Here we are going to discuss about the basics of immunolgy involved in liver transplantation.

1. Liver Transplantation
Basic Immunology of
Dr Awadhesh Narayan
MD. DrNB (Gastro)

2. Since 1963, when the first human
liver transplantation (LT) was
performed by Thomas Starzl
Marked improvement in the
Survival
Surgical
Techniques
Perioperative
Care
Immunosuppr
ession
The use of efficient
immunosuppression starting in
the late 1970s represented a
pivotal change in
acute rejection and LT
survival

3. The Liver as an Immune Organ
Liver is continuously exposed to diverse and large antigenic loads, including
pathogens, toxins, and tumor cells, as well as dietary and commensal proteins
It is and simultaneously
responses
Thus being able to selectively
induce
Immunity Tolerance
The context in which
antigen is presented to T cells
determines whether the responding
T cell is or tolerized.
This includes the nature of the
APC, the presence or absence of
costimulatory molecules and the
cytokine microenvironment

4. Whenever Liver is challanged
with Nonself Antigens
(alloantigen)
Immune Responce
Injury
Tolerance

5. Allorecognition
The major histocompatibility
complex (MHC), located on
chromosome 6 in humans, encodes
the human leukocyte antigens
(HLA), are responsible for eliciting
the strongest of responses to
allogeneic tissues

6. MHC II
Expression is limited to APC
like Kuffer cell & Dendritic
cells
MHC I
Present epitopes
to CD4 + helper T-cells
Present epitopes to CD8 +
cytotoxic T-cells
Constitutively expressed by
all nucleated cells
MHC

8. Tolerance
The liver allograft is more immunoprivileged than the other commonly transplanted solid organs
The lower susceptibility to rejection of human liver allografts, as compared to other solid
organ, has been evidenced by their documented capacity to resist poor HLA matching, ABO-
incompatibility and positive cross-matches.
Drug-free tolerance has been reported much more frequently after liver transplantation than
any other organ
Almost 20% of stable and carefully selected liver transplant recipients can be weaned safely off
all immunosuppression

9. LSECs are the
unique liver
resident APCs
which express
Both MHC-I and MHC-II molecules
LSECs take up alloantigens through Pattern
Recignition Receptors, notably the mannose
receptor (MR), process and transfer them to
for the priming of
Priming of naïve CD8 T cells by LSECs
upregulates the expression of the co-
inhibitory molecule
binding of B7-H1 on
LSECs and PD-1 on
naïve CD8 T cells
Apoptosis of the
alloreactive CD8 T
cells
Tolerogenic
environment within
the liver graft

10. LSECs can prime
naïve CD4 T cells
with expression of
MHC-II
But fail to stimulate the
proliferation of these cells
Low expression of co-
stimulatory
molecules
Secretion of immune
suppressive cytokines
IL10
Production of Tregs
cells

12. Regulatory T cells (T reg) in tolerance
• TRegs (CD4+CD25+T) constitute 5–10% of T cells in the periphery.
• Treg control effector T-cells via several distinct mechanisms:
1. production of immunosuppressive cytokine IL-10, TFG-b and IL-35
2. Consumption of IL-2 via the Treg CD25 receptor, thus depriving activated T-cells
of the main driver of proliferation
3. constitutive Treg expression of CTLA-4 which acts as an alternative inhibitory
ligand for B7 on DC with a higher affinity than the co-stimulatory molecule CD28,
thus impairing DC-T-cell interactions.

14. Liver is more tolerogenic than other organs, and matching of donor and recipients is mainly limited to
ABO blood group compatibility.
So long-term immunosuppression is required to avoid acute and chronic rejection and graft loss
With the current immunosuppression protocols, the risk of acute rejection requiring additional therapy is
10–40%
The risk of chronic rejection is below 5%.
Acute allograft rejection occur in approx 50%t to 75% of liver transplant recipients.

15. Types of Graft

16. Hyperacute
Acute
Chronic
Minutes- Hours Days- Weeks Months- Years

17. Hyperacute Rejection
Preformed Antibody Mediated
ABO system antigen
Major Histocompatibility
Complex (MHC)
Antigen against which
these Ab are directed

18. ABO system Antigen
Though ABO blood group antigens are regarded as RBC antigens.
In the liver ABO antigens are mainly expressed on the vascular endothelium and on
the biliary tract cells but not on hepatocytes.
They are actually expressed on a wide variety of human tissues and are present on
most epithelial and endothelial cells
This suggests that ABO-
incompatible hepatocyte
transplantation (ABOi-
HTx) is theoretically
feasible

19. Pathways of Antibody Mediated Injury
Cell lysis

20. Preexisting host antibodies against
ABO antigens are carried to liver
graft
Antibodies binds to antigens of cappilaries
and activate complement system
complements attract neutrophil, which
release lytic enzymes
Lytic enezymes damage endothelial
cells, platelets adhere to damaged
endothelium causing vasculer
blockag
Mechanism of ABO hypperacute rejection in ABO I LT
Extensive endothelial damage and hemorrhagic necrosis

21. Donor-specific HLA alloantibodies(DSAs)
In contrast to other solid organs, the
liver allograft is relatively spared from
the effects of preexisting HLA
antibodies.

