Prolonged graft survival in older recipient mice is determined by impaired effector T-cell but intact regulatory T-cell responses

Older age is associated with a distinct and marked reduction of functionality of both alloreactive CD4+ and CD8+ T cells

Introduction

Older recipient age is associated with a significant decreased risk for rejection after kidney transplantation which is incompletely understood.

Methods

In a longitudinal study, circulating alloreactive T cells were assessed of young (≤45 years) and older (≥55 years) stable kidney transplant recipients. Alloreactive T-cells were identified by CD137-expression and phenotype, cytokine producing and proliferative capacity, were evaluated using multiparameter flowcytometry.

Results

The results show that before transplantation frequencies of alloreactive CD4+ and CD8+ T-cells in older KT-recipients are significantly higher and shifted towards an effector memory-phenotype. However, the frequency of polyfunctional (≥2 pro-inflammatory cytokines) CD4+ T-cells was significantly lower and less IL2 was produced. The frequency of polyfunctional alloreactive CD4+ T-cells and proliferation of alloreactive T-cells donor-specifically declined after transplantation reaching a nadir at 12 months after transplantation, irrespective of age. A striking difference was observed for the proliferative response of alloreactive CD8+ T-cells. This was not only lower in older compared to younger recipients but could also not be restored by exogenous IL2 or IL15 in the majority of older recipients while the response to polyclonal stimulation was unaffected.

Conclusion

In conclusion, older age is associated with a distinct and marked reduction of functionality of both alloreactive CD4+ and CD8+ T-cells.

Long-term outcomes of kidney transplantation from expanded criteria donors with Chinese novel donation policy: donation after citizens' death

Introduction

The Chinese Government initiated the Donation after Citizens' Death policy in 2010. To now, it has been a major source of organs for transplant. Since it is still a young policy, corresponding clinical evidence is still urgently needed for its improvement. Compared to kidneys donated by SCD (standard criteria donor), increasing the use of ECD (expanded criteria donor) derived kidneys is a way to expand the donor pool but is also a result of the aging demography of China. This study is based on the data of kidney transplantation in our center with the Donation after Citizens' Death policy, aiming to provide a reference for the clinical use of ECD kidneys.

Method

A retrospective study enrolled 415 kidney transplants derived from 211 donors performed between October 2011 and October 2019. A total of 311 (74.9%) organs were donated from 159 (75.4%) SCDs, and the remaining 104 (25.1%) were from 52 (24.6%) ECDs. The log-rank test was used to compare the difference in survival and postoperative complications. The Chi-square test was used to compare the occurrence of postoperative complications and postoperative renal function. The Cox regression analysis was used for risk factor screening.

Result

Analysis showed that grafts from ECD were poorer in survival (P = 0.013), while their recipients had comparable (P = 0.16) survival. Moreover, it also was an independent risk factor for graft loss (HR 2.27, P = 0.044). There were significantly more AR occurrences in the ECD group compared with SCD group (25.0% vs. 15.8%, P = 0.004), but no significant difference was found in infection (51.9% vs. 47.6%, P = 0.497) and DGF (26.0% vs. 21.9%, P = 0.419) between them. Similarly, fewer recipients in the ECD group were free from AR within 1 year after transplantation (P = 0.040), with no statistical difference in all-cause infection prevalence in 1 year (P = 0.168). The eGFR in the ECD group was significantly worse than that in the SCD group at 3 months, 6 months, 1 year, 3 years, and the highest value posttransplant (all < 0.05), but no difference at 5 years posttransplant. Besides, results showed cardiac arrest (uncontrolled vs. controlled, HR 2.49, P = 0.049), HLA mismatch (4–6 loci vs. 0–3 loci, HR 3.61, P = 0.039), and AR occurrence (HR 2.91, P = 0.006) were demonstrated to be independent risk factors for graft loss.

Conclusion

The ECD-derived kidney was worse than the SCD-derived kidney in terms of graft survival and AR occurrence, and trend to an inferior renal function postoperative. However, the recipient survival, DGF occurrence, and all-cause infection occurrence were similar.

