Coadministration of antigen-conjugated and free CpG: effects of in vitro and in vivo interactions in a murine model

Evaluation of cell surface reactive immuno-adjuvant in combination with immunogenic cell death inducing drug for in situ chemo-immunotherapy

Apoptotic cells and cell fragments, especially those produced as a result of immunogenic cell death (ICD), are known to be a potential source of cancer vaccine immunogen. However, due to variation between tumours and between individuals, methods to generate such preparations may require extensive ex vivo personalisation. To address this, we have utilised the concept of in situ vaccination whereby an ICD inducing drug is injected locally to generate immunogenic apoptotic fragments/cells. These fragments are then adjuvanted by a co-administered cell reactive CpG adjuvant. We first evaluate means of labelling tumour cells with CpG adjuvant, we then go on to demonstrate in vitro that labelling is preserved following apoptosis and, furthermore, that the apoptotic body-adjuvant complexes are readily transferred to macrophages. In in vivo studies we observe synergistic tumour growth delays and elevated levels of CD4+ and CD8+ cells in tumours receiving adjuvant drug combination. CD4+/CD8+ cells are likewise elevated in the tumour draining lymph node and activated to a greater extent than individual treatments. This study represents the first steps toward the evaluation of rationally formulated drug-adjuvant combinations for in situ chemo-immunotherapy.

Comparative Study of 5'- and 3'-Linked CpG-Antigen Conjugates for the Induction of Cellular Immune Responses

Conjugation of CpG to an antigen induces a stronger immune response compared to that of the mixture. This study compares the in vitro immunostimulatory activity of CpG conjugated via either its 5' or 3' end to the model antigen ovalbumin (OVA). CpG modified with an amine at either the 5' or 3' end was conjugated to OVA via a stable bis-aryl hydrazone bond. Similar levels of CpG conjugation to OVA were observed for both conjugates on the basis of the absorbance at 360 nm for the formation of the bis-aryl hydrazone bond, which determined 2.8 ± 0.3 CpGs linked per OVA. Both the 5' and 3' CpG-OVA conjugates had similar size-exclusion chromatography elution profiles. The immunostimulatory properties of the conjugates were determined by dendritic cells (DCs) and T-cells isolated from mice. The activation of DCs was determined by the upregulation of activation markers CD86 and CD40. T-cells were co-cultured with stimulated DCs, and the immunogenicity was determined by measuring T-cell proliferation and interferon γ production. Both the CpG 5'- and 3'-linked conjugates induced the same level (p > 0.5) of DC activation markers, which were significantly higher than those of the untreated control. Similarly, T-cell assays showed no significant difference (p > 0.5) between the 5' and 3' conjugates with respect to T-cell proliferation and interferon γ production. The 5' and 3' conjugates induced T-cell activation significantly higher than the mixture of CpG and OVA. This study showed that the end at which CpG is conjugated to an antigen has no influence on the generation of a T-cell-based immune response in vitro.

Intracellular Cleavable CpG Oligodeoxynucleotide-Antigen Conjugate Enhances Anti-tumor Immunity

Conjugation of a vaccine adjuvant to an antigen enhances anti-tumor immune responses. Direct chemical conjugation, however, may limit their processing by the antigen-presenting cell for immune stimulation. To test this hypothesis, antigen-adjuvant conjugates were designed to be cleaved by an intracellular trigger to release antigen and adjuvant from each other. The different reductive environment inside and outside antigen-presenting cells was used as a trigger for targeted intracellular release. Two redox-responsive disulphide linkers were used to conjugate the model antigen ovalbumin to CpG. In vitro stability assays with the reductant glutathione showed that one conjugate (SS) was cleaved by glutathione concentrations of the extra- and intracellular compartments. A second conjugate (HYN-SS) was only cleaved at the higher intracellular glutathione concentration. In vitro cell culture studies showed that high T cell responses were generated by the HYN-SS and the stable conjugate HYN. The SS conjugate induced a lower T cell response similar to a mixture of CpG and ovalbumin. An in vivo therapeutic tumor trial demonstrated a superior survival rate of 9/10 for mice vaccinated with HYN-SS conjugate compared to HYN (6/10), SS (2/10), and the mixture (2/10). This intracellular cleavable conjugation strategy represents a promising approach to improve cancer immunotherapy of soluble vaccines.

