The value of extracorporeal photopheresis as an immunosuppression-modifying approach in solid organ transplantation: a potential solution to an unmet medical need.

Allograft rejection is a critical issue following solid organ transplantation (SOT). Immunosuppressive therapies are crucial in reducing risk of rejection yet are accompanied by several significant side effects, including infection, malignancy, cardiovascular diseases, and nephrotoxicity. There is a current unmet medical need with a lack of effective minimization strategies for these side effects. Extracorporeal photopheresis (ECP) has shown potential as an immunosuppression (IS)-modifying technique in several SOT types, with improvements seen in acute and recurrent rejection, allograft survival, and associated side effects, and could fulfil this unmet need. Through a review of the available literature detailing key areas in which ECP may benefit patients, this review highlights the IS-modifying potential of ECP in the four most common SOT procedures (heart, lung, kidney, and liver transplantation) and highlights existing gaps in data. Current evidence supports the use of ECP for IS modification following SOT, however there is a need for further high-quality research, in particular randomized control trials, in this area.

Tacrolimus's Time Below Therapeutic Range Is Associated With Acute Pancreatic Graft Rejection and the Development of De Novo Donor-specific Antibodies.

Tacrolimus is pivotal in pancreas transplants but poses challenges in maintaining optimal levels due to recipient differences. This study aimed to explore the utility of time spent below the therapeutic range and intrapatient variability in predicting rejection and de novo donor-specific antibody (dnDSA) development in pancreas graft recipients. This retrospective unicentric study included adult pancreas transplant recipients between January 2006 and July 2020. Recorded variables included demographics, immunosuppression details, HLA matching, biopsy results, dnDSA development, and clinical parameters. Statistical analysis included ROC curves, sensitivity, specificity, and predictive values. A total of 131 patients were included. Those with biopsy-proven acute rejection (BPAR, 12.2%) had more time (39.9% ± 24% vs. 25.72% ± 21.57%, p = 0.016) and tests (41.95% ± 13.57% vs. 29.96% ± 17.33%, p = 0.009) below therapeutic range. Specific cutoffs of 31.5% for time and 34% for tests below the therapeutic range showed a high negative predictive value for BPAR (93.98% and 93.1%, respectively). Similarly, patients with more than 34% of tests below the therapeutic range were associated with dnDSA appearance (38.9% vs. 9.4%, p = 0.012; OR 6.135, 1.346-27.78). In pancreas transplantation, maintaining optimal tacrolimus levels is crucial. Suboptimal test percentages below the therapeutic range prove valuable in identifying acute graft rejection risk.

Utility of SARS-CoV-2 Subgenomic RNA in Kidney Transplant Recipients Receiving Remdesivir.

INTRODUCTION: There is no reliable microbiological marker to guide responses to antiviral treatment in kidney transplant recipients (KTR) with COVID-19. We aimed to evaluate the dynamics of subgenomic RNA (sgRNA) RT-PCR before and after receiving treatment with remdesivir compared with genomic RNA (gRNA) RT-PCR and its use as a surrogate marker of viral replication. METHODS: We analyzed gRNA and sgRNA at baseline and after remdesivir treatment in KTR who received remdesivir for SARS-CoV-2 infection from November 2021 to February 2022. RESULTS: Thirty-four KTR received remdesivir for SARS-CoV-2 infection. The median time since transplantation was 80 months (IQR 3-321) and 75% of patients had previously received 3 doses of a mRNA SARS-CoV-2 vaccine. Three patients (8%) were classified with mild, 25 (73%) with moderate, and 6 (17%) with severe SARS-CoV-2 infection. Thirty-two (94%) patients received 5 doses of remdesivir and two patients received 2 doses. The median time between symptom onset to remdesivir treatment was 5 days (IQR 3-8.5). The median days of hospitalization were 6 (IQR 2-112). gRNA was positive in all patients at baseline and after remdesivir. Five (15%) patients had negative sgRNA at baseline and 20 (59%) after receiving remdesivir. Patients presenting with negative sgRNA at baseline were discharged from hospital in ≤ 6 days without complications. Moreover, those with negative sgRNA after remdesivir therapy did not require ICU admission and had favorable outcomes. Nevertheless, patients with positive sgRNA after antiviral treatment presented worse outcomes, with 47% requiring ICU admission and the three (9%) recorded deaths in the study were in this group. CONCLUSIONS: Based on these data, we hypothesize that sgRNA may have clinical utility to help monitor virologic response more accurately than gRNA in KTR who receive remdesivir. Moreover, patients with negative sgRNA at baseline may not require antiviral treatment and others presenting positive sgRNA at day 5 could benefit from prolonged or combined therapies.

