Research prospects for kidney xenotransplantation: a bibliometric analysis

BACKGROUND

Xenograft kidney transplantation has been receiving increasing attention. The purpose of this study is to use bibliometric analysis to identify papers in this research field and explore their current status and development trends.

METHODS

Using the data in the Web of Science core database from Clarivate Analytics as the object of study, we used 'TS = Kidney OR Renal AND xenotransplantation' as the search term to find all literature from 1980 to 2 November 2022.

RESULTS

In total, 1005 articles were included. The United States has the highest number of publications and has made significant contributions in this field. Harvard University was at the forefront of this study. Professor Cooper has published 114 articles in this field. Xenotransplantation has the largest number of relevant articles. Transplantation was the most cited journal. High-frequency keywords illustrated the current state of development and future trends in xenotransplantation. The use of transgenic pigs and the development of coordinated co-stimulatory blockers have greatly facilitated progress in xenotransplantation research. We found that 'co-stimulation blockade', 'xenograft survival', 'pluripotent stem cell', 'translational research', and 'genetic engineering' were likely to be the focus of attention in the coming years.

CONCLUSIONS

This study screened global publications related to xenogeneic kidney transplantation; analyzed their literature metrology characteristics; identified the most cited articles in the research field; understood the current situation, hot spots, and trends of global research; and provided future development directions for researchers and practitioners.

Xenograft recipients and the right to withdraw from a clinical trial

Preclinical xenotransplantation research using genetically engineered pigs has begun to show some promising results and could one day offer a scalable means of addressing organ shortage. While it is a fundamental tenet of ethical human subject research that participants have a right to withdraw from research once enrolled, several scholars have argued that the right to withdraw from xenotransplant research should be suspended because of the public health risks posed by xenozoonotic transmission. Here, we present a comprehensive critical evaluation of the claim that xenotransplant recipients should be required to waive their right to withdraw from lifelong biosurveillance. We conclude that if xenotransplantation requires participants to waive their right to withdraw, then clinical trials may not be justifiable, given the ethical and legal obstacles involved with doing so. Consequently, if clinical trials are permitted with a right to withdraw, then they may pose a significant public health risk.

A pig kidney supporting human physiology

Because of the global shortage of donor kidneys, xenotransplantation emerges as a potential solution for individuals with kidney failure who face challenges in securing a suitable donor kidney. A study featured in this month's issue of Kidney International assesses the kidney physiology of a porcine kidney transplanted into a brain-dead human with kidney failure, demonstrating life-sustaining physiological function for 7 days. Together with preclinical nonhuman primate studies, decedent models provide complementary data for development of clinical kidney xenotransplantation.

Engineering Equity Into the Promise of Xenotransplantation

Two of the greatest challenges facing kidney transplantation are the lack of donated organs and inequities in who receives a transplant. Xenotransplantation holds promise as a treatment approach that could solve the supply problem. Major advances in gene-editing procedures have enabled several companies to raise genetically engineered pigs for organ donation. These porcine organs lack antigens and have other modifications that should reduce the probability of immunological rejection when transplanted into humans. The US Food and Drug Administration and transplantation leaders are starting to chart a path to test xenotransplants in clinical trials and later integrate them into routine clinical care. Here we provide a framework that industry, regulatory authorities, payers, transplantation professionals, and patient groups can implement to promote equity during every stage in this process. We also call for immediate action. Companies developing xenotransplant technology should assemble patient advocacy boards to bring the concerns of individuals with end-stage kidney disease to the forefront. For trials, xenotransplantation companies should partner with transplant programs with substantial patient populations of racial and ethnic minority groups and that have reciprocal relationships with those communities. Those companies and transplant programs should reach out now to those communities to inform them about xenotransplantation and try to address their concerns. These actions have the potential to make these communities full partners in the promise of xenotransplantation.

Physiologic homeostasis after pig-to-human kidney xenotransplantation

Demand for kidney grafts outpaces supply, limiting kidney transplantation as a treatment for kidney failure. Xenotransplantation has the potential to make kidney transplantation available to many more patients with kidney failure, but the ability of xenografts to support human physiologic homeostasis has not been established. A brain-dead adult decedent underwent bilateral native nephrectomies followed by 10 gene-edited (four gene knockouts, six human transgenes) pig-to-human xenotransplantation. Physiologic parameters and laboratory values were measured for seven days in a critical care setting. Data collection aimed to assess homeostasis by measuring components of the renin-angiotensin-aldosterone system, parathyroid hormone signaling, glomerular filtration rate, and markers of salt and water balance. Mean arterial blood pressure was maintained above 60 mmHg throughout. Pig kidneys secreted renin (post-operative day three to seven mean and standard deviation: 47.3 ± 9 pg/mL). Aldosterone and angiotensin II levels were present (post-operative day three to seven, 57.0 ± 8 pg/mL and 5.4 ± 4.3 pg/mL, respectively) despite plasma renin activity under 0.6 ng/mL/hr. Parathyroid hormone levels followed ionized calcium. Urine output down trended from 37 L to 6 L per day with 4.5 L of electrolyte free water loss on post-operative day six. Aquaporin 2 channels were detected in the apical surface of principal cells, supporting pig kidney response to human vasopressin. Serum creatinine down trended to 0.9 mg/dL by day seven. Glomerular filtration rate ranged 90-240 mL/min by creatinine clearance and single-dose inulin clearance. Thus, in a human decedent model, xenotransplantation of 10 gene-edited pig kidneys provided physiologic balance for seven days. Hence, our in-human study paves the way for future clinical study of pig-to-human kidney xenotransplantation in living persons.

