Novel Noninvasive Assays to Predict Transplantation Rejection and Tolerance: Enumeration of Cytokine-Producing Alloreactive T Cells

Getting immunosuppression just right: the role of clinical biomarkers in predicting patient response post solid organ transplantation

INTRODUCTION

Actually, immunosuppression selection isn't based on individual immune alloreactivity, and immunosuppressive drug dosing is mainly based on the development of toxicity and the achievement of specific target concentrations. Since a successful outcome requires optimal patient risk stratification and treatment, several groups have evaluated candidate biomarkers that have shown promise in the assessment of individual immune responses, the prediction of personal pharmacodynamic effects of immunosuppressive drugs and the prognosis and diagnosis of graft outcomes..

AREAS COVERED

This review includes biomarkers that the Scientific Community in Solid Organ Transplantation currently considers to have potential as diagnostic and prognostic biomarkers of graft evolution. We have focused on recent scientific advances and expert recommendations regarding the role of specific and non-specific pharmacodynamic biomarkers that are mainly involved in the T-cell-mediated response.

EXPERT OPINION

Integral pharmacologic monitoring that combines pharmacokinetics, pharmacogenetics and predictive pharmacodynamic biomarkers may provide crucial information and allow personal adjustment of immunosuppressive drugs at an early stage before severe adverse events ensue. Multicentre, randomized, prospective and interventional trials are needed to fine tune the established cut-off values for each biomarker and the optimal monitoring frequency for each biomarker and to accurately evaluate possible clinical confounding factors to enable correct clinical qualification.

T-Cell Cytokines as Predictive Markers of the Risk of Allograft Rejection

Over the last decade, several biomarkers and surrogate markers have surfaced as promising predictive markers of risk of rejection in solid organ transplantation. The monitoring of these markers can help to improve graft and recipient care by personalizing immunomodulatory therapies. The complex immune system response against an implanted graft can change during long-term follow-up, and the dynamic balance between effector and regulatory T-cell populations is a crucial factor in antidonor response, risk of rejection, and immunosuppression requirements. Therefore, at any time before and after transplantation, T-effector activity, which is associated with increased production and release of proinflammatory cytokines, can be a surrogate marker of the risk of rejection and need for immunosuppression. In addition, immunosuppressive drugs may have a different effect in each individual patient. The pharmacokinetics and pharmacodynamics of these drugs show high interpatient variability, and pharmacodynamic markers, strongly associated with the specific mechanism of action, can potentially be used to measure individual susceptibility to a specific immunosuppressive agent. The monitoring of a panel of valid biomarkers can improve patient stratification and the selection of immunosuppressive drugs. After transplantation, therapy can be adjusted based on the prediction of rejection episodes (maintained alloreactivity), the prognosis of allograft damage, and the individual's response to the drugs. This review will focus on current data indicating that changes in the T-cell production of the intracellular cytokines interferon-γ and interleukin-2 could be used to predict the risk of rejection and to guide immunosuppressive therapy in transplant recipients.

In Vitro Influence of Mycophenolic Acid on Selected Parameters of Stimulated Peripheral Canine Lymphocytes

Mycophenolic acid (MPA) is an active metabolite of mycophenolate mofetil, a new immunosuppressive drug effective in the treatment of canine autoimmune diseases. The impact of MPA on immunity is ambiguous and its influence on the canine immune system is unknown. The aim of the study was to determine markers of changes in stimulated peripheral canine lymphocytes after treatment with MPA in vitro. Twenty nine healthy dogs were studied. Phenotypic and functional analysis of lymphocytes was performed on peripheral blood mononuclear cells cultured with mitogens and different MPA concentrations– 1 μM (10⁻³ mol/m³), 10 μM or 100 μM. Apoptotic cells were detected by Annexin V and 7-aminoactinomycin D (7-AAD). The expression of antigens (CD3, CD4, CD8, CD21, CD25, forkhead box P3 [FoxP3] and proliferating cell nuclear antigen [PCNA]) was assessed with monoclonal antibodies. The proliferation indices were analyzed in carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeled cells. All analyses were performed using flow cytometry. The influence of MPA on apoptosis was dependent on the mechanism of cell activation and MPA concentration. MPA caused a decrease in the expression of lymphocyte surface antigens, CD3, CD8 and CD25. Its impact on the expression of CD4 and CD21 was negligible. Its negative influence on the expression of FoxP3 was dependent on cell stimulation. MPA inhibited lymphocyte proliferation. In conclusion, MPA inhibited the activity of stimulated canine lymphocytes by blocking lymphocyte activation and proliferation. The influence of MPA on the development of immune tolerance–expansion of Treg cells and lymphocyte apoptosis–was ambiguous and was dependent on the mechanism of cellular activation. The concentration that MPA reaches in the blood may lead to inhibition of the functions of the canine immune system. The applied panel of markers can be used for evaluation of the effects of immunosuppressive compounds in the dog.

