Chimerism and bone marrow based therapies in transplantation

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.

Harnessing the synergy of perfusable muscle flap matrix and adipose-derived stem cells for prevascularization and macrophage polarization to reconstruct volumetric muscle loss

Muscle flaps must have a strong vascular network to support a large tissue volume and ensure successful engraftment. We developed porcine stomach musculofascial flap matrix (PDSF) comprising extracellular matrix (ECM) and intact vasculature. PDSF had a dominant vascular pedicle, microcirculatory vessels, a nerve network, well-retained 3-dimensional (3D) nanofibrous ECM structures, and no allo- or xenoantigenicity. In-depth proteomic analysis demonstrated that PDSF was composed of core matrisome proteins (e.g., collagens, glycoproteins, proteoglycans, and ECM regulators) that, as shown by Gene Ontology term enrichment analysis, are functionally related to musculofascial biological processes. Moreover, PDSF-human adipose-derived stem cell (hASC) synergy not only induced monocytes towards IL-10-producing M2 macrophage polarization through the enhancement of hASCs' paracrine effect but also promoted the proliferation and interconnection of both human skeletal muscle myoblasts (HSMMs) and human umbilical vein endothelial cells (HUVECs) in static triculture conditions. Furthermore, PDSF was successfully prevascularized through a dynamic perfusion coculture of hASCs and HUVECs, which integrated with PDSF and induced the maturation of vascular networks in vitro. In a xenotransplantation model, PDSF demonstrated myoconductive and immunomodulatory properties associated with the predominance of M2 macrophages and regulatory T cells. In a volumetric muscle loss (VML) model, prevascularized PDSF augmented neovascularization and constructive remodeling, which was characterized by the predominant infiltration of M2 macrophages and significant musculofascial tissue formation. These results indicate that hASCs' integration with PDSF enhances the cells' dual function in immunomodulation and angiogenesis. Owing in part to this PDSF-hASC synergy, our platform shows promise for vascularized muscle flap engineering for VML reconstruction.

The Positive Impact of Donor Bone Marrow Cells Transplantation into Immunoprivileged Compartments on the Survival of Vascularized Skin Allografts

Using the vascularized skin allograft (VSA) model, we compared the tolerogenic effects of different allogeneic bone marrow transplantation (BMT) delivery routes into immunoprivileged compartments under a 7-day protocol immunosuppressive therapy. Twenty-eight fully MHC mismatched VSA transplants were performed between ACI (RT1^a) donors and Lewis (RT1¹) recipients in four groups of seven animals each, under a 7-day protocol of alfa/beta TCRmAb/CsA (alpha/beta-TCR monoclonal antibodies/Cyclosporine A therapy). Donor bone marrow cells (BMC) (100 × 106 cells) were injected into three different immunoprivileged compartments: Group 1: Control, without cellular supportive therapy, Group 2: Intracapsular BMT, Group 3: Intragonadal BMT, Group 4: Intrathecal BMT. In Group 2, BMC were transplanted under the kidney capsule. In Group 3, BMC were transplanted into the right testis between tunica albuginea and seminiferous tubules, and in Group 4, cells were injected intrathecally. The assessment included: skin evaluation for signs and grade of rejection and immunohistochemistry for donor cells engraftment into host lymphoid compartments. Donor-specific chimerism for MHC class I (RT1^a) antigens and the presence of CD4⁺/CD25⁺ T cells were assessed in the peripheral blood of recipients. The most extended allograft survival, 50–78 days, was observed in Group 4 after intrathecal BMT. The T cells CD4⁺/CD25⁺ in the peripheral blood were higher after intrathecal BMC injection than other experimental groups at each post-transplant time point. Transplantation of BMC into immunoprivileged compartments delayed rejection of fully mismatched VSA and induction of robust, donor-specific chimerism.

Heterotopic Transplantation of Allogeneic Vertical Rectus Abdominis Myocutaneous Flaps in Miniature Swine

BACKGROUND

Vascularized composite tissue allotransplantation (VCA) opens new possibilities for reconstruction of complex tissue defects, including upper extremity and facial transplantation. The main challenges in VCA transplantation are the side effects of long-term immunosuppression and chronic graft rejection. Translational preclinical animal models are crucial for VCA research to improve clinical outcomes and to study underlying immunologic mechanisms. Herein, we describe a novel, large animal, non-bone-bearing VCA model in inbred, swine leukocyte antigen-typed miniature swine.

