Chimerism and xenotransplantation. New concepts

Advance of genetically modified pigs in xeno-transplantation

As the standard of living improves, chronic diseases and end-stage organ failure have been a regular occurrence in human beings. Organ transplantation has become one of the hopes in the fight against chronic diseases and end-stage organ failure. However, organs available for transplantation are far from sufficient to meet the demand, leading to a major organ shortage crisis. To solve this problem, researchers have turned to pigs as their target since pigs have many advantages as xenograft donors. Pigs are considered the ideal organ donor for human xenotransplantation, but direct transplantation of porcine organs to humans faces many obstacles, such as hyperacute rejection, acute humoral xenograft rejection, coagulation dysregulation, inflammatory response, coagulation dysregulation, and endogenous porcine retroviral infection. Many transgenic strategies have been developed to overcome these obstacles. This review provides an overview of current advances in genetically modified pigs for xenotransplantation. Future genetic engineering-based delivery of safe and effective organs and tissues for xenotransplantation remains our goal.

What Are the Immune Obstacles to Liver Xenotransplantation Which Is Promising for Patients with Hepatocellular Carcinoma?

PURPOSE

Liver transplantation is the most important achievement in the twentieth and twenty-first century. It is the gold standard treatment for hepatocellular carcinoma. However, it provides the best results when performed under strict selection criteria. Nevertheless, organ supply is overwhelmed by the number of patients on the waiting list. There are certain strategies to expand the donor pool such as split liver transplantation, use of extended criteria donors, and living donor liver transplantation. Xenotransplantation can also be a strategy in decreasing the organ shortage. We reviewed the current status of xenotransplantation.

METHODS

We evaluated the historical attempts of xenotransplantation to humans and also made a summary of the preclinical studies in the field.

RESULTS

Molecular biology and genetic engineering are developing with an incredible speed. There are great achievements made in cell therapy, 3D bioprinting of the organs, and ultimately xenotransplantation. There is a vast amount of problems to be handled before evaluating the efficacy of xenotransplantation in the treatment of hepatocellular carcinoma. Major problems include antibody-mediated rejection to antigens such as galactose ⍺1-3 galactose, N- glycolylneuraminic acid, β1,4-N-acetylgalactosaminyltransferase, lethal thrombocytopenia, and erythrocyte sequestration. Antibody mediated rejection to these specific antigens are addressed using gene editing technology including CRISPR Cas9, TALEN and other recombination methods. Although hyperacute rejection is reduced, long-term survival could not be achieved in experimental models.

CONCLUSION

The future is yet to come, there are developments made in the field of genetic editing, immunosuppressive medication, and pretransplant desensitization techniques. Therefore, we believe that xenotransplantation will be in clinical practice, at least for treatment of critically ill patients.

Psychosocial Outcomes of Donors Whose Recipients Died After Living Donor Liver Transplantation

PURPOSE

Our aim was to investigate the psychosocial outcomes of the donors whose recipients died after living donor liver transplantation (LDLT).

METHODS

Forty-one donors whose recipients died and 87 donors whose recipients were alive after LDLT at Inonu University Liver Transplantation Institute between 2012 and 2017 were included into the study. Demographic data form, Beck anxiety scale, Beck depression scale, Beck Hopelessness Scale, Posttraumatic Growth Inventory, Decision Regret Scale, Multidimensional Scale of Perceived Social Support, and general evaluation questionnaire (24 questions) were used in all donors by face to face questioning. In addition to the descriptive statistical analysis, chi-square and student's t tests were used to evaluate the differences between the groups.

RESULTS

Recipient death after living donor liver transplantation is a factor that negatively increases the level of anxiety, depression, hopelessness levels, and repentance of donors, and adversely affects the psychological growth of the donors after donation experience.

CONCLUSION

Regular follow-up of the donors should be done psychosocially in the postoperative period, especially the donors whose recipients have died should be followed up more frequently, and their support and treatment should be provided when needed. The donors should also be informed about the psychosocial implications of operative management and postoperative period. More studies are needed regarding the psychosocial problems of the donors.

Prolonged survival of rat hepatic allograft after pretransplant intraportal infusion of recipient blood to the donor

AIM: To investigate the effect of pretransplant intraportal administration of recipient blood into the donor on the survival of rat hepatic allograft.

METHODS: Male LEW (RT1) and ACI (RT1^a) rats were used as liver transplant recipients and donors, respectively. In experimental group, 7 d prior to transplantation, ACI donors were anesthetized with ether and transfused with freshly heparinized LEW recipient blood (1 mL) via the portal vein. In control group, the rats only received 1 mL normal saline 7 d before transplantation. The serum levels of interferon-γ (IFN-γ) were determined after transplantation. Immunocompetent cells from the donors were identified with anti-donor classⅡ MHC (RT1B^a) (OX-76) antibodies. The number of donor-derived CD4⁺ and CD8⁺ T cells in hepatic allograft or recipient spleen was examined. Reverse transcription-polymerase chain reaction was used to detect the mRNA expression of cytokines in the allograft.

