*Purpose: BK nephropathy is an important cause of allograft dysfunction or loss. IVIg is hypothesized to be effective by providing passive immunity to BK virus in addition to its immunomodulatory effects on innate and adaptive immunity. We describe our experience with IVIg in treatment of presumptive (plasma BK PCR >10,000 copies/ml) or biopsy proven BK nephropathy and assess predictors of response.

*Methods: All adult kidney transplant recipients at our center from Jan 2011 to May 2018 who were diagnosed with BK viremia and received IVIg were included. Treatment with IVIg was initiated in conjunction with or after failure of reduced immunosuppression and/or lefluonomide therapy if plasma BK PCR was >10,000 copies/ml. IVIg was given at a dose of 2g/kg monthly until response (reduction in plasma BK PCR to <1000 copies/ml) or when patient was deemed to be a non-responder.

*Results: Seventy-one patients were treated with IVIg, of whom 56 (78.9%) had a response. Table 1 shows the baseline characteristics of responders and non-responders. Median time from BK diagnosis to IVIg initiation was 35 days and median plasma BK titer at IVIg initiation was 25750 copies/ml. Figure 1 shows time from IVIg initiation to response. Most of the responders (49/56; 88%) responded within 6 months of IVIg initiation. Using forward stepwise logistic regression (p<0.10 for inclusion), increasing time from transplant to BK diagnosis and increasing time from BK diagnosis to IVIg initiation were negatively associated with response to IVIg therapy (Table 2).

*Conclusions: IVIg may be an effective adjunctive treatment of BK nephropathy, particularly when started early after diagnosis.

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