The Kaposi Sarcoma herpesvirus (KSHV) causes Kaposi sarcoma (KS), primary effusion lymphoma, a lymphoproliferative disease (KSHV-multicentric Castleman's disease), and a cytokine inflammatory syndrome (KICS). These diseases occur more frequently, though not exclusively, among people living with HIV or other types of immune dysregulation. While limited KS can regress with immune reconstitution, such as through antiretroviral therapy (ART) in people living with HIV, there are currently no curative treatments for advanced KS. Preventive or therapeutic vaccines targeting KSHV could have a significant clinical impact; however, the development and testing of such strategies have been limited by the lack of preclinical models that faithfully recapitulate KS, including the presence of infected spindle cells and a relevant immune microenvironment. HIV/AIDS is an important cofactor for KS, and globally, the majority of individuals with KS are HIV-infected. Current evidence indicates that HIV-1 may enable KS progression through immunosuppression and promote pathogenesis by inducing inflammatory cytokines and producing secreted regulatory proteins like Tat and Nef. The design and testing of new therapeutic approaches based on pathogenesis are hampered by the lack of models that replicate KSHV oncogenesis in the context of HIV/AIDS. In the present study, we demonstrate that KSHV-infected cells can form tumors in an immunocompetent mouse model after in vivo passage in nude mice and EcoHIV infection and/or morphine treatment, both of which have immunomodulatory and pro-inflammatory effects. These tumors exhibit gene expression profiles and immune microenvironments that closely resemble those observed in human KS lesions. This novel KSHV tumor model in immunocompetent mice provides a valuable platform to test immunotherapeutic strategies for KS, including immunomodulatory agents, targeted antibody therapies, checkpoint inhibitors, and vaccines.

ABSTRACT Kaposi sarcoma-associated herpesvirus (KSHV), an oncogenic virus associated with several malignancies, including Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease, harbors a DNA replication helicase encoded by ORF44 that is crucial for viral replication and pathogenesis. In this study, we identified the host PFN1 (profilin 1), a well-known actin-binding factor, as an inhibitor of KSHV lytic replication functioning via the macroautophagy/autophagy-lysosomal degradation pathway targeting ORF44. Mechanistic analyses revealed that PFN1 interacts with ORF44, leading to enhanced polyubiquitination of PFN1. Notably, the E3 ubiquitin ligase TRIM37 (tripartite motif containing 37) facilitates the polyubiquitination of lysine residues at position 116 of PFN1, which serves as a critical recognition motif for the cargo receptor SQSTM1/p62 (sequestosome 1), which is pivotal for the subsequent autophagic degradation of ORF44. Overall, our findings revealed a previously uncharacterized antiviral function of PFN1, highlighting its potential as a novel therapeutic avenue for the treatment of KSHV-associated malignancies. Abbreviations: ALS: amyotrophic lateral sclerosis; Baf A1: bafilomycin A1; co-IP: co-immunoprecipitation; KSHV: Kaposi sarcoma-associated herpes virus; LIR: LC3-interacting region; PFN1: profilin 1; SQSTM1/p62: sequestosome 1; TRIM37: tripartite motif containing 37; UBA: ubiquitin-associated domain.

Kaposi’s sarcoma-associated herpesvirus (KSHV) is the etiologic agent of several human cancers, including Kaposi’s sarcoma (KS) and primary effusion lymphoma (PEL), both of which still lack effective treatment options. Members of the bromodomain and extra-terminal domain (BET) family, especially bromodomain-containing protein 4 (BRD4), play important roles in RNA polymerase II–mediated transcriptional regulation and are required for the expression of many tumor-driving oncogenes in various cancer cells. Therefore, BET proteins have become attractive targets for anticancer drug development. Previous studies have demonstrated the high sensitivity of PEL cells to BET inhibitors, and BRD4 silencing effectively blocks tumor cell proliferation. In contrast, KSHV-infected immortalized endothelial cells display strong resistance to BET inhibitors, including (+)-JQ1. To further develop BRD-targeted therapies for KSHV-infected immortalized endothelial cells, we identified MZ-1 and SIM-1, two BRD4 PROTAC degraders, as effective inhibitors of cell growth in these cells. Mechanistically, these inhibitory effects depend on suppression of LANA translation through increased eIF2α phosphorylation in KSHV-infected cells. Similar LANA suppression was also observed following RNAi-mediated silencing of BRD2 or BRD4. Proteomic analysis identified unique protein candidates altered in MZ-1- and SIM-1-treated KSHV-infected immortalized endothelial cells compared with (+)-JQ1-treated cells. In summary, our study develops an effective strategy against KSHV-infected immortalized endothelial cells using selective BRD PROTACs, which may help improve therapeutic outcomes for KSHV-related malignancies in the future.

