Targeting antigens to dendritic cell receptors for vaccine development. J Drug Deliv. 2013;2013:869718. [PMID: 24228179 PMCID: PMC3817681 DOI: 10.1155/2013/869718]

Guiding principles in the design of molecular bioconjugates for vaccine applications

Antigen- and adjuvant-based bioconjugates that can stimulate the immune system play an important role in vaccine applications. Bioconjugates have demonstrated unique physicochemical and biological properties, enabling vaccines to be delivered to key immune cells, to target specific intracellular pathways, or to mimic immunogenic properties of natural pathogens. In this Review we highlight recent advances in such molecular immunomodulators, with an emphasis on the structure-function relationships that provide the foundation for rational design of safe and effective vaccines and immunotherapies.

N-glycosylation of cholera toxin B subunit in Nicotiana benthamiana: impacts on host stress response, production yield and vaccine potential

Plant-based transient overexpression systems enable rapid and scalable production of subunit vaccines. Previously, we have shown that cholera toxin B subunit (CTB), an oral cholera vaccine antigen, is N-glycosylated upon expression in transgenic Nicotiana benthamiana. Here, we found that overexpression of aglycosylated CTB by agroinfiltration of a tobamoviral vector causes massive tissue necrosis and poor accumulation unless retained in the endoplasmic reticulum (ER). However, the re-introduction of N-glycosylation to its original or an alternative site significantly relieved the necrosis and provided a high CTB yield without ER retention. Quantitative gene expression analysis of PDI, BiP, bZIP60, SKP1, 26Sα proteasome and PR1a, and the detection of ubiquitinated CTB polypeptides revealed that N-glycosylation significantly relieved ER stress and hypersensitive response, and facilitated the folding/assembly of CTB. The glycosylated CTB (gCTB) was characterized for potential vaccine use. Glycan profiling revealed that gCTB contained approximately 38% plant-specific glycans. gCTB retained nanomolar affinity to GM1-ganglioside with only marginal reduction of physicochemical stability and induced an anti-cholera holotoxin antibody response comparable to native CTB in a mouse oral immunization study. These findings demonstrated gCTB's potential as an oral immunogen and point to a potential role of N-glycosylation in increasing recombinant protein yields in plants.

Trial watch: Dendritic cell-based anticancer therapy

The use of patient-derived dendritic cells (DCs) as a means to elicit therapeutically relevant immune responses in cancer patients has been extensively investigated throughout the past decade. In this context, DCs are generally expanded, exposed to autologous tumor cell lysates or loaded with specific tumor-associated antigens (TAAs), and then reintroduced into patients, often in combination with one or more immunostimulatory agents. As an alternative, TAAs are targeted to DCs in vivo by means of monoclonal antibodies, carbohydrate moieties or viral vectors specific for DC receptors. All these approaches have been shown to (re)activate tumor-specific immune responses in mice, often mediating robust therapeutic effects. In 2010, the first DC-based preparation (sipuleucel-T, also known as Provenge®) has been approved by the US Food and Drug Administration (FDA) for use in humans. Reflecting the central position occupied by DCs in the regulation of immunological tolerance and adaptive immunity, the interest in harnessing them for the development of novel immunotherapeutic anticancer regimens remains high. Here, we summarize recent advances in the preclinical and clinical development of DC-based anticancer therapeutics.

Optimizing dendritic cell-based approaches for cancer immunotherapy

Dendritic cells (DC) are professional antigen-presenting cells uniquely suited for cancer immunotherapy. They induce primary immune responses, potentiate the effector functions of previously primed T-lymphocytes, and orchestrate communication between innate and adaptive immunity. The remarkable diversity of cytokine activation regimens, DC maturation states, and antigen-loading strategies employed in current DC-based vaccine design reflect an evolving, but incomplete, understanding of optimal DC immunobiology. In the clinical realm, existing DC-based cancer immunotherapy efforts have yielded encouraging but inconsistent results. Despite recent U.S. Federal and Drug Administration (FDA) approval of DC-based sipuleucel-T for metastatic castration-resistant prostate cancer, clinically effective DC immunotherapy as monotherapy for a majority of tumors remains a distant goal. Recent work has identified strategies that may allow for more potent "next-generation" DC vaccines. Additionally, multimodality approaches incorporating DC-based immunotherapy may improve clinical outcomes.

