HHV-6 causes limbic encephalitis in 10% of cord blood transplant patients.

The use of umbilical cord blood (UCB) as the stem cell source puts patients at a high risk for development of HHV-6 post transplant limbic encephalitis (PALE).

Researchers at Brigham and Women’s Hospital and Dana-Farber Cancer Institute monitored 1,344 post-HSCT patients and found that 19 (1.4%) developed HHV-6 PALE. Most notably, 10/101 (10%) of the patients who received UCB as the graft source developed HHV-6 PALE.

Furthermore, the authors report a 50% death rate of patients with HHV-6 PALE following UCB transplant, emphasizing the threat of this particular neurological manifestation. Risk factors that were predictive of the development of HHV-6 PALE were time-dependent acute graft-versus-host disease grades II-IV (p<0.001) and adult mismatched donors (p=0.04). They also found that peak viral loads in the plasma were higher in HHV-6 PALE patients who received UCB versus those who did not. All patients with HHV-6 PALE were positive for HHV-6B.

These findings suggest the importance for HHV-6 monitoring post-HSCT, particularly in patients receiving UCB, and warrants investigation into the possible benefits of prophylactic treatment for this group of patients. A small study of prophylactic treatment in Japan demonstrated a significant reduction in neurological complications.

For more information on the dangers of HHV-6 reactivation in transplantation and HHV-6 encephalitis, please visit the following webpages:

HHV-6 & Transplant Complications

HHV-6 & Encephalitis