Highly efficient induction of type C retroviruses by a human tumor in athymic mice.

Abstract

We have found that 1 of 20 human tumors tranplanted and passaged in nude mice was associated with a massive induction of endogenous murine leukemia virus (MuLV). Separation and growth of these viruses on various substrates indicated that both ecotropic and xenotropic MuLV were present in the induced mixture. Tryptic peptide fingerprints of the p30 and gp7O structural elements of the viruses indicated that all of the known endogenous MuLVs of BALB/c mice were present in the mixture. In addition, a new xenotropic MuLV was identified. The human tumor that induced the viruses was an oat cell carcinoma. The oat cell carcinoma possibly produced a specific hormone or factor that acts as a potent inducer of endogenous type C retroviruses.The use of the athymic nude mouse as a vehicle for the maintenance of heterotransplanted tumor tissue is an established procedure. It has been recognized that xenotropic and ecotropic murine leukemia viruses (MuLV), endogenous to nude mice, can productively infect transplanted tumor cells (1-4). The resulting addition of mouse viral proteins to the tumor cell's antigenic repertoire can complicate immunological and biochemical studies of the tumor, not to mention efforts to identify possible retroviruses endogenous to the tumor cell. In this report we describe a differential effect of various human tumors transplanted into nude mice to induce endogenous MuLV.In contrast to most human tumors established in our mouse colony, it was found that passage of an oat cell carcinoma in nude mice caused the induction of a large variety and quantity of MuLV. The viruses were grown on mouse and heterologous cells in vitro to separate host range types. Peptide mapping of viral gene products gp70 and p30 indicated that all of the known MuLVs endogenous to BALB/c mice were present in the original mixed viral population. This was surprising because some of these viruses had not been inducible by previously reported means. The superior viral inductive qualities of the oat cell carcinoma, relative to other human tumors, suggests that it possessed, induced, or produced and secreted a potent inducer of endogenous MuLV. MATERIALS AND METHODSTumor Transplantation. Oat cell carcinoma and other human tumors were serially transplanted subcutaneously in BALB/c nu/nu mice bred in our laboratory, as described (5). (6,12). Filtered supernatant fluids were concentrated and assayed for reverse transcriptase activity, as described (6). Cultures that were positive for reverse transcriptase activity were further purified according to host range by passage of cell-free virus from mouse to nonmouse cells and conversely for at least two passages.Ecotropic MuLV infectivities were tested on secondary NIH Swiss and BALB/c embryo fibroblasts by the XC or SXC assays (7,8).Virus Purification. Virus was concentrated by centrifugation of filtered supernates through 15% (wt/vol) sucrose onto a cushion of 50% sucrose. Centrifugation was for 60 min at 25,000 rpm (105,000 X g) in a Beckman SW 27 rotor in the Beckman LS-50 cent...

The in vivo malignant transformation of mouse fibroblasts in the presence of human tumour xenografts

“…The mechanisms by which malignant transformation may occur is still not clear but Beattie et al (1982) found high reverse transcriptase activity and intercellular type C virus particles suggesting the presence of murine viruses in their transformed tumour, and it is interesting that the induction of murine leukaemia virus (MuLV) described by Gautsch et al (1980) was by an oat cell carcinoma. Another possibility is that the human xenografts produced large amounts of tumour growth factor which has been shown to cause morphological changes of normal cells to a malignant phenotype (Todaro et al, 1980).…”

“…The occurrence of lymphomas has also been directly linked to the transplantation of human tumours (Gautsch et al, 1980). The apparent induction of malignant lymphoma by human xenografts could conceivably become a problem in the routine passage of human tumours in mice as each transplant generation carries the risk of propagating the induced lymphoma as well as, or instead of, the human tumour under investigation (Figure 1).…”

Characterization, Mapping, and Distribution of the Two XMRV Parental Proviruses

“…Their significance stems from the recombination between the two that ultimately led to the generation of XMRV during the passaging of a human prostate tumor as xenografts in mice. To our knowledge, no other MLV, recombinant or otherwise, acquired by human tissues upon transplantation into mice has ever received this much attention, even though such retroviral acquisitions by heterologous cells occur frequently during passage of human cells in mice or other species and have been known for more than 30 years (1,6,15,56,62,67). Even more frequent is unintentional infection of cell lines with retroviruses in the laboratory, often going unnoticed for many years (3,23,28,41,42,51,54).…”

Generation of Multiple Replication-Competent Retroviruses through Recombination between PreXMRV-1 and PreXMRV-2

“…However, in the context of xenografts, where foreign tissue (i.e., human tumor tissue) has been grafted into an immunocompromised mouse, expressed xenotropic murine endogenous retroviruses (X-MLVs) have the potential to infect and spread in the foreign tissue. This phenomenon was observed as early as the 1970s, when subtype C particles were found to be associated with tumor tissues passaged in mice (6)(7)(8)(9)(10). Surveys of currently used human cell lines have found that some are positive for MLVs, as a result of either xenografting, cross-contamination, recombination of endogenous retroviruses during passage of cultured cells, or recombination of plasmids in helper cell lines (11)(12)(13)(14).…”