Prognostic assays for rejection and tolerance in organ transplantation

Gene expression profiling in acute allograft rejection: challenging the immunologic constant of rejection hypothesis

In humans, the role and relationship between molecular pathways that lead to tissue destruction during acute allograft rejection are not fully understood. Based on studies conducted in humans, we recently hypothesized that different immune-mediated tissue destruction processes (i.e. cancer, infection, autoimmunity) share common convergent final mechanisms. We called this phenomenon the "Immunologic Constant of Rejection (ICR)." The elements of the ICR include molecular pathways that are consistently described through different immune-mediated tissue destruction processes and demonstrate the activation of interferon-stimulated genes (ISGs), the recruitment of cytotoxic immune cells (primarily through CXCR3/CCR5 ligand pathways), and the activation of immune effector function genes (IEF genes; granzymes A/B, perforin, etc.). Here, we challenge the ICR hypothesis by using a meta-analytical approach and systematically reviewing microarray studies evaluating gene expression on tissue biopsies during acute allograft rejection. We found the pillars of the ICR consistently present among the studies reviewed, despite implicit heterogeneity. Additionally, we provide a descriptive mechanistic overview of acute allograft rejection by describing those molecular pathways most frequently encountered and thereby thought to be most significant. The biological role of the following molecular pathways is described: IFN-γ, CXCR3/CCR5 ligand, IEF genes, TNF-α, IL-10, IRF-1/STAT-1, and complement pathways. The role of NK cell, B cell and T-regulatory cell signatures are also addressed.

Induction of tolerance in renal transplantation using splenic transplantation: experimental study in a canine model

OBJECTIVE

To evaluate in a canine model the induction of tolerance to renal transplantation after splenectomy and splenosis.

MATERIALS AND METHODS

This prospective, experimental, comparative, longitudinal study included 4 experimental groups, each comprising 4 dogs. Group 1 (control group) underwent renal transplantation only; group 2 underwent renal transplantation and splenectomy; group 3 underwent renal transplantation and splenosis; and group 4 underwent renal transplantation, splenectomy, and splenosis. Survival and degree of rejection were compared between the 4 groups.

RESULTS

Splenosis improved renal function after transplantation, as indicated by increased serum creatinine concentration (group 3, 6.2 mg/dL vs group 1, 12.9 mg/dL). Comparison of weighted survival curves (corrected for degree of rejection) demonstrated a significant difference between group 2 (66.0 days) and group 4 (66.2 days) vs group 1 (52.7 days) and group 3 (41.2 days) (P = .05, Wilcoxon rank sum test).

CONCLUSION

These results suggest that in this experimental model of renal transplantation, splenosis and splenectomy induce clinical tolerance, as indicated by improved renal function and prolonged recipient survival.

[Sequelae of organ transplantation]

Transplant medicine has significantly changed the prognosis of diseases leading to terminal organ failure. It has evolved from an experimental procedure to standard therapy for liver, kidney and cardio-vascular diseases. Transplant medicine combines operative organ replacement with the management of severely ill patients before transplantation, as well as life-long follow-up of organ graft recipients. Ten year survival rates of 65% to over 90% have led to a steady increase of transplanted patients seen by general medical care providers which represents a challenge for practicing internists. Apart from organ-specific conditions, infectious, immunosuppressant-associated and metabolic consequences determine long-term survival. These include virus reactivation, graft rejection, anastomotic problems but more importantly general mortality determining factors such as diabetes, renal insufficiency and hypertension, which are often a consequence of immunosuppressant administration. They directly impact long-term survival. The awareness and treatment of these secondary conditions of organ transplantation in routine medical practice contributes significantly to secure the long term success of transplant medicine.