Spatiotemporal immune atlas of a clinical-grade gene-edited pig-to-human kidney xenotransplant

Pig-to-human xenotransplantation is rapidly approaching the clinical arena; however, it is unclear which immunomodulatory regimens will effectively control human immune responses to pig xenografts. Here, we transplant a gene-edited pig kidney into a brain-dead human recipient on pharmacologic immunosuppression and study the human immune response to the xenograft using spatial transcriptomics and single-cell RNA sequencing. Human immune cells are uncommon in the porcine kidney cortex early after xenotransplantation and consist of primarily myeloid cells. Both the porcine resident macrophages and human infiltrating macrophages express genes consistent with an alternatively activated, anti-inflammatory phenotype. No significant infiltration of human B or T cells into the porcine kidney xenograft is detectable. Altogether, these findings provide proof of concept that conventional pharmacologic immunosuppression may be able to restrict infiltration of human immune cells into the xenograft early after compatible pig-to-human kidney xenotransplantation.

Lentivirus-Mediated BCL-XL Overexpression Inhibits Stem Cell Apoptosis during Ex Vivo Expansion and Provides Competitive Advantage Following Xenotransplantation

Hematopoietic reconstitution after hematopoietic stem cell transplantation (HSCT) is influenced by the number of transplanted cells. However, under certain conditions donor cell counts are limited and impair clinical outcome. Hematopoietic stem and progenitor cell (HSPC) expansion prior to HSCT is a widely used method to achieve higher donor cell counts and minimize transplantation-related risks such as graft failure or delayed engraftment. Still, expansion in a non-physiological environment can trigger cell death mechanisms and hence counteract the desired effect. We have shown earlier that during HSCT a relevant amount of HSPCs were lost due to apoptosis and that cell death inhibition in donor HSPCs improved engraftment in xenotransplantation experiments. Here, we assessed the effect of combined ex vivo expansion and cell death inhibition on HSPC yield and their reconstitution potential in vivo. During expansion with cytokines and the small molecule inhibitor StemRegenin 1, concomitant lentiviral overexpression of antiapoptotic BCL-XL resulted in an increased yield of transduced HSPCs. Importantly, BCL-XL overexpression enhanced the reconstitution potential of HSPCs in xenotransplantation experiments in vivo. In contrast, treatment with caspase and necroptosis inhibitors had no favorable effects on HSPC yields nor on cell viability. We postulate that overexpression of antiapoptotic BCL-XL, both during ex vivo expansion and transplantation, is a promising approach to improve the outcome of HSCT in situations with limited donor cell numbers. However, such apoptosis inhibition needs to be transient to avoid long-term sequelae like leukemia.

Optimization of Enzymatic and Chemical Decellularization of Native Porcine Heart Valves for the Generation of Decellularized Xenografts

One of the most important medical interventions for individuals with heart valvular disease is heart valve replacement, which is not without substantial challenges, particularly for pediatric patients. Due to their biological properties and biocompatibility, natural tissue-originated scaffolds derived from human or animal sources are one type of scaffold that is widely used in tissue engineering. However, they are known for their high potential for immunogenicity. Being free of cells and genetic material, decellularized xenografts, consequently, have low immunogenicity and, thus, are expected to be tolerated by the recipient's immune system. The scaffold ultrastructure and ECM composition can be affected by cell removal agents. Therefore, applying an appropriate method that preserves intact the structure of the ECM plays a critical role in the final result. So far, there has not been an effective decellularization technique that preserves the integrity of the heart valve's ultrastructure while securing the least amount of genetic material left. This study demonstrates a new protocol with untraceable cells and residual DNA, thereby maximally reducing any chance of immunogenicity. The mechanical and biochemical properties of the ECM resemble those of native heart valves. Results from this study strongly indicate that different critical factors, such as ionic detergent omission, the substitution of Triton X-100 with Tergitol, and using a lower concentration of trypsin and a higher concentration of DNase and RNase, play a significant role in maintaining intact the ultrastructure and function of the ECM.

Cutting edge of genetically modified pigs targeting complement activation for xenotransplantation

In the quest to address the critical shortage of donor organs for transplantation, xenotransplantation stands out as a promising solution, offering a more abundant supply of donor organs. Yet, its widespread clinical adoption remains hindered by significant challenges, chief among them being immunological rejection. Central to this issue is the role of the complement system, an essential component of innate immunity that frequently triggers acute and chronic rejection through hyperacute immune responses. Such responses can rapidly lead to transplant embolism, compromising the function of the transplanted organ and ultimately causing graft failure. This review delves into three key areas of xenotransplantation research. It begins by examining the mechanisms through which xenotransplantation activates both the classical and alternative complement pathways. It then assesses the current landscape of xenotransplantation from donor pigs, with a particular emphasis on the innovative strides made in genetically engineering pigs to evade complement system activation. These modifications are critical in mitigating the discordance between pig endogenous retroviruses and human immune molecules. Additionally, the review discusses pharmacological interventions designed to support transplantation. By exploring the intricate relationship between the complement system and xenotransplantation, this retrospective analysis not only underscores the scientific and clinical importance of this field but also sheds light on the potential pathways to overcoming one of the major barriers to the success of xenografts. As such, the insights offered here hold significant promise for advancing xenotransplantation from a research concept to a viable clinical reality.

Complement networks in gene-edited pig xenotransplantation: enhancing transplant success and addressing organ shortage

The shortage of organs for transplantation emphasizes the urgent need for alternative solutions. Xenotransplantation has emerged as a promising option due to the greater availability of donor organs. However, significant hurdles such as hyperacute rejection and organ ischemia-reperfusion injury pose major challenges, largely orchestrated by the complement system, and activated immune responses. The complement system, a pivotal component of innate immunity, acts as a natural barrier for xenotransplantation. To address the challenges of immune rejection, gene-edited pigs have become a focal point, aiming to shield donor organs from human immune responses and enhance the overall success of xenotransplantation. This comprehensive review aims to illuminate strategies for regulating complement networks to optimize the efficacy of gene-edited pig xenotransplantation. We begin by exploring the impact of the complement system on the effectiveness of xenotransplantation. Subsequently, we delve into the evaluation of key complement regulators specific to gene-edited pigs. To further understand the status of xenotransplantation, we discuss preclinical studies that utilize gene-edited pigs as a viable source of organs. These investigations provide valuable insights into the feasibility and potential success of xenotransplantation, offering a bridge between scientific advancements and clinical application.

