How DNA viruses perturb functional MHC expression to alter immune recognition

Vaccinations for Anal Squamous Cancer: Current and Emerging Therapies

Human papillomavirus (HPV) infection is responsible for 4.3% of the global cancer burden. Since 2006, current HPV vaccines have reduced the prevalence of the virus in adolescent girls, reduced the prevalence of genital warts, and been proven to reduce the progression of anal intraepithelial neoplasia in men. Herein, we review the epidemiology, virology, and immunology behind the prophylactic HPV vaccines and current recommendations for its use. We also review future immune therapies being trialed for use against HPV-related cancers including anal cancer.

T cell receptor variable β gene repertoire in liver and peripheral blood lymphocytes of chronically hepatitis C virus-infected patients with and without mixed cryoglobulinaemia

To characterize the repertoire of T lymphocytes in chronically hepatitis C virus (HCV)-infected patients with and without mixed cryoglobulinaemia (MC). T cell receptor (TCR) variable (V) β clonalities in portal tracts isolated from liver biopsy sections with a laser capture microdissection technique in 30 HCV-positive MC patients were studied by size spectratyping. Complementarity-determining region 3 (CDR3) profiles of liver-infiltrating lymphocytes (LIL) were also compared with those circulating in the blood. The representative results of TCR Vβ by CDR3 were also obtained from liver tissues and peripheral blood lymphocytes (PBL) of 21 chronically HCV-infected patients without MC. LIL were highly restricted, with evidence of TCR Vβ clonotypic expansions in 23 of 30 (77%) and in 15 of 21 (71%) MC and non-MC patients, respectively. The blood compartment contained TCR Vβ expanded clones in 19 (63%) MC and 12 (57%) non-MC patients. The occurrence of LIL clonalities was detected irrespective of the degree of liver damage or circulating viral load, whereas it correlated positively with higher levels of intrahepatic HCV RNA. These results support the notion that TCR Vβ repertoire is clonally expanded in HCV-related MC with features comparable to those found in chronically HCV-infected patients without MC.

Langerhans cells and dendritic cells are cytotoxic towards HPV16 E6 and E7 expressing target cells

Dendritic cells (DC) can be cytotoxic towards tumor cells by means of TNF family molecules expressed on the cell surface of activated DCs. Tumor cells expressing appropriate receptors are killed by DC, generating a source of antigen to be presented to the immune system. It has not been investigated whether Langerhans cells (LC) are selectively cytotoxic to tumor cells. This is of particular interest for epithelial tumor cells that physically interact with LC in vivo. Among epithelial tumors, the oncogenic process of cervical tumors is relatively well defined by their Human Papillomavirus (HPV) mediated etiology. To study whether HPV16 E6 and E7 expressions, otherwise observed in cervical tumor cells, can sensitize normal cervical epithelial cells to DC and LC mediated killing, the E6 and E7 genes were introduced by retroviral transfection, and cells were subsequently used as targets in cytotoxicity assays. Expression of cytotoxic molecules by effector cells was measured in response to the pro-inflammatory cytokine IFN-gamma; cytotoxicity was established and concomitant expression of receptor molecules was assessed on target cells. A correlation between the shrinkage of HPV16 E6 and E7+ tumors versus DC and LC infiltration was evaluated in a murine model of cervical cancer. DC and LC proved to be equally cytotoxic towards E6 and E7 expressing cervical epithelial cells. IFN-gamma induced TRAIL expression by DC and LC, and inhibition of TRAIL partially blocked cytotoxic effects. Expression of TRAIL decoy receptors was reduced following introduction of E6 and E7 into host cells. Shrinkage of HPV16 E6 and E7 expressing tumors correlated with infiltration by S100+ DC and LC, co-localizing with apoptotic mouse tumor cells. In conclusion, DC and LC mediated killing may be exploitable for anti-tumor treatment.

Effective Suppression of Class I Major Histocompatibility Complex Expression by the US11 or ICP47 Genes Can Be Limited by Cell Type or Interferon-γExposure

An impediment encountered in many viral-based gene therapy clinical trials has been the rapid destruction of the transgene by the host's immune response. The processing and presentation of antigens through the class I major histocompatibility complex (MHC) pathway is the initial specific response to viral infection. Disruption of the class I MHC pathway by herpes simplex virus (HSV) or the human cytomegalovirus (HCMV) results in a decrease of the CD8(+) cytotoxic T lymphocyte (CTL) response and prolongs survival of infected cells in the host. Two viral immune suppression genes that interfere with the class I MHC presentation pathway, the HSV type I ICP47 gene and HCMV US11 gene, were cloned and each incorporated into a retroviral vector. HSV ICP47 and HCMV US11 transgenes were expressed in multiple cells lines and compared for their abilities to reduce antigen presentation on the cell surface by class I MHC. Retroviral supernatants were used to transduce human, canine, and rat cell lines. Fluorescence-activated cell sorter (FACS) analysis of US11- and ICP47-transduced cell lines demonstrated substantial reductions in class I MHC cell surface expression in most cell lines except in rodent cells where ICP47 is nonfunctional. The decrease in the level of class I MHC expression for ICP47 transduced cell lines ranged from 31-98% relative to negative controls. US11 decreased class I cell surface MHC by 67-96%. When both ICP47 and US11 are expressed in human cells, a further reduction of class I MHC was observed. Next, human A375 melanoma cells were tested to determine if the resulting reduction in cell surface class I MHC would reduce in vitro cytotoxicity by CTL. A375 cells expressing either ICP47 or US11 demonstrated a twofold to threefold reduction of specific lysis by primed CD8(+) CTL. These data clearly establish an ability to convey immune protection to human cells by viral genes. However, further analysis demonstrated that interferon (IFN)-gamma could reverse part or all of the downregulation of class I MHC induced by the ICP47 or US11 genes. The ICP47 and US11 genes, when expressed in target cells, decrease class I MHC presentation and as such might be used in strategies to create local immunosuppression against transgenes or allografts.

Poxviruses and immune evasion

Large DNA viruses defend against hostile assault executed by the host immune system by producing an array of gene products that systematically sabotage key components of the inflammatory response. Poxviruses target many of the primary mediators of innate immunity including interferons, tumor necrosis factors, interleukins, complement, and chemokines. Poxviruses also manipulate a variety of intracellular signal transduction pathways such as the apoptotic response. Many of the poxvirus genes that disrupt these pathways have been hijacked directly from the host immune system, while others have demonstrated no clear resemblance to any known host genes. Nonetheless, the immunological targets and the diversity of strategies used by poxviruses to disrupt these host pathways have provided important insights into diverse aspects of immunology, virology, and inflammation. Furthermore, because of their anti-inflammatory nature, many of these poxvirus proteins hold promise as potential therapeutic agents for acute or chronic inflammatory conditions.

