Frank J. M. F. Dor

α1,3-galactosyltransferase gene-knockout pig heart transplantation in baboons with survival approaching 6 months

Background. The recent generation of α1,3-galactosyltransferase gene-knockout (GalT-KO) pigs has allowed investigation of the survival of GalT-KO pig organs in nonhuman primates. Methods. Heterotopic heart transplantation from GalT-KO pigs was carried out in baboons (n=8) using a human antihuman CD154 monoclonal antibody-based immunosuppressive regimen. Results. In six of the eight cases, graft survival extended to between approximately 2 and 6 months. All grafts developed thrombotic microangiopathy (TM). In particular, the clinical course of one baboon in which the graft functioned for 179 days is summarized. This baboon received aspirin (40 mg on alternate days) from day 4 in addition to heparin, which may have been a factor in the delay of onset and progression of TM and in prolonged graft survival. Maintenance therapy with anti-CD154 mAb, mycophenolate mofetil, and methylprednisolone was associated with persistently low numbers of CD3+CD4+ and CD3+CD8+ cells. Despite persisting depletion of these cells, no infectious complications occurred. Conclusions. It remains to be established whether TM is related to a very low level of natural preformed or T-cell-induced antibody deposition on the graft, inducing endothelial activation and injury, or to molecular incompatibilities in the coagulation mechanisms between pig and baboon, or to both. However, function of a pig organ in a baboon for a period approaching six months, which has not been reported previously, lends encouragement that the barriers to xenotransplantation will eventually be overcome.

Mesenchymal Stem Cells in Transplantation and Tissue Regeneration

Mesenchymal stem cells (MSC) were identified in the 1960s as bone marrow cells capable of osteogenic differentiation (Friedenstein and Petrakova, 1966). In the following decennia, these cells were further attributed with the capacity to differentiate into adipogenic, chondrogenic, and myogenic lineages (Pittenger et al., 1999), to secrete trophic factors that stimulate other cell types (Caplan and Dennis, 2006), and to possess immunomodulatory properties (Di Nicola et al., 2002). Cells with these properties were found not to be restricted to the bone marrow, but also to reside at other locations including adipose tissue (Zuk et al., 2002), skin (Toma et al., 2001), and in organs like liver, kidney, and brain (da Silva Meirelles et al., 2006). In particular adipose tissue has proven to be a valuable source of MSC due to its accessibility and its abundance. The characteristics of MSC initiated interest in their potential clinical use for tissue regenerative and immunomodulatory purposes. The first clinical applications were in the treatment of osteogenesis imperfecta (Horwitz et al., 1999) and graft versus host disease (Le Blanc et al., 2004). Since then, the use of MSC for the treatment of a variety of diseases has been investigated in clinical trials, including in Crohns disease (Duijvestein et al., 2010), myocardial infarction (Hare et al., 2009), rheumatoid arthritis (Liang et al., 2011), multiple sclerosis (Freedman et al., 2010), and organ transplantation (Dahlke et al., 2009). In organ transplantation, the use of MSC is aimed at the prolongation of allograft survival. Thus, MSC therapy may be used for the treatment of acute rejection, but also to prevent currently untreatable chronic rejection. Furthermore, there is evidence that MSC therapy has a tissue regenerative component that repairs organ injury caused by immunological or ischemic events and thereby prevents the loss of organ transplants in animal models (Morigi et al., 2008; Popp et al., 2008). This may offer another window of opportunity for MSC therapy in particular shortly after transplantation, when organ loss peaks partly due to ischemia–reperfusion injury of the graft. As with all therapies in development, the reasons for the use of MSC as an immunomodulatory and regenerative agent should be taken into careful consideration. Open questions are whether MSC therapy is effective and, if so, whether it is more efficient than existing drugs? Are there safety issues involved? Is MSC therapy cost-effective? Whether MSC can replace existing drugs is not clear at the moment as the efficacy of MSC therapy is difficult to determine. A one to one comparison of efficacy between MSC and conventional drugs is not easy to make. While pharmacological drugs target specific molecular pathways, MSC have a wide range of effects. Furthermore, while pharmaceuticals can be given to patients at a daily frequency, for safety, practical, and financial reasons there is a limit to the frequency at which cell therapy can be applied. However, at these early stages, a head on comparison with standard therapy may not be required as the use of MSC will primarily be aimed at applications where conventional therapies fail. As such, MSC will be applied as an adjuvant for current therapies. In the more distant future, MSC may be used to replace medication that has significant side effects, as may be the case with calcineurin inhibitors in organ transplantation. Although very effective in preventing organ rejection, calcineurin inhibitors are nephrotoxic, thereby limiting the life span of kidney transplants. Side effects of MSC therapy have not been reported yet, but certainly some will occur when MSC are used more widely. A high incidence of infections after MSC therapy in graft versus host disease patients was recently reported (von Bahr et al., 2011). Whether the risk for infection was significantly elevated in MSC treated patients compared to controls was however not demonstrated. To be able to map the side effects of MSC therapy, these effects should be investigated parallel to their clinical effects in placebo-controlled studies. Nevertheless, from where we stand today, we can conclude with considerable certainty that the infusion of MSC does not harbor serious health threats. While the in vitro properties of MSC suggest a beneficial effect of MSC in immunological and degenerative diseases and early clinical trials are triumphant about the feasibility and safety of MSC therapy, there is thus far little evidence that MSC are effective in curing disease. The effectiveness of MSC therapy needs to be established in follow up trials and knowledge of the mechanisms of action of MSC may help optimizing the therapy. The mechanisms of action of MSC after infusion may be very different to those observed in vitro. There is for instance accumulating evidence that MSC are short-lived after infusion (Popp et al., 2008). Even though, long-term effects are observed after infusion of MSC. These effects may be mediated by other cell types to which the effect of MSC is transferred. It has been demonstrated that MSC induce immunoregulatory capacity of T cells (Prevosto et al., 2007) and macrophages (Maggini et al., 2010). More knowledge on how MSC interact with these cell types could provide tools for optimizing MSC therapy. An alternative approach for MSC therapy is to design drugs or therapies that target tissue resident MSC. MSC respond to cytokines and growth factors by changing their immunoregulatory function and/or their differentiation status. Therefore, these factors could be the basis of such drugs, which should induce a specific response in MSC that reside in transplanted organs. In this way, MSC therapy can be more localized and more specific compared to the infusion of MSC. In order for a therapy to be successful, it needs to be cost-effective. MSC treatment is a costly therapy as MSC need to be cultured under GMP conditions. In particular the generation of custom-made, i.e., autologous, MSC of clinical grade is an expensive process. Centralization of MSC production at specialized laboratories can reduce costs. Furthermore, for some applications allogeneic MSC may be suitable and these can be generated in large batches, which further brings down costs. A real cost–effect analysis can however only be made once the efficacy of MSC therapy has become clear. Summarizing, MSC have the potential to be used as an immunomodulatory and regenerative therapy in organ transplantation and immune and degenerative diseases. Basic and clinical research will have to point toward the right directions on the effective use of MSC. In this special feature of Frontiers in Immunology, the most recent findings on the immunomodulatory capacity of MSC, such as their interaction with regulatory T cells, and on their potential to induce regeneration of liver, kidney, and heart after ischemia–reperfusion injury and of bone and cartilage damage in rheumatoid and osteoarthritis, will be presented. Furthermore, challenges on how to generate a high quality and effective cell product will receive attention. Finally, the use of MSC in transplantation and regenerative medicine and ideas on how to drive this field forward will be reviewed and discussed by leaders in the field. We are confident that this special topic will generate new directions to be followed in translational research and clinical trials.