European Consensus on the Management of Sensitized Kidney Transplant Recipients: A Delphi Study.

An increasing number of sensitized patients awaiting transplantation face limited options, leading to fatalities during dialysis and higher costs. The absence of established evidence highlights the need for collaborative consensus. Donor-specific antibodies (DSA)-triggered antibody-mediated rejection (AMR) significantly contributes to kidney graft failure, especially in sensitized patients. The European Society for Organ Transplantation (ESOT) launched the ENGAGE initiative, categorizing sensitized candidates by AMR risk to improve patient care. A systematic review assessed induction and maintenance regimens as well as antibody removal strategies, with statements subjected to the Delphi methodology. A Likert-scale survey was distributed to 53 European experts (Nephrologists, Transplant surgeons and Immunologists) with experience in kidney transplant recipient care. A rate ≥75% with the same answer was considered consensus. Consensus was achieved in 95.3% of statements. While most recommendations aligned, two statements related to complement inhibitors for AMR prophylaxis lacked consensus. The ENGAGE consensus presents contemporary recommendations for desensitization and immunomodulation strategies, grounded in predefined risk categories. The adoption of tailored, patient-specific measures is anticipated to streamline the care of sensitized recipients undergoing renal allografts. While this approach holds the promise of enhancing transplant accessibility and fostering long-term success in transplantation outcomes, its efficacy will need to be assessed through dedicated studies.

Corrigendum: Ex vivo normothermic preservation of a kidney graft from uncontrolled donation after circulatory death over 73 hours.

[This corrects the article DOI: 10.3389/fbioe.2023.1330043.].

Inhibition of BRD4 Attenuates ER Stress-induced Renal Ischemic-Reperfusion Injury.

Renal ischemia-reperfusion injury (IRI) leads to endoplasmic reticulum (ER) stress, thereby initiating the unfolded protein response (UPR). When sustained, this response may trigger the inflammation and tubular cell death that acts to aggravate the damage. Here, we show that knockdown of the BET epigenetic reader BRD4 reduces the expression of ATF4 and XBP1 transcription factors under ER stress activation. BRD4 is recruited to the promoter of these highly acetylated genes, initiating gene transcription. Administration of the BET protein inhibitor, JQ1, one hour after renal damage induced by bilateral IRI, reveals reduced expression of ATF4 and XBP1 genes, low KIM-1 and NGAL levels and recovery of the serum creatinine and blood urea nitrogen levels. To determine the molecular pathways regulated by ATF4 and XBP1, we performed stable knockout of both transcription factors using CRISPR-Cas9 and RNA sequencing. The pathways triggered under ER stress were mainly XBP1-dependent, associated with an adaptive UPR, and partially regulated by JQ1. Meanwhile, treatment with JQ1 downmodulated most of the pathways regulated by ATF4 and related to the pathological processes during exacerbated UPR activation. Thus, BRD4 inhibition could be useful for curbing the maladaptive UPR activation mechanisms, thereby ameliorating the progression of renal disease.

Long-Term Outcomes of Incidental Liver Malignancies in Simultaneous Liver-Kidney Transplant Recipients.

BACKGROUND: The pretransplant diagnosis of liver malignancies in nodular cirrhotic livers remains a diagnostic challenge despite current advances. Although the prognostic impact of incidental hepatocellular carcinoma (HCC) or intrahepatic cholangiocarcinoma (iCC) in liver transplant recipients is well documented, there are no data on the impact in simultaneous liver kidney transplant (LKT) recipients. METHODS: This is a single-center observational, retrospective study of all LKT performed from May 1993 to April 2022. Among these patients, demographic data, immunosuppressive therapy, rejection episodes, and prevalence of incidental HCC or iCC were evaluated. RESULTS: One hundred eight LKTs were performed and 6 were excluded. There were 13 patients with incidental carcinomas in the explanted liver: one of them with both an HCC and iCC, one with an iCC, and the remaining with an HCC. One case of iCC died. No other recurrences occurred. There were no cases of incidental HCC nor iCC in patients with a hereditary or metabolic LKT indication. We found no differences in the 5-year patient survival, and death-censored kidney and liver graft survival rates for those LKT with an incidental HCC and those without it (76.9% vs 84.2%, P = .5; 100% vs 91.6%, P = .28; and 100% vs 94.7%, P = 0.39, respectively). Finally, there were no significant associations between explant carcinoma and rejections of the liver (7.7% vs 17.9%, P = .34) or kidney graft (0% vs 16.8%, P = 0.11). CONCLUSION: Despite a high prevalence of incidental HCC or iCC, patient, kidney, and liver graft 5-year survival were unaffected by incidental HCC.

