Immune Tolerance and Alloreactivity in Liver Transplant Recipients on Different Monotherapy Immunosuppressive Agents

Life-long immunosuppressive therapy is typically required in the majority of liver allograft recipients. In the early years of liver transplantation (LT), the majority of deaths occurred secondary to graft loss from acute or chronic rejection despite immunosuppression (IS). With the advent of more powerful and specific IS agents, e.g. calcineurin-inhibitors (CNIs) cyclosporine (CyA) and tacrolimus (TAC), graft rejection rates significantly declined and short and long term graft/patient survival dramatically improved. However, along with the advance in survival rates came the adverse effects of long term immunosuppression (IS), e.g. morbidity and mortality from cardiovascular events, renal insufficiency, infectious complications, recurrent viral hepatitis and malignancy. These events are exacerbated by pre-existing conditions and an aging transplant population. Immunosuppression tapering or withdrawal could lower the incidence of these complications and improve long term graft and patient survival.

Therefore, the study proposed is a laboratory investigation (using blood samples collected from the subjects) comparing immune tolerance and alloreactivity profiles in LT recipients on monotherapy IS or converted to rapamycin monotherapy, to determine tolerogenic properties of the different IS agents. Knowledge of these properties would support the need for specific IS therapy to promote immune tolerance and consider IS withdrawal.

Monotherapy patients will be identified by the organ transplant database and medical charts at Northwestern. Patients will be invited to participate in the study and asked to undergo venipunctures for our analysis. Patient demographics, laboratories and other clinical data will be recorded. Patients on CNI monotherapy are continuously being identified for conversion to rapamycin monotherapy during clinic visits or chart reviews at Northwestern. Patients are selected for conversion due to significant CNI side effects, e.g. chronic kidney disease (creatinine clearance < 50 in the absence of significant proteinuria > 1g, poorly controlled diabetes mellitus/hypertension/hyperlipidemia, peripheral neuropathy). In general, patients are converted from CNIs to rapamycin over 2-3 weeks once therapeutic rapamycin levels are achieved.

Study procedures will be carried out by the investigators and associated personnel. Patients will be assigned a number in numerical order, to remove patient identifiers from the data analysis. A separate screening/enrollment log will be kept separate from the data. Baseline characteristics of the patients will be recorded: age, sex, liver disease, past medical history, history of acute rejection or other graft dysfunction, other post-LT complications, previous and current IS regimens. Monotherapy patients (10 from CyA, Tacrolimus, and MMF; 5 rapamycin) will be identified as above and asked to participate. Blood will be drawn at one time point for the following analysis:

• Dendritic cell assays: myeloid vs. lymphoid (CD11c; CD123); maturation and ability to process antigens (CD83; CD205); markers that have been shown to induce regulatory T cells (ILT3; ILT4).
• Regulatory/Suppressor Cells (CD4+CD25+FOXP3+CD127low; and CD8+ CD28- FOXP3+CD127low cells).
• HLA microchimerism & HLA G