The decedent model: A new paradigm for de-risking high stakes clinical trials like xenotransplantation

The first 2 living recipients of pig hearts died unexpectedly within 2 months, despite both recipients receiving what over 30 years of nonhuman primate (NHP) research would suggest were the optimal gene edits and immunosuppression to ensure success. These results prompt us to question how faithfully data from the NHP model translate into human outcomes. Before attempting any further heart xenotransplants in living humans, it is highly advisable to gain a more comprehensive understanding of why the promising preclinical NHP data did not accurately predict outcomes in humans. It is also unlikely that additional NHP data will provide more information that would de-risk a xenoheart clinical trial because these cases were based on the best practices from the most successful NHP results to date. Although imperfect, the decedent model offers a complementary avenue to determine appropriate treatment regimens to control the human immune response to xenografts and better understand the biologic differences between humans and NHP that could lead to such starkly contrasting outcomes. Herein, we explore the potential benefits and drawbacks of the decedent model and contrast it to the advantages and disadvantages of the extensive body of data generated in the NHP xenoheart transplantation model.

Comparison of ex vivo bioluminescence imaging, Alu-qPCR and histology for the quantification of spontaneous lung and bone metastases in subcutaneous xenograft mouse models

Bioluminescence imaging (BLI) is a non-invasive state-of-the-art-method for longitudinal tracking of tumor cells in mice. The technique is commonly used to determine bone metastatic burden in vivo and also suitable ex vivo to detect even smallest bone micro-metastases in spontaneous metastasis xenograft models. However, it is unclear to which extent ex vivo BLI correlates with alternative methods for metastasis quantification. Here, we compared ex vivo BLI, human DNA-based Alu-qPCR, and histology for the quantification of bone vs. lung metastases, which are amongst the most common sites of metastasis in prostate cancer (PCa) patients and spontaneous PCa xenograft models. Data from 93 immunodeficient mice were considered, each of which were subcutaneously injected with luciferase/RGB-labeled human PCa PC-3 cells. The primary tumors were resected at ~ 0.75 cm³ and mice were sacrificed ~ 3 weeks after surgery and immediately examined by ex vivo BLI. Afterwards, the right lungs and hind limbs with the higher BLI signal (BLIHi bone) were processed for histology, whereas the left lung lobes and hind limbs with the lower BLI signal (BLILo bone) were prepared for Alu-qPCR. Our data demonstrate remarkable differences in the correlation coefficients of the different methods for lung metastasis detection (r ~ 0.8) vs. bone metastasis detection (r ~ 0.4). However, the BLI values of the BLIHi and BLILo bones correlated very strongly (r ~ 0.9), indicating that the method per se was reliable under identical limitations; the overall level of metastasis to contralateral bones was astonishingly similar. Instead, the level of lung metastasis only weakly to moderately correlated with the level of bone metastasis formation. Summarized, we observed a considerable discrepancy between ex vivo BLI and histology/Alu-qPCR in the quantification of bone metastases, which was not observed in the case of lung metastases. Future studies using ex vivo BLI for bone metastasis quantification should combine multiple methods to accurately determine metastatic load in bone samples.

Transplant nephropathology: Wherefrom, wherein, and whereto

Renal pathology is a relatively recent entry in nephrology. While diseases of the kidney are old, their study began in the 19th century with the report of Richard Bright of the lesions of end-stage kidney disease. Its easy diagnosis from albuminuria soon elevated Bright's nephritis into a leading cause of death. The transformative events in the care of these cases were renal replacement therapy that converted a fatal into a chronic disease, and kidney biopsy that allowed study of the course and pathogenesis of kidney disease. Apart from its fundamental contributions to clinical nephrology, biopsy of renal allografts became an integral component of the evaluation and care of kidney transplant recipients. The Banff transplant pathology conferences launched in 1991 led to developing the classification of allograft pathology into an essential element in the evaluation, treatment, and care of allograft recipients with spirit of discovery. That success came at the cost of increasing complexity leading to the recent realization that it may need the refinement of its consensus-based system into a more evidence-based system with graded statements that are easily accessible to the other disciplines involved in the care of transplanted patients. Collaboration with other medical disciplines, allowing public comment on meeting reports, and incorporation of generative artificial intelligence (AI) are important elements of a successful future. The increased pace of innovation brought about by AI will likely allow us to solve the organ shortage soon and require new classifications for xenotransplantation pathology, tissue engineering pathology, and bioartificial organ pathology.

Treatment of a MyD88 inhibitor alleviates rejection and inflammation in xenotransplantation by inhibiting dendritic cells activation and trained immunity in macrophages

BACKGROUND

Acute vascular rejection (AVR) and systemic inflammation in xenograft recipients (SIXR) negatively impact the xenografts survival, and novel immunosuppressants are required to improve survival outcomes. We previously reported that TJ-M2010-5, a myeloid differentiation factor 88 (MyD88) inhibitor, exerts excellent anti-rejection effects in allogeneic transplantation. The aim of the present study was to evaluate the efficacy of TJ-M2010-5 in preventing AVR and SIXR and to investigate whether combined treatment of TJ-M2010-5 with anti-CD154 antibody (MR1) could prolong xenograft survival furthermore.

METHODS

A model involving heart transplantation from Sprague-Dawley rats to BALB/c mice was established in vivo, and the xenografts developed typical AVR. Bone marrow-derived dendritic cells and macrophages were cultured to study the underlying mechanisms induced by rat cardiomyocyte lysate stimulation in vitro.

RESULTS

TJ-M2010-5 monotherapy prolonged xenograft survival, although combination treatment with MR1 further enhanced the anti-AVR and anti-SIXR effects with about 21 days graft survival, compared to monotherapy. TJ-M2010-5 reduced dendritic cell and macrophage activation induced by xenotransplantation, downregulated CD80/CD86 expression, suppressed B-cell activation and anti-donor antibody generation, reduced pro-inflammatory cytokine production and tissue factor expression, and attenuated epigenetic modifications underlying interleukin-6 and tumor necrosis factor-α production in macrophages by inhibiting nuclear factor kappa B nuclear translocation.

