Solid Organ Transplantation (2)

Question 1

What is the most common type of organ transplant?

Answer 1

Kidney

Question 2

What is the goal of transplant for heart, liver, and lung transplant vs other transplants?

Answer 2

For heart, liver, and lung - the goal is survival

For kidney, pancreas, and intestine - the goal is to initially improve quality of life, which will result in increased survival

For vascularized composite transplants (limb, face, genitals) - the goal is to improve quality of life

And for uterus transplant (due to uterine infertility) - the goal of transplant is to allow childbearing

Question 3

What is an allograft

Answer 3

an organ or tissue graft from a donor of the same species as the recipient but which is not genetically identical.
(human to human transplant)

Question 4

Preventing __________ of the __________ is crucial to optimize graft function and survival

Answer 4

rejection of the allograft

Question 5

Which are some factors that increase risk of rejection?

Answer 5

Younger recipient (stronger immune response)
Black/AA recipient (more mismatches)
Prior transplant recipient
Older donor
Unrelated donor (greater than related donor)
Deceased donor (greater than living donor because there may be more ischemic injury and damage to organ)

Longer ischemia time (time that the organ was not being perfused)…
-longer warm ischemia (in operating room) and longer cold ischemia (on ice) = increased risk

ABO incompatibility
(should ideally by identical, but has to be at least compatible)

HLA compatibility

Question 6

HLA compatibility

Answer 6

The major histocompatibility complex (MHC) is gene that codes for HLA (human leukocyte antigen) … there is high genetic diversity of HLA - mismatched donor antigens can be a target for the recipients immune system
(HLA is how the immune determines self vs non self, which is why if there is a mismatch, it causes a rejection)

Organs do not need to be perfectly matched, but they can not be incompatible (i.e. if the recipient has an antibody against the donor = incompatible)
-perfect match is ideal but not necessary, but the number of mismatched antigens is associated with rejection risk

When there is time, crossmatch testing is done before transplant
-donor and recipient blood is mixed, if the recipient has antibodies to donor they will bind and result in a positive crossmatch meaning they are incompatible

Question 7

How are rejections classified

Answer 7

Time of onset
-hyperacute
-acute
-chronic

Immunologic mechanism
-T cell mediated (TCMR)
-antibody mediated (AMR)

Question 8

Hyperacute rejections

Answer 8

Immediate rejections (occur within minutes/hours of transplant)
Occur due to the presence of pre formed circulating donor specific antibodies (AMR)

This is irreversible
But, it doesn’t occur a lot because we do crossmatch testing prior to the transplant

Question 9

Acute rejections

Answer 9

Usually happen early (days/weeks) but can occur at anytime after transplant

Early acute rejection - within the first 3-6 months … result of recipient/donor rejection risk factors
Late acute rejection - beyond 6-12 months… usually due to under immunosuppression or non-adherence to immunosuppressants

Usually TCMR (but can be AMR)

This is treatable rejection (the only kind that is treatable, so when we talk about treating rejections in practice, we are talking about acute rejections)

Question 10

Chronic rejection

Answer 10

Delayed and slow onset (months/years after transplant)
TCMR and AMR
Progressive and irreversible

Question 11

Transplant rejection immune response

Answer 11

Ischemia/reperfusion injury “primes” the immune system - non-specific innate immune response

Mismatched HLA on donor cells will result in an adaptive immune response
-antigen presents to t cells (which are the primary immune cells that drive the rejection process)
-T cells become activated, those specific t cells replicate (clonal expansion) and differentiate into effector t cells (CD4 and CD8)
-CD8 will cause cytotoxicity, CD4 will release cytokines more cytotoxic t cells or macrophages or activate b cells (which can then form plasma cells and antibodies and cause cell death via CDC or ADCC)

Question 12

3 signal t cell activation

Answer 12

There are 3 steps in the activation of t cells

Signal 1: TCR stimulating… APC presents antigen on MHC which binds to TCR on t cell

Signal 2: Co-simulation … molecule on APC cell binds to molecule on the t cell

Signal 3: Cytokine signaling …
-signal 2 allows for a full synapse to occur, leading to expression of cytokines, the most important one is interleukin 2
-The t cell will produce IL-2, and also has a receptor, that IL-2 will bind to
-When IL-2 binds to the receptor it will lead to DNA synthesis and clonal expansion of t cells

