Monitoring of BK viral load in renal allograft recipients by real-time PCR assays

Strong association of phenylalanine and tryptophan metabolites with activated cytomegalovirus infection in kidney transplant recipients

Infection-induced inflammation triggers catabolism of proteins and amino acids. Phenylalanine and tryptophan are 2 amino acids related to infections that regulate immune responses. Polyomavirus BK (BKV) and cytomegalovirus (CMV) are important pathogens after kidney transplantation. We investigated the clinical relevance of phenylalanine, tryptophan, and tryptophan metabolites (kynurenine and quinolinic acid) plasma levels in kidney transplant recipients with active CMV (BKV(-)CMV(+), n = 12) or BK virus infection (BKV(+)CMV(-), n = 37). Recipients without active viral infections (CMV(-)BKV(-), n = 28) and CMV(-)BKV(-) healthy individuals (HCs, n = 50) served as controls. In contrast to BKV infection, activated CMV infection is tightly linked to increased phenylalanine and tryptophan metabolite plasma levels (p ≤ 0.002). The association of phenylalanine (cutoff 50 μmol/L) with CMV infection demonstrates high sensitivity (100%) and specificity (94%). By contrast, kynurenine (p = 0.029) and quinolinic acid (p = 0.003) values reflect the severity of CMV infection. In this early proof-of-concept trial, evidence indicates that activated CMV infection is strongly associated with increased phenylalanine as well as kynurenine and quinolinic acid plasma levels. Moreover, tryptophan metabolite levels correlate with disease severity. Measurement of these amino acids is an inexpensive and fast method expected to complete conventional diagnostic assays.

The BK virus in renal transplant recipients-review of pathogenesis, diagnosis, and treatment

The BK virus, a DNA virus from the Polyomavirus group, represents an opportunistic infection of immunosuppressed transplant recipients. Though the virus was discovered approximately 40 years ago, the emergence of BK virus nephropathy since 1995 onwards, with associated high graft loss rates, has revolutionized renal transplantation medicine. Kidney transplant professionals realized that the consequences of over-immunosuppression were as severe as the consequences of under-immunosuppression and we entered the era of immunosuppressive minimization. Despite this recognition, the optimal testing type for BK virus infections and frequency of testing are hotly debated. Similarly, optimal treatment strategies remain sources of intense controversy. The authors review the current strategies of screening, diagnosis, and possible treatment, and also review the amount and quality of evidence in favor or against. Similarities and differences between cytomegalovirus, Epstein-Barr virus, and BV virus, the three major viral infections in kidney transplantation, are highlighted.

The influence of immunosuppressive agents on BK virus risk following kidney transplantation, and implications for choice of regimen

The increasing incidence of BK-associated nephropathy following kidney transplantation has prompted an examination of strategies for risk reduction and management through immunosuppression manipulation. Evidence from retrospective and prospective studies suggests that BK viruria and viremia, and the need for BK virus treatment, are higher with tacrolimus than cyclosporine. Combined therapy with tacrolimus and mycophenolic acid may be associated with a particularly higher risk of BK infection, but data are conflicting as to whether mycophenolic acid per se is an independent risk factor. The incidence of BK-related events may be reduced in patients receiving mTOR inhibitors (everolimus or sirolimus) with cyclosporine vs a calcineurin inhibitor with mycophenolic acid. De novo immunosuppression regimens that avoid rabbit antithymocyte globulin and tacrolimus, particularly tacrolimus with mycophenolic acid, may be advantageous, whereas low-exposure cyclosporine with an mTOR inhibitor appears a favorable option. Routine screening for BK infection during the first 2 years posttransplant is recommended to allow preemptive modification of the immunosuppressive regimen. In patients at high risk of BK virus infection, appropriate de novo immunosuppression or very early conversion to an mTOR inhibitor to facilitate reduction or discontinuation of calcineurin inhibitors or antimetabolites should be considered. Extensive further research into optimal avoidance, screening, and treatment strategies is required.

Early monitoring of the human polyomavirus BK replication and sequencing analysis in a cohort of adult kidney transplant patients treated with basiliximab

Background

Nowadays, better immunosuppressors have decreased the rates of acute rejection in kidney transplantation, but have also led to the emergence of BKV-associated nephropathy (BKVAN). Therefore, we prospectively investigated BKV load in plasma and urine samples in a cohort of kidney transplants, receiving basiliximab combined with a mycophenolate mofetil-based triple immunotherapy, to evaluate the difference between BKV replication during the first 3 months post-transplantation, characterized by the non-depleting action of basiliximab, versus the second 3 months, in which the maintenance therapy acts alone. We also performed sequencing analysis to assess whether a particular BKV subtype/subgroup or transcriptional control region (TCR) variants were present.

