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Chronic kidney transplant rejection represents a major cause of renal allograft loss, contributing to increased morbidity and mortality in patients with end-stage kidney disease. This condition involves immune-mediated damage to the transplanted kidney, primarily through T-cell-mediated rejection (TCMR) or antibody-mediated rejection (AMBR), leading to progressive graft dysfunction. Chronic rejection typically develops months to years posttransplantation, with risk factors including prior acute rejection episodes, human leukocyte antigen mismatches, and nonadherence to immunosuppressive therapy. Histopathological lesions, such as interstitial fibrosis, tubular atrophy, and transplant glomerulopathy, characterize chronic rejection, distinguishable from other causes like calcineurin inhibitor toxicity or recurrent disease. Diagnosis relies on kidney biopsy, serum creatinine trends, donor-specific antibody (DSA) testing, and imaging. Management focuses on optimizing immunosuppression, addressing acute rejection to prevent chronicity, and monitoring graft function. Delayed diagnosis or misclassification of TCMR versus ABMR worsens outcomes, as these require distinct treatments, such as T-cell-targeted therapies for TCMR or plasmapheresis for ABMR.

Chronic kidney transplant rejection represents a major cause of renal allograft loss, contributing to increased morbidity and mortality in patients with end-stage kidney disease. This condition involves immune-mediated damage to the transplanted kidney, primarily through T-cell-mediated rejection (TCMR) or antibody-mediated rejection (AMBR), leading to progressive graft dysfunction. Chronic rejection typically develops months to years posttransplantation, with risk factors including prior acute rejection episodes, human leukocyte antigen mismatches, and nonadherence to immunosuppressive therapy. Histopathological lesions, such as interstitial fibrosis, tubular atrophy, and transplant glomerulopathy, characterize chronic rejection, distinguishable from other causes like calcineurin inhibitor toxicity or recurrent disease. Diagnosis relies on kidney biopsy, serum creatinine trends, donor-specific antibody (DSA) testing, and imaging. Management focuses on optimizing immunosuppression, addressing acute rejection to prevent chronicity, and monitoring graft function. Delayed diagnosis or misclassification of TCMR versus ABMR worsens outcomes, as these require distinct treatments, such as T-cell-targeted therapies for TCMR or plasmapheresis for ABMR. This educational activity enhances clinicians’ competence in evaluating and managing chronic kidney transplant rejection by reviewing its epidemiology, immune mechanisms, and histopathological features. Clinicians learn to differentiate T-cell-mediated from antibody-mediated rejection using biopsy and DSA testing, ensuring accurate diagnosis and tailored treatment. The course covers strategies to prevent acute rejection, optimize immunosuppression, and monitor graft function to mitigate chronic rejection risk. Participants learn to interpret biopsy findings, such as interstitial fibrosis and transplant glomerulopathy, and distinguish rejection from other allograft dysfunction causes. Interprofessional collaboration with nephrologists, pathologists, transplant coordinators, and pharmacists enhances patient outcomes by ensuring precise diagnosis through biopsy analysis, timely immunosuppressive adjustments, and comprehensive patient monitoring. This team approach reduces diagnostic delays, improves treatment efficacy, and supports long-term graft survival, ultimately enhancing quality of life for patients with chronic kidney transplant rejection.

This educational activity enhances clinicians’ competence in evaluating and managing chronic kidney transplant rejection by reviewing its epidemiology, immune mechanisms, and histopathological features. Clinicians learn to differentiate T-cell-mediated from antibody-mediated rejection using biopsy and DSA testing, ensuring accurate diagnosis and tailored treatment. The course covers strategies to prevent acute rejection, optimize immunosuppression, and monitor graft function to mitigate chronic rejection risk. Participants learn to interpret biopsy findings, such as interstitial fibrosis and transplant glomerulopathy, and distinguish rejection from other allograft dysfunction causes. Interprofessional collaboration with nephrologists, pathologists, transplant coordinators, and pharmacists enhances patient outcomes by ensuring precise diagnosis through biopsy analysis, timely immunosuppressive adjustments, and comprehensive patient monitoring. This team approach reduces diagnostic delays, improves treatment efficacy, and supports long-term graft survival, ultimately enhancing quality of life for patients with chronic kidney transplant rejection. Objectives: Identify histopathological lesions, such as interstitial fibrosis and transplant glomerulopathy, indicative of chronic kidney transplant rejection. Evaluate the characteristic histopathological lesions of chronic active antibody-mediated and T-cell-mediated rejection. Assess the current diagnostic approach to a patient with suspected chronic kidney transplant rejection. Collaborate among the interprofessional team in preventing and managing chronic kidney transplant rejection. Access free multiple choice questions on this topic.

