Role of interferon regulatory factor 1 in governing Treg depletion, Th1 polarization, inflammasome activation and antitumor efficacy of cyclophosphamide.

The antitumor effectiveness of cyclophosphamide (CTX) and other chemotherapeutics was shown to rely not only on direct cytotoxicity but also on immunogenic tumor cell death and systemic immunomodulatory mechanisms, including regulatory T cell (Treg) depletion, Th1 cell polarization, type I interferon (IFN) and proinflammatory cytokine production. IFN regulatory factor (IRF)-1 is a transcriptional regulator of IFNs and IFN-inducible genes, involved in the control of Th1 and Treg differentiation and in sterile inflammation. Aim of this study was to explore the role of IRF-1 in CTX-induced antitumor effects and related immune activities. This study shows for the first time that IRF-1 is important for the antitumor efficacy of CTX in mice. Moreover, experiments in tumor-bearing C57BL/6 mice showed that Irf1 gene expression in the spleen was transiently increased following CTX administration and correlated with the induction of Th1 cell expansion and of Il12p40 gene expression, which is the main Th1-driving cytokine. At the same time, CTX administration reduced both Foxp3 expression and Treg cell percentages. These effects were abrogated in Irf1-/- mice. Further experiments showed that the gene and/or protein expression of caspase-1, iNOS, IL-1ß, IL-6 and CXCL10 and the levels of nitric oxide were modulated following CTX in an IRF-1-direct- or -indirect-dependent manner, and highlighted the importance of caspase-1 in driving the sterile inflammatory response to CTX. Our data identify IRF-1 as important for the antitumor efficacy of CTX and for the regulation of many immunomodulatory activities of CTX, such as Th1 polarization, Treg depletion and inflammation.

Characterization of a novel murine retrovirus mixture that facilitates hematopoiesis.

A new virus previously arose in BALB/c females mated repeatedly to C57BL/6 (B6) males and then injected with fixed, activated B6 male spleen cells (V. S. Ter-Grigorov, O. Krifuks, E. Liubashevsky, A. Nyska, Z. Trainin, and V. Toder, Nat. Med. 3:37-41, 1997). In the present study, BALB/cJ mice inoculated with virus-containing plasma from affected mice developed splenomegaly, which was caused by increased numbers of Sca-1(+) Lin(-) hematopoietic stem cells (HSC) and their differentiated progeny. Biological and molecular analyses of a new virus revealed a mixture of murine leukemia viruses (MuLVs). These MuLVs comprised ecotropic and mink lung cell focus-forming (MCF) virus classes and are termed Rauscher-like MuLVs because they bear numerous similarities to the ecotropic and MCF viruses of the Rauscher MuLV complex but do not include a spleen focus-forming virus. The ecotropic virus component alone transferred some disease characteristics, while MCF virus alone did not. Thus, we have described a novel virus mixture, termed Rauscher-like MuLV, that causes an increase in hematopoiesis due to activation of pluripotent HSC. Experiments using mice and a protocol that replicated the pregnancy and immunization strategy of the original experiment demonstrated that endogenous BALB/c mouse ecotropic and xenotropic MuLVs are activated by these treatments. Emv1 was expressed in the spleens of multiparous mice but not in those of virgin mice, and Bxv1Emv1-pseudotyped MuLVs were recovered following injection of fixed, activated B6 cells. Thus, multiple pregnancies and allostimuli appear to have provided the signals required for activation of and recombination among endogenous viruses and could have resulted in generation of the Rauscher-like MuLV mixture.

Retrovirally induced switch from production of IL-12 to IL-4 in dendritic cells.

Dendritic cells (DC) in HIV-1 infection show a reduced capacity to stimulate primary T cell proliferation. Exposure of bone marrow-derived DC to Rauscher leukemia virus (RLV) provides a mouse model for studying retrovirally induced reduction in stimulatory capacity for T cells. Treatment with IL-12, a cytokine that promotes the development of Th1 cells, has been postulated as a treatment for AIDS and is effective at restoring cell-mediated immunity in mice infected with mouse AIDS virus or with RLV (see Knight, S. C. and Patterson, S., Annu. Rev. Immunol. 1994. 15: 593-615 for references). Here we studied the direct effect of RLV and of IL-12 on bone marrow-derived DC. Normal DC produced IL-12 and IL-10 and stimulated primary allogeneic T cell proliferation. Exposure of DC to RLV caused reduced production of IL-12, production of IL-4 was seen in DC for the first time and T cell stimulation was inhibited. Addition of IL-12 reinstated and enhanced IL-12 synthesis in RLV-treated DC, abrogated production of IL-10 and IL-4 and restored stimulatory activity. Manipulation of cytokine production in DC could be a stratagem that has evolved in the retrovirus to avoid stimulation of cellular responses.