The E5 protein of human papillomavirus type 16 perturbs MHC class II antigen maturation in human foreskin keratinocytes treated with interferon-gamma

Major histocompatibility complex (MHC) class II antigens are expressed on human foreskin keratinocytes (HFKs) following exposure to interferon gamma. The expression of MHC class II proteins on the cell surface may allow keratinocytes to function as antigen-presenting cells and induce a subsequent immune response to virus infection. Invariant chain (Ii) is a chaperone protein which plays an important role in the maturation of MHC class II molecules. The sequential degradation of Ii within acidic endocytic compartments is a key process required for the successful loading of antigenic peptide onto MHC class II molecules. Since human papillomavirus (HPV) 16 E5 can inhibit the acidification of late endosomes in HFKs, the E5 protein may be able to affect proper peptide loading onto the MHC class II molecule. To test this hypothesis, HFKs were infected with either control virus or a recombinant virus expressing HPV16 E5 and the infected cells were subsequently treated with interferon-gamma. ELISAs revealed a decrease of MHC class II expression on the surface of E5-expressing cells compared with control virus-infected cells after interferon treatment. Western blot analysis showed that, in cells treated with interferon gamma, E5 could prevent the breakdown of Ii and block the formation of peptide-loaded, SDS-stable mature MHC class II dimers, correlating with diminished surface MHC class II expression. These data suggest that HPV16 E5 may be able to decrease immune recognition of infected keratinocytes via disruption of MHC class II protein function.

Identification of genes associated with adenovirus 12 tumorigenesis by microarray

A total of 242 genes were shown to be differentially expressed between haplotypically matched tumorigenic adenovirus 12 (Ad12) and nontumorigenic Ad5-transformed cells using a microarray containing 8734 cDNAs. Eighty-seven of the differentially expressed genes have known roles that include signal transduction, cell growth and proliferation, transcription regulation, protease, and immune functions. The remaining differentially expressed genes are represented by EST cDNAs which have functions that are either completely unknown or proposed, based on sequence similarity to known genes. A subset of 22 differentially expressed genes from the microarray was further examined by Northern blot analyses to verify the identification of new genes associated with Ad12 tumorigenesis. Growth factor receptor binding protein 10 (Grb10) and protease nexin 1 (PN-1) were overexpressed in all of the tumorigenic Ad12-transformed cells examined, whereas expression of these genes was negligible in all of the nontumorigenic Ad5-transformed cells. By contrast, other genes including B cell translocation gene 2 (BTG2) were shown to be significantly up-regulated in Ad5-transformed cells as compared to Ad12-transformed cells.

Myxoma virus leukemia-associated protein is responsible for major histocompatibility complex class I and Fas-CD95 down-regulation and defines scrapins, a new group of surface cellular receptor abductor proteins

Down-modulation of major histocompatibility class I (MHC-I) molecules is a viral strategy for survival in the host. Myxoma virus, a member of the Poxviridae family responsible for rabbit myxomatosis, can down-modulate the expression of MHC-I molecules, but the viral factor(s) has not been described. We cloned and characterized a gene coding for an endoplasmic reticulum (ER)-resident protein containing an atypical zinc finger and two transmembrane domains, which we called myxoma virus leukemia-associated protein (MV-LAP). MV-LAP down-regulated surface MHC-I and Fas-CD95 molecules upon transfection; the mechanism probably involves an exacerbation of endocytosis and was lost when the ER retention signal was removed. In addition, the lytic activity of MHC-I-restricted antigen-specific cytolytic T lymphocytes (CTL) against myxoma virus-infected antigen-presenting target cells was significantly reduced, revealing a strong correlation between MHC-I down-regulation by MV-LAP and CTL killing in vitro. In vivo experiments with a knockout virus showed that MV-LAP is a virulence factor, potentially involved in the immunosuppression characteristic of myxomatosis. Data bank analysis revealed that MV-LAP has homologs in herpesviruses and other poxviruses. We propose the name "scrapins" to define a new group of ER-resident surface cellular receptor abductor proteins. The down-regulation of cell surface molecules by scrapins probably helps protect infected cells during viral infections.

Human papillomavirus infections: epidemiology, pathogenesis, and therapy

BACKGROUND

Human papillomaviruses (HPV) are common human pathogens and are classified into more than 80 different types. These viruses produce benign warts in many cases and aggressive squamous cell carcinomas in other cases.

OBJECTIVE

The goal of this review is to update the reader on the epidemiology, pathogenesis, and therapy of HPV infections. Nonanogenital warts are transmitted by skin-to-skin contact while anogenital warts are usually transmitted sexually. Both types of warts produce much morbidity but rarely undergo malignant transformation. They are commonly treated with surgical or cytodestructive therapy, but immunomodulatory agents, such as imiquimod, have been proven to be very effective in anogenital warts and are being evaluated in nonanogenital warts. Other types of HPV have marked oncogenic potential such that over 99% of all cervical cancers and over 50% of other anogenital cancers are due to infection with oncogenic HPV. Many cofactors, such as cigarette smoking, genetics, and helper viruses, have potential roles in HPV oncogenesis, but their relative contributions are poorly understood. Other control measures for warts and HPV-associated cancers are under study, but the greatest future potential may be from the development of prophylactic and therapeutic vaccines.

CONCLUSIONS

Infection with HPV is very prevalent as are the clinical manifestations of this family of pathogens. Improved therapies for warts (e.g., imiquimod) have recently become available. Vaccines for HPV offer hope for future interventions for warts as well as for prevention of anogenital malignancies.

Human papillomavirus infections: epidemiology, pathogenesis, and host immune response

Human papillomaviruses (HPVs) are ubiquitous and often cause lesions on the skin that come to the attention of the dermatologist. Skin lesions, or warts, often occur on the hands or soles of the feet and can cause embarrassment or discomfort. Genital HPV infections are transmitted by sexual contact. Infections associated with some HPV types have a high risk of progressing to carcinoma. This review discusses the molecular biology and genetics of human papillomaviruses and provides an overview of the virology, pathology, clinical manifestations, and host immune response to infection.

Association of histone deacetylase with COUP-TF in tumorigenic Ad12-transformed cells and its potential role in shut-off of MHC class I transcription

Chicken ovalbumin upstream promoter-transcription factor (COUP-TF) is an orphan nuclear receptor that represses transcription of many genes. In adenovirus type 12 (Ad12) transformed cells, a high level of binding activity of COUP-TF to the major histocompatibility complex (MHC) class I enhancer correlates with the down-regulation of class I transcription, which, in turn, contributes to tumorigenesis. The mechanism by which COUP-TF represses transcription has yet to be elucidated. Here we show that COUP-TF represses transcription through its association with histone deacetylase. This was demonstrated using reciprocal binding assays that determined that the interaction between COUP-TF and histone deacetylase requires the COUP-TF C-terminal repression domain. Moreover, a histone deacetylase enzymatic activity was found to be associated with COUP-TF in Ad12-transformed cells. Transfection experiments further revealed that exogenous histone deacetylase facilitates transcriptional repression by COUP-TF. Also, supershift assays suggest that the transcriptional corepressor N-CoR, which is known to associate with histone deacetylases, is a part of the COUP-TF complex bound to the MHC class I enhancer R2 site. Finally, we provide evidence that inhibition of histone deacetylases relieves the repression of MHC class I expression in Ad12-transformed cells. Taken together these results support the notion that deacetylation of histones, mediated through COUP-TF, serves to down-regulate MHC class I transcription in Ad12-transformed cells.

