Tolerance to limb tissue allografts between swine matched for major histocompatibility complex antigens

Transplantation of limb tissue allografts would greatly expand the realm of reconstructive surgery. However, the toxicity of chronic immunosuppression has adversely tilted the risk-benefit balance for clinical transplant. In this study, a procedure was sought to achieve host tolerance to limb tissue allografts through matching of the major histocompatibility complex (MHC) antigens between donor and host swine using only a 12-day course of cyclosporine. Massachusetts General Hospital (MGH) miniature swine were used as a large animal model with defined MHC, and musculoskeletal grafts from the donor hind limb were transplanted heterotopically to the recipient femoral vessels. Allografts from MHC-mismatched donors treated with cyclosporine (n = 4) were rejected in less than 6 weeks by gross inspection and histologic sections. Allografts from MHC-matched, minor antigen mismatched donors not treated with cyclosporine (n = 4) were rejected between 9 and 12 weeks. Allografts from similarly matched donors treated with 12 days of cyclosporine (n = 7) showed no evidence of rejection until sacrifice between 25 and 47 weeks. Thus allograft tolerance was achieved between MHC-matched swine using a limited course of cyclosporine. Demonstration of limb tissue allograft survival in a large animal model without long-term immunosuppression represents an important step toward clinical transplantation.

TOLERANCE TO MUSCULOSKELETAL ALLOGRAFTS WITH TRANSIENT LYMPHOCYTE CHIMERISM IN MINIATURE SWINE1

BACKGROUND

Although transplantation of musculoskeletal allografts in humans is technically feasible, the adverse effects of long-term immunosuppression subject the patient to high risks for correcting a non-life-threatening condition. Achieving immunologic tolerance to musculoskeletal allografts, without the need for chronic immunosuppression, could expand the clinical application of limb tissue allografting. Tolerance to musculoskeletal allografts has been accomplished previously in miniature swine in our laboratory. Although stable, mixed chimerism has been suggested as the mechanism underlying long-term tolerance in a rat limb model, the mechanism of this tolerance induction has not been established. This report explores the possible relationship between hematopoietic chimerism and tolerance to musculoskeletal allografts in swine.

METHODS

Twelve miniature swine underwent vascularized musculoskeletal allograft transplantation from histocompatibility complex (MHC) matched, minor antigen-mismatched donors. Eight animals received a 12-day coprse of cyclosporine, one of which was excluded due to subtherapeutic levels. Four recipients were not immunosuppressed. Serial biopsies to assess graft viability and flow cytometry to assess chimerism were performed. Donor and third-party skin grafts were placed on recipients with surviving allografts greater than 100 days to validate tolerance.

RESULTS

Both groups developed early peripheral chimerism, but this chimerism became undetectable by postoperative day 19 in the cyclosporine group and by day 13 in the control group. Animals receiving cyclosporine developed permanent tolerance to their allografts, whereas those not receiving cyclosporine rejected their allografts in 6-9 weeks. Animals demonstrating tolerance to their bone allografts also demonstrated prolonged donor skin graft survival.

CONCLUSIONS

Induction of tolerance to musculoskeletal allografts can be achieved in the MHC matched swine. Although hematopoietic chimerism is present in the immediate postoperative period, persistent, long-term chimerism does not seem to be necessary for maintenance of such tolerance.

Strategies for tolerance induction to composite tissue allografts

The emerging field of composite tissue transplantation offers the potential to replace lost tissues from cadaveric sources. Two major obstacles currently limit the future of composite tissue allotransplantation. The first is chronic rejection, attributed to both antibody deposition and cell-mediated destruction of transplanted tissue. The second obstacle is complications associated with the chronic use of immunosuppressive agents. Our laboratory has been investigating several strategies to induce tolerance to limb tissue allografts to provide solutions to many of the current limitations in allotransplantation. Three strategies show promise in the ability to induce tolerance to organ allografts. The first involves genetic matching at the HLA loci followed by a short course of immunosuppression. The second is the application of a "mixed chimerism" regimen followed by transplantation. The third is costimulatory blockade using a short course of monoclonal antibodies, such as anti-CD40 ligand and CTLA4-Ig after transplantation. Inducing a state of tolerance to limb allografts would eliminate the need for chronic immunosuppression and may also prevent the onset of chronic rejection. The ability to induce allograft tolerance would greatly expand the indications for composite tissue transplantation.

