Impact of antiviral therapies on survival in patients with HHV-6B encephalitis after cord blood transplantation: a real-world study.

In this registry-based study, we evaluated the efficacy of different antiviral therapies for adult patients who developed human herpesvirus-6B (HHV-6B) encephalitis after their first cord blood transplantation (CBT). Among 3,862 CBT recipients registered in Japan between January 2019 and December 2023, HHV-6B encephalitis occurred in 289 patients within 100 days post-transplant (7.5%). Antiviral treatments included foscarnet (FCN) monotherapy (n = 190), ganciclovir (GCV) monotherapy (n = 12), and FCN/GCV combination therapy (n = 74). The FCN/GCV group was associated with a potential improvement in 1-year survival compared with the FCN and GCV groups (63.2% vs. 52.5% vs. 41.7%, p = 0.38). Moreover, FCN/GCV therapy was identified as an independent predictor of improved survival compared with FCN monotherapy (HR, 0.60; 95% CI, 0.38-0.95; p = 0.031). Furthermore, the combination FCN/GCV therapy showed better survival than FCN monotherapy in the patients after neutrophil engraftment (1-year survival 68.1% vs. 51.6%), but worse survival in patients before engraftment (1-year survival 34.1% vs. 54.6%). Together, these findings provide real-world evidence linking antiviral regimen selection to post-transplant outcomes in HHV-6B encephalitis and suggest that FCN/GCV combination therapy may offer a survival advantage over FCN monotherapy in selected CBT patients, with treatment strategies potentially tailored according to hematologic recovery.