Jennifer Thorn

Molecular attributes of conjugate antigen influence function of antibodies induced by anti-nicotine vaccine in mice and non-human primates

Anti-nicotine vaccines aim to prevent nicotine entering the brain, and thus reduce or eliminate the reward that drives nicotine addiction. Those tested in humans to date have failed to improve quit rates over placebo, possibly because antibody (Ab) responses were insufficient to sequester enough nicotine in the blood in the majority of subjects. We have previously shown in mice that the carrier, hapten and linker used in the nicotine conjugate antigen each influence the function (nicotine-binding capacity) of the Ab induced. Herein we have evaluated immunogenicity in mice of 27 lots of NIC7-CRM, a conjugate of 5-aminoethoxy-nicotine (Hapten 7) and a mutant nontoxic form of diphtheria toxin (CRM197), that differed in three antigen attributes, namely hapten load (number of haptens conjugated to each molecule of CRM197), degree of conjugate aggregation and presence of adducts (small molecules attached to CRM197 via a covalent bond during the conjugation process). A range of functional responses (reduced nicotine in the brain of immunized animals relative to non-immunized controls) were obtained with the different conjugates, which were adjuvanted with aluminum hydroxide and CpG TLR9 agonist. Trends for better functional responses in mice were obtained with conjugates having a hapten load of 11 to 18, a low level of high molecular mass species (HMMS) (i.e., not aggregated) and a low level of adducts and a more limited testing in cynomolgus monkeys confirmed these results. Thus hapten load, conjugate aggregation and presence of adducts are key antigen attributes that can influence Ab function induced by NIC7-CRM.

Anti-nicotine vaccines: Comparison of adjuvanted CRM197 and Qb-VLP conjugate formulations for immunogenicity and function in non-human primates.

Anti-nicotine vaccines comprise nicotine-like haptens conjugated to a carrier protein plus adjuvant(s). Unfortunately, those tested clinically have failed to improve overall long term quit rates. We had shown in mice that carrier, hapten, linker, hapten load (number of haptens per carrier molecule), aggregation and adducts, as well as adjuvants influence the function of antibodies (Ab) induced. Herein, we tested an optimized antigen, NIC7-CRM, comprised of 5-aminoethoxy-nicotine (NIC7) conjugated to genetically detoxified diphtheria toxin (CRM197), with hapten load of ~16, no aggregation (~100% monomer) and minimal adducts. NIC7-CRM was tested in non-human primates (NHP) and compared to NIC-VLP, which has the same hapten and carrier as the clinical-stage CYT002-NicQb but a slightly different linker and lower hapten load. With alum as sole adjuvant, NIC7-CRM was superior to NIC-VLP for Ab titer, avidity and ex vivo function (83% and 27% nicotine binding at 40ng/mL respectively), but equivalent for in vivo function after intravenous [IV] nicotine challenge (brain levels reduced ~10%). CpG adjuvant added to NIC7-CRM/alum further enhanced the Ab responses and both ex vivo function (100% bound) and in vivo function (~80% reduction in brain). Thus, both optimal antigen design and CpG adjuvant were required to achieve a highly functional vaccine. The compelling NHP data with NIC7-CRM with alum/CpG supported human testing, currently underway.

Systematic Investigation of EDC/sNHS-Mediated Bioconjugation Reactions for Carboxylated Peptide Substrates

1-Ethyl-3-(3-(dimethylamino)propyl)carbodiimide (EDC) bioconjugations have been utilized in preparing variants for medical research. While there have been advances in optimizing the reaction for aqueous applications, there has been limited focus toward identifying conditions and side reactions that interfere with product formation. We present a systematic investigation of EDC/N-hydroxysulfosuccinimide (sNHS)-mediated bioconjugations on carboxylated peptides and small proteins. We identified yet-to-be-reported side products arising from both the reagents and substrates. Model peptides used in this study illustrate particular substrates are more susceptible to side reactions than others. From our studies, we found that bioconjugations are more efficient with high concentrations of amine nucleophile but not sNHS. Performing bioconjugations on a model affibody protein show that the trends established with model peptides hold for more complex systems.

Anti-IgE Qb-VLP Conjugate Vaccine Self-Adjuvants through Activation of TLR7

Qb bacteriophage virus-like particles (Qb-VLP) are utilized as carriers to enhance immune responses to weakly or non-immunogenic antigens such as peptides and haptens. Qb-VLPs are formed through the self-assembly of multiple Qb capsid protein monomers, a process which traps a large amount of bacterial RNA in the core of the VLP. Bacterial RNA is known to activate the innate immune system via TLR 7 and 8 found within the endosomes of certain immune cells and has been shown to contribute to the immunogenicity of Qb-VLP vaccines. Herein, we evaluated an anti-IgE vaccine comprised of two IgE peptides (Y and P) conjugated to Qb-VLP (Qb-Y and Qb-P, respectively) for in vitro stimulation of human PBMCs and in vivo immunogenicity in mice. The in vitro secretion of IFN-α from human PBMCs exposed to Qb-Y is consistent with TLR7 activation. Immunization of mice with the IgE peptide Qb-VLP conjugates induced high titers of anti-IgE antibodies in wild-type mice, but significantly lower titers in TLR7 knockout mice, supporting the self-adjuvanting role of the RNA. Inclusion of alum and alum/CpG as adjuvants partially or completely compensated for the lack of TLR7 activation in TLR7-deficient mice. Our study demonstrates the key role that TLR7 plays in the immunogenicity of the IgE peptide Qb-VLP conjugate vaccine.

