Chimerism and tolerance: past, present and future strategies to prolong renal allograft survival.

PURPOSE OF REVIEW: Immunological factors are a major cause of kidney allograft loss. Calcineurin inhibitors (CNIs) have improved short-term kidney allograft survival; however, they in turn contribute to long-term kidney allograft loss from chronic CNI nephrotoxicity. Tolerance induction in transplantation can avoid the long-term adverse effects of immunosuppressive medications. This review aims to critically discuss recent efforts in inducing transplantation tolerance. RECENT FINDINGS: Tolerance induction mediated by chimerism has shown some promise in minimizing or even complete withdrawal of immunosuppressive treatments in kidney allograft recipients. There has been a number of approaches as varied as the number of centres conducting these trials. However, they can be grouped into those mediated by transient microchimerism and those facilitated by more stable macro or full donor chimerism. The success rates in terms of long-term drug-free graft survival has been limited in microchimerism-mediated tolerance induction approaches. Mixed macrochimerism of less than 50% donor may be unstable with mostly the recipient's native immune system overpowering the donor chimeric status.Tolerance induction leading to chimerism has been limited to living donor kidney transplantation and additional long-term outcomes are required. Furthermore, immune monitoring after tolerance induction has faced a limitation in studying due to a lack of sufficient study participants and appropriate study controls. SUMMARY: Tolerance induction is one of several strategies used to prolong kidney allograft survival, but it has not been routinely utilized in clinical practice. However, future applications from the trials to clinical practice remain limited to living donor kidney transplantation. Once further data regarding tolerance inductions exist and practicality becomes widely accepted, tolerance induction may shift the paradigm in the field of kidney transplantation to achieve the best possible outcome of 'One Organ for Life'.

Immunosuppression Withdrawal in Liver Transplant Recipients on Sirolimus.

BACKGROUND AND AIMS: As conversion from calcineurin inhibitor to sirolimus (SRL), a mechanistic target of rapamycin inhibitor (mTOR-I), has been shown to enhance immunoregulatory profiles in liver transplant (LT) recipients (LTRs), mTOR-I therapy might allow for increased success of immunosuppression (IS) withdrawal. Our aim was to determine if operational tolerance could be observed in LTRs withdrawn from SRL and if blood/graft tolerance biomarkers were predictive of successful withdrawal. APPROACH AND RESULTS: We performed a prospective trial of SRL monotherapy withdrawal in nonimmune, nonviremic LTRs > 3 years post-LT. SRL was weaned over ~6 months, and biopsies were performed 12 months postweaning or at concern for acute rejection. Twenty-one LTRs consented; 6 were excluded due to subclinical acute rejection on baseline biopsy or other reasons, and 15 underwent weaning (age 61.3 ± 8.8 years; LT to SRL weaning 6.7 ± 3 years). Eight (53%) achieved operational tolerance (TOL). Of the 7 who were nontolerant (non-TOL), 6 had mild acute rejection on biopsy near the end of weaning or at study end; 1 was removed from the trial due to liver cancer recurrence. At baseline preweaning, there were statistically increased blood tolerogenic dendritic cells and cell phenotypes correlating with chronic antigen presentation in the TOL versus non-TOL groups. A previously identified biopsy gene signature accurately predicted TOL versus non-TOL in 12/14 LTRs before weaning. At study end, biopsy staining revealed statistically significant increases in antigen-presenting cell:leukocyte pairings, FOXP3+ /CD4+ T cells, Tbet+ /CD8+ T cells, and lobular dendritic cells in the non-TOL group. CONCLUSIONS: This study evaluated IS withdrawal directly from mTOR-I therapy in LTRs and achieved > 50% operational tolerance. Preweaning gene expression and peripheral blood mononuclear cell profiling may be useful as predictors of successful mTOR-I therapy withdrawal. NCT02062944.

Outstanding questions in transplantation: Tolerance.