Advancement of mesenchymal stem cell therapy in solid organ transplantation (MISOT).

There is evolving interest in the use of mesenchymal stem cells (MSC) in solid organ transplantation. Pre-clinical transplantation models show efficacy of MSC in prolonging graft survival and a number of clinical studies are planned or underway. At a recent meeting of the MISOT consortium (MSC In Solid Organ Transplantation) the advances of these studies were evaluated and mechanisms underlying the potential effects of MSC discussed. Continued discussion is required for definition of safety and eventually efficacy endpoints for MSC therapy in solid organ transplantation.

On the interactions between mesenchymal stem cells and regulatory T cells for immunomodulation in transplantation

Experimental studies have established the use of mesenchymal stem cells (MSC) as a candidate immunosuppressive therapy. MSC exert their immunomodulatory function through the inhibition of CD4+ and CD8+ T cell proliferation. It is unknown whether MSC impair the immunosuppressive function of regulatory T cells (Treg). In vitro and in vivo studies suggest that MSC mediate their immunomodulatory effects through the induction of Treg. In this review we will focus on the interactions between MSC and Treg, and evaluate the consequences of these cellular interplays for prospective MSC immunotherapy in organ transplantation.

Mesenchymal Stem Cells in Solid Organ Transplantation (MiSOT) Fourth Meeting: Lessons Learned from First Clinical Trials

The Fourth Expert Meeting of the Mesenchymal Stem Cells in Solid Organ Transplantation (MiSOT) Consortium took place in Barcelona on October 19 and 20, 2012. This meeting focused on the translation of preclinical data into early clinical settings. This position paper highlights the main topics explored on the safety and efficacy of mesenchymal stem cells as a therapeutic agent in solid organ transplantation and emphasizes the issues (proper timing, concomitant immunossupression, source and immunogenicity of mesenchymal stem cells, and oncogenicity) that have been addressed and will be followed up by the MiSOT Consortium in future studies.

