蓝舌病毒湖北株致人肝癌Hep-3B细胞和人肺腺癌A549细胞死亡机制的研究

目的探讨蓝舌病毒湖北株(BTV-HbC3)致人肝癌Hep-3B和人肺腺癌A549细胞死亡的方式及其作用机制。方法观察细胞感染BTV-HbC3的病变效应;原位末端标记(TUNEL)法检测细胞感染BTV-HbC3是否出现凋亡;激光打描共聚焦显微镜检测荧光标记的细胞核及内质网变化;萤光照度仪检测病毒诱导细胞caspase-3/7、caspase-8和caspase-9的活性变化。结果BTV-HbC3感染Hep-3B细胞后有明显的病变效应,大量细胞凋亡,细胞核染色质边聚,内质网大量空泡形成,caspase- 3/7活性升高,caspase-8和caspase-9未升高;BTV-HbC3感染A549细胞后有明显病变效应,仅见零星凋亡细胞,内质网有空泡形成,细胞核未见染色质边聚,caspase-3/7和caspase-9活性升高,caspase-8未升高。结论BTV-HbC3主要通过细胞内内质网途径诱导Hep-3B细胞凋亡而发挥其抑瘤作用,而对人肺腺癌的抑瘤作用则是通过诱导A549细胞的非凋亡性程序性死亡来实现的。     

蓝舌病毒HbC株对人癌细胞感染的研究

目的 探讨蓝舌病毒湖北株(BTV-HbC)对人癌细胞的杀伤作用。方法 采用病毒学、细胞培养、透射电镜和免疫学技术观察BTV-HbC对人正常二倍体细胞和人癌细胞的感染。结果 BTV-HbC对正常二倍体人胚肺HEL细胞不感染，却能在实验组肿瘤细胞中选择性增殖，产生不同程度细胞病变效应(CPE)，终致肿瘤细胞死亡。其中，人肺癌SPC-A1细胞最敏感[CPE出现时间早，病毒接种后36h细胞死亡数达90％，TCID50为10^-3，透射电镜下该肿瘤细胞质内BTV-HbC颗粒量最多，并可见包涵体(inclusion body)形成]，人宫颈癌HeLa细胞次之，人星形胶质瘤U251细胞再次之，而小鼠星形胶质瘤C6细胞敏感性最差。琼脂糖双向扩散试验进一步证实了肿瘤细胞内皆有BTV-HbC存在。同时，透射电镜下实验组4株肿瘤细胞内皆可见核膜下染色质边缘化，高度凝集，细胞固缩等类似细胞凋亡(apoptosis)现象。结论 不感染人正常二倍体细胞的BTV-HbC，却可以在人肿瘤细胞中选择性增殖产生CPE，并诱导凋亡，从而杀灭肿瘤细胞。     

MG132和DDP联合应用诱导Hep-2喉癌细胞凋亡及机制的研究

目的：研究蛋白酶体抑制剂MG132与顺铂（DDP）联合应用对Hep-2喉癌细胞凋亡的影响,同时观察细胞中凋亡相关蛋白Bcl-2、Bad表达水平的变化。方法：体外培养Hep-2细胞分别暴露于MG132、DDP或者MG132和DDP,24h后流式细胞术（FCW）检测Hep-2细胞的凋亡率,Western blot方法测定Hep-2细胞中Bcl-2和Bad两种蛋白的表达情况。结果：流式细胞术检测结果显示,MG132和DDP联合用药24h后Hep-2细胞凋亡率较单独应用MG132、DDP显著增加。Western blot结果显示联合用药组较单独用药组Hep-2细胞中Bcl-2的表达显著减少,而Bad的表达显著增加。结论：MG132联合DDP可能通过降低Bcl-2同时增强Bad的表达而进一步诱导Hep-2细胞的凋亡。可以认为MG132能增强DDP诱导Hep-2细胞凋亡的作用。     