[The coleukemogenic action of Bordetella pertussis]. / Koleikomogennoe deistvie kokliushnogo mikroba

Injection of B. pertussis and Rauscher leukemia virus (RLV) in a dose of 4 ID50 to BALB/c mice susceptible to the above virus significantly increases the incidence of leukosis and shortens the average life duration. Injection of B. pertussis to the AKR mice, carriers of the Gross leukosis virus, induces in the first months a greater number of the mice with leukosis and its earlier development.

Molecular cloning of the Rauscher murine leukemia virus. Disease spectrum and integration pattern.

After transfection of NIH 3T3 cells with DNA from molecularly cloned Rauscher MuLV, virus was isolated which showed a disease spectrum comparable to that of R-MuLV cloned biologically by endpoint dilution. In both cases sites of proviral integration vary from 2-5 per leukemic tissue and occur apparently at random.

Roles of helper and defective retroviral genomes in murine erythroleukemia: studies of spleen focus-forming virus in the absence of helper.

Retroviruses that cause acute oncogenesis are generally complexes of a replication-competent helper virus and a replication-defective component. However, the pure defective components have not been previously available. We prepared the defective spleen focus-forming virus component of Rauscher erythroleukemia virus (R-SFFV) by transfecting a colinear R-SFFV DNA clone into a retroviral packaging cell line (psi 2 cells). The transfected cells released virus (psi 2/SFFV) that was free of helper virus and that induced erythropoietin-dependent erythroid burst formation in bone marrow cultures. When injected into normal adult NIH/Swiss mice in moderate doses, psi 2/SFFV caused a rapid splenic erythroblastosis that regressed. Extensive erythroblastosis could be maintained by repeated injections of psi 2/SFFV into anemic mice or by the addition of a helper virus. We conclude that R-SFFV alone causes proliferation but not immortalization of a population of erythroblasts that is normally replenished from a precursor stem cell pool. Because these precursor cells are inefficiently infected, a single moderate inoculum of psi 2/SFFV causes a wave of erythroblastosis. The properties of the proliferating erythroblasts are substantially determined by the R-SFFV viral component.

A weakly pathogenic Rauscher spleen focus-forming virus mutant that lacks the carboxyl-terminal membrane anchor of its envelope glycoprotein.

A mutant Rauscher spleen focus-forming virus (mutant 4-3) that causes mild splenic erythroblastosis in mice has a 44-base-pair deletion in the 3' region of its envelope glycoprotein (env) gene. The encoded glycoprotein terminates prematurely, lacks a hydrophobic membrane anchor, and has a shortened intracellular lifespan. An active site for causing erythroblast proliferation may occur in the undamaged amino-terminal domain of the env glycoprotein.

Reduced leukemogenicity caused by mutations in the membrane glycoprotein gene of Rauscher spleen focus-forming virus.

We isolated and characterized two spontaneous, weakly leukemogenic mutants of Rauscher spleen focus-forming virus (R-SFFV) that contain mutations in nonoverlapping regions of the membrane envelope (env) glycoprotein gene. As reported previously (M. Ruta and D. Kabat, J. Virol. 35:844-853, 1980), the replication-defective R-SFFV encodes a membrane glycoprotein with an apparent Mr of 54,000 (gp54) which is structurally and immunologically related to the membrane envelope glycoproteins of dual-tropic murine leukemia viruses. Mutant R-SFFV clones 3-25 and 4-3 encode abnormally sized gp54-related glycoproteins with apparent Mrs of 52,000 (gp52) and 45,000 (gp45), respectively. Northern and Southern blot analyses of the mutant R-SFFV nucleic acids indicated that an insertion has occurred in the 3-25 env gene and that a deletion has occurred in the 4-3 env gene. Furthermore, restriction endonuclease analyses and comparisons of the fragmentation patterns of the wild-type and mutant glycoproteins generated by partial proteolysis with Staphylococcus aureus V8 protease indicated that the mutations affect nonoverlapping domains of the envelope glycoprotein (amino-terminal fragment affected in 3-25 glycoprotein and carboxyl-terminal fragment affected in 4-3 glycoprotein). Glycosylation inhibition studies indicated that the reduced size of gp52 is caused at least partly by loss of an asparagine-linked oligosaccharide. In addition, these mutant viruses have dramatically reduced leukemogenicities compared with wild-type R-SFFV. We conclude that the gp54 structural gene is required for initiation or amplification of the splenic erythroblast hyperplasia which characterizes the preleukemic phase of Rauscher disease.

