ALTERED HOMEOSTASIS OF PERIPHERAL BLOOD B CELLS IN PATIENTS WITH CHRONIC HUMAN HERPESVIRUS-8 INFECTION AND KAPOSI¿S SARCOMA: IMPLICATION FOR INFLUENZA VACCINATION

Background: Human herpesvirus-8 (HHV-8) is the etiological agent of classic Kaposi’s sarcoma (cKS), a lymphoangioproliferative disease found mainly in older men of Eastern European and Mediterranean origin. Due to the dual role of B cells in HHV-8 infection, virus reservoir as well as agents of humoral immune control, we analyzed the subset distribution and the functional state of peripheral blood B cells in HHV-8- infected individuals with and without cKS. Furthermore, in order to investigate whether the chronic HHV-8 infection in B cells could alter the functionality of these cells and particularly may impact on humoral responses to antigenic stimulation, we investigated cKS patients’ response to influenza vaccination, in terms of clinical efficacy, antibody production and safety. Methodology: Circulating B cells and their subsets were analyzed by 6-color flow cytometry in the following groups: 1- patients HHV-8 positive with classic KS (cKS); 2- subjects HHV-8 positive and cKS negative (HSP); 3- healthy controls, HHV-8 negative and cKS negative. Adjuvated trivalent influenza vaccine was administered to cKS patients and age- and sex-matched healthy controls. Influenza symptoms and side effects were recorded by daily diary cards supplied to the patients. Blood analysis and measurement of serum antibodies against vaccine antigens (H1N1, H3N2 and B) were performed before, 1 and 3 months post vaccination. Principal Finding: The number of B cells belonging to the preimmune/natural effector compartment, including transitional, pre-naı¨ve, naı¨ve and MZ-like subsets, was significantly higher among HHV-8 positive subjects, with or without cKS, while was comparable to healthy controls in the antigen experienced T-cell dependent compartment. The increased number of preimmune/natural effector B cells was associated with increased resistance to spontaneous apoptosis, while did not correlate with HHV-8 viral load. The clinical efficacy of vaccination was similar in cKS patients and controls. Seroconversion and seroprotection occurred equally in both groups. A mild increase in HHV-8 viremia was observed in a proportion of cKS patients after vaccination, without concomitant worsening of cKS lesions. The safety of vaccination did not differ between cKS patients and controls. The frequency of B cell subpopulations was evaluated and did not change after vaccination both in cKS patients and in healthy controls. Conclusions: For the first time to our knowledge, in this study we report that HHV-8 chronic infection promotes a perturbation of peripheral B cell homeostasis characterized by expansion of B cells of the preimmune/natural effector compartment, in patients with or without cKS. The alterations observed in cKS patients did not lead to an altered response to influenza vaccination that resulted safe and immunogenic in cKS patients as well as in age- and sex-matched controls. This observation may broaden our understanding of the complex interplay between viral and immune factors leading HHV-8-infected individuals to develop HHV-8-associated malignancies. Furthermore, our results have clinical importance because annual influenza vaccination may be particularly recommended for cKS patients considering their advanced age and comorbidity.