CONCLUSIONS

TJ-M2010-5 attenuated AVR and SIXR and contributed to xenograft survival by inhibiting dendritic cell and macrophage activation. A dual-system inhibition strategy combining TJ-M2010-5 with anti-CD154 antibody achieved better results in xenotransplantation.

Evaluating the safety and efficacy of cryopreserved ovarian tissue transplantation in leukemia patients with different bone marrow remission status using xenotransplantation

Background

Leukemia patients undergoing cryopreserved ovarian tissue transplantation (OTT) may carry a high risk of disease induction. Measurable residual disease (MRD) in bone marrow is linked to an elevated risk of relapse. It is controversial whether leukemia patients must be allowed to achieve measurable residual disease negative (MRD-negative) status instead of measurable residual disease positive (MRD-positive) status before ovarian tissue cryopreservation (OTC).

Objective

To explore the safety and efficacy of OTT in acute leukemia patients with different MRD status by using xenotransplantation.

Method

Cryopreserved ovarian tissue from 19 leukemia patients was thawed and xenotransplanted to ovariectomized BALB/C nude mice (n=36). The mice were divided into 2 groups based on the patient's MRD status before OTC: MRD-negative group (n=18) and MRD-positive group (n=18), additionally, a control group consisted of ovariectomized mice (n=9). Body weight was measured weekly and mortality, emaciation, and other abnormalities were recorded. Twenty-six weeks post-surgery, livers, spleens, uteruses, and ovarian grafts were removed for macroscopic and histological examinations to evaluate the efficacy of xenotransplantation and assess malignant cell contamination in mice.

Results

Follicle growth was visible in the ovarian grafts of the MRD-negative and MRD-positive groups. Compared with the ovariectomized group, a significant decrease in body weight (p<0.01) was noted, the uterine volume was notably larger, estradiol (E2) levels were significantly higher (p<0.01), and follicle-stimulating hormone (FSH) levels were significantly lower (p<0.001) in the other two groups. Mice in the MRD-positive group showed a significantly higher incidence of death (p<0.001) and emaciation (p<0.01), compared to the MRD-negative group. Histological observation revealed the presence of malignant cells in the grafts, livers, and spleens of 3 mice in the MRD-positive group. No abnormalities were observed in the mice from the MRD-negative group in both macroscopic and histological observations except one mouse was sacrificed for ascites unrelated to leukemia relapse.

Conclusion

For leukemia patients having ovarian tissue preserved in the first and only centralized human ovarian tissue cryobank in China, immunodeficient mice xenotransplantation can be a method to evaluate the safety and efficacy of OTT; the risk of malignant cell reimplantation due to OTT is higher in leukemia patients with MRD-positive status than those with MRD-negative status before OTC.

Cell morphology best predicts tumorigenicity and metastasis in vivo across multiple TNBC cell lines of different metastatic potential

BACKGROUND

Metastasis is the leading cause of death in breast cancer patients. For metastasis to occur, tumor cells must invade locally, intravasate, and colonize distant tissues and organs, all steps that require tumor cell migration. The majority of studies on invasion and metastasis rely on human breast cancer cell lines. While it is known that these cells have different properties and abilities for growth and metastasis, the in vitro morphological, proliferative, migratory, and invasive behavior of these cell lines and their correlation to in vivo behavior is poorly understood. Thus, we sought to classify each cell line as poorly or highly metastatic by characterizing tumor growth and metastasis in a murine model of six commonly used human triple-negative breast cancer xenografts, as well as determine which in vitro assays commonly used to study cell motility best predict in vivo metastasis.

METHODS

We evaluated the liver and lung metastasis of human TNBC cell lines MDA-MB-231, MDA-MB-468, BT549, Hs578T, BT20, and SUM159 in immunocompromised mice. We characterized each cell line's cell morphology, proliferation, and motility in 2D and 3D to determine the variation in these parameters between cell lines.

RESULTS

We identified MDA-MB-231, MDA-MB-468, and BT549 cells as highly tumorigenic and metastatic, Hs578T as poorly tumorigenic and metastatic, BT20 as intermediate tumorigenic with poor metastasis to the lungs but highly metastatic to the livers, and SUM159 as intermediate tumorigenic but poorly metastatic to the lungs and livers. We showed that metrics that characterize cell morphology are the most predictive of tumor growth and metastatic potential to the lungs and liver. Further, we found that no single in vitro motility assay in 2D or 3D significantly correlated with metastasis in vivo.

CONCLUSIONS

Our results provide an important resource for the TNBC research community, identifying the metastatic potential of 6 commonly used cell lines. Our findings also support the use of cell morphological analysis to investigate the metastatic potential and emphasize the need for multiple in vitro motility metrics using multiple cell lines to represent the heterogeneity of metastasis in vivo.

The Effects of Busulfan on Xenogeneic Transplantation of Human Peripheral Blood Mononuclear Cells in Recipient Mice

BACKGROUND

Humanized mouse models with engraftment of human peripheral blood mononuclear cells (PBMCs) or hematopoietic stem cells (HSCs) are effective tools for the study of human immunity. Busulfan has been used as a substitute for irradiation in human hematopoietic stem cell (HSC) transplantation models, but it has not been tested in human peripheral blood mononuclear cell (PBMC) transplantation models.

METHODS

This study evaluated PBMC engraftment using cytometry and enzyme-linked immunosorbent assay (ELISA) in female NOD.CB17/Prkdcscid/JKrb/ IL2 receptor γ-/- (NIG) mice treated with busulfan.

RESULTS

In this model, the percentage of human CD3+ T cell engraftment in the blood was 28.2%, with dominant infiltration of CD8+ cells in the spleen 3 weeks post PBMC transplantation. Production of human cytokines, including Interleukin (IL)-12p70, IL-4, IL-5, IFN-γ, IL-6, IL-8, IL-22, Tumor Necrosis Factor alpha, and IL-10, was determined in mice treated with busulfan.

CONCLUSIONS

Our findings demonstrate that busulfan treatment is a beneficial alternative for simple and efficient PBMC engraftment in a rodent model, possibly helping to evaluate human immunity in preclinical studies.

