Lung xenotransplantation

Surgeons are apprehensive to use DCD lungs despite similar post-transplant outcomes: A 20-year UNOS retrospective analysis

Purpose

As rates of lung transplants in the US grow, waitlist mortality increases. While the literature reports similar survival outcomes of DBD and DCD transplants, research should investigate improvements to DCD lung recovery protocols to increase the total number recovered. Recently, Choi et al. presented donor variables indicative of ultimate lung recovery1. However, expansion of DCD lung transplants requires a comparison of these indicators to DBD donors for application of similar parameters to increase the rate of DCD lung recovery to ensure that viable DCD organs are not discarded due to overly stringent donor and organ requirements.

Methods

We performed a retrospective analysis of United Network for Organs Sharing (UNOS) Organ Procurement and Transplantation Network/UNOS STAR (Standard Analysis and Research) database. Donors who donated ≥1 organ from 10/1999-01/2019 were extracted and stratified according to DBD and DCD status. Associated characteristics of potential DCD and DBD lung donors were compared, and a multivariable logistic regression model with ≥1 transplanted lung was constructed to evaluate the independent effects of important predictors.

Results

Our data included 179,228 potential lung donors, 162,157 DBD (31,486 donated, 19.4% recovery) and 17,071 DCD (526 donated, 3.1% recovery). Odds of lung non-use between DBD and DCD donors were significantly associated with blood type, alcohol use, cause of death, smoking history, drug use, death circumstance, ethnicity, gender, hypertension, cancer, age, and lung pO2 on 100% P/F ratio (P < 0.001 for all variables). A multivariable regression analysis showed that the odds of a potential DCD donating lungs is 75% lower than (P < 0.001) that of a potential DBD when the cause of death (COD) is stroke, head trauma (44% lower P = 0.076), CNS tumor (22% lower P = 0.174) or MVA (69% lower P = 0.183). A history of diabetes for over 10 years was strongly associated with non-use for DCD lungs (OR, 0.87, P = 0.71), whereas an under 10-year history was associated with increased use (OR 2.33, P = 0.008, OR 1.07 P = 0.819).Lungs from donors ages 40-49 are more likely to be procured than those <30 or >50 in both DBD and DCD. However, likelihood of procurement is 1.84 [95% 1.42, 2.38, p < 0.001] times higher in 40-49-year-old vs. <30-year-old donors when comparing DBD vs. DCD, and 2.43 [95% 1.83, 3.22, p < 0.001] times higher than patients >50 in DBD vs DCD donors. In addition, for each era, the odds for procuring DCD vs. DBD lungs consistently improved [95% 1.46-2.57, p < 0.001].Rejected DCD lungs were associated with donors with higher cardiopulmonary function. Left ventricular ejection fractions in discarded DCD lung donors were higher than those of discarded DBD lung donors (DCD 56.9% ± 13.6 vs. DBD 51.3% ±17.3 P = <0.001). Similar non-use patterns were identified for lung PO2 on 100% O2 (DCD 189.4 ± 121.3 vs. DBD 150.0 ± 106.2 P = <0.001), and when the P/F ratio was above 350.00 (DCD 13.5% vs. DBD 7.7% P = <0.001).

Conclusion

Despite literature reporting comparable survival of DCD and DBD organs, this study highlights discrepancies in lung procurement practices that evaluate donor characteristics differently in DBD and DCD donors. Further study should investigate whether similar discrepancies exist in the procurement process of other organs.

3D Bioprinting of Pig Macrophages and Human Cells Discovered the P2Y14 Receptor as a Mediator of Xenogenic Immune Responses

BACKGROUND

The survival rate of pig lung xenotransplantation (PLXTx) recipients is severely limited by intense xenogenic immune responses, necessitating further insights into xenogeneic immunity and the development of models to study the PLXTx immune response.

METHODS

We identified regulators of PLXTx immune response Using Gene ontology analysis. We assessed the metabolic changes and protein levels in 3D4/31 pig alveolar macrophages (PAMs) through flow cytometry and immunoblotting. To induce a xenogenic immune response, we co-cultured 3D4/31-PAMs with A549 human alveolar epithelial cells and evaluated cytokine expression using qRT-PCR.

