Thermosensitive Hydrogels as Targeted and Controlled Drug Delivery Systems: Potential Applications in Transplantation.

Drug delivery in transplantation plays a vital role in promoting graft survival, preventing rejection, managing complications, and contributing to positive patient outcomes. Targeted and controlled drug delivery can minimize systemic effects. Thermosensitive hydrogels, due to their unique sol-gel transition properties triggered by thermo-stimuli, have attracted significant research interest as a potential drug delivery system in transplantation. This review describes the current status, characteristics, and recent applications of thermosensitive hydrogels for drug delivery. Studies aimed at improving allotransplantation outcomes using thermosensitive hydrogels are then elaborated on. Finally, the challenges and opportunities associated with their use are discussed. Understanding the progress of research will serve as a guide for future improvements in their application as a means of targeted and controlled drug delivery in translational therapeutic applications for transplantation.

Enhancing Immunomodulatory Function of Mesenchymal Stromal Cells by Hydrogel Encapsulation.

Mesenchymal stromal cells (MSCs) showcase remarkable immunoregulatory capabilities in vitro, positioning them as promising candidates for cellular therapeutics. However, the process of administering MSCs and the dynamic in vivo environment may impact the cell-cell and cell-matrix interactions of MSCs, consequently influencing their survival, engraftment, and their immunomodulatory efficacy. Addressing these concerns, hydrogel encapsulation emerges as a promising solution to enhance the therapeutic effectiveness of MSCs in vivo. Hydrogel, a highly flexible crosslinked hydrophilic polymer with a substantial water content, serves as a versatile platform for MSC encapsulation. Demonstrating improved engraftment and heightened immunomodulatory functions in vivo, MSCs encapsulated by hydrogel are at the forefront of advancing therapeutic outcomes. This review delves into current advancements in the field, with a focus on tuning various hydrogel parameters to elucidate mechanistic insights and elevate functional outcomes. Explored parameters encompass hydrogel composition, involving monomer type, functional modification, and co-encapsulation, along with biomechanical and physical properties like stiffness, viscoelasticity, topology, and porosity. The impact of these parameters on MSC behaviors and immunomodulatory functions is examined. Additionally, we discuss potential future research directions, aiming to kindle sustained interest in the exploration of hydrogel-encapsulated MSCs in the realm of immunomodulation.

Exploring the Role of Free Tissue Transfers in the Preservation of Bone Length and Knee Joint Function after Lower Limb Trauma: A Retrospective Analysis.

Lower limb trauma often results in mangled extremities, and in some cases, complete amputation may be necessary. However, limiting the extent of amputation and preserving the major knee joint are crucial to enhance mobility and overall functionality. By providing painless soft tissue coverage on the stump, early prosthesis use and the initiation of physiotherapy become more feasible. Soft tissue transfers hold the potential to benefit patients in two essential aspects: first, resolving soft tissue deficiencies without causing bone shortening, and second, preparing the stump to enhance overall functionality. A retrospective study conducted at Chang Gung Memorial Hospital (2009-2016) focused on lower limb amputation patients who underwent soft tissue transfers at different time periods compared to those without stump reconstruction. Out of the 2391 cases of lower limb injuries treated operatively, 117 amputations were performed in 110 patients (44 above the knee and 73 below the knee). Among them, 12 patients received soft tissue transfers for limb salvage and soft tissue deficiency after amputations. It was observed that patients in this group were typically younger, predominantly female, had longer hospital stays, and underwent a greater number of surgical procedures (p < 0.05). Through the use of soft tissue transfers, successfully preserved tibial bone length and functional knee joint in selected patients was achieved. This approach effectively resolved soft tissue deficiencies following lower limb amputations, optimizing physiotherapy and facilitating functional rehabilitation.

Toward transplantation tolerance with adipose tissue-derived therapeutics.

