Immunosuppression Flashcards
The first step in the alloimmune response involves the recognition of transplant antigens (alloantigens) by recipient T cells.
T-cell activation requires three signals
Signal 1 is initiated by the binding of the alloantigen on the surface of antigen-presenting cell (APC) to the T-cell receptor (TCR)–CD3 complex.
Signal 2 is a non–antigen-specific costimulatory signal provided by the engagement of B7 on the surface of APC with CD28 on T cell.
These dual signals (ie, signals 1 and 2) activate the intracellular pathways that trigger T cells to activate interleukin-2 (IL-2) and other growth-promoting. cytokines.
If a TCR is triggered without the accompanying costimulatory signal 2, then the T cell is driven into an anergic state in which it is both inactivated and refractory to later activation even in the presence of all necessary activation elements.
Signal 3, engagement of IL-2 to its receptor activates the mammalian target of rapamycin (mTOR) pathway to provide signal 3, which leads to cell proliferation.
Lymphocyte proliferation requires the synthesis of purine and pyrimidine nucleotides.
T cells also express cytotoxic T-lymphocyte antigen-4 (CTLA-4), a cell surface molecule that is homologous to CD28.
The binding of B7 to CTLA-4 produces an inhibitory signal that inhibits T-cell proliferation and terminates the immune response.
Calcineurin is a phosphatase that dephosphorylates and facilitates the translocation of nuclear factor of activated T cells (NFAT) (and other nuclear factors) to the nucleus.
Inhibition of calcineurin impairs the expression of IL-2 (and other growth-promoting cytokines) thereby reducing the proliferation of T cells.
Agents targeting both signals 1 and 2
Cyclosporine and tacrolimus are termed calcineurin inhibitors (CNIs) due to their common mechanism of action.
Agents targeting both signals 1 and 2
Calcineurin is a phosphatase that dephosphorylates and facilitates the translocation of the nuclear factor of activated T cells (NFAT) (and other nuclear factors) to the nucleus. Once translocated into the nucleus, NFAT promotes the translation of specific genes, including that of the growth promoting cytokine IL-2. Inhibition of calcineurin impairs the expression of IL-2 (and other growth-promoting cytokines), thereby reducing the proliferation of T cells.
Agents targeting both signals 1 and 2
Inhibition of calcineurin impairs the expression of IL-2 (and other growth-promoting cytokines), thereby reducing the proliferation of T cells.
Agents targeting signal 2
Belatacept (Nulojix) is a humanized fusion protein, composed of CTLA-4 fused with the Fc domain of human immunoglobulin G1 (CTLA-4Ig). Belatacept binds to B7 with high affinity and inhibits the costimulatory pathway.
Agents targeting signal 3
Basiliximab is a humanized monoclonal antibody that targets against the α chain of the IL-2 receptor (also known as anti–interleukin-2 receptor [anti–IL-2R] or anti-CD25 antibody), blocking IL-2–mediated responses.
Agents targeting signal 3
mTOR inhibitors: sirolimus and everolimus
Agents targeting signal 3
The mTOR is a key regulatory kinase in the cell division process. Its inhibition reduces cytokine-dependent cellular proliferation at the G1 to S phase of the cell division cycle.
Lymphocyte-depleting agents
Thymoglobulin is a polyclonal antibody preparation made by immunization of rabbits with human lymphoid tissue. The purified immunosuppressive product contains cytotoxic antibodies directed against a variety of T-cell markers.
Lymphocyte-depleting agents
Thymoglobulin causes lymphocyte depletion through various mechanisms, including (1) complement-mediated lysis of lymphocytes, (2) lymphocyte uptake by the reticuloendothelial system, and (3) masking lymphocyte cell surface receptors.
Lymphocyte-depleting agents
Thymoglobulin use can result in prolonged lymphopenia, and the CD4+ helper T-lymphocyte subsets may be suppressed for several years. Such prolonged immunosuppressive effect may prevent rejection recurrence.
Lymphocyte-depleting agents
Thymoglobulin can also cause rapid expansion of the subset of T cells that express CD4+CD25+ and FOXP3+ also known as regulatory T cells (Tregs). Tregs are different from helper T cells in that their presence may limit antigraft immunity. High levels of Tregs increase the chance of reversal of acute rejection.
Lymphocyte-depleting agents
Alemtuzumab is a humanized monoclonal antibody targeting against CD52 on the surface of both B and T lymphocytes leading to a rapid and profound depletion of peripheral and central lymphoid cells.
Antimetabolites
Mycophenolic acid (MPA) derivatives (mycophenolate mofetil [MMF], mycophenolate sodium) MMF (CellCept) is a prodrug that must be hydrolyzed to the active agent—MPA— in the gastric acidic milieu.
Antimetabolites
MPA is a reversible inhibitor of the enzyme inosine monophosphate dehydrogenase (a rate-limiting enzyme in the de novo synthesis of purines). Depletion of guanosine nucleotides by MPA has a relatively selective antiproliferative effect on lymphocytes due to their reliance on the de novo pathway of nucleotide synthesis.
