First the B cells fall, then the T cells follow: temporal immunological shift with ocrelizumab in multiple sclerosis

Background: Ocrelizumab (OCR) is a humanized anti-CD20 monoclonal antibody approved for multiple sclerosis (MS). While its efficacy has been attributed to early and sustained B cell depletion, emerging evidence suggests a broader immunomodulatory profile. Objectives: To investigate temporal dynamics of OCR-induced immune modulation in MS by analyzing pathway enrichment score changes in transcriptomic data from peripheral blood mononuclear cells (PBMCs) at early (2 weeks) and late (6 months) timepoints following treatment initiation. Methods: We analyzed publicly available microarray data (GSE228330) from PBMCs of 15 MS patients treated with OCR. Immune cell subpopulations were estimated using CIBERSORTx with the LM22 signature matrix. Gene Set Variation Analysis (GSVA) was applied to quantify immune-related pathway enrichment across three timepoints—baseline, 2 weeks, and 6 months. Results: Early effects were characterized by selective suppression of B cell-related pathways, including antigen presentation via MHC-II, B cell proliferation, and survival. These changes were accompanied by compensatory upregulation of anti-inflammatory and innate immune signaling (e.g., IL-10, monocyte chemotaxis). At 6 months, B cell pathway suppression persisted and deepened, while T cell-specific pathways (e.g., CD4+ T-cell activation and cytokine production) showed significant downregulation, indicating a delayed but substantial impact on adaptive cellular immunity. At 6 months, T reg compartment was reconfigured, with overall T reg transcription enhanced versus T effector cells, quiescent and thymic‑mature signatures reduced, and IL‑4-induced T reg program enriched. Conclusions: OCR exerts a biphasic immunomodulatory effect, with rapid direct suppression of B cell pathways followed by delayed indirect modulation of T cell-mediated immunity.