OBJECTIVES: To describe the first in-depth analysis of both the T-cell responses against human herpesvirus-8 (HHV-8) and the HHV-8 viral load in 1 patient who developed iatrogenic HHV-8-associated-Kaposi's sarcoma (KS) following immunosuppressive treatment for undifferentiated arthritis and to review the literature on iatrogenic KS (IKS). METHODS: T-cell responses against HHV-8 lytic and latent antigens were analyzed by ex vivo enzyme-linked immunospot (Elispot) and HHV-8 viral load was assessed by quantitative polymerase chain reaction, in sequential peripheral blood samples from a 55-year-old woman who developed skin/mucosal and visceral KS, while receiving treatment with cyclosporine, methotrexate, and methylprednisolone for undifferentiated arthritis. RESULTS: KS may result from HHV-8 infection in patients undergoing immunosuppressive treatment for rheumatic diseases and this is the first case of IKS occurring in undifferentiated arthritis. A role for immune surveillance in the pathogenesis of IKS is supported by the observation of disease regression following discontinuation of immunosuppressive therapy. In a 4-year follow-up, we showed that variations of the virus-specific immune responses but not of the viral load correlated well with the disease course, characterized by 2 remission and subsequent relapse phases, following changes of immunosuppressive therapy. CONCLUSIONS: We have provided evidence of a clear-cut correlation between changes in immunologic markers of HHV-8 infection and the disease course of this viral associated tumor, concomitant with variations of immunosuppressive treatment. Thus, ex vivo enzyme-linked immunospot for HHV-8-specific T-cell responses represents a new tool for the clinical management of rheumatic patients with IKS.