Effectiveness of topical immunosuppressants in prevention and treatment of rejection in face allotransplantation

Tacrolimus-loaded Drug Delivery Systems in Vascularized Composite Allotransplantation: Lessons and Opportunities for Local Immunosuppression

Long-term systemic immunosuppression is needed for vascularized composite allotransplantation (VCA). The high rate of acute rejection episodes in the first posttransplant year, the development of chronic rejection, and the adverse effects that come along with this treatment, currently prevent a wider clinical application of VCA. Opportunistic infections and metabolic disturbances are among the most observed side effects in VCA recipients. To overcome these challenges, local immunosuppression using biomaterial-based drug delivery systems (DDS) have been developed. The aim of these systems is to provide high local concentrations of immunosuppressive drugs while reducing their systemic load. This review provides a summary of recently investigated local DDS with different mechanisms of action such as on-demand, ultrasound-sensitive, or continuous drug delivery. In preclinical models, ranging from rodent to porcine and nonhuman primate models, this approach has been shown to reduce systemic tacrolimus (TAC) load and adverse effects, while prolonging graft survival. Localized immunosuppression using biomaterial-based DDS represents an encouraging approach to enhance graft survival and reduce toxic side effects of immunosuppressive drugs in VCA patients. Preclinical models using TAC-releasing DDS have demonstrated high local immunosuppressive effects with a low systemic burden. However, to reduce acute rejection events in translational animal models or in the clinical reality, the use of additional low-dose systemic TAC treatment may be envisaged. Patients may benefit through efficient graft immunosuppression and survival with negligible systemic adverse effects, resulting in better compliance and quality of life.

Experimental Models in Penile Transplantation: Translational Insights and Relevance to Clinical Application

Animal research is an essential contributor to the medical achievements of the last century. The first step of studying a disease in animals is the development of a model which is relevant to the clinical situation in humans. Thus, a good animal model is the sine qua non of the experimental research. This review aims to assess the contemporary literature on animal models for penile transplantation, examining their applicability and significance in the context of clinical scenarios. We also revisit, evaluate, and emphasize the interesting and important findings of certain animal models to bring the reader up to date from the perspective of allotransplantation. Their current and future clinical applicability and feasibility have been discussed, shedding light on worldwide experience in Vascularized Composite Allotransplantation (VCA).

Topical Tacrolimus and Mycophenolic Acid Therapy Synergizes with Low Dose Systemic Immunosuppression to Sustain Vascularized Composite Allograft Survival

AIM

The goal of this study was to evaluate whether topical administration of tacrolimus (TAC) and mycophenolic acid (MPA) at the transplant site enables vascularized composite allograft (VCA) survival with significant minimization of the dose and adverse effects of systemic TAC (STAC) immunosuppression.

MATERIALS AND METHODS

Lewis (Lew) rats received orthotopic hind limb allotransplants from fully mismatched Brown Norway (BN) donors. Group 1 (Controls) received no treatment. Other groups were treated with STAC at a dose of 1 mg/kg/day for 7 days. On post-operative day (POD) 8, the STAC dose was dropped to 0.1 mg/kg/day for Group 2 and maintained at 1 mg/kg for Group 3. Group 4 received topical application of TAC and MPA on the transplanted (Tx) limb starting POD 8 without STAC. Group 5 received topical TAC and MPA on the contralateral non-Tx limb and Group 6 received topical TAC and MPA on the Tx limb starting POD 8 along with low dose STAC (0.1 mg/kg/day). Treatment was continued until the study end point was reached, defined as either grade 3 rejection or allograft survival exceeding 100 days. .We conducted sequential LC-MS/MS measurements to assess TAC and MPA concentrations in both blood/plasma and allograft tissues. Additionally, we evaluated markers indicative of organ toxicity associated with STAC immunosuppression.

RESULTS

Compared to controls, topical therapy with TAC+MPA significantly prolonged allograft survival beyond 100 daysat very low dose STAC (0.1 mg/kg/day) (Group 6). The histopathological assessment of the grafts was consistent with the clinical outcomes. .Drug levels in blood/plasma remained low or undetectable, while allograft tissues showed higher drug concentrations compared to contralateral limb tissues (P<0.05). . Urinary creatinine clearance remained within the normal range at 2.5 mL/min.

