Role of time from transplantation to biopsy in histologic ABMR: A single center report.

BACKGROUND: Allograft biopsies with lesions of Antibody-Mediated Rejection (ABMR) with Microvascular Inflammation (MVI) have shown heterogeneous etiologies and outcomes. METHODS: To examine factors associated with outcomes in biopsies that meet histologic ABMR criteria, we retrospectively evaluated for-cause biopsies at our center between 2011 and 2017. We included biopsies that met the diagnosis of ABMR by histology, along with simultaneous evaluation for anti-Human Leukocyte Antigen (HLA) donor-specific antibodies (DSA). We evaluated death-censored graft loss (DCGL) and used a principal component analysis (PCA) approach to identify key predictors of outcomes. RESULTS: Out of the histologic ABMR cohort (n = 118), 70 were DSA-positive ABMR, while 48 had no DSA. DSA(+)ABMR were younger and more often female recipients. DSA(+)ABMR occurred significantly later post-transplant than DSA(-)ABMR suggesting time-dependence. DSA(+)ABMR had higher inflammatory scores (i,t), chronicity scores (ci, ct) and tended to have higher MVI scores. Immunodominance of DQ-DSA in DSA(+)ABMR was associated with higher i+t scores. Clinical/histologic factors significantly associated with DCGL after biopsy were inputted into the PCA. Principal component-1 (PC-1), which contributed 34.8% of the variance, significantly correlated with time from transplantation to biopsy, ci/ct scores and DCGL. In the PCA analyses, i, t scores, DQ-DSA, and creatinine at biopsy retained significant correlations with GL-associated PCs. CONCLUSIONS: Time from transplantation to biopsy plays a major role in the prognosis of biopsies with histologic ABMR and MVI, likely due to ongoing chronic allograft injury over time.

4D flow MRI for the assessment of renal transplant dysfunction: initial results.

OBJECTIVES: (1) Determine inter-observer reproducibility and test-retest repeatability of 4D flow parameters in renal allograft vessels; (2) determine if 4D flow measurements in the renal artery (RA) and renal vein (RV) can distinguish between functional and dysfunctional allografts; (3) correlate haemodynamic parameters with estimated glomerular filtration rate (eGFR), perfusion measured with dynamic contrast-enhanced MRI (DCE-MRI) and histopathology. METHODS: Twenty-five prospectively recruited renal transplant patients (stable function/chronic renal allograft dysfunction, 12/13) underwent 4D flow MRI at 1.5 T. 4D flow coronal oblique acquisitions were performed in the transplant renal artery (RA) (velocity encoding parameter, VENC = 120 cm/s) and renal vein (RV) (VENC = 45 cm/s). Test-retest repeatability (n = 3) and inter-observer reproducibility (n = 10) were assessed by Cohen's kappa, coefficient of variation (CoV) and Bland-Altman statistics. Haemodynamic parameters were compared between patients and correlated to the estimated glomerular filtration rate, DCE-MRI parameters (n = 10) and histopathology from allograft biopsies (n = 15). RESULTS: For inter-observer reproducibility, kappa was > 0.99 and 0.62 and CoV of flow was 12.6% and 7.8% for RA and RV, respectively. For test-retest repeatability, kappa was > 0.99 and 0.5 and CoV of flow was 27.3% and 59.4%, for RA and RV, respectively. RA (p = 0.039) and RV (p = 0.019) flow were both significantly reduced in dysfunctional allografts. Both identified chronic allograft dysfunction with good diagnostic performance (RA: AUC = 0.76, p = 0.036; RV: AUC = 0.8, p = 0.018). RA flow correlated negatively with histopathologic interstitial fibrosis score ci (ρ = - 0.6, p = 0.03). CONCLUSIONS: 4D flow parameters had better repeatability in the RA than in the RV. RA and RV flow can identify chronic renal allograft dysfunction, with RA flow correlating with histopathologic interstitial fibrosis score. KEY POINTS: • Inter-observer reproducibility of 4D flow measurements was acceptable in both the transplant renal artery and vein, but test-retest repeatability was better in the renal artery than in the renal vein. • Blood flow measurements obtained with 4D flow MRI in the renal artery and renal vein are significantly reduced in dysfunctional renal transplants. • Renal transplant artery flow correlated negatively with histopathologic interstitial fibrosis score.

