A role for a new herpes virus (KSHV) in different forms of Kaposi's sarcoma

HIV infection and neoplasia

HIV infection predisposes to several neoplastic conditions, especially non-Hodgkin lymphoma (NHL) and Kaposi's sarcoma (KS), and also intraepithelial cervical neoplasia (CIN) and anal neoplasia (AIN) (but not cervical or anal invasive cancer) and possibly seminoma. For neoplasias associated with oncogenic human viruses (ie, some NHL, CIN, AIN, and probably KS) the role of HIV is most probably linked to its immunosuppressive effect and interference with immune-mediated tumour surveillance. HIV-1, through its regulatory protein tat, might also have a direct promoting effect on KS lesions but it is not essential for their development. The increased frequency of Burkitt's lymphoma and Epstein-Barr-virus-negative large-cell lymphoma in AIDS patients, but not in immunosuppressed transplant patients, and the increased rate of testicular tumours in HIV-infected individuals remain unexplained and may indicate either a direct role for HIV or other cofactors.

The seroepidemiology of human herpesvirus 8 (Kaposi's sarcoma-associated herpesvirus): distribution of infection in KS risk groups and evidence for sexual transmission

Striking differences in Kaposi's sarcoma (KS) risk for AIDS patients who acquire HIV via homosexual activity and those whose HIV infections derive from blood product exposure suggest the presence of a sexually transmitted agent other than HIV in the development of KS. Using an immunofluorescence assay, we examined serum samples from 913 patients for the presence of antibody specific for infection by human herpesvirus 8 (HHV8), an agent whose genome is regularly found in KS tissue. The distribution of HHV8 seropositivity conforms to that expected for a sexually transmitted pathogen and tracks closely with the risk for KS development. Our data support the inference that this virus is the etiologic cofactor predicted by the epidemiology of KS.

Seroconversion to antibodies against Kaposi's sarcoma-associated herpesvirus-related latent nuclear antigens before the development of Kaposi's sarcoma

BACKGROUND

If Kaposi's sarcoma-associated herpesvirus (KSHV) is the cause of Kaposi's sarcoma, serologic evidence of infection should be present in patients before the disease develops.

METHODS

Using an immunoblot assay for two latent nuclear antigens of KSHV, we tested serum samples from homosexual male patients with the acquired immunodeficiency syndrome (AIDS) with and without Kaposi's sarcoma (HIV-infected men with hemophilia), HIV-seronegative blood donors, and HIV-seronegative patients with high titers of antibodies against Epstein-Barr virus (EBV). Serial serum samples obtained from patients with Kaposi's sarcoma before the diagnosis of the disease were tested for evidence of seroconversion.

RESULTS

Of 40 patients with Kaposi's sarcoma, 32 (80 percent) were positive for antibodies against KSHV antigens by the immunoblot assay, as compared with only 7 of 40 homosexual men (18 percent) without Kaposi's sarcoma immediately before the onset of AIDS. Of 122 blood donors, 22 EBV-infected patients, and 20 HIV-infected men with hemophilia, none were seropositive. When studied by the immunoblot assay over a period of 13 to 103 months, 21 of the 40 patients with Kaposi's sarcoma (52 percent) seroconverted 6 to 75 months before the clinical appearance of Kaposi's sarcoma. The median duration of antibody seropositivity for KSHV-related latent nuclear antigens before the diagnosis of Kaposi's sarcoma was 33 months.

CONCLUSIONS

In most patients with kaposi's sarcoma and AIDS, seroconversion to positivity for antibodies against KSHV-related nuclear antigens occurs before the clinical appearance of Kaposi's sarcoma. This supports the hypothesis that Kaposi's sarcoma results from infection with KSHV.

