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Front. Immunol. | doi: 10.3389/fimmu.2019.01144

Bacterial Protein Toll-Like-Receptor Agonists: A Novel Perspective on Vaccine Adjuvants

 Sudeep Kumar1, Raju Sunagar2 and  Edmund J. Gosselin1*
  • 1Albany Medical College, United States
  • 2Ella Foundation, India

Adjuvants have been used in vaccines for over a century, still the search for safe and effective vaccine adjuvants continues. In recent decades toll-like-receptor (TLR) agonists have been investigated as potential vaccine adjuvants. In this regard, the majority of the currently investigated TLR agonists are non-protein microbial components such as lipopolysaccharides, oligonucleotides, and lipopeptides. On the other hand, a growing number of studies reveal that TLR signaling and immune responses can be activated by numerous bacterial proteins. However, their potential roles as adjuvants have been somewhat overlooked. Herein, we discuss several such bacterial proteins, which exhibit adjuvant properties, including the activation of TLR signaling, antigen presenting cell maturation, pro-inflammatory cytokine production and adaptive immune response. The protein nature of these TLR agonists present several unique features not shared by non-protein TLR agonists. These properties include the amenability for modifying the structure and function as necessary for optimal immunogenicity and minimal toxicity. Protein adjuvants can be genetically fused to protein antigens which will ensures co-delivery of adjuvant-antigen not only into the same cell but also in the same endocytic cargo leading to more effective activation of innate and adaptive immune response.

Keywords: adjuvant, Vaccine, Toll like receptor (TLR) agonist, Mucosal vaccine, antigen presentaing cells

Received: 18 Mar 2019; Accepted: 07 May 2019.

Edited by:

Lee M. Wetzler, School of Medicine, Boston University, United States

Reviewed by:

Paola Massari, Tufts University School of Medicine, United States
Pietro Speziale, Department of Electrical, Computer and Biomedical Engineering, University of Pavia, Italy  

Copyright: © 2019 Kumar, Sunagar and Gosselin. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mx. Edmund J. Gosselin, Albany Medical College, Albany, 12208, Georgia, United States, gossele@mail.amc.edu