Human retroviruses after 20 years: a perspective from the past and prospects for their future control

Interplay between endogenous and exogenous human retroviruses

In humans, retroviruses thrive more as symbionts than as parasites. Apart from the only two modern exogenous human retroviruses (human T-cell lymphotropic and immunodeficiency viruses; HTLV and HIV, respectively), ~8% of the human genome is occupied by ancient retroviral DNA [human endogenous retroviruses (HERVs)]. Here, we review the recent discoveries about the interactions between the two groups, the impact of infection by exogenous retroviruses on the expression of HERVs, the effect of HERVs on the pathogenicity of HIV and HTLV and on the severity of the diseases caused by them, and the antiviral protection that HERVs can allegedly provide to the host. Tracing the crosstalk between contemporary retroviruses and their endogenized ancestors will provide better understanding of the retroviral world.

Is the HTLV-1 Retrovirus Targeted by Host Restriction Factors?

Human T cell leukemia virus type 1 (HTLV-1), the etiological agent of adult T cell leukemia/lymphoma (ATLL) and of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), was identified a few years before Human Immunodeficiency Virus (HIV). However, forty years later, our comprehension of HTLV-1 immune detection and the host immune responses to HTLV-1 is far more limited than for HIV. In addition to innate and adaptive immune responses that rely on specialized cells of the immune system, host cells may also express a range of antiviral factors that inhibit viral replication at different stages of the cycle, in a cell-autonomous manner. Multiple antiviral factors allowing such an intrinsic immunity have been primarily and extensively described in the context HIV infection. Here, we provide an overview of whether known HIV restriction factors might act on HTLV-1 replication. Interestingly, many of them do not exert any antiviral activity against HTLV-1, and we discuss viral replication cycle specificities that could account for these differences. Finally, we highlight future research directions that could help to identify antiviral factors specific to HTLV-1.

Restriction factors in human retrovirus infections and the unprecedented case of CIITA as link of intrinsic and adaptive immunity against HTLV-1

Background

Immunity against pathogens evolved through complex mechanisms that only for sake of simplicity are defined as innate immunity and adaptive immunity. Indeed innate and adaptive immunity are strongly intertwined each other during evolution. The complexity is further increased by intrinsic mechanisms of immunity that rely on the action of intracellular molecules defined as restriction factors (RFs) that, particularly in virus infections, counteract the action of pathogen gene products acting at different steps of virus life cycle.

Main body and conclusion

Here we provide an overview on the nature and the mode of action of restriction factors involved in retrovirus infection, particularly Human T Leukemia/Lymphoma Virus 1 (HTLV-1) infection. As it has been extensively studied by our group, special emphasis is given to the involvement of the MHC class II transactivator CIITA discovered in our laboratory as regulator of adaptive immunity and subsequently as restriction factor against HIV-1 and HTLV-1, a unique example of dual function linking adaptive and intrinsic immunity during evolution. We describe the multiple molecular mechanisms through which CIITA exerts its restriction on retroviruses. Of relevance, we review the unprecedented findings pointing to a concerted action of several restriction factors such as CIITA, TRIM22 and TRIM19/PML in synergizing against retroviral replication. Finally, as CIITA profoundly affects HTLV-1 replication by interacting and inhibiting the function of HTLV-1 Tax-1 molecule, the major viral product associated to the virus oncogenicity, we also put forward the hypothesis of CIITA as counteractor of HTLV-1-mediated cancer initiation.

Human T-cell lymphotropic virus type 1 and its oncogenesis

Human T-cell lymphotropic virus type 1 (HTLV-1) is the etiologic agent of adult T-cell leukemia/lymphoma (ATL), a rapidly progressing clonal malignancy of CD4+ T lymphocytes. Exploring the host-HTLV-1 interactions and the molecular mechanisms underlying HTLV-1-mediated tumorigenesis is critical for developing efficient therapies against the viral infection and associated leukemia/lymphoma. It has been demonstrated to date that several HTLV-1 proteins play key roles in the cellular transformation and immortalization of infected T lymphocytes. Of note, the HTLV-1 oncoprotein Tax inhibits the innate IFN response through interaction with MAVS, STING and RIP1, causing the suppression of TBK1-mediated phosphorylation of IRF3/IRF7. The HTLV-1 protein HBZ disrupts genomic integrity and inhibits apoptosis and autophagy of the target cells. Furthermore, it is revealed that HBZ enhances the proliferation of ATL cells and facilitates evasion of the infected cells from immunosurveillance. These studies provide insights into the molecular mechanisms by which HTLV-1 mediates the formation of cancer as well as useful strategies for the development of new therapeutic interventions against ATL. In this article, we review the recent advances in the understanding of the pathogenesis, the underlying mechanisms, clinical diagnosis and treatment of the disease caused by HTLV-1 infection. In addition, we discuss the future direction for targeting HTLV-1-associated cancers and strategies against HTLV-1.

Dynamics of CD4 cell count among HIV-infected individuals in Lagos, Nigeria

Human immunodeficiency virus (HIV) infection leads to progressive loss of CD4 T cells. Antiretroviral therapy has been able to inhibit this process, resulting in significant level of immune recovery and function. Our aim is to investigate the dynamics of CD4 recovery among HIV patients in Lagos, Nigeria. A total of 213 HIV-positive individuals were enrolled between October 2007 and May 2008, and followed up for 9 months based on CD4 count. CD4 analysis was done by flow cytometry at enrollment and after every 3 months. Data were grouped according to age range, antiretroviral treatment (ART), and time between infection and diagnosis. Kaplan-Meier survival analysis was used for data analysis. There was a significant difference in CD4 count between antiretroviral (ART) naïve and ART experienced subjects (P < 0.001). About 50% of the ART experienced population was identified to show poor CD4 reconstitution unable to achieve a CD4 of 500 cells/µl after 9 months of therapy. Time interval between infection and therapy was also identified to contribute to poor CD4 restoration. Further studies need to be done to classify immunological nonresponders among HIV patients in Nigeria. We also recommend introduction of programs that will facilitate early detection of HIV infection.

