Abstract A25: Differentiation of human naive T cells to various effector memory cell subtypes correlates with increased binding of the B subunit of Type-IIb heat-labile enterotoxin (LT-IIb-B5) to its cognate ganglioside receptors

Abstract

Abstract The initial antigenic activation of T cells involves localization of the T-cell receptor to lipid rafts, of which gangliosides are major components. To understand the role of lipid rafts in the activation and differentiation of CD4+ and CD8+ T cells, it is necessary to dissect the ganglioside composition in each respective T-cell subset. In the present study, we used the B subunits of type-II heat-labile enterotoxins (LT-IIa-B5, LT-IIb-B5 and LT-IIc-B5), which possess defined ganglioside-binding specificities, as molecular probes to dissect the membrane ganglioside composition of human T cell subsets. Peripheral blood mononuclear cells isolated from leukocyte reduction filters by Ficoll density gradient centrifugation were stained with recombinant LT-IIa-B5, LT-IIb-B5, mutant LT-IIb-B5(T13I) or LT-IIc-B5 and with monoclonal antibodies to CD4, CD8, CD27, CD45RA, CD45RO and CD62L followed by flow cytometric analysis. Our results show that ligands for LT-IIa (gangliosides GD1b, GM1, and GT-1b), LT-IIb (gangliosides GD1a, GT1b and GM2), and LT-IIc (gangliosides GM1, GM2, and GM3) are increasingly expressed during differentiation from naïve (CD4+ or CD8+CD45RO-CD27+) to memory (CD4+ or CD8+CD45RO+CD27+) T cells, and that discrete subsets of central memory (CD4+ or CD8+CD45RA-CD62L+), effector memory (CD4+ or CD8+CD45RA-CD62L-), and terminally differentiated effector memory (CD4+ or CD8+CD45RO+CD27-) T cells express the highest ganglioside levels, particularly of LT-IIb-ligands. On the other hand, mutant LT-IIb-B5(T13I), which had negligible binding in vitro to gangliosides GD1a, GT1b, and GM2, exhibited no detectable binding to naive or central memory T cells, but significantly bound subsets of terminally differentiated effector memory (CD4+ and CD8+) T cells. Our results suggest an important role for gangliosides GD1b and GM1 in naive T-cell responses, while central memory, effector memory, and terminally differentiated effector memory T-cell responses may be more dependent upon gangliosides GD1a and GT1b. Furthermore, the lymphocyte-binding activities of LT-IIb-B5(T13I) confirm that its parental B-pentameter essentially recognizes gangliosides GD1a, GT1b, and GM2 on T cells and suggest that LT-IIb-B5 (T13I) may bind to one or more unknown receptor(s) expressed on subsets of terminally differentiated effector memory (CD4+ and CD8+) T cells. Citation Format: Taylor A. Johnson, Madison K. Ritter, Mary-Peyton A. Knapp, Robert O. Rainer, Nathalie D. King-Lyons, Terry D. Connell, Sergio Arce. Differentiation of human naive T cells to various effector memory cell subtypes correlates with increased binding of the B subunit of Type-IIb heat-labile enterotoxin (LT-IIb-B5) to its cognate ganglioside receptors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A25.