CD62L is required on effector cells for local interactions in the CNS to cause myelin damage in experimental allergic encephalomyelitis

Adhesion molecules are believed to facilitate infiltration of leukocytes into the CNS of mice with experimental allergic encephalomyelitis (EAE). The role of the adhesion molecule CD62L (L-selectin) in the immunopathology of EAE is not known. To study this, we crossed CD62L-deficient mice with myelin basic protein-specific TCR (MBP-TCR) transgenic mice. CD62L-deficient MBP-TCR transgenic mice failed to develop antigen-induced EAE, and, despite the presence of leukocyte infiltration, damage to myelin in the CNS was not seen. EAE could, however, be induced in CD62L-deficient mice upon adoptive transfer of wild-type macrophages. Our results suggest that CD62L is not required for activation of autoimmune CD4 T cells but is important for the final destructive function of effector cells in the CNS and support a novel mechanism whereby CD62L expressed on effector cells is important in mediating myelin damage.

Injection of allogeneic bone marrow cells into the portal vein of swine in utero

The ability to safely manipulate the immune system of the developing fetus carries the hope of effective treatment strategies for certain congenital disorders that can be diagnosed during gestation. One possible intervention is the induction of specific transplantation tolerance to an adult donor who could provide tissue after birth without the need for immunosuppression. Although the introduction of allogeneic stem cells to a developing immune system has been shown to result in hematopoietic chimerism, donor-specific transplantation tolerance has not been demonstrated in a large animal model. In previous reports of in utero stem-cell transplantation, the cells were injected into the fetus by an intraperitoneal route. We sought to improve upon this technique of cell transplantation by developing a method for the safe delivery of allogeneic stem cells directly into the hepatic circulation of fetal swine. In the second phase of our study, we determined if adult allogeneic bone marrow cells delivered to the fetus by this intravascular route could result in result in hematopoietic chimerism and donor-specific transplantation tolerance. A method of successful intravascular injection was designed in which a laparotomy was performed on a sow at midgestation (50-55 days) to administer 1 cc of inoculum into the portal vein of each fetus using transuterine ultrasound guidance and a 25-gauge spinal needle. In one sow, 10 piglets were injected with saline to test safety, and 8 piglets were born. For transplantation of stem cells to the fetuses, donor bone marrow was harvested from a genetically defined miniature swine. In one sow the marrow was injected without T-cell depletion resulting in abortion. In the third sow, the marrow was depleted of T-cells to less than 0.01% using magnetic beads conjugated to anti-CD3 monoclonal antibodies. No chimerism was detected in these offspring. Only in the fourth sow where the T-cell depletion was reduced to about 1% of the cells in the inoculum did one animal demonstrate chimerism. This piglet showed reproducible blood chimerism (0.95% donor cells) detected by flow cytometry measurement of monoclonal antibodies to the donor MHC. In addition, this animal demonstrated hyporesponsiveness to donor lymphocytes in an MLR assay while reacting strongly to third-party stimulator cells. A split-thickness skin graft from the donor was accepted, and a third-party graft was rapidly rejected.

Infusion port dislodgement of bilateral breast tissue expanders after MRI

Tissue expanders are placed routinely for breast reconstruction, and magnetic resonance imaging (MRI) is a common diagnostic procedure. Many studies have reported on the safety of MRI in patients with nonferromagnetic implants; however, many tissue expanders contain ferromagnetic components. The authors present a case of bilateral tissue expander infusion port dislodgment after MRI. A 56-year-old woman underwent bilateral mastectomy and immediate reconstruction with McGhan BIOSPAN tissue expanders. These implants contain integral nonferromagnetic infusion ports, as well as small, powerful Magna-Site magnets. Several weeks postoperatively the patient underwent MRI of her spine, which was ordered by her primary physician for back pain. Subsequently, the infusion ports could not be located with the finder magnet. A chest radiograph was obtained, which demonstrated bilateral dislodgment of the infusion ports. Surgical removal and replacement of the tissue expanders were required. Safety considerations of MRI have been discussed extensively in the literature, and data on MRI with various implanted devices have been obtained. The potential risks of performing MRI on patients with metallic implants include conduction of electrical currents, heating of the implant, misinterpretation resulting from artifact, and the possibility of movement or dislodgment of the implant. The small magnet integral to many tissue expanders may be overlooked by patients and physicians during pre-MRI screening. All patients undergoing tissue expansion with implants that contain integral ports should be thoroughly warned about the potential hazards of MRI.