Elotuzumab enhances the anti-tumor activity of Vγ9Vδ2T cells against primary effusion lymphoma.

The oncogenic γ-herpesvirus known as the Kaposi's sarcoma-associated herpesvirus (KSHV) is a principal causative agent of several cancers arising in patients with compromised immune systems. One of KSHV-related malignancies, primary effusion lymphoma (PEL), comprises transformed B cells harboring the viral episome and arises preferentially within the pleural or peritoneal cavities of patients including those with HIV infection. PEL is a rapidly progressing malignancy with a median survival time of several months even with conventional chemotherapy. One of the major reasons causing PEL chemotherapy failure is multidrug chemoresistance of lymphoma cells, however, there are only limited data exploring the mechanisms of PEL chemoresistance. In the current study, we demonstrate the role of hyaluronan (HA) signaling activation in rapamycin resistance in PEL cells, and that targeting HA signaling by small HA oligosaccharides (oHA) can augment rapamycin efficacy against PEL expansion in vivo. Our results provide the framework for the development of HA-targeted therapies clinical trials for PEL patients, which may represent promising adjuncts to reduce chemotherapy toxicity, improve treatment and prolong patients' survival.

Human herpesvirus 8 (HHV-8) is the etiologic agent of Kaposi’s sarcoma (KS), primary effusion lymphoma (PEL), multicentric Castleman disease (MCD), and KS-associated immune reconstitution inflammatory syndrome (IRIS-KS). Quantifying HHV-8 DNA in whole blood is clinically relevant, yet laboratory practices remain heterogeneous. Here, we developed and validated an in-house quantitative PCR (qPCR) assay targeting ORF26, optimized for whole blood. Assay calibration used plasmid, BCBL-1 cell–derived, and commercial HHV-8 DNA standards. Analytical validation was performed following the Clinical and Laboratory Standards Institute (CLSI) guidelines and the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines and showed a 95% limit of detection of 65.7 copies/reaction, efficiencies of 90–101% (R2 > 0.99), and intra/inter-assay coefficients of variation < 6.5%. Strong correlations were observed among the three calibrators (R2 > 0.97).Clinical validation against a composite reference yielded 100% sensitivity, specificity, PPV, and NPV. Viral loads (log10 copies/mL) varied by clinical condition: classic KS and transplant-associated KS showed the lowest medians (2.30–2.23), MCD HIV− and PEL intermediate values (2.83–3.72), and epidemic KS, MCD HIV+, and IRIS-KS the highest (4.12, 4.86, and 5.03, respectively). Viremia > 5 log10 copies/mL was associated with uncontrolled E-KS, MCD HIV+, and IRIS-KS. Longitudinal follow-up revealed viral load decline paralleled clinical improvement. This validated assay provides a robust, affordable tool for HHV-8 quantification in whole blood and supports its integration into diagnostic workflows and patient monitoring.