CONCLUSION

Combination therapy with topical TAC and MPA synergizes with a very low dose, corticosteroid- free-STAC regimen and facilitates rejection-free, prolonged VCA survival without morbidity.

Tacrolimus-Eluting Disk within the Allograft Enables Vascularized Composite Allograft Survival with Site-Specific Immunosuppression without Systemic Toxicity

AIM

Widespread clinical application of vascularized composite allotransplantation (VCA) has been limited by the need for lifelong systemic immunosuppression to prevent rejection. Our goal was to develop a site-specific immunosuppressive strategy that promotes VCA allograft survival and minimizes the risk of systemic side effects.

METHODS

Tacrolimus loaded polycaprolactone (TAC-PCL) disks were prepared and tested for their efficacy in sustaining VCA allograft survival via site-specific immunosuppression. Brown Norway-to-Lewis rat hind limb transplantations were performed; animals received one TAC disk either in the transplanted (DTx) or in the contralateral non-transplanted (DnonTx) limbs. In another group, animals received DTx and lymphadenectomy on Tx side. Blood and allograft levels of TAC were measured using LC-MS/MS. Systemic toxicity was evaluated.

RESULTS

Animals that received DTx achieved long-term allograft survival (> 200 days) without signs of metabolic and infectious complications. In these animals, TAC blood levels were low but stable between 2 to 5 ng/mL for nearly 100 days. High concentrations of TAC were achieved in the allografts and the draining lymph nodes (DLN). Animals that underwent lymphadenectomy rejected their allograft by 175 days. Animals that received DnonTx rejected their allografts by day 70.

CONCLUSION

Controlled delivery of TAC directly within the allograft (with a single TAC disk) effectively inhibits rejection and prolongs VCA allograft survival, while mitigating the complications of systemic immunosuppression. There was a survival benefit of delivering TAC within the allograft as compared to a remote site. We believe this approach of local drug delivery has significant implications for drug administration in transplantation.

A systematic review of immunomodulatory strategies used in skin-containing preclinical vascularized composite allotransplant models

BACKGROUND

Acute rejection remains a vexing problem in vascularized composite allotransplantation (VCA). Available immunosuppressive regimens are successful at minimizing alloimmune response and allowing VCA in humans. However, repeated rejection episodes are common, and systemic side effects of the current standard regimen (Tacrolimus, MMF, Prednisone) are dose limiting. Novel immunomodulatory approaches to improve allograft acceptance and minimize systemic toxicity are continuously explored in preclinical models. We aimed to systematically summarize past and current approaches to help guide future research in this complex field.

METHODS

We conducted a systematic review of manuscripts listed in the MEDLINE and PubMed databases. For inclusion, articles had to primarily investigate the effect of a therapeutic approach on prolonging the survival of a skin-containing preclinical VCA model. Non-VCA studies, human trials, anatomical and feasibility studies, and articles written in a language other than English were excluded. We followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines.

RESULTS

The search retrieved 980 articles of which 112 articles were ultimately included. The majority of investigations used a rat model. An orthotopic hind limb VCA model was used in 53% of the studies. Cell and drug-based approaches were investigated 58 and 52 times, respectively. We provide a comprehensive review of immunomodulatory strategies used in VCA preclinical research over a timeframe of 44 years.

CONCLUSION

We identify a transition from anatomically non-specific to anatomical models mimicking clinical needs. As limb transplants have been most frequently performed, preclinical research focused on using the hind limb model. We also identify a transition from drug-based suppression therapies to cell-based immunomodulation strategies.

Local FK506 implants in non-human primates to prevent early acute rejection in vascularized composite allografts

Background

Previous vascularized composite allograft (VCA) studies from our laboratory have shown that topical FK506 delivery in non-human primates (NHPs) was limited by inadequate dermal penetration and rejection persisted. Herein, we report the first utilization of FK506 via subcutaneously implanted discs to mitigate VCA rejection in NHPs.

Methods

Full major histocompatibility complex (MHC)-mismatched NHP pairs underwent partial-face VCA and FK506 disc implantation along the suture line. All allotransplants were maintained post-operatively for two months on the FK506 discs, methylprednisolone, mycophenolate mofetil, and supplemented with intramuscular FK506 if necessary. Group 1 (n=4) was used for optimization of the implant, while Group 2 (n=3) underwent delayed bone marrow transplantation (DBMT) after two months. VCA skin biopsies and peripheral blood samples were obtained for serial assessment of rejection and mixed chimerism by histopathology and flow cytometry respectively.

