Molecular immune monitoring in kidney transplant rejection: a state-of-the-art review

Although current regimens of immunosuppressive drugs are effective in renal transplant recipients, long-term renal allograft outcomes remain suboptimal. For many years, the diagnosis of renal allograft rejection and of several causes of renal allograft dysfunction, such as chronic subclinical inflammation and infection, was mostly based on renal allograft biopsy, which is not only invasive but also possibly performed too late for proper management. In addition, certain allograft dysfunctions are difficult to differentiate from renal histology due to their similar pathogenesis and immune responses. As such, non-invasive assays and biomarkers may be more beneficial than conventional renal biopsy for enhancing graft survival and optimizing immunosuppressive drug regimens during long-term care. This paper discusses recent biomarker candidates, including donor-derived cell-free DNA, transcriptomics, microRNAs, exosomes (or other extracellular vesicles), urine chemokines, and nucleosomes, that show high potential for clinical use in determining the prognosis of long-term outcomes of kidney transplantation, along with their limitations.

Clinical and immunological characteristics for BK polyomavirus-associated nephropathy after kidney transplantation

INTRODUCTION

BK polyomavirus (BKPyV)-associated nephropathy (BKPyVAN) can cause a significant risk of allograft impairment after kidney transplantation (KT). Intact BKPyV-specific immunity is associated with viral containment. This study investigated BKPyV-specific immunological factors among KT recipients.

METHODS

This prospective study in a single transplant center from January 2019 to August 2019 assessed associations between clinical and immunological characteristics, with a focus on BKPyV-cell-specific immunity and BKPyVAN, among KT recipients aged ≥15 years. The numbers of interferon-gamma (IFN-γ)-producing CD4+  T, CD8+  T, natural killer (NK), and natural killer T (NKT) cells were measured after stimulation with large T antigen and viral capsid protein 1 (VP1).

RESULTS

In total, 100 KT recipients were included (mean age ± SD, 42 ± 11 years); 35% of the recipients were female patients, and 70% had received induction immunosuppressive therapy. The 1-year cumulative incidence of high-level BKPyV DNAuria (possible BKPyVAN) and (presumptive BKPyVAN) was 18%. Among 40 patients with immunological factor data, pre-KT %NK cells (hazard ratio [HR], 1.258; 95% confidence interval [CI], 1.077-1.469; p = .004) and %VP1-specific NK cells (HR, 1.209; 95% CI, 1.055-1.386; p = .006) were factors independently associated with possible and presumptive BKPyVAN. KT recipients with possible and presumptive BKPyVAN were more likely to exhibit significant mean coefficients of %NK, %VP1-specific NK, and %NKT cells at 1 month after KT than before KT (all p < .05).

CONCLUSION

Individuals with nonspecific and VP1-specific NK cells before KT and increasing numbers of these cells after KT may be at risk for high-level BKPyV DNAuria and presumptive BKPyVAN. Further studies are needed to determine the utility of BKPyV-specific innate immune surveillance in predicting the occurrence of BKPyVAN.

Infections after organ transplantation and immune response

Organ transplantation has provided another chance of survival for end-stage organ failure patients. Yet, transplant rejection is still a main challenging factor. Immunosuppressive drugs have been used to avoid rejection and suppress the immune response against allografts. Thus, immunosuppressants increase the risk of infection in immunocompromised organ transplant recipients. The infection risk reflects the relationship between the nature and severity of immunosuppression and infectious diseases. Furthermore, immunosuppressants show an immunological impact on the genetics of innate and adaptive immune responses. This effect usually reactivates the post-transplant infection in the donor and recipient tissues since T-cell activation has a substantial role in allograft rejection. Meanwhile, different infections have been found to activate the T-cells into CD₄⁺ helper T-cell subset and CD₈⁺ cytotoxic T-lymphocyte that affect the infection and the allograft. Therefore, the best management and preventive strategies of immunosuppression, antimicrobial prophylaxis, and intensive medical care are required for successful organ transplantation. This review addresses the activation of immune responses against different infections in immunocompromised individuals after organ transplantation.

The effect of BK polyomavirus large T antigen on CD4 and CD8 T cells in kidney transplant recipients

Human BK polyomavirus (BKPyV) can affect the machinery of the host cell to induce optimal viral replication or transform them into tumor cells. Reactivation of BKPyV happens due to immunosuppression therapies following renal transplantation which might result in BK polyomavirus nephropathy (BKPyVAN) and allograft loss. The first protein that expresses after entering into host cells and has an important role in pathogenicity is the Large T antigen (LT-Ag). In this review tries to study the molecular and cellular inter-regulatory counteractions especially between CD4 and CD8 T cells, and BKPyV LT-Ag may have role in nephropathy after renal transplantation.

Current Status, Prevention and Treatment of BK Virus Nephropathy

All renal transplant recipients should undergo a regular screening for BK viral (BKV) viremia. Gradual reduction of immunosuppression is recommended in patients with persistent plasma BKV viremia for 3 weeks after the first detection, reflecting the presence of probable or suspected BKV-associated nephropathy. Reduction of immunosuppression is also a primary intervention in biopsy proven nephropathy associated with BKV (BKVN). Thus, allograft biopsy is not required to treat patients with BKV viremia with stabilized graft function. There is a lack of proper randomised clinical trials recommending treatment in the form of switching from tacrolimus to cyclosporin-A, from mycophenolate to mTOR inhibitors or leflunomide, or the additive use of intravenous immunoglobulins, leflunomide or cidofovir. Fluoroquinolones are not recommended for prophylaxis or therapy. There are on-going studies to evaluate the possibility of using a multi-epitope anti-BKV vaccine, administration of BKV-specific T cell immunotherapy, BKV-specific human monoclonal antibody and RNA antisense oligonucleotides. Retransplantation after allograft loss due to BKVN can be successful if BKV viremia is definitively removed, regardless of allograft nephrectomy.