In 2017, the American Society of Transplantation (AST) launched the Outstanding Questions in Transplantation Research forum to stimulate a community-wide discussion of how the field is evolving and to help identify areas where a better dialogue between clinicians and researchers could result in great advancements. Tolerance emerged as a topic of great interest to the AST community. This minireview provides an overview of clinical transplantation tolerance. Historical background followed by a review of the current status of attempts to establish tolerance in the clinic, highlighting the dynamic online discussion surrounding this important topic from the AST Transplantation Research forum, is provided.

Intragraft Molecular Pathways Associated with Tolerance Induction in Renal Transplantation.

The modern immunosuppression regimen has greatly improved short-term allograft outcomes but not long-term allograft survival. Complications associated with immunosuppression, specifically nephrotoxicity and infection risk, significantly affect graft and patient survival. Inducing and understanding pathways underlying clinical tolerance after transplantation are, therefore, necessary. We previously showed full donor chimerism and immunosuppression withdrawal in highly mismatched allograft recipients using a bioengineered stem cell product (FCRx). Here, we evaluated the gene expression and microRNA expression profiles in renal biopsy samples from tolerance-induced FCRx recipients, paired donor organs before implant, and subjects under standard immunosuppression (SIS) without rejection and with acute rejection. Unlike allograft samples showing acute rejection, samples from FCRx recipients did not show upregulation of T cell- and B cell-mediated rejection pathways. Gene expression pathways differed slightly between FCRx samples and the paired preimplantation donor organ samples, but most of the functional gene networks overlapped. Notably, compared with SIS samples, FCRx samples showed upregulation of genes involved in pathways, like B cell receptor signaling. Additionally, prediction analysis showed inhibition of proinflammatory regulators and activation of anti-inflammatory pathways in FCRx samples. Furthermore, integrative analyses (microRNA and gene expression profiling from the same biopsy sample) identified the induction of regulators with demonstrated roles in the downregulation of inflammatory pathways and maintenance of tissue homeostasis in tolerance-induced FCRx samples compared with SIS samples. This pilot study highlights the utility of molecular intragraft evaluation of pathways related to FCRx-induced tolerance and the use of integrative analyses for identifying upstream regulators of the affected downstream molecular pathways.

Cellular and molecular immune profiles in renal transplant recipients after conversion from tacrolimus to sirolimus.

Tacrolimus and sirolimus are commonly used maintenance immunosuppressants in kidney transplantation. As their effects on immune cells and allograft molecular profiles have not been elucidated, we characterized the effects of tacrolimus to sirolimus conversion on the frequency and function of T cells, and on graft molecular profiles. Samples from renal transplant patients in a randomized trial of 18 patients with late sirolimus conversion and 12 on tacrolimus maintenance were utilized. Peripheral blood was collected at 0, 6, 12, and 24 months post randomization, with T-cell subpopulations analyzed by flow cytometry and T-cell alloreactivity tested by IFN-γ ELISPOT. Graft biopsy samples obtained 24 months post randomization were used for gene expression analysis. Sirolimus conversion led to an increase in CD4(+)25(+++)Foxp3(+) regulatory T cells. While tacrolimus-maintained patients showed a decrease in indirect alloreactivity over time post transplant, sirolimus conversion increased indirect alloreactive T-cell frequencies compared with tacrolimus-maintained patients. No histological differences were found in graft biopsies, but molecular profiles showed activation of the antigen presentation, IL-12 signaling, oxidative stress, macrophage-derived production pathways, and increased inflammatory and immune response in sirolimus-converted patients. Thus, chronic immune alterations are induced after sirolimus conversion. Despite the molecular profile being favorable to calcineurin inhibitor-based regimen, there was no impact in renal function over 30 months of follow-up.

Systemic immunoregulatory and proteogenomic effects of tacrolimus to sirolimus conversion in liver transplant recipients.

