Chronic Kidney Disease Is Characterized by Expansion of a Distinct Proinflammatory Intermediate Monocyte Subtype and by Increased Monocyte Adhesion to Endothelial Cells.

SIGNIFICANCE STATEMENT: CKD is accompanied by abnormal inflammation, which contributes to progressive loss of functional renal tissue and accelerated cardiovascular disease. Although studies have documented that dysregulation of monocyte maturation and function is associated with CKD and its complications, it is not well characterized. This study reveals that a distinctive human monocyte subtype with high propensity for releasing proinflammatory mediators and activating endothelial cells is increased in adults with CKD compared with adults with high cardiovascular risk and normal kidney function. It also demonstrates that human monocyte adhesion to endothelial layers and responses to specific inflammatory migration signals are enhanced in CKD. These findings offer insights into the mechanisms of CKD-associated intravascular and localized inflammation and may suggest potential targets for therapeutic interventions. BACKGROUND: Cardiovascular disease (CVD) in patients with CKD is associated with increased circulating intermediate monocytes (IMs). Dysregulation of monocyte maturation and function is associated with CKD and its complications, but it is incompletely characterized. METHODS: To explore monocyte repertoire abnormalities in CKD, we studied properties of monocyte subpopulations, including IM subpopulations distinguished by HLA-DR expression level, in individuals with or without CKD. Using flow cytometry, we profiled monocyte populations in blood samples from adults with CKD, healthy volunteers (HVs), and patient controls (PCs) with high CVD risk. Monocyte subpopulations were also derived from single-cell RNA-sequencing profiles of paired blood and biopsy samples from kidney transplant recipients. We quantified intracellular cytokine production, migration, and endothelial adhesion in ex vivo assays of PBMCs. RESULTS: Of four predefined blood monocyte subpopulations, only HLA-DR hi IMs were increased in individuals with CKD compared with HVs and PCs. In HVs and patients with CKD, LPS-stimulated HLA-DR hi IMs isolated from blood produced higher amounts of TNF and IL-1 ß than other monocyte populations. Single-cell analysis revealed four monocyte clusters common to blood and kidneys, including an HLA-DR hi IM-like cluster that was enriched in kidneys versus blood. Migration toward CCL5 and CX3CL1 and adhesion to primary endothelial cell layers were increased in monocyte subpopulations in individuals with CKD compared with HVs. Monocyte adhesion to endothelial cells was partly dependent on CX3CR1/CX3CL1 interaction. CONCLUSIONS: CKD is associated with an increased number of a distinctive proinflammatory IM subpopulation and abnormalities of monocyte migration and endothelial adhesion. Dysregulated monocyte maturation and function may represent targetable factors contributing to accelerated CVD in CKD.

Impact of antimetabolite discontinuation following cytomegalovirus or BK polyoma virus infection in kidney transplant recipients.

BACKGROUND: Cytomegalovirus (CMV) and BK polyoma virus (BKV) infection following kidney transplantation have been associated with allograft dysfunction and allograft loss. Reduction in immunosuppression is a mainstay of management yet has been associated with increased risk of rejection. According to international consensus guidelines, one approach to management of these viral infections is to discontinue the antimetabolite. Little is known surrounding long-term outcomes in these patients, and it remains unclear if consideration should be given to resuming the antimetabolite as variable re-escalation strategies have been reported. The objective was to describe episodes of rejection and identify risk factors for rejection following antimetabolite withdrawal after CMV or BKV DNAemia in kidney transplant recipients. METHODS: This single-center, retrospective review evaluated adult kidney transplant recipients with a serum CMV or BKV DNA PCR ≥500 copies/ml who underwent antimetabolite discontinuation. The primary outcome assessed was the incidence of biopsy-proven acute rejection (BPAR). RESULTS: One hundred fifty-nine patients were included. Overall, 14 patients (8.8%) experienced BPAR at a median of 1.6 years after antimetabolite discontinuation. Compared to CMV, discontinuation after BKV DNAemia was associated with a higher incidence of BPAR. Characteristics observed more frequently in patients with BPAR included younger age, female sex, higher initial viral load, and development of de novo donor-specific antibody (DSA). CONCLUSION: These findings suggest that antimetabolite discontinuation after CMV or BKV DNAemia in kidney transplant recipients is a reasonable and safe approach. Further prospective studies investigating optimal immunosuppression management following CMV or BKV DNAemia in kidney transplant recipients are warranted.