Aging Affects the Role of Myeloid-Derived Suppressor Cells in Alloimmunity

Myeloid-derived suppressor cells (MDSC) are defined as a group of myeloid cells with potent immunoregulatory functions that have been shown to be involved in a variety of immune-related diseases including infections, autoimmune disorders, and cancer. In organ transplantation, MDSC promote tolerance by modifying adaptive immune responses. With aging, however, substantial changes occur that affect immune functions and impact alloimmunity. Since the vast majority of transplant patients are elderly, age-specific modifications of MDSC are of relevance. Furthermore, understanding age-associated changes in MDSC may lead to improved therapeutic strategies. Here, we provide a comprehensive update on the effects of aging on MDSC and discuss potential consequences on alloimmunity.

CTLA4-Ig prolongs graft survival specifically in young but not old mice

Elderly organ transplant recipients have remained underrepresented in clinical trials, despite representing a rapidly growing population. Here, we assessed age-specific effects of CTLA4-Ig (cytotoxic T-lymphocyte antigen 4-Ig), a fusion protein blocking costimulatory signaling between antigen-presenting cells and T cells through CD28. Cardiac allografts in young mice (2-3 months) treated with CTLA4-Ig survived indefinitely, whereas 80% of old recipients (18 months) had lost their graft after 100 days. CTLA4-Ig was also significantly less effective in older recipients of skin transplants. CTLA4-Ig reduced CD4⁺ central memory and effector memory T cells and diminished systemic interferon-gamma levels only in young recipients. These differences corresponded to a reduced expression of CD28 on antigen-experienced CD4⁺ T cells in old mice. In support, adoptive transfer of old CD4⁺ T cells that were transfected with a lentiviral vector inducing constant expression of CD28 accelerated the rejection of allogeneic skin grafts in young RAG2^-/- recipient mice. Regulatory T cells (Tregs), in contrast, demonstrated an increased expression of CD28 with aging and CTLA4-Ig treatment in old recipients resulted in reduced frequencies, compromised proliferation, and diminished suppressive capacity of Tregs. These findings may prove to have unique clinical consequences for immunosuppression in the growing population of elderly transplant recipients.

New-Onset Gout as an Independent Risk Factor for Returning to Dialysis After Kidney Transplantation

Background.

The causal relationship between gout and renal transplant outcomes is difficult to assess due to multiple interacting covariates. This study sought to estimate the independent effect of new-onset gout on renal transplant outcomes using a methodology that accounted for these interactions.

Methods.

This study analyzed data on patients in the US Renal Data System (USRDS) who received a primary kidney transplant between 2008 and 2015. The exposure was new-onset gout, and the primary endpoint was returning to dialysis >12 months postindex date (transplant date). A marginal structural model (MSM) was fitted to determine the relative risk of new-onset gout on return to dialysis.

Results.

18 525 kidney transplant recipients in the USRDS met study eligibility. One thousand three hundred ninety-nine (7.6%) patients developed new-onset gout, and 1420 (7.7%) returned to dialysis >12 months postindex. Adjusting for baseline and time-varying confounders via the MSM showed new-onset gout was associated with a 51% increased risk of return to (RR, 1.51; 95% CI, 1.03-2.20).

Conclusions.

This finding suggests that new onset gout after kidney transplantation could be a harbinger for poor renal outcomes, and to our knowledge is the first study of kidney transplant outcomes using a technique that accounted for the dynamic relationship between renal dysfunction and gout.

Evidence for the alloimmune basis and prognostic significance of Borderline T cell-mediated rejection

Prognostic biomarkers of T cell-mediated rejection (TCMR) have not been adequately studied in the modern era. We evaluated 803 renal transplant recipients and correlated HLA-DR/DQ molecular mismatch alloimmune risk categories (low, intermediate, high) with the severity, frequency, and persistence of TCMR. Allograft survival was reduced in recipients with Banff Borderline (hazard ratio [HR] 2.4, P = .003) and Banff ≥ IA TCMR (HR 4.3, P < .0001) including a subset who never developed de novo donor-specific antibodies (P = .002). HLA-DR/DQ molecular mismatch alloimmune risk categories were multivariate correlates of Banff Borderline and Banff ≥ IA TCMR and correlated with the severity and frequency of rejection episodes. Recipient age, HLA-DR/DQ molecular mismatch category, and cyclosporin vs tacrolimus immunosuppression were independent correlates of Banff Borderline and Banff ≥ IA TCMR. In the subset treated with tacrolimus (720/803) recipient age, HLA-DR/DQ molecular mismatch category, and tacrolimus coefficient of variation were independent correlates of TCMR. The correlation of HLA-DR/DQ molecular mismatch category with TCMR, including Borderline, provides evidence for their alloimmune basis. HLA-DR/DQ molecular mismatch may represent a precise prognostic biomarker that can be applied to tailor immunosuppression or design clinical trials based on individual patient risk.