Evasion and exploitation of chemokines by viruses

Chemokines and chemokine receptors play a critical role in the host defense against viruses by mobilizing leukocytes to sites of infection, injury and inflammation. In order to replicate successfully within their host organisms, viruses have devised novel strategies for exploiting or subverting chemokine networks. This review summarizes various mechanisms that are currently known to be used by viruses for modulating chemokine activities including viral homologs of chemokines and chemokine receptors and soluble viral chemokine binding proteins. Insight into these strategies is providing a wealth of information on viral-host interactions, the function of chemokines in host defense and may help to generate novel anti-chemokine agents for treating against viral diseases or inflammatory disorders.

Endosomal/lysosomal retention and degradation of major histocompatibility complex class I molecules is induced by myxoma virus

The highly immunosuppressive leporipoxvirus myxoma, previously was shown to promote the loss of cell surface class I major histocompatibility complex (MHC I) molecules. Here, we show that myxoma virus induces the loss of both cell surface and intracellular post-Golgi, beta(2)-microglobulin-associated MHC I. Myxoma-induced loss of these MHC I molecules is abrogated by vacuolar ATPase inhibitors, NH(4)Cl, and leupeptin. Furthermore, immunofluorescence microscopic studies reveal that in myxoma-infected cells, beta(2)-microglobulin-associated MHC I accumulates in Lamp-1(+) vesicular structures, suggesting that myxoma virus targets MHC I for degradation in late endosomes and/or lysosomes. These events are regulated by early gene product or products because they occur unabated in cells infected with myxoma virus in the presence of cytosine arabinoside, an inhibitor of DNA synthesis. Studies with baby green monkey kidney cells transfected with wild-type and tail-less forms of a mouse MHC I molecule, H-2L(d), indicate that the MHC I cytoplasmic tail is required for myxoma-induced localization in Lamp-1(+) organelles. Myxoma-induced endocytosis and degradation of MHC I may provide the virus with a means of dispensing with cell surface MHC I molecules that were loaded with peptides derived from viral proteins synthesized early in infection.

A Theiler’s Virus Alternatively Initiated Protein Inhibits the Generation of H-2K-Restricted Virus-Specific Cytotoxicity

In susceptible mouse strains, the wild-type Daniel’s (wt-DA) strain of Theiler’s murine encephalomyelitis virus induces a persistent central nervous system (CNS) infection with chronic demyelination. The virus is cleared from resistant mice with no resulting demyelination. We characterized the role of the DA L* protein in late demyelination and persistent infection. The DA genome has two alternative reading frames, encoding the virus polyprotein and L*, respectively. The mutant virus DAL*-1 fails to synthesize L* and does not persist in the CNS of wt-DA-susceptible SJL/J or B10.S mice. Since class I-restricted cytotoxicity has been shown to determine resistance to virus persistence and demyelination in this model, virus-specific cytotoxicity in the CNS of DA-resistant (B6 or B10) and -susceptible (SJL/J and B10.S) mice during the acute stage of DA and DAL*-1 infection was characterized. Following intracerebral inoculation with DAL*-1, virus-specific Db- and Kb-restricted CTLs were demonstrated in the CNS of resistant B10 mice, whereas only Db-restricted CTL were found in wt-DA-inoculated mice. CTLs specific to wt-DA or DAL*-1 recognized class I-presented peptides from either of the viruses. Of particular interest, Ks-restricted virus-specific cytotoxicity-restricted CTLs were identified in the CNS of susceptible SJL/J (H-2s) and B10.S (H-2s) mice inoculated with DAL*-1. In contrast, no virus-specific CTLs were identified in the CNS of SJL/J and B10.S mice inoculated with wt-DA. We propose that L* inhibits the generation of H-2K-restricted virus-specific cytotoxicity in the CNS, permitting a persistent infection in susceptible strains, with subsequent inflammatory demyelination in the CNS similar to that in human multiple sclerosis.

Hepatitis C Virus Infection Involves CD34+Hematopoietic Progenitor Cells in Hepatitis C Virus Chronic Carriers

Although hepatitis C virus (HCV) mainly affects hepatocytes, infection is widespread and involves immunologically privileged sites. Whether lymphoid cells represent further targets of early HCV infection, or whether other cells in the hematopoietic microenvironment may serve as a potential virus reservoir, is still unclear. We studied whether pluripotent hematopoietic CD34+ cells support productive HCV infection and can be used to establish an in vitro infection system for HCV. Six patients were selected as part of a cohort of HCV chronic carriers who developed a neoplastic disease. Reverse transcriptase-polymerase chain reaction (RT-PCR) and branched DNA signal amplification assays were used to detect and quantitate HCV RNA in extracted nucleic acids from purified bone marrow and peripheral blood CD34+ cells. Direct in situ RT-PCR, flow cytometry analysis, and immunocytochemistry were applied to demonstrate specific viral genomic sequences and structural and nonstructural virus-related proteins in intact cells. Results indicated that both positive and negative HCV RNA strands and viral proteins were present in CD34+ cells from all HCV-positive patients and in none of the controls. Additional experiments showed that a complete viral cycle took place in CD34+ cells in vitro. Spontaneous increases in viral titers indicated that virions were produced by infected hematopoietic progenitor cells. To further define the cellular tropism, we attempted to infect CD34+ cells in vitro. We were unable to demonstrate viral uptake by cells. These findings suggest that HCV replication can occur in the early differentiation stages of hematopoietic progenitor cells, and that they may be an important source of virus production.

© 1998 by The American Society of Hematology.

Hepatitis C Virus Infection Involves CD34+Hematopoietic Progenitor Cells in Hepatitis C Virus Chronic Carriers

Although hepatitis C virus (HCV) mainly affects hepatocytes, infection is widespread and involves immunologically privileged sites. Whether lymphoid cells represent further targets of early HCV infection, or whether other cells in the hematopoietic microenvironment may serve as a potential virus reservoir, is still unclear. We studied whether pluripotent hematopoietic CD34+ cells support productive HCV infection and can be used to establish an in vitro infection system for HCV. Six patients were selected as part of a cohort of HCV chronic carriers who developed a neoplastic disease. Reverse transcriptase-polymerase chain reaction (RT-PCR) and branched DNA signal amplification assays were used to detect and quantitate HCV RNA in extracted nucleic acids from purified bone marrow and peripheral blood CD34+ cells. Direct in situ RT-PCR, flow cytometry analysis, and immunocytochemistry were applied to demonstrate specific viral genomic sequences and structural and nonstructural virus-related proteins in intact cells. Results indicated that both positive and negative HCV RNA strands and viral proteins were present in CD34+ cells from all HCV-positive patients and in none of the controls. Additional experiments showed that a complete viral cycle took place in CD34+ cells in vitro. Spontaneous increases in viral titers indicated that virions were produced by infected hematopoietic progenitor cells. To further define the cellular tropism, we attempted to infect CD34+ cells in vitro. We were unable to demonstrate viral uptake by cells. These findings suggest that HCV replication can occur in the early differentiation stages of hematopoietic progenitor cells, and that they may be an important source of virus production.

© 1998 by The American Society of Hematology.

