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Design Investigator-led, prospective, open-labelled marker-based strategy (hybrid) randomised trial. Background Allografts in 3% of kidney transplant patients fail annually. Development of antibodies against human leucocyte antigens is a validated predictive biomarker of allograft failure. Under immunosuppression is recognised to contribute, but whether increasing immunosuppression can prevent allograft failure in human leucocyte antigen Ab+ patients is unclear. Participants Renal transplant recipients > 1 year post-transplantation attending 13 United Kingdom transplant clinics, without specific exclusion criteria. Interventions Regular screening for human leucocyte antigen antibodies followed, in positive patients by interview and tailored optimisation of immunosuppression to tacrolimus, mycophenolate mofetil and prednisolone. Objective To determine if optimisation of immunosuppression in human leucocyte antigen Ab+ patients can cost-effectively prevent kidney allograft failure. Outcome Time to graft failure after 43 months follow-up in patients receiving the intervention, compared to controls, managed by standard of care. Costs and quality-adjusted life-years were used in the cost-effectiveness analysis. Randomisation and blinding Random allocation (1 : 1) to unblinded biomarker-led care or double-blinded standard of care stratified by human leucocyte antigen antibodies status (positive/negative) and in positives, presence of donor-specific antibodies (human leucocyte antigen antibodies against donor human leucocyte antigen) or not (human leucocyte antigen antibodies against non-donor human leucocyte antigen), baseline immunosuppression and transplant centre. Biomaker-led care human leucocyte antigen Ab+ patients received intervention. Human leucocyte antigen Ab-negative patients were screened every 8 months. Recruitment Began September 2013 and for 37 months. The primary endpoint, scheduled for June 2020, was moved to March 2020 because of COVID-19. Numbers randomised From 5519 screened, 2037 were randomised (1028 biomaker-led care, 1009 to standard of care) including 198 with human leucocyte antigen antibodies against donor human leucocyte antigen (106 biomaker-led care, 92 standard of care) and 818 with human leucocyte antigens antibodies against non-donor human leucocyte antigen (427 biomaker-led care, 391 standard of care). Numbers analysed Two patients were randomised in error so 2035 were included in the intention-to-treat analysis. Outcome The trial had 80% power to detect a hazard ratio of 0.49 in biomarker-led care DSA+ group, > 90% power to detect hazard ratio of 0.35 in biomarker-led care non-DSA+ group (with 5% type 1 error). Actual hazard ratios for graft failure in these biomarker-led care groups were 1.54 (95% CI: 0.72 to 3.30) and 0.97 (0.54 to 1.74), respectively. There was 90% power to demonstrate non-inferiority of overall biomarker-led care group with assumed hazard ratio of 1.4: This was not demonstrated as the upper confidence limit for graft failure exceeded 1.4: (1.02, 95% CI 0.72 to 1.44). The hazard ratio for biopsy-proven rejection in the overall biomarker-led care group was 0.5 [95% CI: 0.27 to 0.94: p = 0.03]. The screening approach was not cost-effective in terms of cost per quality-adjusted life-year. Harms No significant differences in other secondary endpoints or adverse events. Limitations Tailored interventions meant optimisation was not possible in some patients. We did not study pathology on protocol transplant biopsies in DSA+ patients. Conclusions No evidence that optimised immunosuppression in human leucocyte antigen Ab+ patients delays renal transplant failure. Informing patients of their human leucocyte antigen antibodies status appears to reduce graft rejection. Future work We need a better understanding of the pathophysiology of transplant failure to allow rational development of effective therapies. Trial registration This trial is registered as EudraCT (2012-004308-36) and ISRCTN (46157828). Funding This project was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation programme (11/100/34) and will be published in full in Efficacy and Mechanism Evaluation; Vol. 10, No. 5. See the NIHR Journals Library website for further project information. Plain language summary Although kidney transplantation is the gold-standard treatment for kidney failure, thousands of transplants fail each year due to damage by the immune system. Finding circulating antibodies against the transplant can identify patients at high risk of failure. Under-treatment with immunosuppressive drugs plays a part in promoting the damage and increasing immunosuppression can slow progression in some but not all patients. In the Optimized TacrolimuS and MMF for HLA Antibodies after Renal Transplantation OuTSMART trial, we screened kidney transplant patients for circulating antibodies then, in the intervention arm, counselled everyone on the importance of taking immunosuppression, before optimising treatments to ‘best available’. We recruited > 2000 patients and split them into two groups randomly; in the first we revealed antibody results, encouraged adherence and tailored treatment to a combination of three drugs called tacrolimus, mycophenolate, and prednisolone, in a regimen that was judged optimal for each. In the second group, we did not release the antibody test results to patients or their doctors, and all treatment decision were based on local standard of care. At the end, we compared the numbers