Itolizumab targets the CD6-ALCAM axis to limit T-cell responses and brain barrier diapedesis in multiple sclerosis

Genetic and preclinical data highlight CD6 as a promising target for multiple sclerosis (MS), yet the impact of clinically available CD6-targeting treatments on MS immunopathogenesis remains insufficiently defined. Itolizumab, a humanized anti-CD6 antibody with established safety and clinical efficacy in other autoimmune disorders, represents a potential candidate to interrogate this pathway in MS.

CD6 expression was quantified by flow cytometry on circulating lymphocytes from MS patients and healthy donors. Functional consequences of CD6 blockade using itolizumab were evaluated using human in vitro models of brain barriers, including T cell diapedesis, barrier integrity, and inflammatory responses. T cell co-cultures with an oligodendrocyte cell line were performed to reveal the impact on survival and differentiation.

Circulating lymphocytes from MS patients displayed increased CD6 levels, associated with heightened activation and proliferation features in CD4⁺ memory T cells. In brain barrier assays, migrated T cells exhibited higher CD6 expression than non-migrated cells. CD6 blockade with itolizumab selectively reduced memory and cytotoxic T cell diapedesis across hCMEC/D3 monolayers, while maintaining naïve and regulatory T cell migration, by disrupting interaction with ALCAM but not CD318, attenuating cytokine-driven upregulation of endothelial adhesion molecules, and strengthening BBB integrity. Itolizumab limited the retention and acquisition of a disease-promoting CD69⁺T_RM phenotype in migrated CD4⁺ T cells, while attenuating their activity in the CNS, thereby promoting oligodendrocyte survival and differentiation.

These findings provide mechanistic support for targeting CD6 in MS with itolizumab as a promising therapeutic strategy to reduce neuroinflammation and pathogenic T cell accumulation in the CNS.