Kidney transplantation is currently the definitive treatment for patients with end-stage kidney disease (ESKD). Compared to dialysis, kidney transplantation is associated with reduced mortality and improved quality of life.[1] Rejection of the kidney is one of the leading causes of allograft loss. Other causes of kidney allograft loss include recurrent glomerular disease, interstitial fibrosis, calcineurin inhibitor (CNI) toxicity, and BK virus-associated nephropathy.[2][3][4] Kidney allograft rejection can be subdivided into hyperacute, accelerated, acute, and chronic rejection.[5] Hyperacute rejection occurs within minutes of transplantation and is caused by preformed donor-specific antibodies. Acute rejection occurs within one year and can be T-cell or antibody-mediated. In 2020, the rate of acute rejection was estimated at 6% to 11%.[6] Chronic kidney transplant rejection (CKTR) refers to graft failure and rejection beyond 1 year post-transplant, in the absence of acute rejection, drug toxicity (particularly CNIs), and other causes of nephropathy. Chronic kidney injury after transplantation was previously often labeled as chronic allograft nephropathy or "CAN” a term that has been discontinued since 2005, replaced by biopsy-specific findings that may point to chronic immune injury or interstitial fibrosis and tubular atrophy (IFTA).[7][8]

CKTR can be due to cell-mediated or humoral immune response and usually occurs in patients with insufficient immunosuppression or medication nonadherence.[9] Acute rejection (AR) is one of the risk factors for late kidney allograft loss. El Ters et al studied the effect of AR on graft histology in a cohort of 797 renal transplant individuals without donor-specific antibodies (DSA) during the time of transplant. AR was the etiology in 15.2% of patients. One and 2-year biopsies of patients with a history of AR were associated with more inflammation, fibrosis, transplant glomerulopathy (TG), and early allograft loss (see Images. Renal Allograft With Endothelial Injury; Renal Allograft With Mononuclear Cells; Renal Allograft With Inflammatory Infiltrate).[10] Lorentz et al further studied the effect of immunosuppression nonadherence on graft histology. Nonadherence with immunosuppressive therapy at 5 years posttransplant was associated with increased fibrosis and inflammation but not TG.[11] Nonimmune risk factors for late allograft loss include delayed graft function, immunosuppressive medication toxicity, recurrence of primary kidney disease, diabetes, hypertension, and hyperlipidemia.[12][13] These factors can potentiate the normal aging process of transplanted kidneys, exacerbate chronic injury, and further contribute to graft loss.

Alloimmunity is one of the most frequent causes of graft loss. Nankivell et al reported a 25.8% incidence of subclinical rejection at 1-year post-transplant.[14] The Deterioration of Kidney Allograft Function Study (DeKAF) group biopsied 173 subjects (7.3 ± 6.0 years posttransplant). Subjects who were positive for DSA, complement component C4d deposition on biopsy (discussed later), or both had an increased risk of kidney allograft failure 2 years posttransplant.[15] Sellares et al studied the causes of allograft loss in 60 patients with failure out of a total cohort of 315 patients.[2] The incidence of antibody-mediated rejection increased over time in those with failure, especially after 5 years posttransplantation. Protocol biopsies by Stegall et al. reported a prevalence of moderate-severe fibrosis in 13% and 17% of patients at one and 5 years post-transplant, respectively. Moreover, 23% of allografts that had a biopsy at 1 and 5 years posttransplant showed progression in fibrosis from mild to severe forms.[16] Only 5% of tacrolimus-treated patients showed evidence of TG, a lesion characteristic of chronic antibody-mediated rejection, suggesting that using tacrolimus may help prevent CKTR.[16]