Question 13

________________ are the primary target of immunosuppression

Answer 13

T cells are the primary target of immunosuppression

Drugs will work extracellularly (large molecules) via interactions with surface receptors or intracellularly (small molecules) to inhibit activation or proliferation signaling pathways
(i.e. to stop the 3 signals that activate t cells)

Note - belatacept works extracellularly, all the other drugs work intracellularly

Question 14

Phases of immunosuppression

Answer 14

Desensitization
-this is done BEFORE transplant, not done much

Induction
-high intensity IV therapy for the first 5-7 days after transplant to prevent early acute rejection

Maintenance
-life long combination therapy to prevent acute and chronic rejection (combo allows us to use lower doses of individual agents to prevent toxicity)

Acute rejection therapy
-done whenever acute rejection occurs (high intensity therapy)

Question 15

Which drugs can be used for maintenance immunosuppression

Answer 15

1. Tacrolimus
2. Cyclosporine
3. Azathioprine
4. Mycophenolate
5. Sirolimus
6. Everolimus
7. Belatacept
8. Steroids

Question 16

Which 2 drugs are calcineurin inhibitors

Answer 16

Tacrolimus
Cyclosporine

Question 17

Calcineurin inhibitor mechanism of action

Answer 17

Block 3rd signal (IL-2 induced proliferation of t cells)

Bind to immunophilins (cyclosporine to CpN and tacrolimus to FKBP) and inhibit calcineurin
(which inhibits production of IL-2)

Why? …
When signal 1 and 2 occur (t cell gets activated) - there is an increase in intracellular calcium
Calcium will activate calmodulin, which will then bind to calcineurin
The calcineurin/calmodulin complex will dephosphorylate NFAT, allowing it to move to the nucleus and cause transcription of IL-2

So, by blocking calcineurin, NFAT never gets dephosphorylated or moves to the nucleus to make IL-2

Question 18

What does cyclosporine and tacrolimus bind to?

Answer 18

They both inhibit calcineurin, but bind to different immunophilins

Cyclosporine binds to CpN
Tacrolimus binds to FKBP

Question 19

Calcineurin inhibitor pharmacokinetics

Answer 19

Low and variable oral bioavailability (effected by food, important to be consistent)

Highly protein bound and erythrocyte bound
-may be varying concentrations in patients with low protein or anemia

Many interactions due to CYP3A4 metabolism
But, is also metabolized by CYP3A5, when it is expressed in some people (some people express it, some don’t, so there is variability in metabolism as well, genetic testing is possible but not done in practice)
Substrate of PgP

Biliary elimination

Because of variability TDM is required

Question 20

Cyclosporine forms (2)

Answer 20

There is a conventional and a modified form
-note there are differences in kinetics of these forms and they are NOT interchangeable

Most of the time when cyclosporine is ordered it is for the modified (micro emulsion form)
-this has more consistent bioavailability

Both are dosed BID

Conventional form has a half life of 10 hours
Modified form has a half life of 8.4 hours

Question 21

Cyclosporine TDM is done by obtaining… (4)

Answer 21

C0, trough, C2, AUC
(C0 used most frequently)

Question 22

Tacrolimus formulations (3)

Answer 22

TAC-IR
-BID
-half life 12-18h

TAC-XL
-QD
-half life 38h

TAC-XR
-QD
-half life 31h

NOTE - formulations are NOT interchangeable

Question 23

Tacrolimus TDM is done by obtaining… (2)

Answer 23

C0, trough
(C0 used most frequently)

Question 24

Calcineurin inhibitor food counseling points

Answer 24

Be consistent with food (whether or not taking with or without food), because food will effect drug concentrations

Question 25

Which ADR is the biggest drawback of calcineurin inhibitors?

Answer 25

Nephrotoxicity (long term use - which they usually are long term - can lead to CKD)

Question 26

Cyclosporine main ADRs (3)

Answer 26

Nephrotoxicity Dyslipidemia Hypertension

Question 27

Tacrolimus main ADRs (5)

Answer 27

Nephrotoxicity Electrolytes (increased potassium, decreased magnesium) Glucose intolerance/diabetes (calcineurin is important to insulin production, so inhibition can result in increased blood sugar) Tremors (neurotoxicity, usually peak level related) Alopecia

Question 28

Calcineurin inhibitor monitoring parameters (7)