Analysis of the Prevalence of HTLV-1 Proviral DNA in Cervical Smears and Carcinomas from HIV Positive and Negative Kenyan Women

The oncogenic retrovirus human T-cell lymphotropic virus type 1 (HTLV-1) is endemic in some countries although its prevalence and relationship with other sexually transmitted infections in Sub-Saharan Africa is largely unknown. A novel endpoint PCR method was used to analyse the prevalence of HTLV-1 proviral DNA in genomic DNA extracted from liquid based cytology (LBC) cervical smears and invasive cervical carcinomas (ICCs) obtained from human immunodeficiency virus-positive (HIV+ve) and HIV-negative (HIV−ve) Kenyan women. Patient sociodemographic details were recorded by structured questionnaire and these data analysed with respect to HIV status, human papillomavirus (HPV) type (Papilocheck^®) and cytology. This showed 22/113 (19.5%) of LBC’s from HIV+ve patients were positive for HTLV-1 compared to 4/111 (3.6%) of those from HIV−ve women (p = 0.0002; odds ratio (OR) = 6.42 (2.07–26.56)). Only 1/37 (2.7%) of HIV+ve and none of the 44 HIV−ve ICC samples were positive for HTLV-1. There was also a significant correlation between HTLV-1 infection, numbers of sexual partners (p < 0.05) and smoking (p < 0.01). Using this unique method, these data suggest an unexpectedly high prevalence of HTLV-1 DNA in HIV+ve women in this geographical location. However, the low level of HTLV-1 detected in HIV+ve ICC samples was unexpected and the reasons for this are unclear.

CD4 Decay Rate as an Indicator of the Time Interval between Initial Infection and First Diagnosis among Drug-Naïve Human Immunodeficiency Virus Seropositive Individuals in Lagos, Nigeria

OBJECTIVE

The aim of this study was to determine the time interval between human immunodeficiency virus (HIV) infection and the first diagnosis among drug-naïve individuals in Badagry, Nigeria.

SUBJECTS AND METHODS

A sample of 213 subjects who tested HIV positive for the first time were enrolled in this study. The HIV diagnosis was performed using Startpak® and Determine® kits, and a CD4 count was carried out using a FACS Count® flow cytometer. The mean CD4 values were determined by gender and age groups. The time interval between initial HIV infection and first testing was calculated based on the average CD4 decay rate per calendar year, and data analysis was performed using SPSS software.

RESULTS

At diagnosis, the mean CD4 values showed that females recorded 270 cells/µl and males 244 cells/µl. By age range, individuals <25 years recorded 437 cells/µl, those between 25 and 40 years of age had 237 cells/µl, and those aged ≥41 years had 192 cells/µl. There was a significant difference between CD4 cell categorization and age range (p < 0.001). Subjects aged between 25 and 40 years recorded the highest distribution of all CD4 cell counts. The time interval between infection and testing for females was 8.1 years and for males 6.7 years. Within the age group <25 years the interval was 5.1 years, whilst it was 8.1 years for those aged ≥41 years.

CONCLUSION

Most of the population presented for testing during the advanced stages of infection. We suggest an upscaling of HIV voluntary counseling and testing to encourage early detection and better treatment outcomes.

Tax posttranslational modifications and interaction with calreticulin in MT-2 cells and human peripheral blood mononuclear cells of human T cell lymphotropic virus type-I-associated myelopathy/tropical spastic paraparesis patients

The human retrovirus human T cell lymphotropic virus type-I (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Axonal degeneration in HAM/TSP patients occurs without neuron infection, with the secreted viral Tax protein proposed to be involved. We previously found that Tax secreted into the culture medium of MT-2 cells (HTLV-1-infected cell line) produced neurite retraction in neuroblastoma cells differentiated to neuronal type. To assess the relevance of Tax posttranslational modifications on this effect, we addressed the question of whether Tax secreted by MT-2 cells and peripheral blood mononuclear cells (PBMCs) of HTLV-1-infected subjects is modified. The interaction of Tax with calreticulin (CRT) that modulates intracellular Tax localization and secretion has been described. We studied Tax localization and modifications in MT-2 cells and its interaction with CRT. Intracellular Tax in MT-2 cells was assessed by flow cytometry, corresponding mainly to a 71-kDa protein followed by western blot. This protein reported as a chimera with gp21 viral protein-confirmed by mass spectrometry-showed no ubiquitination or SUMOylation. The Tax-CRT interaction was determined by confocal microscopy and coimmunoprecipitation. Extracellular Tax from HAM/TSP PBMCs is ubiquitinated according to western blot, and its interaction with CRT was shown by coimmunoprecipitation. A positive correlation between Tax and CRT secretion was observed in HAM/TSP PBMCs and asymptomatic carriers. For both proteins inhibitors and activators of secretion showed secretion through the endoplasmic reticulum-Golgi complex. Tax, present in PBMC culture medium, produced neurite retraction in differentiated neuroblastoma cells. These results suggest that Tax, whether ubiquitinated or not, is active for neurite retraction.

Highlights on distinctive structural and functional properties of HTLV Tax proteins

Human T cell leukemia viruses (HTLVs) are complex human retroviruses of the Deltaretrovirus genus. Four types have been identified thus far, with HTLV-1 and HTLV-2 much more prevalent than HTLV-3 or HTLV-4. HTLV-1 and HTLV-2 possess strictly related genomic structures, but differ significantly in pathogenicity, as HTLV-1 is the causative agent of adult T cell leukemia and of HTLV-associated myelopathy/tropical spastic paraparesis, whereas HTLV-2 is not associated with neoplasia. HTLVs code for a protein named Tax that is responsible for enhancing viral expression and drives cell transformation. Much effort has been invested to dissect the impact of Tax on signal transduction pathways and to identify functional differences between the HTLV Tax proteins that may explain the distinct oncogenic potential of HTLV-1 and HTLV-2. This review summarizes our current knowledge of Tax-1 and Tax-2 with emphasis on their structure, role in activation of the NF-κB (nuclear factor kappa-B) pathway, and interactions with host factors.

