidney cold ischemia time (341 vs 533 minutes, P < .01) and operative time (374 vs 511 minutes, P < .01). Two en bloc patients underwent reoperation for kidney allograft inflow issues due to kinking and renal steal. Early kidney allograft dysfunction (23.5% in both groups), 1-year kidney graft survival (88.2% vs 82.4%, P = 1.0), and posttransplantation eGFR were similar between groups. In our experience, the en bloc SLKT technique is safe and feasible, with comparable outcomes to the traditional method.

Transplantectomy in the First 3 Months After Renal Transplantation: Experience of a Reference Center

INTRODUCTION/OBJECTIVE

Transplantation is the treatment of choice in end-stage renal disease. However, there are complications that require transplantectomy. The objective of this study was to evaluate predictive factors for transplantectomy in the first 3 months after renal transplantation.

MATERIAL AND METHODS

This retrospective study included 770 kidney transplants performed between June 2011 and June 2017. Logistic regression was applied to study the relationship between independent variables and the occurrence of transplantectomy.

RESULTS

Analyzing variables of the recipients, it was verified that age over 65 years; body mass index; dialysis time; history of previous transplant and comorbidities such as obesity, overweight, hypertension, diabetes mellitus, dyslipidemia, peripheral arterial disease; or history of a thrombotic episode were not predictive factors. It was found that the use of expanded criteria donors, their age, or cause of death were not predictive factors. The use of a right renal graft or grafts with multiple arteries; the duration of surgery; the performance of surgery at dawn; the need for transfusion; the cold ischemia time; and hemodynamic parameters at reperfusion (central venous pressure, systolic or diastolic blood pressure) were not predictive factors. The recipient age at transplantation (p = .014; B=-0.059; Exp(B)=0.943 [0.899-0.988]) and reoperation in the first 10 days after transplantation (p < .001; B= -2.574; Exp(B)=0.076 [0.028-0.210]) were predictive factors.

CONCLUSION

Reoperation in the first 10 days after transplantation decreased the risk of transplantectomy in the first 3 months. The lower the age of the recipient, the greater the risk of transplantectomy.

Risk Factors for 1-Year Graft Loss After Kidney Transplantation: Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

With expansion of the pool of kidney grafts, through the use of higher-risk donors, and increased attention to donor management strategies, the 1-year graft survival rate is subject to change. It is, therefore, useful to elucidate 1-year graft survival rates by dissecting the characteristics of the low-risk and high-risk kidney transplant cases. The objective of our study was to evaluate factors purported to influence the risk of 1-year graft loss in kidney transplant recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We searched bibliographic databases from 2000 to 2017 and included observational studies that measured the association between donor, recipient, the transplant operation, or early postoperative complications, and 1-year death-censored graft loss.

RESULTS

We identified 35 eligible primary studies, with 20 risk factors amenable to meta-analysis. Six factors were associated with graft loss, with moderate to high degree of certainty: donor age (hazard ratio [HR], 1.11 per 10-year increase; 95% confidence interval [95% CI], 1.04 to 1.18), extended criteria donors (HR, 1.35; 95% CI, 1.28 to 1.42), deceased donors (HR, 1.54; 95% CI, 1.32 to 1.82), number of HLA mismatches (HR, 1.08 per one mismatch increase; 95% CI, 1.07 to 1.09), recipient age (HR, 1.17 per 10-year increase; 95% CI, 1.09 to 1.25), and delayed graft function (HR, 1.89; 95% CI, 1.46 to 2.47) as risk factors for 1-year graft loss. Pooled analyses also excluded, with a high degree of certainty, any associations of cold ischemia time, recipient race, pretransplant body mass index, diabetes, and hypertension with 1-year graft loss.

CONCLUSIONS

Recipient age, donor age, standard versus extended criteria donor, living versus deceased donor, HLA mismatch, and delayed graft function all predicted 1-year graft survival. The effect of each risk factor is small.