CKTR is, by definition, immune-mediated and generally divides into chronic active antibody-mediated rejection (CAAMR) and chronic active T-cell-mediated rejection (CATMR).[9] CAAMR occurs due to DSA against human leukocyte antigens (HLA) and non-HLA antigens. DSAs can directly and indirectly damage the endothelium through complement-mediated activation and inflammatory cell recruitment. An extended alloreactive immune response over a prolonged period leads to microvascular remodeling of the glomerular and peritubular capillaries, microvascular inflammation, and arterial intimal fibrous thickening. Complement activation, identified by C4d deposition in the peritubular capillaries, also contributes to microvascular inflammation. However, C4d positivity was eliminated as a requirement for diagnosing CAAMR after C4d-negative antibody-mediated kidney rejection emerged.[8][9] Moreover, Loupy et al reviewed 157 protocol biopsies obtained at 3 and 12 months posttransplant from 80 positive DSA recipients. C4d staining was not a sensitive indicator of microvascular inflammation or a marker of increased risk of progression to CAAMR.[17] Cell-mediated injury can involve both the renal tubulointerstitial and arterial components. Antigen-presenting cells present donor antigens to T-cells, which then cross the microcirculation of the donor's kidney and enter the interstitium. Several cytokines are then produced, including interferon-gamma and transforming growth factor-beta, triggering a cascade of inflammation leading to tubulitis, the hallmark feature of CATMR.[18] T-cell-mediated injury can also involve the arteries, leading to arterial inflammation and intimal fibrosis.[8] Ultimately, progressive interstitial fibrosis and tubular atrophy may be a late consequence of CATMR.

Renal biopsies demonstrate that CKTR affects all kidney compartments, including the arteries, tubulointerstitium, and glomeruli. When comparing the Banff criteria for acute and chronic active antibody-mediated rejection, the criterion that differs is the need for histologic evidence of active lesions versus chronic tissue injury, respectively. Histologic evidence of chronic antibody-mediated rejection includes findings resulting from endothelial injury. Transplant glomerulopathy, characterized by duplication of glomerular basement membranes, is the consequence of glomerulitis, a lesion of active antibody-mediated rejection. Similarly, multilayering of peritubular capillary basement membranes results from persistent peritubular capillaritis. New onset intimal fibrosis of arteries results from damage to the tunica intima in the acute phase of humoral injury.[8][9] CATMR involves mainly the tubulointerstitium and arteries, characterized by interstitial inflammation and tubulitis in areas of interstitial fibrosis and non-scarred cortex, and chronic allograft arteriopathy, respectively. Tubulointerstitial inflammation leads to interstitial fibrosis and tubular atrophy (IFTA). Chronic allograft arteriopathy manifests primarily as arterial intimal fibrosis with infiltrating mononuclear cells. Since DSAs in CAAMR can stimulate fibrosis of the arterial intima, it is challenging to differentiate arteriopathy secondary to CAAMR and CATMR on the histological level alone. However, leukocytes within the sclerotic intima favor chronic antibody-mediated rejection if there is no prior history of T-cell-mediated rejection.[8][9] Banff Classification System The Banff classification, originally founded in 1991 and later updated in 2007, 2009, 2013, and 2017, established specific criteria for diagnosing kidney allograft rejection.[8] Based on the Banff update from 2017, and incorporating changes from 2019 and 2022,[19][20] CAAMR and CATMR are diagnosed and classified as follows: I) CAAMR (all 3 criteria must be present) 1. Histological evidence of chronic tissue injury (at least 1 of the following): Transplant glomerulopathy (cg >0) without evidence of thrombotic microangiopathy or glomerulonephritis, including changes evident by electron microscopy alone (eg, cg1a) Severe multilayering of the peritubular capillary basement membranes on electron microscopy

