Abstract PO024: Differential binding of E. coli enterotoxins LT-IIa, LT-IIb and LT-IIc to human B and T cell subsets identifies a potential use as adjuvants in cancer immunotherapy
Authors: Knapp Mary-Peyton A. , Johnson Taylor A. , Ritter Madison K. , Rainer Robert O. , Fiester Steven E. , Grier Jennifer T. , Connell Terry D. , Arce Sergio 
Published: February 2021

Abstract
There is an urgent need for development of new adjuvants to target and drive immune responses in cancer immunotherapies. The E. coli type-II heat-labile enterotoxins (HLEs) LT-IIa, LT-IIb and LT-IIc exhibit strong adjuvant properties with varying capacities to elicit immune responses in mice. The immunomodulatory capabilities of these HLEs depend upon their interactions with specific ganglioside receptors that may vary in expression across immune cell types. Little is known, however, about the lymphoid cells that interact with HLEs in humans. To bridge this gap, human normal PBMCs, isolated by Ficoll density gradient centrifugation, were stained with recombinant B subunits of LT-IIa, LT-IIb, or LT-IIc, and mAbs to CD4, CD8, CD19, CD27, CD38 and CD45RO. Using FACS analysis, we found that LT-IIa, LT-IIb and LT-IIc increasingly bound to CD4+ T cells as the cells transitioned from naive (CD4+CD45RO-CD27+) to memory (CD4+CD45RO+CD27+) cells and from memory cells to effector memory (CD4+CD45RO+CD27-) cells, with LT-IIb exhibiting the most significant increase in binding. Likewise, LT-IIb and LT-IIc increasingly bound to CD8+ T cells as the cells transitioned from naive (CD8+CD45RO-CD27+) to memory (CD8+CD45RO+CD27+) cells and from memory cells to effector memory (CD8+CD45RO+CD27-) cells, with the greatest increase observed for LT-IIb. No major changes in LT-IIa binding were detected during CD8+ T cell differentiation. Finally, LT-IIa and LT-IIc increasingly bound to CD19+ B cells as the cells transitioned from naive (CD19+CD27-) to memory (CD19+CD27+) cells and from memory cells to antibody-secreting (CD19+/-CD27++CD38++) plasma cells, with LT-IIa exhibiting the most significantly increased binding activity. No major changes in LT-IIb binding were observed during B cell differentiation. Taken together, these results suggest that the ganglioside receptors for HLEs (e.g., GD1a, GD1b and GM1) are differentially expressed throughout B and T cell development/differentiation and that binding of HLEs to the various lymphocyte subsets is likely to elicit distinct cellular events associated with immune modulation or immune responsiveness. Understanding of these HLE binding patterns may also prove useful in targeting additional immunomodulating drugs to specific T or B cell subpopulations. Ultimately, characterization of immunological responses to these enterotoxins will lead to a greater understanding of their potential use in targeted cancer immunotherapies for treatment of a wide variety of conditions.
Citation Format: Mary-Peyton A. Knapp, Taylor A. Johnson, Madison K. Ritter, Robert O. Rainer, Steven E. Fiester, Jennifer T. Grier, Terry D. Connell, Sergio Arce. Differential binding of E. coli enterotoxins LT-IIa, LT-IIb and LT-IIc to human B and T cell subsets identifies a potential use as adjuvants in cancer immunotherapy [abstract]. In: Abstracts: AACR Virtual Special Conference: Tumor Immunology and Immunotherapy; 2020 Oct 19-20. Philadelphia (PA): AACR; Cancer Immunol Res 2021;9(2 Suppl):Abstract nr PO024.