Restricted expression of Kaposi sarcoma-associated herpesvirus (human herpesvirus 8) genes in Kaposi sarcoma

Kaposi sarcoma (KS) is the leading neoplasm of HIV-infected patients and is also found in several HIV-negative populations. Recently, DNA sequences from a novel herpesvirus, termed KS-associated herpesvirus (KSHV), or human herpesvirus 8 (HHV-8) have been identified within KS tissue from both HIV-positive and HIV-negative cases; infection with this agent has been proposed as a possible factor in the etiology or pathogenesis of the tumor. Here we have examined the pattern of KSHV/HHV-8 gene expression in KS and find it to be highly restricted. We identify and characterize two small transcripts that represent the bulk of the virus-specific RNA transcribed from over 120 kb of the KSHV genome in infected cells. One transcript is predicted to encode a small membrane protein; the other is an unusual polyadenylylated RNA that accumulates in the nucleus to high copy number. This pattern of viral gene expression suggests that most infected cells in KS are latently infected, with lytic viral replication likely restricted to a much smaller subpopulation of cells. These findings have implications for the therapeutic utility of currently available antiviral drugs targeted against the lytic replication cycle.

Frequency and distribution of herpesvirus-like DNA sequences (KSHV) in different stages of classic Kaposi's sarcoma and in normal tissues from an Italian population

The frequency and distribution of herpesvirus-like DNA sequences (KSHV) were investigated by PCR in the pathologic skin lesions of a series of 22 HIV-negative elderly patients with classic Kaposi's sarcoma (KS) from Italy, one of the few regions of the world where classic KS is prevalent. Viral sequences were clearly identifiable in 15 cases, in particular in 2 of 5 patch, in 3 of 6 plaque and in 10 of 11 nodular lesions. Our findings confirm the association of these herpesvirus-like DNA sequences with KS in unrelated populations, providing evidence of the putative KS-associated agent in all different histologic lesions of the disease, mainly in the nodular stage. The search for other herpesviruses by PCR showed that Epstein-Barr virus (EBV) sequences were present in 7 of 22 pathologic skin lesions. In 4 cases, both EBV and KSHV were present. On the contrary, all 22 classic KS specimens were negative for human herpesvirus-6 sequences. Two of 3 patch and the 1 nodular lesions from AIDS-related KS patients examined were positive for KSHV but negative for both EBV and HHV-6 sequences. Furthermore, we evaluated the prevalence of KSHV sequences in the normal population of the same geographical area. Thirteen peripheral blood mononuclear cell samples, 9 salivary gland tissues and 6 saliva samples from healthy subjects were invariably found negative for KSHV, using the same PCR technique. Of interest, 2 of 11 hyperplastic tonsils harboured these herpesvirus-like sequences, suggesting that, like other herpesviruses, the KS- associated agent may be harboured in a proportion of normal individuals and tonsils may represent at least one of the possible reservoirs of this putative lymphotropic gamma-herpesvirus in vivo.

Antibodies to butyrate-inducible antigens of Kaposi's sarcoma-associated herpesvirus in patients with HIV-1 infection

BACKGROUND

The recent identification in patients with Kaposi's sarcoma of DNA sequences with homology to gammaherpesviruses has led to the hypothesis that a newly identified virus, Kaposi's sarcoma-associated herpeslike virus (KSHV), has a role in the pathogenesis of Kaposi's sarcoma. We developed serologic markers for KSHV infection.

METHODS

KSHV antigens were prepared from a cell line (BC-1) that contains the genomes of both KSHV and the Epstein-Barr virus (EBV). We used immunoblot and immunofluorescence assays to examine serum samples from 102 patients with human immunodeficiency virus type 1 (HIV-1) infection for antibodies to KSHV-associated proteins and to distinguish these antibodies from antibodies to EBV antigens. A positive serologic response was defined by the recognition of an antigenic polypeptide, p40, in n-butyrate-treated BC-1 cells and by the absence of p40 recognition in untreated BC-1 cells or EBV-infected, KSHV-negative cells. The detection by the immunofluorescence assay of 10 to 20 times more antigen-positive cells in n-butyrate-treated BC-1 cells than in untreated cells was considered a positive response.