Accelerating kidney allocation: Simultaneously expiring offers

Using nonideal kidneys for transplant quickly might reduce the discard rate of kidney transplants. We studied changing kidney allocation to eliminate sequential offers, instead making offers to multiple centers for all nonlocally allocated kidneys, so that multiple centers must accept or decline within the same 1 hour. If more than 1 center accepted an offer, the kidney would go to the highest-priority accepting candidate. Using 2010 Kidney-Pancreas Simulated Allocation Model-Scientific Registry for Transplant Recipients data, we simulated the allocation of 12 933 kidneys, excluding locally allocated and zero-mismatch kidneys. We assumed that each hour of delay decreased the probability of acceptance by 5% and that kidneys would be discarded after 20 hours of offers beyond the local level. We simulated offering kidneys simultaneously to small, medium-size, and large batches of centers. Increasing the batch size increased the percentage of kidneys accepted and shortened allocation times. Going from small to large batches increased the number of kidneys accepted from 10 085 (92%) to 10 802 (98%) for low-Kidney Donor Risk Index kidneys and from 1257 (65%) to 1737 (89%) for high-Kidney Donor Risk Index kidneys. The average number of offers that a center received each week was 10.1 for small batches and 16.8 for large batches. Simultaneously expiring offers might allow faster allocation and decrease the number of discards, while still maintaining an acceptable screening burden.

Immunologic Risk Assessment and Approach to Immunosuppression Regimen in Kidney Transplantation

The outcomes of kidney transplantation show a steady improvement with an increasing number of transplantations and decreasing incidence of acute rejection episodes. Successful transplantation begins with a comprehensive immunologic risk assessment and judicious choice of therapeutic agents. In this review, we discuss the trends in transplant immunosuppression practices and outcomes in the United States. We discuss practical testing algorithms for clinical decision making in induction therapy and fine-tuning maintenance immunosuppression. We introduce assessment tools for immune monitoring after transplantation and speculate on future directions in management.

Time of Cold Ischemia and Delayed Graft Function in a Cohort of Renal Transplant Patients in a Reference Center

There are many factors involved in the delayed graft function of a renal graft, with prolonged cold ischemia time being one of the most relevant. The aim of this study is to evaluate the relationship between the time of cold ischemia and the delayed graft function, and acute rejection and graft loss at 1 year of follow-up. A retrospective cohort of 347 renal transplant patients were evaluated during the years 2009-2013. The incidence of delayed graft function was 18.4% (n = 65). The cold ischemia time was an independent risk factor for delayed graft function (odds ratio [OR] 1.10, 95% confidence interval [CI] 1.04-1.16). By grouping the time of cold ischemia by intervals, the risk of delayed graft function was greater in the 12-18 hours group (OR 2.06, 95% CI 1.02-4.15) and in the >18 hours group (OR 3.38, 95% CI 1.57-7.27). The risk of acute rejection did not increase with longer cold ischemia (p = 0.69), and cold ischemia time was not a risk factor for renal graft loss at 1-year follow-up (hazard ratio 0.97, 95% CI 0.88-1.06). In conclusion the time of cold ischemia (>12 hours) in renal transplant recipients of optimal deceased donors increases the risk of delayed graft function; however, this does not negatively impact the results in acute rejection or graft loss in the first year of the transplant.

Pathological Process of Prompt Connection between Host and Donor Tissue Vasculature Causing Rapid Perfusion of the Engineered Donor Tissue after Transplantation

The shortage of donors for transplantation therapy is a serious issue worldwide. Tissue engineering is considered a potential solution to this problem. Connection and perfusion in engineered tissues after transplantation is vital for the survival of the transplanted tissue, especially for tissues requiring blood perfusion to receive nutrients, such as the heart. A myocardial cell sheet containing an endothelial cell network structure was fabricated in vitro using cell sheet technology. Transplantation of the three-dimensional (3D) tissue by layering myocardial sheets could ameliorate ischemic heart disease in a rat model. The endothelial cell network in the 3D tissue was able to rapidly connect to host vasculature and begin perfusion within 24 h after transplantation. In this review, we compare and discuss the engineered tissue⁻host vasculature connection process between tissue engineered constructs with hydrogels and cell sheets by histological analysis. This review provides information that may be useful for further improvements of in vivo engineered tissue vascularization techniques.