溶瘤呼肠孤病毒在肿瘤生物治疗中作用的研究进展

肿瘤生物治疗的重要性日渐获得各方关注，而溶瘤病毒疗法作为肿瘤免疫治疗的一个分支也已成为研究热点。呼肠孤病毒（ReoV）地缘分布广泛，因其天然对肿瘤细胞具有靶向性及人体感染后几乎无症状而被认为是理想的溶瘤病毒载体，目前被广泛应用于临床试验。肿瘤细胞常伴有RAS基因的过度表达，会抑制对病毒有拮抗作用的激酶表达，造成ReoV大量复制致使肿瘤细胞发生凋亡、坏死、自噬等直接溶瘤效应；此外，ReoV 感染肿瘤细胞后释放的促炎性细胞因子和趋化因子逆转了TME的免疫抑制状态，可激活并招募固有免疫效应细胞杀死肿瘤细胞，并促进适应性抗肿瘤免疫反应的产生。另外，ReoV与放化疗、其他免疫制剂的联用可增强了肿瘤治疗的效果。本文从溶瘤ReoV的生物学特性方面，重点介绍了ReoV的基本特征与感染机制及ReoV 的肿瘤嗜性；同时，总结了溶瘤ReoV 的溶瘤机制，主要包括ReoV 诱导程序性细胞死亡及ReoV 诱导非程序性死亡；概括了溶瘤ReoV 所诱导的抗肿瘤免疫反应，如溶瘤ReoV 诱导的抗肿瘤固有免疫、溶瘤ReoV 诱导的获得性抗肿瘤免疫等，并介绍了溶瘤ReoV联合用药的效果。随着溶瘤作用机制的探明及临床试验的开展，溶瘤ReoV在肿瘤的生物治疗中的应用将更为广阔。     

含人TNF-α基因的重组逆转录病毒载体的构建、包装及对人肝癌细胞的感染

利用逆转录病毒载体LN系列的三种载体LXSN,LNCX和LNSX构建了插入TNF_α基因的重组逆转录病毒载体L-tnfSN,LNC-tnf和LNS-tnf。重组载体用磷酸钙沉淀法引入病毒包装细胞PA317,经G418筛选后,用NIH3T3细胞测定病毒滴度,结果表明L-tnfSN产生的病毒滴度最高(1×10~5CFU/ml),LNS-tnf次之(5×10~4CFU/ml),LNC-tnf最低(3×10~4CFU/ml)。应用上述三种重组病毒培养液上清,分别感染人肝癌细胞SMMC7721,经G418筛选获得数株抗性克隆。对每种病毒感染的细胞随机挑取6个克隆扩大培养,测定培养液上清中TNFα的分泌量,结果显示L-tnfSN介导感染的克隆中TNFα分泌量最高(382U/10~6细胞/24h),LNC-tnf次之(221u/10~6细胞/24h),LNS-tnF最低(124u/10~6细胞/24h)。反映不同启动子元件有不同的表达强度。     

溶瘤病毒治疗恶性肿瘤研究进展

据统计,约l5%的人类肿瘤与病毒感染有关.一些病毒可通过表达蛋白或携带遗传调控元件,干扰正常细胞生长周期,导致细胞转化和肿瘤发生;另一方面,许多病毒又可特异性地感染肿瘤细胞并在细胞内复制,杀伤肿瘤细胞,这类病毒称为溶瘤病毒(oncolytic virus,OV).溶瘤病毒能够选择性地在肿瘤细胞中复制,造成细胞病理效应和机体免疫反应,导致肿瘤细胞的裂解死亡,同时对正常细胞和组织却没有破坏作用或影响较小.     

β-catenin拮抗因子Chibby对人喉癌细胞Hep-2增殖凋亡的影响

背景与目的:Wnt信号通路与肿瘤的发生、发展密切相关,Chibby是该信号通路β-catenin的拮抗因子,通过对β-catenin的拮抗,阻止异常Wnt信号,从而可能抑制肿瘤的发生、发展。该研究旨在探讨Chibby对喉癌细胞Hep-2增殖凋亡的影响。方法:采用基因工程技术,构建重组质粒plv-cs2.0-Chibby,经酶切鉴定及序列测定后,转染293FT细胞进行病毒包装、扩增,该重组慢病毒感染喉癌细胞Hep-2后,经puromycin筛选后建立稳定表达Chibby的Hep-2细胞系。采用实时定量PCR(real-time quantitative PCR,realtime qPCR)及蛋白质印迹法(Western blot)检测重组慢病毒感染Hep-2细胞后Chibby的表达情况,MTT比色法检测细胞的增殖能力,流式细胞术检测细胞周期的变化,TUNEL检测细胞的凋亡情况。结果:重组质粒酶切后得到与理论大小相符的基因片段,序列测定与GenBank公布的一致。重组慢病毒感染Hep-2细胞后Chibby的表达水平显著提高(P<0.01)。与对照组及plv-cs2.0组相比较,plv-cs2.0-Chibby组细胞的增殖能力明显减弱(P<0.05);细胞滞留在G1期,而S期细胞明显减少(P<0.05);同时促使了Hep-2细胞的凋亡(P<0.05)。结论:Chibby过表达后抑制了喉癌细胞Hep-2的增殖能力,促使了喉癌细胞的凋亡,为喉癌的基因治疗奠定了基础。     