Association between human papillomavirus and human T-lymphotropic virus in indigenous women from the Peruvian Amazon

Background

No association between the Human T-cell lymphotropic virus (HTLV), an oncogenic virus that alters host immunity, and the Human Papillomavirus (HPV) has previously been reported. Examining the association between these two viruses may permit the identification of a population at increased risk for developing cervical cancer.

Methods and Findings

Between July 2010 and February 2011, we conducted a cross-sectional study among indigenous Amazonian Peruvian women from the Shipibo-Konibo ethnic group, a group with endemic HTLV infection. We recruited women between 15 and 39 years of age who were living in the cities of Lima and Ucayali. Our objectives were to determine the association between HTLV and: (i) HPV infection of any type, and (ii) high-risk HPV type infection. Sexually active Shipibo-Konibo women were screened for HTLV-1 and HTLV-2 infections. All HTLV-1 or -2 positive women, along with two community-matched HTLV negative sexually active Shipibo-Konibo controls were later tested for the presence of HPV DNA, conventional cytology, and HIV. We screened 1,253 Shipibo-Konibo women, observing a prevalence of 5.9% (n = 74) for HTLV-1 and 3.8% (n = 47) for HTLV-2 infections. We enrolled 62 (60.8%) HTLV-1 positive women, 40 (39.2%) HTLV-2 positive women, and 205 community-matched HTLV negative controls. HTLV-1 infection was strongly associated with HPV infection of any type (43.6% vs. 29.3%; Prevalence Ratio (PR): 2.10, 95% CI: 1.53–2.87), and with high-risk HPV infection (32.3% vs. 22.4%; PR: 1.93, 95% CI: 1.04–3.59). HTLV-2 was not significantly associated with either of these HPV infections.

Conclusions

HTLV-1 infection was associated with HPV infection of any type and with high-risk HPV infection. Future longitudinal studies are needed to evaluate the incidence of high-risk HPV infection as well as the incidence of cervical neoplasia among HTLV-1 positive women.

Transcriptional control of HIV replication by multiple modulators and their implication for a novel antiviral therapy

Transcriptional regulation is critical for the human immunodeficiency virus 1 (HIV-1) life cycle and is the only step at which the virus amplifies the content of its genetic information. Numerous known and still unknown transcriptional factors, both host and viral, regulate HIV-1 gene expression and latency. This article is a comprehensive review of transcription factors involved in HIV-1 gene expression and presents the significant implications of nuclear factor kappa B (NF-κB) and the HIV-1 transactivator of transcription (Tat) protein. We include recent findings on chromatin remodeling toward HIV transcription and its therapeutic implication is also discussed. The current status of small-molecular-weight compounds that affect HIV transcription is also described.

Recombinant human T-cell leukemia virus types 1 and 2 Tax proteins induce high levels of CC-chemokines and downregulate CCR5 in human peripheral blood mononuclear cells

Human T-cell leukemia viruses types 1 (HTLV-1) and 2 (HTLV-2) produce key transcriptional regulatory gene products, known as Tax1 and Tax2, respectively. Tax1 and Tax2 transactivate multiple host genes involved in cellular immune responses within the cellular microenvironment, including induction of genes encoding expression of CC-chemokines. It is speculated that HTLV Tax proteins may act as immune modulators. In this study, recombinant Tax1 and Tax2 proteins were tested for their effects on the viability of cultured peripheral blood mononuclear cells (PBMCs), and their ability to induce expression of CC-chemokines and to downregulate the level of CCR5 expression in PBMCs. PBMCs obtained from uninfected donors were cultured in a range of Tax1 and Tax2 concentrations (10-100 pM), and supernatant fluids were harvested at multiple time points for quantitative determinations of MIP-1α/CCL3, MIP-1β/CCL4, and RANTES/CCL5. Treatment of PBMCs with Tax1 and Tax2 proteins (100 pM) resulted in a significant increase in viability over a 7-d period compared to controls (p<0.01). Both Tax1 and Tax2 induced high levels of all three CC-chemokines over the dosing range compared to mock-treated controls (p<0.05). The gated population of lymphocytes treated with Tax2, as well as lymphocytes from HTLV-2-infected donors, showed a significantly lower percentage of CCR5-positive cells compared to those of uninfected donors and from mock-treated lymphocytes, respectively (p<0.05). These results suggest that Tax1 and Tax2 could promote innate immunity in the extracellular environment during HTLV-1 and HTLV-2 infections via CC-chemokine ligands and receptors.

The impact of human T-cell lymphotropic virus I infection on clinical and immunologic outcomes in patients coinfected with HIV and hepatitis C virus

BACKGROUND

HIV, hepatitis C (HCV), and human T-cell lymphotropic virus I (HTLV-1) are associated with high global burdens of disease, notably in resource-poor locales. They share similar routes of transmission and cause chronic infections with associated morbidity. We performed a cross-sectional study to assess the impact of HTLV-1 infection on clinical outcomes in HIV/HCV-coinfected patients.

METHODS

We enrolled 102 (72.3%) with HIV/HCV coinfection (Group 1) and 39 (27.7%) triply infected with HIV, HCV, and HTLV-1 (Group 2). We reviewed medical records of two groups of patients followed in two outpatients services in Salvador, Brazil. We collected and compared demographic, behavioral-related information, immunologic, virologic, and histologic parameters for HIV-1 and HCV infection.

RESULTS

Demographics, virologic, and immunologic characteristics were similar in the two groups; a higher proportion of triply infected patients (Group 2) reported any history of injection drug use compared with dually infected (Group 1) patients (75% vs 45.8%; P = 0.003). No differences were seen between groups in HIV clinical outcomes (CD4 count and viral load). Alanine aminotransferase levels were significantly higher in HIV/HCV-coinfected patients (P = 0.045). Liver fibrosis damage based on Metavir scores was similar between groups (0.97) but was worse with lower CD4 cell count (under 200 cells/mm) (P = 0.01).