METHODS

Transplantation of vertical rectus abdominis myocutaneous (VRAM) flaps was performed between fully swine leukocyte antigen-mismatched miniature swine. The flaps were transferred to the posterolateral aspect of the neck of recipients and anastomosed to the common carotid artery and internal jugular vein. Different immunosuppressive drug regimens were used. Clinical graft evaluation was performed daily, and punch biopsies were taken for histology.

RESULTS

Ten VRAM transplants were performed. The mean ischemia time was 89.4 min (SD ± 47), mean pedicle length 7.5 cm (SD ± 2), mean venous diameter 2.5 mm (SD ± 0.4), and mean arterial diameter 2.2 mm (SD ± 0.3). Follow-up demonstrated good correlation between clinical appearance and progression of graft rejection confirmed by histologic assessment. Complications were intraoperative cardiac arrest in one recipient and one flap loss due to venous compromise.

CONCLUSIONS

VRAM transplantation in miniature swine is an appropriate preclinical VCA model, with the advantage of good clinical and histologic correlation during the course of rejection, as well as easy access to the graft. The availability of inbred, haplotyped animals allows studies across different major histocompatibility complex barriers in a non-bone-bearing VCA.

Predicting Outcomes of Rat Vascularized Composite Allotransplants through Quantitative Measurement of Chimerism with PCR-Amplified Short Tandem Repeat

Chimerism has been associated with the induction and maintenance of tolerance to vascularized composite allotransplants (VCA). Although most VCA studies have examined chimerism using flow cytometry, we proposed that precision in the measurement of chimerism may be better approximated when complimentary polymerase chain reaction (PCR) is applied to a specific short tandem repeat (STR). We identified a STR, D10Rat25, which exhibited a ~20 bp difference in length between two rat strains (BN and LEW) often utilized as the donor and recipient in many allotransplantation studies. D10Rat25 was PCR-amplified and quantified with capillary electrophoresis. With pure LEW and BN DNA, a standard curve was constructed to measure chimerism with good linearity. When applied to rat VCA, the relationship between systematic (in peripheral blood) or local (at specific organ/tissues) chimerism to allograft outcomes was noted. We found that peripheral chimerism was elevated by up to ~9% postoperative month 1 (POM 1) but then reduced regardless of the final VCA outcome. However, differences in VCA skin chimerism between early rejection and POM 1 (shown as ΔChimerism_POM1-ER) were notable with respect to VCA outcomes. ROC analysis identified the optimum cutoff value as 17.7%. In summary, we have developed a reliable method to quantify the percentage of BN cells/DNA in BN-LEW chimeras. The detection limit was characterized, and the acquired data were comparable with flow cytometry. This method can be applied to solid organ and composite tissue allotransplantation studies.

Induced pluripotent stem cell-derived mesenchymal stem cells prolong hind limb survival in a rat vascularized composite allotransplantation model

BACKGROUND

The reduction of systemic immunosuppressive agents is essential for the expansion of vascularized composite allotransplantation (VCA) in a clinical setting. The purpose of this study is to compare human-induced pluripotent stem cell-derived mesenchymal stem cells (iMSCs) with four other types of mesenchymal stem cells (human bone marrow-derived MSCs [BMMSCs], human adipose-derived MSCs [ADMSCs], rat BMMSCs, and rat ADMSCs) in vitro, and to investigate the in vivo immunomodulatory effect of iMSCs in a rat VCA model.