Solid organ and composite tissue allotransplanation have been widely applied to treat end-stage organ failure and massive tissue defects, respectively. Currently there are a lot of research endeavors focusing on induction of transplantation tolerance, to relieve the burden derived from long-term immunosuppressant uptake. The mesenchymal stromal cells (MSCs) have been demonstrated with potent immunomodulatory capacities and applied as promising cellular therapeutics to promote allograft survival and induce tolerance. As a rich source of adult MSCs, adipose tissue provides additional advantages of easy accessibility and good safety profile. In recent years, the stromal vascular fraction (SVF) isolated from adipose tissues following enzymatic or mechanical processing without in vitro culture and expansion has demonstrated immunomodulatory and proangiogenic properties. Furthermore, the secretome of AD-MSCs has been utilized in transplantation field as a potential "cell-free" therapeutics. This article reviews recent studies that employ these adipose-derived therapeutics, including AD-MSCs, SVF, and secretome, in various aspects of organ and tissue allotransplantation. Most reports validate their efficacies in prolonging allograft survival. Specifically, the SVF and secretome have performed well for graft preservation and pretreatment, potentially through their proangiogenic and antioxidative capacities. In contrast, AD-MSCs were suitable for peri-transplantation immunosuppression. The proper combination of AD-MSCs, lymphodepletion and conventional immunosuppressants could consistently induce donor-specific tolerance to vascularized composite allotransplants (VCA). For each type of transplantation, optimizing the choice of therapeutics, timing, dose, and frequency of administration may be required. Future progress in the application of adipose-derived therapeutics to induce transplantation tolerance will be further benefited by continued research into their mechanisms of action and the development of standardized protocols for isolation methodologies, cell culture, and efficacy evaluation.

Reciprocal Donor-Recipient Strain Combinations Present Different Vascularized Composite Allotransplantation Outcomes in Rodent Models.

BACKGROUND: Although vascularized composite allotransplantation (VCA) has been the focus of many animal studies, further research is needed to determine the potential for a generalized model and immunosuppression regimen that applies across different donor-recipient combinations. In this study, the authors evaluated the outcome of VCAs performed on reciprocal rodent donor-recipient combinations. METHODS: VCA was performed in rats using Lewis and Brown Norway (BN) donor-recipient pairs, under the previously reported antilymphocyte serum/cyclosporine/adipose-derived stem cell regimen. Similarly, a published co-stimulatory blockade/rapamycin regimen was performed on the mouse VCA model between Balb/C and C57BL/6 strains. RESULTS: To accommodate the active behaviors of BN recipients, the allograft had to be modified and inset to the neck instead of to the groin. The tolerogenic regimen did not provide the same benefits for BN rats as it did for Lewis recipients. Increasing antilymphocyte serum dose and extending the duration of cyclosporine administration from 10 to 21 days significantly prolonged allograft survival and induced donor-specific tolerance. In mice, the co-stimulatory blockade/rapamycin regimen produced inferior VCA outcomes in BALB/c recipients than in C57BL/6 recipients. In both rats and mice, the authors identified an association between the tolerance outcome and the peripheral chimerism measured on postoperative day 30. CONCLUSIONS: Reciprocal donor-recipient combinations led to different responses toward the immunosuppression regimen and varied VCA outcomes. Sustained donor chimerism that remained in circulation for 1 month after surgery supported long-term VCA survival. Modification of the model and immunosuppression regimen accordingly is recommended. CLINICAL RELEVANCE STATEMENT: Various donor-recipient combinations respond differently to the immunosuppression regimens. Maintaining donor chimerism for 30 days after surgery improves VCA survival. It is recommended to tailor the immunosuppression regimen based on the recipient's background to optimize outcomes.

The intragraft vascularized bone marrow induces secondary donor-specific mystacial pad allograft tolerance.

Introduction: Vascularized bone marrow (VBM) is essential in tolerance induction through chimerism. We hypothesized that the inclusion of VBM contributes to the induction of mystacial pad allotransplantation tolerance. Method: In this study, 19 VBM, nine mystacial pad, and six sequential VBM and mystacial pad allografts were transplanted from Brown Norway (BN) rats to Lewis (LEW) rats to test our hypothesis. The VBM recipients were divided into antilymphocyte serum (ALS) monotherapy group (two doses of ALS on day 3 pretransplantation and day 1 posttransplantation), immunosuppressant group [a week of 2 mg/kg/day tacrolimus (Tac) and 3 weeks of 3 mg/kg/day rapamycin (RPM)], and combined therapy group. The mystacial pad recipients were divided into VBM and non-VBM transplantation groups, and both groups were treated with an immunosuppression regimen that consists of ALS, Tac, and RPM. For the recipients of sequential VBM and mystacial pad allotransplantations, additional Tac was given 1 week after mystacial pad transplantation. Allograft survival, donor-specific tolerance, and chimerism level were evaluated. Results: With the administration of ALS and short-term Tac and RPM treatments, VBM recipients demonstrated long-term graft survival (>120 days) with persistent chimerism for 30 days. CD3+ T cells from tolerant rats showed donor-specific hyporesponsiveness and tolerance to donor skin grafts but not to third-party counterparts. Furthermore, mystacial pad graft recipients with VBM transplantation exhibited a higher allograft survival rate than those without VBM transplantation [median survival time (MST) >90 days vs. 70 days, p < 0.05]. Conclusion: This study demonstrated that VBM transplantation is an efficient strategy to induce and maintain donor-specific tolerance for an osseous-free allograft.