Elevated blood eosinophil count is a valuable biomarker for predicting late acute cellular rejection after liver transplantation

BACKGROUND

Recent studies have indicated the value of increased blood eosinophil counts for the diagnosis of acute cellular rejection (ACR) after orthotopic liver transplantation (OLT). However, the relationship between eosinophil count and late ACR at more than 6 months after OLT is still unclear.

METHODS

We sought to retrospectively analyzed the ACR predictive value of eosinophil counts. In the day before or the day of biopsy among 40 biopsies performed on 37 patients beyond 6 months after OLT.

RESULTS

Relative eosinophil count was significantly higher in the ACR (n = 24) than the non-ACR cohort, albeit with no significant difference in absolute eosinophil count. Receiver operating characteristic (ROC) analysis showed an absolute eosinophil count of 0.145 × 10(9)/L and a relative eosinophil count of 2.3% to show the highest Youden index with area under the ROC curves of 0.746 and 0.813, respectively. When absolute eosinophil count ≥ 0.145 × 10(9)/L or relative eosinophil count ≥ 2.3% was defined to be elevated, the sensitivity and specificity to predict ACR were 45.8% and 87.5%, and 75% and 87.5%, respectively. When the absolute eosinophil count ≥ 0.285 × 10(9)/L or relative eosinophil count ≥ 3% was defined as elevated, the sensitivity and specificity were 25% and 100%, and 50% and 100%, respectively. All patients with an absolute eosinophil count ≥ 0.285 × 10(9)/L showed a relative eosinophil count ≥ 3%.

CONCLUSIONS

Elevated blood eosinophil count was a valuable biomarker to predict late ACR after OLT.

The Potential Use of Allogeneic Platelet-Rich Plasma for Large Bone Defect Treatment: Immunogenicity and Defect Healing Efficacy

Autologous platelet-rich plasma (PRP) has been extensively investigated for large bone defect treatment, but its clinical application is harassed by controversial outcome, due to highly variable PRP quality among patients. Alternatively, allogeneic PRP from well-characterized donors cannot only generate more consistent and reliable therapeutic effect but also avoid harvesting large quantities of blood, an additional health burdens to patients. However, the use of allogeneic PRP for bone defect treatment is generally less investigated, especially for its immunogenicity in such application. Here, we meticulously investigated the immunogenicity of allogeneic PRP and evaluated its healing efficacy for critical-sized defect treatment. Allogeneic PRP contained 4.1-fold and 2.7- to 4.9-fold higher amount of platelets and growth factors than whole blood, respectively. The intramuscular injection of allogeneic PRP to rabbits did not trigger severe and chronic immunoresponse, evidenced by little change in muscular tissue microstructure and CD4+/CD8+ T lymphocyte subpopulation in peripheral blood. The implantation of allogeneic PRP/deproteinized bone matrix (DPB) constructs (PRP + DPB) successfully bridged 1.5-cm segmental radial defects in rabbits, achieving similar healing capacity as autologous MSC/DPB constructs (MSC + DPB), with greater bone formation (1.1–1.5x, p < 0.05) and vascularization (1.3–1.6x, p < 0.05) than DPB alone, shown by histomorphometric analysis, bone mineral density measurement, and radionuclide bone imaging. Furthermore, the implantation of both allogeneic PRP- and autologous MSC-mediated DPB constructs (PRP + MSC + DPB) resulted in the most robust bone regeneration (1.2–2.1x, p < 0.05) and vascularization (1.3–2.0x, p < 0.05) than others (PRP + DPB, MSC + DPB, or DPB alone). This study has demonstrated the promising use of allogeneic PRP for bone defect treatment with negligible immunogenicity, great healing efficacy, potentially more consistent quality, and no additional health burden to patients; additionally, the synergetic enhancing effect found between allogeneic PRP and autologous MSCs may shed a light on developing new therapeutic strategies for large bone defect treatment.

Intracellular IFN-γ and IL-2 expression monitoring as surrogate markers of the risk of acute rejection and personal drug response in de novo liver transplant recipients

Biomarker monitoring is needed in transplantation to reflect individual response to immunosuppressive drugs and graft outcome. We evaluated intracellular expression and soluble production of interferon-(IFN)-γ and interleukin-(IL)-2 as predictive biomarkers of acute rejection (AR) and personal drug response. Pharmacokinetic-pharmacodynamic profiles were determined in 47 de novo liver recipients treated with tacrolimus, mycophenolate mofetil and prednisone. Of the 47 patients, AR occurred in nine. There were no differences in drug concentrations between rejectors and non-rejectors. A pre-transplantation cut-off value of 55.80% for %CD8(+)-IFN-γ(+) identified patients at high risk of AR with a sensitivity of 75% and a specificity of 82%. In the first week post-transplantation, patients with a % inhibition for soluble IFN-γ, %CD8(+)-IFN-γ(+) and %CD8(+)-IL2(+) lower than 40% developed AR, showing low susceptibility to immunosuppressive drugs. Therefore, effector-T-cell response monitoring may help physicians to identify personal response to treatment and patients at high risk of AR.

