Brown adipose tissue (BAT) has a unique capacity to expend calories by decoupling energy expenditure from ATP production, therefore BAT could realize therapeutic potential to treat metabolic diseases such as obesity and type 2 diabetes. Recent studies have investigated markers and function of native BAT, however, successful therapies will rely on methods that supplement the small existing pool of brown adipocytes in adult humans. In this study, we engineered BAT from both human and rat adipose precursors and determined whether these ex vivo constructs could mimic in vivo tissue form and metabolic function. Adipose-derived stem cells (ASCs) were isolated from several sources, human white adipose tissue (WAT), rat WAT, and rat BAT, then differentiated toward both white and brown adipogenic lineages in two-dimensional and three-dimensional (3D) culture conditions. ASCs derived from WAT were successfully differentiated in 3D poly(ethylene glycol) hydrogels into mature adipocytes with BAT phenotype and function, including high uncoupling protein 1 (UCP1) mRNA and protein expression and increased metabolic activity (basal oxygen consumption, proton leak, and maximum respiration). By utilizing this "browning" process, the abundant and accessible WAT stem cell population can be engineered into 3D tissue constructs with the metabolic capacity of native BAT, ultimately for therapeutic intervention in vivo and as a tool for studying BAT and its metabolic properties.

Soft tissue reconstruction remains an intractable clinical challenge as current surgical options and synthetic implants may produce inadequate outcomes. Soft tissue deficits may be surgically reconstructed using autologous adipose tissue, but these procedures can lead to donor site morbidity, require multiple procedures, and have highly variable outcomes. To address this clinical need, we developed an “off-the-shelf” adipose extracellular matrix (ECM) biomaterial from allograft human tissue (Acellular Adipose Tissue, AAT). We applied physical and chemical processing methods to remove lipids and create an injectable matrix that mimicked the properties of lipoaspirate. Biological activity was assessed using cell migration and adipogenesis assays. Characterization of regenerative immune properties in a murine muscle injury model revealed that allograft and xenograft AAT induced pro-regenerative CD4+ T cells and macrophages with xenograft AAT additionally attracting eosinophils secreting interleukin 4 (Il4). In immunocompromised mice, AAT injections retained similar volumes as human fat grafts but lacked cysts and calcifications seen in the fat grafts. The combination of AAT with human adipose-derived stem cells (ASCs) resulted in lower implant volumes. However, tissue remodeling and adipogenesis increased significantly in combination with ASCs. Larger injected volumes of porcine-derived AAT demonstrated biocompatibility and greater retention when applied allogeneicly in Yorkshire cross pigs. AAT was implanted in healthy volunteers in abdominal tissue that was later removed by elective procedures. AAT implants were well tolerated in all human subjects. Implants removed between 1 and 18 weeks demonstrated increasing cellular infiltration and immune populations, suggesting continued tissue remodeling and the potential for long-term tissue replacement.