CONCLUSIONS

HIV/HTLV-1 and HIV/HCV coinfections may worsen clinical related outcomes, but virologic and immunologic outcomes were similar in both groups. Hepatic measures were worse in patients with more severe immunosuppression.

Ubiquitin-independent proteasomal degradation during oncogenic viral infections

Most eukaryotic proteins destined for imminent destruction are first tagged with a chain of ubiquitin molecules and are subsequently dismantled by the proteasome. Ubiquitin-independent degradation of substrates by the proteasome, however, also occurs. The number of documented proteasome-dependent, ubiquitin-independent degradation events remains relatively small but continues to grow. Proteins involved in oncogenesis and tumor suppression make up the majority of the known cases for this type of protein destruction. Provocatively, viruses with confirmed or suspected oncogenic properties are also prominent participants in the pantheon of ubiquitin-independent proteasomal degradation events. In this review, we identify and describe examples of proteasome-dependent, ubiquitin-independent protein degradation that occur during tumor virus infections, speculate why this type of protein destruction may be preferred during oncogenesis, and argue that this uncommon type of protein turnover represents a prime target for antiviral and anticancer therapeutics.

Safety and anti-HIV assessments of natural vaginal cleansing products in an established topical microbicides in vitro testing algorithm

Background

At present, there is no effective vaccine or other approved product for the prevention of sexually transmitted human immunodeficiency virus type 1 (HIV-1) infection. It has been reported that women in resource-poor communities use vaginally applied citrus juices as topical microbicides. These easily accessible food products have historically been applied to prevent pregnancy and sexually transmitted diseases. The aim of this study was to evaluate the efficacy and cytotoxicity of these substances using an established topical microbicide testing algorithm. Freshly squeezed lemon and lime juice and household vinegar were tested in their original state or in pH neutralized form for efficacy and cytotoxicity in the CCR5-tropic cell-free entry and cell-associated transmission assays, CXCR4-tropic entry and fusion assays, and in a human PBMC-based anti-HIV-1 assay. These products were also tested for their effect on viability of cervico-vaginal cell lines, human cervical explant tissues, and beneficial Lactobacillus species.

Results

Natural lime and lemon juice and household vinegar demonstrated anti-HIV-1 activity and cytotoxicity in transformed cell lines. Neutralization of the products reduced both anti-HIV-1 activity and cytotoxicity, resulting in a low therapeutic window for both acidic and neutralized formulations. For the natural juices and vinegar, the IC₅₀ was ≤ 3.5 (0.8-3.5)% and the TC₅₀ ≤ 6.3 (1.0-6.3)%. All three liquid products inhibited viability of beneficial Lactobacillus species associated with vaginal health. Comparison of three different toxicity endpoints in the cervical HeLa cell line revealed that all three products affected membrane integrity, cytosolic enzyme release, and dehydrogenase enzyme activity in living cells. The juices and vinegar also exerted strong cytotoxicity in cervico-vaginal cell lines, mainly due to their acidic pH. In human cervical explant tissues, treatment with 5% lemon or lime juice or 6% vinegar induced toxicity similar to application of 100 μg/ml nonoxynol-9, and exposure to 10% lime juice caused tissue damage comparable to treatment with 5% Triton-X-100.

Conclusions

Lemon and lime juice and household vinegar do not fulfill the safety criteria mandated for a topical microbicide. As a result of their unphysiological formulation for the vaginal tract, they exhibit cytotoxicity to human cell lines, human vaginal tissues, and beneficial vaginal Lactobacillus species.

Loss of correlation between HIV viral load and CD4+ T-cell counts in HIV/HTLV-1 co-infection in treatment naive Mozambican patients

Seven hundred and four HIV-1/2-positive, antiretroviral therapy (ART) naïve patients were screened for HTLV-1 infection. Antibodies to HTLV-1 were found in 32/704 (4.5%) of the patients. Each co-infected individual was matched with two HIV mono-infected patients according to World Health Organization clinical stage, age +/-5 years and gender. Key clinical and laboratory characteristics were compared between the two groups. Mono-infected and co-infected patients displayed similar clinical characteristics. However, co-infected patients had higher absolute CD4+ T-cell counts (P = 0.001), higher percentage CD4+ T-cell counts (P < 0.001) and higher CD4/CD8 ratios (P < 0.001). Although HIV plasma RNA viral loads were inversely correlated with CD4+ T-cell-counts in mono-infected patients (P < 0.0001), a correlation was not found in co-infected individuals (P = 0.11). Patients with untreated HIV and HTLV-1 co-infection show a dissociation between immunological and HIV virological markers. Current recommendations for initiating ART and chemoprophylaxis against opportunistic infections in resource-poor settings rely on more readily available CD4+ T-cell counts without viral load parameters. These guidelines are not appropriate for co-infected individuals in whom high CD4+ T-cell counts persist despite high HIV viral load states. Thus, for co-infected patients, even in resource-poor settings, HIV viral loads are likely to contribute information crucial for the appropriate timing of ART introduction.

Development and validation of a multiplex real-time PCR assay for simultaneous genotyping and human T-lymphotropic virus type 1, 2, and 3 proviral load determination

The human T-lymphotropic virus (HTLV) proviral load remains the best surrogate marker for disease progression. Real-time PCR techniques have been developed for detection and quantification of cosmopolitan HTLV type 1a (HTLV-1a) and HTLV-2. Since a growing level of diversity in subtypes and genotypes is observed, we developed a multiplex quantitative PCR for simultaneous detection, genotyping, and quantification of proviral loads of HTLV-1, 2, and 3. Our assay uses tax type-specific primers and dually labeled probes and has a dynamic range of 10(5) to 10 HTLV copies. One hundred sixty-three samples were analyzed, among which all of the different subtypes within each HTLV genotype could be detected. The performance of proviral load determination of our multiplex assay was compared with that of a previously published HTLV-1 singleplex quantitative PCR based on SYBR green detection, developed at a different institute. Linear regression analysis showed a statistically significant (P < 0.0001) and strong (r(2) = 0.87) correlation between proviral load values measured with the two distinct real-time PCR assays. In conclusion, our novel assay offers an accurate molecular diagnosis and genotyping, together with the determination of the proviral load of HTLV-infected individuals, in a single amplification reaction. Moreover, our molecular assay could offer an alternative when current available serological assays are insufficient.