RESULTS

Antibodies to the p40 antigen expressed by chemically treated BC-1 cells were identified in 32 of 48 HIV-1-infected patients with Kaposi's sarcoma (67 percent), as compared with only 7 of 54 HIV-1-infected patients without Kaposi's sarcoma (13 percent). These results were confirmed by an immunofluorescence assay. The positive predictive value of the serologic tests for Kaposi's sarcoma was 82 percent, and the negative predictive value 75 percent.

CONCLUSIONS

The presence of antibodies to a KSHV antigenic peptide correlates with the presence of Kaposi's sarcoma in a high-risk population and provides further evidence of an etiologic role for KSHV.

Herpesvirus-like DNA sequences and Kaposi's sarcoma: relationship with epidemiology, clinical spectrum, and histologic features

BACKGROUND

The evidence of an infectious agent other than human immunodeficiency virus (HIV) acting as a possible etiologic cause of Kaposi's sarcoma (KS) has received considerable attention in the last years. Recently, DNA sequences from a new herpesvirus (HHV-8) have been observed in several cases of KS. The discovery suggests that this virus may play a role in the pathogenesis of KS. To evaluate these results, we determined the frequency of HHV-8 DNA sequences in 78 specimens of KS according to different epidemiologic origins (sporadic KS: 6, immunosuppressive drug-associated: 11, and AIDS-associated: 61), clinical forms (cutaneous: 69, mucocutaneous: 4 and visceral; 5) and histologic variants (early-patch: 40, late-plaque or nodular: 38).

METHODS

We used the hot start polymerase chain reaction amplification method with KS330 primers specific for HHV-8 DNA. Tumoral or nontumoral skins and visceral specimens free of KS, originating from patients with KS positive for HHV-8 DNA sequences or from immunosuppressed patients without KS, served as controls. Normal skin from healthy HIV seronegative patients was also included.

RESULTS

HHV-8 DNA sequences were found in 3 of the 6 sporadic KS (50%), in 5 of the 11 immunosuppressive drug-associated KS (45%), in 41 of the 61 AIDS-associated KS (67%), in 32 of the 69 cutaneous KS (46%), in 3 of the 4 mucocutaneous KS (75%) in 2 of the 5 systemic KS (40%), in 23 of the 40 early or patchstage KS (58%), in 30 of the 38 late plaque or nodular stages KS (79%). These sequences were also demonstrated in one sample of skin with scabies and in a glomerulonephritis lesion from two immunosuppressed patients with KS who were also positive for herpesvirus-like in their KS lesions. None of the other skin or visceral specimens, originating from healthy, AIDS, or transplanted patients without KS, were positive.

CONCLUSIONS

Our results reinforce the hypothesis that HHV-8 is incriminated in different epidemiologic, clinical and histologic stages of KS and could contribute to the pathogenesis of this tumor. However, the presence of HHV-8 DNA sequences in skin and visceral samples free of KS from KS indicates that the virus is not restricted to the tumor tissue, and thus is able to disseminate in many organs of the target individual. Absence of the virus from healthy, AIDS, or transplanted patients without KS suggests that the viral Sequences either do not spread easily or do not easily maintain themselves in the human population.

High risk of Kaposi's sarcoma and central nervous system lymphoma in the same individuals: a finding related to acquired immunodeficiency syndrome

Kaposi's sarcoma and central nervous system (CNS) lymphoma are the 2 most common malignancies related to HIV infection. To investigate the association between Kaposi's sarcoma and CNS lymphoma, a population-based retrospective cohort study was conducted. Using U.S. Surveillance, Epidemiology and End Results Program data, the gender-specific age- and calendar year-adjusted standardized incidence ratios were calculated for the pre-AIDS (1973-80) and AIDS (1981-1990) eras, as an estimate of the relative risk (RR) of developing one condition following another. For the AIDS era in men, the RR of CNS lymphoma following Kaposi's sarcoma was 979.7 and that of Kaposi's sarcoma following CNS lymphoma was 231.1. There were no instances of the co-occurrence of these malignancies in women in either era or in men for the pre-AIDS era. The extremely high RRs for the co-occurrence of Kaposi's sarcoma and CNA lymphoma in men during the AIDS era suggests that the association of these malignancies occurs within the same HIV-infected individuals.

