Contribution of viral and cellular cytokines to Kaposi's sarcoma-associated herpesvirus pathogenesis

Abstract

Kaposi's sarcoma (KS)-associated herpesvirus is associated with the proliferative/malignant disorders KS, primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD) in patients with AIDS. In spite of recent advances in the treatment of KS, PEL and MCD represent therapeutic challenges. Recent advances in dissecting the pathogenesis of these diseases have indicated that the viral cytokine IL-6 and the cellular cytokines/growth factors IL-10, IL-6, stromal cell-derived factor 1, and vascular endothelial growth factor are important contributors to the growth, survival, and spread of PEL and MCD and are therefore potential targets for drug development.

Fig. 1.

Properties of vIL-6 binding to gp130. (A) Binding of huIL-6 (50 mg/ml) to immobilized, soluble gp130, with or without soluble IL-6R (sIL-6R), analyzed by plasmon resonance (BIAcore 2000 system). (B) Binding of recombinant (Escherichia coli-derived), purified maltose-binding protein (MBP)-vIL-6 to gp130. (C) Schematic representation of the vIL-6/gp130 complex based on crystallographic analyses. gp130 (red and yellow) binds to vIL-6 helices in a tetrameric complex. Site I denotes an epitope recognized by a vIL-6-neutralizing mAb that we have generated.

Fig. 2.

Tumorigenicity of NIH3T3 cells overexpressing vIL-6 in immunodeficient mice. (A) Representative tumors in nude mice 4 weeks after they were injected s.c. with vIL-6-NIH3T3 cells. Control NIH3T3 and vIL-6-NIH3T3 cells were injected at 0.5 × 10⁶ cells/mouse (BALBc nude). (B) Increased vascularization in vIL-6-NIH3T3 tumors. Representative image from tumor tissue stained with H&E (original magnification, ×100). (C, E, and G) VEGF visualized by immunohistochemical staining in tumor tissue (original, ×40), lymph node (original, ×200), and spleen (original, ×100), respectively. (D, F, and H) Control immunostaining of tumor tissue, lymph node, and spleen, respectively.

Fig. 3.

vIL-6 detection in AIDS-associated MCD tissue and blood. Immunohistochemical detection of KSHV LANA (A) and vIL-6 (B) in the mantle zone of a lymph node affected with MCD (original magnification, ×200). The characteristic, nuclear-speckled staining of LANA and the cytoplasmic staining of vIL-6 are shown in the insets (original, ×1000). (C) Serum IL-6 and vIL-6 levels in the circulation of a patient with AIDS-MCD during an active phase of the disease and subsequent clinical remission. Antiretroviral therapy was with stavudine (d4T), lamivudine (3TC), and nelfinavir (NFV); prednisolone was added at the outset of general symptoms and tapered; the antiviral drug foscarnet was added as the clinical symptoms subsided.

Fig. 4.

Effects of vIL-6 and IL-10 neutralization on PEL cell proliferation. BCBL-1 PEL cells were cultured for 3 days, with or without 25% autologous conditioned medium alone or with anti-vIL-6 IgG, control IgG, mAb to IL-10, or a combination of anti-vIL-6 and anti-IL-10 antibodies. Cell proliferation was measured by radioactive thymidine uptake.

Fig. 5.

Schematic representation of autocrine growth factor activity in PEL. KSHV-encoded vIL-6, cellular IL-10, IL-6, and VEGF are constitutively expressed and secreted in the culture supernatants of PEL cells. Cellular IL-10 and vIL-6 bind to the IL-10R and gp130, respectively, activate STAT3, and promote PEL cell growth.

Fig. 6.

Schematic representation of a PEL mouse model. Immunodeficient NOD/SCID mice are injected i.p. with PEL cells (BC-1 cells, 20×10⁶/mouse) on Day 1. On Days 8–10, the mice develop a lymphomatous ascite; in the example shown, the peritoneal cavity is closed. On Days 15–18, 50–75% of the mice develop visible tumors attached to the peritoneal mesothelium. From Day 29 on, most mice have evidence of PEL dissemination outside the peritoneal cavity. In the example shown, PEL cells are identified microscopically under the renal capsule and in the blood.

Fig. 7.

Microscopic evidence of PEL dissemination in a murine model of the disease. Immunodeficient NOD/SCID mice were injected i.p. with PEL cells (BC-1 cells, 20×10⁶/mouse) and were killed on Days 21–30. PEL infiltration of the peritoneal mesothelium (A), the diaphram (B), and the abdominal muscles (C) is visualized by microscopic morphology. Tissue sections were stained with H&E; original magnification, ×20.