Activation of iNKT cells is a potentially potent immunotherapeutic tool, but the excessive potency of the prototypic α-GalCer agonist with simultaneous production of pro- and anti-inflammatory cytokines hampers its clinical use. α-GalCer analogs may overcome these limitations if capable of directing the response to the appropriate effector brand.

We previously showed how a synthetic analog with a modified polar head induced a strong Th1 response and an efficient iNKT cell dependent antitumor response in a lung metastases model. A new analog analyzed induced a stronger and absolutely specific Th1 response, with no traces of Th2 cytokines. These in vivo characteristics of iNKT agonists were not anticipated by in vitro functional assays. The characteristic cytokine storm produced by α-GalCer was not induced, which translates in increased antitumor response both in preventive and therapeutic settings, more efficiently controlling the establishment of lung metastases. Other tumor models, as survival experiments after i.p. administration of tumor lines, also showed a more potent antitumor response.

Secondary transactivation of adaptive and innate effector cells is potently induced, with strong mobilization and activation. In vivo cytotoxicity experiments show differential responses, both quantitative and qualitatively, against NK-sensitive or fully competent targets raised by the different agonists. In vivo depletion experiments demonstrate involvement of NK cells and macrophages in tumor killing, which varies depending on the target tumor and the iNKT agonist. Furthermore, differential activation kinetics and cytokine and chemokine induction, may underline mechanistic differences in the antitumor response.

Additionally, adjuvancy functionality in the induction of humoral response against model antigen is qualitatively different depending on the agonist, with an immunoglobulin subtype change toward opsonizing antibodies, precisely those that mediate anti-pathogenic effector cellular responses. As this new agonist also activates human iNKT cells, it may be an advantageous reagent for future translation to the clinic.