MATERIALS AND METHODS

One Brown Norway (BN) rat, 2 Lewis (LEW) rats, and 1 Wistar rat were used in the mixed lymphocyte reaction (MLR), and 9 BN rats and 3 LEW rats (for donors), and 24 LEW rats (for recipients) were used in the VCA model. The abovementioned five types of MSCs were imaged to examine their morphology and were also tested for suppressor function using a MLR. The 24 recipient LEW rats were divided randomly into four groups, and subjected to orthotopic hind limb transplantation. The three control groups were the Iso group, in which transplantation was performed on from three to six LEW rats without immunosuppressive treatment (n = 6); the FK group, in which transplantation was performed from BN rats to LEW rats and recipient rats were treated with tacrolimus alone (FK 506, 0.2 mg/kg, days 0-6 postoperatively, intraperitoneally) (n = 6); and the UT group, in which transplantation was performed from BN rats to LEW rats without any immunosuppressive treatment (n = 6). The experimental group was the iMSC group, in which transplantation was performed from BN rats to LEW rats and recipient rats were treated with tacrolimus (FK 506, 0.2 mg/kg, days 0-6 postoperatively, intraperitoneally) and injected with iMSCs (2 × 10⁶ cells, day 7, intravenously) (n = 6). Hind limb survival was assessed by daily inspection of gross appearance until 50 days postoperatively. Histology of the skin and muscle biopsy were investigated on day 14 postoperatively. A time series of the plasma cytokine level (before transplantation, and at 10, 14, and 17 days after transplantation) was also analyzed.

RESULTS

The size of adherent and trypsinized iMSCs was 67.5 ± 8.7 and 9.5 ± 1.1 μm, respectively, which was the smallest among the five types of MSCs (p < .01). The absorbance in MLR was significantly smaller with rat ADMSCs (p = .0001), human iMSCs (p = .0006), rat BMMSCs (p = .0014), human ADMSCs (p = .0039), and human BMMSCs (p = .1191) compared to without MSCs. In vivo, iMSC treatment prolonged hind limb survival up to 12.7 days in macroscopic appearance, which is significantly longer than that of the FK group (p < .01). Histology of the skin and muscle biopsy revealed that mononuclear cell infiltration was significantly reduced by iMSC injection (p < .01). iMSC treatment also affected proinflammatory cytokines (interferon-gamma (IFNγ) and tumor necrosis factor α (TNFα)) and the anti-inflammatory cytokine (interleukin-10 (IL-10)) of the recipient plasma. The IFNγ levels at Δ14 and the TNFα levels at Δ14 and Δ17 of the iMSC group were significantly lower than those of the FK group (p = .0226, .0004, and .004, respectively). The IL-10 levels at Δ10 and Δ14 of the iMSC group were significantly higher than those of the FK group (p = .0013 and .0374, respectively).

CONCLUSIONS

iMSCs induce T cell hyporesponsiveness to prolong hind limb survival in a rat VCA model. This immunomodulatory property against acute rejection could provide one of the promising strategies capable of enabling the toxicities of immunosuppressants to be avoided in clinical settings.

Decellularized skin/adipose tissue flap matrix for engineering vascularized composite soft tissue flaps

Using a perfusion decellularization protocol, we developed a decellularized skin/adipose tissue flap (DSAF) comprising extracellular matrix (ECM) and intact vasculature. Our DSAF had a dominant vascular pedicle, microcirculatory vascularity, and a sensory nerve network and retained three-dimensional (3D) nanofibrous structures well. DSAF, which was composed of collagen and laminin with well-preserved growth factors (e.g., vascular endothelial growth factor, basic fibroblast growth factor), was successfully repopulated with human adipose-derived stem cells (hASCs) and human umbilical vein endothelial cells (HUVECs), which integrated with DSAF and formed 3D aggregates and vessel-like structures in vitro. We used microsurgery techniques to re-anastomose the recellularized DSAF into nude rats. In vivo, the engineered flap construct underwent neovascularization and constructive remodeling, which was characterized by the predominant infiltration of M2 macrophages and significant adipose tissue formation at 3months postoperatively. Our results indicate that DSAF co-cultured with hASCs and HUVECs is a promising platform for vascularized soft tissue flap engineering. This platform is not limited by the flap size, as the entire construct can be immediately perfused by the recellularized vascular network following simple re-integration into the host using conventional microsurgical techniques.

STATEMENT OF SIGNIFICANCE

Significant soft tissue loss resulting from traumatic injury or tumor resection often requires surgical reconstruction using autologous soft tissue flaps. However, the limited availability of qualitative autologous flaps as well as the donor site morbidity significantly limits this approach. Engineered soft tissue flap grafts may offer a clinically relevant alternative to the autologous flap tissue. In this study, we engineered vascularized soft tissue free flap by using skin/adipose flap extracellular matrix scaffold (DSAF) in combination with multiple types of human cells. Following vascular reanastomosis in the recipient site, the engineered products successful regenerated large-scale fat tissue in vivo. This approach may provide a translatable platform for composite soft tissue free flap engineering for microsurgical reconstruction.

