Robert A. Seder

Vaccine Adjuvants: Putting Innate Immunity to Work

Adjuvants enhance immunity to vaccines and experimental antigens by a variety of mechanisms. In the past decade, many receptors and signaling pathways in the innate immune system have been defined and these innate responses strongly influence the adaptive immune response. The focus of this review is to delineate the innate mechanisms by which adjuvants mediate their effects. We highlight how adjuvants can be used to influence the magnitude and alter the quality of the adaptive response in order to provide maximum protection against specific pathogens. Despite the impressive success of currently approved adjuvants for generating immunity to viral and bacterial infections, there remains a need for improved adjuvants that enhance protective antibody responses, especially in populations that respond poorly to current vaccines. However, the larger challenge is to develop vaccines that generate strong T cell immunity with purified or recombinant vaccine antigens.

Quality and quantity of TFH cells are critical for broad antibody development in SHIVAD8 infection.

T follicular helper cells associate with development of highly mutated neutralizing antibodies against SHIV. How antibodies mature Antibodies are stalwart protectors against infection, but even antibodies need a little help to do their jobs. T follicular helper (TFH) cells can guide B cells to produce antibodies with improved specificity to a particular pathogen through a process called affinity maturation. Now, Yamamoto et al. report that in nonhuman primates, the frequency and quality of TFH cells were associated with the development of broadly neutralizing antibodies that may be protective against SHIV. These findings suggest that HIV vaccines that incorporate TFH cell stimulation may boost broadly neutralizing antibody production. Broadly neutralizing antibodies (bNAbs) protect against HIV-1 infection, yet how they are generated during chronic infection remains unclear. It is known that T follicular helper (TFH) cells are needed to promote affinity maturation of B cells during an immune response; however, the role of TFH during HIV-1 infection is undefined within lymph node germinal centers (GCs). We use nonhuman primates to investigate the relationship in the early stage of chronic SHIVAD8 (simian-human immunodeficiency virus AD8) infection between envelope (Env)–specific TFH cells, Env-specific B cells, virus, and the generation of bNAbs during later infection. We found that both the frequency and quality of Env-specific TFH cells were associated with an expansion of Env-specific immunoglobulin G–positive GC B cells and broader neutralization across HIV clades. We also found a correlation between breadth of neutralization and the degree of somatic hypermutation in Env-specific memory B cells. Finally, we observed high viral loads and greater diversity of Env sequences in rhesus macaques that developed cross-reactive neutralization as compared to those that did not. These studies highlight the importance of boosting high-quality TFH populations as part of a robust vaccine regimen aimed at eliciting bNabs.

Progress with Plasmodium falciparum sporozoite (PfSPZ)-based malaria vaccines.

Sanaria Inc. has developed methods to manufacture, purify and cryopreserve aseptic Plasmodium falciparum (Pf) sporozoites (SPZ), and is using this platform technology to develop an injectable PfSPZ-based vaccine that provides high-grade, durable protection against infection with Pf malaria. Several candidate vaccines are being developed and tested, including PfSPZ Vaccine, in which the PfSPZ are attenuated by irradiation, PfSPZ-CVac, in which fully infectious PfSPZ are attenuated in vivo by concomitant administration of an anti-malarial drug, and PfSPZ-GA1, in which the PfSPZ are attenuated by gene knockout. Forty-three research groups in 15 countries, organized as the International PfSPZ Consortium (I-PfSPZ-C), are collaborating to advance this program by providing intellectual, clinical, and financial support. Fourteen clinical trials of these products have been completed in the USA, Europe and Africa, two are underway and at least 12 more are planned for 2015–2016 in the US (four trials), Germany (2 trials), Tanzania, Kenya, Mali, Burkina Faso, Ghana and Equatorial Guinea. Sanaria anticipates application to license a first generation product as early as late 2017, initially to protect adults, and a year later to protect all persons >6 months of age for at least six months. Improved vaccine candidates will be advanced as needed until the following requirements have been met: long-term protection against natural transmission, excellent safety and tolerability, and operational feasibility for population-wide administration. Here we describe the three most developed whole PfSPZ vaccine candidates, associated clinical trials, initial plans for licensure and deployment, and long-term objectives for a final product suitable for mass administration to achieve regional malaria elimination and eventual global eradication.