Tubulo-interstitial inflammation increases the risk of graft loss after the recurrence of IgA nephropathy.

Background: Immunoglobulin A nephropathy (IgAN) is the most frequent recurrent disease in kidney transplant recipients and its recurrence contributes to reducing graft survival. Several variables at the time of recurrence have been associated with a higher risk of graft loss. The presence of clinical or subclinical inflammation has been associated with a higher risk of kidney graft loss, but it is not precisely known how it influences the outcome of patients with recurrent IgAN. Methods: We performed a multicentre retrospective study including kidney transplant recipients with biopsy-proven recurrence of IgAN in which Banff and Oxford classification scores were available. 'Tubulo-interstitial inflammation' (TII) was defined when 't' or 'i' were ≥2. The main endpoint was progression to chronic kidney disease (CKD) stage 5 or to death censored-graft loss (CKD5/DCGL). Results: A total of 119 kidney transplant recipients with IgAN recurrence were included and 23 of them showed TII. Median follow-up was 102.9 months and 39 (32.8%) patients reached CKD5/DCGL. TII related to a higher risk of CKD5/DCGL (3 years 18.0% vs 45.3%, log-rank 7.588, P = .006). After multivariate analysis, TII remained related to the risk of CKD5/DCGL (HR 2.344, 95% CI 1.119-4.910, P = .024) independently of other histologic and clinical variables. Conclusions: In kidney transplant recipients with IgAN recurrence, TII contributes to increasing the risk of CKD5/DCGL independently of previously well-known variables. We suggest adding TII along with the Oxford classification to the clinical variables to identify recurrent IgAN patients at increased risk of graft loss who might benefit from intensified immunosuppression or specific IgAN therapies.

Midnight Cortisol is Associated with Changes in Systolic Blood Pressure and Diabetic Neuropathy in Subjects with Type 1 Diabetes Undergoing Simultaneous Kidney-Pancreas Transplantation.

INTRODUCTION: An increased midnight cortisol (MC) has been described in end-stage kidney disease (ESKD) and type 1 diabetes (T1D). Lower circulating levels of the cytokine soluble tumor necrosis factor (TNF)-like weak inducer of apoptosis (sTWEAK) have been found in T1D and ESKD and associated with cardiovascular (CV) events in the latter. We aimed to study MC and sTWEAK in simultaneous pancreas-kidney transplant (SPKT) recipients, and the association of these markers with CV risk factors and transplant outcomes. METHODS: This was a retrospective cohort study including subjects with T1D who received a first SPKT between 2008 and 2020. MC and sTWEAK at baseline were correlated with CV risk factors and evolution 1 year after SPKT. RESULTS: We included 29 subjects (58.6% women, mean age 43.5 ± 7.5 years, diabetes duration 31.9 ± 9.4 years). Systolic blood pressure (SBP) increased directly with MC quartiles, despite similar hypertension prevalence (p < 0.05). At 1 year, antihypertensive treatment was deintensified in those in lower MC quartiles (p < 0.05). Diabetic neuropathy prevalence decreased progressively in higher cortisol quartiles (p for trend = 0.005). Low MC was associated with delayed kidney graft function (p for trend = 0.044), and high sTWEAK with kidney graft rejection (p for trend = 0.018). In multivariate analyses, MC (standardized-ß 0.505, p = 0.004) and age (standardized-ß - 0.460, p = 0.040) were independently correlated with SBP, and MC was independently associated with the presence of diabetic neuropathy (OR 0.633, 95% CI 0.425-0.944, p = 0.025), adjusted for confounders. CONCLUSIONS: In this exploratory study, lower MC was associated with a lower baseline SBP, an improvement of antihypertensive treatment 1 year after transplant, and a higher diabetic neuropathy prevalence in SPKT recipients.

Validation of the Back-table Graft Arterial Anastomosis between the Splenic Artery and Superior Mesenteric Artery: Arterial Complications after a 21-year Single-center Experience of Pancreas Transplantation.