Influence of patient characteristics and immunosuppressant management on mortality in kidney transplant recipients hospitalized with coronavirus disease 2019 (COVID-19).

The influence of patient characteristics and immunosuppression management on COVID-19 outcomes in kidney transplant recipients (KTRs) remains uncertain. We performed a single-center, retrospective review of all adult KTRs admitted to the hospital with confirmed COVID-19 between 03/15/2020 and 05/15/2020. Patients were followed from the date of admission up to 1 month following hospital discharge or study conclusion (06/15/2020). Baseline characteristics, laboratory parameters, and immunosuppression were compared between survivors and patients who died to identify predictors of mortality. 38 KTRs with a mean baseline eGFR of 52.5 ml/min/1.73 m2 were hospitalized during the review period. Maintenance immunosuppression included tacrolimus (84.2%), mycophenolate (89.5%), and corticosteroids (81.6%) in the majority of patients. Eleven patients (28.9%) died during the hospitalization. Older age (OR = 2.05; 1.04-4.04), peak D-dimer (OR = 1.20; 1.04-1.39), and peak white blood cell count (OR = 1.11; 1.02-1.21) were all associated with mortality among KTRs hospitalized for COVID-19. Increased mortality was also observed among KTRs with concomitant HIV infection (87.5% vs. 36.1%; p < .01). Conversely, immunosuppression intensity and degree of reduction following COVID-19 diagnosis were not associated with either survival or acute allograft rejection. Our findings potentially support a strategy of individualization of immunosuppression targets based on patient-specific risk factors, rather than universal immunosuppression reduction for KTRs at risk from COVID-19.

Multiparametric magnetic resonance imaging shows promising results to assess renal transplant dysfunction with fibrosis.

Here we assessed the diagnostic value of a quantitative multiparametric magnetic resonance imaging (mpMRI) protocol for evaluation of renal allograft dysfunction with fibrosis. Twenty-seven renal transplant patients, including 15 with stable functional allografts (eGFR mean 71.5 ml/min/1.73m2), and 12 with chronic dysfunction/established fibrosis (eGFR mean 30.1 ml/min/1.73m2), were enrolled in this prospective single-center study. Sixteen of the patients had renal biopsy (mean 150 days) before the MRI. All patients underwent mpMRI at 1.5T including intravoxel-incoherent motion diffusion-weighted imaging, diffusion tensor imaging, blood oxygen level dependent (BOLD R2*) and T1 quantification. True diffusion D, pseudodiffusion D*, perfusion fraction PF, apparent diffusion coefficient (ADC), fractional anisotropy (FA), R2* and T1 were calculated for cortex and medulla. ΔT1 was calculated as (100x(T1 Cortex-T1 Medulla)/T1 Cortex). Test-retest repeatability and inter-observer reproducibility were assessed in four and ten patients, respectively. mpMRI parameters had substantial test-retest and interobserver repeatability (coefficient of variation under 15%), except for medullary PF and D* (coefficient of variation over 25%). Cortical ADC, D, medullary ADC and ΔT1 were all significantly decreased, while cortical T1 was significantly elevated in fibrotic allografts. Cortical T1 showed positive correlation to the Banff fibrosis and tubular atrophy scores. The combination of ΔT1 and cortical ADC had excellent cross-validated diagnostic performance for detection of chronic dysfunction with fibrosis. Cortical ADC and T1 had good performance for predicting eGFR decline at 18 months (4 or more ml/min/1.73m2/year). Thus, the combination of cortical ADC and T1 measurements shows promising results for the non-invasive assessment of renal allograft histology and outcomes.

