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Kidney transplant (KTx) biopsies showing transplant glomerulopathy (TG) (glomerular basement membrane double contours (cg) > 0) and microvascular inflammation (MVI) in the absence of C4d staining and donor-specific antibodies (DSAs) do not fulfill the criteria for chronic active antibody–mediated rejection (CA-AMR) diagnosis and do not fit into any other Banff category. To investigate this, we initiated a multicenter intercontinental study encompassing 36 cases, comparing the immunomic and transcriptomic profiles of 14 KTx biopsies classified as cg+MVI DSA-/C4d-with 22 classified as CA-AMR DSA+/C4d+through novel transcriptomic analysis using the NanoString Banff-Human Organ Transplant (B-HOT) panel and subsequent orthogonal subset analysis using two innovative 5-marker multiplex immunofluorescent panels. Nineteen genes were differentially expressed between the two study groups. Samples diagnosed with CA-AMR DSA+/C4d+showed a higher glomerular abundance of natural killer cells and higher transcriptomic cell type scores for macrophages in an environment characterized by increased expression of complement-related genes (i.e., C5AR1) and higher activity of angiogenesis, interstitial fibrosis tubular atrophy, CA-AMR, and DSA-related pathways when compared to samples diagnosed with cg+MVI DSA-/C4d-. Samples diagnosed with cg+MVI DSA-/C4d-displayed a higher glomerular abundance and activity of T cells (CD3+, CD3+CD8+, and CD3+CD8-). Thus, we show that using novel multiomic techniques, KTx biopsies with cg+MVI DSA-/C4d-have a prominent T-cell presence and activity, putting forward the possibility that these represent a more T-cell dominant phenotype.

T-cell–mediated help to B cells is required for the development of humoral responses, in which the cytokine interleukin (IL)-21 is key. Here, we studied the mRNA-1273 vaccine–induced SARS-CoV-2–specific memory T-cell IL-21 response, memory B cell response, and immunoglobulin (Ig)G antibody levels in peripheral blood at 28 days after the second vaccination by ELISpot and the fluorescent bead–based multiplex immunoassay, respectively. We included 40 patients with chronic kidney disease (CKD), 34 patients on dialysis, 63 kidney transplant recipients (KTR), and 47 controls. We found that KTR, but not patients with CKD and those receiving dialysis, showed a significantly lower number of SARS-CoV-2–specific IL-21 producing T cells than controls (P< .001). KTR and patients with CKD showed lower numbers of SARS-CoV-2–specific IgG–producing memory B cells when compared with controls (P< .001 and P= .01, respectively). The T-cell IL-21 response was positively associated with the SARS-CoV-2–specific B cell response and the SARS-CoV-2 spike S1–specific IgG antibody levels (both Pearson r= 0.5; P< .001). In addition, SARS-CoV-2–specific B cell responses were shown to be IL-21 dependent. Taken together, we show that IL-21 signaling is important in eliciting robust B cell–mediated immune responses in patients with kidney disease and KTR.

ABSTRACTIntroductionTacrolimus is a potent immunosuppressive drug with many side effects including nephrotoxicity and post-transplant diabetes mellitus. To limit its toxicity, therapeutic drug monitoring (TDM) is performed. However, tacrolimus’ pharmacokinetics are highly variable within and between individuals, which complicates their clinical management. Despite TDM, many kidney transplant recipients will experience under- or overexposure to tacrolimus. Therefore, dosing algorithms have been developed to limit the time a patient is exposed to off-target concentrations.Areas CoveredTacrolimus starting dose algorithms and models for follow-up doses developed and/or tested since 2015, encompassing both adult and pediatric populations. Literature was searched in different databases, i.e. Embase, PubMed, Web of Science, Cochrane Register, and Google Scholar, from inception to February 2023Expert OpinionMany algorithms have been developed, but few have been prospectively evaluated. These performed better than bodyweight-based starting doses, regarding the time a patient is exposed to off-target tacrolimus concentrations. No benefit in reduced tacrolimus toxicity has yet been observed. Most algorithms were developed from small datasets, contained only a few tacrolimus concentrations per person, and were not externally validated. Moreover, other matrices should be considered which might better correlate with tacrolimus toxicity than the whole-blood concentration, e.g. unbound plasma or intra-lymphocytic tacrolimus concentrations.

