Abstract B008: Imprime PGG, an Intravenously Administered Beta Glucan PAMP Activates the Innate Immune System: A Phase I Clinical Study to Evaluate Immunopharmacodynamic Responses

Imprime PGG (Imprime), in combination with both tumor-targeting and anti-angiogenic antibodies, has shown promising efficacy in multiple phase 2 clinical trials. In numerous pre-clinical in vivo tumor models, Imprime also enhances the efficacy of immune checkpoint inhibitor antibodies in addition to tumor-targeting and anti-angiogenic antibodies. Imprime is a yeast-derived, soluble β-1,3/1,6 glucan that acts as a Pathogen Associated Molecular Pattern (PAMP) to trigger activation of innate immune effector cells (macrophages, monocytes, neutrophils, dendritic cells (DC)), which orchestrate a coordinated anti-cancer immune response with cells of the adaptive immune system. Ex vivo studies with human whole blood have shown that Imprime forms an immune complex with endogenous anti-beta glucan antibodies (ABA) to trigger a constellation of innate immune functions. These include complement activation via the classical complement pathway, select chemokine production, phenotypic activation and enhanced tumor cell killing by neutrophils and macrophages. Imprime also activates antigen-presenting cells (e.g. macrophages, DC), enabling T cell expansion and activation. In vivo, intravenous (IV) injection of Imprime in C57BL/6 mice increases select chemokine expression, triggers neutrophil and monocyte mobilization into circulation and secondary lymphoid organs, and also enhances DC maturation and antigen-specific T-cell priming. In this study, we show that the immunopharmacodynamic (IPD) responses elicited by IV administration of Imprime in healthy human subjects are consistent with the innate immune responses observed in ex vivo human and in vivo mouse studies. Healthy human volunteers (18-65 yr) were administered single (Cohort 1) or multiple (once weekly for 3 wks-Cohort 2) doses of Imprime PGG (4 mg/kg) by IV infusion over 2-3 hrs. Physical examination with vital signs, adverse event solicitation and timed blood sampling for IPD changes were performed. IPD endpoints included complement protein levels, circulating blood cell lineage counts, ABA concentrations, circulating immune complex (CIC) levels, cytokine and chemokine concentrations, as well as binding and activation of blood leukocytes. Cohort 1 and 2 results show that the complement activation proteins C5a and SC5b-9 were significantly increased in the plasma at the end of infusion (EOI) of Imprime. The formation of Imprime:ABA complexes was evident in a substantial drop of free ABA and a concomitant increase in CIC in the serum also at the EOI. IL-8 and MCP-1 were consistently detected between EOI and 1 hr post infusion. Additional chemokines, including MIP-1α, MIP-1β, and IP-10 were also detected in some of the subjects. A significant increase in the neutrophil and monocyte counts was seen in the blood after infusion. Cellular analyses showed Imprime binding to neutrophils, monocytes, and subsets of DC (classical and inflammatory) 15-30 mins after the start of infusion. Additionally, 24 hrs after completion of Imprime administration, a population of non-classical monocytes (CD14/CD16 positive), which are known to have higher antigen presentation capability and thus express higher levels of the activation markers CD86, PD-L1, and HLA-DR, was observed. Importantly, these IPD responses were evident only in subjects with higher ABA levels. Collectively, these data provide the first evidence that, when dosed IV in healthy human subjects, Imprime elicits a constellation of innate immune activating events that are consistent with efficacy in preclinical tumor models. Importantly, these human data also provide the first evidence linking pre-treatment ABA levels and Imprime induced IPD changes, suggesting the plausibility of using pre-treatment ABA levels in the selection of patients most likely to benefit from Imprime-based therapy. Citation Format: Nadine C. Ottoson, Richard D. Huhn, Jamie Lowe, Ben Harrison, Jose Iglesias, Blaine Rathmann, Takashi Kangas, Lindsay R. Wurst, Xiaohong Qiu, Anissa Chan, Adria Bykowski Jonas, Kathryn Fraser, Richard M. Walsh, Katie Ertelt, Steven M. Leonardo, Ross Fulton, Keith Gorden, Mark A. Matson, Mark Uhlik, Jeremy Graff, Nandita Bose. Imprime PGG, an intravenously administered beta glucan PAMP activates the innate immune system: A phase I clinical study to evaluate immunopharmacodynamic responses [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B008.