Human and rhesus plasmacytoid dendritic cell and B-cell responses to Toll-like receptor stimulation

Interferon‐α (IFN‐α) produced at high levels by human plasmacytoid dendritic cells (pDCs) can specifically regulate B‐cell activation to Toll‐like receptor (TLR) 7/8 stimulation. To explore the influence of IFN‐α and pDCs on B‐cell functions in vivo, studies in non‐human primates that closely resemble humans in terms of TLR expression on different subsets of immune cells are valuable. Here, we performed a side‐by side comparison of the response pattern between human and rhesus macaque B cells and pDCs in vitro to well‐defined TLR ligands and tested whether IFN‐α enhanced B‐cell function comparably. We found that both human and rhesus B cells proliferated while pDCs from both species produced high levels of IFN‐α in response to ligands targeting TLR7/8 and TLR9. Both human and rhesus B‐cell proliferation to TLR7/8 ligand and CpG class C was significantly increased in the presence of IFN‐α. Although both human and rhesus B cells produced IgM upon stimulation, only human B cells acquired high expression of CD27 associated with plasmablast formation. Instead, rhesus B‐cell differentiation and IgM levels correlated to down‐regulation of CD20. These data suggest that the response pattern of human and rhesus B cells and pDCs to TLR7/8 and TLR9 is similar, although some differences in the cell surface phenotype of the differentiating cells exist. A more thorough understanding of potential similarities and differences between human and rhesus cells and their response to potential vaccine components will provide important information for translating non‐human primate studies into human trials.

A Nonhuman Primate Toxicology and Immunogenicity Study Evaluating Aerosol Delivery of AERAS-402/Ad35 Vaccine: Evidence For Transient T Cell Responses in Peripheral Blood and Robust Sustained Responses in the Lungs

Bacille Calmette-Guérin (BCG), the only licensed vaccine for the prevention of tuberculosis (TB), provides only limited protection against certain forms of Mycobacterium tuberculosis (Mtb) infection. While infection with Mtb can be treated with antibiotics, the therapy is expensive, toxic, and requires several months for treatment. In addition, the emergence of drug resistant strains limits the impact of antibiotics and underlines the importance of developing a more effective vaccine to control this disease. Given that pulmonary TB is the most common form of the disease, a vaccine capable of inducing lung-resident immunity may be advantageous for combating this infection. New advances in pulmonary delivery make this route of vaccination feasible and affordable. Here, we evaluate the safety and immunogenicity of an aerosolized Ad35-based vaccine, AERAS-402, delivered to the lungs in nonhuman primates as part of a GLP acute and chronic toxicology and safety study. In this study, animals received three high doses (1 x 1011 vp) of AERAS-402 by inhalation via a nebulizer at 1-week intervals. Aerosol delivery of AERAS-402 resulted in an increase in relative lung weights as well as microscopic findings in the lungs, mediastinal lymph nodes, bronchus-associated lymphatic tissue, and the naso-oropharynx that were consistent with the induction of an immune response during the acute phase. These findings resolved by the chronic phase and were considered to be non-adverse. Furthermore, we observed transient vaccine-specific immune responses in the peripheral blood as well as sustained high-level polyfunctional CD4+ and CD8+ T cell responses in the bronchoalveolar lavage fluid of vaccinated nonhuman primates. The data suggest that pulmonary delivery of Ad35-based vaccines can be safe and can induce potent lung-resident immunity.

