Feasibility of cryopreserved tracheal xenotransplants with the use of short-course immunosuppression

Comparison of tracheal reconstruction with allograft, fresh xenograft and artificial trachea scaffold in a rabbit model

This study evaluated the possibility of tracheal reconstruction with allograft, pig-to-rabbit fresh xenograft or use of a tissue-engineered trachea, and compared acute rejection of three different transplanted tracheal segments in rabbits. Eighteen healthy New Zealand White rabbits weighing 2.5-3.1 kg were transplanted with three different types of trachea substitutes. Two rabbits and two alpha 1, 3-galactosyltransferase gene-knockout pigs weighing 5 kg were used as donors. The rabbits were divided into three groups: an allograft control group consisting of rabbit-to-rabbit allotransplantation animals (n = 6), a fresh xenograft group consisting of pig-to-rabbit xenotransplantation animals (n = 6), and an artificial trachea scaffold group (n = 6). All animals were monitored for 4 weeks for anastomotic complications or infection. The recipients were sacrificed at 28 days after surgery and the grafts were evaluated. On bronchoscopy, all of the fresh xenograft group animals showed ischemic and necrotic changes at 28 days after trachea replacement. The allograft rabbits and the tissue-engineered rabbits showed mild mucosal granulation. The levels of interleukin-2 and interferon-γ in the fresh xenograft group were higher than in other groups. Histopathologic examination of the graft in the fresh xenograft rabbits showed ischemic and necrotic changes, including a loss of epithelium, mucosal granulation, and necrosis of cartilaginous rings. The pig-to-rabbit xenografts showed more severe acute rejection within a month than the rabbits with allograft or artificial trachea-mimetic graft. In addition, the artificial tracheal scaffold used in the present experiment is superior to fresh xenograft and may facilitate tracheal reconstruction in the clinical setting.

Cryopreservation of the tracheal grafts: Review and perspective

Transplantation of the trachea may become the preferred method for the reconstruction of extensive tracheal defects, however, several unresolved problems must be addressed, such as immunosuppression, preservation and donor shortage. In this manuscript, the cryopreservation of tracheal grafts is reviewed, which potentially is associated with a lessened immunological response. Cryopreservation may be used clinically for long-term preservation and may solve the donor shortage. It is very important to confirm the immunomodulatory effect of cryopreservation on tracheal allografts in order to expand the potential clinical application of tracheal transplantation in the future. The cartilage as well as the epithelium and lamina propria serve as targets for rejection. However, the effect of cryopreservation on chondrocytes could be associated with reduced allogenicity of the trachea. The long-term cryopreservation of cartilage must be investigated in basic research models of chondrocyte viability. Growth of cryopreserved tracheal allografts is less well understood. Further studies are needed to elucidate the mechanism of synergistic effects of both cryopreservation and adequate immunosuppression for tracheal xenografts.

Cryopreserved Tracheal Grafts: A Review of the Literature

Cryopreserved tracheal grafts have been used in several experimental models of long segment replacement. The clinical application of the procedure has been limited due to the fact that contradictory results have been reported. The purpose of this article is to present a review of the literature on tracheal cryopreservation. Despite the fact that most authors indicate that cryopreserved tracheal allografts retain viability and have a low immunological response, though they continue to function after transplantation with good epithelialization and patency, cryopreservation leads to significant damage to cartilage, the degree of which is based on the freezing-storage methods that affect the function and durability of a graft. The long-term storage of cartilage must therefore be investigated in more detail in basic research models of cartilage viability: the evaluation of chondrocyte apoptosis, and the use of different solutions for tracheal cryopreservation other than RPMI-1640, Dulbecco's modified Eagle's, Eurocollins, and TC-199. Furthermore, problems that involve improving the blood supply to the graft after extensive resection and immunosuppression must be resolved before tracheal cryopreservation can become a clinically established method for tracheal grafts.

Efficacy of Multiglycosidorum tripterygii for rat tracheal allografts

BACKGROUND

A new immunosuppressant must be developed because graft rejection remains the leading cause of death after lung transplantation. We evaluated the efficacy of Multiglycosidorum tripterygii as a new immunosuppressant using a heterotopic rat tracheal allotransplantation model.