22. Proposed Mechanisms of liver allograft resistance to DSA-mediated injury
Recipient

23. 924 transplants with complete donor-recipient HLA typing were retrospectively analyzed
The number of HLAcompatibilities had no influence on graft survival, whereas the
number of acute rejections was significantly less in transplants with more HLA
compatibilities (P<0.05)
There is no current recommendation
regarding routine HLA matching
use in matching liver grafts either in
the DDLT or LDLT settings

24. Acute Celluler Rejection
T cell mediated rejection (TCMR) to donor antigens
Most commonly in the early post-transplant period, majority of rejection episodes occur within the
first month and is generally amenable to treatment.
It typically presents with non-specific clinical symptoms and predominantly cholestatic liver
biochemistry.
Liver biopsy is required for diagnosis, which shows a dense portal-based mixed inflammatory
cell infiltrate with evidence of damage to biliary epithelium, portal and hepatic vein endothelium
and hepatocytes

25. Preservation-Reperfusoion Injury (PRI)
A certain degree of ischemic injury to the allograft is an unavoidable consequence of
transplantation
Occurs during organ transportation to the
transplant center (cold ischemia time)
During organ harvesting and
subsequent implantation (warm
ischemia time)

26. Ischemia
Cell damage
and death.
Release
DAMPs
ATP in hepatocytes
and liver sinusoidal
endothelial cells (LSEC)
Activates
Kuffer
cells
Release of pro-
inflammatory cytokines
such as IL1, TNF, IFN
and IL12
The end result of PRI is the
establishment of a
pro-inflammatory
microenvironment within
the liver.

27. Antigens are
recognised by T cells
through 3 pathways
Direct Indirect Semi-direct

28. Alloantigen presentation by DC is a key step in rejection
DC are present in
portal tracts and
around hepatic
veins
In response to pro-
inflammatory environments
such as PRI they become
activated, and migrate to
lymphoid tissue
Activated donor-
derived DC arriving in
the lymph node
provide a potent
immunological
stimulus for recipient-
derived naïve T-cells
Significant numbers
of donor-derived
DC are transferred to
the recipient as
passengers during
transplantation
Alloantigen Presentation, T-Cell Activation and Maturation

29. Signal 2
Costimulatory Pathways
T lymphocytes must receive two distinct but coordinated signals
in order to achieve optimal activation

30. Interaction between the DC and T-cell
dependents on
Activation of TCR by its
cognate peptide-MHC complex
on the DC
Co-stimulatory molecule
interactions
DC
Since dendritic cells express
MHC class I and class II
molecules they are able to
activate both CD4 + and CD8 +
T-cells
Recipient

32. Costimulatory Pathway
Two costimulatory molecule-ligand pairs that are important in the
generation of a complete T-cell response are-
CD28/B7 CD40/CD154

33. The Ligands for CD28, B7-1 (CD80), and B7-2
(CD86),
are found on a variety of APCs including DCs, B cells,
and macrophages.
In conjunction with TCR stimulation,
ligation of CD28 leads to increased
production of cytokines such as IL-2, cellular
proliferation, and induction of antiapoptotic
proteins

34. (CTLA4) is a CD28 related
protein that is upregulated
upon T-cell activation and,
like CD28, binds to B7-1
and B7-2
Because it has a higher affinity for
B7 than CD28 does, it has been
proposed that the physiologic
function of CTLA4 is to dampen
or downregulate T-cell responses
CTLA4 delivers a
negative signal that
attenuates T-cell
function
Whereas CD28 delivers
a positive costimulatory
signal to T cells

35. Belatacept is a fusion protein of the
Fc fragment of a human IgG1
linked to the extracellular domain of
CTLA-4

36. This phase II study evaluated the safety and efficacy of belatacept in de novo adult liver transplant
recipients
Follow-up beyond month 12 revealed an increase in death and graft loss in belatacept group, after which
the study was terminated.