Epidemiology, Risk Factors, and Outcomes of Opportunistic Infections after Kidney Allograft Transplantation in the Era of Modern Immunosuppression: A Monocentric Cohort Study

Epidemiology of opportunistic infections (OI) after kidney allograft transplantation in the modern era of immunosuppression and the use of OI prevention strategies are poorly described. We retrospectively analyzed a single-center cohort on kidney allograft adult recipients transplanted between January 2008 and December 2013. The control group included all kidney recipients transplanted in the same period, but with no OI. We analyzed 538 kidney transplantations (538 patients). The proportion of OI was 15% (80 and 72 patients). OI occurred 12.8 (6.0–31.2) months after transplantation. Viruses were the leading cause (n = 54, (10%)), followed by fungal (n = 15 (3%)), parasitic (n = 6 (1%)), and bacterial (n = 5 (0.9%)) infections. Independent risk factors for OI were extended criteria donor (2.53 (1.48–4.31), p = 0.0007) and BK viremia (6.38 (3.62–11.23), p < 0.0001). High blood lymphocyte count at the time of transplantation was an independent protective factor (0.60 (0.38–0.94), p = 0.026). OI was an independent risk factor for allograft loss (2.53 (1.29–4.95), p = 0.007) but not for patient survival. Post-kidney transplantation OIs were mostly viral and occurred beyond one year after transplantation. Pre-transplantation lymphopenia and extended criteria donor are independent risk factors for OI, unlike induction therapy, hence the need to adjust immunosuppressive regimens to such transplant candidates.

Rapamycin Prolongs Graft Survival and Induces CD4+IFN-γ+IL-10+ Regulatory Type 1 Cells in Old Recipient Mice

BACKGROUND

Although the elderly represents a rapidly growing population among transplant recipients, age-specific aspects have not been considered sufficiently in clinical trials. Moreover, age-specific effects of immunosuppressive therapies remain poorly understood.

METHODS

Here, we assessed the impact of rapamycin on alloimmune responses in old recipients using a fully major histocompatibility complex-mismatched murine transplantation model.

RESULTS

Old untreated recipients displayed a prolonged skin graft survival compared to their young counterparts, an observation that confirmed data of our previous experiments. Rapamycin led to a significant prolongation of graft survival in both young and old recipients. However, graft survival was age-dependent and extended in old versus young recipients (19 days vs 12 days, P = 0.004). This age-specific effect was not linked to changes in frequencies or subset composition of either cluster of differentiation (CD)8 or CD4 T cells. Moreover, antiproliferative effects of rapamycin on CD8 and CD4 T cells as assessed by in vivo bromdesoxyuridine incorporation were comparable and age-independent. In contrast, the systemic production of IL-10 was markedly elevated in old recipients treated with rapamycin. In parallel to this shift in cytokine balance, IFN-γ/IL-10 double-positive regulatory type 1 cells emerged during T helper type 1 differentiation of old T helper cells in presence of rapamycin. Similarly, CD4IFN-γIL-10 cells expanded among Foxp3-negative cells after in vivo treatment of old recipients with rapamycin.

CONCLUSIONS

Our results highlight novel aspects of age-dependent immunosuppressive effects of rapamycin, with relevance for age-specific immunosuppressive regimens.

Personalized immunosuppression in elderly renal transplant recipients

The number of elderly people has increased considerably over the last decades, due to a rising life expectancy and ageing populations. As a result, an increased number of elderly with end-stage-renal-disease are diagnosed, for which the preferred treatment is renal transplantation. Over the past years the awareness of the elderly as a specific patient population has grown, which increases the importance of research in this group. Elderly patients often receive kidneys from elderly donors while younger donor kidneys are preferentially reserved for younger recipients. Although the rate of acute rejection after transplantation is lower in the elderly, these rejections may lead to graft loss more frequently, as kidneys from elderly donors have marginal reserve capacity. To prevent acute rejection, immunosuppressive therapy is needed. On the other hand, elderly patients have a higher risk to die from infectious complications, and thus less immunosuppression would be preferable. Immunosuppressive treatment in the elderly is complicated further by changes in the pharmacokinetics and pharmacodynamics, with increasing age. Adjustments in standard immunosuppressive regimes are therefore suggested for this population. An unmet need in transplantation medicine is a tool to guide a personalized approach to immunosuppression. Recently several promising biomarkers that identify injury to the graft at an early stage or predict acute rejection have been identified. Unfortunately, none of these biomarkers were tested specifically in the elderly. We believe there is an urgent need to perform clinical trials investigating novel immunosuppressive regimens in conjunction with biomarker studies in this specific population.