Incidence of serum antibodies to xenoantigens on triple-knockout pig cells in different human groups

BACKGROUND

Xenoantigens other than Gal, Neu5Gc, and Sda may be playing a role in pig graft rejection. We investigated the incidence of antibodies to unknown pig xenoantigen in different human groups.

METHODS

We collected blood from TKO/hCD55 pigs (n = 3), and isolated PBMCs and RBCs. Serum samples were collected from (i) healthy human volunteers (n = 43), (ii) patients with end-stage renal disease (ESRD) (n = 87), (iii) the same patients after kidney allotransplantation (n = 50), and (iv) renal allotransplant recipients experiencing T cell-mediated rejection (allo-TCMR, n = 10). The sera were initially incubated with TKO/hCD55 pRBCs (1 × 108 cells) for 1 h to absorb anti-pig antibodies (except against SLA and possibly other antigens not expressed on pRBCs) and then the serum (absorbed or unabsorbed) was tested for antibody binding and complement-dependent cytotoxicity (CDC) to TKO/hCD55 pig PBMCs.

RESULTS

A significant reduction in IgM/IgG binding and CDC was observed in the absorbed sera. Serum obtained before and after renal allotransplantation showed no significant difference in IgM or IgG binding to, or in CDC of, TKO/hCD55 pig cells. IgM antibodies (but rarely IgG) against unknown xenoantigens expressed on TKO/hCD55 PBMCs, possibly against swine leukocyte antigens, were documented in healthy humans, patients with ESRD, and those with renal allografts undergoing acute T cell rejection. IgM (but not CDC) was higher in patients experiencing allo-TCMR.

CONCLUSION

Human sera contain IgM antibodies against unknown pig xenoantigens expressed on TKO/hCD55 pPBMCs. Although not confirmed in the present study, the targets for these antibodies may include swine leukocyte antigens.

Human ST3Gal II and ST6GalNAc IV genes increase human serum-mediated cytotoxicity to xenogeneic cells

Carbohydrate-antigens widely existed on glycoproteins and glycosphingolipids of all mammalian cells play a crucial role in self-defense and immunity. Xeno-reactive antibodies included in natural human sera play a protecting role in an acute phase-rejection of xenotransplantation. In this study, we investigated the effect of an alteration of glycosylation-pattern, caused by human sialyltransferases such as hST3Gal II or hST6GalNAc IV, on human serum mediated cytotoxicity in pig kidney PK15 cells. From LDH cytotoxicity assay, cytotoxicity to human serum was significantly increased in hST3Gal II and hST6GalNAc IV-transfected PK15 cells, as compared to the control. In the hST6Gal I-carrying cells, the cytotoxicity to human serum was rather decreased. Moreover, flow cytometry analysis revealed that an alteration of pig glycosylation-pattern by hST3Gal II or hST6GalNAc IV influences on a binding of human IgM or IgG, respectively, in pig kidney cells, regardless of Gal antigen alteration. Finally, we found that hST6GalNAc IV contributed to increase of terminal disialylated tetrasaccharide structure, disialyl T antigen, as evidenced by increase of the MAL II lectin binding capacity in the hST6GalNAc IV-transfected PK15 cells, compared with control. Therefore, our results suggest that carbohydrate antigens, such as disialyl T antigen, newly synthesized by the ST3Gal II- and ST6GalNAc IV are potentially believed to be new xeno-reactive elements.

Long-term control of diabetes by tofacitinib-based immunosuppressive regimen after allo islet transplantation in diabetic rhesus monkeys that rejected previously transplanted porcine islets

Porcine islet xenotransplantation has been highlighted as an alternative to allo islet transplantation. Despite the remarkable progress that has been made in porcine-islet pre-clinical studies in nonhuman primates, immunological tolerance to porcine islets has not been achieved to date. Therefore, allo islet transplantation could be required after the failure of porcine islet xenotransplantation. Here, we report the long-term control of diabetes by allogeneic pancreatic islet transplantation in diabetic rhesus monkeys that rejected previously transplanted porcine islets. Four diabetic male rhesus monkeys received the porcine islets and then allo islets (5700-19 000 IEQ/kg) were re-transplanted for a short or long period after the first xeno islet rejection. The recipient monkeys were treated with an immunosuppressive regimen consisting of ATG, humira, and anakinra for induction, and sirolimus and tofacitinib for maintenance therapy. The graft survival days of allo islets in these monkeys were >440, 395, >273, and 127, respectively, similar to that in allo islet transplanted cynomolgus monkeys that received the same immunosuppressive regimen without xeno sensitization. Taken together, it is likely that prior islet xenotransplantation does not affect the survival of subsequent allo islets under clinically applicable immunosuppressants.

Single-cell transcriptomic analysis reveals transcriptional and cell subpopulation differences between human and pig immune cells

BACKGROUND

The pig is a promising donor candidate for xenotransplantation. Understanding the differences between human and swine immune systems is critical for addressing xenotransplant rejection and hematopoietic reconstitution. The gene transcriptional profile differences between human and pig immune cell subpopulations have not been studied. To assess the similarities and differences between pigs and humans at the levels of gene transcriptional profiles or cell subpopulations are important for better understanding the cross-species similarity of humans and pigs, and it would help establish the fundamental principles necessary to genetically engineer donor pigs and improve xenotransplantation.

OBJECTIVE

To assess the gene transcriptional similarities and differences between pigs and humans.

METHODS

Two pigs and two healthy humans' PBMCs were sorted for 10 × genomics single-cell sequence. We generated integrated human-pig scRNA-seq data from human and pig PBMCs and defined the overall gene expression landscape of pig peripheral blood immune cell subpopulations by updating the set of human-porcine homologous genes. The subsets of immune cells were detected by flow cytometry.

