Immunological changes in psoriasis patients under long-term treatment with fumaric acid esters: risk of Kaposi sarcoma occurrence?

Background: Psoriasis is a chronic skin disorder. The most frequently used systemic anti-psoriatic therapy in Germany is fumaric acid esters (FAE). Objectives: We aimed to characterize immunological changes in psoriasis patients under FAE treatment. Methods and Materials: Over 200 flow-cytometry analyses of blood from 27 psoriasis patients and histological, molecular, and serological analyses of samples from a patient who developed Kaposi sarcoma (KS) during FAE therapy were performed. Results: The patients receiving FAE showed decreased CD8+ T cell counts, in particular during the first six months. The CD4+ T cell decline was less pronounced and delayed in time. In a patient with KS, we found a profound CD4 and CD8 lymphocytopenia, as well as a NK cell number reduction, although leukocyte and lymphocyte counts were within the recommended limits. The patient was HIV negative, but positive for HHV8. After cessation of FAE therapy, KS regressed. Discussion: HHV8 infection and iatrogenic T cell reduction, prominently of CD8+ T cells, could have contributed to KS development in this patient. Therefore, we suggest a control of CD4+ and CD8+ T cell counts in addition to the commonly-used differential blood counts in patients with a higher HHV8 prevalence or at high risk of other latent viral infections.