Adenovirus 5 early region 1A does not induce expression of the ewing sarcoma fusion product EWS-FLI1 in breast and ovarian cancer cell lines

The adenovirus 5 early region 1A (E1A) can function as a tumor suppressor gene and is being used in clinical trials as a therapeutic agent for advanced breast, ovarian, and head and neck cancer. Recently, there has been a dispute regarding whether transfection with the E1A gene can induce expression of the Ewing sarcoma oncogenic fusion transcript EWS-FLI1 (Sanchez-Prieto et al., Nat. Med., 5: 1076-1079, 1999; Melot and Delattre, Nat. Med., 5: 1331, 1999; Kovar et al., Cancer Res., 60: 1557-1560, 2000). In an effort to settle the controversy, we tested several stable E1A transfectants of cell lines MDA-MB-231, MCF-7, MDA-MB-435 (breast cancer), SKOV3-ipl (ovarian cancer), and PC-3 (prostate cancer), as well as parental and vector-transfected controls, HEK 293 cells, and RD-ES (Ewing sarcoma) cells, for the EWS-FLI1 fusion product. The EWS-FLI1 transcript could not be identified with reverse transcription-PCR in any of the 13 E1A-transfected cell lines analyzed. Furthermore, the EWS-FLI1 fusion protein could not be detected by Western blot analysis in E1A-transfected cell lines. These results suggest that E1A transfection does not necessarily lead to expression of the oncogenic EWS-FLI1 fusion transcript. Thus, the potential induction of this gene rearrangement by E1A gene therapy is unlikely to be clinically significant in the treatment of advanced malignant disease.

Xenotransplantation model for vascularized musculoskeletal tissues in rodents

The purpose of this study was to establish a model and to define the mechanism of rejection for the transplantation of vascularized musculoskeletal xenografts between C57BL/6j (B6) mice and Lewis rats. This was accomplished by using conventional skin xenografts to determine immunologic baseline data between these species and by performing musculoskeletal grafts from the B6 mice transplanted into Lewis rats. After the transplant, the xenografts were examined histologically and the recipients were assessed for immune reaction using in vitro assays to measure both cell-mediated and humoral responses. The results obtained from the skin xenografts showed activation of both cellular and humoral immunologic responses. All musculoskeletal xenografts were rejected between 3 and 4 postoperative days. Histologically, the grafts showed extensive vascular injury manifested by thrombosis and hemorrhage, suggesting an early humoral response. Anti-donor antibody production was detected in the recipient's sera soon after rejection of the xenogeneic tissue. The cell-mediated immune response, although detectable by the in vitro assays, was less pronounced than the humoral response and corroborated the histologic findings of mild lymphocyte infiltration in the rejected tissue. These results demonstrate that humoral rejection plays a predominant role in the rejection of vascularized musculoskeletal xenotransplants between concordant species. This mouse-to-rat vascularized xenograft model will be utilized for further studies on inducing tolerance to vascularized musculoskeletal xenografts.

Neonatal induction of tolerance to skeletal tissue allografts without immunosuppression