Answer 28

1. TDM 2. Serum creatinine/GFR 3. Electrolytes 4. Blood pressure 5. Blood sugar 6. Lipids 7. Tremors

Question 29

Which 2 drugs are antimetabolites

Answer 29

Mycophenolate Azathioprine

Question 30

Mycophenolate MOA

Answer 30

Inhibits de novo purine synthesis, therefore inhibiting lymphocyte replication Purine (guanine) is needed for DNA synthesis, and therefore for B and T cell replication IMPDH, is an enzyme that converts IMP to XMP, which is needed for guanine synthesis Mycophenolate inhibits IMPDH, inhibiting guanine synthesis, therefore inhibiting b and t cell replication

Question 31

2 forms of mycophenolate

Answer 31

Mycophenolate mofetil (MMF) and mycophenolate sodium (MPS) -both are BID

Question 32

Mycophenolate pharmacokinetics

Answer 32

high bioavailability -MMF needs acidic pH for dissolution (but MPS does not) - consider drug interactions with PPIs and H2RAs Highly protein bound Metabolism: hydrolyzed to MPA, which undergoes glucuronidation to MPAG MPAG is transported to the bile, and then undergoes enterohepatic recirculation - results in a second peak concentration -this is important because some drugs may inhibit enterohepatic recirculation - eg, cyclosporine, cholestyramine Excreted primarily in the urine

Question 33

Mycophenolate food counseling considerations

Answer 33

Should be taken consistently in regards to meals (food may effect concentrations)

Question 34

Azathioprine MOA

Answer 34

AZA prodrug > 6-mercaptopurine (6-MP) purine analog 6-MP > TIMP by HRPT and eventually to tioguanine nucleotides (TGN) which get incorporated into DNA causing the cell to undergo apoptosis TIMP is also converted to methyl-TIMP which inhibits purine synthesis and cell replication

Question 35

Azathioprine metabolism

Answer 35

6-MP is converted to inactive metabolites by xanthine oxidase and TPMT -this is important to consider, as xanthine oxidase inhibitors (allopurinol, febuxostat) can therefore result in an increase in toxicity NUDT15 converts cytotoxic TGNs to less cytotoxic TGNs

Question 36

Is TDM required for antimetabolites?

Answer 36

No -can be done with mycophenolate, but not done much in practice

Question 37

Antimetabolite ADRs

Answer 37

Both: -myelosuppression (decreased bone marrow function resulting in fewer RBCs, WBCs, and platelets) Mycophenolate: -GI disturbances (n/v/d) - this is the primary limiting toxicity for MPA -teratogenicity

Question 38

Antimetabolite monitoring considerations (2)

Answer 38

1. CBC -due to dose dependent myelosuppression risk 2. TDM can be done with MPA -AUC preferred, not done much in practice

Question 39

Which 3 corticosteroids are used for immunosuppression

Answer 39

Prednisone Prednisolone Methylprednisolone

Question 40

Corticosteroid MOA

Answer 40

Inhibits gene transcription of important cytokines Steroid binds to glucocorticoid receptor, this steroid-GR complex moves to the nucleus affecting gene transcription -inhibits cytokine expression (including IL-1, IL-2, IFN-gamma, TNF-alpha) = reducing inflammation, causing t cell depletion, decreased APC/macrophage function, and altered leukocyte migration

Question 41

Corticosteroid main ADRs

Answer 41

1. Glucose intolerance/diabetes 2. Dyslipidemia 3. Hypertension 4. Increased appetite/weight gain 5. Osteopenia, osteoporosis 6. Neuropsychiatric effects (insomnia, delirium) 7. Cataracts/glaucoma risk

Question 42

Corticosteroid monitoring

Answer 42

1. Blood glucose (CS stimulate gluconeogenesis and reduce insulin sensitivity) 2. Blood pressure 3. Bone density (CS increase osteoclast and decrease osteoblast function) 4. Weight, BMI, waist to hip ratio (Cushingoid features) 5. Lipids -ASCVD risk assessment should be done 6. Ophthalmology examination (annual) (cataracts/glaucoma risk)

Question 43

Which 2 drugs are mTOR inhibitors

Answer 43

Sirolimus Everolimus

Question 44

mTOR inhibitor MOA

Answer 44

Bind to FKBP (like tacrolimus), but they do not inhibit calcineurin, they inhibit mTORC1 mTOR is a important regulator of cell growth, proliferation, metabolism, and survival mTOR forms mTORC1 (mTOR complex 1) which activates proteins needed for cell proliferation (progression from G1 to S phase) So, by inhibiting mTORC1, these drugs lead to cell cycle arrest and decreased cell proliferation

Question 45

mTOR inhibitor pharmacokinetics

Answer 45

(similar to CNIs) Variable bioavailability -effected by food (counsel patients to be consistent) -requires TDM as a result Metabolism: CYP3A4 and PGP substrates Very long half lives: -62 hours for sirolimus -30 hours for everolimus

Question 46

mTOR inhibitor main ADRs (4)

Answer 46

1. proteinuria -not nephrotoxic, but can worsen nephrotoxicity of CNIs if used together 2. dyslipidemia 3. impaired wound healing 4. Aspermia (males)

Question 47

What ADR do mTOR inhibitors NOT cause, that all other immunosuppressants do?