沉默半乳糖凝集素-3体外诱导卵巢癌细胞凋亡和内质网应激的实验研究

目的:研究沉默半乳糖凝集素-3(Galectin-3)对卵巢癌细胞凋亡和内质网应激的影响。方法:卵巢癌SKOV3细胞感染Galectin-3 siRNA 重组慢病毒,Real time PCR和Western blot检测沉默效果。MTT方法测定细胞增殖变化,平板克隆实验检测细胞克隆形成能力变化,流式细胞术检测细胞凋亡变化,Western blot检测细胞中c-caspase-3、CHOP、ATF4蛋白水平变化。结果:与感染阴性对照慢病毒和未感染的细胞比较,Galectin-3 siRNA 重组慢病毒感染后的SKOV3细胞中Galectin-3 mRNA和蛋白表达水平均降低。与感染阴性对照慢病毒和未感染的细胞比较,Galectin-3 siRNA 重组慢病毒可以明显下调SKOV3细胞的增殖、克隆形成能力,提高细胞凋亡率,促进细胞中c-caspase-3、CHOP、ATF4蛋白水平。结论:沉默Galectin-3抑制卵巢癌细胞生长,诱导卵巢癌细胞凋亡,促进细胞内质网应激。     

三种癌细胞对Ad-E1A的敏感程度研究

目的：研究腺病毒介导的E1A基因（Ad-E1A）体外对Hep-2人喉癌细胞、A375人黑色素瘤细胞、SMMC-7721人肝癌细胞的生长抑制作用及敏感程度。方法：RT-PCR鉴定E1A基因的转录;MTT法检测细胞的生长抑制作用;Hoechst染色法检测细胞核形态改变;流式细胞术（FCM）检测细胞周期和细胞凋亡。结果：Ad-E1A在三种癌细胞内均有效表达,在其感染72h和96h后对Hep-2、A375、SMMC-7721细胞的生长抑制率达分别为18.65%和29.95%;33.02%和45.36%;36.32%和54.11%;其中对SMMC-7721细胞的作用最强,FCM 检测发现其凋亡率为36.92%。Hoechst染色表明Ad-E1A诱导肿瘤细胞凋亡,使其呈现典型的核固缩、断裂并出现凋亡小体等核形态改变。结论：Ad-E1A对Hep-2、A375、SMMC-7721三种癌细胞均有生长抑制作用,尤以对SMMC-7721细胞作用最强、A375细胞次之, Hep-2细胞的敏感性相对较低;此外,Ad-E1A还能诱导肿瘤细胞凋亡。     

1，25-二羟基维生素D3对喉癌细胞增殖的抑制作用及其可能机制

背景与目的：1,25-二羟基维生素D,[1,25-dihydroxy-vitamin D3,1,25（OH）2D3]是维生素D的活性形式,体内外实验均已证明它能抑制多种肿瘤细胞的生长。本研究观察其对人喉癌细胞株Hep-2增殖的抑制作用并探讨其可能作用机制。方法：体外培养Hep-2细胞,培养时添加100、10和1nmol／L1,25（OH）2D3,分别作用24、48、72和96h后,用四唑蓝比色实验（MTT）检测细胞的增殖;用流式细胞仪检测细胞凋亡;用Western blot检测MAPK信号转导通路中ERK、P38、JNK蛋白及其磷酸化蛋白的表达。结果：1,25（OH）2D3可以显著抑制Hep-2细胞的增殖,10nmol／L1,25（OH）2D3作用96h可以诱导Hep-2细胞凋亡,凋亡率为（34．08±1．75）％;p38MAPK的磷酸化水平随1,25（OH）2D3浓度的增加而增强,而丝裂原活化蛋白激酶ERK和JNK的磷酸化程度没有明显改变：应用p38MAPK通路特异性抑制剂SB2035080作用后,1,25（OH）2D3诱导的Hep-2细胞凋亡率减少。结论：1,25（OH）2D3可诱导喉癌细胞Hep-2发生凋亡,其作用机制可能与p38MAPK信号转导通路有关。     

Transient infection of freshly isolated human colorectal tumor cells by reovirus T3D intermediate subviral particles