Vascularized allogeneic skeletal tissue transplantation without the need for host immunosuppression would increase reconstructive options for treating congenital and acquired defects. Because the immune system of a fetus or neonate is immature, it may be possible to induce tolerance to allogeneic skeletal tissues by alloantigen injection during this permissive period. Within 12 hours after birth, 17 neonatal Lewis rats were injected through the superficial temporal vein with 3.5 to 5 million Brown Norway bone marrow cells in 0.1 ml normal saline. Ten weeks after the injection, peripheral blood from the Lewis rats was analyzed for the presence of Brown Norway cells to determine hemopoietic chimerism. The Lewis rats then received a heterotopic, vascularized limb tissue transplant (consisting of the knee, the distal femur, the proximal tibia, and the surrounding muscle on a femoral vascular pedicle) from Brown Norway rat donors to determine their tolerance to the allogeneic tissue. A positive control group (n = 6) consisted of syngeneic transplants from Lewis rats into naive Lewis rats to demonstrate survival of transplants. A negative control group (n = 6) consisted of Brown Norway transplants into naive Lewis rats not receiving bone marrow or other immunosuppressive treatment. The animals were assessed for transplant viability 30 days after transplantation using histologic and bone fluorochrome analysis. All the syngeneic controls (Lewis to Lewis) remained viable throughout the experiment, whereas all the Brown Norway to Lewis controls had rejected. Ten of the 17 allografts transplanted into bone marrow recipients were viable at 30 days, with profuse bleeding from the ends of the bone graft and the surrounding graft muscle. The percent of chimerism correlated with survival, with 3.31 percent (SD = 1.9) of peripheral blood, Brown Norway chimerism present in the prolonged survival groups and 0.75 percent (SD = 0.5) of Brown Norway chimerism in the rejected graft group. This study demonstrated prolonged survival of allogeneic skeletal tissue without immunosuppression after early neonatal injection of allogeneic bone marrow in a rat model.

Prolonged survival of musculoskeletal xenografts with combined cyclosporine and 15-deoxyspergualin

This study was undertaken to evaluate the feasibility of performing vascularized musculoskeletal xenografts between mice and rats using immunosuppression. Vascularized musculoskeletal grafts were harvested from the hind limb of C57BL/6J (B6) mice, transplanted heterotopically into Lewis rats, and revascularized by microanastomoses of the graft artery and the recipient femoral artery and the graft vein to the recipient femoral vein. Recipient rats were divided into four groups. Group 1 received no immunosuppression (n = 10), group 2 was treated with cyclosporine (10 mg/kg/day; n = 10), group 3 was treated with 15-deoxyspergualin (5 mg/kg/day; n = 10), and group 4 received both cyclosporine and 15-deoxyspergualin (n = 10). Graft survival was directly examined on postoperative days 4, 7, and 14. In vitro assays were performed using mixed lymphocyte reactions and anti-donor cytotoxic antibody assays to assess the recipient's immune response. Grafts were examined by histology and immunohistochemistry. All grafts in group 1 were rejected by day 4. In groups 2 and 3, all grafts were rejected by day 7. In group 4, however, 8 of 10 recipients had viable grafts on day 14. Data from mixed lymphocyte reactions showed that cell-mediated immune responses were uniformly suppressed in groups 2, 3, and 4 compared with group 1. However, anti-donor antibody production was only partly suppressed in groups 2 and 3, suggesting that graft rejection was primarily caused by circulating cytotoxic anti-donor antibodies in groups 1, 2, and 3. Histologic observations in groups 1, 2, and 3 confirmed the important role of the humoral mechanism in xenograft rejection. Furthermore, immunohistochemical results demonstrated that the small vessels in the rejected grafts showed anti-rat immunoglobulin and complement depositions. Only a combination therapy of cyclosporine and 15-deoxyspergualin attenuated the rejection of xenografts.

Axl-gas6 interaction counteracts E1A-mediated cell growth suppression and proapoptotic activity