Amino acid preferences of retroviral proteases for amino-terminal positions in a type 1 cleavage site

The specificities of the proteases of 11 retroviruses were studied using a series of oligopeptides with amino acid substitutions in the P1, P3, and P4 positions of a naturally occurring type 1 cleavage site (Val-Ser-Gln-Asn-Tyr downward arrowPro-Ile-Val-Gln) in human immunodeficiency virus type 1 (HIV-1). Previously, the substrate specificity of the P2 site was studied for the same representative set of retroviral proteases, which included at least one member from each of the seven genera of the family Retroviridae (P. Bagossi, T. Sperka, A. Fehér, J. Kádas, G. Zahuczky, G. Miklóssy, P. Boross, and J. Tözsér, J. Virol. 79:4213-4218, 2005). Our enzyme set comprised the proteases of HIV-1, HIV-2, equine infectious anemia virus, avian myeloblastosis virus (AMV), Mason-Pfizer monkey virus, mouse mammary tumor virus (MMTV), Moloney murine leukemia virus, human T-lymphotropic virus type 1, bovine leukemia virus, walleye dermal sarcoma virus, and human foamy virus. Molecular models were used to interpret the similarities and differences in specificity between these retroviral proteases. The results showed that the retroviral proteases had similar preferences (Phe and Tyr) for the P1 position in this sequence context, but differences were found for the P3 and P4 positions. Importantly, the sizes of the P3 and P4 residues appear to be a major contributor for specificity. The substrate specificities correlated well with the phylogenetic tree of the retroviruses. Furthermore, while the specificities of some enzymes belonging to different genera appeared to be very similar (e.g., those of AMV and MMTV), the specificities of the primate lentiviral proteases substantially differed from that observed for a nonprimate lentiviral protease.

Upregulation of HTLV-1 and HTLV-2 expression by HIV-1 in vitro

Co-infections with HIV-1 and the human T leukemia virus types 1 and 2 (HTLV-1, HTLV-2) occur frequently, particularly in large metropolitan areas where injection drug use is a shared mode of transmission. Recent evidence suggests that HIV-HTLV co-infections are associated with upregulated HTLV-1/2 virus expression and disease. An in vitro model of HIV-1 and HTLV-1/2 co-infection was utilized to determine if cell free HIV-1 virions or recombinant HIV-1 Tat protein (200-1,000 ng/ml) upregulated HTLV-1/2 expression and infectivity. Exposure to HIV-1 increased the number of HTLV-1 antigen expressing cells, from 6% at baseline to 12% at 24 hr, and 20% at 120 hr (P < 0.05) post-exposure. A similar, although less robust response was observed in HTLV-2 infected cells. HIV-1 co-localized almost exclusively with HTLV-1/2 positive cells. Exposure to HIV-1 Tat protein (1,000 ng/ml) increased HTLV-1 p19 expression almost twofold by 48 hr, and cells co-stimulated with 10 nM phorbol myristate acetate (PMA) showed almost a fourfold increase over baseline. It is concluded that HIV-1 augments HTLV-1/2 infectivity in vitro. The findings also suggest a role for the HIV-1 Tat protein and PMA-inducible cellular factors, in HIV-1 induced HTLV-1/2 antigen expression.

Preferential selection of human T-cell leukemia virus type 1 provirus lacking the 5' long terminal repeat during oncogenesis

In adult T-cell leukemia (ATL) cells, a defective human T-cell leukemia virus type 1 (HTLV-1) provirus lacking the 5' long terminal repeat (LTR), designated type 2 defective provirus, is frequently observed. To investigate the mechanism underlying the generation of the defective provirus, we sequenced HTLV-1 provirus integration sites from cases of ATL. In HTLV-1 proviruses retaining both LTRs, 6-bp repeat sequences were adjacent to the 5' and 3' LTRs. In 8 of 12 cases with type 2 defective provirus, 6-bp repeats were identified at both ends. In five of these cases, a short repeat was bound to CA dinucleotides of the pol and env genes at the 5' end, suggesting that these type 2 defective proviruses were formed before integration. In four cases lacking the 6-bp repeat, short (6- to 26-bp) deletions in the host genome were identified, indicating that these defective proviruses were generated after integration. Quantification indicated frequencies of type 2 defective provirus of less than 3.9% for two carriers, which are much lower than those seen for ATL cases (27.8%). In type 2 defective proviruses, the second exons of the tax, rex, and p30 genes were frequently deleted, leaving Tax unable to activate NF-kappaB and CREB pathways. The HTLV-1 bZIP factor gene, located on the minus strand, is expressed in ATL cells with this defective provirus, and its coding sequences are intact, suggesting its significance in oncogenesis.

Influence of human T cell lymphotropic virus type 2 coinfection on virological and immunological parameters in HIV type 1-infected patients

BACKGROUND

Human T cell lymphotropic virus type 2 (HTLV-2) infection is not rare among injection drug users with human immunodeficiency virus (HIV) infection and may exert a protective role in the progression of HIV disease.

METHODS

Immunological and virological parameters were compared in HIV-HTLV-2-coinfected patients and a control group of HIV-monoinfected subjects. All individuals were antiretroviral therapy naive. HIV-specific CD8+ T cell levels were measured using an interferon-gamma assay in response to 125 optimally defined HIV peptides divided into 5 pools. Immune activation was evaluated by measuring levels of CD38 in different CD4+ and CD8+ T cell subsets. In a subgroup of patients, the production of CCL4 in parallel with interferon-gamma was assessed in response to Gag peptides.

