Role of tumor cell immune escape mechanisms in cytomegalovirus-mediated oncomodulation

Clinical implications of cytomegalovirus in glioblastoma progression and therapy

Glioblastoma (GBM) is one of the deadliest brain cancers with a median survival of only 15 months. This poor prognosis has prompted exploration of novel therapeutic targets for GBM patients. Human cytomegalovirus (HCMV) has been implicated in GBM; however, its impact remains poorly defined, and there is conflicting data over the presence of HCMV in tumors. Nonetheless, clinical trials targeting HCMV have shown promising initial data, and evidence suggests that HCMV may negatively impact GBM patient survival by multiple mechanisms including changes in GBM cell behavior and the tumor microenvironment (TME) that potentiate tumor progression as well as therapy-induced virus reactivation. Moreover, HCMV has many effects on host immunity that could impact tumor behavior by altering the TME, which are largely unexplored. The goal of this review is to describe these potential interactions between HCMV and GBM. Better understanding of these processes may allow the development of new therapeutic modalities to improve GBM patient outcomes.

Cellular Transformation by Human Cytomegalovirus

Epstein-Barr virus (EBV), Kaposi sarcoma human virus (KSHV), human papillomavirus (HPV), hepatitis B and C viruses (HBV, HCV), human T-lymphotropic virus-1 (HTLV-1), and Merkel cell polyomavirus (MCPyV) are the seven human oncoviruses reported so far. While traditionally viewed as a benign virus causing mild symptoms in healthy individuals, human cytomegalovirus (HCMV) has been recently implicated in the pathogenesis of various cancers, spanning a wide range of tissue types and malignancies. This perspective article defines the biological criteria that characterize the oncogenic role of HCMV and based on new findings underlines a critical role for HCMV in cellular transformation and modeling the tumor microenvironment as already reported for the other human oncoviruses.

High-Risk Oncogenic Human Cytomegalovirus

Human cytomegalovirus (HCMV) is a herpesvirus that infects between 40% and 95% of the population worldwide, usually without symptoms. The host immune response keeps the virus in a latent stage, although HCMV can reactivate in an inflammatory context, which could result in sequential lytic/latent viral cycles during the lifetime and thereby participate in HCMV genomic diversity in humans. The high level of HCMV intra-host genomic variability could participate in the oncomodulatory role of HCMV where the virus will favor the development and spread of cancerous cells. Recently, an oncogenic role of HCMV has been highlighted in which the virus will directly transform primary cells; such HCMV strains are named high-risk (HR) HCMV strains. In light of these new findings, this review defines the criteria that characterize HR-HCMV strains and their molecular as well as the phenotypic impact on the infected cell and its tumor microenvironment.

Tumors and Cytomegalovirus: An Intimate Interplay

Human cytomegalovirus (HCMV) is a herpesvirus that alternates lytic and latent infection, infecting between 40 and 95% of the population worldwide, usually without symptoms. During its lytic cycle, HCMV can result in fever, asthenia, and, in some cases, can lead to severe symptoms such as hepatitis, pneumonitis, meningitis, retinitis, and severe cytomegalovirus disease, especially in immunocompromised individuals. Usually, the host immune response keeps the virus in a latent stage, although HCMV can reactivate in an inflammatory context, which could result in sequential lytic/latent viral cycles during the lifetime and thereby participate in the HCMV genomic diversity in humans and the high level of HCMV intrahost genomic variability. The oncomodulatory role of HCMV has been reported, where the virus will favor the development and spread of cancerous cells. Recently, an oncogenic role of HCMV has been highlighted in which the virus will directly transform primary cells and might therefore be defined as the eighth human oncovirus. In light of these new findings, it is critical to understand the role of the immune landscape, including the tumor microenvironment present in HCMV-harboring tumors. Finally, the oncomodulatory/oncogenic potential of HCMV could lead to the development of novel adapted therapeutic approaches against HCMV, especially since immunotherapy has revolutionized cancer therapeutic strategies and new therapeutic approaches are actively needed, particularly to fight tumors of poor prognosis.

