Key words : BK virus infection, Indwelling stent, Magnetic Black Star stent, Renal transplant

Introduction

BK virus is a major cause of chronic renal allograft failure.¹ BK virus is a human polyomavirus with serologic prevalence in 70% to 90% of the general population without specific symptoms or sequelae.² However, recipients of kidney transplants may develop BK virus, which may lead to BK nephropathy in 1% to 10% of cases,1 and BK nephropathy is associated with allograft loss in >50% of cases.³ Risk factors for BK virus infection include a higher degree of human leukocyte antigen (HLA) mismatch, pediatric status, aggressive immunosuppressive regimen, and transplant ureteral stent use.⁴ Indeed, the main hypothesis is that the catheter could cause damage to the urothelial epithelium where the inactivated virus would remain, causing inflammation and erosion, which could trigger the activation and replication of the virus.⁵

Recently, the use of a new type of ureteral stent has been reported in kidney transplant recipients.⁶ This novel double-J stent, the Magnetic Black Star (MBS; Urotech GmbH), which has a hollow magnet at the distal end, has been developed to allow bedside extraction with a customized disposable device. One of the possible advantages of the MBS stent is that it may also reduce inflammation of the urothelial epithelium.

In this preliminary report, we compared BK virus viremia and viruria occurrence depending on the type of double-J stent (standard versus MBS).

Materials and Methods

We included all kidney transplants (exclusion of combined transplant procedures) performed in our center from January to December 2022 by 7 different surgeons. All ureteroneocystostomies were performed by extravesical (Lich-Gregoir) technique with double-J stent placement in each case. Indwelling stents placed were either 6- or 7-Fr standard double-J stents (standard group) or 6-Fr MBS double-J stents (MBS group). For the MBS double-J stent placement, the proximal tip was first inserted into the ureteral lumen and then the distal tip was placed inside the bladder by means of plastic surgical instruments, which are mandatory because of the magnet. The type of double-J stent was chosen according to the surgeon’s preference. Double-J stents (standard or MBS) were removed between 21 days and 28 days post-transplant. Urethral catheters were removed 5 days posttransplant.

Induction therapy was performed according to the immunological status at transplant. When given, the induction therapy included anti-interleukin 2 receptor blockers or polyclonal antibodies. The maintenance immunosuppression included tacroli-mus and steroids, associated with everolimus or mycophenolic acid.

A standard BK virus screening protocol was followed during the study period, which consisted of routine polymerase chain reaction examination of both plasma and urine samples during monthly follow-up. BK virus viremia was defined as >500 copies/mL, and viruria was defined as >100 copies/mL.

Results

From January 1 to December 31, 2022, 201 kidney transplant were performed in our institution (including 11 combined transplant, excluded from our study). Thus, 190 kidney transplant recipients were considered.

After exclusion of transplant recipients with missing data (n = 25 missing data concerning double-J stent type; n = 45 missing data concerning BK viremia and viruria or early graft loss within month 1 posttransplant), we included 120 transplant recipients. Among the 120 recipients, 92 received a standard double-J stent (standard group) and 28 patients received a Magnetic Black Star stent (MBS group). Related living donors represented 28.3% (34/120) of donors; the others were deceased donors. Patient characteristics are summarized in Table 1. Patients were mostly male in the standard group (70.7%) versus the MBS group (42.9%) (P = .01). ABO- and HLA-incompatible kidney transplant rates were similar in both groups (Table 1). Induction therapy was also similar between groups.

Outcomes concerning BK viremia and BK viruria occurrence at 1 month, 3 months, and 6 months are presented in Table 1. BK viremia occurrence and BK viruria occurrence were similar in the standard group and MBS group at 1 month, 3 months, and 6 months.

Discussion

BK virus is a harbinger of BK nephropathy, which may lead to irreparable graft dysfunction or failure. Ureteral stent use has been described as a risk factor for BK virus infection.^4,7 However, ureteral stents are often utilized as they decrease the risk of postoperative ureteral complications by 5- to 10-fold.^8,9 To our knowledge, this study is the first to assess the occurrence of BK virus infection according to the type of double-J stent. Our study suggests the occurrence of BK virus does not depend on the type of double-J stent used during kidney transplant.

The safety and efficacy of the use of MBS double-J stents have been reported by Capocasale and colleagues.⁶ The group reported that intraoperative insertion and extraction were straightforward in all cases. However, the study did not assess the rate of BK virus infection.

Several studies have reported that the extraction time of the double-J stent after kidney transplant and the length of the double-J stent were predictive of BK virus infection, with an advantage of early extraction (<3 weeks) and short double-J stent (12 cm).^7,10-14 It is important to report that our double-J extraction time was >3 weeks and the length of the MBS double-J stent is 15 cm, which may partly explain our results.

Conclusions

This preliminary study showed no differences concerning BK virus infection depending on the type of double-J stents used during kidney transplant. Larger studies are needed to confirm our findings.

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