Viral-associated alterations in hematopoiesis in the mouse.

A variant of Rauscher leukemia virus, designated RLV-A, induces a protracted hematopoietic dysplasia characterized by hepatosplenomegaly with erythroblastosis, severe terminal anemia, thrombocytopenia, and erythroblastemia. Erythrocyte and platelet survival is reduced and the ferrokinetic data suggest that iron utilization is faulty. Stem cells (CFU-S, CFU-C, CFU-MK, CFU-E, BFU-E) are reduced in the bone marrow but increased in terminal spleens. The cause(s) of these viral-associated alterations in stem cell numbers is not known.

[Activation of cellular genes as affected by Rauscher leukemia virus]. / Aktivatsiia kletochnykh genov pod vliianiem virusa leikoza Raushera.

The methods of hybridization in solution and blot hybridization have shown that the BALB/c mice spleen cells contain "silent" genes which can amplificate and change their structure following the infection by the Rauscher leukemia virus (RLV). The product of these gene activation is nuclear 35S RNA detectable by the comparative electrophoretic analysis of heterogeneous nuclear RNA of leukemic and normal cells. The expression of complete copies of 35S RNA was observed in nuclei of RLV-infected cells, while in cytoplasm this RNA is represented by incomplete copies. The expression of the sequences homologous to this 35 S RNA in normal mice spleen cells was not detected.

[Effect of Mycoplasma arthritidis and Rauscher leukosis virus on murine peritoneal macrophages in vitro and in vivo]. / Vliianie Mycoplasma arthritidis i virusa leikoza Raushera na myshinye peritoneal'nye makrofagi in vitro i in vivo.

The interaction of M. arthritidis and Rauscher leukemia virus (RLV) with mouse peritoneal macrophages was studied. When added in vitro, M. arthritidis was shown to exert cytopathic effect on macrophages obtained from normal BALB/c or CBA mice (highly sensitive to RLV) and BAF1 hybrid mice (resistant to RLV) after 4-6 hours of incubation. Macrophages obtained from BALB/c or BAF1 mice infected in vivo with M. arthritidis were functionally defective beginning from day 7. The infection of BALB/c mice with RLV also suppressed the spreading of macrophages, while the infection of RLV-resistant BAF1 mice with the virus did not reduce the spreading and phagocytic activity of peritoneal macrophages on days 1-105. The mixed infection of BALB/c or BAF1 mice with M. arthritidis and RLV markedly reduced the spreading and phagocytic activity of macrophages beginning from day 7. This data is in agreement with earlier findings on the ability of M. arthritidis to stimulate Rauscher leukemia in BAF1 mice. The possible role of M. arthritidis in the mechanism of viral leukemogenesis is discussed.

[Change in the nature of the persistence of alpha- and flaviviruses in the body of BALB/c strain mice with a mixed infection with leukovirus]. / Izmenenie kharaktera persistentsii al'fa- i flavivirusov v organizme myshei linii BALB/c pri smeshannoi infektsii s leikovirusom.

The features of pathogenesis of infection caused in adult Balb/c mice intraperitoneally infected with Sindbis virus, virulent or attenuated strains of West Nile (WN) virus, individually or in combination with Rauscher leukemia virus (RLV) were studied. The influence of the latter on the course of togavirus infections was characterized by 3 features: (a) different effects on the visceral and neural phases of the pathogenesis (increased period of viremia and virus reproduction in the viscera did not lead to stimulation of virus reproduction in the CNS); (b) changes in the time of togavirus persistence in the infectious form; (c) the dependence of the observed effect on the togavirus properties.

Characterization of clones derived from an attenuated strain of Rauscher murine leukaemia virus.

With a view to defining its subpopulations, an attenuated strain of Rauscher leukaemia virus, which comprises a majority of fragile virions, was closed by end-point dilution. The presence in the obtained clones of markers (analyzed by radioimmunoassay and isoelectric focusing) associated with Rauscher virus, together with persistent infectivity and leukaemogenicity, excluded the hypothesis that endogenous virus might have replaced the original Rauscher population. Due to the closing method employed, non fragile virions were obtained. Moreover, despite its selectivity for the lymphatic leukaemia virus component, sporadic cases of atypical erythroblastogenic leukaemia were observed.