Reovirus T3D preferentially kills tumor cells expressing Ras oncogenes and has shown great promise as an anticancer agent in various preclinical tumor models. Here, we investigated whether reovirus can infect and kill tumor cell cultures and tissue fragments isolated from resected human colorectal tumors, and whether this was affected by the presence of endogenous oncogenic KRAS. Tissue fragments and single-cell populations isolated from human colorectal tumor biopsies were infected with reovirus virions or with intermediate subviral particles (ISVPs). Reovirus virions were capable of infecting neither single-cell tumor cell populations nor small fragments of intact viable tumor tissue. However, infection of tumor cells with ISVPs resulted in transient viral protein synthesis, irrespective of the presence of oncogenic KRAS, but this did not lead to the production of infectious virus particles, and tumor cell viability was largely unaffected. ISVPs failed to infect intact tissue fragments. Thermolysin treatment of tumor tissue liberated single cells from the tissue and allowed infection with ISVPs, but this did not result in the production of infectious virus particles. Immunohistochemistry on tissue microarrays showed that junction adhesion molecule 1, the major cellular reovirus receptor, was improperly localized in the cytoplasm of colorectal tumor cells and was expressed at very low levels in liver metastases. This may contribute to the observed resistance of tumor cells to reovirus T3D virions. We conclude that infection of human colorectal tumor cells by reovirus T3D requires processing of virions to ISVPs, but that oncolysis is prevented by a tumor cell response that aborts viral protein synthesis and the generation of infectious viral particles, irrespective of KRAS mutation status.     

Deficiency of caspase 3 in tumor xenograft impairs therapeutic effect of measles virus Edmoston strain

The oncolytic measles virus Edmonston (MV-Edm) strain shows considerable oncolytic activity against a variety of human tumors. In this study, we report MV-Edm is able to trigger apoptosis pathways in infected tumor cells and elucidate the roles of cellular apoptosis in the whole oncolytic process. We also show that activated caspase 3, a key executioner of apoptosis, plays key roles in the oncolytic virotherapy. Activated caspase 3 can accelerate viral replication in cervical cancer cells and enhance the killing effects of the virus. Deficiency of caspase 3 either in tumor cells or in tumor xenograft significantly desensitized tumor to oncolysis with MV-Edm. In the infected cells, caspase 3 regulates interferon α release, which can inhibit viral replication in neighboring tumor cells. We propose that caspase-3 activation enhances the oncolytic effects of MV-Edm, thus inhibiting tumor growth in mice.     

Replicating adenoviral vector-mediated transfer of a heat-inducible double suicide gene for gene therapy

Tumor cells that express a fusion gene of Escherichia coli cytosine deaminase (CD) and herpes simplex virus type 1 thymidine kinase (TK) sequences activate and are subsequently killed by the nontoxic prodrugs 5-fluorocytosine and ganciclovir. We have previously developed a recombinant adenovirus containing the CD-TK fusion gene controlled by the human inducible heat shock protein 70 promoter so that heat at 41 degrees C for 1 hour induces therapeutic gene expression. This adenovirus effectively transduces heat-inducible expression of the CD-TK gene into human prostate carcinoma cells. However, because a limited number of cells in a tumor can actually be infected, we created a replicating adenoviral vector to increase CD-TK gene expression. This vector is a replication-competent, E1B-attenuated adenoviral vector containing the hsp70 promoter-driven CD-TK gene (Ad.E1A(+)HS-CDTK). When human prostate adenocarcinoma DU-145 cells (mutant p53) were infected with the virus at a multiplicity of infection (MOI) of 1 or 10, the viral replication was detected within 2 days at both MOIs. Similar results were observed in human colorectal carcinoma CX-1 cells. When DU-145 cells were infected with the virus at an MOI of 10, incubated for 24 hours, heated at 41 degrees C for 4 hours, and then harvested 20 hours later, Western blot analysis demonstrated that this virus successfully produced viral E1A proteins and heat shock stimulated the CD-TK gene expression by 12.3-fold. In addition, Ad.E1A(+)HS-CDTK effectively suppressed cell proliferation by viral cytopathic effect). Unlike with a replication-incompetent virus (Ad.HS-CDTK), the cytopathic effect of the virus and cytotoxicity in the presence of the prodrugs were still observed even at low MOI (MOI=1.0).     

Infection with oncolytic herpes simplex virus-1 induces apoptosis in neighboring human cancer cells: a potential target to increase anticancer activity.