Functional comparisons among members of the poxvirus T1/35kDa family of soluble CC-chemokine inhibitor glycoproteins

Many poxviruses express a 35-40-kDa secreted protein, termed "T1" (for leporipoxviruses) or "35kDa" (for orthopoxviruses), that binds CC-chemokines with high affinity but is unrelated to any known cellular proteins. Many previously identified poxvirus cytokine-binding proteins display strict species ligand-binding specificity. Because the T1 and 35kDa proteins share only 40% amino acid identity, we compared the abilities of purified myxoma virus-T1 (M-T1) and vaccinia virus (strain Lister)- and rabbitpox virus-35kDa proteins to inhibit human CC-chemokines in vitro. All three proteins were equally effective in preventing several human CC-chemokines from binding to target chemokine receptors and blocking subsequent intracellular calcium release. The inhibitory affinities were comparable (Ki = 0.07-1.02 nM). These proteins also displayed similar abilities to inhibit (IC50 = 6.3-10.5 nM) human macrophage inflammatory protein-1alpha-mediated chemotaxis of human monocytes. None of the viral proteins blocked interleukin-8-mediated calcium flux or chemotaxis of human neutrophils, confirming that the biological specificity of the T1/35kDa family is targeted inhibition of CC-chemokines. Despite the significant sequence divergence between the leporipoxvirus T1 and orthopoxvirus 35kDa proteins, our data suggest that their CC-chemokine binding and inhibitory properties appear to be species nonspecific and that the critical motifs most likely reside within the limited regions of conservation.

Tissue specific HPV expression and downregulation of local immune responses in condylomas from HIV seropositive individuals

OBJECTIVE

To study the effect of tissue specific human papillomavirus (HPV) expression and its effect on local immunity in condylomas from HIV positive individuals.

METHODS

Biopsy specimens of eight penile and eight perianal condylomas from HIV seropositive individuals were analysed. Expression of viral genes (HIV-tat and HPV E7 and L1) was determined by RT-PCR. The status of local immunity also was determined by RT-PCR by measuring CD4, CD8, CD16, CD1a, HLA-DR, and HLA-B7 mRNA levels in the tissues. Differentiation was determined by measuring involucrin, keratinocyte transglutaminase, as well as cytokeratins 10, 16, and 17. Proliferation markers such as PCNA and c-myc were also determined.

RESULTS

The transcription pattern of HPV in perianal condylomas, which preferentially expressed the early (E7) gene, was different from that of penile condylomas, which primarily expressed the late (L1) gene. This transcription pattern is in good correlation with the keratinisation and differentiation patterns of the two epithelia: perianal biopsies preferentially expressed K16 and K17 while penile warts mainly expressed K10, markers of parakeratotic and orthokeratotic epithelia, respectively. Perianal biopsies also showed a higher degree of proliferation (PCNA and c-myc). Interestingly, transcription of HIV-tat was also higher in perianal than in penile biopsies. A high degree of local immunodeficiency was observed in perianal biopsies--that is, levels of CD4, CD16, and CD1a mRNAs were significantly lower. A negative correlation between CD1a (Langerhans cells) levels and HPV E7 levels was established. HPV E7 levels positively correlated with HIV-tat levels. Perianal tissues demonstrated more CD1a depression and tat associated HPV upregulation.

CONCLUSION

HIV influences the expression of HPV genes resulting in local immunosuppression that might lead to an inappropriate immune surveillance of viral infection. Also, tissue type is an important factor in controlling viral transcription in a differentiation dependent manner. These findings may explain the higher rate of dysplasia and neoplasia in the perianal area.

Effects of retinoic acid combined with irradiation on the expression of major histocompatibility complex molecules and adhesion/costimulation molecules ICAM-1 in human cervical cancer

OBJECTIVES

Radiation treatment is one of the most standardized and effective modalities for contemporary cervical cancer therapy. In addition, the radiation-potentiating effects of retinoic acid have been recently described. In order to investigate whether enhanced immunogenicity might be responsible for such potentiation, we have evaluated the effects of retinoic acid combined with high doses of gamma-irradiation on the expression of major histocompatibility complex (MHC) Class I and II and intercellular adhesion molecule-1 (ICAM-1) in human cervical carcinoma cell lines.

METHODS

The expression of surface antigens (MHC Class I and II and ICAM-1) was evaluated by FACS analysis in untreated control cells and in cells following their exposure to retinoic acid, high doses of gamma-irradiation (i.e., 5000 and 10,000 cGy), or the combination of the two procedures.

RESULTS

HT-3 and SiHa cervical cancer cells expressed variable levels of MHC Class I and ICAM-1 antigens while Class II surface antigens were not detectable. Exposure to either 5000 or 10,000 cGy completely inhibited cell replication in both cell lines and significantly and consistently increased the expression of all surface antigens present on the cells prior to irradiation. Irradiation was unable to induce neoexpression of antigens previously not expressed by these cells (i.e., MHC Class II). In a similar fashion, retinoic acid was also able to significantly increase the expression of MHC Class I and ICAM-1 antigens when compared to untreated tumor cells but was not able to induce the expression of HLA Class II surface antigens. Exposure to the combination of radiation plus retinoic acid significantly upregulated HLA Class I and ICAM-1 molecules in an additive manner when compared to the levels obtainable with the exposure to radiation or retinoic acid alone.

CONCLUSIONS

These data indicate that the combination of these two treatments could induce an additive effect on the expression of immunologically important surface antigens in human cervical cancer cells. These findings, together with the powerful antiproliferative effect of retinoids and irradiation on tumor cells, suggest that the combined regimen may be a promising and more effective combination for the treatment of cervical cancer.

Adenovirus-Mediated Human Immunodeficiency Virus-1 Nef Expression in Human Monocytes/Macrophages and Effect of Nef on Downmodulation of Fcγ Receptors and Expression of Monokines

To characterize the effect of human immunodeficiency virus-1 (HIV-1)nef expression in human monocytes/macrophage (HMØ) and U937 on the levels of FcγRs, HLA antigens, and monokines, elutriated HMØs and U937 cells were transfected with an adenovirus-mediated Nef expression system. Nef-expressing cells downmodulated FcγRI, FcγRII, and upregulated HLA class I molecules. Nef-expressing HMØs, treated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA), overexpressed tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-10. However, IL-6 was induced by LPS and inhibited by PMA. Additionally, a subpopulation of Nef-expressing HMØs underwent apoptosis. Our data suggest that HIV-1 nefdownmodulated FcγRs in myeloid cells in a manner similar to that previously reported for its effect on CD4+ in T cells.

Adenovirus-Mediated Human Immunodeficiency Virus-1 Nef Expression in Human Monocytes/Macrophages and Effect of Nef on Downmodulation of Fcγ Receptors and Expression of Monokines

To characterize the effect of human immunodeficiency virus-1 (HIV-1)nef expression in human monocytes/macrophage (HMØ) and U937 on the levels of FcγRs, HLA antigens, and monokines, elutriated HMØs and U937 cells were transfected with an adenovirus-mediated Nef expression system. Nef-expressing cells downmodulated FcγRI, FcγRII, and upregulated HLA class I molecules. Nef-expressing HMØs, treated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA), overexpressed tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-10. However, IL-6 was induced by LPS and inhibited by PMA. Additionally, a subpopulation of Nef-expressing HMØs underwent apoptosis. Our data suggest that HIV-1 nefdownmodulated FcγRs in myeloid cells in a manner similar to that previously reported for its effect on CD4+ in T cells.