Results

In Group 1, two technical failures occurred. Of the remaining two NHPs, one developed supratherapeutic levels of FK506 (50–120 ng/mL) and had to be euthanized on postoperative day (POD) 12. Reformulation of the implant resulted in stable FK506 levels (20–30 ng/mL) up to POD12 when further intramuscular (IM) FK506 injections were necessitated. In Group 2, two NHPs survived to undergo conditioning and one successfully developed chimerism at 2–3 weeks post-DBMT (96–97% granulocytes and 7–11% lymphocytes of recipient-origin). However, all three NHPs had to be terminated from study at POD64, 77 and 86 due to underlying post-transplant lymphoproliferative disorder. All VCAs remained rejection-free up to study endpoint otherwise.

Conclusions

This study shows preliminary results of local FK506 implants in potentially mitigating VCA acute rejection for tolerance protocols based on mixed chimerism approach.

Local immunosuppression in vascularized composite allotransplantation (VCA): A systematic review

BACKGROUND

Local immunosuppression in vascularized composite allotransplantation (VCA) aims to minimize immunosuppressant-related toxic and malignant side effects. Promising allograft survival data have been published by multiple workgroups. In this systematic review, we examine preclinical animal studies that investigated local immunosuppression in VCA.

MATERIAL AND METHODS

We conducted a systematic review of manuscripts listed in the MEDLINE and PubMed database concerning preclinical VCA models. Papers included had to be available as full-text and written in English. Non-VCA studies, human trials, and studies using cell-based therapy strategies were excluded. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Literature research retrieved 980 articles. Ten studies published between 2010 and 2019 met the inclusion and exclusion criteria. Seven out of ten articles demonstrated a significant prolongation of allograft survival by using local immunosuppression. Five articles employed tacrolimus (TAC) as the main immunosuppressive agent. Seven studies performed hind-limb VCA in a rat model.

CONCLUSION

The easily accessible location of skin containing VCAs makes it an ideal candidate for local immunosuppression. Published preclinical data are very promising in terms of improved allograft survival and reduced systemic toxicity.

Pharmacokinetics and Biodistribution of Tacrolimus after Topical Administration: Implications for Vascularized Composite Allotransplantation

AIM

The high doses of oral tacrolimus (TAC) (1,2) necessary to prevent acute rejection (AR) after vascularized composite allotransplantation (VCA) are associated with systemic adverse effects. The skin is the most antigenic tissue in VCA and the primary target of AR. However, the short-term use of topical TAC (Protopic®), as an off-label adjunct to oral TAC, to treat AR episodes pro re nata (PRN), has yielded inconsistent results. There is lack of data on the pharmacokinetics and tissue distribution of topical TAC in VCA, that hampers our understanding of the reasons for unreliable efficacy. Toward this goal, we evaluated the ability of topical TAC to achieve high local tissue concentrations at the site of application with low systemic concentrations.

MATERIALS AND METHODS

We assessed the pharmacokinetics and tissue distribution of topical TAC (Protopic®, 0.03%) after single or repeated topical application in comparison to those after systemic delivery in rats. Animals received a single topical application of TAC ointment (Group 1) or an intravenous (IV) injection of TAC (Group 2) at a dose of 0.5 mg/kg. In another experiment, animals received daily topical application of TAC ointment (Group 3), or daily intraperitoneal (IP) injection of TAC (Group 4) at a dose of 0.5 mg/kg for 7 days. TAC concentrations in blood and tissues were analyzed by Liquid Chromatography-Mass Spectrometry (LC/MS-MS).

RESULTS

Following single topical administration, TAC was absorbed slowly with a Tmax of 4 h and an absolute bioavailability of 11%. The concentrations of TAC in skin and muscle were several folds higher than whole blood concentrations. Systemic levels remained subtherapeutic (< 3 ng/ml) with repeated once daily applications.

