Cellular activation pathways and interaction networks in vascularized composite allotransplantation

A comparative analysis of lesional skin, sentinel flap, and mucosal biopsies in assessing acute face transplant rejection

Background

Face transplant rejection is primarily monitored through skin biopsies, but mucosal tissue may detect immune rejection events missed by skin biopsies.

Methods

We retrospectively reviewed 47 paired mucosal and facial skin biopsies and 37 paired facial skin and sentinel flap biopsies from nine face transplant recipients. Rejection was graded using the 2007 Banff classification. Correlation, sensitivity, and specificity metrics were assessed.

Results

Mucosa and facial skin rejection grades correlated strongly (r = 0.72, p < 0.0001), with mucosa showing a negative predictive value (NPV) of 0.85 for facial skin rejection. Mucosal biopsies identified rejection in 10 cases missed by facial skin biopsies. Sentinel skin biopsies had high correlation but an NPV of 0.76, missing 24% of rejection cases.

Conclusion

Mucosal biopsies tend to capture the full spectrum of rejection, whereas skin biopsies alone may miss important rejection events occurring in the mucosa. Mucosal biopsies should be integrated into routine monitoring alongside skin biopsies, as they not only sensitively function as sentinel tissue but also provide critical insights into rejection activity that may otherwise go undetected. This dual approach could improve overall transplant surveillance. Inconsistencies in rejection patterns between the two tissues highlight the need for a reworked grading system.

The prognostic relevance of donor-specific antibodies in facial transplantation - A retrospective cohort study

BACKGROUND

Little is known about the prognostic relevance of donor-specific antibodies (DSAs) and C4d tissue deposition for acute and chronic rejection in facial vascularized composite allotransplantation.

METHODS

We conducted a retrospective analysis of nine face transplant patients. Outcome measures, such as DSA positivity, were determined by the local tissue typing laboratory, whereas C4d deposition was assessed by immunostaining. Acute rejection events, occurrence of chronic rejection, and transplant-related outcomes were collected.

RESULTS

Five (5/9) patients developed de novo DSAs. Among the 56 time points when rejection grade, DSA, and C4d levels were measured concurrently, 25 (44.6%) had only one positive parameter (DSA or C4d), 23 (41.1%) had two negative values, and 8 (14.3%) had both parameters positive. A trend was observed where acute rejection grades were higher at time points with both DSA positivity and C4d deposition compared with time points where both parameters were negative. Chronic rejection was observed in four patients, two of whom developed DSAs and two who did not. Among the five patients who developed de novo DSAs, graft loss occurred in one patient. The remaining four patients with de novo DSAs retained their allografts [mean follow-up: 118 (63-162) months].

CONCLUSION

We identified a potential association between DSAs and grade of acute cellular rejection. Chronic rejection was observed in four patients, with no clear association with DSA status. Only one out of five patients who developed DSAs underwent graft loss. Further studies need to explore the mechanistic role of DSAs in the setting of VCA rejection.

Urinary bladder transplantation in humans - current status and future perspectives

Urinary bladder vascularized allograft transplantation in humans is currently extensively being investigated worldwide, owing to the theoretical potential of this approach as a therapeutic option for individuals with end-stage, non-oncological bladder conditions or congenital bladder pathologies. To date, a successful attempt at urinary bladder autotransplantation was carried out in a heart-beating brain-dead research human donor. The robot-assisted surgical technique was shown to be optimal for performing this procedure, achieving a good performance in terms of both bladder allograft collection as well as vascular, ureterovesical and vesicourethral anastomoses. The urinary bladder vascularized allograft would be an alternative to traditional urinary diversion methods that rely on the use of intestinal segments, potentially avoiding adverse effects associated with these approaches. However, different from ileal urinary diversion, bladder transplantation would require lifelong immune suppression. Clinical trials are in progress to assess the vascularized bladder allograft transplantation technique, as well as the safety of this procedure in oncological and non-oncological indications.

