Methods of ex vivo analysis of tissue status in vascularized composite allografts

Abstract

Vascularized composite allotransplantation can improve quality of life and restore functionality. However, the complex tissue composition of vascularized composite allografts (VCAs) presents unique clinical challenges that increase the likelihood of transplant rejection. Under prolonged static cold storage, highly damage-susceptible tissues such as muscle and nerve undergo irreversible degradation that may render allografts non-functional. Skin-containing VCA elicits an immunogenic response that increases the risk of recipient allograft rejection. The development of quantitative metrics to evaluate VCAs prior to and following transplantation are key to mitigating allograft rejection. Correspondingly, a broad range of bioanalytical methods have emerged to assess the progression of VCA rejection and characterize transplantation outcomes. To consolidate the current range of relevant technologies and expand on potential for development, methods to evaluate ex vivo VCA status are herein reviewed and comparatively assessed. The use of implantable physiological status monitoring biochips, non-invasive bioimpedance monitoring to assess edema, and deep learning algorithms to fuse disparate inputs to stratify VCAs are identified.

Keywords: Bioanalytical methods; Biomarkers; Transplantation; VCA; Vascularized composite tissue allografts.

Fig. 1

Perfusion bioreactor design and implementation. The general layout of the machine extracorporeal perfusion system commonly used in VCA ex-vivo perfusion. A A schematic illustration of the perfusate circulation as a system comprising a the porcine forelimb in the perfusion box on top of a b metal grid that allows c passive venous drainage of the preservation fluid, d a 15 mm needle probe that measures muscle temperature, e collection reservoir, f a centrifugal pump, regulating in-line pressure at ≤ 30 mmHg, g a membrane oxygenator, infusing the fluid with a mix of 95% O₂ and 5% CO₂, h heater-cooler machine, cooling the fluid to 8–10 °C, i drug administration point/fluid sampling port, and j flowmeter. (Image reproduced with permission from [54] ©2020 Anne Sophie Kruit et al. Transplant International published by John Wiley & Sons Ltd on behalf of Steunstichting ESOT.) B An actual perfusion system showing a human arm in the bioreactor chamber. C and D Photos of actual perfusion bioreactor systems consisting of an allograft housing, perfusate pump, perfusate oxygenator, heater, sampling port, and flow meter. (Images reproduced with permission from [47] © 2017 Wolters Kluwer Health)

Fig. 2

An illustrative summary of methods of analysis of tissue status during preservation of allografts in VCA. Clockwise: Metabolic, Biochemical, Histopathological, and Biophysical. (Images reproduced with permission from [60, 61] © 2015 Royal College of Ophthalmologists, 2019 American Chemical Society, respectively.)

Fig. 3

Edema is the main Indicator of acute rejection in VCA. A Representative images of edema manifestation in face allograft acute rejection i. No rejection (POM21), ii. early rejection (POM 8) and iii. late rejection (POM26). (Images reproduced with permission from [2] © 2019 Mary Ann Liebert, Inc.) B Edema manifestation in hand allograft acute rejection (Images reproduced with permission from [107] © John Wiley & Sons, Inc.) C Skin allograft acute rejection graded based on Banff Scoring System. Normal skin: unaffected skin, GradeI: mild perivascular infiltration, GradeII: mild perivascular infiltration with/without mild epidermal or adnexal involvement. No epidermal dyskeratosis or apoptosis, Grade III: dense inflammation and epidermal involvement with apoptosis, dyskeratosis, and/or keratinolysis, Grade IV: necrotizing acute rejection. necrosis of skin structures. (Images reproduced with permission from [108] © 2013 Ravi Starzl et al.) D Association of clinical signs or subtherapeutic tacrolimus levels with acute rejection episodes. (Image reproduced with permission from [2] © 2019 Mary Ann Liebert)