Adoptive immunotherapy of a Gross virus producing lymphoma and a methylcholanthrene-induced fibrosarcoma in tolerant rats. (1/181)

Immunological tolerance to Gross virus-specific transplantation antigens in rats given neonatae transfer of donor lymphoid cells beneath the kidney capsule of syngeneic recipient rats. Immune or normal donor cells invariably developed a cell-mediated immune reaction in kidneys of GV-tolerant recipients, presumably against GV antigens present on the surface of recipient lymphoid cells in the kidney. Spleen and lymph node cells from tolerant rats failed to develop a reaction in tolerant recipients, but developed a strong reaction to histoincompatible antigens in the kidneys of semisyngeneic tolerant rats. The immunologically tolerant state in the rats could be broken by adoptive transfer of spleen and lymph node cells from syngeneic rats immunized with GV-induced lymphoma cells. Immunotherapy of a GV-induced and also a GV-infected methylcholanthrene-induced fibrosarcoma growing in tolerant rats was successful when immune spleen and lymph node cells were administered i.p. 3 days after s.c. inoculation of 2 X 10(7) tumor cells in the case of the lymphoma, and 1 day after inoculation of 5 X 10(6) tumor cells in the case of the fibrosarcoma.  (+info)

Antiretroviral cytolytic T-lymphocyte nonresponsiveness: FasL/Fas-mediated inhibition of CD4(+) and CD8(+) antiviral T cells by viral antigen-positive veto cells. (2/181)

C57BL/6 (H-2(b)) mice generate type-specific cytolytic T-lymphocyte (CTL) responses to an immunodominant Kb-restricted epitope, KSPWFTTL located in the membrane-spanning domain of p15TM of AKR/Gross murine leukemia viruses (MuLV). AKR.H-2(b) congenic mice, although carrying the responder H-2(b) major histocompatibility complex (MHC) haplotype, are low responders or nonresponders for AKR/Gross MuLV-specific CTL, apparently due to the presence of inhibitory AKR. H-2(b) cells. Despite their expression of viral antigens and Kb, untreated viable AKR.H-2(b) spleen cells cause dramatic inhibition of the C57BL/6 (B6) antiviral CTL response to in vitro stimulation with AKR/Gross MuLV-induced tumor cells. This inhibition is specific (AKR.H-2(b) modulator spleen cells do not inhibit allogeneic MHC or minor histocompatibility antigen-specific CTL production), dependent on direct contact of AKR.H-2(b) cells in a dose-dependent manner with the responder cell population, and not due to soluble factors. Here, the mechanism of inhibition of the antiviral CTL response is shown to depend on Fas/Fas-ligand interactions, implying an apoptotic effect on B6 responder cells. Although B6.gld (FasL-) responders were as sensitive to inhibition by AKR.H-2(b) modulator cells as were B6 responders, B6.lpr (Fas-) responders were largely insensitive to inhibition, indicating that the responder cells needed to express Fas. A Fas-Ig fusion protein, when added to the in vitro CTL stimulation cultures, relieved the inhibition caused by the AKR.H-2(b) cells if the primed responders were from either B6 or B6.gld mice, indicating that the inhibitory AKR.H-2(b) cells express FasL. Because of the antigen specificity of the inhibition, these results collectively implicate a FasL/Fas interaction mechanism: viral antigen-positive AKR.H-2(b) cells expressing FasL inhibit antiviral T cells ("veto" them) when the AKR.H-2(b) cells are recognized. Consistent with this model, inhibition by AKR.H-2(b) modulator cells was MHC restricted, and resulted in approximately a 10- to 70-fold decrease in the in vitro expansion of pCTL/CTL. Both CD8(+) CTL and CD4(+) Th responder cells were susceptible to inhibition by FasL+ AKR.H-2(b) inhibitory cells as the basis for inhibition. The CTL response in the presence of inhibitory cells could be restored by several cytokines or agents that have been shown by others to interfere with activation-induced cell death (e.g. , interleukin-2 [IL-2], IL-15, transforming growth factor beta, lipopolysaccharide, 9-cis-retinoic acid) but not others (e.g., tumor necrosis factor alpha). These results raise the possibility that this type of inhibitory mechanism is generalized as a common strategy for retrovirus infected cells to evade immune T-cell recognition.  (+info)