Ten-year follow-up after face transplantation-A single-center retrospective cohort study

Face transplantation has emerged as reconstructive option for the most challenging facial deformities. A comprehensive analysis of functional outcomes, medical complications, incidence of malignancy, and chronic rejection in face transplantation recipients over an extended follow-up period has not yet been published leaving a notable gap in the literature. We retrospectively collected data of morbidity, rejection, vasculopathy, metabolic side effects, as well as functional outcome of sensory return, facial motor function, and speech from 9 patients who underwent face transplantation at Brigham and Women's Hospital between 2009 and 2020. The median follow-up was 120 months (54 and 154 months). Four grafts (40%) developed signs of clinical and histopathologic chronic rejection without evidence of vasculopathy on computed tomography angiograms. Sensory return assessed with Weinstein enhanced sensory testing-monofilament showed an increase in 6 patients (66.7%), and facial expression analysis showed improvement throughout the whole cohort at their most recent follow-up. Speech intelligibility was stable or increasing for 5 patients (55.6%). In conclusion, the long-term outcomes reveal promising results in terms of overall graft retention and functional recovery. Metabolic, malignant, and infectious complications, as well as graft rejection episodes, are expected to occur in this population, and some may be related to patient's age and lifestyle.

Long-term posttransplant-related bone volumetric changes in eight face transplant recipients - A single-center retrospective case series

BACKGROUND

The long-term stability of allograft or native bone in facial vascularized composite allograft (fVCA) recipients is unclear. This study quantified long-term bone volume changes in facial transplants.

METHODS

Computed tomography scans of eight fVCA recipients (2011-2023) were analyzed with Materialise Mimics. Native bone (soft tissue-only VCAs, n=4) and allotransplanted bone (n=4) were compared. Median bone volumes were assessed for significance using the WilcoxonRanked-Sum Test.

RESULTS

Mean follow-up was 10 years (range 5-13). A significant median decrease in both mandibular (-6520 mm3; p=0.0078) and maxillary (-3548 mm3; p=0.0078) bone volumes was seen in all patients, irrespective of bone origin. Median bone volume loss was -9.92% in the bony allograft cohort and -22.60% in the soft tissue-only cohort, respectively. The histopathological analysis of the limited samples (n=2) showed physiological bone even after ten years.

CONCLUSION

Patients with allotransplanted bone showed less pronounced volume loss compared to those with native bone receiving soft tissue-only allografts. This finding suggests that allotransplanted vascularized bone in fVCAs may not be a primary target of chronic rejection processes that compromise bone volume stability and functionality. Bone volume changes are likely influenced by multiple factors, such as tooth loss, nutrition, chronic immunosuppression (e.g., steroids), mechanical stress/load, varying bone remodeling rates, and other medical comorbidities. Further research is needed to clarify the factors affecting bone volume and remodeling after fVCA.

B-cell infiltration distinguishes mucosal from skin patterns of rejection in facial vascularized composite allografts

Rejection monitoring in facial vascularized composite allotransplantation traditionally focuses on skin biopsies. However, mucosal rejection frequently presents with more pronounced signs of immune activity. To explore mechanistic differences between skin and mucosal rejection, rejection and nonrejection biopsies from allograft skin and oral mucosa of 9 facial vascularized composite allotransplantation recipients were retrospectively analyzed using histology, multiplex immunostaining, and gene expression profiling, with peripheral blood mononuclear cells quantified via mass cytometry. Both skin and mucosa exhibited similar patterns of granzyme B expressing (GZMB+) T cells, indicating T cell-mediated rejection in both tissues. However, mucosa demonstrated additional CD19+ B cell infiltration and occasional plasma cells, which were absent in skin. These intramucosal B cells expressed AHNAK and CD43, suggesting they may be innate-like B cells (Bin cells). CD8+/GZMB+ cells and B cell populations were enriched in peripheral blood mononuclear cells during combined skin and mucosal rejection but not isolated skin rejection. These findings suggest distinct rejection mechanisms in skin and mucosa, with mucosa uniquely involving B cells. Current skin-focused rejection monitoring may overlook important mucosal rejection events, emphasizing the need to monitor both tissues concurrently. Mucosal biopsies could improve the accuracy in detecting acute rejection.

Vascularised Composite Allotransplantation - A guide to optimal dissemination of scientific outputs

Purpose

The impact of academic research is not just important within the clinical domain but within society as a whole. Altmetric Attention Score (AAS) offers a means of assessing how scholarly outputs are interacted with online. Vascularised Composite Allotransplantation (VCA) is a modern but rapidly evolving topic which encompasses a broad range of complex and clinically significant surgical interventions. Primarily VCA is utilised in the reconstruction of complex, composite tissue defects, including limb and face transplantation. There is also a growing interest in the role of VCA as an early means of real-time immuno-monitoring, in sentinel skin flap transplant (SSF).