Development of a Multivariate Prediction Model for Early-Onset Bronchiolitis Obliterans Syndrome and Restrictive Allograft Syndrome in Lung Transplantation

BACKGROUND

Chronic lung allograft dysfunction and its main phenotypes, bronchiolitis obliterans syndrome (BOS) and restrictive allograft syndrome (RAS), are major causes of mortality after lung transplantation (LT). RAS and early-onset BOS, developing within 3 years after LT, are associated with particularly inferior clinical outcomes. Prediction models for early-onset BOS and RAS have not been previously described.

METHODS

LT recipients of the French and Swiss transplant cohorts were eligible for inclusion in the SysCLAD cohort if they were alive with at least 2 years of follow-up but less than 3 years, or if they died or were retransplanted at any time less than 3 years. These patients were assessed for early-onset BOS, RAS, or stable allograft function by an adjudication committee. Baseline characteristics, data on surgery, immunosuppression, and year-1 follow-up were collected. Prediction models for BOS and RAS were developed using multivariate logistic regression and multivariate multinomial analysis.

RESULTS

Among patients fulfilling the eligibility criteria, we identified 149 stable, 51 BOS, and 30 RAS subjects. The best prediction model for early-onset BOS and RAS included the underlying diagnosis, induction treatment, immunosuppression, and year-1 class II donor-specific antibodies (DSAs). Within this model, class II DSAs were associated with BOS and RAS, whereas pre-LT diagnoses of interstitial lung disease and chronic obstructive pulmonary disease were associated with RAS.

CONCLUSION

Although these findings need further validation, results indicate that specific baseline and year-1 parameters may serve as predictors of BOS or RAS by 3 years post-LT. Their identification may allow intervention or guide risk stratification, aiming for an individualized patient management approach.

Aging and the immune response to organ transplantation

An increasing number of older people receive organ transplants for various end-stage conditions. Although organ transplantation is an effective therapy for older patients (i.e., older than 65 years of age), such as in end-stage renal disease, this therapy has not been optimized for older patients because of our lack of understanding of the effect of aging and the immune response to organ transplantation. Here, we provide an overview of the impact of aging on both the allograft and the recipient and its effect on the immune response to organ transplantation. We describe what has been determined to date, discuss existing gaps in our knowledge, and make suggestions on necessary future studies to optimize organ transplantation for older people.

Age-Dependent Metabolic and Immunosuppressive Effects of Tacrolimus

Immunosuppression in elderly recipients has been underappreciated in clinical trials. Here, we assessed age-specific effects of the calcineurin inhibitor tacrolimus (TAC) in a murine transplant model and assessed its clinical relevance on human T cells. Old recipient mice exhibited prolonged skin graft survival compared with young animals after TAC administration. More important, half of the TAC dose was sufficient in old mice to achieve comparable systemic trough levels. TAC administration was able to reduce proinflammatory interferon-γ cytokine production and promote interleukin-10 production in old CD4⁺ T cells. In addition, TAC administration decreased interleukin-2 secretion in old CD4⁺ T cells more effectively while inhibiting the proliferation of CD4⁺ T cells in old mice. Both TAC-treated murine and human CD4⁺ T cells demonstrated an age-specific suppression of intracellular calcineurin levels and Ca²⁺ influx, two critical pathways in T cell activation. Of note, depletion of CD8⁺ T cells did not alter allograft survival outcome in old TAC-treated mice, suggesting that TAC age-specific effects were mainly CD4⁺ T cell mediated. Collectively, our study demonstrates age-specific immunosuppressive capacities of TAC that are CD4⁺ T cell mediated. The suppression of calcineurin levels and Ca²⁺ influx in both old murine and human T cells emphasizes the clinical relevance of age-specific effects when using TAC.