UNLABELLED: Immunosuppression (IS) withdrawal from calcineurin inhibitors is only possible in ≈ 20% of liver transplant recipients. However, mammalian target of rapamycin inhibitors (e.g., sirolimus; SRL) appear to be more immunoregulatory and might promote a tolerant state for withdrawal. Our aim was to determine whether systemic (i.e., blood, marrow, and allograft) signatures of immunoregulation are promoted by conversion from tacrolimus (TAC) to SRL. We therefore performed the following serial assays before and after SRL conversion in liver transplant recipients to test for enhanced markers of immunoregulation: (1) flow-cytometry immunophenotyping of peripheral blood mononuclear cells (PBMCs) and bone marrow aspirates for regulatory T cells (Tregs) (e.g., CD4(+) CD25(+++) FOXP3(+) ) and regulatory dendritic cells (DCregs) (immunoglobulin-like transcript 3(+) /4(+) ); (2) liver biopsy immunohistochemical staining (e.g., FOXP3:CD3 and CD4:CD8 ratios) and immunophenotyping of biopsy-derived Tregs after growth in culture; (3) effects of pre- versus postconversion sera on Treg generation in mixed lymphocyte reactions; (4) peripheral blood nonspecific CD4 responses; and (5) peripheral blood gene transcripts and proteomic profiles. We successfully converted 20 nonimmune, nonviremic recipients (age, 57.2 ± 8.0; 3.5 ± 2.1 years post-liver transplantation) from TAC to SRL for renal dysfunction. Our results demonstrated significant increases in Tregs in PBMCs and marrow and DCregs in PBMCs (P < 0.01) after conversion. In biopsy staining, FOXP3:CD3 and CD4:CD8 ratios were significantly higher after conversion and a number of biopsy cultures developed new or higher FOXP3(+) cell growth. Nonspecific CD4 responses did not change. Both pre- and postconversion sera inhibited mixed lymphocyte reactions, although only TAC sera suppressed Treg generation. Finally, 289 novel genes and 22 proteins, several important in immunoregulatory pathways, were expressed after conversion. CONCLUSIONS: TAC to SRL conversion increases systemic Tregs, DCregs, and immunoregulatory proteogenomic signatures in liver transplant recipients and may therefore facilitate IS minimization or withdrawal.

Genomic biomarkers correlate with HLA-identical renal transplant tolerance.

The ability to achieve immunologic tolerance after transplantation is a therapeutic goal. Here, we report interim results from an ongoing trial of tolerance in HLA-identical sibling renal transplantation. The immunosuppressive regimen included alemtuzumab induction, donor hematopoietic stem cells, tacrolimus/mycophenolate immunosuppression converted to sirolimus, and complete drug withdrawal by 24 months post-transplantation. Recipients were considered tolerant if they had normal biopsies and renal function after an additional 12 months without immunosuppression. Of the 20 recipients enrolled, 10 had at least 36 months of follow-up after transplantation. Five of these 10 recipients had immunosuppression successfully withdrawn for 16-36 months (tolerant), 2 had disease recurrence, and 3 had subclinical rejection in protocol biopsies (nontolerant). Microchimerism disappeared after 1 year, and CD4(+)CD25(high)CD127(-)FOXP3(+) regulatory T cells and CD19(+)IgD/M(+)CD27(-) B cells were increased through 5 years post-transplantation in both tolerant and nontolerant recipients. Immune/inflammatory gene expression pathways in the peripheral blood and urine, however, were differentially downregulated between tolerant and nontolerant recipients. In summary, interim results from this trial of tolerance in HLA-identical renal transplantation suggest that predictive genomic biomarkers, but not immunoregulatory phenotyping, may be able to discriminate tolerant from nontolerant patients.

Differentiation of regulatory myeloid and T-cells from adult human hematopoietic stem cells after allogeneic stimulation.