Systemic immune responses to an inactivated, whole H9N2 avian influenza virus vaccine using class B CpG oligonucleotides in chickens

Commercial vaccines against avian influenza viruses (AIV) in chickens consist mainly of inactivated AIV, requiring parenteral administration and co-delivery of an adjuvant. Limitations in T helper 1 or T helper 2 biased responses generated by these vaccines emphasize the need for alternative, more efficacious adjuvants. The Toll-like receptor (TLR) 21 ligand, CpG oligodeoxynucleotides (ODN), has been established as immunomodulatory in chickens. Therefore, the objective of this study was to investigate the adjuvant potential of high (20μg) and low (2μg) doses of CpG ODN 2007 (CpG 2007) and CpG ODN 1826 (CpG 1826) when administered to chickens with a formalin-inactivated H9N2 AIV. Antibody responses in sera were evaluated in 90 specific pathogen free (SPF) chickens after intramuscular administration of vaccine formulations at 7 and 21 days post-hatch. Antibody responses were assessed based on haemagglutination inhibition (HI) and virus neutralization (VN) assays; virus-specific IgM and IgY antibody responses were evaluated by ELISA. The results suggest that the vaccine formulation containing low dose CpG 2007 was significantly more effective at generating neutralizing (both HI and VN) responses than formulations with high or low doses of CpG 1826 or high dose CpG 2007. Neutralizing responses elicited by low dose CpG 2007 significantly exceeded those generated by a squalene-based adjuvanted vaccine formulation during peak responses. A significantly higher IgM response was elicited by the formulation containing low dose CpG 2007 compared to high and low doses of 1826. Although the low dose of CpG 2007 elicited a higher IgY response than CpG 1826, the difference was not statistically significant. In conclusion, 2μg of CpG 2007 is potentially promising as a vaccine adjuvant when delivered intramuscularly with inactivated H9N2 virus to chickens. Future studies may be directed at determining the mucosal antibody responses to the same vaccine formulations.

Progress in vaccine development

Vaccination has a proven record as one of the most effective medical approaches to prevent the spread of infectious diseases. Traditional vaccine approaches involve the administration of whole killed or weakened microorganisms to stimulate protective immune responses. Such approaches deliver many microbial components, some of which contribute to protective immunity, and assist in guiding the type of immune response that is elicited. Despite their impeccable record, these approaches have failed to yield vaccines for many important infectious organisms. This has prompted a move towards more defined vaccines ('subunit vaccines'), where individual protective components are administered. This unit provides an overview of the components that are used for the development of modern vaccines including: an introduction to different vaccine types (whole organism, protein/peptide, polysaccharide, conjugate, and DNA vaccines); techniques for identifying subunit antigens; vaccine delivery systems; and immunostimulatory agents ('adjuvants'), which are fundamental for the development of effective subunit vaccines.

Effective induction of anti-tumor immunity using p5 HER-2/neu derived peptide encapsulated in fusogenic DOTAP cationic liposomes co-administrated with CpG-ODN

Cationic liposomes have been used as efficient antigen delivery systems for cancer vaccination. The current study has investigated whether the incorporation of the helper-fusogenic lipid dioleoylphosphatidylethanolamine (DOPE) in cationic liposomes composed of 1,2-dioleoyl-3-trimethylammonium propane (DOTAP)-cholesterol enhances the cytosolic delivery of p5 HER-2/neu derived peptide (p5) and promotes cytotoxic T lymphocytes (CTL) response. The p5, which is a very hydrophobic peptide, was encapsulated into liposomes by using three different methods and characterized for their colloidal properties. A chaotropic loading method using 7 M urea provided the highest encapsulation yields. Mice were first immunized with encapsulated p5 in liposomes composed of either DOTAP-cholesterol or DOTAP-cholesterol-DOPE, alone or co-administered with CpG-ODN, as an immunoadjuvant, then, inoculated with a subcutaneous injection of TUBO tumor cells. Results obtained from enzyme-linked immunospot, cytotoxicity and intracellular cytokine assays as well as tumor sizes and animal survival analysis demonstrated that p5 encapsulated in DOTAP-cholesterol-DOPE liposomes co-administered with CpG-ODN greatly enhanced the cytotoxic T lymphocytes response and highly inhibited the tumor progression. The outperformance of DOTAP-cholesterol-DOPE liposomes+CpG-ODN was found to be attributed to its capability in induction of both CD8+ and CD4+ responses. This formulation could be a suitable vaccine candidate against Her2 positive cancers and merits further investigations.