CONCLUSION

Topical application of TAC ointment (Protopic®, 0.03%) at a dose of 0.5 mg/kg/day provided high concentrations in the local tissues with low systemic exposure. Repeated topical administration of TAC is well tolerated with no local or systemic adverse effects. This study confirms the feasibility of topical application of TAC for site specific graft immunosuppression and enables future applications in VCA.

Local Immunosuppression for Vascularized Composite Allografts: Application of Topical FK506-TyroSpheres in a Nonhuman Primate Model

Transplantation of vascularized composite allografts (VCAs) provides a means of restoring complex anatomical and functional units following burns and other disfigurement otherwise not amenable to conventional autologous reconstructive surgery. While short- to intermediate-term VCA survival is largely dependent on patient compliance with medication, the myriad of side effects resulting from lifelong systemic immunosuppression continue to pose a significant challenge. Topical immunosuppression is therefore a logical and attractive alternative for VCA. Current formulations are limited though, by poor skin penetration but this may be mitigated by conjugation of immunosuppressive drugs to TyroSpheres for enhanced delivery. Therefore, we investigated the topical application of FK506-TyroSpheres (in the form of a gel dressing) in a clinically relevant nonhuman primate VCA model to determine if allograft survival could be prolonged at reduced levels of maintenance systemic immunosuppression. Six Major Histocompatibility Complex (MHC)-mismatched cynomolgus macaques (Macaca fascicularis) served as reciprocal donors and recipients of radial forearm fasciocutaneous flaps. Standard Bacitracin ointment and FK506-TyroSpheres were applied every other day to the VCAs of animals in groups 1 (controls, n = 2) and 2 (experimental, n = 4), respectively, before gradual taper of systemic FK506. Clinical features of VCA rejection still developed when systemic FK506 fell below 10 ng/ml despite application of FK506-TyroSpheres and prolonged VCA survival was not achieved. However, unwanted systemic FK506 absorption was avoided with TyroSphere technology. Further refinement to optimize local drug delivery profiles to achieve and maintain therapeutic delivery of FK506 with TyroSpheres is underway, leveraging significant experience in controlled drug delivery to mitigate acute rejection of VCAs.

Evaluation of PLGA microspheres with triple regimen on long-term survival of vascularized composite allograft - an experimental study

Systemic immunosuppression is indispensable for vascularized composite allotransplantation (VCA). Daily administration of standard triple therapy regimen of tacrolimus (FK506), mycophenolate mofetil (MMF), and steroid has severe side effects and reduces the compliance of VCA recipients. To overcome these hurdles, FK506/MMF/prednisolone (PDNN) was loaded into PLGA microspheres (PGLA MS). A single injection of FK506/MMF/PDNN-PLGA MS significantly prolonged the survival time of allograft in a rat hind limb transplantation model with a median survival time (MST) of more than 150 days compared to 34.5 days in the group treated orally with FK506/MMF/PDNN and 11 days in the nontreatment allograft and MS control groups. Analysis of showed that FK506/MMF/PDNN-PLGA MS could maintain relatively higher plasma and tissue drug concentrations for a long time. Moreover, histopathology and flow cytometry of circulating mononuclear cells revealed significantly prolonged immunosuppression by the FK506/MMF/PDNN-PLGA MS compared with the orally given FK506/MMF/PDNN. In conclusion, a single injection of FK506/MMF/PDNN-PLGA MS may provide a new approach for long-term prevention of immune rejection in VCA.

Biomaterials for topical and transdermal drug delivery in reconstructive transplantation

Lifelong systemic immunosuppression remains the biggest challenge in vascularized composite allotransplantation (VCA) due to the adverse effects it causes. Since VCA is a life-enhancing procedure as compared with solid organ transplant which is life-saving; one needs to weigh the benefits and risks carefully. Thus, there is a huge unmet clinical need to design biomaterial-based vehicles that can deliver drugs more efficiently, topically and locally to eliminate adverse effects of systemic immune suppression. This review discusses several biomaterial-based systems that have been carefully designed, conceived and attempted to make VCA a more patient compliant approach. Variety of promising preclinical studies has shown the feasibility of the approaches, and clinical trials are required to bridge the gap. Several challenges for the future and new approaches have been discussed.