Plasmablastic lymphoma (PBL) is a rare CD20-negative aggressive lymphoma with poor prognosis when treated with standard treatment options. Although PBL is associated with HIV infection and other immunosuppressed states, it can also affect immunocompetent individuals. The diagnosis of PBL requires a high clinical suspicion and pathological confirmation. EBV-encoded RNA (EBER) expression and MYC gene rearrangements are frequently detected in the malignant cells. The differential diagnosis includes EBV+ diffuse large B-cell lymphoma (DLBCL), extracavitary primary effusion lymphoma, ALK+ DLBCL, and HHV8+ large B-cell lymphoma, among others. Age ≥ 60 years, advanced clinical stage, and high International Prognostic Index scores are associated with worse survival. Combination chemotherapy regimens, such as infusional EPOCH, are recommended. The addition of bortezomib or daratumumab might improve outcomes. B-cell maturation antigen-targeted therapies have shown early efficacy. The participation of patients with PBL in prospective clinical trials is warranted.

AimsPrimary effusion lymphoma (PEL) is an aggressive, human herpesvirus 8 (HHV8)-associated large B-cell lymphoma characterised by malignant effusions in serous cavities (classic PEL). However, a subset of tumours may present exclusively as solid masses, referred to as extracavitary primary effusion lymphoma (EC-PEL). Despite the high regional prevalence of human immunodeficiency virus (HIV) and Kaposi sarcoma-associated virus /HHV8, PEL is likely under-reported in Sub-Saharan Africa. This study reports on the clinicopathologic features and differential diagnoses of EC-PEL.MethodsA retrospective review of biopsies with a diagnosis of PEL from 2010 to 2019 was performed. Seven patients met the 2024 WHO criteria for PEL. Clinical information was collected and histopathological and immunohistochemical features were reviewed independently.ResultsSeven patients with a median age of 38 years (range, 25-51 years) were identified. Most patients were men (86%), and all were Black African. Five patients (71%) were living with HIV, with CD4 + counts ranging from 137 to 348 cells/µL. Tumour sites were lymph nodes, stomach, maxillary sinus, and soft tissue. All tumours showed diffuse sheets of plasmablastic or immunoblastic cells. Immunohistochemistry showed expression of plasma-cell markers (VS38C, CD138), lacked pan B-cell markers (CD20 and PAX5), and had high proliferative indices (Ki-67: 90-95%). All tumours were positive for HHV8 (LANA-1) and EBER in situ hybridisation was positive in 86%.ConclusionExtracavitary PEL in Sub-Saharan Africa exhibits the characteristic clinicopathologic profile described globally and remains strongly associated with HIV-related immunosuppression. Improved recognition of this rare but aggressive lymphoma can be achieved with increased awareness of the diagnosis and improved access to HHV8 immunohistochemistry.

Long interspersed nuclear element-1 (LINE-1/L1) retrotransposons are expressed in various human cancers. Kaposi’s sarcoma-associated herpesvirus (KSHV) is the etiologic agent of Kaposi’s Sarcoma (KS) and Primary Effusion Lymphoma (PEL), which are characterized by global transcriptional reprogramming. Previously, we have found upregulation of L1 in PEL. Here, we show that knockdown of L1 in PEL cells significantly impaired their proliferation and induced broad transcriptional changes encompassing DNA replication, mitotic progression, and genome maintenance pathways. Analysis of KSHV-infected mouse and human mesenchymal stem cell models revealed that the KS-mimicking microenvironment robustly upregulates L1 expression, with sustained expression observed in KSHV-induced tumor cells even after the loss of the viral episome. Reanalysis of RNA-seq data from KS patient biopsies further showed elevated L1 expression in both endemic and AIDS-associated epidemic KS, with partial reduction following antiretroviral therapy. L1 ORF1p protein expression was confirmed by immunohistochemistry in KS tissues. Reanalysis of the enzymes that can modulate DNA methylation, a process that regulates L1 expression, revealed upregulation of DNMT3A and TET2 in both mouse KSHV tumor models and human KS. Altogether, our findings establish the L1 activation as a hallmark of KSHV-driven oncogenesis.

β-catenin: A crucial transcriptional activator of KSHV latency genes and small molecule target in primary effusion lymphoma.

