In vivo tracking of [89Zr]Zr-labeled engineered extracellular vesicles by PET reveals organ-specific biodistribution based upon the route of administration.

Extracellular vesicles (EVs) have garnered increasing interest as delivery vehicles for multiple classes of therapeutics based on their role as mediators in an important, natural intercellular communication system. We recently described a platform to allow the design, production and in vivo study of human EVs with specific properties (drug or tropism modifiers). This article seeks to compare and expand upon historical biodistribution and kinetic data by comparing systemically and compartmentally administered labeled engineered EVs using in vivo and ex vivo techniques. METHODS: EVs were surface-labeled to high radiochemical purity and specific activity with 89Zirconium deferoxamine ([89Zr]Zr-DFO) and/or cy7-scrambled antisense oligonucleotide (Cy7-ExoASOscr), or luminally loaded with GFP for in vivo tracking in rodents and non-human primates (NHPs). Positron Emission Tomography (PET) and subsequent immunohistochemistry (IHC) and autoradiography (ARG) cross-validation enabled assessment of the anatomical and cellular distribution of labeled EVs both spatially and temporally. RESULTS: Over time, systemic administration of engineered EVs distributed preferentially to the liver and spleen (Intravenous, IV), gastrointestinal tract and lymph nodes (Intraperitoneal, IP) and local/regional lymph nodes (Subcutaneous, SC). Immunostaining of dissected organs displaying PET signal revealed co-localization of an EV marker (PTGFRN) with a subset of macrophage markers (CD206, F4/80, IBA1). Compartmental dosing into NHP cerebrospinal fluid (CSF) resulted in a heterogenous distribution of labeled EVs depending upon whether the route was intrathecal (ITH), intracisterna magna (ICM) or intracerebroventricular (ICV), compared to the homogeneous distribution observed in rodents. Thus anatomically, ITH administration in NHP revealed meningeal distribution along the neuraxis to the base of the skull. In contrast ICM and ICV dosing resulted in meningeal distribution around the skull and to the cervical and thoracic spinal column. Further characterization using IHC shows uptake in a subset of meningeal macrophages. CONCLUSIONS: The present studies provide a comprehensive assessment of the fate of robustly and reproducibly labeled engineered EVs across several mammalian species. The in vivo distribution was observed to be both spatially and temporally dependent upon the route of administration providing insight into potential targeting opportunities for engineered EVs carrying a therapeutic payload.

ExoSTING, an extracellular vesicle loaded with STING agonists, promotes tumor immune surveillance.

Cyclic dinucleotide (CDN) agonists of the STimulator of InterferoN Genes (STING) pathway have shown immune activation and tumor clearance in pre-clinical models. However, CDNs administered intratumorally also promote STING activation leading to direct cytotoxicity of many cell types in the tumor microenvironment (TME), systemic inflammation due to rapid tumor extravasation of the CDN, and immune ablation in the TME. These result in a failure to establish immunological memory. ExoSTING, an engineered extracellular vesicle (EV) exogenously loaded with CDN, enhances the potency of CDN and preferentially activates antigen presenting cells in the TME. Following intratumoral injection, exoSTING was retained within the tumor, enhanced local Th1 responses and recruitment of CD8+ T cells, and generated systemic anti-tumor immunity to the tumor. ExoSTING at therapeutically active doses did not induce systemic inflammatory cytokines, resulting in an enhanced therapeutic window. ExoSTING is a novel, differentiated therapeutic candidate that leverages the natural biology of EVs to enhance the activity of CDNs.

A versatile platform for generating engineered extracellular vesicles with defined therapeutic properties.

Extracellular vesicles (EVs) are an important intercellular communication system facilitating the transfer of macromolecules between cells. Delivery of exogenous cargo tethered to the EV surface or packaged inside the lumen are key strategies for generating therapeutic EVs. We identified two "scaffold" proteins, PTGFRN and BASP1, that are preferentially sorted into EVs and enable high-density surface display and luminal loading of a wide range of molecules, including cytokines, antibody fragments, RNA binding proteins, vaccine antigens, Cas9, and members of the TNF superfamily. Molecules were loaded into EVs at high density and exhibited potent in vitro activity when fused to full-length or truncated forms of PTGFRN or BASP1. Furthermore, these engineered EVs retained pharmacodynamic activity in a variety of animal models. This engineering platform provides a simple approach to functionalize EVs with topologically diverse macromolecules and represents a significant advance toward unlocking the therapeutic potential of EVs.

Exosome Surface Display of IL12 Results in Tumor-Retained Pharmacology with Superior Potency and Limited Systemic Exposure Compared with Recombinant IL12.

The promise of IL12 as a cancer treatment has yet to be fulfilled with multiple tested approaches being limited by unwanted systemic exposure and unpredictable pharmacology. To address these limitations, we generated exoIL12, a novel, engineered exosome therapeutic that displays functional IL12 on the surface of an exosome. IL12 exosomal surface expression was achieved via fusion to the abundant exosomal surface protein PTGFRN resulting in equivalent potency in vitro to recombinant IL12 (rIL12) as demonstrated by IFNγ production. Following intratumoral injection, exoIL12 exhibited prolonged tumor retention and greater antitumor activity than rIL12. Moreover, exoIL12 was significantly more potent than rIL12 in tumor growth inhibition. In the MC38 model, complete responses were observed in 63% of mice treated with exoIL12; in contrast, rIL12 resulted in 0% complete responses at an equivalent IL12 dose. This correlated with dose-dependent increases in tumor antigen-specific CD8+ T cells. Rechallenge studies of exoIL12 complete responder mice showed no tumor regrowth, and depletion of CD8+ T cells completely abrogated antitumor activity of exoIL12. Following intratumoral administration, exoIL12 exhibited 10-fold higher intratumoral exposure than rIL12 and prolonged IFNγ production up to 48 hours. Retained local pharmacology of exoIL12 was further confirmed using subcutaneous injections in nonhuman primates. This work demonstrates that tumor-restricted pharmacology of exoIL12 results in superior in vivo efficacy and immune memory without systemic IL12 exposure and related toxicity. ExoIL12 is a novel cancer therapeutic candidate that overcomes key limitations of rIL12 and thereby creates a therapeutic window for this potent cytokine.