Delivery of Rapamycin Using In Situ Forming Implants Promotes Immunoregulation and Vascularized Composite Allograft Survival

Vascularized composite allotransplantation (VCA), such as hand and face transplantation, is emerging as a potential solution in patients that suffered severe injuries. However, adverse effects of chronic high-dose immunosuppression regimens strongly limit the access to these procedures. In this study, we developed an in situ forming implant (ISFI) loaded with rapamycin to promote VCA acceptance. We hypothesized that the sustained delivery of low-dose rapamycin in proximity to the graft may promote graft survival and induce an immunoregulatory microenvironment, boosting the expansion of T regulatory cells (T_reg). In vitro and in vivo analysis of rapamycin-loaded ISFI (Rapa-ISFI) showed sustained drug release with subtherapeutic systemic levels and persistent tissue levels. A single injection of Rapa-ISFI in the groin on the same side as a transplanted limb significantly prolonged VCA survival. Moreover, treatment with Rapa-ISFI increased the levels of multilineage mixed chimerism and the frequency of T_reg both in the circulation and VCA-skin. Our study shows that Rapa-ISFI therapy represents a promising approach for minimizing immunosuppression, decreasing toxicity and increasing patient compliance. Importantly, the use of such a delivery system may favor the reprogramming of allogeneic responses towards a regulatory function in VCA and, potentially, in other transplants and inflammatory conditions.

Local release of tacrolimus from hydrogel-based drug delivery system is controlled by inflammatory enzymes in vivo and can be monitored non-invasively using in vivo imaging

BACKGROUND

Local drug delivery systems that adjust the release of immunosuppressive drug in response to the nature and intensity of inflammation represent a promising approach to reduce systemic immunosuppression and its side effects in allotransplantation. Here we aimed to demonstrate that release of tacrolimus from triglycerol monostearate hydrogel is inflammation-dependent in vivo. We further report that by loading the hydrogel with a near-infrared dye, it is possible to monitor drug release non-invasively in an in vivo model of vascularized composite allotransplantation.

MATERIALS AND METHODS

Inflammation was induced by local challenge with lipopolysaccharides in naïve rats 7 days after injection of tacrolimus-loaded hydrogel in the hind limb. Tacrolimus levels in blood and tissues were measured at selected time points. A near-infrared dye was encapsulated in the hydrogel together with tacrolimus in order to monitor hydrogel deposits and drug release in vitro and in vivo in a model of vascularized composite allotransplantation.

RESULTS

Injection of lipopolysaccharides led to increased blood and skin tacrolimus levels (p = 0.0076, day 7 vs. day 12 in blood, and p = 0.0007 in treated limbs, 48 h after injection compared to controls). Moreover, lipopolysaccharides-injected animals had higher tacrolimus levels in treated limbs compared to contralateral limbs (p = 0.0003 for skin and p = 0.0053 for muscle). Imaging of hydrogel deposits and tacrolimus release was achieved by encapsulating near-infrared dye in the hydrogel for 160 days. The correlation of tacrolimus and near-infrared dye release from hydrogel was R2 = 0.6297 and R2 = 0.5619 in blood and grafts of transplanted animals respectively and R2 = 0.6066 in vitro.

CONCLUSIONS

Here we demonstrate the inflammation-responsiveness of a tacrolimus-loaded hydrogel in vivo. Moreover, we show that encapsulating a near-infrared dye in the hydrogel provides a reliable correlation of tacrolimus and dye release from the hydrogel, and an accessible non-invasive method for monitoring drug release from hydrogel deposits.

Mycophenolic Acid for Topical Immunosuppression in Vascularized Composite Allotransplantation: Optimizing Formulation and Preliminary Evaluation of Bioavailability and Pharmacokinetics

Mycophenolic acid (MPA), is the active form of the ester prodrug mycophenolate mofetil (MMF). MMF is an FDA approved immunosuppressive drug that has been successfully used in systemic therapy in combination with other agents for the prevention of acute rejection (AR) following solid organ transplantation (SOT) as well as in vascularized composite allotransplantation (VCA). Systemic use of MMF is associated with gastrointestinal adverse effects. Topical delivery of the prodrug could thus provide graft-targeted immunosuppression while minimizing systemic drug exposure. Our goal was to develop a topical formulation of MPA with optimal in vitro/in vivo characteristics such as release, permeation, and tissue bioavailability to enable safety and efficacy evaluation in clinical VCA.