Introduction: Donor hematopoietic stem cell (DHSC) infusions are increasingly being studied in transplant patients for tolerance induction. Methods: To analyze the fate of infused DHSCs in patients, we developed an in vitro culture system utilizing CD34+DHSCs stimulated with irradiated allogeneic cells in cytokine supplemented medium long-term. Results: Flow cytometric analyses revealed loss of the CD34 marker and an increase in CD33+ myeloid and CD3+ T-cell proportion by 10.4% and 72.7%, respectively, after 21 days in culture. T-cells primarily expressed TcR-αß and were of both CD4+ and CD8+ subsets. Approximately 80% of CD3+ T cells lacked expression of the co-stimulatory receptor CD28. The CD4+ compartment was predominated by CD4+CD25+CD127-FOXP3+ Tregs (>50% CD4+CD127- compartment) with <1% of all leukocytes exhibiting a CD4+CD127+ phenotype. Molecular analyses for T-cell receptor excision circles showed recent and increased numbers of TcR rearrangements in generated T cells over time suggesting de novo differentiation from DHSCs. CD33+ myeloid cells mostly expressed HLA-DR, but lacked expression of co-stimulatory receptors CD80 and CD83. When studied as modulators in primary mixed lymphocyte reactions where the cells used to stimulate the DHSC were used as responders, the DHSC-lines and their purified CD8+, CD4+, CD33+ and linage negative subsets inhibited the responses in a dose-dependent and non-specific fashion. The CD8+ cell-mediated inhibition was due to direct lysis of responder cells. Discussion: Extrapolation of these results into the clinical situation would suggest that DHSC infusions into transplant recipients may generate multiple subsets of donor "chimeric" cells and promote recipient Treg development that could regulate the anti-donor immune response in the periphery. These studies have also indicated that T cell maturation can occur in vitro in response to allogeneic stimulation without the pre-requisite of a thymic-like environment or NOTCH signaling stimulatory cell line.

CD4+CD25+FOXP3+ regulatory T cells: a potential "armor" to shield "transplanted allografts" in the war against ischemia reperfusion injury.

Despite the advances in therapeutic interventions, solid organ transplantation (SOT) remains the "gold standard" treatment for patients with end-stage organ failure. Recently, vascularized composite allotransplantation (VCA) has reemerged as a feasible treatment option for patients with complex composite tissue defects. In both SOT and VCA, ischemia reperfusion injury (IRI) is inevitable and is a predominant factor that can adversely affect transplant outcome by potentiating early graft dysfunction and/or graft rejection. Restoration of oxygenated blood supply to an organ which was previously hypoxic or ischemic for a period of time triggers cellular oxidative stress, production of both, pro-inflammatory cytokines and chemokines, infiltration of innate immune cells and amplifies adaptive alloimmune responses in the affected allograft. Currently, Food and Drug Administration (FDA) approved drugs for the treatment of IRI are unavailable, therefore an efficacious therapeutic modality to prevent, reduce and/or alleviate allograft damages caused by IRI induced inflammation is warranted to achieve the best-possible transplant outcome among recipients. The tolerogenic capacity of CD4+CD25+FOXP3+ regulatory T cells (Tregs), have been extensively studied in the context of transplant rejection, autoimmunity, and cancer. It was not until recently that Tregs have been recognized as a potential cell therapeutic candidate to be exploited for the prevention and/or treatment of IRI, owing to their immunomodulatory potential. Tregs can mitigate cellular oxidative stress, produce anti-inflammatory cytokines, promote wound healing, and tissue repair and prevent the infiltration of pro-inflammatory immune cells in injured tissues. By using strategic approaches to increase the number of Tregs and to promote targeted delivery, the outcome of SOT and VCA can be improved. This review focuses on two sections: (a) the therapeutic potential of Tregs in preventing and mitigating IRI in the context of SOT and VCA and (b) novel strategies on how Tregs could be utilized for the prevention and/or treatment of IRI.

Evaluation of Immunocompetence and Biomarkers of Tolerance in Chimeric and Immunosuppression-free Kidney Allograft Recipients.