RESULTS

Lower plasma HIV-RNA levels were found in HIV-HTLV-2-coinfected patients than in HIV-monoinfected patients, despite the 2 groups having similar CD4+ T cell counts. Coinfected patients also had significantly lower levels of CD38 expression in total CD8+ T cells and in its naive subset. CD8+ T cell levels specific for each pool of peptides were similar in both groups, but cells mainly contributing to HIV Gag-specific responses in coinfected patients were CCL4 positive and interferon-gamma negative, whereas for HIV-monoinfected subjects, the response was dominated by CCL4-positive and interferon-gamma-positive cells.

CONCLUSIONS

HTLV-2 coinfection may exert a protective role on HIV disease progression by lowering HIV replication and immune activation. A predominance of CCL4 single positive HIV-specific CD8+ T cells in HIV-HTLV-2-coinfected patients could explain this effect.

Women infected with HIV type 1 Brazilian variant, subtype B (B'-GWGR motif) have slower progression to AIDS, compared with patients infected with subtype B (B-GPGR motif)

INTRODUCTION

The Brazilian variant of human immunodeficiency virus (HIV) type 1 (HIV-1) subtype B (serotype B'-GWGR) has a tryptophan replacing a proline in position 328 of the HIV-1 envelope, a feature that may induce a different HIV disease progression. We aimed to evaluate the role of the B subtypes of HIV-1 (serotypes B-GPGR and B'-GWGR) on HIV disease progression.

METHODS

A total of 137 HIV-infected individuals who had been admitted to the hospital were tested with an anti-V3 serologic assay, using peptides representing 2 HIV-1 subtype B strains, MN and SF2, and 2 Brazilian variant B'-GWGR strains, BR1 and BR2.

RESULTS

Of 137 serum samples tested with the anti-V3 serologic assay, 4 (3%) yielded indeterminate results, 74 (54%; from 25 women and 49 men) were found to be B-GPGR, and 59 (43%; from 20 women and 39 men) were found to be the B'-GWGR variant. In general, a longer interval from the first known positive HIV test result to an AIDS-defining event was observed in the B'-GWGR group than in the B-GPGR group (21 vs. 7 months). The CD4+ T cell counts were higher in the B'-GWGR group (median CD4+ T cell count, 65 vs. 31 cells/mm3; P=.01), and women infected with the B'-GWGR variant were less likely to die than were men infected with the same variant (P=.01). The median viral load in the B'-GWGR group was 3.395 copies/mL, compared with 39.350 copies/mL in the B-GPGR group (P=.01).

CONCLUSIONS

Taken together, our results indicate that B'-GWGR-infected women may have more-favorable outcomes than B-GPGR-infected subjects.

The Vif and Vpr accessory proteins independently cause HIV-1-induced T cell cytopathicity and cell cycle arrest

HIV type I (HIV-1) can cause G(2) cell cycle arrest and death of CD4(+) T lymphocytes in vitro and inexorable depletion of these cells in vivo. However, the molecular mechanism of viral cytopathicity has not been satisfactorily elucidated. Previously, we showed that HIV-1 kills T cells by a necrotic form of cell death that requires high level expression of an integrated provirus but not the env or nef genes. To determine which viral protein(s) are required for cell death, we systematically mutated, alone and in combination, the ORFs of the NL4-3 strain of HIV-1. We found that the elimination of the viral functions encoded by gag-pol and vpu, tat, and rev did not mitigate cytopathicity. However, elimination of the vif and vpr accessory genes together, but not individually, renders the virus incapable of causing cell death and G(2) cell cycle blockade. We thus identify vif and vpr as necessary for T cell cytopathic effects induced by HIV-1. These findings may provide an important insight into the molecular mechanism of viral pathogenesis in AIDS.

HTLV-I basic leucine zipper factor gene mRNA supports proliferation of adult T cell leukemia cells

Human T cell leukemia virus type I (HTLV-I) causes adult T cell leukemia (ATL) in 2-5% of carriers after a long latent period. An HTLV-I encoded protein, Tax, induces proliferation and inhibits apoptosis, resulting in clonal proliferation of infected cells. However, tax gene expression in ATL cells is disrupted by several mechanisms, including genetic changes in the tax gene and DNA methylation/deletion of the 5' long terminal repeat (LTR). Because Tax is the major target of cytotoxic T-lymphocytes in vivo, loss of Tax expression should enable ATL cells to escape the host immune system. The 5' LTR of HTLV-I is frequently hypermethylated or deleted in ATL cells, whereas the 3' LTR remains unmethylated and intact, suggesting the involvement of the 3' LTR in leukemogenesis. Here we show that a gene encoded by the minus strand of the HTLV-I proviral genome, HTLV-I basic leucine zipper factor (HBZ), is transcribed from 3'-LTR in all ATL cells. Suppression of HBZ gene transcription by short interfering RNA inhibits proliferation of ATL cells. In addition, HBZ gene expression promotes proliferation of a human T cell line. Analyses of T cell lines transfected with mutated HBZ genes showed that HBZ promotes T cell proliferation in its RNA form, whereas HBZ protein suppresses Tax-mediated viral transcription through the 5' LTR. Thus, the single HBZ gene has bimodal functions in two different molecular forms. The growth-promoting activity of HBZ RNA likely plays an important role in oncogenesis by HTLV-I.