Autologous bone marrow–derived mesenchymal stromal cell (MSC) therapy and withdrawal of calcineurin inhibitors (CNIs) has been shown to improve systemic blood pressure control and left ventricular hypertrophy regression in kidney transplant recipients. In the current subanalysis, we aimed to evaluate the impact of this novel immunosuppressive regimen on the longitudinal changes of left atrial (LA) structure and function after kidney transplantation.

The use of extended criteria donor grafts is a promising strategy to increase the number of organ transplantations and reduce waitlist mortality. However, these organs are often compromised and/or damaged, are more susceptible to preservation injury, and are at risk for developing post-transplant complications. Ex vivo organ perfusion is a novel technology to preserve donor organs while providing oxygen and nutrients at distinct perfusion temperatures. This preservation method allows to resuscitate grafts and optimize function with therapeutic interventions prior to solid organ transplantation. Stem cell-based therapies are increasingly explored for their ability to promote regeneration and reduce the inflammatory response associated with in vivo reperfusion. The aim of this review is to describe the current state of stem cell-based therapies during ex vivo organ perfusion for the kidney, liver, lung, and heart. We discuss different strategies, including type of cells, route of administration, mechanisms of action, efficacy, and safety. The progress made within lung transplantation justifies the initiation of clinical trials, whereas more research is likely required for the kidney, liver, and heart to progress into clinical application. We emphasize the need for standardization of methodology to increase comparability between future (clinical) studies.

After renal transplantation, there is a need for immunosuppressive regimens which effectively prevent allograft rejection, while preserving renal function and minimizing side effects. From this perspective, mesenchymal stromal cell (MSC) therapy is of interest. In this randomized prospective, single-center, open-label trial, we compared MSCs infused 6 and 7 weeks after renal transplantation and early tacrolimus withdrawal with a control tacrolimus group. Primary end point was quantitative evaluation of interstitial fibrosis in protocol biopsies at 4 and 24 weeks posttransplant. Secondary end points included acute rejection, graft loss, death, renal function, adverse events, and immunological responses. Seventy patients were randomly assigned of which 57 patients were included in the final analysis (29 MSC; 28 controls). Quantitative progression of fibrosis failed to show benefit in the MSC group and GFR remained stable in both groups. One acute rejection was documented (MSC group), while subclinical rejection in week 24 protocol biopsies occurred in seven patients (four MSC; three controls). In the MSC group, regulatory T cell numbers were significantly higher compared to controls (p= .014, week 24). In conclusion, early tacrolimus withdrawal with MSC therapy was safe and feasible without increased rejection and with preserved renal function. MSC therapy is a potentially useful approach after renal transplantation.

Supplemental Digital Content is available in the text.

Supplemental Digital Content is available in the text.

Mesenchymal stromal cells (MSCs) are immunomodulatory and tissue homeostatic cells that have shown beneficial effects in kidney diseases and transplantation. Perivascular stromal cells (PSCs) identified within several different organs share characteristics of bone marrow‐derived MSCs (BM‐MSCs). These PSCs may also possess tissue‐specific properties and play a role in local tissue homeostasis. We hypothesized that human kidney‐derived PSCs (hkPSCs) would elicit improved kidney repair in comparison with BM‐MSCs. Here we introduce a novel, clinical‐grade isolation method of hkPSCs from cadaveric kidneys by enriching for the perivascular marker, NG2. hkPSCs show strong transcriptional similarities to BM‐MSCs but also show organotypic expression signatures, including the HoxD10 and HoxD11 nephrogenic transcription factors. Comparable to BM‐MSCs, hkPSCs showed immunosuppressive potential and, when cocultured with endothelial cells, vascular plexus formation was supported, which was specifically in the hkPSCs accompanied by an increased NG2 expression. hkPSCs did not undergo myofibroblast transformation after exposure to transforming growth factor‐β, further corroborating their potential regulatory role in tissue homeostasis. This was further supported by the observation that hkPSCs induced accelerated repair in a tubular epithelial wound scratch assay, which was mediated through hepatocyte growth factor release. In vivo, in a neonatal kidney injection model, hkPSCs reintegrated and survived in the interstitial compartment, whereas BM‐MSCs did not show this potential. Moreover, hkPSCs gave protection against the development of acute kidney injury in vivo in a model of rhabdomyolysis‐mediated nephrotoxicity. Overall, this suggests a superior therapeutic potential for the use of hkPSCs and their secretome in the treatment of kidney diseases. StemCellsTranslationalMedicine2017;6:405–418

Recently, several B cell–related markers have been described to be upregulated during operational tolerance in kidney allograft recipients. Little data exist on these markers during allograft rejection.

