Characteristics of Circulating KSHV-Infected Cells during Active KSHV+ Multicentric Castleman Disease

Background: Kaposi Sarcoma-associated herpesvirus/ Human Herpesvirus 8 (KSHV/HHV8)-associated multicentric Castleman disease (KSHV+ MCD) is a polyclonal B-cell lymphoproliferative disorder mainly occurring in immunocompromised hosts. The diagnosis relies on lymph node biopsy demonstrating KSHV-infected cells located in the mantle zone with a marked interfollicular plasma-cell infiltration. Infected cells are large cells positive for IgM, λ light chain, and CD38, and described as infected "plasmablasts".

Methods: 18 patients with KSHV+ MCD flares and 40 controls were included (19 patients with a history of KSHV infection and 21 KSHV-negative controls). PBMCs were analyzed using multiparametric extracellular and intracellular flow cytometry. Expression of lytic and latent KSHV transcripts was assessed on PBMCs using flow-fluorescence in situ hybridization (Flow-FISH) detecting Latent Nuclear Antigen (LNA) and viral Interleukin-6 (vIL-6) RNAs.

Results: We showed that IgM+λ+CD38high cells observed in KSHV+MCD lymph nodes were also detectable in the peripheral blood of 14/18 (78%) patients with active KSHV+ MCD and were absent from 40 controls (panel A and B). We used this opportunity to better characterize the phenotype of these cells.

Using flow-FISH, we demonstrated that these cells were all KSHV-infected and expressed both latent (LNA) and lytic (v-IL6) KSHV transcripts.

These KSHV-infected cells harbored a distinct phenotype when compared to conventional plasmablasts (panel B). We also identified several putative mechanisms of KSHV immune escape, as KSHV-infected cells displayed an overall decrease of surface co-stimulatory molecules (with a marked reduced expression of surface CD40) and were IL-10 producing cells, establishing a tolerogenic environment.

Conclusion: The identification of a singular KSHV-infected circulating population paves the way for a new approach to the study of KSHV+ MCD pathophysiology.

Galicier:EusaPharma: Consultancy, Honoraria, Other: Presentations, manuscript writing, educational events, Speakers Bureau; Lilly: Honoraria, Other: Presentations, manuscript writing, educational events, Speakers Bureau; Sanofi: Honoraria, Other: Presentations, manuscript writing, educational events, Speakers Bureau; Amgen: Honoraria, Other: Presentations, manuscript writing, educational events, Speakers Bureau; Novartis: Other: Support for meetings and/or travel; Janssen: Other: Support for meetings and/or travel; Cillag: Other: Support for meetings and/or travel. Oksenhendler:EusaPharma: Consultancy; CSL Behring: Consultancy.