1. Histological evidence of chronic tissue injury (at least 1 of the following): Transplant glomerulopathy (cg >0) without evidence of thrombotic microangiopathy or glomerulonephritis, including changes evident by electron microscopy alone (eg, cg1a) Severe multilayering of the peritubular capillary basement membranes on electron microscopy 2. Evidence of antibody interaction with vascular endothelium (one or more of the following): Linear C4d staining in peritubular capillaries or medullary vasa recta (note that there are different thresholds for positive C4d depending on test modality; IF on frozen section (C4d2 or C4d3) and immunohistochemistry on paraffin sections (C4d >0). Moderate or severe microvascular inflammation in the absence of glomerulonephritis.  In the presence of interstitial inflammation greater than 10%, or infection, ptc >/= 2 is insufficient for this criterion; thus, g must be 1 or greater. Increased gene expression of gene transcripts strongly suggests antibody-mediated rejection. 3. Positive DSA antibodies to HLA and non-HLA antigens (including ABO antibodies in ABO incompatible cases). II) CATMR - is classified as follows (after ruling out other causes of IFTA, including pyelonephritis or BK nephropathy): Grade IA: More than 25% interstitial inflammation of the total cortex (ti ≥2), and inflammation involivng >25% of areas of interstitial fibrosis and tubular atrophy (iIFTA >/=2), with moderate tubulitis in 1 or more tubules, excluding severely atrophic tubules (t2). Grade IB: More than 25% interstitial inflammation of the total cortex (ti  ≥2), and inflammation involving >25% of areas of interstitial fibrosis and tubular atrophy (iIFTA >/=2), with severe tubulitis in 1 or more tubules, excluding severely atrophic tubules (t3). Grade II: Chronic allograft arteriopathy indicated by neointima formation, intimal arterial fibrosis, and mononuclear infiltration

The diagnosis of CKTR begins with clinical evaluation, including a thorough history and a comprehensive physical exam. Important items to ask about in the history include medication nonadherence, recurrence of the original nephropathy, prior transplantation, prior AR, and baseline HLA sensitization. Unexplained decreases in immunosuppression levels can also point towards nonadherence as a cause for CKTR.[21] Medication nonadherence can also be due to health insurance problems. Asking about insurance coverage of immunosuppression medications is crucial. Medication history is also essential, as many drugs can affect the metabolism of immunosuppression medications, decreasing or increasing blood levels, leading to rejection and toxicity, respectively. Physical examination findings are usually nonspecific but may include hypertension, lower extremity edema, or fatigue. Symptoms of severe AR, such as fever or graft tenderness, are typically absent in CKTR. More progressive stages of rejection can manifest as signs of kidney failure and uremia, including oliguria, nausea, vomiting, a metallic taste in the mouth, pericardial friction rub, and asterixis.

As discussed above, the diagnosis of CKTR starts with clinical evaluation. The Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend biweekly clinic visits 3 to 6 months post-transplant, monthly visits 7 to 12 months post-transplant, and every 2 to 3 months after that.[22] Laboratory tests can help differentiate various causes of allograft dysfunction. Kidney allograft function assessed by serum creatinine (Cr) and estimated glomerular filtration rate (eGFR) requires measurement at or before each visit. The eGFR is suggested to be a more accurate indicator and predictor of graft function and long-term graft loss, respectively.[23][24] Iothalamate GFR and cystatin C can also be used to evaluate graft function, especially in situations where Cr may be inaccurate due to extremes of muscle mass. Proteinuria over 500 mg/day may be an early marker of chronic kidney allograft dysfunction.[25] DSA is typically measured in an HLA laboratory using flow cytometry and the single antigen bead technique. Positive DSA is a relatively sensitive marker for CAAMR. A decrease or disappearance of DSA can be used to monitor response to treatment.[23] DSA, however, may not always correlate with tissue injury. In the Deterioration of Kidney Allograft Function (DeKAF) trial, C4d-positive biopsies showed an equal risk of graft failure regardless of the presence or absence of DSA.[15] De novo DSA (dnDSA) formation after transplantation has been implicated as a major cause of chronic graft loss and can be detected before graft dysfunction ensues. Prospective monitoring for dnDSA can provide an opportunity for early treatment before irreversible graft injury occurs.[26]