Lytic growth of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in culture

Kaposi's sarcoma (KS) is the leading neoplasm of AIDS patients, and HIV infection is known to be a major risk factor for its development. However, KS can occur in the absence of HIV infection and the risk of KS development varies widely even among HIV-infected patients, with homosexual men with AIDS being 20 times more likely to develop KS than AIDS-afflicted children or hemophiliacs. These and other data strongly suggest that a sexually transmitted agent or co-factor may be involved in KS pathogenesis. Recently, DNA sequences corresponding to the genome of a novel member of the herpesvirus family have been identified within AIDS-KS biopsies, and several reports indicate that these sequences are also present in all forms of HIV-negative KS. These and other findings suggest this new agent, referred to as KS-associated herpesvirus (KSHV) or human herpesvirus 8 (HHV8), as a candidate for the putative etiologic cofactor. However, the role of this agent in KS remains hotly debated. Further progress in understanding its biology has been severely hampered by the lack of a cell culture system for virus growth. Here we report the development of a system for the lytic growth of this virus in a latently infected B cell line and present the first ultrastructural visualization of the virus. This system will facilitate the detailed study of the molecular biology of viral replication, the testing of antiviral drugs and the development of diagnostic tests for viral infection.

Novel human herpesviruses (human herpesviruses 6, 7 and 8)

The number of members in the family Herpesviridae has increased in the last 10 years due to the description of three novel human herpesviruses: human herpesvirus 6 (HHV-6) in 1986, human herpesvirus 7 (HHV-7) in 1990, and human herpesvirus 8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), in 1994. HHV-6 and HHV-7 were first isolated from blood lymphocyte cultures, while HHV-8 was identified following a specific molecular biology approach in the search for the etiologic agent of Kaposi's sarcoma. The three viruses are lymphotropic, T-cells being the targets of HHV-6 and HHV-7, and B-cells being probably those of HHV-8. The ability to be propagated in cell cultures in vitro differs according to the virus concerned: this can be done readily with HHV-6, with more difficulties in the case of HHV-7, and has not yet been achieved in the case of HHV-8. Human infection with HHV-6 and HHV-7 is ubiquitous, widespread and acquired early in life. HHV-8 epidemiology is still unclear, and there are two hypotheses: a restricted dissemination in the general population like herpes simplex virus type 2, or a widespread infection like all other human herpesviruses. The polymerase chain reaction is the common method for the detection of infection using specific primers and probes for HHV-6, HHV-7 and HHV-8 respectively. Serologic assays are only available for HHV-6 and HHV-7, with limitations being due, in particular, to possible cross-reactions with cytomegalovirus. HHV-6 is the causative agent of exanthem subitum (sixth disease). Its role as an opportunistic agent and immune dysfunction inducer is debated and currently under investigation. The pathogenic role of HHV-7 seems to be modest, with one case of exanthem subitum reported so far. HHV-8 is strongly associated with three diseases: Kaposi's sarcoma, Castleman's disease and body-cavity-based lymphomas. The therapy against these novel viruses has to be considered in the future.

Primary characterization of a herpesvirus agent associated with Kaposi's sarcomae

Detection of novel DNA sequences in Kaposi's sarcoma (KS) and AIDS-related body cavity-based, non-Hodgkin's lymphomas suggests that these neoplasms are caused by a previously unidentified human herpesvirus. We have characterized this agent using a continuously infected B-lymphocyte cell line derived from an AIDS-related lymphoma and a genomic library made from a KS lesion. In this cell line, the agent has a large episomal genome with an electrophoretic mobility similar to that of 270-kb linear DNA markers during clamped homogeneous electric field gel electrophoresis. A 20.7-kb region of the genome has been completely sequenced, and within this region, 17 partial and complete open reading frames are present; all except one have sequence and positional homology to known gammaherpesvirus genes, including the major capsid protein and thymidine kinase genes. Phylogenetic analyses using both single genes and combined gene sets demonstrated that the agent is a gamma-2 herpesvirus (genus Rhadinovirus) and is the first member of this genus known to infect humans. Evidence for transient viral transmission from infected to uninfected cells is presented, but replication-competent virions have not been identified in infected cell lines. Sera from patients with KS have specific antibodies directed against antigens of infected cell lines, and these antibodies are generally absent in sera from patients with AIDS without KS. These studies define the agent as a new human herpesvirus provisionally assigned the descriptive name KS-associated herpesvirus; its formal designation is likely to be human herpesvirus 8.

