Development of a combined radiation and full thickness burn injury minipig model to study the effects of uncultured adipose-derived regenerative cell therapy in wound healing

Abstract

Purpose: To develop an approach that models the cutaneous healing that occurs in a patient with full thickness thermal burn injury complicated by total body radiation exposure sufficient to induce sub-lethal prodromal symptoms. An assessment of the effects of an autologous cell therapy on wound healing on thermal burn injury with concomitant radiation exposure was used to validate the utility of the model.

Methods: Göttingen minipigs were subjected to a 1.2 Gy total body irradiation by exposure to a 6 MV X-ray linear accelerator followed by ∼10 cm² full thickness burns (pre-heated brass block with calibrated spring). Three days after injury, wounds were excised to the underlying fascia and each animal was randomized to receive treatment with autologous adipose-derived regenerative cells (ADRC) delivered by local or intravenous injection, or vehicle control. Blood counts were used to assess radiation-induced marrow suppression. All animals were followed using digital imaging to assess wound healing. Full-thickness biopsies were obtained at 7, 14, 21 and 30 days’ post-treatment.

Results: Compared to animals receiving burn injury alone, significant transient neutropenia and thrombocytopenia were observed in irradiated subjects with average neutrophil nadir of 0.79 × 10³/μl (day 15) and platelet nadir of 60 × 10³/μl (day 12). Wound closure through a combination of contraction and epithelialization from the wound edges occurred over a period of approximately 28 days’ post excision and treatment. Re-epithelialization was accelerated in wounds treated with ADRC (mean 3.5-fold increase at 2 weeks post-treatment relative to control). This acceleration was accompanied by an average 67% increase in blood vessel density and 30% increase in matrix (collagen) deposition. Similar results were observed when ADRC were injected either directly into the wound or by intravenous administration.

Conclusions: Although preliminary, this study provides a reproducible minipig model of thermal burn injury complicated by myelosuppressive total body irradiation that utilizes standardized procedures to evaluate novel countermeasures for potential use following attack by an improvised nuclear device.

Keywords:

• Adipose-derived regenerative cells
• combined injuries
• radiation
• thermal burn

Disclosure statement

PF, AG, ZA, SZ and JKF are paid employees and stock holders of Cytori Therapeutics, Inc., San Diego. MT receives consulting fees from Cytori Therapeutics, Inc. DZ, MDE, FB and WW have no conflicts of interest with regard to this study. The authors alone are responsible for the content and writing of the paper.

Funding

This work was supported by contract HHSO100201200008C from the Biomedical Advanced Research and Development Authority (BARDA), Department of Health and Human Services. DZ was supported by a grant from the California Institute for Regenerative Medicine (CIRM; TB1-01175).