RESULTS: LEW rats transplanted with hepatic allograft from ACI rats survived a mean of 11.1 ± 2.1 d. Intraportal preadministration of recipient LEW blood significantly increased the survival of LEW recipients with ACI livers to 31.7 ± 7.6 d (P < 0.05). The serum level of IFN-γ was significantly increased in the experimental group as compared with that in the control group. Cellular infiltration of the hepatic allograft in experimental group was significantly lower than that in the control group. The ratio of OX76⁺CD4⁺ or OX76⁺CD8⁺ T cells to CD4⁺ or CD8⁺ cells was significantly greater in hepatic allograft pretreated with LEW recipient blood than that in the controls (OX76⁺CD4⁺ cells: 25.6% vs 6.2%, P < 0.05; OX76⁺CD8⁺ cells: 26.6% vs 7.4%, P < 0.05), but not in recipient spleen. OX76⁺CD8⁺ T cells from hepatic allograft in the experimental group expressed IFN-γ and interleukin-10 mRNA, but not interleukin-2 mRNA.

CONCLUSION: Pretransplant intraportal infusion of recipient blood to the donor rats prolonged the survival of hepatic allograft, which may be associated with the regional graft-versus-host reaction.

Oral feeding with pig peripheral lymphocytes decreases the xenogeneic delayed type hypersensitivity reaction in galactosyltransferase knockout mice

PURPOSE

Oral tolerance induction has shown promising results in experimental allotransplantation models but is not well investigated in xenotransplantation. We investigated the possibility to induce tolerance against pig peripheral lymphocytes (pPBL) in galactosyltransferase knockout mice (gal -/-), which produce antibodies against Galalpha1-3Gal.

MATERIAL AND METHODS

Female (gal -/-) mice 6 to 8 weeks old weighing 35 to 40 g (n = 10) were fed orally every third day five times with 2 x 10(7) isolated, viable pPBL, or with phosphate-buffered saline (PBS) only (n = 7). They were then immunized subcutaneously on day 0 with a subcellular lysate from 4 x 10(7) isolated, viable pPBL. On day 13, 25 microL of a subcellular lysate corresponding to 1 x 10(7) isolated, viable pPBL was injected in the right dorsal foot pad, and the delayed type hypersensitivity (DTH) reaction was calculated after 24 hours by subtracting the swelling response from 25 microL PBS in the left footpad. Anti-Galalpha1-3Gal immunoglobulin IgG and IgM antibody titers were measured in the serum before oral feeding and at day 14.

RESULTS

The DTH reaction of the pPBL fed mice was 0.07 +/- 0.05 mm vs 0.57 +/- 0.23 mm for the controls (P < .001). No significant differences in anti Gal alpha1-3 Gal IgG and IgM antibody titers were seen.

CONCLUSIONS

This study demonstrates for the first time that oral delivery of pPBL can counteract the indirect T-cell reaction against xenogeneic subcellular antigens from pPBL. These observations warrant further investigation in immunologically modified mice and perhaps in primate models of xenotransplantation.

Early onset of rejection in concordant hamster xeno hearts display signs of necrosis, but not apoptosis, correlating to the phosphocreatine concentration

BACKGROUND

The importance of apoptosis contra necrosis for ischemia/reperfusion (RP) and acute rejection in concordant rodent xenotransplantation is largely unknown. We explored this question by comparing rodent allo and concordant xenotransplants with different morphological methods to detect apoptosis and biochemical data on the levels of high-energy phosphates obtained with in vitro 31Phosphorous Magnetic Resonance Spectroscopy (31P MRS). More specifically, we applied a hitherto unused method in transplantation research, apoptosis specific biotin labeled oligonucleotides designed with a 10 base pair stem region and a 20 nucleotides large loop that form a hairpin like shape. The results obtained with this method were compared to results obtained with the more widely used in situ 3'-end labeling of DNA (TUNEL) assay and extraction and gel electrophoresis of labeled DNA (DNA laddering).

METHODS

Cervical heart transplantations were performed between inbred Lewis (L) (RT1l) to L, L to DA (RT1a) rats, hamster (H) to H and H to L (X) (n=5 for all groups except for X, n=9). All hearts were subjected to 30 min of cold ischemia (+4 degrees C) and 6 h of RP before explantation. In vitro 31P MRS was used to determine the phosphocreatine (PCr), beta-adenosine triphosphate (beta-ATP) concentrations and the PCr/beta-ATP ratio of the transplants. We correlated the biochemical data to haematoxylin and eosin (H & E) stained tissue slides scored for rejection, infiltration of antibodies and complement depositions, DNA extraction and gel electrophoresis of labeled DNA (DNA laddering), in situ 3'-end labeling of DNA (TUNEL) and the apoptosis specific hairpin probe assays scoring.