PURPOSE: The antitumor efficacy of a herpes simplex virus (HSV)-1 oncolytic virus depends on the cytotoxic effect of the virus, but also on viral replication and spread within the tumor. Apoptosis is considered a defense mechanism of infected cells that minimizes the spread of viral progeny by limiting cellular production of virus. We sought to determine whether oncolytic HSV-1 infection induces apoptosis in neighboring, uninfected cells and whether manipulation of apoptosis can increase viral replication and cytotoxicity. EXPERIMENTAL DESIGN: NV1066 is an oncolytic HSV-1 mutant that contains the marker gene for enhanced green fluorescent protein. OCUM human gastric cancer cells were infected with NV1066 in vitro and inspected for apoptosis by Hoechst and terminal deoxynucleotidyltransferase-mediated nick end labeling staining and for infection by expression of green fluorescence. RESULTS: A significant increase in apoptosis was seen in cells infected by NV1066. More interestingly, a significant percentage (10%) of uninfected cells also proceeded to apoptosis. After NV1066 infection, cells were also treated with N-acetylcysteine (NAC), an inhibitor of apoptosis. By day 4 after infection, 2.7x more NV1066 was produced in cells exposed to NAC than in those not exposed to NV1066 (P = 0.04). NAC also increased tumor kill when administered with virus. CONCLUSIONS: These data suggest that NV1066 induces apoptosis in uninfected cocultured cells, potentially hindering propagation of viral progeny and concomitant tumor kill. Inhibition of apoptosis may improve the efficacy of oncolytic HSV-1 therapy.     

Lysosomal changes in lytic and nonlytic infections with the simian vacuolating virus (SV40)

Lysosomal changes have been observed by histochemical methods in the BSC-1 green monkey kidney cell line and the 3T3 mouse cell line infected with high multiplicities of simian vacuolating virus (SV40) and in 3T3 cells infected with herpes simplex virus. BSC-1 cells infected with SV40 showed marked cytoplasmic vacuolation and lysis. The lysosomes were enlarged and aggregated and there was second-stage activation with release of enzyme into the cytoplasm. Possibly, some product of viral replication in the nucleus is released into the cytoplasm and brings about changes in lysosomes and other cytoplasmic organelles. Lysosomal enzymes probably contribute to the dissolution of cells and release of virus from nuclei. 3T3 cells infected with SV40 under these conditions do not lyse, but a large proportion may become transformed. First-stage activation of lysosomes was seen for at least 6 days. After 6 days these changes disappeared. The possible relationship of lysosomal changes to the events occurring in transformed cells is discussed. The cells infected with herpes simplex virus showed marked cytopathic effects associated with second-stage lysosomal activation.     

The enhanced tumor selectivity of an oncolytic vaccinia lacking the host range and antiapoptosis genes SPI-1 and SPI-2

The ability of cancer cells to evade apoptosis may permit survival of a recombinant vaccinia lacking antiapoptotic genes in cancer cells compared with normal cells. We have explored the deletion of two vaccinia virus host range/antiapoptosis genes, SPI-1 and SPI-2, for their effects on the viral replication and their ability to induce cell death in infected normal and transformed cells in vitro. Indeed, in three paired normal and transformed cell types, the SPI-1 and SPI-2 gene-deleted virus (vSP) preferentially replicates in transformed cells or p53-null cells when compared with their normal counterparts. This selectivity may be derived from the fact that vSP-infected normal cells died faster than infected cancer cells. A fraction of infected cells died with evidence of necrosis as shown by both flow cytometry and detection of high-mobility group B1 protein released from necrotic cells into the culture supernatant. When administered to animals, vSP retains full ability to replicate in tumor tissues, whereas replication in normal tissues is greatly diminished. In a model of viral pathogenesis, mice treated with vSP survived substantially longer when compared with mice treated with the wild-type virus. The mutant virus vSP displayed significant antitumoral effects in an MC38 s.c. tumor model in both nude (P < 0.001) and immunocompetent mice (P < 0.05). We conclude that this recombinant vaccinia vSP shows promise for oncolytic virus therapy. Given its enhanced tumor selectivity, improved safety profile, and substantial oncolytic effects following systemic delivery in murine models, it should also serve as a useful vector for tumor-directed gene therapy.     