Permeation studies were performed with a solution of MPA (10 mg/ml). In vitro release and permeation studies were performed for different semisolid formulations (Aladerm, Lipoderm, emollient, and VersaBase) of MPA (1% w/w) using a Franz Diffusion Cell System (FDCS). In vivo pharmacokinetic characterization of MPA release from Lipoderm was performed in rats.

MPA in solution exhibited a steady state flux (3.8 ± 0.1 µg/cm²/h) and permeability (1.1 × 10⁻⁷ ± 3.2 × 10⁻⁹ cm/s). MPA in Lipoderm exhibited a steady state flux of 1.12 ± 0.24 µg/cm²/h, and permeability of 6.2 × 10⁻⁰⁹ ± 1.3 × 10⁻⁹ cm/s across the biomimetic membrane. The cumulative release of MPA from Lipoderm, showed a linear single-phase profile with a R² of 0.969. In vivo studies with MPA in Lipoderm showed markedly higher local tissue MPA levels and lower systemic MPA exposure as compared to values obtained after intravenous delivery of the same dose of drug (p < 0.05).

We successfully developed for the first time, a topical formulation of MPA in Lipoderm with optimal in vitro/in vivo permeability characteristics and no undesirable local or systemic adverse effects in vivo. Our study provides key preliminary groundwork for translational efficacy studies of topical MPA in pre-clinical large animal VCA models and for effectiveness evaluation in patients receiving VCA.

Vascularized composite allotransplantation: current standards and novel approaches to prevent acute rejection and chronic allograft deterioration

The advent of more potent immunosuppressants led to the first successful human upper extremity transplantation in 1998. At this time, >100 upper extremity transplants, 30 face transplants, and a variety of other vascularized composite allotransplantation (VCA) procedures have been performed around the world. VCA recipients present unique challenges for transplantation. The incidence of acute rejection exceeds 80% in hand and face transplantation and is well documented, whereas reports about antibody-mediated rejection and chronic rejection remain scarce. Immunosuppression protocols commonly used at US centers are derived from solid organ transplantation protocols. Novel approaches to minimize rejections in VCA may include improved HLA matching and considerations toward cytomegalovirus infection status. New graft preservation techniques may decrease immunogenicity prior to transplant. Novel monitoring methods such as valid biomarkers, ultrasound biomicroscopy, and sentinel flaps may enable earlier diagnosis of rejection. Cell-based therapies are being explored to achieve immunosuppressive regimen minimization or even tolerance induction. The efficacy of local immunosuppression in clinical VCA remains controversial. In conclusion, although immunosuppressive strategies adapted from SOT have demonstrated good midterm results, focusing on the unique features of VCA grafts may enable additional, more specific treatment strategies in the future and improved long-term graft outcomes.

Vascularization of the facial bones by the facial artery: implications for full face allotransplantation

BACKGROUND

The maxillary artery is recognized as the main vascular supply of the facial bones; nonetheless, clinical evidence supports a codominant role for the facial artery. This study explores the extent of the facial skeleton within a facial allograft that can be harvested based on the facial artery.

METHODS

Twenty-three cadaver heads were used in this study. In 12 heads, the facial, superficial temporal, and maxillary arteries were injected. In one head, facial artery angiography was performed. Ten facial allografts were raised. The soft tissues were dissected to show the arterial anastomotic connections. Radiographs and computed tomographic scans were obtained.

RESULTS

Constant anastomosis between the facial, inferior alveolar, and infraorbital arteries at the mental and infraorbital foramina were found. The facial artery vascularized the homolateral mandibular symphysis, body, and ramus. The condylar and coronoid processes were vascularized in 67 percent of the allografts. The homolateral maxilla was contrasted in all allografts. The alveolar and palatine processes contained the contrast in 83 percent of specimens. The maxillary process of the zygomatic bone was perfused in all allografts, followed by the body, frontal (83 percent), and temporal processes (67 percent). The nasal lateral wall and septum were vascularized in 83 percent of the allografts. The medial and lateral orbital walls and the orbital floor were stained in all specimens. The zygomatic process of the temporal bone was the least perfused bone.

CONCLUSION

A composite allograft containing 90 to 95 percent of the facial bones can be based on bilateral facial arteries.