BACKGROUND: Thirty-seven patients have received a living-donor kidney transplant in a phase 2 study designed to induce tolerance with facilitated allogeneic hematopoietic stem cell transplant. The study protocol is based on tolerogenic CD8 + /T-cell receptor - facilitating cells (FCR001; also including hematopoietic stem cells and αß-T-cell receptor + T cells) and low-dose, nonmyeloablative conditioning. Persistent chimerism allowing full immunosuppression (IS) withdrawal was achieved in 26 patients (time off IS 36-123 mo). METHODS: We evaluated biomarkers of tolerance through urinary cell mRNA profiling and immunocompetence to respond to vaccination in these patients. We also assessed kidney function and metabolic parameters compared with standard-of-care patients on IS. RESULTS: Persistently chimeric patients retained chimerism after removal of IS and remained rejection free without donor HLA-specific antibody development. The presence of donor chimerism at >50% correlated with a signature of tolerance in urinary cell mRNA profiles, with a uniquely elevated increase in the ratio of cytotoxic T lymphocyte-associated protein 4 to granzyme B mRNA. Tolerance was associated with protection from recurrence of immune-mediated causes of kidney disease. Tolerant participants were safely vaccinated, developed protective immune responses, and did not lose chimerism after vaccination. When compared with kidney transplant recipients treated with standard IS, tolerant participants showed stable kidney function and reduced medication use for hypertension and hyperlipidemia. CONCLUSIONS: These results suggest that elimination of IS has distinct advantages in living-donor kidney allograft recipients.

Foxp3+ regulatory T cell therapy for tolerance in autoimmunity and solid organ transplantation.

Regulatory T cells (Tregs) are critical for tolerance in humans. The exact mechanisms by which the loss of peripheral tolerance leads to the development of autoimmunity and the specific role Tregs play in allograft tolerance are not fully understood; however, this population of T cells presents a unique opportunity in the development of targeted therapeutics. In this review, we discuss the potential roles of Foxp3+ Tregs in the development of tolerance in transplantation and autoimmunity, and the available data regarding their use as a treatment modality.

Microchimerism in promoting graft acceptance in clinical transplantation.

PURPOSE OF REVIEW: Infusions of bone marrow-derived cells together with 'space making' continue to be tested in clinical organ transplant tolerance protocols. These trials are based on the hypothesis that this might produce initial multilineage chimerism. There is some evidence that this in turn induces regulatory cells that control alloimmunity. Although a wealth of knowledge is available from animal models, this review deals with what we know or can speculate about donor bone marrow cells and chimerism in human organ transplantation. RECENT FINDINGS: Calcineurin inhibitors are employed in most of these protocols to blunt the initial immune response. One protocol also has a stepwise regulatory cell generating treatment with sirolimus before total withdrawal. A number of donor chimeric lineages including stem cells, dendritic cells, myeloid precursors, and various lymphoid subpopulations have been described. Currently, it is recognized that the nature of cells that make up the chimerism could influence graft rejection versus acceptance. Tolerogenic donor chimeric cells may also generate regulatory subsets, thus controlling alloimmunity on two fronts. SUMMARY: It might be speculated that prolonged and sustained regulation or possible anergy induced by chimerism may eventually lead to clonal deletion, thereby bringing about classical immunologic tolerance.

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises.

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

Immune and gene expression profiling during tacrolimus to everolimus conversion early after liver transplantation.

Early elimination of tacrolimus in favor of everolimus can improve renal function in liver transplant recipients. However, as this approach increases the risk of acute rejection, it may benefit from predictive biomarkers guiding weaning. We enrolled 20 recipients on stable tacrolimus + everolimus to undergo tacrolimus withdrawal early post-liver transplant. Blood samples were collected at month 3 (withdrawal initiation), 4 (withdrawal completion), 4.5 and 6 (both everolimus alone). 15 patients did not reject and 5 had mild rejection responding to tacrolimus resumption. Before tacrolimus withdrawal, eventual rejecters had higher percentages of CD56+ NK cells and CD19+CD27+CD24+ memory B cells, and lower levels of T cells expressing the exhaustion marker PD-1. Over time, memory B cells, Ki-67+CD3+ (proliferating) cells and CD4+CD127-CD25HIGH FOXP3+ Tregs increased in rejecters. Tregs also increased in non-rejecters over time. The number of differentially expressed genes progressively increased in rejecters, particularly in mTOR, Eukaryotic Initiation Factor 2, and Neuroinflammation signaling pathways. There was no difference in anti-HLA antibodies between the groups. In summary, blood mononuclear cell and gene expression may predict successful vs. failed early tacrolimus withdrawal in liver transplant recipients. While needing validation, these preliminary findings highlight the potential for cellular and molecular biomarkers to guide decision-making during tacrolimus weaning.