Conversion to belatacept maintenance immunosuppression in HIV-positive kidney transplant recipients.

There are only scattered case reports documenting belatacept use in HIV + kidney transplant recipients. We performed a retrospective review to describe short-term outcomes following conversion to belatacept in a cohort of HIV + patients. Patients were included if they were converted to belatacept between May 2015 and May 2019, had an HIV- donor, and received ≥4 doses of belatacept. All patients were treated with non-depleting induction and triple maintenance immunosuppression. Allograft and HIV-related outcomes were collected from the date of belatacept infusion until May 2020. Ten HIV + kidney transplant recipients were identified, who were converted to belatacept a median of 364 days post-transplant. At last follow-up (median 3.3 years), 8 patients remained on belatacept therapy, and all patients were alive with functioning allografts. Mean estimated glomerular filtration rates (eGFR) improved from 31.6 mL/min at baseline to 42.8 mL/min at 1 year (P = .03). Two patients developed acute rejection, with one necessitating conversion back to tacrolimus. All patients maintained undetectable HIV-1 viral loads at last follow-up. One patient each developed pneumocystis pneumonia and Kaposi sarcoma following conversion, which were responsive to standard medical therapy. In our cohort of stable HIV + kidney transplant recipients, conversion to belatacept was associated with excellent early patient and allograft survival and improved eGFR at 1 year.

Conversion to belatacept within 1-year of renal transplantation in a diverse cohort including patients with donor-specific antibodies.

Early conversion from a calcineurin inhibitor to belatacept has the potential to improve long-term renal allograft function; however, there remains limited experience with this strategy among African Americans and patients with preformed donor-specific antibodies (DSA). To examine these subgroups, we performed a single-center review of kidney transplant recipients converted to belatacept within 1-year of transplant between 01/2011 and 10/2017. All patients received lymphocyte-depleting induction with maintenance tacrolimus and mycophenolate +/- corticosteroids. Patients were switched to belatacept for clinical indication and followed from date of conversion until allograft failure or study conclusion. The primary endpoint at 1-year was a composite of allograft loss, biopsy proven rejection, de novo DSA formation, proteinuria, and declining renal function. Thirty-two patients were included in the review. The majority were African American, and 28.1% had DSA at transplant. Patient and allograft survival at 1-year was 96.9% and 93.8%, respectively, and estimated glomerular filtration rate improved from 41.9 to 58.4 mL/min. No African Americans or patients with pretreatment DSA developed rejection or allograft failure within 1-year. The only clinical variable correlated with suboptimal allograft function was baseline weight ≥80 kg (OR = 6.2; 95% CI, 1.2-32.3). Early conversion to belatacept appears safe for select patients with DSA and African Americans receiving lymphocyte-depleting induction.

Kidney transplantation using lymphocyte depleting induction and standard maintenance immunosuppression at the height of the SARS-CoV-2 pandemic in New York City: A single-center experience.

BACKGROUND: Concerns have been raised regarding proceeding with kidney transplantation using standard immunosuppression in COVID-19 endemic areas. METHODS: We performed a single-center review of all adult kidney transplants performed during the COVID-19 pandemic in New York City. Patients were managed with standard immunosuppression protocols, including lymphocyte depleting induction and trough-guided tacrolimus. Retrospective data were collected for 3 months from the date of transplantation or until study conclusion (5/7/2020). The primary outcomes assessed included patient and allograft survival as well as COVID-19 related hospital readmission. RESULTS: 30 kidney transplants were performed during the height of the COVID-19 pandemic. After a median follow-up of 51.5 days, 93.3% of patients were alive with 100% death-censored allograft survival. 9 patients were readmitted to the hospital during the study period, 4 (13.3%) related to infection with COVID-19. Infections were mild in 3/4 patients, with one patient developing severe disease leading to respiratory failure. Patients readmitted with COVID-19 were numerically more likely to be African American, have a BMI > 30 kg/m2, have a lymphocyte count ≤ 300 cells/mL, and be on maintenance corticosteroids. CONCLUSIONS: Kidney transplantation in areas endemic to COVID-19 using standard induction and maintenance immunosuppression appears to be associated with a modest risk for severe COVID-19 related disease.