CAR-T therapy in solid organ transplant recipients with treatment refractory posttransplant lymphoproliferative disorder.

Chimeric antigen receptor T cells (CAR-T) are genetically modified T cells with a chimeric antigen receptor directed against a specific tumor-associated antigen like CD19 in lymphoma. CAR-T cells have shown encouraging activity against recurrent and refractory diffuse large B cell lymphomas (DLBCL). However concurrent use of immunosuppressive agents was prohibited in most CAR-T trials effectively excluding patients with prior solid organ transplantation (SOT) and posttransplant lymphoproliferative disorders (PTLD). We report the outcomes for three patients with PTLD refractory to immunochemotherapy 10-20 years after SOT who received CAR-T therapy between January 2018 and December 2019. One patient had an orthotopic heart transplant, the second had a deceased donor kidney transplant, and the third had a pancreas after kidney transplant (PAK). All patients developed complications of CAR-T therapy such as cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and acute kidney injury requiring renal replacement therapy in the two out of three patients. All patients expired after withdrawal of care due to lack of response to CAR-T therapy. In addition, the PAK patient developed acute pancreatitis after CAR-T therapy. This case series identifies the challenges of using CAR-T therapy to manage refractory PTLD in SOT recipients and its possible complications.

Harnessing Expressed Single Nucleotide Variation and Single Cell RNA Sequencing To Define Immune Cell Chimerism in the Rejecting Kidney Transplant.

BACKGROUND: In solid organ transplantation, donor-derived immune cells are assumed to decline with time after surgery. Whether donor leukocytes persist within kidney transplants or play any role in rejection is unknown, however, in part because of limited techniques for distinguishing recipient from donor cells. METHODS: Whole-exome sequencing of donor and recipient DNA and single-cell RNA sequencing (scRNA-seq) of five human kidney transplant biopsy cores distinguished immune cell contributions from both participants. DNA-sequence comparisons used single nucleotide variants (SNVs) identified in the exome sequences across all samples. RESULTS: Analysis of expressed SNVs in the scRNA-seq data set distinguished recipient versus donor origin for all 81,139 cells examined. The leukocyte donor/recipient ratio varied with rejection status for macrophages and with time post-transplant for lymphocytes. Recipient macrophages displayed inflammatory activation whereas donor macrophages demonstrated antigen presentation and complement signaling. Recipient-origin T cells expressed cytotoxic and proinflammatory genes consistent with an effector cell phenotype, whereas donor-origin T cells appeared quiescent, expressing oxidative phosphorylation genes. Finally, both donor and recipient T cell clones within the rejecting kidney suggested lymphoid aggregation. The results indicate that donor-origin macrophages and T cells have distinct transcriptional profiles compared with their recipient counterparts, and that donor macrophages can persist for years post-transplantation. CONCLUSIONS: Analysis of single nucleotide variants and their expression in single cells provides a powerful novel approach to accurately define leukocyte chimerism in a complex organ such as a transplanted kidney, coupled with the ability to examine transcriptional profiles at single-cell resolution.

Impact of metformin on malignancy in solid organ transplantation.

Malignancy after solid organ transplant is a common occurrence that is associated with increased morbidity and mortality. Literature in the general diabetic population has identified possible antineoplastic properties of metformin. This retrospective study aims to determine if metformin results in a malignancy risk reduction in a cohort of diabetic kidney, liver, and heart transplant recipients. The population included transplant recipients without use of metformin at any time point (DMO arm, n = 147) and those with use of metformin (DMM arm, n = 172); the two arms were matched based on organ type and transplant date prior to application of exclusion criteria. Recipients with prior malignancy, malignancy before diabetes diagnosis, and metformin duration <30 days were excluded. The primary endpoint of malignancy first occurrence post-transplant was not found to be statistically significant at 1, 5, 10, and 15 years. In the subgroup of heart transplant recipients, there was a significant reduction in malignancy at 15 years post-transplant. Older age and Caucasian race were identified as significant risk factors for malignancy, while never smoker was a protective factor. Metformin use in this solid organ transplant cohort was not found to significantly reduce malignancy risk compared to use of other anti-diabetic agents.

WNT pathway signaling is associated with microvascular injury and predicts kidney transplant failure.