Kaposi's sarcoma-associated herpesvirus (KSHV), also named HHV-8, is the etiological agent of Kaposi sarcoma (KS), Primary effusion lymphoma (PEL), and Multicentric Castleman's disease. After de novo infection, KSHV genomes rapidly circularize and acquire a chromatin state that favors latency. During latency, the KSHV episome is decorated with distinct epigenetic marks that segregate the viral genome into transcriptionally active and repressed domains, enabling persistent silencing of lytic genes while retaining the capacity for reactivation. Transcription activity of chromatin is regulated at multiple levels, including the incorporation of histone variants such as H3.3, by a specific set of histone chaperones such as HIRA and DAXX. The interaction between LANA and these interphase active chaperones suggests that H3.3 deposition is a critical driver of early chromatinization and the long-term stability of KSHV latency. We detected rapid H3.3 deposition on KSHV episomes and on episomes within long-term infected cells. Moreover, we demonstrated that genetically disrupting the host H3.3 chaperone HIRA pathway by CRISPR/Cas9-mediated knockout impacted the regulation of LANA and maintenance of viral latency that was not altered in DAXX knockout cells. Collectively, these results support a role for HIRA-mediated H3.3 deposition in the regulation of KSHV latency.

26-CCC-14869-ACC PRIMARY EFFUSION LYMPHOMA DIAGNOSED VIA PERICARDIAL WINDOW

26-CCC-19263-ACC PERICARDIAL PRIMARY EFFUSION LYMPHOMA PRESENTING AS ACUTE CORONARY SYNDROME WITH IMMEDIATE STENT THROMBOSIS AND MALIGNANT VENTRICULAR TACHYCARDIA

Kaposi’s sarcoma-associated herpesvirus (KSHV) encodes multiple short and long noncoding RNAs which contribute to viral latency, persistence, host gene regulation, and immune evasion. The Antisense-to-Latency Transcript (ALT) is a ~ 10 kb long noncoding RNA (lncRNA) located on the opposite strand of the major latency-associated region encoding the latency associated nuclear antigen, vCyclin, vFLIP, the Kaposin’s and 12 microRNA genes. ALT is a nuclear lncRNA that is lowly expressed during latency, but strongly upregulated during lytic replication. Using RNA antisense purification and quantitative mass spectrometry (RAP-MS) in lytically induced primary effusion lymphoma cells, we identified 51 human and 3 viral proteins that directly interact with ALT. Of these enriched proteins, 48 are splicing factors, including core and alternative splicing proteins, such as U2AF2, PTBP1/2, SRSF1/3 and MBNL1. Interaction and co-localization of ALT was confirmed with various splicing factors in ribonucleoprotein complexes. We further identified that induction of lytic replication in lymphoid and epithelial cells leads to thousands of host gene splicing changes, which are partially restored upon perturbation of ALT expression. Finally, transient knockdown of ALT strongly inhibits viral reactivation and virion production. Hence, by splicing factors interactions, ALT interferes with host gene expression. Our results uncover a novel mechanism that shifts gene expression from the host to the virus late during the viral replication cycle to efficiently produce progeny virus and potentially antagonize host immune defenses.

Kaposi sarcoma-associated herpesvirus (KSHV) causes several diseases among people with HIV (PWH), including Kaposi sarcoma (KS), multicentric Castleman disease (MCD), primary effusion lymphoma (PEL), and KSHV inflammatory cytokine syndrome (KICS), known as KSHV-associated diseases (KAD). Genetic diversity in the viral K1 gene defines KSHV subtypes, but clinical significance remains unclear. We conducted a retrospective study of 143 PWH with KAD treated between 2004-2024. KSHV-DNA was extracted from various clinical samples and sequenced using next-generation and Sanger methods. Phylogenetic analysis was performed to classify K1 subtypes; associations with KAD presentation and survival were assessed. Among 143 patients, 40% had KS alone, 12% had MCD and KS, 17% had KICS and KS and 31% had PEL+/-MCD+/-KS. Subtype A was the most prevalent (46%), followed by C (27%); subtypes did not vary by KAD presentations. Patients with concurrent KAD had worse survival than those with KS alone, irrespective of KSHV subtype. Twenty-one patients with PEL and subtype A had poorer survival outcomes as compared with PEL with other subtypes (median overall survival 1.6 vs. 7.2 years, p=0.0041). Apart from a trend towards lower albumin levels, there were no other differences in clinical characteristics in patients with PEL and Subtype A vs other subtypes. Overall, K1 subtypes did not vary by KAD diagnosis and did not impact survival. Individuals with PEL had poorer outcomes, and subtype A in PEL was associated with worse survival. Further studies are required to investigate the functional impact of KSHV genetic variation on disease pathogenesis.