Virus attenuation after deletion of the cytomegalovirus Fc receptor gene is not due to antibody control

The murine cytomegalovirus (MCMV) fcr-1 gene codes for a glycoprotein located at the surface of infected cells which strongly binds the Fc fragment of murine immunoglobulin G. To determine the biological significance of the fcr-1 gene during viral infection, we constructed MCMV fcr-1 deletion mutants and revertants. The fcr-1 gene was disrupted by insertion of the Escherichia coli lacZ gene. In another mutant, the marker gene was also deleted, by recombinase cre. As expected for its hypothetical role in immunoevasion, the infection of mice with fcr-1 deletion mutants resulted in significantly restricted replication in comparison with wild-type MCMV and revertant virus. In mutant mice lacking antibodies, however, the fcr-1 deletion mutants also replicated poorly. This demonstrated that the cell surface-expressed viral glycoprotein with FcR activity strongly modulates the virus-host interaction but that this biological function is not caused by the immunoglobulin binding property.

Effects of retinoic acid combined with interferon-gamma on the expression of major-histocompatibility-complex molecules and intercellular adhesion molecule-1 in human cervical cancer

Retinoids and interferons are important regulators of human epithelial cell differentiation and have been successfully used in the clinical treatment of HPV-involved cervical cancer. In this study, 2 HPV-positive human cervical-carcinoma cell lines were analyzed for their surface expression of MHC-Class-I, MHC-Class-II and ICAM-1 surface antigens before and after exposure to all-trans retinoic acid, interferon-gamma and the combination of the 2 compounds. In addition, the effects on HLA-Class-I-mRNA expression were evaluated after such treatments. Both cell lines expressed MHC-Class-I molecules, and their levels were markedly up-regulated after exposure to IFN-gamma. Similarly, MHC-Class-II and ICAM-1 antigens were either induced or significantly up-regulated by IFN-gamma. Exposure to all-trans retinoic acid was also able to significantly increase the expression of MHC-Class-I and ICAM-I antigens as compared with untreated tumor cells. However, unlike IFN-gamma, retinoids were not able to induce the expression of HLA-Class-II surface antigens. Exposure to the combination of IFN-gamma plus retinoic acid significantly up-regulated (in an additive manner) HLA-Class-I and ICAM-1 molecules as compared with the levels obtainable after exposure to IFN-gamma alone. Finally, Northern-blot analysis of HLA-Class-I-mRNA expression confirmed that the activity of both of these biologic response modifiers was at transcriptional level. These data indicate that the combination of these modalities could induce an additive effect on the expression of immunologically important surface antigens on human cervical-cancer cells. These findings, together with the known anti-proliferative effects mediated by retinoids and IFN-gamma on tumor cells, further support the combination of these agents in the treatment of pre-invasive and invasive human cervical cancer.

Effects of irradiation on the expression of major histocompatibility complex class I antigen and adhesion costimulation molecules ICAM-1 in human cervical cancer

PURPOSE

We initiated studies to analyze the effects of high doses of gamma irradiation on the surface antigen expression of MHC Class I, Class II, and ICAM-1 on human cervical carcinoma cell lines.

METHODS AND MATERIALS

The expression of surface antigens (MHC Class I, Class II, and ICAM-1) was evaluated by FACS analysis on two cervical cell lines at different time points, following their exposure to high doses of gamma irradiation (i.e., 25.00, 50.00, and 100.00 Gy).

RESULTS

The CaSki and SiHa cervical cancer cells we analyzed in this study expressed variable levels of MHC Class I and ICAM-1 antigens, while Class II surface antigens were not detectable. Whereas irradiation doses of 25.00 Gy were not sufficient to totally block cell replication in both cell lines, exposure to 50.00 or 100.00 Gy was able to completely inhibit cell replication. Range doses from 25.00 to 100.00 Gy significantly and consistently increased the expression of all surface antigens present on the cells prior to irradiation but were unable to induce neoexpression of antigens previously not expressed by these cells (i.e., MHC Class II). Importantly, such upregulation was shown to be dose dependent, with higher radiation doses associated with increased antigen expression. Moreover, when the kinetic of this upregulation was studied after 2 and 6 days after irradiation, it was shown to be persistent and lasted until all the cells died.

CONCLUSIONS

These findings may partially explain the increased immunogenicity of tumor cells following irradiation and may suggest enhanced immune recognition in tumor tissue in patients receiving radiation therapy.

Trypanosoma cruzi infection does not impair major histocompatibility complex class I presentation of antigen to cytotoxic T lymphocytes

Trypanosoma cruzi (T. cruzi), the etiological agent of Chagas' disease, lives free within the cytoplasm of infected host cells. This intracellular niche suggests that parasite antigens may be processed and presented on major histocompatibility complex (MHC) class I molecules for recognition by CD8+ T cells. However, the parasite persists indefinitely in the mammalian host, indicating its success at evading immune clearance. It has been shown that T. cruzi interferes with processing and presentation of antigenic peptides in the MHC class II pathway. This investigation sought to determine whether interference in MHC class I processing and presentation occurs with T. cruzi infection. Surface expression of MHC class I molecules was found to be unaffected or up-regulated by T. cruzi infection in vitro. A model system employing a beta-galactosidase (beta-gal)-specific murine cytotoxic T lymphocyte (CTL) line (0805B) showed: (i) in vitro infection of mouse peritoneal macrophages or J774 cells with T. cruzi did not inhibit MHC class I presentation of exogenous peptide (a nine-amino acid epitope of beta-gal) to the CTL line, (ii) in vitro infection of a beta-gal-expressing 3T3 cell line (LZEJ) with T. cruzi did not inhibit MHC class I presentation of the endogenous protein to the CTL line and (iii) mouse renal adenocarcinoma cells infected with T. cruzi and subsequently infected with adenovirus expressing beta-gal were able to present antigen to the beta-gal-specific CTL line. These findings indicate that the failure of the immune response to clear T. cruzi does not result from global interference by the parasite with MHC class I processing and presentation. Parasites engineered to express beta-gal were unable to sensitize infected antigen-presenting cells in vitro to lysis by the CTL 0805B line. This was probably due to the intracellular localization of the beta-gal within the parasite and its inaccessibility to the host cell cytoplasm.