BACKGROUND: AB154 is a humanized antibody that blocks human TIGIT (T-cell immunoreceptor with Ig and ITIM domains), an inhibitory receptor expressed on natural killer (NK) cells, CD8+ T cells, CD4+ T cells and regulatory T cells (Treg). DNAM-1 (DNAX Accessory Molecule-1) is an activating receptor found on NK cells, monocytes and a subset of T cells that competes with TIGIT for shared ligands CD155 (PVR) and CD112 (Nectin-2), expressed by cancer and antigen-presenting cells. TIGIT blockade prevents binding to its ligands and shifts the immune balance towards a more favorable DNAM-1 interaction. AB154 has the potential to promote sustained immune activation and tumor clearance, particularly in combination with other immunotherapies such as AB122 (α-PD1). METHODS: Binding affinity of AB154 was determined in CHO cells over-expressing human TIGIT and in human T cells. TIGIT blockade was quantified using a TIGIT-expressing reporter gene cell line. TIGIT and PD-1 expression in cancer patient PBMCs and dissociated tumor cells (DTCs) were assessed by flow cytometry. Gene expression of these markers were also derived from TCGA (The Cancer Genome Atlas), GTEX (Genotype-Tissue Expression Project), RNAseq, and by immunohistochemistry in various tumor types and normal tissues. A receptor occupancy (RO) assay was developed using a competing α-TIGIT antibody and validated ex vivo in whole blood leukocytes from healthy donors and cancer patients. RESULTS: AB154 binds to and blocks human TIGIT with sub-nanomolar affinity. Data assembled from TCGA identified tumor types in which expression of TIGIT is greater than PD-1, equivalent to PD-1, or less than PD-1. Expression of TIGIT and CD155 at the protein level was confirmed by IHC. Immunophenotyping performed on dissociated human tumor cells demonstrated strong correlation between TIGIT and PD-1 expression on immune cells. The intensity of TIGIT staining was lowest on conventional CD4+ T cells while its intensity in Treg and CD8+ T cells was 1.5 to 3-fold higher on average. Using flow cytometry, we profiled lymphocyte populations in peripheral whole blood and demonstrated target engagement by AB154 on T cells and NK cells in the low nanomolar range in both healthy and cancer patients (ex vivo). This receptor occupancy assay is being used to monitor target engagement in AB154 dosed patient samples in an ongoing Phase 1 dose escalation study in oncology patients. CONCLUSION: Blockade of multiple immune checkpoint proteins can confer effective and durable responses in the treatment of cancer. The data presented will provide: 1) the basis for selection of tumor types by TIGIT RNA and protein expression profiles, 2) rationale for combining AB154 with AB122 (α-PD-1) in upcoming clinical trials, 3) methodology to evaluate TIGIT receptor occupancy and 4) preliminary PK/PD data from the AB154 Phase 1 dose escalation study in oncology subjects. Citation Format: Amy E. Anderson, Daniel DiRenzo, Susan Lee, Akshata Udyavar, Kimberline Gerrick, Hema Singh, Xiaoning Zhao, Lixia Jin, Lisa Seitz, Nigel P. Walker, Matthew J. Walters, Joanne B. Tan. Characterization of AB154, a humanized anti-TIGIT antibody, for use in combination studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1557.

Soft tissue reconstruction remains an intractable clinical challenge as current surgical options and synthetic implants may produce inadequate outcomes. Soft tissue deficits may be surgically reconstructed using autologous adipose tissue, but these procedures can lead to donor site morbidity, require multiple trips to the operating room, and have highly variable outcomes. To address the clinical need for soft tissue reconstruction, we developed an off-the-shelf adipose matrix from allograft human adipose tissue (acellular adipose tissue, AAT). We applied physical and chemical processing methods to remove lipids and create an injectable matrix that mimicked the properties of fat grafting materials. Biological activity was assessed using cell migration and stem cell adipogenesis assays. Characterization of the regenerative immunology properties in a murine muscle injury model revealed allograft and xenograft AAT induced pro-regenerative CD4+ T cells and macrophages with xenograft AAT attracting additional eosinophils secreting interleukin 4 (Il4). In immunocompromised mice, AAT injections retained similar tissue volumes as human fat grafts but did not have the cysts and calcifications that formed in the human fat graft implants. Combination of AAT with human adipose-derived stem cells (ASCs) resulted in lower implant volumes. However, tissue remodeling and new adipose development increased significantly with the addition of cells. Larger injected volumes of porcine-derived AAT demonstrated biocompatibility and greater volume retention when applied allogeneicly in Yorkshire cross pigs. Under a biologic IND application, AAT was implanted in healthy volunteers in abdominal tissue that was later removed (panniculectomy or abdominoplasty). The AAT implants were well tolerated and biocompatible in all eight human subjects. Analysis of implants removed between 1 and 18 weeks demonstrated increasing cellular infiltration and immune populations, suggesting continued tissue remodeling and the potential for long term tissue replacement.

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