Kaposi's Sarcoma-associated herpesvirus (KSHV) has been etiologically linked to several human cancers, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). However, recent studies suggest that KSHV infection may also be associated with the development of other diseases or increased risks, such as KSHV inflammatory cytokine syndrome (KICS), diabetes, malaria, heart disease, and other cancers. In this review, we summarize these findings from clinical observations, epidemiological studies or laboratory research, though more studies are needed in these emerging areas. We believe that this work will enhance our understanding of the molecular mechanisms underlying KSHV pathogenesis and contribute to improving treatments for related human diseases.

Kaposi sarcoma (KS) is an angioproliferative tumor caused by Kaposi sarcoma herpesvirus (KSHV) that occurs in people with HIV. Concurrent KSHV-associated diseases (KAD), including multicentric Castleman disease, primary effusion lymphoma, and KSHV-associated inflammatory cytokine syndrome may modify KS biology and impact clinical outcomes. Transcriptomic profiling of archival KS tissue enables investigation of molecular heterogeneity associated with these overlapping disease states. Archival formalin-fixed paraffin-embedded (FFPE) KS skin biopsies from 42 patients with HIV-associated KS between 2017 and 2022 were analyzed based on confirmed histopathologic diagnosis, tissue adequacy for RNA profiling, and availability of linked clinical data. Bulk transcriptomic analyses were conducted using Nanostring nCounter PanCancer ImmunoOncology panel supplemented with KSHV-specific probes. Spatial RNA profiling was performed on four tissues from participants with KS and concurrent KAD (KS+KAD) using GeoMx digital spatial profiling (DSP) platform. Regions of interest were selected using LANA-1, CD45 and CD31 staining to characterize tumor (LANA-1+, CD31+), vessel (LANA-1-negative, CD31+) and immune cells (CD45+) areas. For bulk transcriptomic analyses and spatial transcriptomic analyses, p-values were adjusted for multiple comparisons using the Benjamin-Hochberg FDR approach, and adjusted p-values (padj) are reported. KS samples were obtained from 42 men with HIV (median age 40 years). Median HIV viral load of 27 copies/mL and median CD4+ T-cell count was 211 cells/µL. Forty-eight percent had KS alone and 52% had KS+KAD. Patients with KS+KAD had worse survival compared to those with KS alone. Transcriptomic analyses identified increased expression of STC1 (log2FC = 2.02, padj = 0.001), a secreted glycoprotein, and MKI67 (log2FC = 1.11, padj = 0.02), a common proliferation marker, in KS+KAD lesions, along with lower expression of cytokine-associated pathways. Spatial RNA profiling from 4 KS samples from patients with KS+KAD identified increased abundance of lymphatic endothelial cells, elevated LYVE1 expression in LANA-1+ tumor areas as compared to LANA-negative areas. Bulk and spatial transcriptomic profiling of archival HIV-associated KS lesions revealed disease-specific molecular programs associated with concurrent KAD that altered tumor and microenvironment features. These findings demonstrate the heterogeneity of HIV-associated KS lesions that may guide future studies on KS pathogenesis and potential therapeutic targets.