T1ρ mapping for assessment of renal allograft fibrosis.

BACKGROUND: There is an unmet need for noninvasive methods to diagnose and stage renal allograft fibrosis. PURPOSE: To investigate the utility of T1ρ measured with MRI for the assessment of fibrosis in renal allografts. STUDY TYPE: Institutional Review Board (IRB)-approved prospective. SUBJECTS: Fifteen patients with stable functional allograft (M/F 9/6, mean age 56 years) and 12 patients with allograft dysfunction and established fibrosis (M/F 6/6, mean age 51 years). FIELD STRENGTH/SEQUENCE: T1ρ imaging at 1.5T using a custom-developed sequence. ASSESSMENT: Average T1ρ in the cortex and medulla was quantified and T1ρ repeatability (expressed by the coefficient of variation [CV]) was measured in four patients. STATISTICAL TESTS: Differences in T1ρ values between the 2 groups were assessed using Mann-Whitney U-tests. Diagnostic performance of T1ρ for differentiation between functional and fibrotic allografts was evaluated using receiver operating characteristic (ROC) analysis. Spearman correlations of T1ρ with Masson's trichrome-stained fractions and serum estimated glomerular filtration rate (eGFR) were assessed. RESULTS: Higher T1ρ repeatability was found for cortex compared with medulla (mean CV T1ρ cortex 7.4%, medulla 13.3%). T1ρ values were significantly higher in the cortex of fibrotic vs. functional allografts (111.8 ± 17.2 msec vs. 99.0 ± 11.0 msec, P = 0.027), while there was no difference in medullary T1ρ values (122.6 ± 20.8 msec vs. 124.3 ± 20.8 msec, P = 0.789). Cortical T1ρ significantly correlated with Masson's trichrome-stained fractions (r = 0.515, P = 0.044) and eGFR (r = -0.546, P = 0.004), and demonstrated an area under the curve (AUC) of 0.77 for differentiating between functional and fibrotic allografts (sensitivity and specificity of 75.0% and 86.7%, using threshold of 106.9 msec). DATA CONCLUSION: Our preliminary results suggest that T1ρ is a potential imaging biomarker of renal allograft fibrosis. These results should be verified in a larger study. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1085-1091.

Higher rates of rejection in HIV-infected kidney transplant recipients on ritonavir-boosted protease inhibitors: 3-year follow-up study.

Rejection rates in HIV-infected kidney transplant (KTx) recipients are higher than HIV-negative recipients. Immunosuppression and highly active antiretroviral therapy (HAART) protocols vary with potentially significant drug-drug interactions, likely influencing outcomes. This is an IRB-approved, single-center, retrospective study of adult HIV-infected KTx patients between 5/2009 and 12/2014 with 3-year follow-up, excluding antibody-depleting induction. A total of 42 patients were included; median age was 52 years, 81% male, 50% African American, 29% Hispanic, 17% Caucasian. The most common renal failure etiology was hypertensive nephrosclerosis (50%) with 5.8 median years of pre-transplant dialysis. All patients received IL-2 receptor antagonist, were maintained on tacrolimus (76%) or cyclosporine (17%), and 40% received ritonavir-boosted PI-based HAART (rtv+) regimen. Patient and graft survival at 3 years were 93% and 90%. At 1-, 2-, and 3-year time points, median serum creatinine was 1.49, 1.35, and 1.67; treated biopsy-proven rejection was 38%, 38%, and 40.5%; and 92% of episodes were acute rejection. At these time points, rejection rates were significantly higher with boosted PI HAART regimens compared to other HAART regimens, 59% vs 24% (P = 0.029), 59% vs 24% (P = 0.029), and 68% vs 24% (P = 0.01). Despite higher rejection rates, HIV-infected KTx recipients have reasonable outcomes. Given significantly higher rejection rates using rtv+ regimens, alternative HAART regimens should be considered prior to transplantation.