Fc receptor-targeting of immunogen as a strategy for enhanced antigen loading, vaccination, and protection using intranasally administered antigen-pulsed dendritic cells

Dendritic cells (DCs) play a critical role in the generation of adaptive immunity via the efficient capture, processing, and presentation of antigen (Ag) to naïve T cells. Administration of Ag-pulsed DCs is also an effective strategy for enhancing immunity to tumors and infectious disease organisms. Studies have also demonstrated that targeting Ags to Fcγ receptors (FcγR) on Ag presenting cells can enhance humoral and cellular immunity in vitro and in vivo. Specifically, our studies using a Francisella tularensis (Ft) infectious disease vaccine model have demonstrated that targeting immunogens to FcγR via intranasal (i.n.) administration of monoclonal antibody (mAb)-inactivated Ft (iFt) immune complexes (ICs) enhances protection against Ft challenge. Ft is the causative agent of tularemia, a debilitating disease of humans and other mammals and a category A biothreat agent for which there is no approved vaccine. Therefore, using iFt Ag as a model immunogen, we sought to determine if ex vivo targeting of iFt to FcγR on DCs would enhance the potency of i.n. administered iFt-pulsed DCs. In this study, bone marrow-derived DCs (BMDCs) were pulsed ex vivo with iFt or mAb-iFt ICs. Intranasal administration of mAb-iFt-pulsed BMDCs enhanced humoral and cellular immune responses, as well as protection against Ft live vaccine strain (LVS) challenge. Increased protection correlated with increased iFt loading on the BMDC surface as a consequence of FcγR-targeting. However, the inhibitory FcγRIIB had no impact on this enhancement. In conclusion, targeting Ag ex vivo to FcγR on DCs provides a method for enhanced Ag loading of DCs ex vivo, thereby reducing the amount of Ag required, while also avoiding the inhibitory impact of FcγRIIB. Thus, this represents a simple and less invasive strategy for increasing the potency of ex vivo-pulsed DC vaccines against chronic infectious diseases and cancer.

Dendritic cell immunotherapy: clinical outcomes

The use of tumour-associated antigens for cancer immunotherapy studies is exacerbated by tolerance to these self-antigens. Tolerance may be broken by using ex vivo monocyte-derived dendritic cells (DCs) pulsed with self-antigens. Targeting tumour-associated antigens directly to DCs in vivo is an alternative and simpler strategy. The identification of cell surface receptors on DCs, and targeting antigens to DC receptors, has become a popular approach for inducing effective immune responses against cancer antigens. Many years ago, we demonstrated that targeting the mannose receptor on macrophages using the carbohydrate mannan to DCs led to appropriate immune responses and tumour protection in animal models. We conducted Phase I, I/II and II, clinical trials demonstrating the effectiveness of oxidised mannan-MUC1 in patients with adenocarcinomas. Here we summarise DC targeting approaches and their efficacy in human clinical trials.

Hepatitis B Virus-Related Hepatocellular Carcinoma: Pathogenic Mechanisms and Novel Therapeutic Interventions

BACKGROUND

Infection with the hepatitis B virus (HBV) is one of most important risk factors for hepatocellular carcinoma (HCC). Indeed, HBV is considered a group 1 human carcinogen and is a highly oncogenic agent. HBV cannot be effectively controlled or completely eliminated, so chronic HBV infection is a public health challenge worldwide.

SUMMARY

It is now believed that HBV-induced HCC involves a complex interaction between multiple viral and host factors. Many factors contribute to HBV-associated HCC, including products of HBV, viral integration and mutation, and host susceptibility. This review outlines the main pathogenic mechanisms with a focus on those that suggest novel targets for the prevention and treatment of HCC.

KEY MESSAGE

HBV infection is an important risk factor for HCC. Understanding the interaction between viral and host factors in HBV-induced HCC will reveal potential targets for future therapies.

PRACTICAL IMPLICATIONS

The two main therapeutic strategies consist of antiviral agents and immunotherapy-based approaches. Dendritic cell-based immunotherapy is promising for restoring the T cell-mediated antiviral immune response. Another approach is the specific expansion of the host's pool of HBV-specific T cells. Stimulation of the Toll-like receptors (TLRs), particularly TLR9, provides another means of boosting the antiviral response. Combination therapy with cytokines (interferon gamma and tumor necrosis factor alpha) plus lamivudine is more effective than these agents used alone. Therapeutic vaccines are being developed as an alternative to long-term antiviral treatment or as an adjunct.

Immunotherapeutic interventions in chronic hepatitis B virus infection: a review

Chronic hepatitis B virus (HBV) infection is a public health challenge worldwide. Antiviral agents (nucleos(t)ide analogues, NAs) and immune-based therapies (IFN-α or Pegylated-IFN-α) are two therapeutic approaches available currently against chronic hepatitis B (CHB). However, these approaches are associated with the development of acquired drug resistance or poor response rates and are accompanied by numerous side effects. Furthermore, due to defective innate and adaptive immune responses, HBV cannot be effectively controlled or completely eliminated, which may ultimately result in liver decompensation and hepatocelluar carcinoma. The imperative for development of new approaches targeting CHB cannot be overstated. Various immunotherapeutic interventions have been tried as adjuvants to inhibit HBV replication. In this paper, we will review immunotherapeutic interventions in the treatment of CHB.