Microvascular injury is associated with accelerated kidney transplant dysfunction and allograft failure. Molecular pathology can identify new mechanisms of microvascular injury while improving on the diagnostic and prognostic capabilities of traditional histology. We conducted a case-control study of archived kidney biopsy specimens stored up to 10 years with microvascular injury (n = 50) compared with biopsy specimens without histologic injury (n = 45) from patients of similar age, race, and sex. We measured WNT gene expression with a multiplex quantification platform by using digital barcoding, given the importance of WNT reactivation to the response to wounding in the kidney microvasculature and other compartments. Of 210 genes from a commercial WNT panel, 71 were associated with microvascular injury and 79 were associated with allograft failure, with considerable overlap of genes between each set. Molecular pathology identified 46 biopsy specimens with molecular evidence of microvascular injury; 18 (39%) were either C4d negative, donor-specific antibody negative, or had no microvascular injury by histology. The majority of cases with molecular evidence of microvascular injury had poor long-term outcomes. We identified novel WNT pathway genes associated with microvascular injury and allograft failure in residual clinical biopsy specimens obtained up to 10 years earlier. Further mechanistic studies may identify the WNT pathway as a new diagnostic and therapeutic target.

Pathogenicity of a Human Laminin ß2 Mutation Revealed in Models of Alport Syndrome.

Pierson syndrome is a congenital nephrotic syndrome with eye and neurologic defects caused by mutations in laminin ß2 (LAMB2), a major component of the glomerular basement membrane (GBM). Pathogenic missense mutations in human LAMB2 cluster in or near the laminin amino-terminal (LN) domain, a domain required for extracellular polymerization of laminin trimers and basement membrane scaffolding. Here, we investigated an LN domain missense mutation, LAMB2-S80R, which was discovered in a patient with Pierson syndrome and unusually late onset of proteinuria. Biochemical data indicated that this mutation impairs laminin polymerization, which we hypothesized to be the cause of the patient's nephrotic syndrome. Testing this hypothesis in genetically altered mice showed that the corresponding amino acid change (LAMB2-S83R) alone is not pathogenic. However, expression of LAMB2-S83R significantly increased the rate of progression to kidney failure in a Col4a3-/- mouse model of autosomal recessive Alport syndrome and increased proteinuria in Col4a5+/- females that exhibit a mild form of X-linked Alport syndrome due to mosaic deposition of collagen α3α4α5(IV) in the GBM. Collectively, these data show the pathogenicity of LAMB2-S80R and provide the first evidence of genetic modification of Alport phenotypes by variation in another GBM component. This finding could help explain the wide range of Alport syndrome onset and severity observed in patients with Alport syndrome, even for family members who share the same COL4 mutation. Our results also show the complexities of using model organisms to investigate genetic variants suspected of being pathogenic in humans.

Single-Cell Transcriptomics of a Human Kidney Allograft Biopsy Specimen Defines a Diverse Inflammatory Response.

Background Single-cell genomics techniques are revolutionizing our ability to characterize complex tissues. By contrast, the techniques used to analyze renal biopsy specimens have changed little over several decades. We tested the hypothesis that single-cell RNA-sequencing can comprehensively describe cell types and states in a human kidney biopsy specimen.Methods We generated 8746 single-cell transcriptomes from a healthy adult kidney and a single kidney transplant biopsy core by single-cell RNA-sequencing. Unsupervised clustering analysis of the biopsy specimen was performed to identify 16 distinct cell types, including all of the major immune cell types and most native kidney cell types, in this biopsy specimen, for which the histologic read was mixed rejection.Results Monocytes formed two subclusters representing a nonclassical CD16+ group and a classic CD16- group expressing dendritic cell maturation markers. The presence of both monocyte cell subtypes was validated by staining of independent transplant biopsy specimens. Comparison of healthy kidney epithelial transcriptomes with biopsy specimen counterparts identified novel segment-specific proinflammatory responses in rejection. Endothelial cells formed three distinct subclusters: resting cells and two activated endothelial cell groups. One activated endothelial cell group expressed Fc receptor pathway activation and Ig internalization genes, consistent with the pathologic diagnosis of antibody-mediated rejection. We mapped previously defined genes that associate with rejection outcomes to single cell types and generated a searchable online gene expression database.Conclusions We present the first step toward incorporation of single-cell transcriptomics into kidney biopsy specimen interpretation, describe a heterogeneous immune response in mixed rejection, and provide a searchable resource for the scientific community.