Definitive evidence that the murine C-type virus inducing locus Akv-1 is viral genetic material. (3/181)

DNA of the AKR mouse contains a set of murine leukemia virus sequences that are not present in DNA of the NIH Swiss mouse. NIH mice partially congenic for the AKR murine-leukemia-virus-inducing locus Akv-1 contain this set of sequences, and, in a three-point cross segregating for Akv-1 on an NIH background, the sequences segregated with Akv-1. It is concluded that the Akv-1 locus contains viral sequences.  (+info)

Mutations of the kissing-loop dimerization sequence influence the site specificity of murine leukemia virus recombination in vivo. (4/181)

The genetic information of retroviruses is retained within a dimeric RNA genome held together by intermolecular RNA-RNA interactions near the 5' ends. Coencapsidation of retrovirus-derived RNA molecules allows frequent template switching of the virus-encoded reverse transcriptase during DNA synthesis in newly infected cells. We have previously shown that template shifts within the 5' leader of murine leukemia viruses occur preferentially within the kissing stem-loop motif, a cis element crucial for in vitro RNA dimer formation. By use of a forced recombination approach based on single-cycle transfer of Akv murine leukemia virus-based vectors harboring defective primer binding site sequences, we now report that modifications of the kissing-loop structure, ranging from a deletion of the entire sequence to introduction of a single point mutation in the loop motif, significantly disturb site specificity of recombination within the highly structured 5' leader region. In addition, we find that an intact kissing-loop sequence favors optimal RNA encapsidation and vector transduction. Our data are consistent with the kissing-loop dimerization model and suggest that a direct intermolecular RNA-RNA interaction, here mediated by palindromic loop sequences within the mature genomic RNA dimer, facilitates hotspot template switching during retroviral cDNA synthesis in vivo.  (+info)

Radioimmunoassay for intact Gross mouse leukemia virus. (5/181)

A radioimmunoassay for intact Gross leukemia virus has been developed using 125I-labeled Gross virus grown in tissue culture and guinea pig antisera to Gross virus grown either in tissue culture or harvested from leukemic C3H(f) mice. Separation of bound from free labeled virus was effected using the double antibody method. The assay can detect fewer than 10(8) virus particles and has been used to measure the viral content of individual organs from inoculated leukemic C3H(f) mice and from Ak mice with spontaneous leukemia. Organs from noninoculated healthy C3H(f) mice crossreacted poorly in the system, virus generally being detectable only in the thymus and spleen and at low concentration. In some of the inoculated C3H(f) leukemic mice the viral content of as little as 0.5 mul of plasma is measurable. That this assay is for intact virus and not for soluble antigens of the viral envelope was proven by the observation that the immunoreactive material of plasma and extracts from thymus and liver of leukemic mice has a buoyant denisty in sucrose of 1.17-1.18 g/ml, corresponding to that of intact virus grown in tissue culture. With this sensitivity it may now be possible to quantitate viral concentrations in tissue and body fluids from the time of inoculation through the development of obvious pathology.  (+info)

Treatment of spontaneous leukemia in AKR mice with chemotherapy, immunotherapy, or interferon. (6/181)