Immune Landscape of CMV Infection in Cancer Patients: From "Canonical" Diseases Toward Virus-Elicited Oncomodulation

Human Cytomegalovirus (HCMV) is an immensely pervasive herpesvirus, persistently infecting high percentages of the world population. Despite the apparent robust host immune responses, HCMV is capable of replicating, evading host defenses, and establishing latency throughout life by developing multiple immune-modulatory strategies. HCMV has coexisted with humans mounting various mechanisms to evade immune cells and effectively win the HCMV-immune system battle mainly through maintaining its viral genome, impairing HLA Class I and II molecule expression, evading from natural killer (NK) cell-mediated cytotoxicity, interfering with cellular signaling, inhibiting apoptosis, escaping complement attack, and stimulating immunosuppressive cytokines (immune tolerance). HCMV expresses several gene products that modulate the host immune response and promote modifications in non-coding RNA and regulatory proteins. These changes are linked to several complications, such as immunosenescence and malignant phenotypes leading to immunosuppressive tumor microenvironment (TME) and oncomodulation. Hence, tumor survival is promoted by affecting cellular proliferation and survival, invasion, immune evasion, immunosuppression, and giving rise to angiogenic factors. Viewing HCMV-induced evasion mechanisms will play a principal role in developing novel adapted therapeutic approaches against HCMV, especially since immunotherapy has revolutionized cancer therapeutic strategies. Since tumors acquire immune evasion strategies, anti-tumor immunity could be prominently triggered by multimodal strategies to induce, on one side, immunogenic tumor apoptosis and to actively oppose the immune suppressive microenvironment, on the other side.

Cytomegalovirus infection in malignant pleural mesothelioma

Human cytomegalovirus (HCMV) is a highly prevalent herpes virus which persists as a latent infection and has been detected in several different tumor types. HCMV disease is rare but may occur in high-risk settings, often manifesting as a pulmonary infection. To date HCMV has not been investigated in malignant pleural mesothelioma (MPM). In a consecutive case series of 144 MPM patients we evaluated two biomarkers of HCMV: IgG serostatus (defined as positive and negative) and DNAemia (>100 copies/mL of cell free HCMV DNA in serum). Approximately half of the MPM patient population was HCMV IgG seropositive (51%). HCMV DNAemia was highly prevalent (79%) in MPM and independent of IgG serostatus. DNAemia levels consistent with high level current infection (>1000 copies/mL serum) were present in 41% of patients. Neither IgG serostatus nor DNAemia were associated with patient survival. In tissues, we observed that HCMV DNA was present in 48% of tumors (n = 40) and only 29% of normal pleural tissue obtained from individuals without malignancy (n = 21). Our results suggest nearly half of MPM patients have a high level current HCMV infection at the time of treatment and that pleural tissue may be a reservoir for latent HCMV infection. These findings warrant further investigation to determine the full spectrum of pulmonary infections in MPM patients, and whether treatment for high level current HCMV infection may improve patient outcomes.

The cytomegalovirus UL146 gene product vCXCL1 promotes the resistance of hepatic cells to CD8+ T cells through up-regulation of PD-L1

The HCMV (human cytomegalovirus) encodes numerous proteins which function to evade the immune response, which allows the virus to replicate. Exploring the mechanisms of HCMV immune escape helps to find the strategy to inhibit HCMV replicate. CD8⁺ T cells play a critical role in the immune response to viral pathogens. However, the mechanisms of HCMV to evade the attack by CD8⁺ T cells remain largely unknown. Viral CXCL1 (vCXCL1) is the production of HCMV UL146 gene. Here, we found that vCXCL1 promoted the resistance of hepatic cells to CD8⁺ T cells. vCXCL1 increased the levels of PD-L1 protein expression and mRNA expression. VCXCL1 enhanced the binding of STAT3 transcription factor to the promoter of PD-L1 and increased the activity of PD-L1 promoter. Furthermore, down-regulation of PD-L1 reduced the effects of vCXCL1 on the resistance of hepatic cells to CD8⁺ T cells. Taken together, vCXCL1 promotes the resistance of hepatic cells to CD8⁺ T cells through up-regulation of PD-L1. This finding might provide a new mechanism of HCMV immune escape.

Cytomegalovirus Infection Is a Risk Factor in Gastrointestinal Cancer: A Cross-Sectional and Meta-Analysis Study

BACKGROUND

This study was planned to investigate the association betweenhuman cytomegalovirus (HCMV) infection and gastrointestinal cancer (GIC) risk, by undertaking a meta-analysis and case-control cross-sectional study.

