Transgenic mice were generated expressing c-fos genes under the control of the human metallothionein promoter. Although high levels of c-fos messenger RNA were detectable in a variety of tissues, deregulated c-fos expression specifically interfered with normal bone development without inducing malignant tumours.

SummaryA splice variant of CD44 (CD44v) originally discovered on metastases of a rat pancreatic adenocarcinoma (BSp73ASML) has been shown by transfection to confer metastatic behavior to nonmetastatic tumor cells (Gfinthert U., M. Hofmann, W. Rudy, S. Reber, M. Z611er, I. Haussmann, S. Matzku, A. Wenzel, H. Ponta, and P. Herrlich. 1991. Cell. 65:13). A monoclonal antibody (mAb), 1.1ASML, to the metastasis-specific domain of the CD44v molecule retards growth of lymph node and lung metastases of the metastatic tumor line BSp73ASML, and can efficiently prevent formation of metastases by the transfected line. The antibody is only effective when given before lymph node colonization. Anti-CD44v does not downregulate the expression of CD44v, and prevention of metastatic growth by antioCD44v is not due to activation of any kind of immune defense. We suggest that the mAb interferes with proliferation of metastasizing tumor cells in the draining lymph node, most probably by blocking a ligand interaction. The interference with metastatic spread will greatly facilitate the exploration of the function of CD44v and, in particular, may also open new strategies for the therapy of human metastases.C D44 is an integral membrane glycoprotein (1-7), originally described as a homing receptor of lymphocytes (8)(9)(10)(11)(12)(13)(14)(15)(16)(17). Beside the involvement of CD44 in adhesion of lymphocytes to specialized endothelial cells, CD44 is known to bind to hyaluronate and probably also to collagen (7,(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), suggesting roles in the interaction between cells and extracellular matrix. Moreover, several variants of CD44 with additional extracellular domains have been detected in a variety of tissues and frequently on tumor cells (1,(31)(32)(33)(34)(35)(36)(37)(38)(39)(40).The fact that metastatic spread involves interaction between tumor cells and extracellular matrix as well as between tumor cells and endothelial cells has led to the hypothesis that especially the variant forms of CD44 may be involved in the process of metastatic spread (32, 35). Starting from a metastasisspecific mAb (1.1ASML) (41) that has been raised against the highly metastatic pancreatic adenomcarcinoma line BSp-73ASML (42), we have cloned a splice variant of CD44 (CD44v) 1 (35). The splice variant carries an expanded extracellular domain. Overexpression of this variant in any one of several nonmetastatizing tumor cell lines confers full metastatic behavior to these cells (35, 42a).l Abbreviations used in this paper: CD44s, standard CD44; CD44v, splice variant of CD44.We now report on the specific interference of mAb 1.1ASML with metastasis formation. Intravenous injections of 1.LASML inhibited or prevented the colonization of lymph nodes and lung. No evidence for an antibody-mediated immune attack could be detected. Furthermore, 1.1ASML did not interfere with surface expression of CD44v. The data support the view that CD44v catalyzes embedding/outgrowth of tumor cells in the draining lymph nodes. Materials and M...

A syngeneic model system for the study of tumor metastases and cell-mediated immunity is described. The system consists of two related, chemically induced murine lymphomas, the non-metastasizing parental line Eb and i t s metastasizing variant ESb. A n unrelated, chemically induced tumor (MDAY) i s included for specificity controls. Serological typing revealed that both Eb and ESb were of T lymphoid origin and expressed the H-2K and H-2D molecules of the host strain DBA/2. By various electron microscope techniques, morphological differences were observed between the t w o cell lines. I n comparison t o Eb cells, ESb tumor cells had a more polymorphic nucleus with many invaginations of the nuclear envelope and a more prominent expression of microvilli on the cell surface. A n in vitro organ culture test for tumor invasiveness, presented here for the f i r s t t i m e In a syngeneic murine system, revealed that ESb but not Eb tumor cells had the ability t o attach t o and invade normal tissue. Accordingly, ESb tumor cells showed higher malignancy in vivo. This was apparent from their higher tumorigenicity and their ability t o disseminate and metastasize and t o kill recipient mice more quickly. Upon histological examination of the local primary tumors a striking difference was noticed with regard t o the degree of infiltration by host-derived mononuclear cells, mostly histiocytes. The non-metastasizing tumor Eb was heavily infiltrated while tumor ESb contained only a few of these cells. The differences between the tumor lines ESb and Eb are considered i n the light of their possible relevance for metastases in general. The etiology of the t w o tumors i s discussed in particular with respect t o their relatedness.Metastasis, the spread of malignant cells from a primary site to distant organs, represents one of the most intriguing problems in the pathogenesis and treatment of cancer (see Willis, 1973;Fidler and Kripkie, 1977; Carter, 1978). While primary tumors in many instances can be removed surgically it is the subsequent development of metastases which often cannot be prevented and is responsible for most therapeutic failures (Krokowski, 1978). In spite of its importance, relatively little is known about the processes which either lead to or prevent formation of tumor metastases. One reason for this is that experimental tumors in animals are often not suitable for the study of metastasis: they either do not metastasize or they grow so fast that they kill the host before metastases can develop (Kim, 1970;Mellgren, 1976 The majority of experimental tumors induced by either tumor viruses or chemical carcinogens and maintained by long-term transplantations usually express immunogenic tumor-associated transplantation antigens (TATA) against which syngeneic animals can be successfully immunized. When similar immunization procedures were applied to humans, a significant protective effect was observed only occasionally (see Terry and Windhorst, 1978). The meager success in cancer patients of specific immunotherapy prot...