RESULTS

Gene ontology analysis identified STAT1 and alveolar macrophages as contributors to lung autoimmunity and transplant rejection. In 3D4/31-PAMs, phorbol myristate acetate-induced glycogen accumulation and cyclooxygenase-2 expression were inhibited by the P2Y14 inhibitor PPTN. Co-culturing 3D4/31-PAMs with A549 human alveolar epithelial cells via 3D bioprinting resulted in a more pronounced inflammatory response than 2D co-culture, with increased expression of genes related to the P2Y14 cascade and inflammation. This inflammatory gene expression was prevented by PPTN treatment.

CONCLUSION

Based on these results, we propose alginate bioprinting as an in vitro model for PLXTx and suggest that P2Y14 is a key regulator of xenogeneic immune responses in PAMs.

Future directions for xenotransplantation in lungs

PURPOSE OF REVIEW

Advancements in preclinical xenotransplant studies have opened doors for clinical heart and kidney xenotransplantation. This review assesses recent progress in lung xenotransplantation research and its potential clinical implications.

RECENT FINDINGS

The efficacy of the humanized von Willebrand factor in reducing platelet sequestration in ex-vivo and in-vivo lung xenotransplant models was showcased. Combining human tissue factor pathway inhibitor and CD47 expression with selectin and integrin inhibition delayed neutrophil and platelet sequestration. Enhanced expression of human complement regulatory proteins and thrombomodulin in genetically engineered pig lungs improved graft survival by reducing platelet activation and modulating coagulation disruptions. Knocking out the CMAH gene decreased antibody-mediated inflammation and coagulation activation, enhancing compatibility for human transplantation. Furthermore, CMAH gene knockout in pigs attenuated sialoadhesin-dependent binding of human erythrocytes to porcine macrophages, mitigating erythrocyte sequestration and anemia. Meanwhile, in-vivo experiments demonstrated extended survival of xenografts for up to 31 days with multiple genetic modifications and comprehensive treatment strategies.

SUMMARY

Experiments have uncovered vital insights for successful xenotransplantation, driving further research into immunosuppressive therapy and genetically modified pigs. This will ultimately pave the way for clinical trials designed to improve outcomes for patients with end-stage lung disease.

The perspective for next-generation lung replacement therapies: functional whole lung generation by blastocyst complementation

PURPOSE OF REVIEW

Blastocyst complementation represents a promising frontier in next-generation lung replacement therapies. This review aims to elucidate the future prospects of lung blastocyst complementation within clinical settings, summarizing the latest studies on generating functional lungs through this technique. It also explores and discusses host animal selection relevant to interspecific chimera formation, a challenge integral to creating functional human lungs via blastocyst complementation.

RECENT FINDINGS

Various gene mutations have been utilized to create vacant lung niches, enhancing the efficacy of donor cell contribution to the complemented lungs in rodent models. By controlling the lineage to induce gene mutations, chimerism in both the lung epithelium and mesenchyme has been improved. Interspecific blastocyst complementation underscores the complexity of developmental programs across species, with several genes identified that enhance chimera formation between humans and other mammals.

SUMMARY

While functional lungs have been generated via intraspecies blastocyst complementation, the generation of functional interspecific lungs remains unrealized. Addressing the challenges of controlling the host lung niche and selecting host animals relevant to interspecific barriers between donor human and host cells is critical to enabling the generation of functional humanized or entire human lungs in large animals.

Emerging Paradigms in Bioengineering the Lungs

In end-stage lung diseases, the shortage of donor lungs for transplantation and long waiting lists are the main culprits in the significantly increasing number of patient deaths. New strategies to curb this issue are being developed with the help of recent advancements in bioengineering technology, with the generation of lung scaffolds as a steppingstone. There are various types of lung scaffolds, namely, acellular scaffolds that are developed via decellularization and recellularization techniques, artificial scaffolds that are synthesized using synthetic, biodegradable, and low immunogenic materials, and hybrid scaffolds which combine the advantageous properties of materials in the development of a desirable lung scaffold. There have also been advances in the design of bioreactors in terms of providing an optimal regenerative environment for the maturation of functional lung tissue over time. In this review, the emerging paradigms in the field of lung tissue bioengineering will be discussed.

