Galectin-9 controls the activity of 4-1BB (CD137) (P1009)

Abstract

4-1BB is an inducible stimulatory molecule in the TNFR superfamily expressed on activated T cells, dendritic cells, NK cells, and other lymphoid cell types. Although known to bind the TNF family molecule 4-1BBL, we searched for novel binding partners that might modulate or control the activity of 4-1BB. We found that 4-1BB can bind to Galectin-9, a member of the beta-galactoside binding lectins containing homologous carbohydrate recognition domains (CRDs). Surface plasmon resonance analysis for mouse and human molecules demonstrated that the equilibrium binding constant (KD) of this interaction was very strong at ~11 nM and ~85 nM respectively. Functional studies in vitro showed that the stimulatory activity of 4-1BB was dependent on Galectin-9 in that Galectin-9-/- NK cells, CD4 T cells, or CD8 T cells, were largely unresponsive when 4-1BB was ligated but had normal activity when other stimulatory receptors were engaged. Similarly, 4-1BB activity on dendritic cells was impaired when Galectin-9 was absent. Additionally, in EAE and Asthma models, where an agonist of 4-1BB can suppress disease via induction of CD8β+CD11c+ regulatory cells, we found that this protective effect of anti-4-1BB was lost in Galectin-9-/- mice. Thus, our data demonstrate a novel function of Galectin-9 in facilitating signaling through 4-1BB, and suggest that Galectin-9 may allow 4-1BB to oligomerize and/or cluster in a manner that allows efficient engagement of intracellular signaling pathways.