Human herpesvirus 6 (HHV-6) causes only minor symptoms in healthy individuals but in immunosuppressed patients, e.g., patients after allogeneic stem cell transplantation (HSCT), HHV-6 reactivations can lead to diseases in different organ systems. HHV-6 reactivations have also been reported to be a cause for delayed engraftment, a trigger of graft-versus-host disease and a co-factor for other virus reactivations. T-lymphocytes play an important role in the control of virus reactivations. Little is known about the development of virus-specific T-cells after allogeneic HSCT.

Background:

Human herpesvirus 6 (HHV-6) causes only minor symptoms in healthy individuals but in immunosuppressed patients, e.g., patients after allogeneic stem cell transplantation (HSCT), HHV-6 reactivations can lead to diseases in different organ systems. HHV-6 reactivations have also been reported to be a cause for delayed engraftment, a trigger of graft-versus-host disease and a co-factor for other virus reactivations. T-lymphocytes play an important role in the control of virus reactivations. Little is known about the development of virus-specific T-cells after allogeneic HSCT.

Objective:

The aim of this study was the description of the HHV-6 specific cellular immunity in children and adolescents after allogeneic HSCT in the context of the clinical course.

Study design and participants:

For this prospective, cross-sectional study, 28 children and adolescents after allogeneic HSCT who received follow-up support at the respective centers were included. Patients were enrolled up to 24 months after allogeneic HSCT.. Peripheral venous blood was drawn 3, 6, 9, 12, 18, and 24 months after allogeneic HSCT. Furthermore, a blood sample was taken from 25 age- and sex-matched healthy controls without any inflammatory, immunological, or infectious diseases. This study was approved by the Institutional Review Board of the Medical University Graz and patients, parents or legal guardians of patients gave written informed consent in accordance with the Declaration of Helsinki.

Methods:

3, 6, 9, 12, 18 and 24 months after allogeneic HSCT peripheral blood mononuclear cells were isolated from patient blood, stimulated with HHV-6-specific antigen (U54) and cultured for 10 days. Furthermore, a blood sample was taken from 25 age- and sex-matched healthy controls without any inflammatory, immunological, or infectious diseases.

On day 10, peripheral blood mononuclear cells were re-stimulated with the virus antigen U54 for 6 hours and, thereafter, stained for surface markers (CD3, CD4, CD8, CD56) and intracytoplasmatic activation markers IL-2 (Interleukin-2), IFN-γ (Interferon-γ), TNF-α (tumor necrosis factor-α) for flow cytometric detection of virus-specific T-cells. T-cells with intracytoplasmic expression of activation markers after stimulation with the virus antigen are HHV-6-specific T-cells. This indicated HHV-6 specific cellular immunity.

The virus-specific immunity of patients to HHV-6 was compared to the virus-specific immunity of children and adolescents of a control group.

Inclusion Criteria:

Patients who have undergone allogeneic SCT (stem cell transplantation) at one of the participating centers in the last 24 months or who will undergo allogeneic SCT during the study period (up to 3 months before the end of the study) and complete follow-up care at the respective centers

• Age> 1 year
• Written consent by participant or legal guardian

Exclusion Criteria:

• severe SCT-associated complications during the study period: Rejection of the transplant ("graft failure") severe graft-versus-host disease (GVHD grade 3 or 4)
• Relapse of the (malignant) underlying disease or occurrence of another complication (e.g. secondary malignancy), which represents an indication for cytotoxic chemotherapy (or re-transplantation) during the examination period.

28 children with adolescent after allogeneic HSCT 25 healthy cildren as control (age and sex mached)