Functional assessment of a novel COL4A5 splice region variant and immunostaining of plucked hair follicles as an alternative method of diagnosis in X-linked Alport syndrome.

BACKGROUND: Many COL4A5 splice region variants have been described in patients with X-linked Alport syndrome, but few have been confirmed by functional analysis to actually cause defective splicing. We sought to demonstrate that a novel COL4A5 splice region variant in a family with Alport syndrome is pathogenic using functional studies. We also describe an alternative method of diagnosis. METHODS: Targeted next-generation sequencing results of an individual with Alport syndrome were analyzed and the results confirmed by Sanger sequencing in family members. A splicing reporter minigene assay was used to examine the variant's effect on splicing in transfected cells. Plucked hair follicles from patients and controls were examined for collagen IV proteins using immunofluorescence microscopy. RESULTS: A novel splice region mutation in COL4A5, c.1780-6T>G, was identified and segregated with disease in this family. This variant caused frequent skipping of exon 25, resulting in a frameshift and truncation of collagen α5(IV) protein. We also developed and validated a new approach to characterize the expression of collagen α5(IV) protein in the basement membranes of plucked hair follicles. Using this approach we demonstrated reduced collagen α5(IV) protein in affected male and female individuals in this family, supporting frequent failure of normal splicing. CONCLUSIONS: Differing normal to abnormal transcript ratios in affected individuals carrying splice region variants may contribute to variable disease severity observed in Alport families. Examination of plucked hair follicles in suspected X-linked Alport syndrome patients may offer a less invasive alternative method of diagnosis and serve as a pathogenicity test for COL4A5 variants of uncertain significance.

A novel missense mutation of Wilms' Tumor 1 causes autosomal dominant FSGS.

FSGS is a clinical disorder characterized by focal scarring of the glomerular capillary tuft, podocyte injury, and nephrotic syndrome. Although idiopathic forms of FSGS predominate, recent insights into the molecular and genetic causes of FSGS have enhanced our understanding of disease pathogenesis. Here, we report a novel missense mutation of the transcriptional regulator Wilms' Tumor 1 (WT1) as the cause of nonsyndromic, autosomal dominant FSGS in two Northern European kindreds from the United States. We performed sequential genome-wide linkage analysis and whole-exome sequencing to evaluate participants from family DUK6524. Subsequently, whole-exome sequencing and direct sequencing were performed on proband DNA from family DUK6975. We identified multiple suggestive loci on chromosomes 6, 11, and 13 in family DUK6524 and identified a segregating missense mutation (R458Q) in WT1 isoform D as the cause of FSGS in this family. The identical mutation was found in family DUK6975. The R458Q mutation was not found in 1600 control chromosomes and was predicted as damaging by in silico simulation. We depleted wt1a in zebrafish embryos and observed glomerular injury and filtration defects, both of which were rescued with wild-type but not mutant human WT1D mRNA. Finally, we explored the subcellular mechanism of the mutation in vitro. WT1(R458Q) overexpression significantly downregulated nephrin and synaptopodin expression, promoted apoptosis in HEK293 cells and impaired focal contact formation in podocytes. Taken together, these data suggest that the WT1(R458Q) mutation alters the regulation of podocyte homeostasis and causes nonsyndromic FSGS.

Rare hereditary COL4A3/COL4A4 variants may be mistaken for familial focal segmental glomerulosclerosis.

Focal segmental glomerulosclerosis (FSGS) is a histological lesion with many causes, including inherited genetic defects, with significant proteinuria being the predominant clinical finding at presentation. Mutations in COL4A3 and COL4A4 are known to cause Alport syndrome (AS), thin basement membrane nephropathy, and to result in pathognomonic glomerular basement membrane (GBM) findings. Secondary FSGS is known to develop in classic AS at later stages of the disease. Here, we present seven families with rare or novel variants in COL4A3 or COL4A4 (six with single and one with two heterozygous variants) from a cohort of 70 families with a diagnosis of hereditary FSGS. The predominant clinical finding at diagnosis was proteinuria associated with hematuria. In all seven families, there were individuals with nephrotic-range proteinuria with histologic features of FSGS by light microscopy. In one family, electron microscopy showed thin GBM, but four other families had variable findings inconsistent with classical Alport nephritis. There was no recurrence of disease after kidney transplantation. Families with COL4A3 and COL4A4 variants that segregated with disease represent 10% of our cohort. Thus, COL4A3 and COL4A4 variants should be considered in the interpretation of next-generation sequencing data from such patients. Furthermore, this study illustrates the power of molecular genetic diagnostics in the clarification of renal phenotypes.