Cytotoxicity, apoptosis, and viral replication in tumor cells treated with oncolytic ribonucleotide reductase-defective herpes simplex type 1 virus (hrR3) combined with ionizing radiation

The viral ribonucleotide reductase (rR)-defective herpes simplex type-1 (HSV-1) virus (hrR3) has been shown previously to preferentially replicate in and kill tumor cells. This selectivity is associated with tumor cell up-regulation of mammalian rR. Ionizing radiation (IR) is currently used in the therapy of many malignancies, including glioblastoma, cervical carcinoma, and pancreatic carcinoma. IR has been shown to up-regulate mammalian rR in tumor cells and appears to increase the efficacy of at least one non-rR-deleted HSV-1 strain in an in vivo tumor model. Here, we test the hypothesis that a single therapeutic radiation fraction will increase the replication and toxicity of hrR3 for malignant cell lines in vitro. PANC-1 pancreatic carcinoma, U-87 glioblastoma, and CaSki cervical carcinoma cell lines were treated with varying doses of IR and subsequently infected with hrR3 or KOS (wild-type HSV-1 strain). Cell survival was then measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and trypan blue exclusion cytometry. At 72 hours posttreatment, irradiation with 2 Gy reduced survival from 100% to 76% in noninfected cells, from 61% to 48% in KOS-infected cells, and from 39% to 27% in hrR3-infected PANC-1 cells. As such, analysis of variance indicated that the toxicity of the two modalities was additive. Similar additivity was seen in U-87 MG and CaSki cells. Absolute survival of hrR3-infected or KOS-infected PANC-1 cells decreased as a function of time after treatment (24-72 hours) and multiplicity of infection (MOI) (0.05-5.0). However, the relative decrease in survival with the addition of IR to hrR3 or KOS in PANC-1 cells was not markedly affected by altering MOI (0.05-5.0), time (24-72 hours), radiation dose (2-20 Gy), or cell culture conditions (confluent/growth arrested). We used fluorescence-activated cell sorter analysis with the cationic lipophilic dye DiOC6 to quantify a reduction in mitochondrial membrane potential that'is associated with apoptosis. Fluorescence-activated cell sorter analysis indicated increased apoptosis in both hrR3- and IR-treated cells at 48-72 hours, with hrR3 alone producing the most induction. Viral yields from PANC-1 cells after irradiation and infection were examined. No significant differences were seen between irradiated and nonirradiated cells in viral replication, with hrR3 producing single-step titers of 3.1 +/- 0.9 x 10(5) and 4.0 +/- 1.2 x 10(5) plaque-forming units/mL in nonirradiated and irradiated cells. Thus, complementary toxicity was seen between IR and hrR3 or KOS, regardless of cell type, time, MOI, IR dose, or culture conditions, without evidence of augmented apoptosis or viral replication.     

Adhesive function of newcastle-disease virus hemagglutinin in tumor-host interaction

Infection of metastatic lymphoma cells (ESbL) by a low dose of a non-lytic strain of Newcastle disease virus (NDV) leads to viral replication followed by strong cell surface expression of viral antigens, especially hemagglutinin neuraminidase (HN). The expressed HN was functional and facilitated cell-cell interactions and cell attachment. This was shown for NDV infected tumor cells, lymphocytes, fibroblasts and endothelial cells. The interactions could be strongly inhibited by antibodies against the viral HN protein. Increased binding was also seen with HN c-DNA transfectants expressing the HN as the only viral protein. Viral infection did not influence proliferation and lysability of the infected tumor cells. Following intravenous injection of tumor cells, the number of hepatic metastases was significantly reduced when the cells had been pre-infected with NDV. This reduction of metastases correlated with an increased survival time of the animals. As potential mechanisms of these NDV effects we propose augmentation of cell-eel interactions and immune functions and reduction of invasive capacity of NDV infected, as compared to non-infected tumor cells.     

Mouse mammary tumor virus infections: viral expression and tumor risk.

Concentrations of murine mammary tumor virus (MuMTV) antigen in the milk of individual naturally infected BALB/cfC3H and BALB/c mice given injections of MuMTV were related to their risk of developing a mammary tumor. Two distinct groups of MuMTV-infected mice were identified. One group exhibited high viral antigen levels in their milk (greater than or equal to 100 micrograms/ml), whereas the other group exhibited low viral antigen levels in their milk (less than or equal to 3 micrograms/ml). Mice that exhibited high levels developed tumors by 17 months of age, whereas those with low levels did not. Viral expression levels in mice having high risks of tumor development were also related to the length of the latency period preceding overt tumor development. The tumor risk potential of naturally infected mice was frequently that of their mothers. Various doses of MuMTV were injected into BALB/c mice, and the resulting infections differed in latency period, level of viral expression, and potential for neoplastic transformation.