OBJECTIVE: To determine the role of the arterial splenomesenteric anastomosis (ASMA) vascular reconstruction technique in terms of arterial vascular complications in pancreas transplant (PT) recipients. SUMMARY BACKGROUND DATA: The ASMA technique was first described in 1992 by Hospital Clínic Barcelona group. Regardless that the iliac Y-graft technique is the most frequently used worldwide, evidence of arterial complications and implications of using a different back-table reconstruction is conspicuously absent in the literature. METHODS: Descriptive review of 407 PTs performed at a single center (1999-2019) by analyzing the type of arterial reconstruction technique, focusing on ASMA. The endpoints were the management of arterial complications and long-term patient and graft survival. RESULTS: ASMA was performed in 376 cases (92.4%) and a Y-graft in 31 cases (7.6%). A total of 34 arterial complications (8.3%) were diagnosed. In the ASMA group (n=30, 7.9%) they comprised: 15 acute thrombosis; 4 stenosis; 1 pseudoaneurysm and 10 diverse chronic arterial complications while in the Y-graft group (n=4, 12.9%) 3 acute thrombosis and 1 chronic artery-duodenal fistula occurred. Graft salvage was achieved in 16 patients (53.3%) from the ASMA group and in 2 (50%) from the Y-graft. After a median follow-up of 129.2 (IQR 25-75%, 77.2 -182) months the overall graft and patient survival for the whole cohort at 1, 5, and 10 years was 86.7%, 79.5%, 70.5%, and 98.5%, 95.3%, 92.5%, respectively. CONCLUSIONS: The ASMA proves to be a safe and more easily reproducible technique and should therefore be considered for first-line back-table reconstruction in the PT population.

Challenges in perioperative blood transfusions in kidney transplantation and the need for Patient Blood Management.

BACKGROUND: Anemia is highly prevalent in end-stage chronic kidney disease patients, increasing their risk of receiving blood transfusions during and on the days after a kidney transplant (KTx) surgery. However, there is currently a lack of data that thoroughly describes this phenomenon in this population, the associated risk factors, and how they could benefit from the application of Patient Blood Management (PBM) guidelines. MATERIALS AND METHODS: Observational study. All adult patients who received a KTx between January 1st, 2020, and December 31st, 2021, were included and followed up to six months after transplantation. Those who received a multiorgan transplant, whose data was missing in the electronic health records, and who had primary non-function were excluded. We recorded donor and recipient characteristics, cold ischemia time, preoperative hemoglobin concentration, iron status deficiency biomarkers, incidence of delayed graft function and biopsy-proven graft rejections, and graft function at discharge and 6 months after transplantation. RESULTS: We found that a high amount (39%) of KTx recipients required at least one blood transfusion during the perioperative period. And that 1) most of these patients had anemia at the time of transplantation (85.4%), 2) iron status upon admission was associated with the transfusion of more blood units (3.9 vs 2.7, p=0.019), 3) surgical reintervention (OR 7.28, 2.35-22.54) and deceased donor donation (OR 1.99, 1.24-3.21) were associated with an increased risk of transfusion, and finally, 4) there was an association between a higher number of blood units transfused and impaired kidney graft function six months after hospital discharge (1.6 vs 1.9, p=0.02). CONCLUSIONS: In conclusion, PBM guidelines should be applied to patients on the KTx deceased donor waiting list and especially those scheduled to receive a transplant from a living donor. This could potentially increase the utilization efficiency of blood products and avoid transfusion-related severe adverse effects.

Early kinetics of donor-derived cell-free DNA after transplantation predicts renal graft recovery and long-term function.

BACKGROUND: Ischemia-reperfusion injury (IRI) upon transplantation is one of the most impactful events that the kidney graft suffers during its life. Its clinical manifestation in the recipient, delayed graft function (DGF), has serious prognostic consequences. However, the different definitions of DGF are subject to physicians' choices and centers' policies, and a more objective tool to quantify IRI is needed. Here, we propose the use of donor-derived cell-free DNA (ddcfDNA) for this scope. METHODS: ddcfDNA was assessed in 61 kidney transplant recipients of either living or deceased donors at 24 h, and 7, 14 and 30 days after transplantation using the AlloSeq cfDNA Kit (CareDx, San Francisco, CA, USA). Patients were followed-up for 6 months and 7-year graft survival was estimated through the complete and functional iBox tool. RESULTS: Twenty-four-hour ddcfDNA was associated with functional DGF [7.20% (2.35%-15.50%) in patients with functional DGF versus 2.70% (1.55%-4.05%) in patients without it, P = .023] and 6-month estimated glomerular filtration rate (r = -0.311, P = .023). At Day 7 after transplantation, ddcfDNA was associated with dialysis duration in DGF patients (r = 0.612, P = .005) and worse 7-year iBox-estimated graft survival probability (ß -0.42, P = .001) at multivariable analysis. Patients with early normalization of ddcfDNA (<0.5% at 1 week) had improved functional iBox-estimated probability of graft survival (79.5 ± 16.8%) in comparison with patients with 7-day ddcfDNA ≥0.5% (67.7 ± 24.1%) (P = .047). CONCLUSIONS: ddcfDNA early kinetics after transplantation reflect recovery from IRI and are associated with short-, medium- and long-term graft outcome. This may provide a more objective estimate of IRI severity in comparison with the clinical-based definitions of DGF.