Characterization of Mono- and Bi-Transgenic Pig-Derived Epidermal Keratinocytes Expressing Human FUT2 and GLA Genes-In Vitro Studies

Pig-to-human xenotransplantation seems to be the response to the contemporary shortage of tissue/organ donors. Unfortunately, the phylogenetic distance between pig and human implies hyperacute xenograft rejection. In this study, we tested the hypothesis that combining expression of human α1,2-fucosyltransferase (hFUT2) and α-galactosidase A (hGLA) genes would allow for removal of this obstacle in porcine transgenic epidermal keratinocytes (PEKs). We sought to determine not only the expression profiles of recombinant human α1,2-fucosyltransferase (rhα1,2-FT) and α-galactosidase A (rhα-Gal A) proteins, but also the relative abundance (RA) of Galα1→3Gal epitopes in the PEKs stemming from not only hFUT2 or hGLA single-transgenic and hFUT2×hGLA double-transgenic pigs. Our confocal microscopy and Western blotting analyses revealed that both rhα1,2-FT and rhα-Gal A enzymes were overabundantly expressed in respective transgenic PEK lines. Moreover, the semiquantitative levels of Galα1→3Gal epitope that were assessed by lectin fluorescence and lectin blotting were found to be significantly diminished in each variant of genetically modified PEK line as compared to those observed in the control nontransgenic PEKs. Notably, the bi-transgenic PEKs were characterized by significantly lessened (but still detectable) RAs of Galα1→3Gal epitopes as compared to those identified for both types of mono-transgenic PEK lines. Additionally, our current investigation showed that the coexpression of two protective transgenes gave rise to enhanced abrogation of Galα→3Gal epitopes in hFUT2×hGLA double-transgenic PEKs. To summarize, detailed estimation of semiquantitative profiles for human α-1,2-FT and α-Gal A proteins followed by identification of the extent of abrogating the abundance of Galα1→3Gal epitopes in the ex vivo expanded PEKs stemming from mono- and bi-transgenic pigs were found to be a sine qua non condition for efficiently ex situ protecting stable lines of skin-derived somatic cells inevitable in further studies. The latter is due to be focused on determining epigenomic reprogrammability of single- or double-transgenic cell nuclei inherited from adult cutaneous keratinocytes in porcine nuclear-transferred oocytes and corresponding cloned embryos. To our knowledge, this concept was shown to represent a completely new approach designed to generate and multiply genetically transformed pigs by somatic cell cloning for the needs of reconstructive medicine and dermoplasty-mediated tissue engineering of human integumentary system.

Xenotransplantation: Current Status in Preclinical Research

The increasing life expectancy of humans has led to a growing numbers of patients with chronic diseases and end-stage organ failure. Transplantation is an effective approach for the treatment of end-stage organ failure; however, the imbalance between organ supply and the demand for human organs is a bottleneck for clinical transplantation. Therefore, xenotransplantation might be a promising alternative approach to bridge the gap between the supply and demand of organs, tissues, and cells; however, immunological barriers are limiting factors in clinical xenotransplantation. Thanks to advances in gene-editing tools and immunosuppressive therapy as well as the prolonged xenograft survival time in pig-to-non-human primate models, clinical xenotransplantation has become more viable. In this review, we focus on the evolution and current status of xenotransplantation research, including our current understanding of the immunological mechanisms involved in xenograft rejection, genetically modified pigs used for xenotransplantation, and progress that has been made in developing pig-to-pig-to-non-human primate models. Three main types of rejection can occur after xenotransplantation, which we discuss in detail: (1) hyperacute xenograft rejection, (2) acute humoral xenograft rejection, and (3) acute cellular rejection. Furthermore, in studies on immunological rejection, genetically modified pigs have been generated to bridge cross-species molecular incompatibilities; in the last decade, most advances made in the field of xenotransplantation have resulted from the production of genetically engineered pigs; accordingly, we summarize the genetically modified pigs that are currently available for xenotransplantation. Next, we summarize the longest survival time of solid organs in preclinical models in recent years, including heart, liver, kidney, and lung xenotransplantation. Overall, we conclude that recent achievements and the accumulation of experience in xenotransplantation mean that the first-in-human clinical trial could be possible in the near future. Furthermore, we hope that xenotransplantation and various approaches will be able to collectively solve the problem of human organ shortage.

Xenogeneic Lung Transplantation Models

Study of lung xenografts has proven useful to understand the remaining barriers to successful transplantation of other organ xenografts. In this chapter, the history and current status of lung xenotransplantation will be briefly reviewed, and two different experimental models, the ex vivo porcine-to-human lung perfusion and the in vivo xenogeneic lung transplantation, will be presented. We will focus on the technical details of these lung xenograft models in sufficient detail, list the needed materials, and mention analysis techniques to allow others to adopt them with minimal learning curve.