The purified myxoma virus gamma interferon receptor homolog M-T7 interacts with the heparin-binding domains of chemokines

The myxoma virus T7 protein M-T7 is a functional soluble gamma interferon receptor homolog that has previously been shown to bind gamma interferon and inhibit its antiviral activities in a species-specific manner, but gene knockout analysis has suggested a further role for M-T7 in blocking leukocyte influx into infected lesions. We purified M-T7 to apparent homogeneity and showed that M-T7 is an N-linked glycoprotein that appears to be a stable homotrimer with a molecular mass of approximately 113 kDa in solution. M-T7, in addition to forming inhibitory complexes with rabbit gamma interferon, was also shown to bind to human interleukin-8, a prototypic member of the chemokine superfamily. Moreover, M-T7 was able to interact promiscuously with all members of the CXC, CC, and C chemokine subfamilies tested. Binding of human RANTES to M-T7 can be competed by rabbit gamma interferon and also by cold RANTES competitor with a 50% inhibitory concentration of 900 nM. Although M-T7 retains binding to a number of interleukin-8 N-terminal (ELR) deletion mutants, binding to mutants containing deletions in the C-terminal heparin-binding domain of interleukin-8 is abrogated. Furthermore, heparin effectively competes the interaction of M-T7 with the chemokine RANTES but not with rabbit gamma interferon. We propose that this novel M-T7 interaction with members of the chemokine superfamily may be facilitated through the conserved heparin-binding domains found in a wide spectrum of chemokines and that M-T7 may function by modulating chemokine-glycosaminoglycan interactions in virus-infected tissues.

The human immunodeficiency virus type 1 (HIV-1) Vpu protein interferes with an early step in the biosynthesis of major histocompatibility complex (MHC) class I molecules

The human immunodeficiency virus type 1 (HIV-1) vpu gene encodes a small integral membrane phosphoprotein with two established functions: degradation of the viral coreceptor CD4 in the endoplasmic reticulum (ER) and augmentation of virus particle release from the plasma membrane of HIV-1-infected cells. We show here that Vpu is also largely responsible for the previously observed decrease in the expression of major histocompatibility complex (MHC) class I molecules on the surface of HIV-1-infected cells. Cells infected with HIV-1 isolates that fail to express Vpu, or that express genetically modified forms of Vpu that no longer induce CD4 degradation, exhibit little downregulation of MHC class I molecules. The effect of Vpu on class I biogenesis was analyzed in more detail using a Vpu-expressing recombinant vaccinia virus (VV). VV-expressed Vpu induces the rapid loss of newly synthesized endogenous or VV-expressed class I heavy chains in the ER, detectable either biochemically or by reduced cell surface expression. This effect is of similar rapidity and magnitude as the VV-expressed Vpu-induced degradation of CD4. Vpu had no discernible effects on cell surface expression of VV-expressed mouse CD54, demonstrating the selectivity of its effects on CD4 and class I heavy chains. VV-expressed Vpu does not detectably affect class I molecules that have been exported from the ER. The detrimental effects of Vpu on class I molecules could be distinguished from those caused by VV-expressed herpes virus protein ICP47, which acts by decreasing the supply of cytosolic peptides to class I molecules, indicating that Vpu functions in a distinct manner from ICP47. Based on these findings, we propose that Vpu-induced downregulation of class I molecules may be an important factor in the evolutionary selection of the HIV-1-specific vpu gene by contributing to the inability of CD8+ T cells to eradicate HIV-1 from infected individuals.

Human cytomegalovirus US2 destabilizes major histocompatibility complex class I heavy chains

Human cytomegalovirus (HCMV) infection causes down-regulation of major histocompatibility complex class I heavy chains. We determined previously that there are two HCMV loci which encode functions responsible for that phenotype and that US11 is one of these loci (T. R. Jones, L. A. Hanson, L. Sun, J. S. Slater, R. M. Stenberg, and A. E. Campbell, J. Virol. 69:4830-4841, 1995). Through the construction and analysis of defined viral mutants and stably transfected cell lines, we identify US2 as the other locus. US2 is expressed from very early through late times postinfection, with its predominant product being a relatively unstable 24-kDa endoglycosidase H-resistant glycoprotein. In cell lines constitutively expressing US2, free class I heavy chains are proximal targets for US2-induced degradation, shortly after their synthesis. Both US2 and US11 can function in concert with US3 to down-regulate class I. Beta-2-microglobulin-associated heavy chains which are retained in the endoplasmic reticulum as a result of binding to the US3 glycoprotein are susceptible to destabilization caused by both US2 and US11 gene products. Thus, three HCMV genes which affect either the stability or the transport of class I heavy chains have been identified. The observation that each of these proteins is most abundant early in the replicative cycle suggests that they may play an important immunomodulatory role in vivo prior to productive infection, either during the latent or persistent phase or during reactivation.

Down-regulation of MHC class I synthesis by murine cytomegalovirus occurs in immortalized but not primary fibroblasts

Murine cytomegalovirus downregulates expression of MHC class I molecules required for recognition of virus-specific CD8+ CTL, effector cells which mediate clearance of virus from the host. We previously identified two mechanisms of MHC class I downregulation in MCMV-infected immortalized fibroblasts: a defect in transport of the class I molecules from the endoplasmic reticulum to the cell surface, and a significant inhibition in class I heavy chain synthesis. We now report that these two mechanisms are independently regulated at early times post MCMV infection. The defect in MHC class I transport, evident at 4 hr postinfection, precedes the defect in synthesis at 6-8 hr postinfection. Levels of MHC class I heavy chain mRNA decline between 4-12 hr postinfection. Levels of mRNA for some cellular genes also declined at approximately the same rate in MCMV-infected but not mock-infected cells. The defect in MHC class I synthesis and transport was evident in several fibroblast cell lines immortalized by a variety of agents. However, only the defect in transport of MHC class I heavy chain was seen in primary fibroblast cells. In primary cells, synthesis of heavy chain molecules was unaffected by MCMV infection. Thus, MCMV infection alters expression of host cell proteins at multiple levels in a cell-specific manner, perhaps dependent upon the state of differentiation or transcriptional activity of the cell.

Identification of a cis-acting element in the class I major histocompatibility complex gene promoter responsive to activation by retroviral sequences

The infection of cells with Moloney murine leukemia virus (M-MuLV) causes an increase in specific cellular gene products, including the major histocompatibility complex (MHC) class I antigens. This upregulation occurs through a transactivation process mediated by the long terminal repeat (LTR) of M-MuLV, and we show here that the gene activation response to the LTR requires at least one specific cis element within the MHC proximal promoter region. Nested deletions of MHC class I H-2Kb gene promoter sequence were subcloned into a chloramphenicol acetyltransferase (CAT) reporter vector and then transiently introduced into BALB/c-3T3 cells expressing M-MuLV or cotransfected into BALB/c-3T3 cells with a vector containing subgenomic portions of the virus, including the LTR. CAT activity assays demonstrated that a minimal H-2Kb gene promoter (-64 to +12) contained elements sufficient for this transactivation. DNase I footprinting assays located a protein-binding site in the region of -64 to -34 bp from the transcriptional start site, and point mutation analysis confirmed the location of this cis-acting element, designated the let response element (LRE), and defined a binding motif. This LRE is distinct from binding sites for currently known transcription factors in the class I MHC gene promoter and is conserved in the promoters of human and murine MHC class I genes. Mutation of the LRE resulted in dramatic reduction in both DNA-protein binding activity in electrophoretic mobility shift assay and in the ability of the mutated promoter to respond to retroviral transactivation. Addition of the LRE to a heterologous promoter conferred the ability to respond to retroviral transactivation.