RESULTS

There were significantly less T cells, NK cells and monocytes but more B cells in pig peripheral blood than those in human peripheral blood. High oxidative phosphorylation, HIF-1, glycolysis, and lysosome-related gene expressions in pig CD14+ monocytes were observed, whereas pig CD14+ monocytes exhibited lower levels of cytokine receptors and JAK-STAT-related genes. Pig activated CD4+T cells decreased cell adhesion and inflammation, while enriched for migration and activation processes. Porcine GNLY+CD8+T cells reduced cytotoxicity and increased proliferation compared with human GNLY+CD8+T cells. Pig CD2+CD8+γδT cells were functionally homologous to human CD2+CD4+ γδT cells. Pig CD2-CD8-γδT cells expressed genes with quiescent and precursor characteristics, while CD2-CD8+γδT cells expressed migration and memory-related molecules. Pig CD24+ and CD5+B cells are associated with inflammatory responses.

CONCLUSION

Our research with integrated scRNA-seq assays identified the different distribution of pig immune cell subpopulations and the different transcriptional profiles of human and pig immune cells. This study enables a deeper understanding of the development and function of porcine immune cells.

Ethics, virtues and xenotransplantation

Early in 2022 the first pig to human cardiac xenotransplant was performed. The graft initially performed well, and rejection was well controlled. However, the graft failed, and the patient died 60 days after the procedure. The ethical issues relating to xenotransplantation include the risk/benefit to the individual, the risk of porcine-derived infectious agents crossing into humans, animal welfare and rights, issues of human and animal identity and concerns relating to fair allocation of organs and appropriate use of resources.These ethical issues are often addressed using emotional arguments, or through consequentialist or deontological lens. An alternative is to use approaches based on virtue ethics to understand the moral purpose (telos) of the research and the virtues (character traits) needed to be a good research clinician. In this review we will consider the virtues of justice, courage, temperance and practical wisdom, as well as the role of clinical curiosity, and their application to xenotransplantation. This provides an alternative approach for the clinical academic and others involved in the research to reflect on their practice.

A murine groin site cardiac transplantation model-applicable tool for studying roles of peripheral lymph nodes in transplantation

The murine heterotopic cardiac transplantation model has been widely used to study antigen-specific immune responses or new immunosuppressive agents, which have a strong correlation with peripheral lymph nodes. Thus, a new organ transplantation model that is applicable to related studies is needed. Here, we describe a groin-site murine heart transplantation model using a cuff technique, in which the donor aorta and pulmonary artery are anastomosed to the truncated femoral vessels of the recipient. The mean survival time (MST) of the grafts in BALB/c-to-C57BL/6 allo-transplant group was 7.2 ± 0.3 days, and 1.9 ± 0.2 days in BALB/c-to-Sprague-Dawley (SD) rat xeno-transplant group. H&E results show that donor hearts from both groups demonstrate typical pathological features at the endpoint. Evans Blue tracing revealed that the popliteal lymph nodes of the grafted side hindlimb are larger than those of the contralateral side. Moreover, IHC staining for CD3, CD20 shows that the germinal center and cortex region of the grafted side of popliteal lymph nodes is apparently increased than that of the contralateral side. To sum up, this model may serve as an ideal model to study the role of peripheral lymph nodes in organ transplant rejection. In addition, extra-peritoneal grafting makes a step forward in animal welfare under the 3Rs' principle (Replacement, Reduction, Refinement).

Emergence of novel circoviruses in humans and pigs and their possible importance for xenotransplantation and blood transfusions

BACKGROUND

As sequencing is becoming more broadly available, virus discovery continues. Small DNA viruses contribute to up to 60% of the overall virus load in pigs. Porcine circoviruses (PCVs) are small DNA viruses with a single-stranded circular genome. They are common in pig breeds and have not been properly addressed for their potential risk in xenotransplantation. Whereas PCV1 is non-pathogenic in pigs, PCV2 has been associated with various disease manifestations. Recently two new circoviruses have been described, PCV3 and PCV4. While PCV4 is currently present mainly in Asia, PCV3 is widely distributed, and has been identified in commercial pigs, wild boars, and pigs generated for xenotransplantation. In one case PCV3 was transmitted by pigs to baboons via heart transplantation. PCV3 pathogenicity in pigs was controversial initially, however, the virus was found to be associated with porcine dermatitis and nephropathy syndrome (PDNS), reproductive failure, and multisystemic inflammation. Inoculation studies with PCV3 infectious clones confirmed that PCV3 is pathogenic. Most importantly, recently discovered human circoviruses (CV) are closely related to PCV3.

METHODS

Literature was evaluated and summarized. A dendrogram of existing circoviruses in pigs, humans, and other animal species was created and assessed at the species level.

RESULTS

We found that human circoviruses can be divided into three species, human CV1, CV2, and CV3. Human CV2 and CV3 are closest to PCV3.

CONCLUSIONS

Circoviruses are ubiquitous. This communication should create awareness of PCV3 and the newly discovered human circoviruses, which may be a problem for blood transfusions and xenotransplantation in immune suppressed individuals.

Barriers toward xenotransplantation in Arab World

Organ transplant is a crucial therapeutic strategy offering a life-saving and transformative medical intervention. It provides an opportunity to improve their quality of life and increase their lifespan. The shortage of organs remains a critical global challenge, leading to a prolonged waiting times for organ receivers, which contributes to an increase in morbidity and mortality rates. Hence, xenotransplantation offered a promising solution to the global shortage of organs through the use of animal organs, leading to an increase in donor availability, reducing waiting times, minimizing organ trafficking, improving genetic engineering advancements, and driving scientific innovation. Even though xenotransplantation has many benefits in the clinical setting, it has many barriers that are hindering its achievements and constraining its occurrence. Some barriers to xenotransplant are general, such as the immunological barrier, while others are specific to certain regions due to local causes. The Arab region exhibits disparities in clinical settings compared to the global context, marked by the huge economic crisis and a shortage of trained healthcare professionals. Considering the huge resources and advancements needed in the field of xenotransplantation, this review aims to explore the specific barriers toward xenotransplantation in the Arab countries, highlighting the challenges to overcome these barriers.