Molecular approaches to the identification of unculturable infectious agents

New molecular biologic techniques, particularly representational difference analysis, consensus sequence-based polymerase chain reaction, and complementary DNA library screening, have led to the identification of several previously unculturable infectious agents. New agents have been found in tissues from patients with Kaposi's sarcoma, non-A, non-B hepatitis, hantavirus pulmonary syndrome, bacillary angiomatosis, and Whipple's disease by using these techniques without direct culture. The new methods rely on identifying subgenomic fragments from the suspected agent. After a unique nucleic acid fragment belonging to an agent is isolated from diseased tissues, the fragment can be sequenced and used as a probe to identify additional infected tissues or obtain extended portions of the agent's genome. For agents that cannot be cultured by standard techniques, these approaches have proved invaluable for identification and characterization studies. Applying these techniques to other human diseases of suspected infectious etiology may rapidly elucidate novel candidate pathogens.

[Human herpesvirus 8]

Human herpesvirus 8 (HHV-8, KSHV) was discovered in 1994 by means of a molecular biology approach which permitted to characterize fragments of its genomic sequence. The partial analysis of nucleotide sequence showed that HHV-8 was closely related to herpesvirus saimiri and Epstein-Barr virus, two members of Gammaherpesvirinae sub-family. So far, the virus has been neither isolated nor observed using electron microscopy. It is only detected by means of polymerase chain reaction (PCR) and molecular hybridization. HHV-8 detection in human tissues is strongly associated with three diseases: Kaposi's sarcoma, body-cavity-based lymphomas and Castleman's disease. This association raises the question of the causative role of HHV-8 in the occurrence of these three disease.

Kaposi's sarcoma-associated herpesvirus infects endothelial and spindle cells

Kaposi's sarcoma (KS), a vascular tumour that contains characteristic spindle cells forming slit-like spaces, may have an infectious aetiology. Recently, sequences of a new human herpesvirus, KSHV/HHV-8, have been identified in both HIV-associated and classical KS. We sought to identify the target cell of this virus in KS tumour tissue. Using PCR in situ hybridization (PCR-ISH) we show that KSHV/HHV-8 is present in the flat endothelial cells lining vascular spaces of KS lesions as well as in typical KS spindle cells. These findings show that KSHV/HHV-8 is present in the cell types thought to represent neoplastic cells in these lesions.

Detection of Kaposi sarcoma associated herpesvirus in peripheral blood of HIV-infected individuals and progression to Kaposi's sarcoma

Kaposi sarcoma-associated herpesvirus (KSHV) is consistently found in biopsy samples from patients with AIDS-related and "classical" Kaposi's sarcoma (KS). Although highly suggestive of a causal role of KSHV in the pathogenesis of KS, this observation does not exclude the possibility that KSHV, like other herpesviruses, is widely distributed and is a mere "passenger" in these lesions. Here we report that KSHV was detectable in peripheral blood mononuclear cells of 24/46 (52%) of KS patients, but in none of 134 blood donors or 26 HIV-uninfected hospital controls. KSHV detection increased with immunosuppression, as shown by a correlation with a reduced number of CD4-positive T-cells. Moreover, KSHV detection in peripheral blood cells of HIV-infected individuals without KS predicted the subsequent appearance of KS lesions. 143 patients who did not have KS at the time of their first (or only) blood sample were followed up for a median of 30 months. Of the 11 who had been KSHV positive 6 developed KS compared with only 12 out of 132 who were KSHV negative. These findings are compatible with a causative role of KSHV in KS. KSHV was rarely detected in sputum and throat swabs of HIV-infected patients, providing a potential explanation for the apparently limited spread of this virus.