Sequencing of Physically Interacting Cells in Human Kidney Allograft Rejection to Infer Contact-dependent Immune Cell Transcription.

BACKGROUND: Rejection requires cell-cell contact involving immune cells. Inferring the transcriptional programs of cell-cell interactions from single-cell RNA-sequencing (scRNA-seq) data is challenging as spatial information is lost. METHODS: We combined a CD45 pos enrichment strategy with Cellular Indexing of Transcriptomes and Epitopes by sequencing based quantification of leukocyte surface proteins to analyze cell-cell interactions in 11 human kidney transplant biopsies encompassing a spectrum of rejection diagnoses. scRNA-seq was performed using the 10X Genomics platform. We applied the sequencing physically interacting cells computational method to deconvolute the transcriptional profiles of heterotypic physically interacting cells. RESULTS: The 11 human allograft biopsies generated 31 203 high-quality single-cell libraries. Clustering was further refined by combining Cellular Indexing of Transcriptomes and Epitopes by sequencing data from 6 different leukocyte-specific surface proteins. Three of 6 doublet clusters were identified as physically interacting cell complexes; macrophages or dendritic cells bound to B cells or plasma cells; natural killer (NK) or T cells bound to macrophages or dendritic cells and NK or T cells bound to endothelial cells. Myeloid-lymphocyte physically interacting cell complexes expressed activated and proinflammatory genes. Lymphocytes physically interacting with endothelial cells were enriched for NK and CD4 T cells. NK cell-endothelial cell contact caused increased expression of endothelial proinflammatory genes CXCL9 and CXCL10 and NK cell proinflammatory genes CCL3 , CCL4 , and GNLY . CONCLUSIONS: The transcriptional profiles of physically interacting cells from human kidney transplant biopsies can be inferred from scRNA-seq data using the sequencing physically interacting cells method. This approach complements previous methods that estimate cell-cell physical contact from scRNA-seq data.

Steroid-sensitive nephrotic syndrome candidate gene CLVS1 regulates podocyte oxidative stress and endocytosis.

We performed next-generation sequencing in patients with familial steroid-sensitive nephrotic syndrome (SSNS) and identified a homozygous segregating variant (p.H310Y) in the gene encoding clavesin-1 (CLVS1) in a consanguineous family with 3 affected individuals. Knockdown of the clavesin gene in zebrafish (clvs2) produced edema phenotypes due to disruption of podocyte structure and loss of glomerular filtration barrier integrity that could be rescued by WT CLVS1 but not the p.H310Y variant. Analysis of cultured human podocytes with CRISPR/Cas9-mediated CLVS1 knockout or homozygous H310Y knockin revealed deficits in clathrin-mediated endocytosis and increased susceptibility to apoptosis that could be rescued with corticosteroid treatment, mimicking the steroid responsiveness observed in patients with SSNS. The p.H310Y variant also disrupted binding of clavesin-1 to α-tocopherol transfer protein, resulting in increased reactive oxygen species (ROS) accumulation in CLVS1-deficient podocytes. Treatment of CLVS1-knockout or homozygous H310Y-knockin podocytes with pharmacological ROS inhibitors restored viability to control levels. Taken together, these data identify CLVS1 as a candidate gene for SSNS, provide insight into therapeutic effects of corticosteroids on podocyte cellular dynamics, and add to the growing evidence of the importance of endocytosis and oxidative stress regulation to podocyte function.

APOL1 risk variants in kidney transplantation: a modulation of immune cell function.

APOL1 G1 and G2 variants are established risk factors for nondiabetic kidney disease. The presence of two APOL1 risk variants in donor kidneys negatively impacts kidney allograft survival. Because of evolutionary pressure, the APOL1 risk variants have become common in people from Africa and in those with recent African ancestry. APOL1 risk variant proteins are expressed in kidney cells and can cause toxicity to these cells. In this issue of the JCI, Zhang, Sun, and colleagues show that recipient APOL1 risk variants negatively affect kidney allograft survival and T cell-mediated rejection rates, independent of donor APOL1 genotype or recipient ancestry. The authors provide evidence that APOL1 risk variants play an immunomodulatory role in T cells and NK cells in the setting of kidney transplantation. These findings have important clinical implications that require further investigation.