Physiopathological role of extracellular vesicles in alloimmunity and kidney transplantation and their use as biomarkers.

Antibody-mediated rejection is the leading cause of kidney graft dysfunction. The process of diagnosing it requires the performance of an invasive biopsy and subsequent histological examination. Early and sensitive biomarkers of graft damage and alloimmunity are needed to identify graft injury and eventually limit the need for a kidney biopsy. Moreover, other scenarios such as delayed graft function or interstitial fibrosis and tubular atrophy face the same problem. In recent years, interest has grown around extracellular vesicles, specifically exosomes actively secreted by immune cells, which are intercellular communicators and have shown biological significance. This review presents their potential as biomarkers in kidney transplantation and alloimmunity.

Chimeric HLA antibody receptor T cells for targeted therapy of antibody-mediated rejection in transplantation.

The presence of donor-specific antibodies (DSA), mainly against HLA, increases the risk of allograft rejection. Moreover, antibody-mediated rejection (ABMR) remains an important barrier to optimal long-term outcomes after solid organ transplantation. The development of chimeric autoantibody receptor T lymphocytes has been postulated for targeted therapy of autoimmune diseases. We aimed to develop a targeted therapy for DSA desensitization and ABMR, generating T cells with a chimeric HLA antibody receptor (CHAR) that specifically eliminates DSA-producing B cells. We have genetically engineered an HLA-A2-specific CHAR (A2-CHAR) and transduced it into human T cells. Then, we have performed in vitro experiments such as cytokine measurement, effector cell activation, and cytotoxicity against anti-HLA-A2 antibody-expressing target cells. In addition, we have performed A2-CHAR-Tc cytotoxic assays in an immunodeficient mouse model. A2-CHAR expressing T cells could selectively eliminate HLA-A2 antibody-producing B cells in vitro. The cytotoxic capacity of A2-CHAR expressing T cells mainly depended on Granzyme B release. In the NSG mouse model, A2-CHAR-T cells could identify and eradicate HLA-A2 antibody-producing B cells even when those cells are localized in the bone marrow. This ability is effector:target ratio dependent. CHAR technology generates potent and functional human cytotoxic T cells to target alloreactive HLA class I antibody-producing B cells. Thus, we consider that CHAR technology may be used as a selective desensitization protocol or an ABMR therapy in transplantation.

Impact of robotic-assisted kidney transplantation on post-transplant infections: a case-control study.

BACKGROUND: The aim of this study was to determine the differences in the incidence, epidemiology, clinical characteristics and risk factors of infections in living donor kidney transplant recipients using robotic-assisted kidney transplantation (RAKT) and open approach. METHODS: We conducted a retrospective observational study from January 2016 to December 2019. For the risk factor analysis, a matched case-control study (1:1 ratio) was performed (robotic vs open). Control subjects were matched for living donor and time of transplantation. The data included de novo immunosuppressive regimen, delayed graft function, urological complications, acute allograft rejection and incidence, clinical features, microbiological findings and outcomes of infections. RESULTS: Ninety-four RAKT and 84 controls were included. There were no differences between groups in terms of age, gender, BMI, median days of hospitalization, immunosuppressive regimen, need for surgical urologic procedures post-transplantation, presence of urinary leak or acute allograft rejection. Thirty-five percent of all recipients analyzed presented an infection, mostly asymptomatic bacteriuria (49%), symptomatic urinary tract infection (31%) and surgical site infection (10%). Pseudomonas aeruginosa was the most frequent isolated microorganism in 67%, followed by E. coli (20%), Enterococcus faecalis (17%) and Klebsiella pneumoniae (10%). Eight percent of the microorganisms were multidrug resistant. The open kidney transplantation group presented more infections compared to RAKT (43 vs 27%, p = 0.04). After multivariate analysis, need for surgical urologic procedure post-transplantation (OR 6.2, 95% CI 1.1-35), BMI ≥ 30 (OR 3.6, 95% CI 1.5-9) and acute allograft rejection (OR 3.2, 95% CI 1.2-8.5) were associated with infection, whereas RAKT (OR 0.5, 95% CI 0.2-0.9) and the use of JJ catheter (OR 0.36, 95% CI 0.17-0.72) were protective factors. CONCLUSIONS: Infection is a frequent event in patients receiving a living donor kidney transplant. Acute allograft rejection, need for surgical urologic procedure post-transplantation and BMI were associated with infection, whereas robotic surgery was a protective factor in living donor kidney transplantation.