Different outcomes after kidney transplantation between African Americans and Whites: A matter of income? A single-center study.

BACKGROUND: Our center has one of the largest representations of African Americans in listed and transplanted patients. We investigated if and how racial differences affect outcomes in our patient population. METHODS: We performed a retrospective analysis of all kidney transplants in African American and (non-Hispanic) White patients in our center from 1/1/2005 to 12/31/2014. Cox regression was performed to evaluate the adjusted hazard ratios for graft loss. We investigated the influence of socioeconomic status on transplant outcomes. We stratified our patients into three groups based on income: lower (<$50 000 annual household income), medium ($50 000-100 000 annual household income), and higher (>$100 000 annual household income. RESULTS: There were 1333 patients in our study, 696 Whites and 637 African Americans. The 1-, 5-, and 10-year graft survival between the two groups was 96.5% vs 91.1%, 89% vs 80.7%, and 77% vs 66.3%, respectively (P < .001 by Log Rank, Breslow and Taron-Ware). When we compared the two groups separately in each income category, we found no statistical difference between African Americans and Whites in graft survival. In the regression model, income and not race was the significant factor influencing graft survival (P < .001 vs P = .61).

Analysis of OPTN/UNOS registry suggests the number of HLA matches and not mismatches is a stronger independent predictor of kidney transplant survival.

HLA matching and mismatching, while inversely related, are not exact opposites. Here we determined the independent effects of HLA matching and mismatching on outcomes in deceased donor kidney transplant recipients. The United Network for Organ Sharing database (1995-2012) was utilized and analyzed for delayed graft function, one-year acute rejection, and death-censored graft survival using combined multivariable models including HLA matching and mismatching. Sensitivity analyses were performed using the subgroup of deceased donor kidney transplant patients after 2003 with more uniform HLA nomenclature and resampling analyses using bootstrapping on complete data available from 96,236 recipients. Individually, both HLA matching and mismatching showed significant associations with graft survival. Adjusting the model to take into account both matching and mismatching simultaneously, the degree of HLA mismatching lost significance while matching continued to have a significant prediction for delayed graft function, the one-year acute rejection rate, and graft survival. Sensitivity analyses and bootstrapping showed similar results for all studied outcomes. Thus, analysis of this large cohort demonstrates the apparent greater association of HLA matching over HLA mismatching on both early allograft events as well as graft survival. Future analyses should preferentially utilize HLA matching as a covariate over mismatching for accurately reflecting impact on graft outcomes.

Pre-liver transplant renal dysfunction and association with post-transplant end-stage renal disease: A single-center examination of updated UNOS recommendations.

Simultaneous liver-kidney allocation protocols allocate dual organs based on a sustained eGFR of 30 mL/min or less. A 2017-UNOS update includes CKD3 as dual organ candidates but only when the listing eGFR is <30 mL/min while recommending a "safety net" for prioritized kidney listing post-LT. We retrospectively reviewed adult LTs examine whether the UNOS proposal captured the LT population at highest risk for developing post-LT ESRD. Among 290 LT recipients, 67 had pre-LT CKD3, 141 had AKI, of whom 47 required dialysis (<4 weeks). During follow-up, 25 (8.62%) developed ESRD, while 70 (24.1%) died. In adjusted Cox models, CKD3 had an independent association with post-LT ESRD (adjusted HR 4.8; P = 0.001), independent of AKI. Interestingly, CKD3 with listing GFR >30 mL/min was still significantly associated with post-LT ESRD. AKI was associated with reduced post-LT survival (adjusted HR 1.9; P = 0.02), albeit only in the first-year post-LT. Severe AKI-D was associated with post-LT ESRD and mortality. The safety net would have captured only 60% of all post-LT ESRD cases in our cohort. Pre-LT CKD3 was associated with increased risk of post-LT ESRD above the recommended cutoff for listing GFR. These findings, if generalizable in larger cohorts have important implications for dual organ allocation.

