Higher Risk Of HHV6 Reactivation Among Patients Undergoing Umbilical Cord Blood Transplantation

Human herpesviruses may cause severe complications after allogeneic hematopoietic stem cell transplantation (HSCT) such as interstitial pneumonia, encephalitis, delayed engraftment and post-transplant lymphoproliferative disease. A prospective survey on the incidence of primary infection or reactivation and clinical features of the eight human herpesviruses after HSCT has not yet been performed in Brazilian patients. Additionally, the impact of most of these infections on the transplant outcome is still unclear.

Between August 2010 and December 2012, peripheral blood samples from 99 allogeneic HSCT recipients were collected weekly after transplant until day +100, totalizing 824 samples. Median age was 15 years (range: 2-72), 60% were male, and acute leukemias were the most frequent diagnosis (54%). Stem cell sources were bone marrow in 62%, umbilical cord blood in 22% and mobilized peripheral blood in 16%. Fifty–one percent of donors were related. In a semi-automated workflow, the DNA was extracted from plasma in the QIAcube robot. A test based on quantitative real-time PCR (Taqman^®) was optimized to screen and quantify all known human herpesviruses (CMV, EBV, HSV1, HSV2, VZV, HHV6, HHV7 and HHV8). The PCR reactions were set up using QIAgility robot for high-precision pipetting, and have been performed in a 7900HT (Life Technologies). Infected cell cultures and plasma specimens with a known viral load/amplicon copy number have been used as controls. The limit of detection of the qPCR was 5 copies per reaction, representing 250 copies/mL of plasma for all of the viruses.

The incidences of primary infection or reactivation of herpesviruses were as follows: CMV=41%, HHV6=11%, HHV8=5.5%, EBV=3%, HSV1=3%, VZV=3%, HHV7=2%, and HSV2=1%. CMV reactivation was significantly more frequent in adults (72% vs. 27% for children, p<0.0001), and in those or receiving fludarabine (60% vs. 29%, p=0.03) and TBI (68% vs. 32%, p=0.01) in the conditioning regimen, but in a multivariate analysis, only age greater than 18 years remained significant (HR 3.4, 95%CI 1.7-6.7). HHV6 reactivation was significantly more frequent after umbilical cord blood transplant than after transplant from other sources (41% vs. 6%, respectively, p<0.0001) and in those receiving TBI in the conditioning regimen (19% vs. 3%, p=0.01) and in those receiving mycophenolate mofetil as GVHD prophylaxis (22% vs. 2%, p=0.004). In a multivariate analysis, only the use of cord blood remained significantly associated with the risk of HHV6 reactivation (HR 5.7, 95%CI 1.2-26.2). CMV reactivation was associated with a higher risk of acute graft-versus-host disease (GVHD), with a cumulative incidence at 100 days of 37% vs. 17% (p=0.02), but had no impact on the other outcomes. HHV6 reactivation had no significant impact on outcomes. HHV8 reactivation was associated with an increased risk of chronic GVHD (83% vs. 49%, p=0.001).

HHV6 primary infection or reactivation is more frequent after umbilical cord blood transplantation. CMV and HHV6 primary infection or reactivation are frequent after HSCT, but had no significantly impact on the transplant outcomes, possibly due to monitoring and preemptive measures. Monitoring these viruses constitute an essential measure to improve outcomes.

No relevant conflicts of interest to declare.