of transplant failures in each group. We confirmed that patients with antibodies were at higher risk of transplant failure, but found no differences in failures between those in whom we had intervened compared to those treated by standard of care. Although more developed rejection after standard care, there were no differences in the other things we measured, including the numbers who died, developed diabetes, infections or cancer and no differences in the number who developed new side effects. We therefore conclude that there is no basis for optimising drug treatment in those with antibodies at risk of transplant failure. Instead, novel treatments are needed. This trial will influence current practice around the world and hopefully incentivise research into new strategies to prevent transplant failure. Scientific summary Background Kidney transplants do not last for the natural lifespan of most recipients, and many patients eventually suffer progressive decline in transplant function leading to graft failure and need to return to dialysis. Around the world, this problem is significant, as 3% of kidney transplant patients return to dialysis each year. The single biggest cause of allograft dysfunction leading to transplant failure is immune-mediated damage and a prevalent hypothesis in the field is that inappropriately low levels of immunosuppression, either physician-led or due to patient non-adherence, is an important contributor to the initiation and progression of this immune-mediated damage. There are still no effective treatments for allograft dysfunction that is proven to be due to immune-mediated damage. Enhancing baseline immunosuppression appears to stabilise graft function in some patients. Two recent randomised trials of the anti-CD20 monoclonal antibody rituximab showed no impact, although both were stopped prematurely as they were underpowered. More recent reports indicate that anti-IL-6 monoclonals show promise at stabilising estimated Glomerular Filtration Rate (eGFR), but these have yet to be tested in large randomised trials. Since the development of circulating antibodies (Ab) against human leucocyte antigens (HLA) has been validated as a strong prognostic biomarker of kidney transplant failure, and there is genuine equipoise about whether increasing or optimising immunosuppression can benefit patients at risk of transplant failure, in the OuTSMART trial we tested the hypothesis that screening for these Ab followed by optimising oral immunosuppression treatment, could prevent allograft failure. Objectives Primary Determine the time to graft failure in patients testing positive for HLA Ab at baseline or within 32 months of randomisation who receive an optimised anti-rejection medication intervention with prednisolone, tacrolimus (Tac) and mycophenolate mofetil (MMF) (‘treatment’), compared to a control group who test positive for HLA Ab at baseline or within 32 months post-randomisation who remain on their established immunotherapy and whose clinicians are not aware of their Ab status. The primary endpoint was to be assessed remotely when 43 months post-randomisation was achieved by all. Secondary Determine the time to graft failure in patients randomised to ‘unblinded’ HLA Ab screening, compared to a control group randomised to ‘blinded’ HLA Ab screening. Determine whether treatment influences patient survival. Determine whether ‘treatment’ influences the development of graft dysfunction as assessed by presence of proteinuria (protein:creatinine ratio > 50 or albumin:creatinine ratio > 35) and change in eGFR. Determine whether ‘treatment’ influences the rates of acute rejection in these groups. Determine the adverse effect profiles of ‘treatment’ in this group, in particular whether they are associated with increased risk of infection, malignancy or diabetes mellitus. Determine the cost-effectiveness of routine screening for HLA Ab and prolonging transplant survival using this screening/treatment protocol. Determine the impact of biomarker screening and ‘treatment’ on the patients’ adherence to drug therapy and their perceptions of risk to the health of the transplant. Methods OuTSMART was an investigator-led, prospective, open-labelled marker-based strategy (hybrid) randomised trial. Eligible patients were recipients of cross-match negative transplants aged 18–75, more than 1 year post-transplant with an eGFR ≥30 ml/min willing to consent to the screening/treatment process. Patients were excluded if they were recipients of cross-match positive transplant requiring HLA desensitisation to remove Ab, recipients of additional solid organ transplants (e.g. pancreas, heart, etc.), had a history of malignancy (except non-melanomatous lesions restricted to the skin), had recent acute rejection, had a history of hepatitis B, C or human immunodeficiency virus (HIV), were known to have HLA Ab and received specific treatment for that Ab, had known hypersensitivity to any of the investigational medicinal products (IMPs), had known hereditary disorders of carbohydrate metabolism, were pregnant at the time of consent, or were females who refused to consent to using suitable contraception through the trial. Additionally, patients enrolled in any other studies involving administration of another IMP at time of recruitment were excluded. Stratified randomisation was 1 : 1 to two arms, blinded standard care (SC) or unblinded biomarker-led care (BLC). Randomisation was stratified first by the result from blood test screening for HLA Ab. The HLA Ab+ patients were further