Gene-targeted mice have recently revealed a role for lymphocytes and interferon-gamma (IFNgamma) in conferring protection against cancer, but the mechanisms remain unclear. Here, we have characterized a successful primary antitumor immune response initiated by naive CD4+ T cells. Major histocompatibility complex class II (MHC-II)-negative myeloma cells injected subcutaneously into syngeneic mice were surrounded within 3 days by macrophages that captured tumor antigens. Within 6 days, naive myeloma-specific CD4+ T cells became activated in draining lymph nodes and subsequently migrated to the incipient tumor site. Upon recognition of tumor-derived antigenic peptides presented on MHC-II by macrophages, the myeloma-specific CD4+ T cells were reactivated and started to secrete cytokines. T cell-derived IFNgamma activated macrophages in close proximity to the tumor cells. Tumor cell growth was completely inhibited by such locally activated macrophages. These data indicate a mechanism for immunosurveillance of MHC-II-negative cancer cells by tumor-specific CD4+ T cells through collaboration with macrophages.

IntroductionThe formation of new capillaries from pre-existing vessels (angiogenesis) appears to be essential for tumor growth and survival. [1][2][3][4][5][6] Whereas hypoxic conditions in expanding tumors often initiate a cascade of endothelial cell sprouting and formation of new vessels, tumor growth can be arrested by inadequate blood supply and a lack of metabolic exchange, often leading to tumor necrosis and regression. 7 Several tumor-derived, circulating angiogenesis inhibitors generated in vivo by proteolytic degradation have been recently identified (reviewed in Cao 8 and Marneros and Olsen 9 ). In particular, a 20-kDa C-terminal proteolytic fragment of collagen XVIII, termed endostatin, inhibits tumor growth in several animal models. [10][11][12][13][14][15] Although the mechanisms of action are incompletely understood, endostatin reportedly interacts with several endothelial cell-surface receptors that are critically involved in angiogenesis. Endostatin binds directly to the fibronectin receptor ␣ 5 ␤ 1 16,17 and also interacts with ␣ v ␤ 3 and ␣ v ␤ 5 integrins. 17 In keeping with these interactions, endostatin inhibits endothelial cell binding to the ␣ v ␤ 3 -ligand gelatin 17 and also their binding to collagen type I in a dose-dependent manner. 18 Moreover, endostatin binds to heparan sulfate, [19][20][21][22] tropomyosin, 23 caveolin-1, 16 VEGFR-1 (vascular endothelial growth factor receptor-1; Flt-1), and VEGFR-2 (Flk-1) 24 and was recently shown to depend on E-selectin expression to be effective in vivo. 25 Interaction of endostatin with endothelial cells leads to a variety of downstream effects, [26][27][28] including inhibition of the Wnt/␤-catenin pathway, 29 and actin reorganization in endothelial cells. 16,[30][31][32][33] In fact, this wide variety of effects elicited by 1 endogenous inhibitor of angiogenesis was recently supported by 2 studies of global gene expression in endostatin-treated endothelial cells. 27,34 There is general agreement that the in vitro action of endostatin involves inhibition of endothelial cell migration, but less clear whether endostatin also affects endothelial cell apoptosis and proliferation. 6,12,26,[35][36][37][38][39] Furthermore, even less is known about how endostatin affects endothelial cell function in vivo, as readouts have been restricted to analysis of vascular density or blood flow in tumors, [12][13][14]35,40 or neovascularization of the chick allantoic membrane. 10,12,39 Moreover, studies that focused in more detail on endothelial cell behavior in vivo either failed to detect substantial effects of endostatin 41 or found subtle signs of impaired blood vessel maturation. 42 Finally, several studies failed to observe an antitumor effect of endostatin (reviewed in Marshall 43 ). Thus, there is an obvious need to more carefully analyze the effect of endostatin at the level of single endothelial cells during angiogenesis.Here, we describe the effect of endostatin in an in vivo model of human endothelial cell behavior in which the final stages of angio...

To establish a model for adoptive transfer of endothelial cells, we transferred human umbilical vein endothelial cells (HUVECs) to immunodeficient mice (Rag