The pharmacokinetics and pharmacodynamics of mycophenolate mofetil in younger and elderly renal transplant recipients

AIMS

Elderly transplant recipients have a lower incidence of acute rejection, and a higher risk to die from infectious complications. A potential cause may be differences in the pharmacokinetics (PK) or pharmacodynamics (PD) of the immunosuppressive drugs they are taking. This study was designed to comprehensively evaluate the influence of age on the PK and PD of mycophenolic acid (MPA).

METHODS

In this study the PK and PD of MPA was studied in 26 elderly and 54 younger renal transplant recipients treated with mycophenolate mofetil and tacrolimus. Patients were sampled repetitively, both before and during the first 6 months after kidney transplantation. Age-related variability in MPA PK, baseline IMPDH activity, as well as MPA-induced IMPDH inhibition were studied.

RESULTS

The IMPDH activity pre-transplantation did not differ between elderly and younger patients. Neither IMPDH activity pre-transplantation nor maximum IMPDH inhibition was significantly correlated with the patients' age. The area under the MPA plasma concentration-time curve (AUC_0-12h ) and the area under the effect (IMPDH activity)-time curve (AEC_0-12h ) from 0 to 12 h were also not significantly different between the two groups. We found no significant differences in EC₅₀ and E_max between elderly and younger patients.

CONCLUSIONS

Age did not significantly affect the PK or PD of MPA. It is unlikely that the lower incidence of acute rejection in elderly patients, or the higher risk to die from a severe infection in elderly patients is due to different handling of MPA in the elderly.

Defective CD8 Signaling Pathways Delay Rejection in Older Recipients

CD8+ T cells play a cardinal feature in response to alloantigens and are able to generate effector/memory T cells independently from CD4+ T cells. To investigate the impact of aging on CD8 T cells, we used a fully mismatched mouse skin transplant model. Our findings showed a prolonged allograft survival in older recipients associated with a significant increase of CD4+ and CD8+ CD44high CD62Llow effector/memory T cells and a reduced systemic IFNγ production. When reconstituting young CBA Rag-1 mice that lack mature T and B cells with old CD8+ T cells expressing clonal anti-H2K T cell receptor (TCR) alloreactive for MHC I, graft survival was significantly prolonged and comparable to those receiving young CD8+ T cells. Moreover, our data showed that reduced systemic IFNγ levels observed in old recipients had been linked to a compromised expression of the IL-2R β subunit (CD122) by old CD8+ T cells. In addition, we observed an impaired IFNγ production on IL-2 receptor activation. At the same time, gene profiling analysis of old CD8 T cells demonstrated reduced chemokine ligand-3 and CD40L expression that resulted in compromised CD8+ T cell/dendritic cell communication, leading to impaired migratory and phagocytic activity of CD11c cells.Collectively, our study demonstrated that aging delays allograft rejection. CD8 T cells play a critical role in this process linked to a compromised production of IFNγ, in addition to a defective IL-2 receptor signaling machinery and a defective communication between CD8 T cells and dendritic cells.

Pharmacokinetics and pharmacodynamics of immunosuppressive drugs in elderly kidney transplant recipients

Elderly patients are a fast growing population among transplant recipients over the past decades. Both the innate and adaptive immune reactivity decrease with age, which is believed to contribute to the decreased incidence of acute rejection and increased infectious death rate in elderly transplant recipients. In contrast to recipient age, donor age is associated with a higher incidence of acute rejection. Pharmacokinetic studies in renal transplant recipients show that CNI troughs are >5% higher in elderly compared to younger patients given the same dose normalized by body weight. This may impact the starting dose of tacrolimus and cyclosporine. Possibly in elderly patients the intracellular (in lymphocyte) concentrations are relatively high in relation to the whole blood concentration, resulting in a stronger pharmacodynamic effect at the same whole blood trough concentration. For cyclosporine this has been shown, but it is not clear if the same is true for other immunosuppressive drugs. Pharmacodynamic studies have compared the inhibition of target enzymes, or more downstream effects of immunosuppressive drugs, in younger and older patients. Measurement of nuclear factor of activated T-cell (NFAT)-regulated gene expression (RGE), a pharmacodynamic read-out of CNI, is a promising biomarker of immunosuppression. Low levels of NFAT RGE are associated with increased risk of infection and non-melanoma skin cancer in elderly patients. Clinical trials to evaluate the safety and efficacy of immunosuppression regimens in this specific patient population, which is underrepresented in published trials, are lacking. More studies in elderly patients are needed to investigate the impact of age on the pharmacokinetics or pharmacodynamics of immunosuppressive drugs, and to decide on the optimal regimen and target levels for elderly transplant recipients.