DSA is typically measured in an HLA laboratory using flow cytometry and the single antigen bead technique. Positive DSA is a relatively sensitive marker for CAAMR. A decrease or disappearance of DSA can be used to monitor response to treatment.[23] DSA, however, may not always correlate with tissue injury. In the Deterioration of Kidney Allograft Function (DeKAF) trial, C4d-positive biopsies showed an equal risk of graft failure regardless of the presence or absence of DSA.[15] De novo DSA (dnDSA) formation after transplantation has been implicated as a major cause of chronic graft loss and can be detected before graft dysfunction ensues. Prospective monitoring for dnDSA can provide an opportunity for early treatment before irreversible graft injury occurs.[26] Doppler ultrasonography (US) is a non-invasive and inexpensive tool for assessing kidney allograft vasculature. Resistance indices exceeding 0.8 at three months are associated with deterioration in graft function.[27] Contrast-enhanced US (CES) can help detect a decrease in graft function before the resistance index increases.[28] CES uses gas microbubbles to determine vascular perfusion. After intravenous contrast application, a flush with an increased mechanical index leads to the detection of kidney perfusion through “burst imaging.” One analysis showed that allograft perfusion was related to serum creatinine levels. CES evaluation of blood flow was also more sensitive, specific, and accurate than determining blood flow through conventional indices.[28]

Doppler ultrasonography (US) is a non-invasive and inexpensive tool for assessing kidney allograft vasculature. Resistance indices exceeding 0.8 at three months are associated with deterioration in graft function.[27] Contrast-enhanced US (CES) can help detect a decrease in graft function before the resistance index increases.[28] CES uses gas microbubbles to determine vascular perfusion. After intravenous contrast application, a flush with an increased mechanical index leads to the detection of kidney perfusion through “burst imaging.” One analysis showed that allograft perfusion was related to serum creatinine levels. CES evaluation of blood flow was also more sensitive, specific, and accurate than determining blood flow through conventional indices.[28] A biopsy is imperative for diagnosing CKTR. Graft histology (as described previously) provides visual evidence of the underlying pathology of graft dysfunction. C4d complement fragment deposition in the peritubular capillaries could be a marker for antibody-mediated tissue injury.[21] Although C4d complement fragment deposition can help diagnose C4d-negative antibody-mediated rejection, it is also well recognized.[17][29] Genetic analysis of biopsy tissue has also been suggested to aid the diagnosis of allograft rejection in conjunction with histology. Researchers have identified increased expression of genes primarily related to natural killer cells and microvascular inflammation in both antibody-mediated and T-cell-mediated rejection. Immunostaining can help differentiate antibody and T-cell-mediated rejection, with CD56 and CD68 positivity linked more to antibody-mediated rejection.[30] Recently, noninvasive tests have emerged as tools that allow for risk stratification and guide decisions regarding whether or not to perform a biopsy, especially in high-risk individuals. These tests include tissue-based analysis (Formalin Fixed Paraffin embedded “FFPE”) and body fluid assays (AlloSure, Prospera).[31][32] To date, these noninvasive tests are not sensitive or specific. Graft biopsy remains the gold standard procedure to diagnose graft rejection.

The management of CKTR remains challenging, mainly due to irreversibility at diagnosis. Management, therefore, focuses on the prevention and early management of AR rather than treating CKTR. Adequacy of immunosuppression and patient adherence are pivotal for preventing AR, which later translates into a lower incidence of CKTR. Optimizing HLA matching reduces the chances of early allograft injury, decreasing the risk of chronic allograft loss.[33] Moreover, early treatment of acute antibody-mediated rejection with intravenous immunoglobulin, plasmapheresis, or steroids will reduce the risk of chronic allograft loss.[10] Most immunosuppressive regimens in the United States include a CNI, an antimetabolite, and corticosteroids. Although extremely effective, CNIs carry a high risk of chronic nephrotoxicity. Two suggested methods to balance efficacy and toxicity are (1) Guiding dosage by monitoring blood drug levels and (2) CNI sparing strategies. The four main approaches to minimize CNI exposure are CNI minimization, conversion, withdrawal, and avoidance. CNI Minimization: Minimization refers to lowering target blood trough levels of CNIs, with or without another immunosuppressive agent. A systematic review and meta-analysis showed that CNI minimization was associated with a relatively low risk of AR and overall improved allograft function.[34] The timing of CNI minimization was also studied. CNI minimization during the first six months post-transplant reduced the incidence of rejection compared to reducing CNI doses in the second 6 months post-transplant. No head-to-head trials, however, were conducted to compare early and late minimization directly. Combining low-dose CNI with mycophenolic acid (MPA) preparations also reduced the risk of AR with no difference in mortality. Pairing CNI minimization with a mammalian target of rapamycin (mTOR) inhibitor (such as sirolimus or everolimus) did not increase the risk of biopsy-proven AR. This led to an improvement in kidney function in some studies. It is worth noting, however, that full-dose CNI plus mTOR inhibitor therapy increases the risk of nephrotoxicity.[34]

