PERIPHERAL IMMUNE CELL RESPONSES TO TOCILIZUMAB TREATMENT IN PLASMA CELL-TYPE CASTLEMAN DISEASE WITH RENAL INVOLVEMENT USING SINGLE-CELL RNA SEQUENCING

Plasma cell-type Castleman disease (PCD) is a rare lymphoproliferative disorder characterized by IL-6 overproduction, systemic inflammation, and potential renal involvement. Tocilizumab, an IL-6 receptor antagonist, effectively improves clinical symptoms, but molecular mechanisms underlying therapeutic responses remain unclear. We performed single-cell RNA sequencing (scRNA-seq) of peripheral blood mononuclear cells (PBMCs) to elucidate immune cell gene expression changes following tocilizumab treatment in PCD with renal involvement.

A 61-year-old male with PCD, proven by lymph node biopsy showing characteristic plasmacytic histology, presented with anemia, proteinuria, and chronic kidney disease and was treated with tocilizumab (8mg/kg every 2 weeks). The pre-treatment blood IL-6 level was 36.4 pg/mL. Renal biopsy before treatment revealed glomerulosclerosis, mesangial matrix expansion and mesangial cell proliferation as the predominant findings. The interstitium showed prominent infiltration of plasma cells and lymphocytes forming tertiary lymphoid-like structures without evidence of amyloid deposition. Additional findings included hyaline arteriolosclerosis and polar vasculosis. Ultrasound examination revealed no evidence of cardiac dysfunction or carotid artery plaques. PBMCs were collected from the patient before treatment and 3 weeks post-treatment, as well as from two healthy controls. All samples underwent scRNA-seq analysis using 10x Genomics platform. Clinical parameters were monitored during the follow-up period.

Tocilizumab treatment resulted in dramatic clinical improvement: hemoglobin rose from 8.7 to 10.4 g/dL, serum albumin improved from 1.9 to 2.5 g/dL, proteinuria declined from 1.76 to 0.73 g/gCr, and creatinine modestly recovered from 1.66 to 1.58 mg/dL. HIF-PH inhibitor and anti-hypertensive agents were discontinued. scRNA-seq analysis of 30,741 cells identified T/NK cells, B cells, and monocytes, with 2,450–3,023 genes detected per sample. At baseline, the patient exhibited reduced proportions of naïve B cells and non-classical monocytes, alongside elevated frequencies of Tfh, Treg, Th17, and exhausted CD8+ T cells compared with healthy controls. After tocilizumab, naïve B cells and non-classical monocytes were restored, whereas exhausted CD8+ T cells further accumulated. Differential expression genes are abundant in monocytes and NK/T cells. Enrichment analysis revealed that, at baseline, interferon response genes were suppressed while hypoxia and IL-6 signaling genes were upregulated in both monocytes and NK/T cells. Post-treatment, monocytes showed reactivation of interferon response and attenuation of hypoxia and inflammatory response; NK/T cells displayed diminished hypoxia, IL-6, and TNF-α signaling.

This study demonstrates remarkable clinical improvement in PCD-associated renal involvement following tocilizumab treatment, with concurrent improvements in urinary biomarkers of tubular injury and glomerular function. The presence of tertiary lymphoid structures in renal interstitium may contribute to local inflammatory responses that respond to IL-6 blockade. scRNA-seq analysis provides molecular insights into tocilizumab's therapeutic mechanisms, potentially identifying predictive biomarkers for treatment response in PCD with renal complications.