SUMMARY

A cross-sectional study analysis of 160 GIC patients and 100 control subjects indicated significantly higher HCMV prevalence in GIC patients based on the HCMV IgM test. However, a similar analysis based on an IgG test revealed no significant relationship. Further meta-analysis of 11 studies, including 1,044 patients and 991 healthy subjects, displayed HCMV infection as an important risk factor for not only colorectal cancer occurrence and development based on a HCMV DNA test, but also for GIC based on a HCMV IgM test. However, the IgG test again displayed no significant relationship between HCMV infection and GIC occurrence. Key Message: Overall, our study revealed that HCMV infection is associated with an increased GIC risk. However, additional studies are warranted to elucidate the molecular mechanism underlying this association.

Epstein-Barr virus, but not human cytomegalovirus, is associated with a high-grade human papillomavirus-associated cervical lesions among women in North Carolina

STATEMENT OF THE PROBLEM

Human papillomavirus (HPV) infection is known to contribute to cervical carcinogenesis, yet other cofactors that may contribute to oncogenesis are poorly understood. Herein, we examine whether the Epstein-Barr virus (EBV) and human cytomegalovirus (CMV), two oncomodulatory viruses, are associated with HPV-mediated cervical neoplastic progression.

METHODS

Sixty patient cervical brush samples from a study of North Carolina women were obtained. HPV RNA positivity was determined by Aptima testing (Hologic Corporation, Marlborough, MA). The level of viral transcripts for EBV and CMV was quantified (reverse transcription polymerase chain reaction analysis), and the coinfection status with HPV was then compared with the patient's cervical cytology grade.

RESULTS

Over one-third (38.3%) of the study population was CMV positive, whereas 43.3% was EBV positive. When sample data were stratified by the cytology grade, 36.5% (19/52) of normal patients, 75% (3/4) of low-grade squamous intraepithelial lesions (LSIL), and 100% (4/4) of patients with high-grade SIL (HSIL) were EBV positive. Conversely, 35.2% (18/52) of normal patients, 25% (1/4) of patients with LSIL, and 50% (2/4) of patients with HSIL were CMV positive. When examining only HPV positive-associated HSIL, 100% (4/4) were positive for both HPV and EBV detection. This suggests that co-viral detection with HPV and EBV is associated with more advanced HSIL cervical lesions, while CMV displayed no clear association with a higher grade of cervical cytology.

CONCLUSIONS

Co-viral detection with EBV may increase the oncogenicity and/or serve as a viral marker of progression to HPV-associated high-grade cervical dysplasia.

Impact of human cytomegalovirus on glioblastoma cell viability and chemotherapy treatment

The relationship between human cytomegalovirus (HCMV) and tumours has been extensively investigated, mainly in glioblastoma multiforme (GBM), a malignant tumour of the central nervous system with low overall survival rates. Several reports have demonstrated the presence of HCMV in GBM, although typically restricted to a low number of cells, and studies have indicated that viral proteins have the ability to dysregulate cellular processes and increase tumour malignancy. Treatment of GBM involves the use of the chemotherapeutic agents temozolomide (TMZ) and carmustine (bis-chloroethylnitrosourea, BCNU), which lead to the attachment of adducts to the DNA backbone, causing errors during replication and consequent cell death. It is known that HCMV infection can modulate DNA repair pathways, but what effects the virus may exhibit during chemotherapy are unknown. Here we approach this question by analysing HCMV infection and viral protein accumulation in GBM cell lines with different genotypes and their response to TMZ and BCNU in the presence of the virus. We demonstrate that A172, TP365MG and U251MG GBM cells are efficiently infected by both low-passage (TB40E) and high-passage (AD169) HCMV strains. However, the GBM cell lines vary widely in their permissiveness to viral gene expression and exhibit very different patterns of immediate early, early and late protein accumulation. HCMV reduces the viability of permissive GBM cells in a multiplicity-dependent manner in both the absence and presence of TMZ or BNCU. In sum, we demonstrate that GBM cell lines are equally susceptible but differentially permissive to infection by both low- and high-passage strains of HCMV. This observation not only indicates that viral replication is largely controlled by cellular factors in this system, but also provides a possible explanation for why viral gene products are only found in a subset of cells in GBM tumours. Furthermore, we conclude that the virus does not confer increased resistance to chemotherapeutic drugs in various GBM cell lines, but instead reduces tumour cell viability. These results highlight that the oncomodulatory potential of HCMV is not limited to cancer-promoting activities, but also includes adverse effects on tumour cell proliferation or survival.