Identifying the degree of major histocompatibility complex matching in genetically unrelated dogs with the use of microsatellite markers

BACKGROUND

The dog has served as an important experimental model for biomedical research such as transplantation and developing immunosuppressive agents. Although major histocompatibility complex (MHC) in dogs is a dominant factor of graft rejection, it has not been well investigated in dogs compared with human. For that reason, imprecise cross-matching or time-consuming sequence-based typing methods have generally been used to choose specific donor and recipient pairs. Investigation of matching distribution of MHC in dogs with the use of simple and accurate methods would be beneficial for biomedical researchers. The aim of this study was to identify the diversity of dog leukocyte antigen (DLA) types in genetically unrelated dogs by means of microsatellite markers.

METHODS

Thirty-three Beagle and Shih-Tzu dogs, which were negative in cross-matching, were chosen. The genomic DNA was isolated from peripheral blood leukocytes, and highly polymorphic short tandem repeats located in MHC class I and II were amplified with the use of specific primers.

RESULTS

Among all of the dogs, MHC matching groups, including class I full match-class II full match (M-M), class I full match-class II haplo match (M-H), class I haplo match-class II full match (H-M), class I haplo match-class II haplo match (H-H) groups, were ∼1.55%, 0.39%, 1.94%, and 6.59%, respectively. MHC class I nonmatch-class II nonmatch (U-U) groups were 58.14% of the total dogs.

CONCLUSIONS

Because differences of histocompatibility between donor and recipient leads to various allograft rejections, knowledge of the distribution of MHC matching in unrelated dogs would be helpful in designing studies and to get more accurate results from experiments using dog transplantation models.

Tolerance and chimerism and allogeneic bone marrow/stem cell transplantation in liver transplantation

The liver has particular tolerogenic properties that allow its spontaneous acceptance in some animal species. Liver structure is considered to favor a tolerogenic environment. The peripheral tolerance mechanisms also play a role in spontaneous tolerance to liver graft. In a clinical setting, the main challenge nowadays facing liver transplantation is minimization of immunosuppression with the goal of donor-specific tolerance. Mechanisms involved in tolerance to transplanted organs are complex and partly unknown. A significant mechanism in tolerance induction is chimerism. Chimerism can be induced through transplantation of allogeneic donor bone marrow/stem cells under appropriate host conditioning. This review focuses on the tolerance mechanisms in liver transplantation and highlights the role of chimerism and allogeneic bone marrow/stem cell transplantation in tolerance development.

Current landscape for T-cell targeting in autoimmunity and transplantation

In recent years, substantial advances in T-cell immunosuppressive strategies and their translation to routine clinical practice have revolutionized management and outcomes in autoimmune disease and solid organ transplantation. More than 80 diseases have been considered to have an autoimmune etiology, such that autoimmune-associated morbidity and mortality rank as third highest in developed countries, after cardiovascular diseases and cancer. Solid organ transplantation has become the therapy of choice for many end-stage organ diseases. Short-term outcomes such as patient and allograft survival at 1 year, acute rejection rates, as well as time course of disease progression and symptom control have steadily improved. However, despite the use of newer immunosuppressive drug combinations, improvements in long-term allograft survival and complete resolution of autoimmunity remain elusive. In addition, the chronic use of nonspecifically targeted immunosuppressive drugs is associated with significant adverse effects and increased morbidity and mortality. In this article, we discuss the current clinical tools for immune suppression and attempts to induce long-term T-cell tolerance induction as well as much-needed future approaches to produce more short-acting, antigen-specific agents, which may optimize outcomes in the clinic.

Vascularized bone marrow transplantation model in rats as an alternative to conventional cellular bone marrow transplantation: preliminary results

The aim of the study was to follow the development of microchimerism after allogeneic vascularized bone marrow transplantation (VBMT) versus conventional bone marrow transplantation (BMT). In one group, a VBMT model consisted of donor Brown Norway rat hind limb heterotopic transplanted on recipient Lewis rats. An intravenous infusion of donor bone marrow cells in suspension equivalent to that grafted in the vascularized femur limb was administered intravenously to recipient rats in the second group. Cellular microchimerism was investigated in recipients of VBMT versus BMT. Donor-derived cells could be detected in VBMT recipients at 30 and 60 days but not in recipients of intravenous suspension of BMC. VBMT provides a theoretical alternative to conventional cellular bone marrow transplantation by addressing crucial clinical problems such as failure of engraftment or graft-versus-host disease.

