Purpose: Kaposi sarcoma (KS) is a vascular tumor initiated by infection of endothelial cells (ECs) with KS-associated herpesvirus (KSHV). KS is dependent on sustained proinflammatory signals provided by intralesional leukocytes and continued infection of new ECs. However, the sources of these cytokines and infectious virus within lesions are not fully understood. Here, mast cells (MCs) are identified as proinflammatory cells within KS lesions that are permissive for, and activated by, infection with KSHV. Experimental Design: Three validated MC lines were used to assess permissivity of MCs to infection with KSHV and to evaluate MCs activation following infection. Biopsies from 31 AIDS-KS cases and 11 AIDS controls were evaluated by IHC for the presence of MCs in KS lesions and assessment of MC activation state and infection with KSHV. Plasma samples from 26 AIDS-KS, 13 classic KS, and 13 healthy adults were evaluated for levels of MC granule contents tryptase and histamine. Results: In culture, MCs supported latent and lytic KSHV infection, and infection-induced MC degranulation. Within KS lesions, MCs were closely associated with spindle cells. Furthermore,MCactivation was extensive within patients with KS, reflected by elevated circulating levels of tryptase and a histamine metabolite. One patient with clinical signs of extensive MC activation was treated with antagonists of MC proinflammatory mediators, which resulted in a rapid and durable regression of AIDS-KS lesions. Conclusions: Using complimentary in vitro and in vivo studies we identify MCs as a potential long-lived reservoir for KSHV and a source of proinflammatory mediators within the KS lesional microenvironment. In addition, we identify MC antagonists as a promising novel therapeutic approach for KS.
Bibliographical noteFunding Information:
The work was supported by Young Investigator Pilot Award from the AIDS and Cancer Specimen Resource NCI (ACSR) (UM1 CA181255 sub-award 7854SC; to C. King) and grant support from the NIH/NIAID (R03 AI122221; to C. King), by The Ohio State University (CCC-OSU 5OD160-201467; to L. Ayers), by funding from the NIH (P30 AI027763, UM1 CA181255, U54 CA190153, R01 CA119903; to J. Martin), and (R01 CA102667; to R. Rochford). A Barbachano-Guerrero is a fellow of the Mexican National Council on Science and Technology (CONACYT). We thank David Nohle, David Kellough, and Dr. Mamut Akgul for their expert technical assistance with this project.