Detection of human cytomegalovirus in patients with colorectal cancer by nested-PCR

BACKGROUND

The association of colorectal cancer with human cytomegalovirus (HCMV) is a controversial issue in cancer research. This study aimed to identify the HCMV virus in colorectal cancer tissues and to investigate the association of HCMV with colorectal cancer. In this study, 50 cancer tissue samples and 50 samples without colon cancer were studied in order to identify the HCMV virus through nested-polymerase chain reaction. The virus was identified in 15 cases of colorectal cancer tissues (15/50) and in 5 cases of normal tissues (5/50). Eight cases of adenocarcinoma tissues were in a moderately differentiated stage, and 7 cases had well-differentiated stage tissues that were positive for viral DNA. The findings were statistically evaluated at a significance level of p<0.05. The HCMV virus could play a role in creating malignancy and the progress of cancer through the process of oncomodulation.

Upregulation of Toll-like receptor 2 expression in colorectal cancer infected by human cytomegalovirus

The aim of the present study was to investigate the association between Toll-like receptor 2 (TLR2) expression and human cytomegalovirus (HCMV) in colorectal carcinoma by detecting the expression of IE1-72, TLR2, TLR4 and tumor necrosis factor (TNF)-α in colorectal carcinoma and colon adenoma samples, as well as by analyzing the mRNA levels of the proteins in colon cancer cell lines, following HCMV infection. For this study, 56 colorectal cancer and 36 colon adenoma samples were collected, and normal mucosal tissue adjacent to the tumor was used as the control. The expression of the IE1-72, TLR2, TLR4, nuclear factor (NF)-κB and TNF-α protein was detected by immunohistochemistry. Cells from the SW480 human colon carcinoma cell line were infected with HCMV. The expression of IE1-72, TLR2, TLR4, NF-κB and TNF-α mRNA was quantified at different time points prior to and following infection. The positive expression rate of IE1-72 was 44.6% (25/56) in colorectal cancer and 41.7% (15/36) in colon adenoma. These rates were significantly higher when compared with the 12.5% (7/56) observed in the normal tissues adjacent to the cancer tissues (P<0.05). The expression levels of TLR2, TLR4, NF-κB and TNF-α in colorectal cancer and adenoma were also higher than those in the control tissues. Furthermore, the expression of IE1-72 in colorectal cancer tissues was found to correlate with TLR2 and TLR4, and the correlation coefficients were 0.515 and 0.462, respectively. Following the infection of SW480 cells, the mRNA levels of TLR2 and TNF-α increased gradually from 6 h, peaked at 48 h, and then decreased gradually. No significant differences in TLR4 and NF-κB expression were identified. The results of the present study indicated that there is a specific association between HCMV and the occurrence and development of colorectal cancer, which may be facilitated by the TLR2 signaling pathway.

Cytomegalovirus and brain tumor: epidemiology, biology and therapeutic aspects

PURPOSE OF REVIEW

First described in 2002, the presence and role of human cytomegalovirus (HCMV) infection in glioblastoma (GBM) has remained a controversial topic. New research indicates HCMV gene products likely promote GBM pathogenesis and that therapies aimed at HCMV might influence disease progression.

RECENT FINDINGS

Recently, investigators have begun to analyze HCMV genome and proteins present in GBM cells in vivo. Furthermore, the research has demonstrated that several HCMV gene products that have oncomodulatory properties are expressed in GBM and may be impacting tumor pathogenesis in vivo. These HCMV gene products modulate GBM proliferation, apoptosis, angiogenesis, invasion and immune evasion. A recent mouse model provides mechanistic information as to how CMV may promote gliomagenesis in the setting of tumor suppressor dysfunction and STAT3 signaling. In addition, clinical outcomes of GBM patients are associated with the degree of HCMV infection. Novel therapies aimed at direct antiviral and immunotherapy approaches to HCMV suggest that these modalities may impact the future treatment of this disease.

SUMMARY

A more precise understanding of the role of HCMV infection in gliomagenesis and GBM pathogenesis could reveal novel therapeutic and preventive strategies.