Combining low-dose CNI with mycophenolic acid (MPA) preparations also reduced the risk of AR with no difference in mortality. Pairing CNI minimization with a mammalian target of rapamycin (mTOR) inhibitor (such as sirolimus or everolimus) did not increase the risk of biopsy-proven AR. This led to an improvement in kidney function in some studies. It is worth noting, however, that full-dose CNI plus mTOR inhibitor therapy increases the risk of nephrotoxicity.[34] CNI  Conversion: Conversion refers to switching from CNI to another maintenance drug. Converting from CNI to an mTOR inhibitor improved kidney function, which was observed more with the conversion from cyclosporine than tacrolimus.[34] Conversion to an mTOR inhibitor was also associated with a lower cytomegalovirus (CMV) infection risk.[34] Conversion to sirolimus showed better outcomes in patients with GFR exceeding 40 ml/min with less proteinuria, suggesting that conversion should occur before significant parenchymal damage.[35] Grimbert et al. suggested that early conversion to mTOR inhibitors within one year was associated with increased production of dnDSA, which increased the risk of antibody-mediated rejection. Therefore, conversion to mTOR inhibitor therapy with the elimination of CNI therapy should be performed with great caution and may increase the risk of CKD. Late conversion after one year was not associated with increased dsDNA.[36] Evidence from studies of conversion to azathioprine, mycophenolate sodium, and belatacept was insufficient to conclude.[34] CNI  Withdrawal: Withdrawal refers to tapering CNIs until they are completely discontinued. CNI withdrawal with either MPA or mTOR inhibitor-based regimens was associated with an increased risk of rejection. Early withdrawal (<6 months post-transplant) was associated with an increased risk of graft loss, with insufficient evidence for both rejection and a decrease in renal function. Late withdrawal with the continuation of MPA preparations was associated with an overall greater risk of rejection.[34] CNI withdrawal from azathioprine-based regimens was also associated with increased rejection.[35]

CNI  Withdrawal: Withdrawal refers to tapering CNIs until they are completely discontinued. CNI withdrawal with either MPA or mTOR inhibitor-based regimens was associated with an increased risk of rejection. Early withdrawal (<6 months post-transplant) was associated with an increased risk of graft loss, with insufficient evidence for both rejection and a decrease in renal function. Late withdrawal with the continuation of MPA preparations was associated with an overall greater risk of rejection.[34] CNI withdrawal from azathioprine-based regimens was also associated with increased rejection.[35] CNI  Avoidance: Avoidance refers to CNI-free regimens planned from the start. Initial trials to avoid CNIs while using daclizumab or anti-thymocyte globulin were associated with an increased risk of AR, which required reintroduction of CNIs in some patients.[35] Sirolimus-based immunosuppression regimens were also compared to CNI-based regimens. Comparing sirolimus to tacrolimus in MPA-based regimens showed an increased risk of graft loss. Sirolimus, however, was associated with improved kidney function and reduced risk of CMV infection.[34] Belatacept, a novel fusion protein that inhibits T-cell activation, was also compared to CNI-based regimens. Vincenti et al. randomized patients into three groups: a cyclosporine, an intensive belatacept, and a less intensive belatacept-based regimen. Patients were followed for seven years. Patients on belatacept-based regimens showed a 43% reduction in risk of graft loss and death, compared to cyclosporine. Kidney function improved in both belatacept-based regimens, while it declined with cyclosporine.[37]

