Characterization of a double-CRD-mutated Gal-8 recombinant protein that retains costimulatory activity on antigen-specific T cell response

SCHROEDER, MATÍAS NICOLÁS*; TRIBULATTI, MV*(PRIMERA AUTORÍA COMPARTIDA); CARABELLI, JULIETA; GWENAËLLE ANDRÉ-LEROUX; CARAMELO, JULIO; CATTANEO, VALENTINA; CAMPETELLA, OSCAR

BIOCHEMICAL JOURNAL

PORTLAND PRESS LTD

Lugar: Londres; Año: 2016 vol. 473 p. 887 - 898

0264-6021

Galectins (Gals) constitute a family of mammalian lectins with affinity for beta-galactosides, characterized by the presence of conserved carbohydrate-recognition domains (CRDs). We have previously found that Gal-8, from tandem-repeat group with two linked CRDs, exerts two separate actions on CD4+ T cells: antigen-independent proliferation and, at lower concentration, antigen-specific costimulation. While proliferation can be ascribed to the pro-inflammatory role of Gal-8, the costimulatory activity of borderline T cell specific-responses allows proposing Gal-8 as an adjuvant in vaccination. To study the relevance of glycan-lectin interaction on these T cell activities, we generated a double-mutated protein (Gal-8mut) by replacing canonical arginine residues on each CRD, as to abolish sugar-binding capacity. As expected, Gal-8mut was unable to bind to lactosyl-Sepharose confirming that lactose recognition was precluded, however, preservation of lectin activity was still evident since Gal-8mut displayed hemoagglutinatory effect and binding capacity to T cell surface. To search for glycan affinity, a glycan-microarray analysis was conducted which revealed that Gal-8mut lost most low and intermediate, but retained high affinity interactions, mainly to polyllactosamines and blood group antigens. These findings were further supported by molecular modeling. Regarding biological activity, Gal-8mut was unable to induce T cell proliferation, but efficiently costimulated antigen-specific responses, both in vitro and in vivo. Therefore, Gal-8mut represents a useful tool to dissect the specificities of lectin-glycan interactions underlying distinctive Gal-8 activities on T cell biology. Moreover, given its distinguishing properties, Gal-8mut could be used to enhance borderline immune responses without the non-specific pro-inflammatory activity or other potential adverse effects.