The adenovirus type 5 early region 1A gene (E1A) has previously been known as an immortalization oncogene because E1A is required for transforming oncogenes, such as ras and E1B, to transform cells in primary cultures. However, E1A has also been shown to downregulate the overexpression of the Her-2/neu oncogene, resulting in suppression of transformation and tumorigenesis induced by that oncogene. In addition, E1A is able to promote apoptosis induced by anticancer drugs, irradiation, and serum deprivation. Many tyrosine kinases, such as the epidermal growth factor receptor, Her-2/Neu, Src, and Axl, are known to play a role in oncogenic signals in transformed cells. To study the mechanism underlying the E1A-mediated tumor-suppressing function, we exploited a modified tyrosine kinase profile assay (D. Robinson, F. Lee, T. Pretlow, and H.-J. Kung, Proc. Natl. Acad. Sci. USA 93:5958-5962, 1996) to identify potential tyrosine kinases regulated by E1A. Reverse transcription (RT)-PCR products were synthesized with two degenerate primers derived from the conserved motifs of various tyrosine kinases. A tyrosine kinase downregulated by E1A was identified by analyzing the AluI-digested RT-PCR products. We isolated the DNA fragment of interest and found that E1A negatively regulated the expression of the transforming receptor tyrosine kinase Axl at the transcriptional level. To study whether downregulation of the Axl receptor is involved in E1A-mediated growth suppression, we transfected axl cDNA into E1A-expressing cells (ip1-E1A) to establish cells that overexpressed Axl. The Axl ligand Gas6 triggered a greater mitogenic effect in these ip1-E1A-Axl cells than in ip1-E1A control cells and protected the Axl-expressing cells from serum deprivation-induced apoptosis. These results indicate that downregulation of the Axl receptor by E1A is involved in E1A-mediated growth suppression and E1A-induced apoptosis and thereby contributes to E1A's antitumor activities.

VEGF antagonism reduces edema formation and tissue damage after ischemia/reperfusion injury in the mouse brain

VEGF is mitogenic, angiogenic, and a potent mediator of vascular permeability. VEGF causes extravasation of plasma protein in skin bioassays and increases hydraulic conductivity in isolated perfused microvessels. Reduced tissue oxygen tension triggers VEGF expression, and increased protein and mRNA levels for VEGF and its receptors (Flt-1, Flk-1/KDR) occur in the ischemic rat brain. Brain edema, provoked in part by enhanced cerebrovascular permeability, is a major complication in central nervous system pathologies, including head trauma and stroke. The role of VEGF in this pathology has remained elusive because of the lack of a suitable experimental antagonist. We used a novel fusion protein, mFlt(1-3)-IgG, which sequesters murine VEGF, to treat mice exposed to transient cortical ischemia followed by reperfusion. Using high-resolution magnetic resonance imaging, we found a significant reduction in volume of the edematous tissue 1 day after onset of ischemia in mice that received mFlt(1-3)-IgG. 8-12 weeks after treatment, measurements of the resultant infarct size revealed a significant sparing of cortical tissue. Regional cerebral blood flow was unaffected by the administration of mFlt(1-3)-IgG. These results demonstrate that antagonism of VEGF reduces ischemia/reperfusion-related brain edema and injury, implicating VEGF in the pathogenesis of stroke and related disorders.

Antepartum predictors of the development of type 2 diabetes in Latino women 11-26 months after pregnancies complicated by gestational diabetes

In this study, we sought to identify antepartum characteristics that predict the de novo development of diabetes 11-26 months after the index pregnancy in a carefully characterized cohort of women with gestational diabetes mellitus (GDM). Oral and frequently sampled intravenous glucose tolerance tests (OGTTs and FSIGTs), hyperinsulinemic-euglycemic clamps with labeled glucose, and body composition studies were performed on 91 islet cell antibody-negative Latino women with GDM during the third trimester of pregnancy. The women were documented to be diabetes-free within 6 months postpartum. Their diabetes status was ascertained again between 11 and 26 months postpartum. Logistic regression analysis was used to identify independent predictors of the development of diabetes within that interval. Fourteen of the women developed diabetes by World Health Organization criteria 11-26 months after delivery of the index pregnancy. Three antepartum variables were independent predictors of diabetes: the 1-h postchallenge plasma glucose concentration from the 100-g OGTT at which GDM was diagnosed (higher = increased risk; P = 0.003); an index of pancreatic beta-cell compensation for insulin resistance, defined as the product of the 30-min incremental plasma insulin:glucose ratio on a 75-g OGTT and the insulin sensitivity index from a hyperinsulinemic-euglycemic clamp (lower = increased risk, P = 0.009); and the basal glucose production rate after an overnight fast (higher = increased risk; P = 0.04). We conclude that postchallenge hyperglycemia, poor pancreatic beta-cell compensation for insulin resistance, and elevated endogenous glucose production during pregnancy precede the development of type 2 diabetes in young Latino women by at least 1-2 years.

