738 Intratumoral administration of alum-tethered engineered inflammatory cytokines safely elicits potent local and systemic immunity

Background While immune checkpoint blockade therapy has improved progression-free survival in patients suffering from cancer over other treatments, 1–4 these typically elicit durable responses only minority of patients, part because the highly immunosuppressive tumor microenvironment (TME). 5 6 Rational combinations with inflammatory cytokines can relieve some immunosuppression, 7 8 but systemic dosing proteins is impeded by severe immune-related adverse events (irAE). 9–14 One approach to focus activity immunostimulatory agents tumors while lowering toxicity administer drugs intratumorally. However, intratumoral injection alone generally achieves limited persistence TME, as quickly clear via lymphatics and vasculature, rapidly leading harmful accumulation circulation. 15 16 Thus, approaches promote vivo retention intratumorally administered are necessary maximize local stimulation. Methods We engineered Interleukin-12 (IL-12) a peptide tag containing multiple phosphoserine (pSer) residues, through in-cell phosphorylation during recombinant expression mammalian cells. then inoculated mice B16F10, or Ag104A tumors, treated established single dose IL-12 mixed alum, monitored size weights time. Immunophenotyping draining lymph nodes (dLNs) was conducted at several timepoints after treatment. Tumors serum were also collected perform bead-based Luminex analysis many (including IFN-γ). Results Cytokines pSer tags bind tightly common vaccine adjuvant aluminum hydroxide (alum) ligand exchange (72% pSer-IL-12 vs 3.5% IL-12, P<0.0001). Alum particles form physical depot sites that persistent weeks. So, pSer-IL-12-loaded alum led >400-fold greater protein relative unanchored 2-fold lower ALT (a biomarker for toxicity). Further, alum-tethered induced 5-fold IFN-γ secretion (P=0.0031) primarily CD8+ T cells doubled (P<0.0001) proportion antigen-carrying, CD86-expressing CD103+ DCs dLN free IL-12. alum/pSer-IL-12 enhanced (anti-PD1), cure rate 52% poorly immunogenic B16F10 compared 0% Local treatment ipsilateral clearance large, untreated contralateral 9/15 animals vs. 5/17 (P=0.04). Conclusions alum-anchored presents safe, tumor-agnostic improve anti-cancer immunity. References Wolchok JD, Chiarion-Sileni V, Gonzalez R, Rutkowski P, Grob JJ, Cowey CL, et al. Overall combined nivolumab ipilimumab advanced melanoma. New England Journal Medicine 2017; 377 (14):1345–56. Ansell SM, Lesokhin AM, Borrello I, Halwani A, Scott EC, Gutierrez M, PD-1 Blockade relapsed refractory Hodgkin's lymphoma. [Internet] . 2015; 372 (4):311–9. Available from: http://www.nejm.org/doi/10.1056/NEJMoa1411087. 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