Early conversion to belatacept after renal transplantation.

Belatacept is a non-nephrotoxic immunosuppressive agent, which may make it the ideal agent for patients with delayed or slow graft function on calcineurin inhibitors. There are limited data on conversion of patients to belatacept within 6 months of transplantation. Between January 2012 and December 2015, 16 patients were converted to belatacept for delayed or poor graft function (eGFR<30 mL/min/1.73 m2 , MDRD); three were HIV positive. Conversion protocols were analyzed in patients ≤4 months and 4-6 months post-transplantation. Mean serum creatinine levels after belatacept conversion were compared with preconversion levels. Patient survival was 100%, and graft survival was 88%. The mean creatinine fell from 3.9±1.82 mg/dL prebelatacept conversion to 2.1±1.1 mg/dL at 6 months and 1.9±0.47 mg/dL (median 1.8 mg/dL) at 12 months postconversion. There was no significant increased risk of rejection, infection, or malignancy. HIV parameters remained largely stable. Early conversion to belatacept in patients with DGF or slow graft function is safe and efficacious, in a single-center nonrandomized retrospective analysis.

Comparison of Intensive Insulin Versus Oral Regimens on Early Glycemic Control Following Kidney Transplant.

Introduction: Insulin is commonly prescribed to manage early post-kidney transplant hyperglycemia due to its flexibility. Studies comparing the effectiveness of oral therapies on glycemic outcomes remain limited. Project aims: The purpose of this program evaluation was to analyze our experience using oral antiglycemic agents immediately post-kidney transplant, compared to patients managed with insulin monotherapy. Design: This was a single-center, retrospective review of adult kidney transplant recipients with new or worsening hyperglycemia between 01/2014-05/2020. Patients were excluded if they had a prior or combined organ transplant, type 1 diabetes, or were previously on intensive insulin. Patients discharged on oral medications were 1:1 matched to patients receiving intensive insulin based on pre-specified clinical parameters. The primary endpoint was the number of diabetes-related readmissions within 6-months of transplant. Key secondary endpoints included mean serum glucose and hemoglobin A1c levels. Results: Thirty patients prescribed oral therapies were successfully matched to patients receiving intensive insulin. Baseline characteristics were similar between groups, except for more whites in the insulin group. There were no differences in diabetes-related (6.7% vs 3.3%; P = 1.00) or all-cause readmissions within 6-months. Mean serum glucose (P = .99) and hemoglobin A1c (P = .49) levels were also similar between patients receiving oral agents and insulin. However, 7 patients in the oral group were eventually converted to standing insulin. Conclusion: Our experience suggested that the early use of oral antiglycemics post-kidney transplant in select patients can result in similar outcomes relative to insulin. Meticulous follow-up is necessary as one-quarter of patients may require conversion to insulin within 1-month.

Magnetic resonance elastography vs. point shear wave ultrasound elastography for the assessment of renal allograft dysfunction.