Antimetabolites
Mycophenolate sodium (Myfortic) is an enteric-coated formulation of MPA that dissolves at pH >5.5. Therefore, unlike MMF, mycophenolate sodium bypasses the acidic milieu of the stomach and is absorbed in the intestines.
Antimetabolites
The use of antacids or proton pump inhibitors (PPIs) can reduce the dissolution of MMF by increasing gastric pH. In contrast, the bioavailability of mycophenolate sodium is not affected by antacids or PPIs.
Azathioprine (AZA)
AZA is a precursor of 6-mercaptopurine. AZA inhibits DNA replication and subsequent T-cell proliferation. MMF/mycophenolate sodium has largely replaced AZA due to its greater efficacy in reducing acute rejection.
Corticosteroid
Key component of all immunosuppressive regimens Modulates inflammatory mediators Blocks interleukin-1 (IL-1) and IL-2 production, thereby suppressing the early phase of the immune response
A standard immunosuppressive protocol consists of induction and maintenance immunosuppression
All kidney transplant recipients also receive prophylactic therapy with an antibiotic, antiviral and antifungal agent, and a nondihydropyridine calcium channel blocker to boost CNI or mTOR inhibitor levels.
Induction therapy
Lymphocyte-depleting or non–lymphocyte- depleting agent
Standard triple-maintenance immunosuppression
- Calcineurin inhibitor
- Adjunctive agent
- Corticosteroids
- Cyclosporine or tacrolimus
- Mycophenolic acid derivatives, sirolimus (or everolimus), or azathioprine.
- Maintenance dose: prednisone 5 mg daily
Supplementary agents
Nondihydropyridine calcium channel blockers
Infection prophylaxis
PJP (trimethoprim and sulfamethoxazole, dapsone, atovaquone), CMV (acyclovir, valganciclovir), antifungals (nystatin, fluconazole)
Induction therapy
Induction therapy can be classified into lymphocyte-depleting and non–lymphocyte-depleting agents. The choice of one induction agent over the other is generally based on each individual immunologic risk factors or anticipated delayed graft function (DGF) or both
Induction therapy
In the presence of anticipated DGF due to donor acute tubular necrosis (ATN), it is important to maintain adequate immunosuppression.
Induction therapy
It has been suggested that endothelial injury upregulates and exposes donor histocompatibility antigens, adhesion molecules, and costimulatory molecules, heightening the risk for acute rejection.
Induction therapy
Induction therapy with lymphocyte-depleting agent and delayed introduction of CNI may avoid the additive injury associated with CNI nephrotoxicity (due to afferent arteriolar vasoconstriction) while reducing the risk of allograft rejection at the time of heightened immunogenicity.
Lymphocyte-depleting agents:
Thymoglobulin
Alemtuzumab
Non–lymphocyte-depleting agents:
Basiliximab
Daclizumab - No longer commercially available in the U.S.
Lymphocyte-depleting agents:
Thymoglobulin
Alemtuzumab
Lymphocyte-depleting agents can cause first-dose reaction or cytokine release syndrome including chills, fever, arthralgia, and rarely serum sickness.
Alemtuzumab is used at a small number of transplant centers in the United States.
Thymoglobulin vs basiliximab induction
Thymoglobulin: commonly used in high immunologic risk patients (eg, highly sensitized or re-allograft transplant recipient, DSA positive) or anticipated delayed graft function to avoid early exposure to cyclosporine or tacrolimus (nephrotoxic)
Thymoglobulin vs basiliximab induction
Basiliximab: commonly used in low to moderate immunologic risk transplant recipients
Maintenance immunosuppression is used to sustain a therapeutic net state of immunosuppression in order to prevent rejection.
A standard maintenance immunosuppressive regimen consists of triple drug therapy: CNI (cyclosporine or tacrolimus) + adjunctive agent + corticosteroid.
CNI: The choice of tacrolimus over Cyclosporine A (CSA) or vice versa is generally based on the potential adverse effects of these agents
Tacrolimus is the preferred agent for women and pediatric patients due to the cosmetic side effects of CSA such as hirsutism or hypertrichosis and gingival hyperplasia.
Cyclosporine is less diabetogenic than tacrolimus, and it may be the preferred agent for patients at risk for posttransplantation diabetes mellitus (PTDM) such as those with a strong family history of diabetes or African American race, particularly those with concomitant hepatitis C infection.
Tacrolimus-treated patients with tremors or hair loss can be switched over to CSA.
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Nephrotoxicity
CSA > Tac
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Hypertension and sodium retention
CSA > Tac
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Hyperlipidemia
CSA > Tac
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Diabetes mellitus
Tac > CSA
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Neurotoxicity (headache, tremors, confusion, paresthesia)
Tac > CSA
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Thrombotic microangiopathy
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Gastrointestinal side effects (hepatotoxicity approximately 4% first month, dose related)
Side Effect Profiles of Cyclosporine and Tacrolimus
Both cause Hyperkalemia