RESULTS

The rejection score of the xeno grafts differed significantly compared to their syngeneic hamster to hamster controls (2.40 +/- 0.25 vs. 1.20 +/- 0.20; P=0.005) and they had a significantly higher TUNEL score, 228 +/- 15 vs. 2.44 +/- 0.32 (P=0.009), that correlated to changes in PCr concentration (P<0.001) and to the PCr/beta-ATP ratio (P=0.01). The uptake was mainly (90-95%) located to 1-2 microm large extra cellular 'granule'. A picture resembling early necrosis was seen on the H & E stainings and reflected in the Billingham rejection score above.

CONCLUSIONS

After 6 h of RP the onset of acute rejection in the concordant hamster xeno hearts displayed features of early, possibly mitochondrial, necrosis, but not apoptosis, which correlated to changes in the PCr concentration and the PCr/beta-ATP ratio. The mechanism for the early rejection observed is unclear and might be caused by other factors in the sera apart from cellular components, antibodies and complement factors. Identification of the underlying mechanisms could enable us to design rational therapies that prevent activation of the recipient's innate immune response.

Prospective study of microchimerism in renal allograft recipients: association between HLA-DR matching, microchimerism and acute rejection

The presence of donor-derived hematopoietic cells in blood and various tissues of the organ recipients, termed allogeneic microchimerism, has been considered to play an essential role in establishment of organ acceptance. In this study, we prospectively determined the presence of peripheral blood microchimerism (PBM) in 20 male-to-female renal allograft recipients up to 30 months post-transplantation. Recipients were categorized according to the pattern of microchimerism into microchimeric and nonmicrochimeric groups, and then state of human leukocyte antigens (HLA) Class II (DR/DQ) matching, episodes of acute rejection, age at transplantation, renal function, and history of blood transfusion were compared. DNA was extracted from donor, pre-transplant, and post-transplant (1 wk; 1, 3, 6, 12, 18, 24, and 30 months) peripheral blood samples. We analyzed PBM using nested polymerase chain reaction (PCR) amplification specific for the SRY region of the Y chromosome with a sensitivity up to 1:1 000 000. Microchimerism was detected in 13 (65%) of 20 recipients at various intervals. The highest frequency of microchimerism was at 1 wk (55%). Among microchimeric recipients, none were positive on all post-transplant analyses. Interestingly, nonmicrochimeric cases were negative throughout the study. The three recipients with an episode of acute rejection during the first week after transplantation were all in the nonmicrochimeric group with completely mismatched HLA-DR antigens. HLA-DR incompatibility was significantly lower (t-test, p<0.05) in microchimeric cases (1.0+/-0.58) than in nonmicrochimeric ones (1.9+/-0.38). But regarding HLA-DQ and other clinical parameters mentioned above, significant difference was not observed. We propose that there is an association between HLA-DR matching, microchimerism and acute graft rejection in our recipients. Our study demonstrates that, with routine immunosuppressive protocols, higher compatibility of HLA-DR antigens facilitates microchimerism induction. Then, development of new stronger immunosuppressive protocols (including conditioning) or augmentation of chimeric state (by donor-specific bone marrow infusion), especially in completely mismatched HLA-DR renal allograft recipients, may be useful for graft acceptance.

Liver transplantation. Living donor, hepatocyte, and xenotransplantation

Liver transplantation is now accepted as effective therapy in the treatment of acute and chronic hepatic failure. Improvements in surgical techniques and immune suppression have led to 5-year survival rates that exceed 70% in most centers. The success of transplantation has led to a dramatic increase in the number of candidates to over 14,000 places on the national waiting list. While the number of patients in need of transplantation increases, there has been little growth in the supply of available cadaveric organs, resulting in an organ shortage crisis. With waiting times often exceeding 1 to 2 years, the waiting list mortality now exceeds 10% in most regions. Several novel approaches have been developed to address the growing disparity between the limited supply and excessive demand for suitable organs.

Bioartificial pancreas: materials, devices, function, and limitations

The term "bioartificial endocrine pancreas" (BEP) was introduced by Anthony Sun in 1980. It was in 1968, however, that Thomas Chang proposed the use of microencapsulated islets as artificial beta-cells. By applying a semipermeable membrane on the top of microcapsules, a system can be produced that is impermeable to viable islet cells and large effector molecules of the immune system, thus providing a protection for transplanted islets against rejection. Since then, the term BEP has not often appeared in papers. Instead, the term "bioartificial pancreas" (BAP) has gained widespread use. In a broader sense, BAP would include an application of suitable endocrine cells and protective polymeric vehicles, but not necessarily providing a filtration barrier of precisely defined properties (e.g., cells injected into a gel of hyaluronate).