A preclinical canine model for composite tissue transplantation

The feasibility of composite tissue allografts (CTAs) has been demonstrated by the successful transplantation of the hand, abdomen, and face. However, the survival of these transplants depends on immunosuppression. Our laboratory is interested in achieving tolerance to decrease the risks associated with the use of chronic immunosuppression. The purpose of this experiment was to develop a large-animal model for CTA. Four canine flaps were autotransplanted to examine the use of a myocutaneous rectus flap based on the deep inferior epigastric vessels. Five CTA transplants were performed between dog leukocyte antigen (DLA)-identical littermates without posttransplant immunosuppression. The allografts were followed clinically and underwent routine biopsies. The anatomic dissections and autotransplants were all successful and revealed that the flap could be divided into two separate components. Skin was perfused by the superficial epigastric artery. Rectus muscle was perfused by the deep inferior epigastric system. This allowed the allografts to be transplanted as muscle or skin or with both components based on the external iliac artery and veins. The DLA-identical littermates rejected the allografts in 15 to 30 days. This study demonstrated the versatility of the myocutaneous rectus flap for use in canines as CTA models.

CD8+ T-Cell depletion and rapamycin synergize with combined coreceptor/stimulation blockade to induce robust limb allograft tolerance in mice

The growing development of composite tissue allografts (CTA) highlights the need for tolerance induction protocols. Herein, we developed a mouse model of heterotopic limb allograft in a stringent strain combination in which potentially tolerogenic strategies were tested taking advantage of donor stem cells in the grafted limb. BALB/c allografts were transplanted into C57BL/6 mice treated with anti-CD154 mAb, nondepleting anti-CD4 combined to either depleting or nondepleting anti-CD8 mAbs. Some groups received additional rapamycin. Both depleting and nondepleting mAb combinations without rapamycin only delayed limb allograft rejection, whereas the addition of rapamycin induced long-term allograft survival in both combinations. Nevertheless, robust donor-specific tolerance, defined by the acceptance of a fresh donor-type skin allograft and simultaneous rejection of third-party grafts, required initial CD8(+) T-cell depletion. Mixed donor-recipient chimerism was observed in lymphoid organs and recipient bone marrow of tolerant but not rejecting animals. Tolerance specificity was confirmed by the inability to produce IL-2, IFN-gamma and TNF-alpha in MLC with donor antigen while significant alloreactivity persisted against third- party alloantigens. Collectively, these results show that robust CTA tolerance and mixed donor-recipient chimerism can be achieved in response to the synergizing combination of rapamycin, transient CD8(+) T-cell depletion and costimulation/coreceptor blockade.

Prospective analysis between the therapy of immunosuppressive medication and allogeneic microchimerism after liver transplantation

After liver transplantation, migration of donor-derived hematopoietic cells to recipient can be detected in peripheral blood. This state is termed microchimerism. The aim of this study was to investigate prospectively the presence of allogeneic microchimerism, the occurrence of acute cellular rejection and the level of immunosuppression in transplanted patients. Microchimerism occurrence between 10 days and 12 months after liver transplantation was analyzed in 47 patients aged between 15 and 65 by a two-stage nested PCR/SSP technique to detect donor MHC HLA-DR gene specifically. A pre-transplant blood sample was collected from each patient to serve as individual negative control. Microchimerism was demonstrated in 32 (68%) of the 47 patients; of these, only 10 patients (31.2%) presented rejection. Early microchimerism was observed in 25 patients (78.12%) and late microchimerism in 7 patients (21.8%). Among the patients with microchimerism, 14 were given CyA and 18 were given FK506. In the group without microchimerism, 12 patients were given CyA and 03 were given FK506. There was a significant association between the presence of microchimerism and the absence of rejection (p=0.02) and also between microchimerism and the type of immunosuppression used. Our data indicate that microchimerism and probably differentiation of donor-derived leukocytes can have relevant immunologic effects both in terms of sensitization of recipient and in terms of immunomodulation toward tolerance induction.