A xenotransplantation mouse model to study physiology of the mammary gland from large mammals

Although highly conserved in structure and function, many (patho)physiological processes of the mammary gland vary drastically between mammals, with mechanisms regulating these differences not well understood. Large mammals display variable lactation strategies and mammary cancer incidence, however, research into these variations is often limited to in vitro analysis due to logistical limitations. Validating a model with functional mammary xenografts from cryopreserved tissue fragments would allow for in vivo comparative analysis of mammary glands from large and/or rare mammals and would improve our understanding of postnatal development, lactation, and premalignancy across mammals. To this end, we generated functional mammary xenografts using mammary tissue fragments containing mammary stroma and parenchyma isolated via an antibody-independent approach from healthy, nulliparous equine and canine donor tissues to study these species in vivo. Cryopreserved mammary tissue fragments were xenotransplanted into de-epithelialized fat pads of immunodeficient mice and resulting xenografts were structurally and functionally assessed. Preimplantation of mammary stromal fibroblasts was performed to promote ductal morphogenesis. Xenografts recapitulated mammary lobule architecture and contained donor-derived stromal components. Mammatropic hormone stimulation resulted in (i) upregulation of lactation-associated genes, (ii) altered proliferation index, and (iii) morphological changes, indicating functionality. Preimplantation of mammary stromal fibroblasts did not promote ductal morphogenesis. This model presents the opportunity to study novel mechanisms regulating unique lactation strategies and mammary cancer induction in vivo. Due to the universal applicability of this approach, this model serves as proof-of-concept for developing mammary xenografts for in vivo analysis of virtually any mammals, including large and rare mammals.

[Renal xenotransplantation : state of the art]

Xenotransplantation could be an inexhaustible source of organs and change the life of end-stage kidney disease patients with reduction of morbidity and mortality. Through genetic engineering it is now possible to reduce the risk of hyperacute and acute graft rejection and improve the overall immune compatibility between two different species. Some experiments have already brought promising perspectives. Nevertheless, there are still difficulties to overcome. The risk of animal-related infectious diseases, ethnic limitations, safety, and applicability of large-scale xenotransplantation should be assessed. We still need to improve the technical aspects and define the purpose of these procedures: definitive replacement or temporary solution?

Combined islet and kidney xenotransplantation for diabetic nephropathy: an update in ongoing research for a clinically relevant application of porcine islet transplantation

Combined islet and kidney xenotransplantation for the treatment of diabetic nephropathy represents a compelling and increasingly relevant therapeutic possibility for an ever-growing number of patients who would benefit from both durable renal replacement and cure of the underlying cause of their renal insufficiency: diabetes. Here we briefly review immune barriers to islet transplantation, highlight preclinical progress in the field, and summarize our experience with combined islet and kidney xenotransplantation, including both challenges with islet-kidney composite grafts as well as our recent success with sequential kidney followed by islet xenotransplantation in a pig-to-baboon model.

Moral approval of xenotransplantation in Egypt: associations with religion, attitudes towards animals and demographic factors

Xenotransplantation has great potential as an alternative to alleviate the shortage of organs for donation. However, given that the animal most suited for xenotransplantation is the pig, there are concerns that people in Muslim countries may be more hesitant to morally approve of these procedures. In this study, the moral approval of xenotransplantation was assessed in a group of 895 participants in Egypt. The results showed that religiosity itself does not predict moral approval of xenotransplantation, but religious identity does, as Muslims are less likely to approve of xenotransplantation than Christians. However, the strongest predictor of moral approval of xenotransplantation was gender, with women displaying less approval. A partial mediating factor in this association was concern for animal welfare. Based on these results, some implications for public policy are discussed.

Xenograft: a suitable treatment of eyelid complications in long-standing necrobiotic xanthogranuloma

A porcine xenograft was successfully used as a temporary biological cover for severe xanthogranulomatous defects of the eyelid. Xenografts were successfully used in both upper and lower eyelid reconstructions. Other surgical techniques or the use of full-thickness skin grafts were not possible.

Successful xenotransplantation of testicular cells following fractionated chemotherapy of recipient birds

An essential step in the success of germ cell transplantation is the preparation of the recipient's testicular environment to increase the availability of stem cell niches. However, most methods for this purpose in birds face serious limitations such as partial germ cell depletion, high toxicity and mortality, or the need to use expensive technologies. Here, we validated a simple and practical technique of transferring quail testicular cells into chicken testes depleted of endogenous spermatozoa by fractioned chemotherapy (20 mg/kg/week busulfan for 5 weeks). This protocol resulted in a very low mortality of the treated day-old chicks and, despite maintenance of androgenic activity, sperm production was decreased by 84.3% at 25 weeks of age. NANOG immunostaining revealed that very few to no germ cells were present following treatment with 20 and 40 mg/kg, respectively. RT-qPCR data also showed that c-MYC and NANOG expression declined in these treatments, but GRFα1 and BID expressions remained unaltered among groups. After xenotransplantation, quail germ cells were immunodetected in chicken testes using a species-specific antibody (QCPN), and quail ovalbumin DNA was found in seminal samples collected from chicken recipients. Together, these data confirm that fractionated administration of busulfan in hatchlings is a practical, effective, and safe protocol to prepare recipient male birds capable of supporting xenogeneic spermatogenesis.

Ethical and legislative advances in xenotransplantation for clinical translation: focusing on cardiac, kidney and islet cell xenotransplantation

In this state-of-the-art review we detail the journey of xenotransplantation from its infancy, detailing one of the first published cases and the subsequent journey the field took in its inception and development. With a focus on the science, technological advances, precautions required along with the potential limitations in application, the ethics, guidance's, and legislative advances that are required to reach the safe and efficacious clinical application of xenotransplantation. Along with a view over the past several decades with the overall significant advancements in pre-clinical study outcomes particularly in islet, kidney, and heart xenotransplantation, to ultimately reach the pinnacle of successful clinical heart and kidney xenotransplants. It outlines the importance for the appropriate guidance's required to have been developed by experts, scientists, clinicians, and other players who helped develop the field over the past decades. It also touches upon patient advocacy along with perspectives and expectations of patients, along with public opinion and media influence on the understanding and perception of xenotransplantation. It discusses the legislative environment in different jurisdictions which are reviewed in line with current clinical practices. All of which are ultimately based upon the guidance's developed from a strong long-term collaboration between the International Xenotransplantation Association, the World Health Organisation and The Transplantation Society; each having constantly undertaken consultation and outreach to help develop best practice for clinical xenotransplantation application. These clearly helped forge the legislative frameworks required along with harmonization and standardization of regulations which are detailed here. Also, in relation to the significant advances in the context of initial xeno-kidney trials and the even greater potential for clinical xeno-islet trials to commence we discuss the significant advantages of xenotransplantation and the ultimate benefit to our patients.