Taking the Next Step: a Neural Coaptation Orthotopic Hind Limb Transplant Model to Maximize Functional Recovery in Rat.

Limb transplant in particular and vascularized composite allotransplant (VCA) in general have wide therapeutic promise that have been stymied by current limitations in immunosuppression and functional neuromotor recovery. Many animal models have been developed for studying unique features of VCA, but here we present a robust reproducible model of orthotopic hind limb transplant in rats designed to simultaneously investigate both aspects of current VCA limitation: immunosuppression strategies and functional neuromotor recovery. At the core of the model rests a commitment to meticulous, time-tested microsurgical techniques such as hand sewn vascular anastomoses and hand sewn neural coaptation of the femoral nerve and the sciatic nerve. This approach yields durable limb reconstructions that allow for longer lived animals capable of rehabilitation, resumption of daily activities, and functional testing. With short-term treatment of conventional immunosuppressive agents, allotransplanted animals survived up to 70 days post-transplant, and isotransplanted animals provide long lived controls beyond 200 days post-operatively. Evidence of neurologic functional recovery is present by 30 days post operatively. This model not only provides a useful platform for interrogating immunological questions unique to VCA and nerve regeneration, but also allows for in vivo testing of new therapeutic strategies specifically tailored for VCA.

Mechanistic analyses in kidney transplant recipients prospectively randomized to two steroid free regimen-Low dose Tacrolimus with Everolimus versus standard dose Tacrolimus with Mycophenolate Mofetil.

Calcineurin inhibitors (CNI), the cornerstone of immunosuppression after transplantation are implicated in nephrotoxicity and allograft dysfunction. We hypothesized that combined low doses of CNI and Everolimus (EVR) may result in better graft outcomes and greater tolerogenic milieu. Forty adult renal transplant recipients were prospectively randomized to (steroid free) low dose Tacrolimus (TAC) and EVR or standard dose TAC and Mycophenolate (MMF) after Alemtuzumab induction. Baseline characteristics were statistically similar. EVR levels were maintained at 3-8 ng/ml. TAC levels were 4.5±1.9 and 6.4±1.5 ng/ml in the TAC+EVR and TAC+MMF group respectively. Follow up was 14±4 and 17±5 months respectively and included protocol kidney biopsies at 3 and 12 months post-transplantation. Rejection-rate was lower in the TAC+EVR group. However patient and overall graft survival, eGFR and incidence of adverse events were similar. TAC+EVR induced expansion of CD4+CD25hiFoxp3+ regulatory T cells as early as 3 months and expansion of IFN-γ+CD4+CD25hiFoxp3+ regulatory T cells at 12 months post-transplant. Gene expression profile showed a trend toward decreased inflammation, angiogenesis and connective tissue growth in the TAC+EVR Group. Thus, greater tolerogenic mechanisms were found to be operating in patients with low dose TAC+EVR and this might be responsible for the lower rejection-rate than in patients on standard dose TAC+MMF. However, further studies with longer follow up and evaluating impact on T regulatory cells are warranted.

Varying levels of X chromosome coalescence in female somatic cells alters the balance of X-linked dosage compensation and is implicated in female-dominant systemic lupus erythematosus.