Inhibition of atherogenesis in LDLR knockout mice by systemic delivery of adeno-associated virus type 2-hIL-10

Atherosclerosis is an inflammatory disease of the arteries. Interleukin-10 (IL-10) is known to be an anti-inflammatory cytokine which might be useful for counteracting the development of atherosclerosis. As long-term systemic cytokine delivery is prohibitively expensive, gene therapy might be a suitable approach. To test this idea, low-density lipoprotein receptor (LDLR) knockout mice were injected with recombinant adeno-associated virus type 2 (AAV)/interleukin-10 virus or AAV/granulocyte macrophage-colony stimulating factor (GM-CSF) virus and then put on a high-cholesterol diet. Upon harvesting the animals at 18 weeks, elevated blood lipids could be documented and AAV/IL-10 and AAV/GM-CSF DNA and mRNA could be found in various mouse organs. The mice receiving the AAV/IL-10 virus had significantly lower levels of atherogenesis (Sudan IV-staining and histology) than the untreated or the AAV/GM-CSF-treated animals, dropping from 53% to 17% (p < 0.05). The aortas of the AAV/IL-10-treated animals displayed higher IL-10 expression and lower CD68 and nitrotyrosine expression. These data are similar to those of Yoshioka et al. [Yoshioka, T, Okada, T, Maeda, Y, et al. Adeno-associatedvirus vector-mediated interleukin-10 gene transfer inhibits atherosclerosis in apolipoprotein E-deficient mice. Gene Ther 2004;11:1772-9] in which AAV/IL-10 was delivered into the tibial muscle of ApoE-deficient mice, instead of tail vein injection used here. These data indicate that systemic AAV/IL-10 gene delivery, with resulting inhibition of inflammation and oxidative stress, was able to limit atherogenesis, and suggest that this approach is worthy of further study.

Molecular epidemiology of HTLV-2 infection among intravenous drug users in Spain

BACKGROUND

HTLV-2 infection is prevalent among intravenous drug users (IDUs), which often are coinfected with HIV-1. Two main subtypes, HTLV-2a and -2b, have been described among European IDUs, with a characteristically geographic distribution: IIa in northern Europe and IIb in the south. Although frequent traveling within Europe might have favoured a wide dissemination of diverse HTLV-2 variants, HTLV-2b was so far the only subtype reported in Spain.

OBJECTIVE

To investigate the current molecular epidemiology of HTLV-2 in Spain.

STUDY DESIGN

Twenty-six new HTLV-2 strains isolated from IDUs over the last 11 years in different geographic regions were examined. The HTLV LTR region (620bp) was sequenced and phylogenetic analyses were performed. Endonuclease restriction sites were examined to further characterize the HTLV-2 subgroup.

RESULTS

All 26 individuals infected with HTLV-2 showed viruses belonging to the HTLV-2 b4 clade and were closely related to the previously reported HTLV-2 Spanish and Italian IDU isolates.

CONCLUSIONS

HTLV-2 subtype b4 continues to be the only HTLV-2 subgroup recognized so far in Spain and no introduction of other HTLV-2 variants has occurred over the last 11 years.

Valproate activates bovine leukemia virus gene expression, triggers apoptosis, and induces leukemia/lymphoma regression in vivo

Leukemogenic viruses like human T-lymphotropic virus and bovine leukemia virus (BLV) presumably persist in the host partly by latent integration of the provirus in a fraction of infected cells, leading to accumulative increase in the outgrowth of transformed cells. Furthermore, viral infection also correlates with a blockade of the apoptotic mechanisms concomitant with an apparent latency of the host cell. Conceptually, induction of viral or cellular gene expression could thus also be used as a therapeutic strategy against retroviral-associated leukemia. Here, we provide evidence that valproate, an inhibitor of deacetylases, activates BLV gene expression in transient transfection experiments and in short-term cultures of primary B-lymphocytes. In vivo, valproate injection into newly BLV-inoculated sheep did not abrogate primary infection. However, valproate treatment, in the absence of any other cytotoxic drug, was efficient for leukemia/lymphoma therapy in the sheep model leading to decreased lymphocyte numbers (respectively from 25.6, 35.7, and 46.5 x 10(3) cells per mm3 to 1.0, 10.6, and 24.3 x 10(3) cells per mm3 in three leukemic sheep) and tumor regression (from >700 cm3 to undetectable). The concept of a therapy that targets the expression of viral and cellular genes might be a promising treatment of adult T cell leukemia or tropical spastic paraparesis/human T-lymphotropic virus-associated myelopathy, diseases for which no satisfactory treatment exists so far.

Infectious agents and cancer: criteria for a causal relation

Infectious agents, mainly viruses, are among the few known causes of cancer and contribute to a variety of malignancies worldwide. The agents and cancers considered here are human papillomaviruses (cervical carcinoma); human polyomaviruses (mesotheliomas, brain tumors); Epstein-Barr virus (B-cell lymphoproliferative diseases and nasopharyngeal carcinoma); Kaposi's Sarcoma Herpesvirus (Kaposi's Sarcoma and primary effusion lymphomas); hepatitis B and hepatitis C viruses (hepatocellular carcinoma); Human T-cell Leukemia Virus-1 (T-cell leukemias); and helicobacter pylori (gastric carcinoma), which account for up to 20% of malignancies around the globe. The criteria most often used in determining causality are consistency of the association, either epidemiologic or on the molecular level, and oncogenicity of the agent in animal models or cell cultures. However use of these generally applied criteria in deciding on causality is selective, and the criteria may be weighted differently. Whereas for most of the tumor viruses the viral genome persists in an integrated or episomal form with a subset of viral genes expressed in the tumor cells, some agents (HBV, HCV, helicobacter) are not inherently oncogenic, but infection leads to transformation of cells by indirect means. For some malignancies the viral agent appears to serve as a cofactor (Burkitt's lymphoma-EBV; mesothelioma - SV(40)). For others the association is inconsistent (Hodgkin's Disease, gastric carcinomas, breast cancer-EBV) and may either define subsets of these malignancies, or the virus may act to modify phenotype of an established tumor, contributing to tumor progression rather than causing the tumor. In these cases and for the human polyomaviruses the association with malignancy is less consistent or still emerging. In contrast despite the potent oncogenic properties of some strains of human adenovirus in tissue culture and animals the virus has not been linked with any human cancers. Finally it is likely that more agents, most likely viruses, both known and unidentified, have yet to be implicated in human cancer. In the meantime study of tumorigenic infectious agents will continue to illuminate molecular oncogenic processes.