The prevalence of chronic kidney disease and end-stage renal disease is increasing each year and currently the best therapeutic option for end-stage renal disease patients is kidney transplantation. However, although short-term graft outcomes after transplantation have improved substantially as a result of new and more potent immunosuppressive drugs, the long-term survival has hardly changed. This most likely is caused by a combination of nonimmunologic side effects and sustained alloreactivity to the graft resulting in fibrosis. In addition, current immunosuppressive drugs have side effects, including nephrotoxicity, infections, and malignancies that compromise long-term outcomes. Consequently, there is a strong interest in immunosuppressive therapies that maintain efficacy, while reducing side effects. Because mesenchymal stromal cells have potent anti-inflammatory and antifibrotic properties, these cells are of particular interest as new candidates in transplant recipients. Mesenchymal stromal cells might play roles in the treatment of allograft rejection and fibrosis and in calcineurin minimization and induction protocols. In the present review we discuss both preclinical as well as clinical evidence of their therapeutic potential in kidney transplantation. In addition, challenges and obstacles for clinical translation are discussed.

Kidney transplantation has improved the life expectancy and quality of life for patients with end-stage renal failure. However, despite the impressive improvements in short-term outcome parameters because of better and more potent immunosuppressive drugs, the long-term survival of renal allografts has changed little over the last decades. Sustained inflammation in the areas of interstitial fibrosis and tubular atrophy (IFTA) is a strong predictor of allograft failure. Mesenchymal stromal cells (MSCs) have potent anti-inflammatory and reparative properties, and could thus play a role in controlling these processes.

Recent insights suggest that endothelial cell (EC) activation plays a major role in renal ischemia-reperfusion (IR) injury. Interactions between ECs and pericytes via signaling molecules, including angiopoietins, are involved in maintenance of the vascular integrity. Experimental data have shown that enhancement of Angiopoietin (Ang)-1 signaling might be beneficial in renal IR injury. However, little is known about the role of angiopoietins in human renal IR injury.

Ischemiareperfusion (IR) injury has a major impact on kidney graft function and survival. Animal studies have suggested a role for complement activation in mediating IR injury; however, results are not unambiguous. Whether complement activation is involved in clinical IR injury in humans is still unclear.

Despite impressive improvements in short-term survival after solid organ transplantation (SOT), the long-term outcome remains an important challenge. In recent years, it has become evident that ongoing alloreactivity, cellular andor humoral, may play a critical role in the premature loss of kidney allografts. Clinical trials with mesenchymal stromal cells (MSCs) are currently underway for the treatment of various inflammatory disorders. Due to their immunosuppressive and reparative properties MSC immunotherapy constitutes an attractive intervention for chronic rejection, while avoiding the undesired adverse effects associated with excessive use of immunosuppressive drugs.

This study addresses a mechanism by which lymphocytes may promote vascular endothelial growth factor (VEGF) expression and angiogenesis in immune inflammation. Resting human umbilical endothelial cells (HUVECs) were found to express low levels of VEGF messenger RNA (mRNA) by reverse transcription polymerase chain reaction and ribonuclease protection assay with little or no change in expression following activation by cytokines, including tumor necrosis factor-α, interleukin (IL)–1, interferon γ, or IL-4. In contrast, treatment of HUVECs and monocytes with soluble CD40 ligand (sCD40L) resulted in a marked dose-dependent induction of VEGF mRNA (approximately 4-fold), which peaked between 1 and 5 hours post-stimulation. Transient transfection of HUVECs was performed with a luciferase reporter construct under the control of the human VEGF promoter. Treatment of transfected HUVECs with sCD40L was found to enhance luciferase activity (approximately 4-fold) compared with controls, similar to the relative fold induction in mRNA expression in parallel cultures. Thus, CD40-dependent VEGF expression was a result of transcriptional control mechanisms. Treatment of HUVECs with sCD40L was also found to function in vitro to promote growth and proliferation in a VEGF-dependent manner, and CD40-dependent HUVEC growth was comparable to that found following treatment with recombinant human VEGF. Furthermore, subcutaneous injection of sCD40L in severe combined immunodeficient and nude mice induced VEGF expression and marked angiogenesis in vivo. Taken together, these findings are consistent with a function for CD40L-CD40 interactions in VEGF-induced angiogenesis and define a mechanistic link between the immune response and angiogenesis.