Leflunomide inhibits the apoptosis of human embryonic lung fibroblasts infected by human cytomegalovirus

BACKGROUND

The immunomodulatory drug leflunomide (LEF) is frequently used for treating human cytomegalovirus (HCMV), but its antiviral mechanism is still unclear. In this study,we therefore investigated the effects of the active LEF metabolite A771726 on the HCMV lifecycle in human embryonic lung fibroblasts. We clarified the mechanism of LEF antiviral infection, and provide a new way to treat immune dysfunction patients with HCMV infection.

METHODS

The experiment was divided into four groups: the control group, the HCMV group, the ganciclovir+HCMV group as well as the LEF+HCMV group. MTT was used for assessment of the cell inhibitory rate. Apoptosis was measured by staining with fluorescein isothiocyanate Annexin V and propidium iodide. Statistical significance was determined by paired t-test using SPSS software.

RESULTS

The results of the study showed that cell proliferation was significantly inhibited by HCMV at 24 hours and 48 hours. With increasing HCMV concentration, the value-added inhibition of the cells was significantly decreased compared with the control group, and was statistically significant (P<0.01). Ganciclovir can increase proliferation of cells infected with HCMV; compared with the control group it was statistically significant (P<0.05). Meanwhile, with LEF treatment cell proliferation was significantly improved at 24 hours and 48 hours, with statistical significance (P<0.05). The apoptosis rate of human embryonic lung fibroblasts infected with HCMV increased significantly at 24 hours, 48 hours and 72 hours, and as time goes on the apoptosis rate increases statistically significantly (P<0.01) compared with the control group The apoptosis rate of the HCMV infection group decreased by adding LEF,and was statistically significant (P<0.05).

CONCLUSIONS

In this study we show that LEF is an exciting new drug for cytomegalovirus infection. LEF significantly inhibited HCMV infection-induced apoptosis and proliferation, playing an important role in the treatment of patients infected by HCMV. In this study we explored the potential usefulness of LEF for cytomegalovirus infection and found it to be a cost-effective new treatment for cytomegalovirus infection that deserves further study.

Human cytomegalovirus UL97 kinase alters the accumulation of CDK1

The UL97 protein kinase is a serine/threonine kinase expressed by human cytomegalovirus (CMV) that phosphorylates ganciclovir. An investigation of the subcellular localization of pUL97 in infected cells indicated that, early in infection, pUL97 localized to focal sites in the nucleus that transitioned to subnuclear compartments and eventually throughout the entire nucleus. When UL97 kinase activity was eliminated with a K355M mutation or pharmacologically inhibited with maribavir, the expansion and redistribution of pUL97 foci within the nucleus was delayed, nuclear reorganization did not occur and assembly complexes in the cytoplasm failed to form normally. As UL97 kinase and its homologues appear to be functionally related to CDK1, a known regulator of nuclear structural organization, the effects of the UL97 kinase on CDK1 were investigated. Expression of CDK1 in infected cells appeared to be induced by UL97 kinase activity at the level of transcription and was not tied to other virus life-cycle events, such as viral DNA replication or virion assembly. These results suggest that, in addition to phosphorylating CDK1 targets, the UL97 kinase modifies G₂/M cell-cycle checkpoint regulators, specifically CDK1, to promote virus replication.

Cytomegalovirus exposure, immune exhaustion and cancer occurrence in renal transplant recipients

The role of Cytomegalovirus (CMV) in carcinogenesis is controversial. We studied whether CMV may contribute to cancer occurrence in renal transplant recipients. We studied a prospective cohort of 455 consecutive patients who received a kidney transplant between January 1995 and December 2006. All cancers and types of cancers were assessed. Lymphocyte phenotype and cytokines production were analysed according to CMV status in a subset population of this cohort. Mean follow-up was 84 ± 29 months. One hundred and nineteen cancers (26.2%) occurred during the study follow-up. There was a higher cumulated incidence of cancers in CMV-exposed patients (30.4% vs. 20%; P=0.018). Mean time to cancer occurrence was shorter in CMV-exposed patients than in CMV-naïve patients (4.7 ± 2.6 vs. 6.7 ± 2.8; P = 0.001). Cox regression analysis revealed that both pretransplant CMV exposure (HR, 1.83; 95% CI, 1.17-2.88; P = 0.009) and post-transplant CMV replication (HR, 2.17; 95% CI, 1.02-4.59; P = 0.044) were risk factors for cancer. Among CD8+ T cells, exhausted T cells assessed as CD57+CD28- were expanded in CMV-exposed patients (26 ± 20 vs. 9 ± 8%; P < 0.0001), whereas CD8+CD57+IL2- cells were more frequent in CMV-exposed patients. Our results highly suggest that CMV increases the risk of cancer after transplantation.