Implantable Immunosuppressant Delivery to Prevent Rejection in Transplantation.

An innovative immunosuppressant with a minimally invasive delivery system has emerged in the biomedical field. The application of biodegradable and biocompatible polymer forms, such as hydrogels, scaffolds, microspheres, and nanoparticles, in transplant recipients to control the release of immunosuppressants can minimize the risk of developing unfavorable conditions. In this review, we summarized several studies that have used implantable immunosuppressant delivery to release therapeutic agents to prolong allograft survival. We also compared their applications, efficacy, efficiency, and safety/side effects with conventional therapeutic-agent administration. Finally, challenges and the future prospective were discussed. Collectively, this review will help relevant readers understand the different approaches to prevent transplant rejection in a new era of therapeutic agent delivery.

Cell therapy in vascularized composite allotransplantation.

Allograft rejection is one of the obstacles in achieving a successful vascularized composite allotransplantation (VCA). Treatments of graft rejection with lifelong immunosuppression (IS) subject the recipients to a lifelong risk of cancer development and opportunistic infections. Cell therapy has recently emerged as a promising strategy to modulate the immune system, minimize immunosuppressant drug dosages, and induce allograft tolerance. In this review, the recent works regarding the use of cell therapy to improve allograft outcomes are discussed. The current data supports the safety of cell therapy. The suitable type of cell therapy in allotransplantation is clinically dependent. Bone marrow cell therapy is more suitable for the induction phase, while other cell therapies are more feasible in either the induction or maintenance phase, or for salvage of allograft rejection. Immune cell therapy focuses on modulating the immune response, whereas stem cells may have an additional role in promoting structural regenerations, such as nerve regeneration. Source, frequency, dosage, and route of cell therapy delivery are also dependent on the specific need in the clinical setting.

Thermosensitive Polyester Hydrogel for Application of Immunosuppressive Drug Delivery System in Skin Allograft.

Tacrolimus (FK506) is a common immunosuppressive drug that is capable of suppressing acute rejection reactions, and is used to treat patients after allotransplantation. A stable and suitable serum concentration of tacrolimus is desirable for better therapeutic effects. However, daily drug administration via oral or injection routes is quite inconvenient and may encounter drug overdose or low patient compliance problems. In this research, our objective was to develop an extended delivery system using a thermosensitive hydrogel of poly ethylene glycol, D,L-lactide (L), and ϵ-caprolactone (CL) block copolymer, mPEG-PLCL, as a drug depot. The formulation of mPEG-PLCL and 0.5% PVP-dissolved tacrolimus was studied and the optimal formulation was obtained. The in vivo data showed that in situ gelling is achieved, a stable and sustained release of the drug within 30 days can be maintained, and the hydrogel was majorly degraded in that period. Moreover, improved allograft survival was achieved. Together, these data imply the potential of the current formulation for immunosuppressive treatments.

Preconditioned Mesenchymal Stromal Cells to Improve Allotransplantation Outcome.

Mesenchymal stromal cells (MSCs) are tissue-derived progenitor cells with immunomodulatory as well as multilineage differentiation capacities, and have been widely applied as cellular therapeutics in different disease systems in both preclinical models and clinical studies. Although many studies have applied MSCs in different types of allotransplantation, the efficacy varies. It has been demonstrated that preconditioning MSCs prior to in vivo administration may enhance their efficacy. In the field of organ/tissue allotransplantation, many recent studies have shown that preconditioning of MSCs with (1) pretreatment with bioactive factors or reagents such as cytokines, or (2) specific gene transfection, could prolong allotransplant survival and improve allotransplant function. Herein, we review these preconditioning strategies and discuss potential directions for further improvement.

Unraveling the Crucial Roles of FoxP3+ Regulatory T Cells in Vascularized Composite Allograft Tolerance Induction and Maintenance.