Albumin/vaccine nanocomplexes that assemble in vivo for combination cancer immunotherapy

Subunit vaccines have been investigated in over 1000 clinical trials of cancer immunotherapy, but have shown limited efficacy. Nanovaccines may improve efficacy but have rarely been clinically translated. By conjugating molecular vaccines with Evans blue (EB) into albumin-binding vaccines (AlbiVax), here we develop clinically promising albumin/AlbiVax nanocomplexes that self-assemble in vivo from AlbiVax and endogenous albumin for efficient vaccine delivery and potent cancer immunotherapy. PET pharmacoimaging, super-resolution microscopies, and flow cytometry reveal almost 100-fold more efficient co-delivery of CpG and antigens (Ags) to lymph nodes (LNs) by albumin/AlbiVax than benchmark incomplete Freund’s adjuvant (IFA). Albumin/AlbiVax elicits ~10 times more frequent peripheral antigen-specific CD8+ cytotoxic T lymphocytes with immune memory than IFA-emulsifying vaccines. Albumin/AlbiVax specifically inhibits progression of established primary or metastatic EG7.OVA, B16F10, and MC38 tumors; combination with anti-PD-1 and/or Abraxane further potentiates immunotherapy and eradicates most MC38 tumors. Albumin/AlbiVax nanocomplexes are thus a robust platform for combination cancer immunotherapy.Albumin conjugates can enhance drug delivery. Here, the authors repurpose albumin-binding Evans blue to develop nanovaccines that co-deliver adjuvants and tumor neoantigens to antigen-presenting cells in lymph nodes, resulting in potent and durable antitumour immunity in combination immunotherapy.

Gaps in knowledge and prospects for research of adjuvanted vaccines

A panel of researchers working in different areas of adjuvanted vaccines deliberated over the topic, Gaps in knowledge and prospects for research of adjuvanted vaccines at, Enhancing Vaccine Immunity and Value conference held in July 2014. Several vaccine challenges and applications for new adjuvant technologies were discussed.

Malaria Vaccines: Recent Advances and New Horizons.

The development of highly effective and durable vaccines against the human malaria parasites Plasmodium falciparum and P. vivax remains a key priority. Decades of endeavor have taught that achieving this goal will be challenging; however, recent innovation in malaria vaccine research and a diverse pipeline of novel vaccine candidates for clinical assessment provides optimism. With first-generation pre-erythrocytic vaccines aiming for licensure in the coming years, it is important to reflect on how next-generation approaches can improve on their success. Here we review the latest vaccine approaches that seek to prevent malaria infection, disease, and transmission and highlight some of the major underlying immunological and molecular mechanisms of protection. The synthesis of rational antigen selection, immunogen design, and immunization strategies to induce quantitatively and qualitatively improved immune effector mechanisms offers promise for achieving sustained high-level protection.

Progress with PfSPZ Vaccine, a radiation attenuated Plasmodium falciparum sporozoite vaccine

Sanaria® PfSPZ Vaccine is composed of aseptic, purified, cryopreserved, attenuated (non-replicating), metabolically active Plasmodium falciparum (Pf ) sporozoites (SPZ) produced in compliance with good manufacturing practices (GMPs) that meet all regulatory standards. This vaccine provided full protection against Pf infection in 100% (6/6) volunteers, who received five doses of 1.35 × 105 PfSPZ administered intravenously in a study at the Vaccine Research Center (VRC), NIAID, NIH [1]. Based on these data, the PfSPZ Vaccine Clinical Consortium composed of investigators from USA, Africa, and Europe has developed a four stage clinical development plan (CDP) that maps out a 4-5 year timeline to licensure and a large scale demonstration project to eliminate malaria from an island population in Africa. In 2014, six different clinical trials of PfSPZ Vaccine at seven clinical sites in the United States (Bethesda, Baltimore, Silver Spring), Mali, Tanzania, Equatorial Guinea, and Germany will be underway. These six clinical trials, which include >450 subjects, comprise Stage 1 of the four stage PfSPZ Vaccine CDP. They are designed to 1) assess the reproducibility of the data generated in the VRC study and 2) assess and optimize durability of protection, protection against heterologous strains of Pf, reduction in numbers of doses, immune assays that predict protection, implementation of immunization, and alternative route of administration. We will provide an update of these stage 1 clinical trials and plans for stage 2 studies that will address questions required for progressing to pivotal phase 3 clinical trials in stage 3, and to demonstration projects for focal elimination in small populations.