Oncomodulation by human cytomegalovirus: novel clinical findings open new roads

The question whether human cytomegalovirus may affect cancer diseases has been discussed (very controversially) for decades. There are convinced believers and strict opponents of the idea that HCMV might be able to play a role in the course of cancer diseases. In parallel, the number of published reports on the topic is growing. Recently published and presented (Ranganathan P, Clark P, Kuo JS, Salamat S, Kalejta RF. A Survey of Human Cytomegalovirus Genomic Loci Present in Glioblastoma Multiforme Tissue Samples. 35th Annual International Herpes Workshop, Salt Lake City, 2010) data on HCMV detection in glioblastoma tissues and colocalisation of HCMV proteins with cellular proteins known to be relevant for glioblastoma progression motivated us to recapitulate the current state of evidence.

Epidemiology of human cytomegalovirus (HCMV) in an urban region of Germany: what has changed?

Since the dynamics of transmission of human cytomegalovirus (HCMV) have not been clarified yet, we assessed a possible change in HCMV seroprevalence in Frankfurt am Main, Germany during the past twenty years and tried to detect variables with an impact on epidemiology. Between 1/1/1988 and 10/15/2008, a total of 54443 serum samples were collected for routine diagnostics and analyzed using Enzygnost Anti HCMV-IgG enzyme immunoassay (Siemens/Dade Behring, Marburg, Germany). Two decades, 1/1/1988-12/31/1997 and 1/1/1998-10/15/2008, and several groups (type of health insurance, gender, age, HIV-status) were evaluated to assess changes in seroprevalence. Regarding both decades, the overall age-adjusted prevalence of HIV-negative patients dropped from 63.70% (confidence interval (CI) 95% 63.15-64.25) to 57.25% (CI 95% 56.57-57.93; P < 0.0001). Private health insurance (PHI) patients showed significant lower HCMV seroprevalences than members of obligatory health insurances (OHI) in both decades (1988-1997: PHI = 55.79%, OHI = 64.27%; P < 0.0001; 1998-1908: PHI = 47.02%, OHI = 58.74%; P < 0.0001). Furthermore, comparing the two decades, there was generally a gender-specific statistically significant decrease in HCMV seroprevalence for males (63.54-55.54%) and females (63.83-58.73%) as well as for members of PHI and OHI (PHI males: 57.59% to 47.19%, PHI females 54.10-46.80%; OHI males: 64.00-57.06%, OHI females 64.50-60.11%). Also, while female HIV-positive patients showed significant difference in HCMV seroprevalence between the two decades (83.17 and 87.80%, P = 0.023), there was no significant difference in male patients with HIV (88.76 and 87.32% in the first and second decade, respectively (P = 0.196). The cumulative HCMV prevalence of all HIV-negative patients tested in the past 20 years demonstrates a biphasic, age-related rise of HCMV seroprevalence throughout all age-groups. The seroprevalence of HCMV has declined between 1988-1997 and 1998-2008 in Frankfurt am Main, Germany. The decline varied between different age-groups. HCMV prevalence correlates with the type of health insurance, gender, age, and HIV-status.

Evidence of measles virus antigens and RNA in endometrial cancer

OBJECTIVES

To look for an association between the measles virus and endometrial carcinoma, the most frequent cancer of the female genital tract in our area.

STUDY DESIGN

Thirty-six of 49 patients with endometrial carcinoma were studied to detect fingerprints of the measles virus. Immunohistochemistry with the avidin-biotin complex method and in situ hybridization were used to demonstrate the association. The clinicopathological correlations were carried out to support a relationship between the virus and the cancer if any was found.

RESULTS

Twenty-six of the 36 cases (72%) of endometrial cancer showed the presence of measles virus antigens in the tumor cells. Sixteen of 21 cases were positive for measles virus RNA by in situ hybridization. Although type I endometrial carcinoma was more positive for viral particles than type II, type II cancer, when allied with the measles virus, was more often associated with the depth of myometrial invasion and with death from tumor.