BACKGROUND: The role of regulatory T cells (Treg) in tolerance induction of vascularized composite allotransplantation (VCA) remains unclear. This study was designed to examine characteristics of Treg after VCA and their capacity to rescue allografts from rejection. METHODS: Osteomyocutaneous allografts were transplanted from Balb/c to C57BL/6 mice. All mice received costimulatory blockade and a short course of rapamycin. To elucidate the role of Treg for tolerance induction, Treg depletion was performed at postoperative day (POD) 0, 30, or 90. To assess capacity of Treg to rescue allografts from rejection, an injection of 2 × 106 Treg isolated from tolerant mice was applied. RESULTS: Eighty percent of VCA recipient mice using costimulatory blockade and rapamycin regimen developed tolerance. The tolerant recipients had a higher ratio of circulating Treg to effector T cells and elevated interleukin-10 at POD 30. A significantly higher rejection rate was observed when Treg were depleted at POD 30. But Treg depletion at POD 90 had no effect on tolerance. Treg from tolerant recipients showed stronger suppressive potential and the ability to rescue allografts from rejection. Furthermore, transplanted Treg-containing skin grafts from tolerant mice delayed rejection elicited by adoptively transferred effector T cells to Rag2-/- mice. CONCLUSIONS: Circulating Treg are crucial for inducing VCA tolerance in the early posttransplant phase, and allograft-residing Treg may maintain tolerance. Treg may, therefore, serve as a potential cellular therapeutic to improve VCA outcomes.

A Mixed Thermosensitive Hydrogel System for Sustained Delivery of Tacrolimus for Immunosuppressive Therapy.

Tacrolimus is an immunosuppressive agent for acute rejection after allotransplantation. However, the low aqueous solubility of tacrolimus poses difficulties in formulating an injection dosage. Polypeptide thermosensitive hydrogels can maintain a sustained release depot to deliver tacrolimus. The copolymers, which consist of poloxamer and poly(l-alanine) with l-lysine segments at both ends (P-Lys-Ala-PLX), are able to carry tacrolimus in an in situ gelled form with acceptable biocompatibility, biodegradability, and low gelling concentrations from 3 to 7 wt %. By adding Pluronic F-127 to formulate a mixed hydrogel system, the drug release rate can be adjusted to maintain suitable drug levels in animals with transplants. Under this formulation, the in vitro release of tacrolimus was stable for more than 100 days, while in vivo release of tacrolimus in mouse model showed that rejection from skin allotransplantation was prevented for at least three weeks with one single administration. Using these mixed hydrogel systems for sustaining delivery of tacrolimus demonstrates advancement in immunosuppressive therapy.

Impairment of preimplantation and postimplantation embryonic development through intrinsic apoptotic processes by ginsenoside Rg1 in vitro and in vivo.

Ginsenoside Rg1, which is the most abundant compound found in Asian ginseng (Panax ginseng), has demonstrated various pharmacological actions, including neuroprotective, immune-stimulatory, and antidiabetic effects. Pregnant women, especially in the Asian community, consume ginseng as a nutritive supplement. Thus, the effects of ginsenoside-Rg1 on embryonic development need to be investigated, such as in a mouse model. As previous investigations have found that ginsenoside Rg1 appears to either trigger or prevent apoptosis in different cell lines, the effects of this agent on apoptosis remain to be clarified. In this study, we investigated whether ginsenoside Rg1 exerts a hazardous effect on mouse blastocysts and/or affects subsequent embryonic development in vitro and in vivo. Blastocysts treated with 25-100 µM ginsenoside Rg1 exhibited significant induction of apoptosis and a corresponding decrease in the inner cell mass (ICM) cell number. Importantly, the implantation rate was lower among ginsenoside Rg1-treated blastocysts compared to untreated controls. Moreover, embryo transfer assays revealed that blastocysts treated with 100 µM ginsenoside Rg1 exhibited increased resorption of postimplantation embryos and decreased weight among surviving fetuses. In vivo, intravenous injection of mice with ginsenoside Rg1 (2, 4, or 6 mg/kg body weight/day) for 4 days was associated with increased apoptosis of blastocyst-stage embryos and negatively impacted early embryonic development. Further experiments revealed that these effects may reflect the ability of ginsenoside Rg1 to trigger oxidative stress-mediated intrinsic apoptotic signaling. Our in vitro results indicate that ginsenoside　Rg1 treatment increases intracellular oxidative stress, decreases mitochondrial membrane potential, increases the Bax/Bcl-2 ratio, and activates caspase-9 and caspase-3, but not caspase-8. Taken together, our study results strongly suggest that ginsenoside Rg1 induces apoptosis and impairs the early preimplantation and postimplantation development of mouse embryos, both in vitro and in vivo.