Belatacept, a novel fusion protein that inhibits T-cell activation, was also compared to CNI-based regimens. Vincenti et al. randomized patients into three groups: a cyclosporine, an intensive belatacept, and a less intensive belatacept-based regimen. Patients were followed for seven years. Patients on belatacept-based regimens showed a 43% reduction in risk of graft loss and death, compared to cyclosporine. Kidney function improved in both belatacept-based regimens, while it declined with cyclosporine.[37] Non-immunological management of CKTR includes tight control of blood pressure and lipid levels.[12] The KDIGO recommends maintaining a blood pressure of over 130/80 in kidney transplant recipients.[25] Hyperlipidemia control with HMG-CoA reductase inhibitors also improves patient survival in kidney transplant recipients.[38] The data regarding angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) is contradictory, with a possible benefit in patients with chronic allograft dysfunction and proteinuria.[39][40][41][42] ACE inhibitors and ARBs should be used cautiously with CNIs due to an increased risk of hyperkalemia and azotemia. Some authors suggest a possible role for vitamin D in increasing graft survival; however, prospective studies are required to confirm efficacy.[13] Sodium-glucose cotransporter-2 inhibitors (SGL2i) are a trending class of medication that has been reported to be associated with better graft outcomes in diabetic and non diabetic kidney transplant recipients. SGL2i are associated with significantly reducing body weight, blood pressure, HbA1c, proteinuria, all-cause mortality, death-censored graft failure, and doubling serum creatinine in the kidney transplant population. [43] Moreover, SGLT2i and Glucagon-like peptide-1 receptor agonists (GLP1RA) are effective and safe in diabetic kidney transplant recipients with good outcomes.[44] Clinical trials are being conducted to confirm these findings and establish guidelines. [The Efficacy, Mechanism & Safety of Sodium Glucose Co-Transporter-2 Inhibitor & Glucagon-Like Peptide 1 Receptor Agonist Combination Therapy in Kidney Transplant Recipients (HALLMARK), NCT05938712 (2023). Available at: https://clinicaltrials.gov/study/NCT05938712.]

CKTR requires differentiation from other causes of late kidney allograft dysfunction, including: Calcineurin Inhibitor Toxicity Calcineurin inhibitors (CNIs) are among kidney transplantation's most widely used immunosuppressive medications. The introduction of cyclosporine and tacrolimus in the early 1980s and late 1990s improved clinical outcomes.[35] Acute CNI toxicity is associated with hypertension, thrombotic microangiopathy, and kidney dysfunction secondary to afferent arteriolar vasoconstriction and up-regulation of fibrotic cytokines such as transforming growth factor-beta. CNIs also increase the risk of hypertension, post-transplant type 2 diabetes, and hyperlipidemia, all of which are risk factors for late kidney allograft loss. Histologically, chronic CNI toxicity presents with IFTA, similar to what may present as a consequence of CKTR. Therefore, it is imperative to differentiate CKTR from CNI toxicity on biopsy. Histologically, CNI toxicity characteristically demonstrates striped interstitial fibrosis, medial arteriolar hyalinosis, tubular microcalcification, vacuolization, and atrophy. The presence of TG, peritubular capillary inflammation, and C4d deposition is all more specific for CKTR.[35] BK-Virus-Associated Nephropathy BK-virus-associated nephropathy (BKVAN) is also a significant cause of late allograft dysfunction and requires differentiation from CKTR. BKVAN occurs when the BK virus, a polyomavirus, propagates in the face of immunosuppression. Most transplant centers screen for BK virus in the bloodstream during the first year post-transplant, and particularly high-level viremia, higher than 10,000 copies/mL, tends to correlate with BKVAN. Histologically, BKVAN can present with tubulointerstitial scarring similar to CKTR. Suspicious biopsy findings need confirmation by polymerase chain reaction detection of viral DNA in the blood, characteristic intranuclear viral particle inclusions on electron microscopy, or BK virus detection using immunohistochemistry and in situ hybridization (eg, staining for the SV40 large T antigen).[3] Recurrent or De-Novo Glomerular Disease