Recent advances in lung transplantation

Lung transplantation can improve quality of life and prolong survival for individuals with end-stage lung disease, and many advances in the realms of both basic science and clinical research aspects of lung transplantation have emerged over the past few decades. However, many challenges must yet be overcome to increase post-transplant survival. These include successfully bridging patients to transplant, expanding the lung donor pool, inducing tolerance, and preventing a myriad of post-transplant complications that include primary graft dysfunction, forms of cellular and antibody-mediated rejection, chronic lung allograft dysfunction, and infections. The goal of this manuscript is to review salient recent and evolving advances in the field of lung transplantation.

Antigenicity of tissues and organs from GGTA1/CMAH/β4GalNT2 triple gene knockout pigs

Clinical xenotransplantations have been hampered by human preformed antibody-mediated damage of the xenografts. To overcome biological incompatibility between pigs and humans, one strategy is to remove the major antigens [Gal, Neu5Gc, and Sd(a)] present on pig cells and tissues. Triple gene (GGTA1, CMAH, and β 4GalNT2) knockout (TKO) pigs were produced in our laboratory by CRISPR-Cas9 targeting. To investigate the antigenicity reduction in the TKO pigs, the expression levels of these three xenoantigens in the cornea, heart, liver, spleen, lung, kidney, and pancreas tissues were examined. The level of human IgG/IgM binding to those tissues was also investigated, with wildtype pig tissues as control. The results showed that αGal, Neu5Gc, and Sd(a) were markedly positive in all the examined tissues in wildtype pigs but barely detected in TKO pigs. Compared to wildtype pigs, the liver, spleen, and pancreas of TKO pigs showed comparable levels of human IgG and IgM binding, whereas corneas, heart, lung, and kidney of TKO pigs exhibited significantly reduced human IgG and IgM binding. These results indicate that the antigenicity of TKO pig is significantly reduced and the remaining xenoantigens on porcine tissues can be eliminated via a gene targeting approach.

Remaining Physiological Barriers in Porcine Kidney Xenotransplantation: Potential Pathways behind Proteinuria as well as Factors Related to Growth Discrepancies following Pig-to-Kidney Xenotransplantation

Considerable shortages in the supply of available organs continue to plague the field of solid organ transplantation. Despite changes in allocation, as well as the utilization of extended criteria and living donors, the number of patients waiting for organs continues to grow at an alarming pace. Xenotransplantation, cross-species solid organ transplantation, offers one potential solution to this dilemma. Previous extensive research dedicated to this field has allowed for resolution of xenograft failure due to acute rejection, leaving new areas of unresolved challenges as barriers to success in large animal models. Specific to kidney xenotransplantation, recent data seems to indicate that graft compromise can occur due to discrepancies in growth between breeds of donors and significant proteinuria leading to nephrotic syndrome in the recipient. Given these potential limitations, herein, we review potential pathways behind proteinuria, as well as potential causative factors related to growth discrepancies. Control of both of these has the potential to allow xenotransplantation to become clinically applicable in an effort to resolve this organ shortage crisis.

Overexpressing dominant-negative FGFR2-IIIb impedes lung branching morphogenesis in pigs

Genetic studies with mouse models have shown that fibroblast growth factor receptor 2-IIIb (FGFR2-IIIb) plays crucial roles in lung development and differentiation. To evaluate the effect of FGFR2-IIIb in pig lung development, we employed somatic cell nuclear transfer (SCNT) technology to generate transgenic pig fetuses overexpressing the transmembrane (dnFGFR2-IIIb-Tm) and soluble (dnFGFR2-IIIb-HFc) forms of the dominant-negative human FGFR2-IIIb driven by the human surfactant protein C (SP-C) promoter, which was specifically expressed in lung epithelia. Eight dnFGFR2-IIIb-Tm transgenic and twelve dnFGFR2-IIIb-HFc transgenic pig fetuses were collected from three and two recipient sows, respectively. Repression of FGFR2-IIIb in lung epithelia resulted in smaller lobes and retardation of alveolarization in both forms of dnFGFR2-IIIb transgenic fetuses. Moreover, the dnFGFR2-IIIb-HFc transgenic ones showed more deterioration in lung development. Our results demonstrate that disruption of FGFR2-IIIb signaling in the epithelium impedes normal branching and alveolarization in pig lungs, which is less severe than the results observed in transgenic mice. The dnFGFR2-IIIb transgenic pig is a good model for the studies of blastocyst complementation as well as the mechanisms of lung development and organogenesis.