The effect of preexisting anti-carrier immunity on subsequent responses to CRM197 or Qb-VLP conjugate vaccines

Abstract Context: Certain antigens, such as haptens (small molecules), short peptides, and carbohydrates (e.g. bacterial polysaccharides) are non- or poorly immunogenic unless conjugated to a carrier molecule that provides a structural scaffold for antigen presentation as well as T cell help required for B-cell activation and maturation. However, the carriers themselves are immunogenic and resulting carrier-specific immune responses may impact the immunogenicity of other conjugate vaccines using the same carrier that are administered subsequently. Objective: Herein, using two different carriers (cross-reactive material 197, CRM and Qb-VLP), we examined in mice the impact that preexisting anti-carrier antibodies (Ab) had on subsequent immune responses to conjugates with either the same or a different carrier. Method: For this purpose, we used two nicotine hapten conjugates (NIC7-CRM or NIC-Qb), two IgE peptide conjugates (Y-CRM or Y-Qb), and a pneumococcal polysaccharide conjugate (Prevnar 13®). Results: Prior exposure to CRM or Qb-VLP significantly reduced subsequent responses to the conjugated antigen having the homologous carrier, with the exception of Prevnar 13® where anti-polysaccharide responses were similar to those in animals without preexisting anti-carrier Ab. Conclusion: Collectively, the data suggest that the relative sizes of the antigen and carrier, as well as the conjugation density for a given conjugate impact the extent of anti-carrier suppression. All animals developed anti-carrier responses with repeat vaccination and the differences in Ab titer between groups with and without preexisting anti-carrier responses became less apparent; however, anti-carrier effects were more durable for Ab function.

Immunogenicity of a peptide‐based anti‐IgE conjugate vaccine in non‐human primates

The anti‐human immunoglobulin E (IgE) monoclonal antibody, omalizumab (Xolair®, Genentech, South San Fransisco, CA), is effective in the treatment of poorly controlled moderate to severe allergic asthma and chronic idiopathic urticaria. It acts by specifically binding to the constant domain (Cϵ3) of free human IgE in the blood and interstitial fluid. Although efficacious, use of omalizumab is limited due to restrictions on patient weight and pre‐existing IgE levels, and frequent dosing (q2–4 weeks). A vaccine inducing anti‐IgE antibodies has the potential for similar clinical benefits with less frequent dosing and relatively lower cost of goods. We developed a vaccine containing two IgE peptide‐conjugates targeting the Cϵ3 domain of human IgE. As part of preclinical evaluation of the vaccine to optimize formulation and dose prior to initiating clinical studies, we evaluated the vaccine in non‐human primates, and demonstrate the induction of anti‐peptide antibodies that can bind to conformationally intact human IgE and are capable, at least in some animals, of substantial lowering circulating IgE levels.

The Effect of Physicochemical Modification on the Function of Antibodies Induced by Anti-Nicotine Vaccine in Mice

Smoking remains one of the major causes of morbidity and mortality worldwide. One approach to assisting smoking cessation is via anti-nicotine vaccines, composed of nicotine-like haptens conjugated to a carrier protein plus adjuvant(s). We have previously shown that the carrier, hapten, linker, hapten load, degree of conjugate aggregation, and presence of adducts can each influence the function (nicotine-binding capacity) of the antibody (Ab) induced. Herein, we extend those findings and show that tertiary structure is also critical to the induction of functional immune responses and that this can be influenced by conjugation conditions. We evaluated immunogenicity in mice using six lots of NIC7-CRM, a conjugate of 5-aminoethoxy-nicotine (Hapten 7), and a single point (glycine 52 to glutamic acid) mutant nontoxic form of diphtheria toxin, cross-reactive material 197 (CRM197), which were synthesized under different reaction conditions resulting in conjugates with equivalent molecular characteristics (hapten load, aggregates, adducts), but a different tertiary structure. When tested in mice, better functional responses (reduced nicotine in the brain of immunized animals relative to non-immunized controls) were obtained with conjugates with a more closed structure than those with an open conformation. These studies highlight the need for a better understanding of the physicochemical properties of small molecule conjugate vaccines.