Injection Route and TLR9 Agonist Addition Significantly Impact Heroin Vaccine Efficacy

Abstract

Active immunization is an effective means of blocking the pharmacodynamic effects of drugs and holds promise as a treatment for heroin addiction. Previously, we demonstrated the efficacy of our first-generation vaccine in blocking heroin self-administration in rats, however, many vaccine components can be modified to further improve performance. Herein we examine the effects of varying heroin vaccine injection route and adjuvant formulation. Mice immunized via subcutaneous (sc) injection exhibited inferior anti-heroin titers compared to intraperitoneal (ip) and sc/ip coadministration injection routes. Addition of TLR9 agonist cytosine-guanine oligodeoxynucleotide 1826 (CpG ODN 1826) to the original alum adjuvant elicited superior antibody titers and opioid affinities compared to alum alone. To thoroughly assess vaccine efficacy, full dose–response curves were generated for heroin-induced analgesia in both hot plate and tail immersion tests. Mice treated with CpG ODN 1826 exhibited greatly shifted dose–response curves (10–13-fold vs unvaccinated controls) while non-CpG ODN vaccine groups did not exhibit the same robust effect (2–7-fold shift for ip and combo, 2–3-fold shift for sc). Our results suggest that CpG ODN 1826 is a highly potent adjuvant, and injection routes should be considered for development of small molecule–protein conjugate vaccines. Lastly, this study has established a new standard for assessing drugs of abuse vaccines, wherein a full dose–response curve should be performed in an appropriate behavioral task.