A 20-year history of childhood HIV-associated nephropathy

In 1984, physicians in New York and Miami reported HIV-infected adult patients with heavy proteinuria and rapid progression to end-stage renal disease. These patients showed large edematous kidneys with a combination of focal segmental glomerulosclerosis (FSGS) and tubulointerstitial lesions. This renal syndrome, named HIV-associated nephropathy (HIVAN), was found predominantly in African Americans. Subsequent studies confirmed the presence of HIVAN in children, who frequently develop nephrotic syndrome in association with FSGS and/or mesangial hyperplasia with microcystic tubular dilatation. Since then, substantial progress has been made in our understanding of the etiology and pathogenesis of HIVAN. This article reviews 20 years of research into the pathogenesis of HIVAN and discusses how these concepts could be applied to the treatment of children with HIVAN. HIV-1 infection plays a direct role in the pathogenesis of childhood HIVAN, at least partially by affecting the growth and differentiation of glomerular and tubular epithelial cells and enhancing the renal recruitment of infiltrating mononuclear cells and cytokines. An up-regulation of renal heparan sulfate proteoglycans seems to play a relevant role in this process, by increasing the recruitment of heparin-binding growth factors (i.e., FGF-2), chemokines, HIV-infected cells, and viral proteins (i.e., gp120, Tat). These changes enhance the infectivity of HIV-1 in the kidney and induce injury and proliferation of intrinsic renal cells. Highly active anti-retroviral therapy (HAART) appears to be the most promising treatment to prevent the progression of childhood HIVAN. Hopefully, in the near future, better education, prevention, and treatment programs will lead to the eradication of this fatal childhood disease.

Development of a microtiter plate fluorescent assay for inhibition studies on the HTLV-1 and HIV-1 proteinases

The proteinase of human T-cell leukemia virus type-1 (HTLV-1), similar to the proteinase of human immunodeficiency virus type-1 (HIV-1), is a potential target for chemotherapy, since the virus is associated with a number of human diseases. A microtiter plate fluorescent assay was developed for the HTLV-1 and HIV-1 proteinases for direct comparison of the inhibition profiles of the enzymes. It was established that, except for Indinavir, none of the inhibitors designed against the HIV-1 proteinase were able to inhibit the HTLV-1 proteinase in the studied concentration range, while two reduced peptide bond-containing peptides having the sequence of HTLV-1 cleavage sites were inhibitors of the HTLV-1 proteinase. One of these was potent enough to be used for active site titration of the HTLV-1 proteinase.

Loss of thioredoxin-binding protein-2/vitamin D3 up-regulated protein 1 in human T-cell leukemia virus type I-dependent T-cell transformation: implications for adult T-cell leukemia leukemogenesis

Human T-cell leukemia virus type I (HTLV-I) is the causative agent of adult T-cell leukemia (ATL). However, the low incidence of ATL among HTLV-I-infected carriers, together with a long latent period, suggests that multiple host-viral events are involved in the progression of HTLV-I-dependent transformation and subsequent development of ATL. Human thioredoxin (TRX) is a redox active protein highly expressed in HTLV-I-transformed cell lines, whereas the TRX-binding protein-2/vitamin D3 up-regulated protein 1 (TBP-2/VDUP1) was recently identified as a negative regulator of TRX. We report here that expression of TBP-2 is lost in HTLV-I-positive, interleukin-2-independent T-cell lines but maintained in HTLV-I-positive, interleukin-2-dependent T-cell lines, as well as HTLV-I-negative T-cell lines. Ectopic overexpression of TBP-2 in HTLV-I-positive T cells resulted in growth suppression. In the TBP-2-overexpressing cells, a G1 arrest was observed in association with an increase of p16 expression and reduction of retinoblastoma phosphorylation. The results suggest that TBP-2 plays a crucial role in the growth regulation of T cells and that the loss of TBP-2 expression in HTLV-I-infected T cells is one of the key events involved in the multistep progression of ATL leukemogenesis.

Prevalence of human T-cell leukemia virus types I and II in Switzerland

The retroviruses human immunodeficiency virus (HIV)-1/2 and human T-cell leukemia virus (HTLV)-I/II share modes of transmission, suggesting that efforts to monitor the current HIV-1 epidemic in Switzerland should be complemented by assessment of HTLV-I/II prevalence. This study presents an updated evaluation of HTLV-I/II infection among groups within the Swiss population polarized towards either low or increased risk of infection. Archived serum and peripheral blood mononuclear cell (PBMC) samples were examined for evidence of HTLV-I/II infection by enzyme-linked immunosorbant assay (ELISA), type-specific Western blot, type-specific polymerase chain reaction (PCR), DNA sequence analysis, and virus culture. Among blood donations obtained from low-risk Swiss donors, we report a complete lack of HTLV-II infection and the occurrence of HTLV-I infection limited to a prevalence of 0.079 per 100,000 (1/1,266,466). Among high-risk HIV-positive persons and HIV-negative persons at increased risk of HIV-infection, we report a focus of HTLV-I and HTLV-II infection at prevalence rates of 62 per 100,000 (1/1,620) and 309 per 100,000 (5/1,620), respectively. The finding of low HTLV-I/II prevalence among Swiss blood donors and containment of HTLV-I/II infection within known risk-groups does not support initiation of HTLV-I/II screening for Swiss blood, tissue, and organ donations.

Human immunodeficiency virus-1 Tat protein interacts with distinct proteasomal α and β subunits

The human immunodeficiency virus-1 (HIV-1) Tat protein was previously reported to compete the association of PA28 regulator with the alpha rings of the 20S proteasome and to inhibit its peptidase activity. However, the distinct interaction sites within the proteasome complex remained to be determined. Here we show that HIV-1 Tat binds to alpha4 and alpha7, six beta subunits of the constitutive 20S proteasome and the interferon-gamma-inducible subunits beta2i and beta5i. A Tat-proteasome interaction can also be demonstrated in vivo and leads to inhibition of proteasomal activity. This indicates that Tat can modulate or interfere with cellular proteasome function by specific interaction with distinct proteasomal subunits.