Vascular Endothelial Growth Factor and Kaposi ’ s Sarcoma Cells in Human Skin Grafts 1

Human cancer cells often produce tumors in animal models that incompletely reproduce the histology of the parental tumor. Kaposi’s sarcoma (KS) cells, in particular, have not produced durable angiogenic lesions in animal models that resemble those of KS in humans. We investigated the contribution of transformed KS cells, vascular endothelial growth factor (VEGF), and human skin tissue on tumor development in a human skin graft/mouse model. High levels of serum VEGF (322 pg/ml) were seen in HIV-1-infected persons with KS compared with HIV1-infected persons without KS (115 pg/ml). Human KS lesions expressed VEGF in the spindle cells. Transformed KS cells expressed the mitogenically active 121-amino acid and 165-amino acid isoforms of VEGF. Tumors induced by KS cells implanted in the SCID mice grew preferentially in human skin grafts rather than in ungrafted murine skin. Tumors induced in the presence of human skin grafts developed numerous lumens expressing v 3 integrin. KS cells inoculated with neutralizing antiVEGF antibody did not form tumors. This study supports an important role for VEGF in tumor development and shows how a human tissue can preferentially promote tumor growth. Introduction KS is an angioproliferative disease that frequently appears in persons infected with HIV-1, particularly homosexual men. Although many infectious agents have been associated with the emergence of KS, only HIV-1 and HHV-8 (also known as KS-associated herpesvirus) have been strongly implicated in the induction of KS (1–3). All clinical epidemiological forms of KS contain HHV-8 in tumor tissue. HHV-8 is present in most cells of KS lesions with the majority of cells containing the virus in latent form. The cells containing HHV-8 share marker expression of endothelial and macrophage/monocyte cell lineages. The association of HHV-8 with all of the clinicalepidemiological types of KS (HIV-1-associated, those affecting solid organ transplant recipients, classical, and African) and their common histopathological appearance suggest a common pathogenesis but disparate rates of clinical progression (4). In addition, KS has been regarded as an infrequent and indolent disorder that in the last decades has been shown to be a very frequently occurring and progressive disorder in individuals with HIV-1 infection (5–7). We and others have suggested that, at least in the early stages of KS, tissue inflammation drives cellular proliferation to produce the characteristic hyperplastic and angiogenic features of KS lesions (8, 9). KS lesions are composed of a mixed-cell infiltrate with hyperplastic spindle-shaped cells that resemble cytokine-activated ECs and monocytes/ macrophages by their expression of tissue-specific markers (CD34, vascular-endothelial cadherin, endothelial leukocyte adhesion molecule type 1, CD4, CD14, CD68, and PECAM-1; Refs. 9–12). The most common cell type isolated from HIV-1-associated KS (AIDS-KS) has been the spindleshaped endothelial-like cells that proliferate in response to inflammatory cytokines and have a limited replicating life span. The highly angiogenic tissue of AIDS-KS lesions is believed to be mediated by bFGF, VEGF (13), and (in HIV-1related KS) the transactivating protein HIV-1 Tat (14, 15). VEGF and bFGF coupled with integrins interact synergistically to promote angiogenesis. An angiogenic factor paired with an anchorage signal through integrins are prerequisites for angiogenesis. AIDS-KS spindle cells, cell isolates from KS lesions of HIV-1-infected individuals, are hyperplastic nontransformed cells that proliferate in culture with inflammatory cytokines. These cell isolates initially contain HHV-8 that is rapidly lost as the cells are passaged in culture. AIDS-KS spindle cells are characterized by morphological characteristics, marker expression, and angiogenic factor production (16–18). Endothelial cells treated with inflammatory cytokines acquired many of the features of AIDS-KS spindle cells, suggesting that endothelial lineage may give rise to the KS tumor cells. Cell lines composed of transformed cells have also been isolated from advanced KS lesions. KS cell lines have been Received 4/5/02; revised 6/20/02; accepted 6/20/02. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 Supported in part by Concern Foundation and NIH Grant K08 CA808915-02 (to F. S.) and Core Grant CA16672. 2 To whom requests for reprints should be addressed, at Department of Lymphoma/Myeloma, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Box 429, Houston, TX 77030. Phone: (713) 792-2860; Fax: (713) 794-5656; E-mail: fsamaniego@mdanderson.org. 3 The abbreviations used are: KS, Kaposi’s sarcoma; EC, endothelial cell; HHV, human herpes virus; PECAM-1, platelet endothelial cell adhesion marker-1; bFGF, basic fibroblast growth factor; VEGF, vascular endothelial growth factor; IL, interleukin; FBS, fetal bovine serum; SCID, severe combined immunodeficient; TBS, Tris-buffered saline. 387 Vol. 13, 387–395, August 2002 Cell Growth & Differentiation