Materials & methods

In July 2024, a search was conducted using the Altmetric Explorer (AE) database using the search term 'vascular-composite' AND 'allograft' OR 'allotransplant'. A simultaneous literature search was carried out using Web of Science (WoS) database utilising the same search terms with extraction of traditional citation-based metrics as well as relevant 'meso' and 'micro' subject headings. Corresponding citation-based metrics were extracted utilising SCImago. Data was compiled and analysed using a linear regression model with level of significance set at p < 0.05.

Results

The Top 100 (T100) performing articles relating to VCA displayed a mean Altmetric Attention Score (AAS) of 3.31. All T100 papers were published in the English language. Sixty percent (n = 60) of T100 papers were published in Q1 Journals. News outlet mentions (r = 6.95), blog mentions (r = 6.20), and Twitter/X mentions (r = 0.52) demonstrated the greatest positive impact on AAS upon application of a linear regression model (p < 0.05).

Conclusion

Altmetric Scores offer a means of appraising the impact of research outputs in both academic and societal domains. Such modern metrics are useful in evolving topics such as VCA as AAS is not dependent on citation counts. Publishing of outputs in high quartile, open access journals with timely utilisation of news and social media outlets should be utilised by researchers aiming to maximise dissemination of research outputs in the field of VCA.

The role of C4d and donor specific antibodies in face and hand transplantation-a systematic review

To date, little is known about the mechanisms of rejection in vascularized composite allotransplantation, particularly for antibody mediated rejection. Additionally, no clear guidelines exist for the diagnosis and management of antibody-mediated rejection in vascularized composite allotransplantation. A systematic review of electronic databases (Embase and PubMed) was conducted to evaluate the relationship of donor specific antibodies and C4d deposition in correlation with cellular rejection following hand and face transplantation reported by centers between 1998 and July 2023. We extracted data on serum donor specific antibodies at the time of biopsy proven rejection according to Banff classification and C4d staining of target tissues. Mann-Whitney U tests were performed to compare rejection grade between groups divided by status of C4d deposition and serum donor specific antibodies, and Fisher's Exact test was used to assess association between the two markers. This review adhered to PRISMA guidelines. A total of 26 patients (5 face, 21 hand) were identified and data on 90 acute rejection episodes with information on Banff grade, donor specific antibody status, and C4d deposition were available. Donor specific antibodies were found to be associated with higher rejection grade (p = 0.005). C4d was not found to be associated with higher rejection grade (p = 0.33). Finally, no significant association was found between concurrent status of the two markers (p = 0.23). These findings suggest that the presence of donor specifc antibodies may be associated with higher grades of acute cellular rejection following hand and face transplantation. More consistent reporting on rejection episodes is needed in order to better understand antibody-mediated rejection in vascularized composite allotransplantation.

Transcriptome profiling of immune rejection mechanisms in a porcine vascularized composite allotransplantation model

Background

Vascularized composite allotransplantation (VCA) offers the potential for a biological, functional reconstruction in individuals with limb loss or facial disfigurement. Yet, it faces substantial challenges due to heightened immune rejection rates compared to solid organ transplants. A deep understanding of the genetic and immunological drivers of VCA rejection is essential to improve VCA outcomes.

Methods

Heterotopic porcine hindlimb VCA models were established and followed until reaching the endpoint. Skin and muscle samples were obtained from VCA transplant recipient pigs for histological assessments and RNA sequencing analysis. The rejection groups included recipients with moderate pathological rejection, treated locally with tacrolimus encapsulated in triglycerol-monostearate gel (TGMS-TAC), as well as recipients with severe end-stage rejection presenting evident necrosis. Healthy donor tissue served as controls. Bioinformatics analysis, immunofluorescence, and electron microscopy were utilized to examine gene expression patterns and the expression of immune response markers.