Relevance of regulatory T cell promotion of donor-specific tolerance in solid organ transplantation

Current clinical strategies to control the alloimmune response after transplantation do not fully prevent induction of the immunological processes which lead to acute and chronic immune-mediated graft rejection, and as such the survival of a solid organ allograft is limited. Experimental research on naturally occurring CD4⁺CD25^highFoxP3⁺ Regulatory T cells (Tregs) has indicated their potential to establish stable long-term graft acceptance, with the promise of providing a more effective therapy for transplant recipients. Current approaches for clinical use are based on the infusion of freshly isolated or ex vivo polyclonally expanded Tregs into graft recipients with an aim to redress the in vivo balance of T effector cells to Tregs. However mounting evidence suggests that regulation of donor-specific immunity may be central to achieving immunological tolerance. Therefore, the next stages in optimizing translation of Tregs to organ transplantation will be through the refinement and development of donor alloantigen-specific Treg therapy. The altering kinetics and intensity of alloantigen presentation pathways and alloimmune priming following transplantation may indeed influence the specificity of the Treg required and the timing or frequency at which it needs to be administered. Here we review and discuss the relevance of antigen-specific regulation of alloreactivity by Tregs in experimental and clinical studies of tolerance and explore the concept of delivering an optimal Treg for the induction and maintenance phases of achieving transplantation tolerance.

Mechanisms of tolerance to parental parathyroid tissue when combined with human allogeneic thymus transplantation

BACKGROUND

The induction of tolerance toward third-party solid organ grafts with allogeneic thymus tissue transplantation has not been previously demonstrated in human subjects.

OBJECTIVE

Infants with complete DiGeorge anomaly (having neither thymus nor parathyroid function) were studied for conditions and mechanisms required for the development of tolerance to third-party solid organ tissues.

METHODS

Four infants who met the criteria received parental parathyroid with allogeneic thymus transplantation and were studied.

RESULTS

Two of 3 survivors showed function of both grafts but subsequently lost parathyroid function. They demonstrated alloreactivity against the parathyroid donor in mixed lymphocyte cultures. For these 2 recipients, parathyroid donor HLA class II alleles were mismatched with the recipient and thymus. MHC class II tetramers confirmed the presence of recipient CD4(+) T cells with specificity toward a mismatched parathyroid donor class II allele. The third survivor has persistent graft function and lacks alloreactivity toward the parathyroid donor. All parathyroid donor class II alleles were shared with either the recipient or the thymus graft, with minor differences between the parathyroid (HLA-DRB1∗1104) and thymus (HLA-DRB1∗1101). Tetramer analyses detected recipient T cells specific for the parathyroid HLA-DRB1∗1104 allele. Alloreactivity toward the parathyroid donor was restored with low doses of IL-2.

CONCLUSION

Tolerance toward parathyroid grafts in combined parental parathyroid and allogeneic thymus transplantation requires matching of thymus tissue to parathyroid HLA class II alleles to promote negative selection and suppression of recipient T cells that have alloreactivity toward the parathyroid grafts. This matching strategy may be applied toward tolerance induction in future combined thymus and solid organ transplantation efforts.

Biomarkers of immunoregulatory status in stable liver transplant recipients undergoing weaning of immunosuppressive therapy

Biomarkers that reflect immune response recovery and predict clinical events during withdrawal or minimization of immunosuppressive therapy have not been evaluated. This study aimed to evaluate whether immune response recovers after withdrawal of long-term immunosuppressive treatment in stable liver transplant patients and to determine whether specific biomarkers reflect immune response reactivity and predict rejection. Pharmacokinetic-pharmacodynamic profiles were determined in 24 patients and 80 healthy donors before immunosuppressive treatment reduction began, at 50%, and at complete withdrawal. In patients who rejected, effector-T-cell response mediated by soluble IFN-γ, %CD4(+)IFN-γ and %CD8(+)IL-2/IFN-γ were significantly increased, while TGF-β1 production and the TGF-β1/IFN-γ ratio were significantly decreased. In patients with rejection, soluble IFN-γ and %CD8(+)IL-2 were significantly higher before immunosuppressive treatment was reduced. Further studies are required, but this battery of biomarkers performed in whole blood could be a useful tool to monitor immunosuppressive treatment minimization or withdrawal protocols and identify patients at increased risk of rejection.