Transplantation of allograft transforming growth factor-β1 transfected CD103⁺ lamina propria dendritic cells could effectively induce antigen-specific regulatory T cells in vivo

Organ transplantation is the best treatment of some end-stage diseases such as renal failure. Unfortunately, not every transplant is successful due to rejection or dysfunction of the transplanted organ. Induction of allograft tolerance is the most important goal of clinical transplantation. Regulatory T cells (Tregs) have opened up exciting opportunities for this enterprise. Because Tregs can be induced from naïve CD4 T cells (induced Tregs [iTregs]) by lamina propria dendritic cells (LpDCs) via transforming growth factor-β (TGF-β) and retinoic acid (RA) iTregs show in vitro and in vivo functions similar to those of natural Tregs (nTregs), we sought to convert naive CD4 T cells to iTregs using mTGF-β1-modified allograft LpDCs in vivo. Adoptive transfer of mTGF-β1-modified LpDCs of BALB/c mice into C57BL/6 mice induced higher levels of mTGF-β1 and mIL-10 in sera as well as a greater proportion of antigen-specific Tregs. These data support the role of mTGF-β1-modified allograft LpDCs to induce high levels of antigen-specific Tregs in vivo.

Report of the joint ESOT and TTS basic science meeting 2013: current concepts and discoveries in translational transplantation

A joint meeting organized by the European (ESOT) and The Transplantation (TTS) Societies for basic science research was organized in Paris, France, on November 7-9, 2013. Focused on new ideas and concepts in translational transplantation, the meeting served as a venue for state-of-the-art developments in basic transplantation immunology, such as the potential for tolerance induction through regulation of T-cell signaling. This meeting report summarizes important insights which were presented in Paris. It not only offers an overview of established aspects, such as the role of Tregs in transplantation, presented by Nobel laureate Rolf Zinkernagel, but also highlights novel facets in the field of transplantation, that is cell-therapy-based immunosuppression or composite tissue transplantation as presented by the emotional story given by Vasyly Rohovyy, who received two hand transplants. The ESOT/TTS joint meeting was an overall productive and enjoyable platform for basic science research in translational transplantation and fulfilled all expectations by giving a promising outlook for the future of research in the field of immunological transplantation research.

Immunosenescence does not abrogate engraftment of murine allogeneic bone marrow

BACKGROUND

Allogeneic bone marrow transplantation is under investigation for a range of nonmalignant indications, including tolerance induction through mixed chimerism. This strategy has so far been tested experimentally only in young recipients. Due to immunosenescence, older patients have an increase in memory T cells (TMEM) as well as other alterations to their immune system, which may influence the potential to induce tolerance. We therefore investigated the impact of immunosenescence on chimerism-based tolerance induction.

METHODS

Groups of young (2 months) and old (12 months) C57BL/6 recipients received BALB/c bone marrow under nonmyeloablative (3 Gy) and minimal (1 Gy) total body irradiation and treatment with costimulation blockade, T-cell depletion, or rapamycin. Multilineage chimerism, clonal deletion, and lymphocyte subsets were analyzed by flow cytometry. Tolerance was assessed by skin and heart grafts and enzyme-linked immunospot, intracellular cytokine, and mixed lymphocyte reaction assays.

RESULTS

Unexpectedly, chimerism and tolerance were established in old recipients with comparable-and in some cases increased-efficacy as in young recipients employing costimulation blockade-based or T-cell depletion-based conditioning with 1 or 3 Gy total body irradiation. TMEM reactivity in (naïve) old mice was augmented in response to polyclonal but not to allogeneic stimulation, providing a mechanistic underpinning for the susceptibility to chimerism induction despite increased TMEM frequencies. Tolerance in old recipients was associated with peripheral and central clonal deletion and a higher frequency of regulatory T cells.

