*Purpose: Polyomavirus BK (BKV) has been suggested as a surrogate marker of overimmunosuppression. Due to recent advances in monitoring strategies and pre-emptive therapy, progression to BKV-associated nephropathy (BKVN) has been reduced. Reduction of maintenance immunosuppression during BKVN, however, has been associated with both T-cell mediated rejection (TCMR), antibody-mediated rejection (ABMR), and inferior kidney allograft outcomes. Although the administration of intravenous immunoglobulins (IVIG) failed to treat BKVN, IVIG may have properties to reduce allosensitization.

*Methods: We studied 860 kidney transplant recipients (KTRs) predominantly under tacrolimus-based triple-drug maintenance immunosuppression from 2009 to 2018. We identified 130 KTRs (15.1%) with high-level BK viremia >10,000 copies/mL (presumptive BKVN), 180 KTRs (20.9%) with low-level BK viremia <10,000 copies/mL, 85 KTRs (9.9%) with isolated BK viruria, and 465 KTRs (54.1%) with no BK viruria/viremia. Kidney allograft outcomes with respect to TCMR, ABMR, development of de novo donor-specific antibodies (DSA), kidney allograft survival, and estimated glomerular filtration rate (eGFR) slope were analysed. Due to the increased incidence of TCMR and ABMR among KTRs with presumptive BKVN, 48 of 130 KTRs (36.9%) with high-level BK viremia starting from 2015 received IVIG (0.5 g/kg of body weight) on a biweekly basis during BKV replication.

*Results: Very interestingly, KTRs with low-level BK viremia/viruria showed a significantly lower incidence of TCMR compared to KTRs with no BK viremia/viruria and KTRs with high-level BK viremia (p<0.05). In addition, KTRs with low-level BK viremia/viruria showed a significantly lower incidence of ABMR compared to KTRs with high-level BK viremia (p<0.05). No differences were observed with respect to the development of de novo DSA (MFI>5000) between KTRs with low-level BK viremia/viruria, KTRs with no BK viremia/viruria, and KTRs with high-level BK viremia (p>0.05). KTRs with low-level BK viremia/viruria showed superior kidney allograft survival and lower eGFR slope compared to KTRs with no BK viremia/viruria and KTRs with high-level BK viremia (p<0.05). The administration of IVIG during high-level BK viremia didn’t impact the development of TCMR, ABMR, development of de novo DSA, kidney allograft survival and eGFR slope (p<0.05).

*Conclusions: Our results suggest low-level BK viremia/viruria as a surrogate marker for ideal immunosuppression to sufficiently suppress the development of TCMR and ABMR in the early period posttransplantation, and to preserve kidney allograft function in the long-term. The administration of IVIG didn’t prove beneficial to reduce allosensitization among KTRs with high-level BK viremia.

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