AKR mice are genetically destined to develop Gross (RNA) virus-induced lymphatic leukemia. Leukemic AKR mice treated with combination vincristine, cyclophosphamide (Cytoxan), and 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea sustained a 180% increase of life-span. Combination chemotherapy plus immunization with neuraminidase-treated allogeneic (Gross virus-induced) G2G leukemic cells intradermally resulted in 35% of animals surviving beyond 150 days without evidence of the disease. It is significant that allogeneic E2G leukemic cells as immunogen were as effective in prolonging the life-span of the immunized leukemic AKR mice as were syngeneic leukemic thymocytes. Virazole (1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide), an antiviral compound, alone showed no apparent antitumor effect. However, in experiments in which the clinically diagnosed leukemic AKR mice received a combination of cytoreductive therapy [vincristine plus prednisone or, more effectively, vincristine, Cytoxan plus 1-(2-chloroethyl)-3-(trans-4-methylcyclohexyl)-1-nitrosourea, followed by Virazole], there was a noticeable reduction of the viral titer, a delay in the reappearance of viable clonogenic cells, and an increase in the survival time for the leukemic AKR mice as compared to those receiving cytoreductive therapy alone. The effectiveness of purified mouse interferon in AKR mice was also examined. The decrease in the viral titer of animals that received interferon treatment was markedly greater than of those receiving a combination of cytoreductive therapy with Virazole or immunotherapy. The administration of mouse interferon had a direct effect on the appearance of the spontaneous leukemia in AKR mice. The median life-span of the control animals was 36 weeks, whereas 45% of the AKR mice treated with five doses of 5 X 10(4) units of interferon are still alive at 54 weeks of age. Thus, interferon not only reduces the Gross murine leukemia virus titer in the chronically infected AKR mice but also significantly delays the appearance of the primary lymphoma.  (+info)

The generation and specificity of cytotoxic T cells raised against syngeneic tumor cells bearing AKR/Gross murine leukemia virus antigens. (7/181)

Efforts were made to generate C57BL/6 cytotoxic effector cells to a syngeneic leukemia (E{male}G2) bearing AKR/Gross virus antigens. As we were unable to induce significant cytotoxic activity by immunization with up to 10(8) irradiated E{male}G2 cells, even when cells from such primed animals were subsequently restimulated with E{male}G2 cells in vitro, C57BL/6 mice were immunized with an aliogeneic, virus-producing AKR leukemic cell line (AKR SL3). Peritoneal exudate cells and, to a lesser degree, spleen cells from these mice showed significant lytic activity toward the immunizing allogeneic tumor but not toward E{male}G2. When spleen cells were harvested from animals {approximately equal to}10 d after injection of AKR SL3 and rechallenged in vitro with either E{male}G2 or AKR.H-2(b) SL1, another tumor that displays AKR/Gross virus antigens, then a vigorous cytotoxic response against E{male}G2 and AKR. H-2(b) SL1 was obtained. Effector cells generated by AKR SL3 priming followed by in vitro stimulation with E{male}G2 or AKR.H-2(b) SL1 lysed only cells of H-2(b) haplotype which were strongly positive for the display of serologically detectable AKR/Gross virus antigens. Thus, AKR SL3 cells were not lysed nor were EL4 cells (H-2(b); but only weakly positive for gp70). Cells not bearing the MuLV antigens tested for, such as P815 mastocytoma cells and spleen cell "blasts" from C57BL/6 and CBA (H-2(k)) mice, were also insusceptible to attack. The cytotoxic effector cells induced bore Thy 1.2 alloantigen and were of the Lyt 1+2+ phenotype. Collectively, these findings are consistent with the conclusion that the cytotoxic T cells raised against E{male}G2 are directed against AKR/Gross virus-associated antigens and are H-2 restricted. It will be of interest to determine the relevance of such effector cells to the known resistance of the C57BL/6 mouse to AKR/Gross virus-induced leukemia.  (+info)

The role of serum factors in the acceleration by Freund's complete adjuvant of the growth of transplanted murine leukemic cells. (8/181)

Attempted nonspecific immunotherapy led to acceleration rather than retardation of tumor growth. Mice given injections of Freund's adjuvant were more susceptible to transplanted syngeneic Gross virus-induced leukemic cells when Freund's complete adjuvant was administered i.p. 0 to 7 days before or 1 day after tumor; thereafter, the adjuvant had no effect. Two serum-mediated phenomeana were demonstrated in vitro: (a) sera from mice immunized with Freund's complete adjuvant and tumor facilitated killing of tumor cells by peritoneal exudate cells from nonimmune mice; (b) sera from all mice with progressive tumor blocked the cytotoxicity of a xenogeneic tumor-specific serum. Certain sera produced both effects. However, sera that either blocked or facilitated tumor killing in vitro had no effect on the growth in vivo of transplanted tumor cells.  (+info)

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