Efficacy of ABX196, a new NKT agonist, in prophylactic human vaccination.

We have assessed the immune-regulatory and adjuvant activities of a synthetic glycolipid, ABX196, a novel analog of the parental compound α-GalCer. As expected, ABX196 demonstrated a measurable and significant adjuvant effect in mice and monkeys with no appreciable toxicity at the doses used to promote immune responses. We performed a phase I/II dose escalation study of ABX196 in healthy volunteers, with the objectives to evaluate its safety profile, as well as its ability to be utilized as an adjuvant in the context of a prophylactic vaccine against hepatitis B. ABX196 was administered at three doses: 0.2, 0.4, and 2.0µg, in 44 subjects. In all the individuals injected with ABX196, peripheral blood NKT cells displayed hallmarks of activation, and 45% of them had measurable circulating IFN-γ 24h after the first administration. More importantly, the addition of ABX196 to the very poorly immunogenic HBs antigen resulted in protective anti-HBs antibody responses in majority of patients, demonstrating the adjuvant properties of ABX196 in human. Further analysis of the cohort of subjects receiving ABX196 with HBs antigen also indicates that a single injection appears sufficient to provide protection. A limited set of adverse events linked to the systemic delivery of ABX196 and access to the liver, is discussed in the context of formulation and the need to limit transport of ABX196 to secondary lymphoid tissues for maximal efficacy (Eudra-CT 2012-001566-15).

Outlining novel cellular adjuvant products for therapeutic vaccines against cancer.

Despite the library of new adjuvants available for use in vaccines, we remain, at present, almost reliant on aluminum-based compounds for clinical use. The increasing use of recombinant subunit vaccines, however, makes the need for improved adjuvant of particular interest. Adjuvants are crucial components of all cancer vaccines whether they are composed of whole cells, proteins or peptides. For the purposes of this article, cellular adjuvant products are defined as adjuvants associated with cellular or T-cell immunity. Several pharmaceutical companies are developing new adjuvants or immune enhancers for the treatment of cancers such as melanoma and non-small-cell lung carcinoma. Several products are being developed and have entered clinical trials either alone or in combination. In this article, we discuss recent adjuvant development and novel cellular adjuvant products for therapeutic cancer vaccines.

NKT cell responses to glycolipid activation.

NKT cells are a distinct lineage of T lymphocytes that are usually identified by the co-expression of the semi-invariant CD1d-restricted alphabeta TCR and the NK1.1 allelic marker of NK lineage receptors in the C57BL/6 mice and related strains. NKT cells can be subdivided based on CD4/CD8 expression and on tissue of origin. NKT cells express significantly the TCR gene products Valpha24 JalphaQ in humans, the homolog of mouse Valpha14 Jalpha18, paired with Vbeta11, the homolog of mouse Vbeta8.2. NKT cells are most frequent in liver (up to 30% of T cells in mice and approximately 4% of hepatic T cells in human), bone marrow, and thymus and represent a smaller proportion of T cells in other tissues including spleen, lymph nodes, blood, and lung. NKT cells recognize a broad array of glycolipids in the context of CD1d presentation, and many studies have characterized a cascade of functions following in vitro and in vivo stimulation by alpha-GalCer, including production of high levels of immune-regulatory cytokines and bystander activation of several cell types including NK, B, T, and dendritic cells. Both in vitro and in vivo methods have been developed for the study of NKT responses to glycolipid presentation by CD1d. In practice, CD1d-glycolipid-loaded tetramers would most reliably identify these cells. In vitro, splenocytes can be used to monitor cytokine release as this population contains all the cells necessary for sequestering, loading onto CD1d molecules, and presentation of glycolipids to NKT cells. Another system involves the use of NKT cell hybridoma and CD1d coated onto plastic plates to measure responses limited to NKT cells more precisely. In vivo, responses are typically measured by injecting the glycolipid into mice and monitoring plasma cytokine levels or DC maturation in the spleen. This chapter describes methods that can be used to identify NKT cells and to asses in vitro and in vivo their activation and expansion.