WT1 Tumor Antigen is Overexpressed in Kaposi Sarcoma and is Regulated by KSHV vFLIP

PurposeWilms tumor 1 (WT1) is overexpressed in several cancers, and WT1 expression levels are associated with poor prognosis. As a host protein that functions as an oncogene, it represents an important immunotherapeutic target. This study evaluated WT1 expression in Kaposi sarcoma (KS) tumors to assess whether immunotherapy targeting WT1 is a potential therapeutic approach for KS. We also investigated the role of the causal agent of KS, Kaposi sarcoma herpesvirus (KSHV/HHV-8) in regulating WT1 expression. Experimental designImmunohistochemistry for WT1, KSHV, and B and T cells subsets, followed by image analysis, was performed in 363 KS tumor biopsies. Expression of KSHV vFLIP was evaluated by immunofluorescence. Primary endothelial cell cultures and cell lines were infected with KSHV in vitro, or transduced with an inducible vFLIP vector and induced with doxycycline, and then assessed for WT1 expression. Binding of ESK-1, a T cell receptor mimic therapeutic antibody that recognizes WT1 peptides presented on MHC HLA-A0201, was assessed using flow cytometry. ResultsWe report overexpression of WT1 in KS tumors, which was associated with increased with increasing histopathologic stage and the proportion of KSHV-infected cells. Areas with high WT1 expression showed sparse T cell infiltrates. KSHV infection in vitro resulted in WT1 upregulation, mediated by the viral protein vFLIP, which resulted in stronger binding of ESK1. ConclusionsKS lesions express high levels of WT1, a process regulated by the KSHV-encoded vFLIP. These findings suggest that immunotherapy directed against WT1 may represent a therapeutic approach for this cancer. Translational RelevanceKaposi sarcoma (KS) is a vascular neoplasm caused by the Kaposi sarcoma herpesvirus (KSHV/HHV-8). People living with HIV are not only at a significantly higher risk of developing KS, but also often have a more aggressive clinical course. Although antiretroviral therapy may cause regression of HIV-associated KS lesions, advanced cases of KS also require chemotherapy, which is rarely curative. Wilms tumor 1 (WT1) has been reported to be overexpressed in various cancers, functioning as an oncogene and associated with a poor prognosis. WT1 is also an important immunotherapeutic target, with several WT1-directed therapies showing promising results in early clinical trials for leukemias and solid tumors. Here we report high expression of WT1 in KS, especially in higher histological stages. Our findings provide pre-clinical evidence that supports conducting anti-WT1 immunotherapy trials in KS, and evaluating WT1 expression as a potential biomarker to identify individuals most likely to benefit.