The three-dimensional organization of the genome in mammalian interphase nuclei is intrinsically linked to the regulation of gene expression. Whole chromosome territories and their encoded gene loci occupy preferential positions within the nucleus that changes according to the expression profile of a given cell lineage or stage. To further illuminate the relationship between chromosome organization, epigenetic environment, and gene expression, here we examine the functional organization of chromosome X and corresponding X-linked genes in a variety of healthy human and disease state X diploid (XX) cells. We observe high frequencies of homologous chromosome X colocalization (or coalescence), typically associated with initiation of X-chromosome inactivation, occurring in XX cells outside of early embryogenesis. Moreover, during chromosome X coalescence significant changes in Xist, H3K27me3, and X-linked gene expression occur, suggesting the potential exchange of gene regulatory information between the active and inactive X chromosomes. We also observe significant differences in chromosome X coalescence in disease-implicated lymphocytes isolated from systemic lupus erythematosus (SLE) patients compared to healthy controls. These results demonstrate that X chromosomes can functionally interact outside of embryogenesis when X inactivation is initiated and suggest a potential gene regulatory mechanism aberration underlying the increased frequency of autoimmunity in XX individuals.

Author Correction: Varying levels of X chromosome coalescence in female somatic cells alters the balance of X-linked dosage compensation and is implicated in female-dominant systemic lupus erythematosus.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Evaluation of the tolerogenic effects of donor bone marrow cells using a severe combined immunodeficient mouse-human islet transplant model.

The immunoregulatory role of human donor bone marrow cells (DBMC) has been studied extensively in our laboratory using in vitro and ex vivo assays. However, new experimental systems that can overcome the limitations of tissue culture assays but with more clinical relevance than purely animal experimentation, needed to be generated. Therefore we have developed a new human peripheral blood lymphocyte (PBL) severe combined immunodeficient (SCID) mouse islet transplantation model without the occurrence of graft-versus-host disease (GvHD) and have used it to evaluate the tolerogenic effects of DBMC. Nonobese diabetogenic (NOD)-SCID mice were transplanted with human deceased donor islets and were reconstituted with human PBL (allogeneic to islets; denoted as recipient) with or without DBMC from the islet donor. It was observed that the most cellularly economical dose was 3000 islets per animal and that injection into the portal vein was better than implantation under the kidney capsule. Even though maximal lymphoid reconstitution was observed with 40-million fresh and anti-CD3 activated recipient PBL (conventional method), the mice developed severe graft GvHD. However, with the new method of reconstitution where animals were injected with 20-million anti-CD3-activated plus 40-million anti-donor-activated recipient PBL, no discernible GvHD was observed. More importantly, this latter method was associated with islet transplant rejection, which in turn could be abrogated by co-injection of the animals with DBMC. These in vivo results confirmed our previous in vitro observations that human DBMC have regulatory activity.

Cellular and functional biomarkers of clinical transplant tolerance.

Development of tolerance protocols requires assays or biomarkers that distinguish tolerant recipients from non-tolerant ones to be established. In addition, a thorough understanding of the plausible mechanisms associated with clinical transplant tolerance is necessary to take the field forward. Unlike the majority of molecular signature analyses utilized by others, the emphasis of this article is on the cellular and functional biomarkers of induced transplant tolerance. Immunity to an organ transplant is very complex, comprised of two broad categories - innate and acquired or adaptive immune responses. Innate immunity can be avoided by eliminating or preventing ischemic injuries to the donor organ and tolerance at the level of adaptive immunity can be induced by infusions of a number of cellular products. Since adaptive immune response consists of inflammatory hypersensitivity, cellular (cytotoxic and helper) and humoral aspects, all these need to be measured, and the recipients who demonstrate donor-specific unresponsiveness in all can be considered tolerant or candidates for immunosuppression minimization and/or withdrawal. The mechanisms by which these agents bring about transplant tolerance include regulation, anergy, exhaustion, senescence and deletion of the recipient immune cells. Another proven mechanism of tolerance is full or mixed donor chimerism. However, it should be cautioned that non-deletional tolerance can be reversed.