BBIQ, a pure TLR7 agonist, is an effective influenza vaccine adjuvant

ABSTRACT

Better adjuvants are needed for vaccines against seasonal influenza. TLR7 agonists are potent activators of innate immune responses and thereby may be promising adjuvants. Among the imidazoquinoline compounds, 1-benzyl-2-butyl-1H-imidazo[4,5-c]quinolin-4-amine (BBIQ) was reported to be a highly active TLR7 agonist but has remained relatively unexplored because of its commercial unavailability. Indeed, in silico molecular modeling studies predicted that BBIQ had a higher TLR7 docking score and binding free energy than imiquimod, the gold standard TLR7 agonist. To circumvent the availability issue, we developed an improved and higher yield method to synthesize BBIQ. Testing BBIQ on human and mouse TLR7 reporter cell lines confirmed it to be TLR7 specific with significantly higher potency than imiquimod. To test its adjuvant potential, BBIQ or imiquimod were admixed with recombinant influenza hemagglutinin protein and administered to mice as two intramuscular immunizations 2 weeks apart. Serum anti-influenza IgG responses assessed by ELISA 2 weeks after the second immunization confirmed that the mice that received vaccine admixed with BBIQ had significantly higher anti-influenza IgG1 and IgG2c responses than mice immunized with antigen alone or admixed with imiquimod. This confirmed BBIQ to be a TLR7-specific adjuvant able to enhance humoral immune responses.

KEYWORDS:

• Imidazoquinoline
• TLR7
• TLR8
• imiquimod
• vaccine
• adjuvant
• influenza
• in-silico modeling

Acknowledgments

The support from UGC-CAS, DST-PURSE and Panjab University Development fund is gratefully acknowledged. DBS is thankful to UGC New Delhi for start-up research grant and DBT New Delhi for the award of Ramalingaswami Fellowship. Ministry of Human Resource Development, Govt. of India is gratefully acknowledged for the award of Scheme for Promotion of Academic and Research Collaboration (SPARC/2018-2019/P386/SL). DK is thankful to UGC New Delhi for the award of Junior Research Fellowship. MTP is thankful to DST for the award of Women Scientist Scheme-A (WOS-A). VK, SP, JF, YHO, IS and NP were supported by the National Institutes of Health, under Contracts HHSN272201400053C and HHSN272201800044C. This publication’s contents are solely the responsibility of the authors and do not necessarily represent the official views of the funding bodies.

Disclosure of potential conflicts of interest

VK, SP, JF, YHO, IS and NP are affiliated with Vaxine, which has commercial interests in Advax adjuvant. The other authors declare that they have no known competing financial interests.

Supplementary material

Supplemental data for this article can be accessed online at http://dx.doi.org/10.1080/21645515.2019.1710409.

Additional information

Funding

This project has been funded in part with Federal funds from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, USA under contract no. HHSN272201400053C and HHSN272201800044C to Vaxine Pty Ltd. and MHRDs SPARC Grant of Govt. of India [SPARC/2018-2019/P386/SL].