Results

Our comprehensive analyses encompassed differentially expressed genes, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes pathways, spanning various composite tissues including skin and muscle, in comparison to the healthy control group. The analysis revealed a consistency and reproducibility in alignment with the pathological rejection grading. Genes and pathways associated with innate immunity, notably pattern recognition receptors (PRRs), damage-associated molecular patterns (DAMPs), and antigen processing and presentation pathways, exhibited upregulation in the VCA rejection groups compared to the healthy controls. Our investigation identified significant shifts in gene expression related to cytokines, chemokines, complement pathways, and diverse immune cell types, with CD8 T cells and macrophages notably enriched in the VCA rejection tissues. Mechanisms of cell death, such as apoptosis, necroptosis and ferroptosis were observed and coexisted in rejected tissues.

Conclusion

Our study provides insights into the genetic profile of tissue rejection in the porcine VCA model. We comprehensively analyze the molecular landscape of immune rejection mechanisms, from innate immunity activation to critical stages such as antigen recognition, cytotoxic rejection, and cell death. This research advances our understanding of graft rejection mechanisms and offers potential for improving diagnostic and therapeutic strategies to enhance the long-term success of VCA.

Depletion of donor dendritic cells ameliorates immunogenicity of both skin and hind limb transplants

Acute cellular rejection remains a significant obstacle affecting successful outcomes of organ transplantation including vascularized composite tissue allografts (VCA). Donor antigen presenting cells (APCs), particularly dendritic cells (DCs), orchestrate early alloimmune responses by activating recipient effector T cells. Employing a targeted approach, we investigated the impact of donor-derived conventional DCs (cDCs) and APCs on the immunogenicity of skin and skin-containing VCA grafts, using mouse models of skin and hind limb transplantation. By post-transplantation day 6, skin grafts demonstrated severe rejections, characterized by predominance of recipient CD4 T cells. In contrast, hind limb grafts showed moderate rejection, primarily infiltrated by CD8 T cells. Notably, the skin component exhibited heightened immunogenicity when compared to the entire VCA, evidenced by increased frequencies of pan (CD11b-CD11c+), mature (CD11b-CD11c+MHCII+) and active (CD11b-CD11c+CD40+) DCs and cDC2 subset (CD11b+CD11c+ MHCII+) in the lymphoid tissues and the blood of skin transplant recipients. While donor depletion of cDC and APC reduced frequencies, maturation and activation of DCs in all analyzed tissues of skin transplant recipients, reduction in DC activities was only observed in the spleen of hind limb recipients. Donor cDC and APC depletion did not impact all lymphocyte compartments but significantly affected CD8 T cells and activated CD4 T in lymph nodes of skin recipients. Moreover, both donor APC and cDC depletion attenuated the Th17 immune response, evident by significantly reduced Th17 (CD4+IL-17+) cells in the spleen of skin recipients and reduced levels of IL-17E and lymphotoxin-α in the serum samples of both skin and hind limb recipients. In conclusion, our findings underscore the highly immunogenic nature of skin component in VCA. The depletion of donor APCs and cDCs mitigates the immunogenicity of skin grafts while exerting minimal impact on VCA.

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

Lymphadenopathy and lymph node rejection following facial vascularized composite allotransplantation

BACKGROUND

Apart from the skin, little is known about the immunological processes in deeper tissues, which are typically not accessible to biopsy and inspection, of vascularized composite allografts (VCAs). Face transplant patients develop prominent adenopathy shortly after transplantation that resolves over time. The mechanisms underlying this process are not understood.

MATERIALS AND METHODS

A retrospective cohort study was conducted on 9 patients who underwent 10 facial VCAs at the Brigham and Women's Hospital, Boston, MA, between April 2009 and July 2019. Clinical, radiological, and histological data related to lymphadenopathy of the head and neck were reviewed.

RESULTS

Patients who received donor-derived lymph nodes (LNs) developed bilateral lymphadenopathy of the submental or submandibular superficial LNs. Median time of presentation was POD18 (range POD6-POM3). Notably, bilateral adenopathy of the neck was not observed in later stages of follow-up (mean follow-up, 115 months). Histology of 3 LNs showed increased histiocytes and apoptosis, with the features reminiscent of necrotizing histiocytic lymphadenitis, and B and T lymphocytes (mostly CD8 + T) admixed with CD163 + histiocytes and dendritic cells. Molecular chimerism analysis in one case showed the coexistence of donor (81%) and recipient (19%) derived lymphocytes. Granzyme B (GZMB) expression confirmed the presence of increased cytotoxic T cells in this LN sample.