Extracorporeal Photopheresis Improves Graft Survival in a Full-Mismatch Rat Model of Kidney Transplantation.

Extracorporeal photopheresis (ECP) is an immunomodulatory therapy based on the infusion of autologous cellular products exposed to ultraviolet light (UV) in the presence of a photosensitizer. The study evaluates the ECP efficacy as induction therapy in a full-mismatch kidney transplant rat model. Dark Agouti to Lewis (DA-L) kidney transplant model has been established. ECP product was obtained from Lewis rat recipients after DA kidney graft transplantation (LewDA). Leukocytes of those LewDA rats were exposed to 8-methoxy psoralen, and illuminated with UV-A. The ECP doses assessed were 10 × 106 and 100 × 106 cells/time point. Lewis recipients received seven ECP infusions. DA-L model was characterized by the appearance of donor-specific antibodies (DSA) and kidney function deterioration from day three after kidney transplant. The dysfunction progressed rapidly until graft loss (6.1 ± 0.5 days). Tacrolimus at 0.25 mg/kg prolonged rat survival until 11.4 ± 0.7 days (p = 0.0004). In this context, the application of leukocytes from LewDA sensitized rats accelerated the rejection (8.7 ± 0.45, p = 0.0012), whereas ECP product at high dose extended kidney graft survival until 26.3 ± 7.3 days, reducing class I and II DSA in surviving rats. ECP treatment increases kidney graft survival in full-mismatch rat model of acute rejection and is a suitable immunomodulatory therapy to be explored in kidney transplantation.

Drug-drug interactions of ritonavir-boosted SARS-CoV-2 protease inhibitors in solid organ transplant recipients: experience from the initial use of lopinavir-ritonavir.

OBJECTIVES: To review the drug-drug interactions between tacrolimus and lopinavir/ritonavir in 23 patients who received solid organ transplant during the first wave of COVID-19 and to determine the efficacy as well as safety of prednisone monotherapy. METHODS: Observational study performed between March and June 2020 in solid organ transplant recipients admitted with an established diagnosis of SARS-CoV-2 infection who received lopinavir/ritonavir (≥2 doses). Once lopinavir/ritonavir therapy was initiated, calcineurin inhibitor treatment was temporarily switched to prednisone monotherapy (15-20 mg/d) to avoid drug-drug interactions and toxicity. After lopinavir/ritonavir treatment completion, immunosuppressive treatment was restarted with reduced doses of prednisone-tacrolimus (target minimum blood concentration -C0- approximately 5 ng/mL). Patients were observed for 3 months to confirm the absence of rejection. RESULTS: The median time from discontinuation of tacrolimus to initiation of lopinavir/ritonavir was 14 hours (interquartile range [IQR], 12-15) and from discontinuation of lopinavir/ritonavir to resumption of tacrolimus 58 hours (IQR, 47-81). The duration of lopinavir/ritonavir treatment was 7 days (IQR, 5-7). Nine of the 21 (42.8%) patients on tacrolimus treatment had C0 above the cutoff point after lopinavir/ritonavir initiation, despite having been substituted with prednisone before lopinavir/ritonavir initiation. Three patients had very high concentrations (>40 ng/mL) and developed toxicity. No episodes of acute rejection were diagnosed. DISCUSSION: We did not observe toxicity in patients for whom tacrolimus was discontinued 24 hours before starting lopinavir/ritonavir and reintroduced at half dose 48 to 72 hours after lopinavir/ritonavir discontinuation. Prednisone monotherapy during lopinavir/ritonavir therapy was safe with no episodes of acute rejection. Experience with lopinavir/ritonavir may be applicable to the use of nirmatrelvir/ritonavir, but larger multicentre studies are needed to confirm these findings.