Effect of early mobilization on healing of nerve repair: histologic observations in a canine model

The effect of early mobilization on the healing of nerve repair was studied in a canine model. Median and ulnar nerves in the left wrist of 16 adult mongrel dogs were transected and immediately repaired. No motion of the repaired forelimb was allowed in the immobilized group (n = 10), while controlled passive motion between 30 and 90 degrees of wrist flexion was begun on the first postoperative day for 10 minutes twice daily in the mobilized group (n = 6). The pattern of revascularization and collagen formation at neurorrhaphy was examined by transillumination of India ink-injected specimen and by conventional histologic sections. Revascularization of nerve repair was found to occur by ingrowth of capillaries from proximal and distal nerve ends, which typically crossed the neurorrhaphy by 3 weeks in the immobilized group. Following early mobilization, there was a persistent "hypovascular zone" at the nerve repair site for up to 6 weeks. In addition, more scar tissue was generated by early motion according to gross observation and quantitative collagen analysis. Early mobilization, therefore, seems to impede nerve regeneration by delaying revascularization and enhancing scar formation.

A comparative study of nerve healing in adult, neonatal, and fetal rabbits

This experiment quantitatively compared the human equivalent of a nerve repair following surgical division in the fetal, adult, and early childhood period of development using a rabbit as an experimental animal model. Twelve time-dated pregnant New Zealand White rabbits at 24 days' gestation (term = 31 days) underwent hysterotomy; one hind limb was delivered through the uterine opening. The sciatic nerve was divided and repaired by primary neurorrhaphy using two 11-0 epineural sutures. Sciatic nerve repair was also performed in 10 neonatal and 10 adult New Zealand White rabbits. Following repair, each group was assessed using electromyography examination, measuring distal motor latency and amplitude at 1, 2, 3, and 4 months postrepair. There was no difference in any of the groups in distal motor latency. The amplitude rose incrementally in all groups, and the fetal group had significantly higher amplitudes (p < 0.02) at 1, 2, 3, and 4 months in comparison with the adult group. There was no statistically significant difference between fetal and neonatal nerve repairs at any of the time periods. At the completion of the study, the nerve repair sites were harvested for histologic estimation of mean myelinated fiber density and fiber diameter distribution distal and proximal to the repair site. A greater percentage of myelinated axons crossed the repair site in the fetal group (83 percent) in comparison with the adult group (63 percent) (p < 0.03). Our study also demonstrated significant increases in the number of larger myelinated fibers crossing the repair site in comparison with the neonatal and adult groups (p < 0.04). This study found that fetal nerve healing following surgical repair is superior to that found in adult animals and results in a higher number of larger myelinated fibers crossing the repair site in comparison with adult and neonatal repairs.

Hand transplantation: pertinent data and future outlook

Transplantation of composite tissue allografts, such as a hand, offers immense potential in reconstructive surgery. Review of current replantation literature suggests the prospect for significant functional return following hand transplant, provided appropriate patient is selected and allograft rejection is prevented. Experimental studies of limb transplantation in rodents have demonstrated the efficacy of combination therapy using multiple immunosuppressants. However, long-term survival of limb allografts could not be achieved in large animal models without significant drug toxicity. Given the potential for organ failure, opportunistic infection, and malignancy resulting from long-term immunosuppression, the risk-benefit ratio for hand transplant must be carefully weighed. Our laboratory has been able to achieve allograft survival with minimum immunosuppression by MHC matching or donor antigen exposure prior to immune maturity in the swine. Future transplantation of composite tissue allografts, therefore, may depend upon such modalities to induce host tolerance without long-term immunosuppression.

Measurement of gluconeogenesis and mass isotopomer analysis based on [U-(13)C]glucose