BK-virus-associated nephropathy (BKVAN) is also a significant cause of late allograft dysfunction and requires differentiation from CKTR. BKVAN occurs when the BK virus, a polyomavirus, propagates in the face of immunosuppression. Most transplant centers screen for BK virus in the bloodstream during the first year post-transplant, and particularly high-level viremia, higher than 10,000 copies/mL, tends to correlate with BKVAN. Histologically, BKVAN can present with tubulointerstitial scarring similar to CKTR. Suspicious biopsy findings need confirmation by polymerase chain reaction detection of viral DNA in the blood, characteristic intranuclear viral particle inclusions on electron microscopy, or BK virus detection using immunohistochemistry and in situ hybridization (eg, staining for the SV40 large T antigen).[3] Recurrent or De-Novo Glomerular Disease Recurrent glomerulonephritis (GN) causes approximately 8.4% of late renal allograft loss.[3] Dense deposit disease and focal segmental glomerulonephritis (FSGS) are associated with a high risk of recurrence after transplantation, with a poor prognosis.[3] Differentiating GN from CKTR can be done by history, laboratory, and histopathology testing. A history of GN pre-transplantation with similar findings on urinary sediment posttransplantation supports a recurrence of GN, particularly if nephrotic range proteinuria is present, while DSA positivity supports CKTR. Histologically, both can be differentiated by light, electron, and immunofluorescence.

The prognosis of CKTR and late allograft loss depends on the degree of fibrosis and the reversibility of rejection at diagnosis. Denisov et al suggested that measuring hemoglobin, creatinine, and proteinuria 1 year post-transplant can be beneficial in the prognostication of kidney transplantation.[45] Indeed, a calculator for prognostication was patented and is available on the internet in Russian, with a reported 92% accuracy in the prediction of renal graft function three years post-transplant.[45] However, further studies are needed to confirm its accuracy.

The main complication of CKTR is allograft loss, which leads to kidney failure and possibly death, especially in patients who are poor candidates for repeat kidney transplantation. Patient complications include anxiety and depression, with an increased risk of mortality and worse quality of life with dialysis reinitiation. Kaplan et al reported a less than 40% chance of at least 10-year survival in patients with kidney allograft failure.[46] Cardiovascular disease is the most common cause of death, followed by infection, which is mainly due to prior exposure to immunosuppression medications.[47] The economic burden of rejection and dialysis re-initiation is also detrimental for both the patient and the community.[1]

Renal transplant recipients require counseling and education regarding each of the following: The importance of medication adherence in maintaining a healthy allograft and prolonging its viability The importance of regular follow-up with their transplant nephrologist The risk factors and causes of chronic kidney transplant rejection The signs and symptoms of chronic kidney transplant rejection The complications and consequences of chronic kidney transplant rejection The available treatment options for chronic kidney transplant rejection

Chronic kidney transplant rejection poses a risk of allograft loss, increasing patient morbidity and mortality. Acute rejection is a significant risk factor for chronic rejection. Thus, an interprofessional team approach to diagnosis and management is crucial. Interprofessional teams have been found to provide superior outcomes and may include transplant nephrologists, transplant surgeons, primary care providers, pharmacists, nurses, nutritionists, social workers, and other health care professionals. Understanding a patient's social support is particularly important. Evaluation starts with a thorough history-taking and the necessary lab tests ordered by the specialist/clinician. Immunosuppression medication levels need regular monitoring; this should include the services of a board-certified pharmacotherapy pharmacist. The pharmacist can also verify dosing and perform medication reconciliation. Renal ultrasonography is an inexpensive and non-invasive tool that can aid diagnosis. Noninvasive blood and body fluid tests such as Allosure and Prospera can assist with risk stratification. A biopsy is often necessary for definitive diagnosis and ruling out other causes of allograft injury. The management of chronic kidney transplant rejection remains challenging, mainly due to irreversibility at the time of diagnosis. Management, therefore, focuses on preventing and early managing acute rejection rather than treating chronic rejection. Patient adherence to immunosuppressive medications is essential in preventing acute rejection and late allograft loss; nursing staff are critical to following and assessing patient compliance. Improving healthcare professionals' knowledge of how to evaluate and treat this condition promptly will help improve patient outcomes. Early and effective communication between the patient, primary care clinician, pharmacist, community-based nephrologist, and transplant nephrologist is crucial for early diagnosis and treatment to prevent allograft loss. Transplantation nurses monitor patients, provide education, and document these for the team. These interprofessional case dynamics are vital to achieving optimal outcomes for patients with CKTR.