The Role Of Early Natural Killer Cell Adoptive Infusion Before Engraftment In Protecting Against Human Herpesvirus-6b Encephalitis After Naive T-Cell-Depleted Allogeneic Stem Cell Transplantation

Background Naive T-cell-depleted grafts have been employed as an ex vivo T-cell depletion (TCD) platform to prevent graft-versus-host disease (GvHD) and improve immune reconstitution by providing rapid donor memory T-cell reconstitution after allogenic hematopoietic stem cell transplantation (allo-HSCT). CD45RA(-) memory T cells confer protection against viruses such as cytomegalovirus, Epstein-Barr virus, and adenovirus; however, reports have shown an unexpectedly high incidence of human herpesvirus (HHV)-6B encephalitis among pediatric allo-HSCT patients.Methods We report the first 18 consecutive allo-HSCT, 16 haplo-HSCT, and two human leukocyte antigen-matched related donors implanted with naive TCD grafts. All donors were administered three cell products: first, a CD34(+) stem cell product; second, a CD45RA(+) TCD graft, followed by an adoptive natural killer (NK) cell infusion within 10 days after HSCT. The study's primary endpoint was the incidence of HHV-6B encephalitis.Results Engraftment was achieved in 94.5% of cases; 2-year overall survival, event-free survival, and GvHD/relapse-free survival were 87.2% (95% CI 78.6-95.8), 67.3% (95% CI 53.1-81.5), and 64% (95% CI 50.5-78.1), respectively. HHV-6B reactivation occurred in 7 of the haplo-HSCT patients, six of who received a cell infusion with an NK/CD4 ratio <2. None of the patients developed encephalitis.Conclusions In this clinical study, we show that early adoptive NK cell infusion after a 45RA(+) TCD allo-HSCT graft is safe and can prevent HHV-6B encephalitis. We recommend infusing adoptive NK cells after allo-HSCT using CD45RA(+) TCD grafts.