Two methods of measuring rates of gluconeogenesis based on label redistribution after the introduction of [U-(13)C]glucose into the whole body are examined. These methods are compared with methods previously derived for carbon-14 tracers. It is shown that the three approaches (stoichiometric, dilution, and combinatorial) are equivalent, provided the same set of assumptions are used. Barring a factor of two [see Am. J. Physiol. 270 (Endocrinol. Metab. 33): E709-E717, 1996], the differences ( approximately 10-15%) in the carbon-based dilutional and the molecule-based estimates of the rate of gluconeogenesis from published isotopomer data likely arise from small differences in the assumptions that concern the relative rate of label loss from the different isotopomers. The production of unlabeled substrate for glucose synthesis (phosphoenolpyruvate) from the different isotopomers of lactate is shown to be a potential source of error in these methods. This error is estimated using models of the interaction of the gluconeogenetic pathway and the tricarboxylic acid (TCA) cycle and is shown to vary from negligible to 30% depending on the relative flux of the two pathways through the oxaloacetate pool. Because the estimates obtained by both methods considered are lower than is physiologically expected, some of the assumptions made may not hold. Future work will exploit the rich information content of isotopomer data to yield improved estimates.

Skin allograft survival following intrathymic injection of donor bone marrow

BACKGROUND

Success has been reported using intrathymic injection in the preconditioning regimen to induce allograft tolerance. Although long-term stable tolerance has been achieved in numerous rodent vascularized solid organ allograft models, tolerance to skin transplants has only been achieved across minor antigenic or concordant species disparities. This study sought to induce tolerance across an allogeneic barrier in a rat model with a major genetic disparity.

MATERIALS AND METHODS

Lewis rats were injected intrathymically with 1 x 10(8) Brown-Norway (BN) bone marrow cells and intraperitoneally with 1.0 cc of rabbit anti-rat anti-lymphocyte serum (ALS). Twenty-one days later, BN skin grafts were placed on the injected animals. Control groups were included to isolate the effect of technique, thymic manipulation, strain specificity, and ALS.

RESULTS

Animals receiving both intrathymic bone marrow cells and ALS had a skin graft median survival time of 24 days versus 8 days for the control group (P = 0.003). Groups receiving anti-lymphocyte serum alone or intrathymic bone marrow cell injection alone exhibited no skin graft survival prolongation. Mixed lymphocyte reactions revealed normal responsiveness of tolerant animal lymphocytes to donor strain lymphocytes.

CONCLUSION

This protocol utilizing the intrathymic injection of donor bone marrow cells along with short-term immunosuppression with anti-lymphocyte serum produced markedly prolonged survival of skin allografts transplanted across a major histocompatibility barrier. Although tolerance was incomplete, significant prolongation has not previously been reported in genetic disparities of this degree. These results suggest that the application of this technique for central immune modulation may be beneficial for allograft tolerance induction and deserves further study in large animals models.

Multiple metabolic defects during late pregnancy in women at high risk for type 2 diabetes

Detailed metabolic studies were carried out to compare major regulatory steps in glucose metabolism in vivo between 25 normal pregnant Latino women without and 150 pregnant Latino women with gestational diabetes mellitus (GDM). The two groups were frequency-matched for age, BMI, and gestational age at testing in the third trimester. After an overnight fast, women with GDM had higher fasting plasma glucose (P = 0.0001) and immunoreactive insulin (P = 0.0003) concentrations and higher glucose production rates (P = 0.01) but lower glucose clearance rates (P = 0.001) compared with normal pregnant women. During steady-state hyperinsulinemia (approximately 600 pmol/l) and euglycemia (approximately 4.9 mmol/l), women with GDM had lower glucose clearance rates (P = 0.0001) but higher glucose production rates (P = 0.0001) and plasma free fatty acid (FFA) concentrations (P = 0.0002) than the normal women. These intergroup differences persisted when a subgroup of 116 women with GDM who were not diabetic < or = 6 months after pregnancy were used in the analysis. When all subjects were considered, there was a very close correlation between glucose production rates and plasma FFA concentrations throughout the glucose clamps in control (r = 0.996) and GDM (r = 0.995) groups. Slopes and intercepts of the relationships were nearly identical, suggesting that blunted suppression of FFA concentrations contributed to blunted suppression of glucose production in the GDM group. In addition to these defects in insulin action, women with GDM had a 67% impairment of pancreatic beta-cell compensation for insulin resistance compared with normal pregnant women. These results demonstrate that women with GDM have multiple defects in insulin action together with impaired compensation for insulin resistance. Our findings suggest that defects in the regulation of glucose clearance, glucose production, and plasma FFA concentrations, together with defects in pancreatic beta-cell function, precede the development of type 2 diabetes in these high-risk women.