Monocytes and Macrophages in Kidney Transplantation and Insights from Single Cell RNA-Seq Studies.

Single-cell RNA sequencing (scRNA-seq) is a powerful technology that allows for the identification of minority cell types in complex tissues, such as immune cells in the kidney. Previously, gene expression from infrequent cell types was missed using bulk RNA-sequencing methods due to an averaging effect. Additionally, scRNA-seq facilitates assignment of cell origin in a sample, a shortcoming of previous bulk sequencing technologies. Thus, scRNA-seq is ideal to study the immune cell landscape and the alloimmune response in the human kidney transplant. However, there are few studies published to date. Macrophages are known to play an important role in health and disease in the kidney. Furthermore, it is known that macrophages play key roles in rejection of the kidney transplant. The definition, ontogeny, and function of these cells is complex and nomenclature has evolved as new technologies have become available. In this review, an overview is provided of monocyte and macrophage nomenclature, ontogeny, and function, with a specific focus on kidney transplantation, and including novel scRNA-seq findings. scRNA-seq offers an unbiased transcriptional approach to defining macrophages and provides insights into macrophage ontogeny and function not possible with contemporary methods.

Choice of Acid Suppressant Therapy and Long-Term Graft Outcomes After Kidney Transplantation.

STUDY OBJECTIVE: The purpose of this study was to comprehensively evaluate the long-term adverse effects of proton pump inhibitors (PPIs) compared with histamine-2 receptor antagonists (H2RAs) in kidney transplant recipients. METHODS: This retrospective cohort compared 582 patients treated with PPI with 705 patients treated with H2RA and evaluated adverse effects throughout their course of acid suppressant therapy to a maximum of nine years posttransplant. The primary outcome of interest was renal function at 1 year posttransplant; secondary outcomes included renal function at 30 days, 3, 5, and 9 years posttransplant as well as rejection, electrolyte and laboratory abnormalities, osteoporosis, pneumonia, and Clostridium difficile infections. RESULTS: Renal function did not significantly differ at any timepoint posttransplant. Rejection rates and Clostridium difficile infections were similar between groups; osteoporosis and pneumonia rates were numerically higher in the PPI treated arm but did not reach statistical significance. Proton pump inhibitor (PPI) treated patients were more likely to experience hypomagnesemia requiring supplementation. High dose PPI treated patients had significantly higher rates of pneumonia and osteoporosis compared with H2RA treated patients. Patients were maintained on PPI therapy for an average of 5 years and H2RA therapy for 3 years posttransplant, the majority without a clear indication for therapy. CONCLUSIONS: There was no difference in renal function, rejection, or graft loss between PPI and H2RA treated patients. The majority of patients were maintained on PPI therapy for several years posttransplant without a clear indication; critical evaluation of ongoing need for acid suppressant therapy in the posttransplant course should be an area of future focus.

Poor Outcomes With the Use of Checkpoint Inhibitors in Kidney Transplant Recipients.

BACKGROUND: Checkpoint inhibitors are now frequently used for oncologic conditions. The impact of these therapies in solid organ transplant recipients was not assessed in clinical trials. Subsequent case reports highlight the major detrimental interactions of checkpoint inhibitors and the high risk of allograft rejection with their use. Patient outcomes have not been assessed in long-term follow-up. METHODS: We conducted a retrospective review of kidney transplant recipients with metastatic cancer who received checkpoint inhibitors at a single center between April 2015 and May 2018. RESULTS: Six kidney transplant recipients with metastatic cancers that were not responding to first-line treatments met study criteria. These include 2 with squamous cell cancers, 2 with melanoma, 1 with renal cell cancer, and 1 with adenocarcinoma of the lung. Four patients received anti-programmed cell death protein-1 (PD-1) antibody and 2 received a combination of anticytotoxic T-lymphocyte-associated protein 4 and anti-PD-1 antibodies. Three out of 6 patients developed acute kidney injury. Two were biopsy-proven acute rejections with subsequent graft failures. The third was attributed to rejection, but improved after discontinuing the checkpoint inhibitor. Five out of 6 patients had cancer progression and only 1 patient had remission. CONCLUSIONS: Providers and patients need to be aware of the high risk of rejection and the poor remission rate with the use of checkpoint inhibitors in kidney transplant patients. More research is warranted to assess the optimal maintenance immunosuppression during the use of checkpoint inhibitor therapy that would not diminish the chances of remission.