METHODS

We performed short- and long-term experiments using a short-course of treatment with Multiglycosidorum tripterygii. To assess the immunosuppessive power of Multiglycosidorum tripterygii, we compared its efficacy (at 90, or 150 mg/kg/day) with that of tacrolimus (at 0.5, 1.0, or 1.5 mg/kg/day) at 4 weeks after transplantation. We then evaluated the effect of 150 mg/kg/day of Multiglycosidorum tripterygii treatment at 12 weeks after transplantation.

RESULTS

The efficacy of 150 mg/kg/day Multiglycosidorum tripterygii was superior to that of 90 mg/kg/day of the same drug and was comparable to that of 1.0 mg/kg/day tacrolimus, as demonstrated by morphologic assessment of the graft. Treatment with 150 mg/kg/day Multiglycosidorum tripterygii maintained graft morphology for 4 weeks but could not maintain graft viability for 12 weeks. Animals tolerated this dosage of Multiglycosidorum tripterygii for 12 weeks after administration.

CONCLUSIONS

We conclude that the efficacy of Multiglycosidorum tripterygii is acceptable for rat tracheal allografts. Further studies are necessary to investigate Multiglycosidorum tripterygii treatment for clinical use in humans.

Experimental study of a new tracheal prosthesis: Pored Dacron tube

OBJECTIVE

This study was designed to evaluate how various sizes and densities of pores in Dacron tubing might enhance its utility as a tracheal prosthesis.

METHODS

A vascular prosthesis made of knitted external velour polyester was prepared for pore formation with a laser. The first set compared different pore sizes (300, 500, and 700 microm) and pore densities (25/cm(2) or 100/cm(2)). Grafts were reinforced with an externally heat-sealed silicone ring. The second set tested grafts with a pore density of 64/cm(2) and a pore size of 500 microm internally reinforced with a stainless-steel spiral stent. In all experiments, a canine mediastinal trachea 10 cartilage rings in length was resected, and the prosthesis was then implanted with an omental flap.

RESULTS

Lower pore size and density (300 microm, 25 pores/cm(2)) led to essentially no tissue ingrowth. Larger pore size (700 microm) and low density (25 pores/cm(2)) led to rapid and excessive ingrowth of granulation. Midrange pore size (500 microm) and high density (100 pores/cm(2)) invited steady tissue ingrowth, but marked luminal stenosis eventually developed. Stent-reinforced prostheses with 500-microm pores at 64 pores/cm(2), as used in the second set, maintained an average patency rate of 60% or more (range, 20%-100%) at least 12 months after implantation.

CONCLUSION

Our data show that porosity is a key factor for tissue growth through our Dacron tracheal prostheses. This artificial trachea model has led to long-term survivors up to 27 months after the operation and seems promising as a basic model for clinical tracheal repair.

The immunomodulatory effect of cryopreservation in rat tracheal allotransplantation

BACKGROUND

Cryopreservation is one solution to the problem of donor organ deficit. To investigate the effect of cryopreservation on tracheal allografts, we performed 2 experiments in rats.

METHODS

In Experiment 1, we assessed second-set graft rejection. Two weeks after primary heterotopic transplantation (Group 1, fresh isografts; Group 2, fresh allografts from Lewis rats; and Group 3, cryopreserved allografts from Lewis rats; n = 5, respectively), each animal underwent secondary heterotopic grafting with isografts and allografts from Lewis and Wistar Furth rats (n = 5, respectively). Four weeks after the secondary transplantation, all grafts were retrieved for histologic analysis. In Experiment 2, we assessed the long-term results of allograft cryopreservation, without immunosuppression therapy. Six months after transplantation of fresh (Group 4) and cryopreserved (Group 5) allografts, the tracheal segments (each group, n = 5) were histologically evaluated.

RESULTS

In Experiment 1, only the secondary allografts from Lewis rats in Group 2 did not maintain lumen structure and often showed dislocated or destroyed cartilage. Second-set graft rejection was specifically recognized in Group 2, but not in Group 1 or 3. In Experiment 2, the cryopreserved allografts appeared almost normal and lumen rigidity was preserved 6 months after transplantation. These allografts were superior to the fresh allografts in patency and in cartilage dislocation and mononuclear cell infiltration scores, but not in the viable chondrocyte ratio.

CONCLUSIONS

We conclude that cryopreservation may produce successful long-term results because of its immunomodulatory effect on tracheal allografts.