Methods

We monitored BK viruria and viremia by quantitative polymerase chain reaction (Q-PCR) at 12 hours (Tx), 1 (T1), 3 (T2) and 6 (T3) months post-transplantation among 60 kidney transplant patients. Sequencing analysis was performed by nested-PCR with specific primers for TCR and VP1 regions. Data were statistically analyzed using χ² test and Student's t-test.

Results

BKV was detected at Tx in 4/60 urine and in 16/60 plasma, with median viral loads of 3,70 log GEq/mL and 3,79 log GEq/mL, respectively, followed by a significant increase of both BKV-positive transplants (32/60) and median values of viruria (5,78 log GEq/mL) and viremia (4,52 log GEq/mL) at T2. Conversely, a significantly decrease of patients with viruria and viremia (17/60) was observed at T3, together with a reduction of the median urinary and plasma viral loads (4,09 log GEq/mL and 4,00 log GEq/mL, respectively). BKV TCR sequence analysis always showed the presence of archetypal sequences, with a few single-nucleotide substitutions and one nucleotide insertion that, interestingly, were all representative of the particular subtypes/subgroups we identified by VP1 sequencing analysis: I/b-2 and IV/c-2.

Conclusions

Our results confirm previous studies indicating that BKV replication may occur during the early hours after kidney transplantation, reaches the highest incidence in the third post-transplantation month and then decreases within the sixth month, maybe due to induction therapy. Moreover, it might become clinically useful whether specific BKV subtypes or rearrangements could be linked to a particular disease state in order to detect them before BKVAN onset.

Prospective monitoring of BK virus reactivation in renal transplant recipients in North India

BACKGROUND

BK nephropathy (BKN) is an important complication of renal transplantation with a reported incidence between 1% and 10% in different parts of the world. Early diagnosis is important to plan early therapeutic strategies. The epidemiology and evolution of BKN is relatively unknown in India and hence, the present study has been designed to prospectively monitor the activation of BK virus (BKV) in renal transplant recipients in India.

PATIENTS AND METHODS

In this study, 32 renal allograft recipients were prospectively monitored with protocol biopsies of allografts, BKV DNA load in plasma, and viral particles in urine by electron microscopy (EM) on day 1, and at 1, 3, and 6 months. Additionally, the baseline BKV DNA load in plasma was quantitated in 21 corresponding donors.

RESULTS

On follow-up in 32 recipients, 9.7%, 23.8%, 19.2%, and 13.3% of patients showed viral profiles by EM at day 1, 1 month, 3 months, and 6 months, respectively. BKV DNA positivity in plasma was 25.8%, 42.9%, 15.4%, and 20% at day 1, 1 month, 3 months, and 6 months, respectively, with mean BKV copy number/mL plasma of 1796, 1029, 2611, and 3318, respectively. A total of 15.7% (17/108) urine samples of 32 renal recipients were positive by urine EM. Out of 100 protocol biopsies, none developed histologically demonstrable cytopathic effects of BKN, although 8% biopsies were SV-40 large T antigen (SV-40 T Ag) positive. By quantitative real-time polymerase chain reaction assay, 27/108 (25%) of recipients' plasma samples were positive for BKV. Peak viremia and viruria occurred at 1-3 months post transplantation. The baseline viremia in donors was predictive of viremia positivity in the post-transplantation period at 1 month. Twenty-four episodes of graft dysfunction were attributed mainly to rejection.

CONCLUSION

The study shows a total of 15.7% and 25% urine and plasma samples were positive for BKV at any time during a 6-month follow-up. The highest incidence of BK viruria and viremia occurred at 1 month. In protocol biopsies, focal positivity of SV-40 T Ag was seen in 8% biopsies.

Monthly screening for BK viremia is an effective strategy to prevent BK virus nephropathy in renal transplant recipients

BACKGROUND

BK polyomavirus virus (BKV) nephropathy (BKVN) is the most common viral infection that affects renal allografts. Because a specific antiviral therapy is lacking, BKVN may result in graft dysfunction and/or loss. We prospectively analyzed whether monthly nucleic acid testing (NAT) for BKV replication in blood and immediate reduction of immunosuppression (IS) could prevent BKVN.

METHODS

NAT was performed at monthly intervals for 6 months and then at 12 months in 119 de novo renal transplant recipients. In viremic patients (presumptive BKVN), a graft biopsy was systematically performed and IS was immediately reduced.

RESULTS

BKV viremia occurred in 13 (10.9%) patients after a median time of 90 days (23-241); 77% of patients were viremic before month 4. After reduction of IS, viral load was undetectable in 11 patients, remained low in 1, and continued to increase in 1 patient who developed definitive BKVN despite reduction of IS, and finally returned to dialysis 6 months after transplantation.

CONCLUSION

BKV infection is an early complication. Monthly NAT in blood during the first 6 months and immediate reduction of IS in viremic patients almost completely prevent definitive BKVN.