CONCLUSION

Advanced age does not impair bone marrow engraftment, thereby widening the clinical potential of experimental protocols inducing transplantation tolerance through mixed chimerism.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Kidney transplantation and the ageing immune system

The world population is rapidly growing and ageing at a pace that is projected to continue for at least three decades. This shift towards an older populace has invariably increased the number of individuals with diseases related to ageing, such as chronic kidney disease. The increase in chronic kidney disease is associated with a growing number of elderly patients receiving kidney transplants. Understanding how the immune system changes with increasing age will help to define the risks of rejection and infection in the elderly population and will focus attention on the need for individualized immunosuppression for patients in this age group. This Review addresses what is currently known about ageing and the immune system, highlighting age-related changes that affect the outcome of transplantation in elderly individuals. The need for new strategies to improve outcomes in this growing population of elderly renal transplant recipients is also emphasized.

Role of donor-specific regulatory T cells in long-term acceptance of rat hind limb allograft

BACKGROUND

Vascularized bone marrow transplantation (VBMT) is widely accepted as an efficient means of establishing chimerism and inducing tolerance. However, the mechanism underlying is poorly understood. Recently, regulatory T cells (Tregs) have been shown to play an important role in regulating immune responses to allogeneic antigens. In this study, we explored the role of Tregs in the induction of tolerance in an allogeneic hind limb transplantation model.

METHODOLOGY/PRINCIPAL FINDINGS

Forty-eight Lewis rats were divided into 6 groups. They received isografts and allografts from Brown-Norway hind limbs. Recipients in groups 1 and 2 received isografts and those in the other groups received allografts. The bone components of donor limbs were kept intact in groups 1, 3, and 5 but removed before transplantation into groups 2, 4, and 6. Tapered cyclosporin A (CsA) was administered to recipients in groups 5 and 6 after transplantation. During the 100-day observation period, all isografts survived, but the allografts in groups 3 and 4 were rejected within 8 to 12 days. CsA-treated intact allografts survived rejection-free for more than 100 days, and CsA-treated allografts lacking bone elements were rejected within 2 months. Stable peripheral chimerism and myeloid chimerism were observed in group 5. Declining peripheral chimerism and a lack of myeloid chimerism were observed in group 6. Donor-specific Tregs were exclusively detected in both peripheral blood and in the spleens of long-term recipient rats in group 5, with an increased FoxP3 mRNA expression in the allografts. This was further demonstrated to be responsible for donor-specific hyporeactivity by in vitro one-way mixed lymphocyte reaction (MLR).

CONCLUSION/SIGNIFICANCE

Bone components in the allogeneic hind limbs can induce myeloid chimerism and donor-specific Tregs may be essential to tolerance induction. The bone-removal hind limb model may be a suitable counterpart to the induction of tolerance in the study of limb transplantation.

The combination of donor and recipient age is critical in determining host immunoresponsiveness and renal transplant outcome

OBJECTIVE

To evaluate the interaction of donor and recipient age on transplant outcome and immune response.

SUMMARY BACKGROUND DATA

The age of donor and recipient is becoming increasingly important in organ transplantation. We tested the relevance and consequences of recipient and donor age on immunoresponsiveness and transplant outcome in a uni- and multilateral cohort analysis.

METHODS

We obtained and analyzed data from 108,188 recipients of deceased donor kidneys of the United Network for Organ Sharing database transplanted between 1995 and 2008. Univariate analysis of allograft and patient survival was calculated by Kaplan Meyer. Multivariate analyses were performed using the Cox Proportional Hazards method. Data were assessed and compared by decades of increasing donor and recipient age with and without censoring transplant loss for death with a functioning graft. This approach allowed a detailed analysis of interacting factors.

RESULTS

Transplant survival was lowest in elderly recipients. However, when the analysis was censored for patient's death with a functioning kidney transplant, survival improved incrementally with each decade of increasing recipient age. This was even more surprising as older recipients had received less well-matched organs of poorer quality. The frequency of acute rejection decreased dramatically with increasing age, emphasizing the effect of age on the vigor of the recipient's immune responses. In contrast, increasing donor age was associated with more frequent acute rejection rates. The effects of donor and recipient age in combination demonstrated that grafts of older donors fared significantly better in older recipients.

CONCLUSIONS

Our results show that increasing recipient age is associated with an improved transplant survival, lower rates of rejection, and superior outcome of older donor organs. Physiological and/or immunologic aspects of organ and recipient age seem to determine, at least in part, the success of renal transplantation.