Case Report: BKV-specific T cells: a fast, safe and potentially effective treatment option for refractory BKV infections in pediatric patients after allogeneic stem cell transplantation.

BK virus reactivation is frequently observed in patients following allogeneic stem cell transplantation and can cause nephropathy and hemorrhagic cystitis. Current treatments are mainly supportive, and antiviral therapy with cidofovir lacks clear evidence of efficacy. Therefore, novel therapeutic strategies are needed. Since adoptive transfer of virus-specific T cells has proven effective for other viral infections, this case series with four cases of post-transplant severe BKV infections evaluated the feasibility, safety, and efficacy of BKV-specific T cells in patients with refractory BKV infection using the CliniMACS Prodigy system. Three of the four patients demonstrated a reduction in BKV viral load following adoptive T-cell transfer, with detectable in vivo expansion of BKV-specific T cells in these individuals. However, complete viral clearance was not achieved in all cases. One patient with extensive immunosuppression showed minimal viral response and no detectable BKV-specific T cells after infusion. Treatment was well tolerated, with no infusion-related toxicities and no severe de novo graft-versus-host disease observed. Overall, this case series suggests that rapidly manufactured BKV-specific T cells produced via the CliniMACS Prodigy system represent a feasible, safe, and potentially effective treatment option for refractory BKV viremia after stem cell transplantation. Early administration and limited concurrent immunosuppression may improve therapeutic outcomes. Further studies are needed to confirm these findings.