Dclre1c-Mutation-Induced Immunocompromised Mice Are a Novel Model for Human Xenograft Research

Severe combined immunodeficient (SCID) mice serve as a critical model for human xenotransplantation studies, yet they often suffer from low engraftment rates and susceptibility to graft-versus-host disease (GVHD). Moreover, certain SCID strains demonstrate 'immune leakage', underscoring the need for novel model development. Here, we introduce an SCID mouse model with a targeted disruption of the dclre1c gene, encoding Artemis, which is essential for V(D)J recombination and DNA repair during T cell receptor (TCR) and B cell receptor (BCR) assembly. Artemis deficiency precipitates a profound immunodeficiency syndrome, marked by radiosensitivity and compromised T and B lymphocyte functionality. Utilizing CRISPR/Cas9-mediated gene editing, we generated dclre1c-deficient mice with an NOD genetic background. These mice exhibited a radiosensitive SCID phenotype, with pronounced DNA damage and defective thymic, splenic and lymph node development, culminating in reduced T and B lymphocyte populations. Notably, both cell lines and patient-derived tumor xenografts were successfully engrafted into these mice. Furthermore, the human immune system was effectively rebuilt following peripheral blood mononuclear cells (PBMCs) transplantation. The dclre1c-knockout NOD mice described herein represent a promising addition to the armamentarium of models for xenotransplantation, offering a valuable platform for advancing human immunobiological research.

Glioblastoma research on zebrafish xenograft models: a systematic review

Glioblastoma (GBM) constitutes the most common primary brain tumor in adults. The challenges in GBM therapeutics have shed light on zebrafish used as a promising animal model for preclinical GBM xenograft studies without a standardized methodology. This systematic review aims to summarize the advances in zebrafish GBM xenografting, compare research protocols to pinpoint advantages and underlying limitations, and designate the predominant xenografting parameters. Based on the PRISMA checklist, we systematically searched PubMed, Scopus, and ZFIN using the keywords "glioblastoma," "xenotransplantation," and "zebrafish" for papers published from 2005 to 2022, available in English. 46 articles meeting the review criteria were examined for the zebrafish strain, cancer cell line, cell labeling technique, injected cell number, time and site of injection, and maintenance temperature. Our review designated that AB wild-type zebrafish, Casper transparent mutants, transgenic Tg(fli1:EGFP), or crossbreeding of these predominate among the zebrafish strains. Orthotopic transplantation is more commonly employed. A number of 50-100 cells injected at 48 h post-fertilization in high density and low infusion volume is considered as an effective xenografting approach. U87 cells are used for GBM angiogenesis studies, U251 for GBM proliferation studies, and patient-derived xenograft (PDX) to achieve clinical relevance. Gradual acclimatization to 32-33 °C can partly address the temperature differential between the zebrafish and the GBM cells. Zebrafish xenograft models constitute valuable tools for preclinical studies with clinical relevance regarding PDX. The GBM xenografting research requires modification based on the objective of each research team. Automation and further optimization of the protocol parameters could scale up the anticancer drug trials.

Revisiting the Use of Ulysses Contracts in Xenotransplantation

BACKGROUND

Xenotransplantation clinical trials may begin soon. A persistent risk of xenotransplantation, known for decades, is the possibility that a xenozoonotic infection could be transferred from a xenograft to its recipient and then to other human contacts. Because of this risk, guidelines and commentators have advocated for xenograft recipients to agree to either long-term or lifelong surveillance mechanisms.

METHODS

For the past few decades, one solution that has been proposed to ensure that xenograft recipients will comply with surveillance protocols is the use of a heavily modified Ulysses contract, which we review.

RESULTS

These contracts are most often used in psychiatry, and their application to xenotransplantation has been espoused several times with minimal criticism.

CONCLUSIONS

In this article, we argue against the applicability of Ulysses contracts in xenotransplantation based upon (1) the telos of the advance directive that may not be applicable to this clinical context, (2) the suspect nature of enforcing Ulysses contracts in xenotransplantation, and (3) the ethical and regulatory hurdles that such enforcement would require. Although our focus is on the US regulatory landscape in preparation for clinical trials, there are applications globally.

Developing Humanized Animal Models with Transplantable Human iPSC-Derived Cells

Establishing reliable and reproducible animal models for disease modelling, drug screening and the understanding of disease susceptibility and pathogenesis is critical. However, traditional animal models differ significantly from humans in terms of physiology, immune response, and pathogenesis. As a result, it is difficult to translate laboratory findings into biomedical applications. Although several animal models with human chimeric genes, organs or systems have been developed in the past, their limited engraftment rate and physiological functions are a major obstacle to realize convincing models of humans. The lack of human transplantation resources and insufficient immune tolerance of recipient animals are the main challenges that need to be overcome to generate fully humanized animals. Recent advances in gene editing and pluripotent stem cell-based xenotransplantation technologies offer opportunities to create more accessible human-like models for biomedical research. In this article, we have combined our laboratory expertise to summarize humanized animal models, with a focus on hematopoietic/immune system and liver. We discuss their generation strategies and the potential donor cell sources, with particular attention given to human pluripotent stem cells. In particular, we discuss the advantages, limitations and emerging trends in their clinical and pharmaceutical applications. By providing insights into the current state of humanized animal models and their potential for biomedical applications, this article aims to advance the development of more accurate and reliable animal models for disease modeling and drug screening.