Answer 47

Malignancy -unlike other immunosuppressants which can cause malignancy, mTOR inhibitors can actually be used to treat malignancy (may be an incentive to switch someone with cancer to a mTOR inhibitor, but not necessarily used for all cancer patients with transplants)

Question 48

mTOR inhibitor monitoring

Answer 48

Before initiation: 1. Wound healing -generally surgical wounds should be healed before starting mTORi because they can cause impaired wound healing 2. Urinary protein to creatinine ratio -due to proteinuria risk (avoid if significant proteinuria) 3. Lipids -due to dyslipidemia risk (initiate dyslipidemia therapy if needed) While on therapy: 1. TDM 2. Urinary protein to creatinine ratio 3. Lipids 4. CBC (myelosuppression risk)

Question 49

Which drug is a costimulation blocker?

Answer 49

Belatacept

Question 50

Belatacept MOA

Answer 50

Inhibits signal 2 Signal 2 is the costimulatory signal of CD80/86 (B7) on the APC binding to CD28 on the T cell (without this costimulation, the T cell will undergo apoptosis) Once the T cell gets activated, it produced CTLA-4, which has a higher affinity for CD80/86, so it will bind and cause t cell cycle arrest Belatacept is a fusion protein of CTLA-4 and a human IgG antibody - so it will bind to CD80/86 (preventing signal 2 from happening) and cause t cell cycle arrest

Question 51

Belatacept adminstration

Answer 51

IV only, monthly infusion

Question 52

Belatacept ADRs and BBW

Answer 52

BBW for: post-transplant lymphoproliferative disorder (PTLD) (type of lymphoma) -high risk if recipient is Epstein barr negative and donor is Epstein Barr positive, so this can only be used in patients (recipients) who are have positive Epstein Barr serology Other ADRs: -infection -infusion reactions -malignancy

Question 53

Belatacept monitoring

Answer 53

Before initiation: Epstein Barr Serology -recipient MUST have positive EBV (otherwise high risk of PTLD) During therapy Weight -because dose adjustments are required if >10% change in body weight IV access

Question 54

Maintenance therapy regimen considerations

Answer 54

Therapy is life long combination therapy, usually a 3 drug regimen -steroid free regimens may be tried in lower risk patients -substitutions may be made to avoid toxicities -rarely some transplant recipients may be able to wean down to one drug or no drugs overtime But in general the regimen is... Primary agent + Secondary Agent +/- Steroid Primary agent: -Calcineurin Inhibitor (Tacrolimus or cyclosporine) Possible substitutions: mTOR inhibitor (sirolimus, everolimus) or belatacept Secondary Agent: -Antimetabolites (MMF or MPS or AZA) Possible substitutions: mTOR inhibitor (sirolimus, everolimus) or belatacept Steroid: -Corticosteroids (Prednisone or prednisolone or methylprednisolone)

Question 55

How to determine new dose for tacrolimus, cyclosporine, sirolimus, and everolimus if concentration was not being met? How is mycophenolate different?

Answer 55

These follow linear kinetics, so you can just use a proportion to find what the new dose should be if you have a trough level and a goal level. The difference with mycophenolate is you use and AUC level - so multiple levels need to be taken and a calculation needs to be done to determine AUC, but then you just plug in the AUC into the proportion the same way... Dose(new) / Css(goal) = Dose(old) / Css(old)

Question 56

IV cyclosporine and tacrolimus considerations

Answer 56

There is a risk of anaphylactoid reaction with IV form because it contains castor oil - so we avoid IV if we can It's important that if IV is used PVC free tubing and bags are used - otherwise the drug will leach to the bags and the patient will not get the full dose

Question 57

Cyclosporine IV to PO conversion

Answer 57

1:3 (IV to PO)

Question 58

Tacrolimus IV to PO conversion

Answer 58

1:4 (IV to PO)

Question 59

Mycophenolate IV to PO conversion

Answer 59

1:1 but it needs to be MMF first and MMF to MPA PO is 1000:720