Status of local cellular immunity in interferon-responsive and -nonresponsive human papillomavirus-associated lesions

BACKGROUND AND OBJECTIVES

Anogenital warts are caused by human papillomaviruses (HPVs), which should induce cellular immune responses in immunocompetent patients. However, the natural history of these warts shows considerable variation between persons, ranging from spontaneous regression to prolonged persistence. In addition, the efficiency of immunologically based modalities for the therapy of anogenital warts, such as interferon (IFN) treatment, is highly variable.

METHODS

Considering that preexisting conditions of the host are important factors in an appropriate immune response, the authors determined the pretreatment status of local cell-mediated immune response to HPV infection by reverse transcription-polymerase chain reaction in patients with condyloma acuminatum, who later received IFN treatment and responded well or poorly to that therapy.

RESULTS AND CONCLUSIONS

The authors found that biopsies from nonresponders were depleted markedly in Langerhans cells, leading to decreases in major histocompatibility complex class II expression and, therefore, to diminished attraction of CD4+ T cells. An inappropriate major histocompatibility complex class I expression also was observed in those nonresponders with decreased CD8+ levels. The mRNA levels of cytokines (interleukin-1a, interleukin-1b, granulocyte-macrophage-colony stimulating factor, tumor necrosis factor that participate in immune responses were low in nonresponders. In contrast, responders demonstrated high macrophage-natural killer cell (CD16-positive) and activated CD4 (IL-2, interferon gamma-positive, TH1 cells) T-cell recruitment against HPV-infected keratinocytes, which is consistent with a delayed-type hypersensitivity-like cellular immune response. Lack of immune response in nonresponders appeared to correlate with high expression levels of the HPV E7 gene. These differences in local cellular immunity might determine the response rate of HPV-infected cells to immunomodulatory therapies.

Human cytomegalovirus US3 impairs transport and maturation of major histocompatibility complex class I heavy chains

The human cytomegalovirus (HCMV) early glycoprotein products of the US11 and US2 open reading frames cause increased turnover of major histocompatibility complex (MHC) class I heavy chains. Since US2 is homologous to another HCMV gene (US3), we hypothesized that the US3 gene product also may affect MHC class I expression. In cells constitutively expressing the HCMV US3 gene, MHC class I heavy chains formed a stable complex with beta 2-microglobulin. However, maturation of the N-linked glycan of MHC class I heavy chains was impaired in US3+ cells. The glycoprotein product of US3 (gpUS3) occurs mostly in a high-mannose form and coimmunoprecipitates with beta 2-microglobulin associated class I heavy chains. Mature class I molecules were detected at steady state on the surface of US3+ cells, as in control cells. Substantial perinuclear accumulation of heavy chains was observed in US3+ cells. The data suggest that gpUS3 impairs egress of MHC class I heavy chains from the endoplasmic reticulum.

Molecular mechanisms of class I major histocompatibility complex antigen processing and presentation

The presentation of antigenic peptides by class I major histocompatibility complex molecules plays a central role in the cellular immune response, since immune surveillance for detection of viral infections or malignant transformations is achieved by CD8+ T lymphocytes which inspect peptides, derived from intracellular proteins, bind to class I molecules on the surface of most cells. The transporter associated with antigen processing selectively translocates cytoplasmically derived peptides of appropriate sequence and length into the lumen of the endoplasmic reticulum where they associate with newly synthesized class I molecules. The translocated peptides are generated by multicatalytic and multisubunit proteasomes which degrade cytoplasmic proteins in a ATP-ubiquitin-dependent manner. This review discusses our current molecular understanding of class I antigen processing and presentation.

The extracellular domain of the Epstein-Barr virus BZLF2 protein binds the HLA-DR beta chain and inhibits antigen presentation

The Epstein-Barr virus BZLF2 gene encodes a glycoprotein that associates with gH and gL and facilitates the infection of B lymphocytes. In order to determine whether the BZLF2 protein recognizes a B-cell-specific surface antigen, a soluble protein containing the extracellular portion of the BZLF2 protein linked to the Fc portion of human immunoglobulin G1 (BZLF2.Fc) was expressed from mammalian cells. BZLF2.Fc was used in an expression cloning system and found to bind to a beta-chain allele of the HLA-DR locus of the class II major histocompatibility complex (MHC). Analysis of amino- and carboxy-terminal deletion mutants of the BZLF2.Fc protein indicated that the first 90 amino acids of BZLF2.Fc are not required for HLA-DR beta-chain recognition. Site-directed mutagenesis of an HLA-DR beta-chain cDNA and subsequent immunoprecipitation of expressed mutant beta-chain proteins using BZLF2.Fc indicated that the beta1 domain, which participates in the formation of peptide binding pockets, is required for BZLF2.Fc recognition. The addition of BZLF2.Fc to sensitized peripheral blood mononuclear cells in vitro abolished their proliferative response to antigen and inhibited cytokine-dependent cytotoxic T-cell generation in mixed lymphocyte cultures. Flow-cytometric analysis of Akata cells induced to express late Epstein-Barr virus antigens indicated that expression of BZLF2 did not result in reduced surface expression levels of MHC class II. The ability of BZLF2.Fc to bind to the HLA-DR beta chain suggests that the BZLF2 protein may interact with MHC class II on the surfaces of B cells.

Disruption of M-T5, a novel myxoma virus gene member of poxvirus host range superfamily, results in dramatic attenuation of myxomatosis in infected European rabbits

Myxoma virus is a pathogenic poxvirus that induces a lethal myxomatosis disease profile in European rabbits, which is characterized by fulminating lesions at the primary site of inoculation, rapid dissemination to secondary internal organs and peripheral external sites, and supervening gram-negative bacterial infection. Here we describe the role of a novel myxoma virus protein encoded by the M-T5 open reading frame during pathogenesis. The myxoma virus M-T5 protein possesses no significant sequence homology to nonviral proteins but is a member of a larger poxviral superfamily designated host range proteins. An M-T5- mutant virus was constructed by disruption of both copies of the M-T5 gene followed by insertion of the selectable marker p7.5Ecogpt. Although the M-T5- deletion mutant replicated with wild-type kinetics in rabbit fibroblasts, infection of a rabbit CD4+ T-cell line (RL5) with the myxoma virus M-T5- mutant virus resulted in the rapid and complete cessation of both host and viral protein synthesis, accompanied by the manifestation of all the classical features of programmed cell death. Infection of primary rabbit peripheral mononuclear cells with the myxoma virus M-T5-mutant virus resulted in the apoptotic death of nonadherent lymphocytes but not adherent monocytes. Within the European rabbit, disruption of the M-T5 open reading frame caused a dramatic attenuation of the rapidly lethal myxomatosis infection, and none of the infected rabbits displayed any of the characteristic features of myxomatosis. The two most significant histological observations in rabbits infected with the M-T5-mutant virus were (i) the lack of progression of the infection past the primary site of inoculation, coupled with the establishment of a rapid and effective inflammatory reaction, and (ii) the inability of the virus to initiate a cellular reaction within secondary immune organs. We conclude that M-T5 functions as a critical virulence factor by allowing productive infection of immune cells such as peripheral lymphocytes, thus facilitating virus dissemination to secondary tissue sites via the lymphatic channels.

