AIDS and endemic Kaposi's sarcoma development : comparison by histopathology, virology (HHV8/KSHV) and cytogenetics

Abstract

Kaposi’s sarcoma (KS) is a highly and abnormally vascularized tumor-like lesion with spindle cells (SC) affecting the skin, lymphnodes and viscera which is found in four different clinico-epidemiological forms as Classic KS (CKS), Iatrogenic KS (IKS), Endemic KS (EKS) and AIDS-associated KS (AKS). All KS forms develop from early stages of patch/plaque to late, nodular tumors and are associated with Kaposi's sarcomaassociated herpesvirus or human herpesvirus-8 (KSHV/ HHV-8). HHV-8 is also associated with primary effusion lymphoma (PEL) and multicentric castleman's disease (MCD). Various studies favour an endothelial origin (CD34+) of the KS SC but whether of vascular (VEC) or lymphatic endothelial cell (LEC) origin has not been settled. The HHV-8 latency-associated nuclear antigen type 1 (LANA-1) protein is the most frequently expressed viral antigen in infected cells. KS is promoted by HIV infection mainly by the angiogenic and proinflammatory effects of HIV-Tat. Whether KS represents a predominantly monoclonal neoplastic cell proliferation or a hyperplastic, reactive polyclonal process is still controversial. Reports on cytogenetic and molecular genetic changes in KS are few indicating that initially KS may develop as a reactive polyclonal cell proliferation associated with chromosome instability, followed by clonal chromosome changes in later stages.

In the present KS histopathological studies (paper I & V) by triple antibody immunofluorescence we observed that: (a) the frequency of LANA+/CD34+ cells increased from early patch to late KS nodular lesions; (b) 30- 40% of the CD34+ SC were LANA- in both early and late KS, suggesting a continuous recruitment of noninfected endothelial cell into the KS lesion; (c) LANA+/CD34- cells were more frequent in early as compared to late KS and most of them expressed LEC markers such as LYVE-1 and D2-40, suggesting that the resident LECs represent an early target of primary HHV-8 infection; (d) LANA+/CD34-/LYVE-1+ cells decreased from early (25%) to late (4%) KS suggesting a phenotype switch from LEC to VEC; (e) the frequency of proliferating cells (Ki67+) was higher in early as compared to late KS stages and no significant difference in cell proliferation was observed between nodular AKS and EKS, suggesting that the growth of the usually more aggressive AKS tumors may reflect a higher rate of SC progenitor recruitment as compared to the slower growing EKS lesions, consistent with the observed increase in non-proliferative SC during KS (AKS) evolution to nodular stage; (f) infiltrating lymphocytes were LANA negative, whereas some CD68+ monocyte-macrophase appeared to be LANA+.

To validate our results from LANA immunostaining, we established and optimized a semi-quantitative PCR assay for HHV-8 detection in formalin-fixed paraffin-embedded KS biopsies (paper III) and two different protocols for DNA extraction were compared namely the Chelex 100 and Qia-gene kit method. Our result indicate a better performance for Chelex-extracted DNA in paraffin embedded archival biopsies. In late, nodular stage of both AKS and EKS the virus load per unit tissue actin (HHV-8/actin) is higher than in early stages (patch/plaque), which corroborates our findings from double immunostaining for LANA and CD34 of the same cases. Thus these PCR results by serial dilutions of HHV-8 DNA show a correlation between virus load and progressive stages of KS development i.e. the increase in LANA+ SC and does not indicate an increase in viral content of individual tumor cells.

With quantitative real time PCR on sera (paper II), we found higher HHV8 DNA load in AKS compared to EKS, patch compared to nodular KS and males compared to females as well as a significantly higher serum viral DNA load in KS compared to non-KS patients’ sera.

AKS patient sera studied by ELISA for HIV-Tat antibodies showed that patients with high HHV8-DNA level had no or low levels of anti-Tat antibodies while patients with very low HHV8-DNA levels had several fold higher anti-Tat IgG titers. Analysis of these KS sera for epitope specificity showed reactivity to various Tat epitopes but not to the transcriptional (functional) epitopes 46-60 (TAR-binding region). To determine cytogenetic changes during the development of KS as well as possible differences between AKS and EKS we studied 27 KS (10 nodular AKS, 8 patch AKS, 8 nodular EKS and 1 patch EKS) cases by laser microdissection, global amplification of DNA and comparative genomic hybridization (paper IV). Deletion of Chromosome Y was detected in 20 of 23 male KS and was the only chromosomal deletion observed in early (patch) KS biopsies. Late AKS and EKS apart from random aberrations also showed recurrent chromosomal deletions of chromosome 16, 17, Y and a gain of chromosome 21. The deletion of chromosome 16 and Y was confirmed by interphase FISH on paraffin embedded sections. EKS had higher number of chromosomal abnormalities than AKS.

In summary KS SC apparently represents a mixed pool endothelial cells including cells from both VEC and LEC the later being a possible early target for HHV-8 infection. Non-infected CD34+ progenitor cells appears to be continuously recruited to the developing KS lesion and locally infected during the development of KS. Serum HHV-8 DNA load is higher in AKS compared to EKS and HIV-Tat titers were inversely correlated to HHV-8 DNA load in AKS patients. Increased number of recurrent and sporadic chromosomal abnormalities found mostly in a subset of late nodular KS cases may indicate the onset of a clonal cell population (sarcoma).