CONCLUSION

Our data suggested the involvement of an immunological process within the donor-derived LNs after facial allotransplantation between the recipient and donor cells. GZMB expression suggested LN rejection that can occurred independently of skin rejection. This finding supports the need to better define the role of donor-derived immune cells in the context of allograft rejection.

Reconstructive Paradigms: A Problem-Solving Approach in Complex Tissue Defects

The field of plastic surgery is continuously evolving, with faster-emerging technologies and therapeutic approaches, leading to the necessity of establishing novel protocols and solving models. Surgical decision-making in reconstructive surgery is significantly impacted by various factors, including the etiopathology of the defect, the need to restore form and function, the patient's characteristics, compliance and expectations, and the surgeon's expertise. A broad surgical armamentarium is currently available, comprising well-established surgical procedures, as well as emerging techniques and technologies. Reconstructive surgery paradigms guide therapeutic strategies in order to reduce morbidity, mortality and risks while maximizing safety, patient satisfaction and properly restoring form and function. The paradigms provide researchers with formulation and solving models for each unique problem, assembling complex entities composed of theoretical, practical, methodological and instrumental elements.

Immunogenicity and tolerance induction in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is the transplantation of multiple tissues such as skin, muscle, bone, nerve, and vessels, as a functional unit (i.e., hand or face) to patients suffering from major tissue trauma and functional deficits. Though the surgical feasibility has been optimized, issues regarding graft rejection remains. VCA rejection involves a diverse population of cells but is primarily driven by both donor and recipient lymphocytes, antigen-presenting cells, macrophages, and other immune as well as donor-derived cells. In addition, it is commonly understood that different tissues within VCA, such as the skin, elicits a stronger rejection response. Currently, VCA recipients are required to follow potent and lifelong immunosuppressing regimens to maximize graft survival. This puts patients at risk for malignancies, opportunistic infections, and cancers, thereby posing a need for less perilous methods of inducing graft tolerance. This review will provide an overview of cell populations and mechanisms, specific tissue involved in VCA rejection, as well as an updated scope of current methods of tolerance induction.

Defining chronic rejection in vascularized composite allografts - do we have reliable surrogates to look for?

PURPOSE OF REVIEW

Chronic rejection (CR) is a major threat in the field of vascularized composite tissue allografts (VCAs) as it causes graft dysfunction and usually graft loss. Unfortunately, knowledge of CR in VCA is incomplete because of the limited number of VCA recipients, the heterogeneous nature of VCAs and the short follow-up.

RECENT FINDINGS

The diagnosis of CR in VCA has relied on clinical and pathological findings. Clinical changes include graft fibrosis, dyschromia and ischemic/necrotic ulcerations. Pathological changes primarily affect allograft vessels and manifest with graft vasculopathy (i.e. myo-intimal proliferation and luminal narrowing of allograft vessels, leading to graft ischemia). Attempts are made to diagnose CR with non- or minimally-invasive techniques, such as imaging studies (ultrasound biomicroscopy, functional magnetic resonance imaging) and serum biomarkers. These techniques provide interesting results and further insight into the mechanisms of CR in VCA.

SUMMARY

The diagnosis of CR in VCA still relies mainly on clinicopathological graft alterations; unfortunately, these become overt rather late during the rejection process, when reversal of CR is problematic. More recent, minimally- or non-invasive techniques have provided encouraging results, but their usefulness in the diagnosis of CR requires further studies. These data highlight the paramount importance of CR prevention.

Application possibilities of artificial intelligence in facial vascularized composite allotransplantation-a narrative review

Facial vascularized composite allotransplantation (FVCA) is an emerging field of reconstructive surgery that represents a dogmatic shift in the surgical treatment of patients with severe facial disfigurements. While conventional reconstructive strategies were previously considered the goldstandard for patients with devastating facial trauma, FVCA has demonstrated promising short- and long-term outcomes. Yet, there remain several obstacles that complicate the integration of FVCA procedures into the standard workflow for facial trauma patients. Artificial intelligence (AI) has been shown to provide targeted and resource-effective solutions for persisting clinical challenges in various specialties. However, there is a paucity of studies elucidating the combination of FVCA and AI to overcome such hurdles. Here, we delineate the application possibilities of AI in the field of FVCA and discuss the use of AI technology for FVCA outcome simulation, diagnosis and prediction of rejection episodes, and malignancy screening. This line of research may serve as a fundament for future studies linking these two revolutionary biotechnologies.