CONCLUSIONS

We demonstrate for the first time a link between endometrial cancer and the presence of viral antigens and RNA of the measles virus, although these findings do not necessarily signify a causal relationship between the cancer and the virus.

The story of human cytomegalovirus and cancer: increasing evidence and open questions

Although human cytomegalovirus (HCMV) is generally not regarded to be an oncogenic virus, HCMV infection has been implicated in malignant diseases from different cancer entities. On the basis of our experimental findings, we developed the concept of "oncomodulation" to better explain the role of HCMV in cancer. Oncomodulation means that HCMV infects tumor cells and increases their malignancy. By this concept, HCMV was proposed to be a therapeutic target in a fraction of cancer patients. However, the clinical relevance of HCMV-induced oncomodulation remains to be clarified. One central question that has to be definitively answered is if HCMV establishes persistent virus replication in tumor cells or not. In our eyes, recent clinical findings from different groups in glioblastoma patients and especially the detection of a correlation between the numbers of HCMV-infected glioblastoma cells and tumor stage (malignancy) strongly increase the evidence that HCMV may exert oncomodulatory effects. Here, we summarize the currently available knowledge about the molecular mechanisms that may contribute to oncomodulation by HCMV as well as the clinical findings that suggest that a fraction of tumors from different entities is indeed infected with HCMV.

HCMV microinfections in inflammatory diseases and cancer

Human cytomegalovirus (HCMV) is a wide-spread human virus that was mainly known to cause disease in immunocompromised patients. A new entity of infection can be diagnosed with high sensitive techniques; HCMV microinfections that often exhibit an altered pattern of IE protein expression. We have recently discovered that HCMV microinfections are very common in patients with inflammatory diseases and certain cancers. The discovery of active HCMV infections in tissue specimens from patients with inflammatory diseases raises the question of whether the infection is an epiphenomenon or whether the virus plays a causative role in disease development. After a primary infection, which is generally asymptomatic in immunocompetent individuals, HCMV establishes latency and persists in its host. In infected cells, the virus can produce over 250 proteins, but only about 50-60 are believed to be essential for viral replication. Thus, the vast majority of these viral proteins enable the virus to co-exist with its host. Such proteins act through highly sophisticated mechanisms to control different cellular and immunological functions in order to facilitate viral production and to avoid detection and elimination of the virus by the immune system. These proteins may also contribute to the development of common inflammation-related diseases.

Downregulation of CD4+CD25+ regulatory T cells may underlie enhanced Th1 immunity caused by immunization with activated autologous T cells

Regulatory T cells (Treg) play important roles in immune system homeostasis, and may also be involved in tumor immunotolerance by suppressing Th1 immune response which is involved in anti-tumor immunity. We have previously reported that immunization with attenuated activated autologous T cells leads to enhanced anti-tumor immunity and upregulated Th1 responses in vivo. However, the underlying molecular mechanisms are not well understood. Here we show that Treg function was significantly downregulated in mice that received immunization of attenuated activated autologous T cells. We found that Foxp3 expression decreased in CD4+CD25+ T cells from the immunized mice. Moreover, CD4+CD25+Foxp3+ Treg obtained from immunized mice exhibited diminished immunosuppression ability compared to those from naïve mice. Further analysis showed that the serum of immunized mice contains a high level of anti-CD25 antibody (about 30 ng/ml, p<0.01 vs controls). Consistent with a role of anti-CD25 response in the downregulation of Treg, adoptive transfer of serum from immunized mice to naïve mice led to a significant decrease in Treg population and function in recipient mice. The triggering of anti-CD25 response in immunized mice can be explained by the fact that CD25 was induced to a high level in the ConA activated autologous T cells used for immunization. Our results demonstrate for the first time that immunization with attenuated activated autologous T cells evokes anti-CD25 antibody production, which leads to impeded CD4+CD25+Foxp3+ Treg expansion and function in vivo. We suggest that dampened Treg function likely contributes to enhanced Th1 response in immunized mice and is at least part of the mechanism underlying the boosted anti-tumor immunity.

