CD4⁺ and CD8⁺ effector T cell subpopulations can display regulatory potential characterized by expression of the prototypically anti-inflammatory cytokine IL-10. However, the underlying cellular mechanisms that regulate expression of IL-10 in different T cell subpopulations are not yet fully elucidated. We recently showed that TNF inhibitors (TNFi) promote IL-10 expression in human CD4⁺ T cells, including IL-17⁺ CD4⁺ T cells. Here, we further characterized the regulation of IL-10 expression via blockade of TNF signaling or other cytokine/co-stimulatory pathways, in human T cell subpopulations. Addition of the TNFi drug adalimumab to anti-CD3-stimulated human CD4⁺ T cell/monocyte cocultures led to increased percentages of IL-10⁺ cells in pro-inflammatory IL-17⁺, IFNγ⁺, TNFα⁺, GM-CSF⁺, and IL-4⁺ CD4⁺ T cell subpopulations. Conversely, exogenous TNFα strongly decreased IL-10⁺ cell frequencies. TNF blockade also regulated IL-10 expression in CD4⁺ T cells upon antigenic stimulation. Using time course experiments in whole peripheral blood mononuclear cell (PBMC) cultures, we show that TNF blockade maintained, rather than increased, IL-10⁺ cell frequencies in both CD4⁺ and CD8⁺ T cells following in vitro stimulation in a dose- and time-dependent manner. Blockade of IL-17, IFNγ, IL-6R, or CD80/CD86-mediated co-stimulation did not significantly regulate IL-10 expression within CD4⁺ or CD8⁺ T cell subpopulations. We show that TNF blockade acts directly on effector CD4⁺ T cells, in the absence of monocytes or CD4⁺ CD25^highCD127^low regulatory T cells and independently of IL-27, resulting in higher IL-10⁺ frequencies after 3 days in culture. IL-10/IL-10R blockade reduced the frequency of IL-10-expressing cells both in the presence and absence of TNF blockade. Addition of recombinant IL-10 alone was insufficient to drive an increase in IL-10⁺ CD4⁺ T cell frequencies in 3-day CD4⁺ T cell/monocyte cocultures, but resulted in increased IL-10 expression at later time points in whole PBMC cultures. Together, these data provide additional insights into the regulation of IL-10 expression in human T cells by TNF blockade. The maintenance of an IL-10⁺ phenotype across a broad range of effector T cell subsets may represent an underappreciated mechanism of action underlying this widely used therapeutic strategy.

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