Differential impact of TNFRSF co-stimulation on CD8+ T cell cytokine production by feedback control of surface receptor expression

T cell responses towards infections and cancers are regulated by a host of co-signalling receptors that are largely grouped into the binary categories of co-stimulation and co-inhibition. The TNF receptor superfamily (TNFRSF) members 4-1BB, CD27, GITR, and OX40 are well-established co-stimulation receptors with largely shared molecular pathways raising the question of whether they also have a similar impact on quantitative T cell responses, such as the efficacy, sensitivity, and duration of T cell responses. Here, we systematically stimulated primary human CD8+ T cell blasts with dose ranges of antigen and ligands for TNFRSF members to screen for their quantitative effects on cytokine production. Although both 4-1BB and CD27 increased efficacy, only 4-1BB was able to prolong the duration of cytokine production, and both had only a modest impact on antigen sensitivity. An operational model could explain these divergent quantitative phenotypes using a shared signalling mechanism based on the surface expression of 4-1BB, but not CD27, being regulated through a signalling feedback. The model predicted that CD27 co-stimulation would increase 4-1BB expression and subsequent 4-1BB co-stimulation, which we confirmed experimentally. Although GITR and OX40 produced only minor changes in cytokine production on their own, we found that like 4-1BB, CD27 could enhance GITR expression and subsequent GITR co-stimulation. Thus, feedback control of induced TNFRSF surface expression explains both synergy and differential impact on cytokine production. The work highlights that different co-stimulation receptors can have different quantitative phenotypes on the same output allowing for highly regulated control of T cell responses. ### Competing Interest Statement The authors have declared no competing interest.