PURPOSE: To investigate the utility of magnetic resonance elastography (MRE) vs. ultrasound (US) point shear wave elastography (pSWE) for the assessment of chronic renal allograft dysfunction, prediction of outcome and determine the correlation with Banff pathology scores. METHODS: In this IRB approved prospective study, 27 enrolled patients with functional (n = 15) and chronic dysfunctional (n = 12) renal allografts underwent same day 2D MRE and pSWE. Histogram parameters [including mean, median, standard deviation, kurtosis and skewness] of the magnitude of the complex shear modulus (MRE) and median Young's modulus (pSWE) were measured in the cortex (MRE and pSWE) and combined corticomedullary regions (MRE). Histopathology was available for 16 patients (4 functional, 12 dysfunctional). RESULTS: MRE and pSWE stiffness were not significantly different between functional and dysfunctional groups (p range 0.139-0.347). The skewness of MRE corticomedullary stiffness was significantly lower (p = 0.04) in patients with chronic dysfunction and correlated significantly with Banff histopathologic scores (range r=-0.518-0.567, p = 0.035-0.040). MRE cortical and corticomedullary mean stiffness showed strong performance in predicting graft loss/relist (AUC 0.958, p = 0.011 for both). Reliable pSWE measurements were obtained in 13 patients (48 %). pSWE stiffness did not correlate with Banff scores and did not predict outcome. CONCLUSIONS: The skewness of MRE corticomedullary stiffness is sensitive to changes in chronic allograft dysfunction, while mean/median MRE renal stiffness and median US stiffness did not differentiate patients with stable function vs those with chronic renal allograft dysfunction. MRE corticomedullary mean stiffness appears to be a predictor of graft loss/relist. pSWE was not found to be a useful method for assessing renal allografts.

Hepatitis C and Human Immunodeficiency Virus Kidney Transplantation: The Mount Sinai Experience.

Mount Sinai Hospital in New York has a long history in the field of organ transplantation. The first kidney transplant at Mount Sinai was performed in 1967 by the late Dr. Lewis Burrows and the first laparoscopic donor nephrectomy in New York was performed at Mount Sinai in 1996. Over 3000 kidney transplantations have been performed at Mount Sinai. In the early 1990s, the first hepatitis C virus (HCV) positive patient at Mount Sinai underwent a kidney transplant and the first kidney transplant in a patient with human immunodeficiency virus (HIV) in New York was performed at Mount Sinai in 2001. In general, these patients have done well after renal transplantation, with outcomes similar to those seen in non-infected patients. This chapter will describe the evolution of immunosuppressive regimens in HCV positive and HIV positive patients, and will describe the outcomes of kidney transplantation in these patients. Given the favorable outcomes, it is reasonable to continue to offer renal transplantation as a treatment for end stage renal disease patients with HCV and/or HIV.

Improved freedom from rejection after a loading dose of sirolimus.

BACKGROUND: Sirolimus (SIR) in combination with cyclosporine reduces the incidence of acute rejection in renal transplant recipients. Limited data are available regarding SIR in combination with tacrolimus (TAC). METHODS: A single-center, retrospective review of renal transplant recipients receiving SIR, TAC, and corticosteroids postoperatively was conducted. A total of 118 consecutive renal transplant recipients were included on the basis of availability of day 1 SIR dose information. Seventy-seven patients received an SIR loading dose (SIR-LD) immediately posttransplantation, and 41 patients did not (SIR no loading dose [SIR-NLD]). RESULTS: The two groups showed similar demographic and transplant characteristics. SIR doses and trough levels were significantly higher in the SIR-LD patients at 1 and 7 days posttransplantation; however, no differences occurred beyond day 7. Patients receiving an SIR-LD experienced significantly better freedom from rejection at 1, 3, and 6 months posttransplantation (P<0.05). This rejection benefit in the SIR-LD group was independent of donor source and use of antibody induction. SIR-LD patients experienced fewer serious infections (12% SIR-LD vs. 27% SIR-NLD, P=0.04) and a lower incidence of delayed graft function (21% SIR-LD vs. 39% SIR-NLD, P<0.05). No significant differences in serum creatinine, hemoglobin, and platelet counts occurred in the first 180 days posttransplantation, but the patients in the SIR-NLD group experienced lower hemoglobin levels at day 30 than those in the SIR-LD group (10.8 g/dL SIR-LD vs. 9.7 g/dL SIR-NLD, P=0.03). CONCLUSION: SIR-LD significantly improves early posttransplantation freedom from rejection in renal transplant recipients without increasing other complications.