Moloney virus (M-MuLV) leukemogenesis: virus spread, antibody production and antigenic expression in neonatally virus-inoculated young mice

Role of Infectious Virus Expression and Immune Response in Retrovirus-Induced Oncogenesis

Some of the parameters involved in retrovirus-induced oncogenesis were analyzed in newborn mice injected with Moloney-murine leukemia virus (M-MuLV) as well as in adults who received the virus by the intraperitoneal (i.p.) or intrathymic (i.t.) route. The neonatally injected mice were permissive for both viral replication and virus-induced cell-surface antigen expression on thymus cells, peripheral T and B lymphocytes, and macrophages, whereas the M-MuLV was not present in the adult i.p. injected mice. Instead, in i.t. injected mice, the virus was expressed in thymus and peripheral T cells only, but was not detected in tail extracts as assessed by means of the UV-XC plaque assay. Lack of virus spread in adult-treated animals correlated with a prompt humoral and cellular immune response, whereas the highly viremic newborn inoculated mice showed negligible virus-specific antibody production and an extremely low frequency of splenic cytotoxic T lymphocyte precursors. Moreover, immune response in both groups of adult-treated mice efficiently prevented tumor induction by Moloney-murine sarcoma virus (M-MuSV), which has the same antigenic determinants as M-MuLV, its natural helper. In contrast, M-MuSV sarcomas grew progressively in newborn inoculated mice and killed the host. Finally, 80 % of neonatally injected mice developed lymphomas, whereas all treated adults remained free of disease for more than 15 months. These findings imply that the immune response may, in fact, prevent retrovirus-induced oncogenesis through restriction of virus replication and/or destruction of virus-infected cells.

The drug monosodium luminol (GVT) preserves crypt-villus epithelial organization and allows survival of intestinal T cells in mice infected with the ts1 retrovirus

Of the cytopathic retroviruses that affect mammals, including HIV-1, many selectively infect CD4+ T cells and cause immunosuppressive syndromes. These diseases destroy both the thymus and the small and large intestines, after infecting and killing T-lineage cells in both tissues. A mutant of the murine leukemia retrovirus MoMuLV-TB, called ts1, causes this syndrome in susceptible strains of mice. In FVB/N strain mice that are infected at birth, thymic atrophy, CD4+ T cell loss, intestinal collapse, body wasting, and death occur by approximately 30-40 days postinfection (dpi). Apoptosis of ts1-infected T-lineage cells, in the thymus, peripheral lymphoid system and intestines is caused by accumulation of the ts1 mutant viral envelope preprotein gPr80(env), which is inefficiently cleaved into the mature viral proteins gp70 and PrP15E. We show here that ts1 infection in the small intestine is followed by loss of intestinal epithelial cell (IEC) thyroid-stimulating hormone (TSH) and cell cycling gradients (along the crypt-villus axes), accumulation of gPr80(env) in intestinal cells, apoptosis of developing T cells in the lamina propria (LP), and intestinal collapse by approximately 30 dpi. In infected mice treated with the antioxidant drug monosodium luminol (GVT), however, normal intestinal epithelial cell gradients are still in place at 30 dpi, and IECs covering both the crypts and villi contain large amounts of the antioxidant transcription factor Nrf2. In addition, no apoptotic cells are present, and accumulated gpr80(env) is absent from the tissue at this time. We conclude that GVT treatment can make ts1 a noncytopathic virus for intestinal lymphoid cells, as it does for thymocytes [25]. As in the thymus, GVT may protect the intestine by reducing oxidant stress in infected intestinal T cells, perhaps by prevention of gPr80(env) accumulation via Nrf2 upregulation in the IECs. These results identify GVT as a potential therapy for intestinal diseases or inflammatory conditions, including HIV-AIDS, in which oxidative stress is a triggering or exacerbating factor.

Spontaneous and induced leukemias of myeloid origin in recombinant inbred BXH mice

BXH-2 recombinant inbred (RI) mice produce high titers of B-ecotropic murine leukemia virus beginning early in life and have a high incidence of non-T-cell leukemias that occur before 1 year of age. The leukemias that develop are in some cases associated with hind limb paralysis. In addition, a dualtropic mink cell focus-forming virus has been isolated from leukemic cells of BXH-2 mice. Immunological and cytochemical characterization of the BXH-2 leukemias showed that they are of the myeloid lineage. To assess the oncogenicity of the BXH-2 viruses, newborn mice of several BXH RI strains were inoculated at birth with biologically cloned B-ecotropic or mink cell focus-forming murine leukemia virus. These studies demonstrated that the B-ecotropic virus can induce myeloid leukemias in other BXH RI strains, whereas the dualtropic mink cell focus-forming isolates were nononcogenic in the strains tested. DNA-DNA reassociation analysis indicated that the organotropism of the B-ecotropic murine leukemia virus is confined to lymphoid tissues. Southern analysis of tumor DNAs showed that there was amplification of ecotropic virus-specific sequences in BXH-2 myeloid tumors and in all leukemias induced in other BXH RI strains by inoculation of the BXH-2 B-ecotropic virus. Although B-ecotropic virus is expressed in central nervous tissues of paralyzed BXH-2 mice, we were unable to induce the disorder in several BXH RI strains inoculated intracranially at birth with either the B-ecotropic or dualtropic virus. These results suggest that the paralysis that occurs in BXH-2 mice is due to the infiltration of leukemic cells into the central nervous system.

Genetic control of the organ specificity of lymphoproliferative disease virus (LPDV) of turkeys

In a previous study based on the kinetics of virus replication and tumor formation (Gazit et al., 1982), it was shown that the organotropism of lymphoproliferative disease virus (LPDV) is confined to lymphoid tissues. The present paper demonstrates that this organ specificity is controlled at the level of infection and integration, that is, the lymphoid organs, which are the only organs sustaining virus replication, and also the only organs in whose cells integrated LPDV proviruses are detectable. At the same time, the efficiency of virus replication within the various target organs is regulated both at the level of infection and integration and at the level of viral gene transcription.

Antigenic and chromosomal changes in thymus and spleen of Balb/Mo mice during leukemogenesis

The Balb/Mo mouse strain carries a single copy of the germ line integrated Moloney leukemia virus (M-MuL V) and shows a high leukemia frequency. According to the clinical manifestations lymphomas can be divided into two major categories. In one type the thymus appears to be the primary site for lymphoma development. The second type is dominated by the generalized enlargement of spleen and lymph nodes. Individual lymphomas differ in the cell surface expression of Thy 1.2, MCSA (designated operationally as the M-MuL V-determined cell surface antigen) and viral p30 antigens. In addition, spleen and thymus of the same leukemic animal often differ antigenically. The karyotype of cells from enlarged organs is diploid or shows trisomy of chromosome 15. Lymphomas developing in Balb/Mo mice are thus heterogeneous with regard to clinical manifestations, cell surface antigens and karyotype and, in this respect, do not differ from lymphomas arising after the inoculation of exogenous M-MuL V. Amplification of the M-MuL V genome in young Balb/Mo mice is not accompanied by the appearance of MCSA on thymus cells. Still, 32% of lymphomas are MCSA positive. The results suggest that MCSA is related to a virus activated in a minority of Balb/Mo mice during the late phase of leukemogenesis.