The lymph node transcriptome of unicentric and idiopathic multicentric Castleman disease

Castleman disease is polyclonal lymphoproliferative disorder characterized by unicentric or multicentric lymphadenopathy with characteristic histomorphologic features, in addition to variable inflammatory symptomatology. The molecular mechanisms and etiologies of unicentric Castleman disease (UCD) and idiopathic multicentric Castleman disease (iMCD) are poorly understood, and identification of targetable disease mediators remains an unmet clinical need. We performed whole exome sequencing on lymph node biopsies from patients with UCD and iMCD; and compared the transcriptomic profile to that of benign control lymph nodes. We identified significantly upregulated genes in UCD (443), iMCD (316) or both disease subtypes (51); in addition to downregulated genes in UCD (321), iMCD (105) or both (10). The transcriptomes of UCD and iMCD showed enrichment and upregulation of elements of the complement cascade. By immunohistochemistry, C4d deposits indicative of complement activation were present in UCD and iMCD mostly within abnormally regressed germinal centers, but also in association with plasma cell clusters, endothelial cells and stroma cells proliferations. Other enriched gene sets included collagen organization, S1P3 pathway and VEGFR pathway in UCD; and humoral response, oxidative phosphorylation and proteosome in iMCD. Analysis of cytokine transcripts showed upregulation of CXCL13 but not IL-6 in UCD and iMCD. Among angiogenic mediators, the VEGFR1 ligand placental growth factor (PGF) was upregulated in both disease subtypes. We hereby report for the first time the whole lymph node transcriptome of UCD and iMCD, underscoring findings that could aid in the discovery of targetable disease mediators. Whole exome sequecing was performed on 24 fresh frozen lymph node samples from 22 patients with uncentric Castleman disease; 7 lymph nodes and 1 spleen sample from 8 patients with idiopathic multicentric Castleman disease; and 19 control lymph node samples consistent with unremarkable lymph node tissue.