Lack of association of herpesviruses with brain tumors

Gliomas are the most frequent primary brain tumors in humans. Many studies have been carried out on their etiology; however, the only confirmed risk factors are hereditary predisposing conditions and high dose of ionizing radiation. Recently, human cytomegalovirus (HCMV) gene products and nucleic acids were reported to be present in all of 27 glioma samples investigated in contrast to other brain tissues, and it was hypothesized that HCMV might play a role in glioma pathogenesis. To evaluate these findings, samples of 40 gliomas, 31 meningiomas, and 6 acoustic neurinomas (ACNs) were analyzed for the presence of HCMV macromolecules using polymerase chain reaction (PCR) and immunohistochemistry. Additionally, corresponding blood samples from 72 patients were analyzed for the presence of HCMV DNA to check for a possible contamination of tumor tissues with HCMV-infected blood cells. No HCMV DNA sequences were found, neither in brain tumor tissues nor in corresponding blood samples. Immunohistochemistry did not detect HCMV-specific proteins. Addressing a possible role of other herpesviruses as has been suggested in seroepidemiological studies, seroprevalence of antibodies to HCMV, herpes simplex virus (HSV), Epstein-Barr virus (EBV), and varicella-zoster virus (VZV) were determined by enzyme-linked immunosorbent assay (ELISA). Serological analyses of brain tumor patients showed no significant differences in the prevalences of antibodies to HCMV, HSV, EBV, or VZV compared to the general population. Thus, the data of the present study do not support the hypothesis of an association of herpesviruses with the development of primary brain tumors.

Immunization with autologous T cells enhances in vivo anti-tumor immune responses accompanied by up-regulation of GADD45β

Immunization with inactivated autoreactive T cells may induce idiotype anti-idiotypic reactions to deplete autoreactive T cells, which are involved in autoimmune diseases. However, it is unknown whether attenuated activated healthy autologous T-cell immunization could increase anti-tumor immune responses. To this end, C57Bl/6 mice were immunized with attenuated activated autologous T cells. The splenocytes from immunized mice showed a higher proliferative ability than that from naive mice. The special phenotype analysis showed that there were more CD8+ T cells and CD62L+ T cells in immunized mice after 24 h of culture with 10% fetal calf serum complete medium in vitro (P<0.01). These results demonstrated that this immunization may activate T cells in vivo. Furthermore, the splenocytes from immunized mice revealed resistance to activation-induced cell death (AICD) in vitro. To further study the relative genes that are responsible for the higher proliferation and resistance to AICD, the expression of Fas/Fas ligand (FasL) and GADD45b was measured by real-time PCR. The results indicated that GADD45beta transcription was higher in the splenocytes from immunized mice than that in the naive mice. In addition, the Fas expression showed a parallel higher, but FasL did not change obviously. To investigate the biologic functions induced by immunization in vivo, a tumor model was established by EL-4 tumor cell inoculation in C57/Bl mice. Mice receiving autologous T-cell immunization had significantly inhibited tumor growth in vivo (P<0.01). This study implicated that immunization with attenuated activated autologous T cells enhances anti-tumor immune responses that participate in tumor growth inhibition.

Does cytomegalovirus play a causative role in the development of various inflammatory diseases and cancer?

Human cytomegalovirus (HCMV) is a herpes virus that infects and is carried by 70-100% of the world's population. During its evolution, this virus has developed mechanisms that allow it to survive in an immunocompetent host. For many years, HCMV was not considered to be a major human pathogen, as it appeared to cause only rare cases of HCMV inclusion disease in neonates. However, HCMV is poorly adapted for survival in the immunosuppressed host and has emerged as an important human pathogen in AIDS patients and in patients undergoing immunosuppressive therapy following organ or bone marrow transplantation. HCMV-mediated disease in such patients has highlighted the possible role of this virus in the development of other diseases, in particular inflammatory diseases such as vascular diseases, autoimmune diseases and, more recently, with certain forms of cancers. Current research is focused on determining whether HCMV plays a causative role in these diseases or is merely an epiphenomenon of inflammation. Inflammation plays a central role in the pathogenesis of HCMV. This virus has developed a number of mechanisms that enable it to hide from the cells of the immune system and, at the same time, reactivation of a latent infection requires immune activation. Numerous products of the HCMV genome are devoted to control central functions of the innate and adaptive immune responses. By influencing the regulation of various cellular processes including the cell cycle, apoptosis and migration as well as tumour invasiveness and angiogenesis, HCMV may participate in disease development. Thus, the various drugs now available for treatment of HCMV disease (e.g. ganciclovir, acyclovir and foscarnet), may also prove to be useful in the treatment of other, more widespread diseases.