Tese de Doutoramento Medicina 2024 Faculdade de Ciências Médicas, Universidade NOVA de Lisboa

KT is the best treatment option for eligible patients with end-stage kidney disease (ESKD). Contemporary immunosuppression for KT significantly reduced the incidence of graft rejection but, conversely, increased the risk of infection and virally mediated malignancies. As new immunosuppressive agents and antimicrobial prophylaxis are likely to be introduced, a special attention is needed for the changes in the patterns of infectious diseases and malignancy post KT. Until now, no reliable biomarker for the risk of infection has emerged to guide clinicians in adjusting the level of immunosuppression. The use of non-pathogenic viruses in combination with immune biomarkers to monitor the intensity of immunosuppression is appealing, but is yet to be proved. Increased research is required to develop and validate biomarkers that could predict rejection, infection and malignancy. This document presents a series of scientific studies that aim to enrich the current knowledge about the role of specific human viruses in different clinical outcomes both in kidney recipients and kidney donors. The 10 manuscripts included in this thesis were grouped into four main topics. The first topic refers to ethical issues concerning living kidney donation. It is of utmost importance to consider the ethical contours in which organ transplantation takes place and to make all possible efforts to assure the basic ethical principles of living kidney donation. A critical review of the most relevant ethical problems regarding financial incentives for living kidney donation was presented, providing useful additional strategies to optimize live donation. The second topic dealt with the viral biomarkers in living kidney donors (LKD). Due to organ shortage, LKD becomes an important complement to deceased donor KT, but a careful selection of LKD is crucial in order to minimize the potential risks associated with donor nephrectomy. Two manuscripts highlighted a possible role of John Cunningham virus (JCV) in the evaluation and long-term follow-up of LKD. Several factors were postulated to justify a higher prevalence of JCV viruria in LKD candidates when compared with living kidney receptors (LKR) candidates. Possible mechanisms toexplain a lower estimated glomerular filtration rate (eGFR) recovery 3 years after donation in JCV viruric donors were presented. The third topic evaluated the reactivation of potential pathogenic viruses after KT. Some viruses can establish persistent infection in immunocompetent hosts and two patterns of persistent infections are known: chronic and latent infections. Continuous prolonged viral replication and shedding are observed in chronic viral infections, as Hepatitis B (HBV), while maintenance of the viral genome without replication is found in latent viral infections, such as polyomavirus. Albeit no clear association has been detected between JCV viruria and inferior outcomes after KT, exceptional cases of JCV‐associated nephropathy have already been described. One of those cases was presented in a case report form, highlighting the role of a molecular quantitative polymerase chain reaction (qPCR) technique to confirm the presence of JCV in the allograft tissue. Previously published data showed that either JCV viremia or simultaneous urinary reactivation of JCV and BK polyomavirus (BKV) after KT are rare phenomena. To study this phenomenon, the relationships between BKV or JCV infection with graft and patient survival in a cohort of 288 KT patients followed for a median of almost 4 years were assessed. Sustained BKV viremia lead to a novel off-label approach of immunosuppression modulation. Instead of the standard approach of tacrolimus and mycophenolate reduction or suppression, we opted for combining a low dose of calcineurin inhibitor and a mammalian target of rapamycin (mTOR) inhibitor. Episodes of acute rejection, patient and graft survival and eGFR were evaluated at the end of follow-up in one of the largest studies evaluating the outcomes of KT recipients expressing JCV or BKV viruria and viremia for a prolonged period. KT recipients are at an increased risk for urothelial carcinoma. Nevertheless, human polyomaviruses have recently been categorized as “possible carcinogens”, and a role for JCV in human cancers is not yet proved. A case report establishing the oncogenicity of JCV in the development of bladder cancer through specific immunochemical staining and specific in‐house real‐time qPCR was presented, highlighting the potential long‐ term risk for urothelial malignancies in KT patients with JCV nephropathy. In patients with resolved HBV infection, i.e., those with positive antibody to hepatitis B core antigen (anti-HBc) but negative plasmatic hepatitis B surface antigen (HBsAg), viral reactivation can occur at any time after the introduction of immunosuppressive therapies and can lead to life‐threatening complications. To clarify the incidence of HBV reactivation after KT, a cohort of 70 patients with previous resolved HBV infection was studied. Outcome data regarding patient and graft survival comparing anti‐HBc‐ positive patients and global population of transplant unit were presented. In addition, the prescription of prophylactic antiviral therapy for HBsAg‐negative/anti‐HBc‐positive patients after KT was critically reviewed. The fourth and last topic refers to a recent concept of viruses as biomarkers of immunosuppression status after KT. The main focus is on Torque teno virus (TTV). This virus has not been associated with any specific disease, but recent studies evaluated whether peripheral blood levels of TTV might reflect the overall strength of innate and specific immunity. An inverse correlation between immune competence and TTV replication might be a promising strategy to contribute to evaluate immune function in KT patients. Initially, a case report was presented, unveiling the kinetics of TTV DNA load during a mild course of Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) infection with prolonged viral shedding and failed antibody response, in a patient infected 3 months after receiving a KT. Thereafter, an original study performed to evaluate if TTV load before vaccination was associated with anti-spike (anti-S) total antibody formation in response to two doses of SARS-CoV-2 mRNA BNT162b2 vaccine in KT patients was described. Seroconversion rates after vaccination under different immunosuppressive medications were presented, as well as, the potential of TTV loads at baseline to predict the development of anti-S antibodies after two doses of vaccine. A cut-off of TTV viral load was calculated and proved to be able to predict the failure to develop antibodies. The third study on this topic focused on a prospective observational cohort study designed to evaluate TTV viral load in KT patients during the first year post-transplant, examining the overall kinetics and their relationships with deleterious events, including episodes of infection and the formation of de novo donor-specific antibodies (DSAs). The detection of an infectious event in the first year after KT was more probable among patients with higher increases in TTV viral load between the 1 st week and the 1st month after KT. Additionally, a cut-off value of TTV viral load variation between these time points which best discriminated patients with and without infection was established. Finally, a reflection was made about the major results of this compilation of studies and the future perspectives that lie ahead