screened with single antigen beads to determine whether donor-specific Ab (DSA) were present or whether the only Ab detected was non-DSA. Thus, biomarker stratification led to three groups within each arm (DSA+, non-DSA+ and HLA Ab-neg). The second stratification was based on current immunosuppression, to ensure balanced numbers already on Tac or MMF in each group. The final stratification was by site. Patients in the SC arm were blinded to their biomarker status, as were their physicians, and remained on baseline immunotherapy, whereas patients in the BLC arm were told their HLA Ab status and were offered intervention. HLA Ab-negative patients in either arm remained on their existing immunotherapy and were rescreened for new HLA Abs every 8 months. Those patients who become positive during subsequent screening rounds were moved to the appropriate HLA Ab positive groups (DSA+ or non-DSA+) for final data analysis. All patients in the unblinded arm found to be positive on second or subsequent rounds were offered the same intervention as those patients who were positive in the first screening round, and these were intensively followed up for an additional 32 months from the time they become positive. Thus the maximum amount of time any single patient remained in intensive follow-up was 64 months. New patients were recruited to the study at each successive screening round. Intervention in the unblinded HLA Ab + patients consisted of informing patients of their HLA Ab status, followed by, in those with DSA or non-DSA, an interview to encourage medication adherence followed by medication changes to optimised doses of Tac, MMF and Prednisolone. Medication changes were tailored to each individual and failure to change, or to tolerate changes was not regarded as treatment failure, so some patients stayed on the same drug regimen. Patients with DSA and non-DSA were offered the same intervention. The primary outcome was originally transplant failure rates over 3 years, but this was changed to time to graft failure after an audit revealed that the prevalence and incidence rates of HLA Ab + patients were less than expected when planning the trial. With a planned minimum follow-up period of 43 months, the trial had 80% power to detect a hazard ratio (HR) of 0.49 in donor-specific antibody+ patients. Secondary endpoints were collected at 32 months and included patient death/survival, rates of biopsy-proven acute rejection, diabetes, infection and cancer, a health economic analysis and formal assessment of adherence. Results Recruitment started in September 2013. Over 37 months, 5519 patients were screened for eligibility and 2037 were randomised (1028 to unblinded BLC and 1009 to double-blinded SC). We identified 198 with DSA and 818 with non-DSA, and at the end of screening, there were 1021 in the Ab-neg groups. Baseline variables were well-matched between groups at the end of Ab-screening. Forty-five per cent of the DSA detected were directed against HLA-DQB antigens. Although the majority of patients were taking Tac (73%), MMF (67%) or prednisolone (55%), only 22% with DSA and 27% with non-DSA were taking all three drugs. Baseline immunosuppression use was balanced across arms and did not change during the trial in the SC arm. Ninety-seven per cent of HLA Ab+ recruits in the BLC arm had the formal interview, and the proportion taking all three drugs in the BLC arm increased to 54% (DSA) and 44% (non-DSA). There were 34 graft failures in HLA Ab+ recruits in the SC arm over the course of the study compared to 42 in the BLC arm. The HRs for graft failure in BLC DSA+ and non-DSA+ groups were 1.54 [95% confidence interval (CI) 0.72 to 3.30] and 0.97 (0.54 to 1.74), respectively, providing no evidence of a difference. The data for DSA+ groups confirmed that the presence of DSA was associated with an increased risk of graft failure, but non-DSA were not associated with graft failure compared to patients without Ab. Non-inferiority for the overall unblinded versus blinded comparison was not demonstrated as the upper confidence limit of the HR for graft failure exceeded 1.4 : (1.02, 95% CI 0.72 to 1.44). The HR for the secondary endpoint biopsy-proven rejection in the overall unblinded BLC group was 0.5 (95% CI 0.27 to 0.94; p = 0.03), but there were no significant differences in patient survival, biopsy-proven rejection, proven infections, malignancies, diabetes, development of proteinuria or mean eGFRs at the end of the trial. After adjusting for baseline quality of life, there was no significant gain of quality-adjusted life-year (QALY) in the BLC arm, but an incremental cost-effectiveness ratio per QALY that was significantly higher than the threshold set by the National Institute for Health and Care Excellence. Our analysis of adherence revealed significantly improved adherences for all three drugs in the BLC DSA+ group. Conclusions Thus, we conclude that the development of DSA (but not non-DSA) is associated with an increased risk of graft failure, but there is no evidence to support the primary hypothesis, that optimisation of immunosuppression in DSA+ patients can prevent this from happening. Trial registration This trial is registered as EudraCT (2012-004308-36) and ISRCTN (46157828). Funding This project was funded by the National Institute for Health and Care Research (NIHR) Efficacy and Mechanism Evaluation programme (11/100/34) and will be published in full in Efficacy and Mechanism Evaluation; Vol. 10, No. 5. See the NIHR Journals Library website for further project information.