Neuritin-specific antibody impedes the Treg-mediated suppression of anti-tumor immunity and enhances response to anti-PD1

Regulatory T cells (Tregs) and effector T cells play critical roles in tumor immunity, with Tregs suppressing immune responses and contributing to an immunosuppressive tumor microenvironment (TME). Neuritin-1 (Nrn), a neuropeptide, has been identified to enhance Treg expansion. However, its role in T cell biology and tumor development remains unclear. We demonstrated that Nrn is highly expressed in the in-vitro-induced Tregs (iTregs). Functionally, Nrn promoted iTreg differentiation in a dose-dependent manner, while Nrn deletion or anti-Nrn antibody treatment significantly inhibited iTreg differentiation. Additionally, Nrn suppressed IL-2 transcription and secretion in T cells, impairing T cell activation and pro-inflammatory cytokine production. Treg-specific Nrn knockout mice exhibited reduced B16 melanoma tumor growth, decreased Treg infiltration, and increased effector T cell infiltration. Conversely, overexpression of Nrn accelerated B16 melanoma tumor progression by enhancing Treg-mediated suppression. Importantly, we developed the first anti-Nrn antibody, which effectively reduced tumour growth, decreased Treg infiltration, and enhanced effector T-cell activity. Importantly, anti-Nrn synergistically worked with anti-PD1 and improved the anti-PD1 response by reducing Tregs and increasing effector function in tumor-infiltrated T cells, resulting in enhanced tumor regression. Our findings identify Nrn as a critical regulator of Treg differentiation and effector T cell suppression, contributing to tumor progression. Targeting Nrn alone or combined with anti-PD1 therapy represents a promising strategy to enhance anti-tumor immunity.