Regulatory T cells in skin regeneration and wound healing

As the body's integumentary system, the skin is vulnerable to injuries. The subsequent wound healing processes aim to restore dermal and epidermal integrity and functionality. To this end, multiple tissue-resident cells and recruited immune cells cooperate to efficiently repair the injured tissue. Such temporally- and spatially-coordinated interplay necessitates tight regulation to prevent collateral damage such as overshooting immune responses and excessive inflammation. In this context, regulatory T cells (Tregs) hold a key role in balancing immune homeostasis and mediating cutaneous wound healing. A comprehensive understanding of Tregs' multifaceted field of activity may help decipher wound pathologies and, ultimately, establish new treatment modalities. Herein, we review the role of Tregs in orchestrating the regeneration of skin adnexa and catalyzing healthy wound repair. Further, we discuss how Tregs operate during fibrosis, keloidosis, and scarring.

Modeling human anti-pig xenoimmune responses in a pig artery tissue grafted humanized mouse model

BACKGROUND

Blood vessels that contain endothelial cells (ECs) on the surface are in direct contact with host blood and are the first target of xenograft rejection. Currently, our understanding of human anti-pig vessel immune responses is primarily based on in vitro assays using pig ECs. Therefore, it is necessary to develop an animal model that permits in vivo study of human immunological rejection of pig vessels.

METHODS

Pig artery tissues (PAT) were transplanted into human immune system (HIS) mice or immunodeficient NSG mice (as controls). Intragraft human immune cell infiltration and antibody deposition were quantified using histology and immunohistochemistry. Donor antigen-specific immune responses were quantified using a mixed lymphocyte reaction and a complement-dependent killing assay.

RESULTS

Pig CD31+ ECs were detected and increased 2-fold from weeks 3 to 5 in PAT xenografts from immunodeficient NSG mice. However, compared with NSG mice, PAT xenografts in HIS mice had significantly lower numbers of porcine CD31+ ECs and showed a marked reduction from week 3 to week 5. PAT xenograft rejection in HIS mice is associated with intensive infiltration of human immune cells, deposition of human IgM and IgG antibodies, and the formation of a tertiary lymphoid structure. Robust donor pig antigen-specific human T cells and antibody responses were detected in PAT-transplanted HIS mice.

CONCLUSION

We have developed a humanized mouse model to evaluate human anti-pig xenoimmune responses by PAT transplantation in vivo. This model is expected to facilitate the refinement of pig gene-editing strategies (the expression on EC surface) and the testing of local immunosuppressive strategies for clinical pig organ xenotransplantation.

Histomorphometry of the Sural Nerve for Use as a CFNG in Facial Reanimation Procedures

Facial palsy (FP) is a debilitating nerve pathology. Cross Face Nerve Grafting (CFNG) describes a surgical technique that uses nerve grafts to reanimate the paralyzed face. The sural nerve has been shown to be a reliable nerve graft with little donor side morbidity. Therefore, we aimed to investigate the microanatomy of the sural nerve. Biopsies were obtained from 15 FP patients who underwent CFNG using sural nerve grafts. Histological cross-sections were fixated, stained with PPD, and digitized. Histomorphometry and a validated software-based axon quantification were conducted. The median age of the operated patients was 37 years (5-62 years). There was a significant difference in axonal capacity decrease towards the periphery when comparing proximal vs. distal biopsies (p = 0.047), while the side of nerve harvest showed no significant differences in nerve caliber (proximal p = 0.253, distal p = 0.506) and axonal capacity for proximal and distal biopsies (proximal p = 0.414, distal p = 0.922). Age did not correlate with axonal capacity (proximal: R = -0.201, p = 0.603; distal: R = 0.317, p = 0.292). These novel insights into the microanatomy of the sural nerve may help refine CFNG techniques and individualize FP patient treatment plans, ultimately improving overall patient outcomes.