Mesenchymal stem cells derived from adipose tissue are not affected by renal disease

Mesenchymal stem cells are a potential therapeutic agent in renal disease and kidney transplantation. Autologous cell use in kidney transplantation is preferred to avoid anti-HLA reactivity; however, the influence of renal disease on mesenchymal stem cells is unknown. To investigate the feasibility of autologous cell therapy in patients with renal disease, we isolated these cells from subcutaneous adipose tissue of healthy controls and patients with renal disease and compared them phenotypically and functionally. The mesenchymal stem cells from both groups showed similar morphology and differentiation capacity, and were both over 90% positive for CD73, CD105, and CD166, and negative for CD31 and CD45. They demonstrated comparable population doubling times, rates of apoptosis, and were both capable of inhibiting allo-antigen- and anti-CD3/CD28-activated peripheral blood mononuclear cell proliferation. In response to immune activation they both increased the expression of pro-inflammatory and anti-inflammatory factors. These mesenchymal stem cells were genetically stable after extensive expansion and, importantly, were not affected by uremic serum. Thus, mesenchymal stem cells of patients with renal disease have similar characteristics and functionality as those from healthy controls. Hence, our results indicate the feasibility of their use in autologous cell therapy in patients with renal disease.

Shifting paradigms in eligibility criteria for live kidney donation: a systematic review

As the organ shortage increases, inherently the demand for donor kidneys continues to rise. Thus, live kidney donation is essential for increasing the donor pool. In order to create successful expansion, extended criteria live kidney donors should be considered. This review combines current guidelines with all available literature in this field, trying to seek and establish the optimal extended criteria. Comprehensive searches were carried out in major databases until November 2013 to search for articles regarding older age, overweight and obesity, hypertension, vascular anomalies/multiplicity, nulliparous women, and minors as donors. Of the 2079 articles found, 152 fell within the scope of the review. Five major guidelines were included and reviewed. Based on the literature search, live kidney donation in older donors (up to 70 years of age) seems to be safe as outcome is comparable to younger donors. Obese donors have comparable outcome to lean donors, in short- and mid-term follow-up. Since little literature is available proving the safety of donation of hypertensive donors, caution is advised. Vascular multiplicity poses no direct danger to the donor and women of childbearing age can be safely included as donors. Although outcome after donation in minors is shown to be comparable to adult donors, they should only be considered if no other options exist. We conclude that the analyzed factors above should not be considered as absolute contraindications for donation.

Living organ donation practices in Europe – results from an online survey

In Europe, living organ donation (LOD) is increasingly accepted as a valuable solution to overcome the organ shortage. However, considerable differences exist between European countries regarding frequency, practices and acceptance of donor–recipient relations. As a response, the Coordination Action project ‘Living Organ Donation in Europe’ (www.eulod.eu), funded by the Seventh Framework Programme of the European Commission, was initiated. Transplant professionals from 331 European kidney and liver transplant centres were invited to complete an online survey on living kidney donation (LKD) and living liver donation (LLD). In total, 113 kidney transplant centres from 40 countries and 39 liver transplant centres from 24 countries responded. 96.5% and 71.8% performed LKD and LLD respectively. The content of the medical screening of donors was similar, but criteria for donor acceptance varied. Few absolute contraindications for donation existed. The reimbursement policies diverged and the majority of the donors did not get reimbursed for their income loss during recovery. Large discrepancies were found between geographical European regions (the Eastern, the Mediterranean and the North‐Western). As a result of this survey we suggest several recommendations to improve quality and safety of LOD in Europe.

A systematic review and meta-analysis of the influence of peritoneal dialysis catheter type on complication rate and catheter survival

Peritoneal dialysis (PD) is an effective treatment for end-stage renal disease. There are several configurations of PD catheter design that may impact catheter function, such as the shape of the intraperitoneal segment, the number of cuffs, and the subcutaneous configuration. This review and meta-analysis was carried out to determine whether there is a clinical advantage for one of the catheter types or configurations. Comprehensive searches were conducted in MEDLINE, Embase, and CENTRAL (the Cochrane Library 2012, issue 10). The methodology was in accordance with the Cochrane Handbook for Interventional Systematic Reviews and written based on the PRISMA statement. The initial search yielded 682 hits from which 13 randomized controlled trials were identified. Outcomes of interest were as follows: catheter survival, drainage dysfunction, migration, leakage, exit-site infections, peritonitis, and catheter removal. Comparing straight vs. swan neck and single vs. double-cuffed catheters, no differences were found when results were pooled. Comparison of straight vs. coiled-tip catheters demonstrated that survival was significantly different in favor of straight catheters (hazard ratio 2.05; confidence interval 1.10-3.79, P=0.02). For surgically inserted catheters, the removal rate and survival at 1 year after insertion were significantly in favor of straight catheters. Our meta-analysis clearly demonstrates benefits for catheters with a straight intraperitoneal segment.

New Classification of ELPAT for Living Organ Donation

In the literature, varying terminology for living organ donation can be found. However, there seems to be a need for a new classification to avoid confusion. Therefore, we assessed existing terminology in the light of current living organ donation practices and suggest a more straightforward classification. We propose to concentrate on the degree of specificity with which donors identify intended recipients and to subsequently verify whether the donation to these recipients occurs directly or indirectly. According to this approach, one could distinguish between “specified” and “unspecified” donation. Within specified donation, a distinction can be made between “direct” and “indirect” donation.