Kaposi sarcoma-associated herpesvirus (KSHV) infection is the cause of Kaposi sarcoma (KS), certain lymphoproliferative disorders, and the inflammatory condition Kaposi sarcoma-associated herpesvirus inflammatory cytokine syndrome (KICS). In solid organ transplant recipients, KSHV-related complications can result from reactivation of latent infection, new posttransplant infection, or transmission of virus from the transplanted organ. However, testing of donors and recipients is not routinely performed. During January 2021-September 2025, after transplantation of 185 organs into 153 recipients, 46 deceased donors were identified whose transplanted organs were suspected of having transmitted KSHV, approximately five times the number of such donors (nine) reported during 2016-2020. As of February 2026, a posttransplantation KSHV infection has been identified among 74 (48%) of these 153 transplant recipients. Among the 74 recipients with KSHV infection, 45 (61%) developed KS; 10 (14%) of these recipients with KS also developed a lymphoproliferative disorder (multicentric Castleman disease [eight], posttransplant lymphoproliferative disorder [one], and primary effusion lymphoma [one]) and six (8%) developed KICS; four (5%) recipients developed a lymphoproliferative disorder alone (primary effusion lymphoma [one] and posttransplant lymphoproliferative disorder [three]); and one (1%) developed KICS alone. To date, 25 (16%) of the 153 transplant recipients have died. Most donors and recipients were HIV-negative, and nonmedical drug use was common among donors. Clinicians should maintain a high index of suspicion for KSHV in transplant recipients, particularly when donors have risk factors including nonmedical drug use, or when another recipient from the same donor is found to be infected. Development and implementation of effective testing strategies and timely reporting could guide clinical management, reduce risk for KSHV-related complications, and improve transplant safety.

PEL is an aggressive B-cell lymphoma that in the majority of cells harbors latent KSHV, although appropriate stimuli can induce viral replication. These include HDAC inhibitors such as butyrate, activation of endoplasmic reticulum (ER)/UPR stress, and exogenous administration of ceramide 18. These treatments reduce cell survival, but also activate adaptive branches of the UPR such as the Ire1α-XBP1s axis and/or trigger macroautophagy to counteract cell death, processes whose output may be manipulated by KSHV. HSPs are also upregulated by several cytotoxic treatments and support both cell survival and KSHV replication, suggesting a complex relationship between cell and viral fate. In this study, we demonstrate that HSP27 inhibition reduces PEL cell survival, activates ER stress including XBP1s, and upregulates CerS1, the enzyme that synthesizes ceramide 18. We further discovered a crosstalk between XBP1s and CerS1 that enhances protection against ER stress during HSP27 inhibition also promoting DRP1-dependent pro-survival mitophagy and triggers KSHV reactivation from latency. In conclusion this study suggests that HSP27 plays a previously unrecognized central role in controlling the UPR, CerS1 and mitochondrial autophagy, influencing both cell survival and KSHV lytic cycle in PEL cells.

Summary/Histone methylation is a dynamic and reversible epigenetic modification that critically controls the progression of human diseases, including infections and cancers. Here we reported that histone lysine demethylases (KDMs) in the KDM5 family KDM5A/B play profound roles in suppressing lytic reactivation of oncogenic human herpesvirus 8 (HHV-8), i.e., Kaposi’s sarcoma-associated herpesvirus (KSHV), as well as antiviral/antitumor innate immune responses in KSHV-infected B-cell lymphomas. We showed that KSHV lytic replication decreases KDM5A/B protein stability by enhancing their K-48 linked polyubiquitination while KDM5A/B depletion facilitates KSHV lytic reactivation. Mechanistic studies illustrated that KDM5A/B associate with KSHV LANA protein and dampen its chromatin association at both KSHV viral lytic promoter and promoters of antitumor immune-responsive genes (IRGs). In comparisons to normal B cells, KDM5A/B expression significantly increased in B-cell lymphoma cells, including KSHV-positive primary effusion lymphoma (PEL). We demonstrated that KDM5A/B inhibition remarkably induces both KSHV lytic reactivation and innate immune responses in PEL cells, resulting in a strong viral oncolytic effect, both in vitro in cell cultures and in vivo using a PEL xenograft mouse model. Overall, our studies identified the novel functions of KDM5A/B to silence KSHV lytic replication and antiviral/antitumor innate immune responses, which can be blocked to benefit the treatment of KSHV-associated B-cell lymphomas that are usually aggressive and difficult to treat.