Activation of local cell-mediated immunity in interferon-responsive patients with human papillomavirus-associated lesions

Successful immune response to viral infection, such as human papillomavirus (HPV) infection, involves presentation of viral antigens to the immune system, recruitment of T cells and macrophages, and activation of a diverse array of cytokines. Interferons (IFN) are known to exert immunomodulatory functions via activating these pathways. However, the presence of HPV can interact with this process. We employed a reverse transcription-polymerase chain reaction (RT-PCR)-based method to study this phenomenon in biopsies of patients responding well or poorly to IFN treatment. We found that responders show a delayed-type hypersensitivity (DTH) reaction after IFN treatment, in which TH1 cells (interleukin-2, IL-2, IFN-gamma) and macrophages/NK cells (CD16) predominate. Antigen presentation capability (e.g., upregulation of MHC molecules, cytokines) is also enhanced after IFN treatment in responders. The lack of upregulation of MHC molecules (HLA-DR, beta 2-microglobulin) and certain cytokines (IL-1 alpha, IL-2, IFN-gamma) in nonresponders may be due to the overexpression of HPV early (E7) gene in contrast to responders, where HPV late (L1) gene expression predominates. We concluded that differential HPV expression in infected cells can be responsible for an inappropriate IFN-mediated immune response.

Transcriptional regulation of the MHC class I HLA-A11 promoter by the zinc finger protein ZFX

Regulation of the human MHC class I HLA-A11 promoter is governed by a complex array of regulatory elements. One of these elements, shown here to be critical for the transcriptional activity of the promoter, was used to screen a lambda gt11 library and allowed the identification of a cDNA which coded for the zinc finger protein ZFX. ZFX was shown to bind the sequences AGGGCCCCA and AGGCCCCGA, located respectively at positions -271 to -263 and -242 to -234 of the HLA-A11 promoter, with similar affinities through its three C-terminal zinc fingers. ZFX575, a short isoform of ZFX, activates transcription from the HLA-All promoter in a Leydig cell line.

A recombinant adenovirus expressing an Epstein-Barr virus (EBV) target antigen can selectively reactivate rare components of EBV cytotoxic T-lymphocyte memory in vitro

While the bulk of a virus-induced cytotoxic T-lymphocyte (CTL) response may focus on a few immunodominant viral antigens, in certain tumor virus systems the detectability of clones recognizing other, subdominant antigens can assume particular importance. By using the human CTL response to Epstein-Barr virus (EBV) as a model system, here we show that even rare components of virus-specific memory can be selectively reactivated in vitro when the relevant target antigen is expressed in autologous stimulator cells from a recombinant adenovirus (RAd) vector. We generated a replication-deficient adenovirus, RAd-E3C, which in skin fibroblast cultures expressed the EBV nuclear antigen EBNA3C at a 10- to 100-fold-higher level than that naturally present in EBV-transformed lymphoblastoid cell lines (LCLs). Initial experiments with a donor whose polyclonal CTL response to LCL stimulation contained a strong EBNA3C-specific component showed that these CTLs could be efficiently reactivated by in vitro stimulation either with RAd-E3C-infected fibroblasts or with RAd-E3C-infected peripheral blood mononuclear cells. Then we studied donors whose responses to LCL stimulation contained little if any detectable EBNA3C reactivity but were dominated by clones recognizing other EBV target antigens; in vitro stimulation with RAd-E3C-infected peripheral blood mononuclear cells selectively reactivated EBNA3C-specific CTL clones from these individuals, with the epitope specificities of responses subsequently identified at the peptide level. This RAd-based approach could be applied more generally to screen for human CTL responses against any candidate target antigen expressed by tumor cells.

One step ahead of the game: viral immunomodulatory molecules

For decades cell biologists have relied on viruses to facilitate the study of complex cellular function. More recently, the tragedy of the AIDS epidemic has focused considerable human and financial resources on both virology and immunology, resulting in the generation of new information relating these disciplines. As the miracle of the mammalian immune system unfolds in the laboratory, the elegance of the mechanisms used by co-evolving viruses to circumvent detection and destruction by the host becomes inescapably obvious. Although many observation of virus-induced phenomena that likely contribute to the virus's escape of immune surveillance are still empirical, many other such phenomena have now been defined at the molecular level and confirmed in in vivo models. Immune modulators encoded within viral genomes include proteins that regulate antigen presentation, function as cytokines or cytokine antagonists, inhibit apoptosis, and interrupt the complement cascade. The identification of such gene products and the elucidation of their function have substantially strengthened our understanding of specific virus-host interactions and, unexpectedly, have contributed to the recognition of potent synergy between viruses, which can result in an unpredictable exacerbation of disease in co-infected individuals. Because many viral immune modulators clearly have host counterparts, viruses provide a valuable method for studying normal immune mechanisms. It is conceivable that an improved understanding of virus-encoded immunomodulators will enhance our ability to design reagents for use in therapeutic intervention in disease and in vaccine development.

Cytokines and viral anti-immune genes

Cytokines, the pleomorphic and pleiotropic director proteins of an increasingly defined diversity of differentiation and growth, are potent modulators of immune function and homeostasis. The antiviral and immunostimulatory actions of cytokines, like the interferons, have also been recognized for many years. In more recent developments, virus genomes were discovered in 1990 to contain anti-immune genes that control the synthesis of host cell proteins that disarm immune defenses. Many of the virus anti-immune genes are directed against cytokines. Recent discoveries of cytokine homologs and cytokine receptor homologs, and other viral gene products that disarm host immune defenses, provide a molecular basis for improved understanding of virus diseases and new targets for development of innovative therapeutic approaches against viral, cancer and perhaps a number of other diseases.

The implications for childhood leukemia of infection with adenovirus

Adenoviruses have mechanisms that allow persistence in lymphoid cells and immunoevasion. They downregulate major histocompatibility complex (MHC) class I antigen expression and may trigger an autoimmune reaction against MHC class II antigens through mimicry. Adenoviral persistence could be facilitated by human leukocyte antigens A2 and DR53, thereby allowing a preleukemic clone to escape immune surveillance and progress to leukemia.

Gene therapy for brain tumors

Gene therapy has opened new doors for treatment of neoplastic diseases. This new approach seems very attractive, especially for glioblastomas, since treatment of these brain tumors has failed using conventional therapy regimens. Many different modes of gene therapy for brain tumors have been tested in culture and in vivo. Many of these approaches are based on previously established anti-neoplastic principles, like prodrug activating enzymes, inhibition of tumor neovascularization, and enhancement of the normally weak anti-tumor immune response. Delivery of genes to tumor cells has been mediated by a number of viral and synthetic vectors. The most widely used paradigm is based on the activation of ganciclovir to a cytotoxic compound by a viral enzyme, thymidine kinase, which is expressed by tumor cells, after the gene has been introduced by a retroviral vector. This paradigm has proven to be a potent therapy with minimal side effects in several rodent brain tumor models, and has proceeded to phase 1 clinical trials. In this review, current gene therapy strategies and vector systems for treatment of brain tumors will be described and discussed in light of further developments needed to make this new treatment modality clinically efficacious.