37. CD40/CD154

38. In presence of costimuation
In abscence of costimuation

39. T cell receptor-mediated signaling pathways for T cell
activation and development
Various signaling pathways are involved in TCR signaling
• Ras-extracellular signal-related kinase (ERK)-activator protein (AP)-1
pathway
• Protein kinase C (PKC)θ-IĸB kinase (IKK)-nuclear factor (NF)-κB
pathway
• Tuberous sclerosis complex (TSC)1/2-mammalian target of rapamycin
(mTOR) pathway

40. Ras-ERK pathway
Transcription of c-Fos
and Jun B.
Induces interleukin
synthesis

41. IP3-Ca2+-nuclear factor of activated T cells (NFAT) pathway
Production of the T cell
proliferative cytokine IL-2

42. Tuberous sclerosis complex (TSC)1/2- mTOR pathway

44. Once primed
Exert direct cell
damage on the
allograft
CD8 + T-cells
differentiate into
cytotoxic T-cells (Tc)
CD4 + T-cells
differentiate into a
number of activated
subtypes
Th1, Th2 ,Th17 and
Treg subsets

45. CD8+ Tc Cells
Main effector lymphocytes responsible for mediating tissue damage
Granzyme/perforin
pathway
Fas-FasL pathway

46. CD4 + Th
Cells
Induce
tolerance
Interact with
activated B-cells to
produce DSA.
Also important for
the recruitment of
eosinophils
Th17 cause tissue damage by
IL-17 production which acts as
a powerful signal for neutrophil
recruitment.
Th2
Th17
Th1
Treg
Production of and
IFN-g is important for
macrophage activation and
stimulation of CD8 + Tc cell

48. Principal Categories Morphological Criteria Score
Portal inflammation Inflammation of lymphocytes compromises a minority of the triads. 1
Expansion of portal triad due to inflammation of lymphocytes, plasma cells,
neutrophils, eosinophils and some blasts.
2
Marked portal expansion due to heterogeneous inflammatory infiltrate with numerous
blasts and eosinophils in all or the vast majority of the portal triads extending to the
periportal area
3
Bile duct
inflammation and
damage
Occasional ducts have epithelial inflammation and damage with some reactive changes 1
Most ducts are inflamed, and there are degenerative changes 2
All ducts are compromised by inflammatory cells, and there are severe degenerative
alterations in the ductal epithelium, with obstruction of ducts.
3
Inflammation of
venous
endothelia
Subendothelial infiltration of lymphocytes compromising some portal and/or hepatic
venules.
1
Subendothelial inflammation of lymphocytes into most hepatic and/or portal venules,
endothelial cell detachment
2
Moderate to severe subendothelial inflammation of lymphocytes in hepatic and/or
portal veins, central venous compromise, endothelial detachment and perivenular
necrosis.
3
Rejection Activity Index (RAI) for Acute Cellular Rejection

49. Overall evaluation Criteria
No rejection:
0-1 Indeterminate or
borderline: score of 2-3
Inflammation of portal lymphocytes that does not meet minimum
criteria for diagnosis.
Mild: score of 3-4 (grade I) Infiltrate characteristic of acute heterogeneous cellular rejection in a
minority of portal triads and confined to the portal space
Moderate: score of 5-7
(grade ii)
Infiltrate characteristic of acute cellular rejection in most of the
portal triads
Severe: score of 8-9
(grade iii)
Infiltrate characteristic of acute cellular rejection in almost all portal
triads, moderate to severe cell density extending the periportal
region and to the hepatic parenchyma with perivenular necrosis

50. Before initiating treatment of ACR,
the other diagnoses should be
confirmed

51. Chronic rejection
Chronic rejection is less well-defined than either hyperacute or acute rejection
Chronic rejection is an indolent but progressive form of allograft injury which eventually results
in the failure of most vascularised solid organ allografts
By 5 years after transplantation, it affects as many as 30-50% of heart, lung, pancreas and kidney
allograft recipients, but only 4-8% of patients who undergo liver replacement
It is the single most significant obstacle to morbidity-free long-term survival
Liver allografts differ from other solid
organs in that chronic rejection is
potentially reversible.
This feature has been mainly attributed to
its unique immunobiological privilege
and the of the
process

52. Chronic rejection is often asymptomatic, with gradual worsening results in liver function
tests—predominantly elevation of alkaline phosphatase and mild transaminitis
Graft biopsy is required to differentiate chronic rejection from disease recurrence, biliary
complications, and other diseases
Episodes of acute rejection regardless of the immunosuppressive regimen
often precedes the onset of chronic rejection
When diagnosed early, however, alterations of the immunosuppressive regimen can
sometimes salvage the graft
younger recipient age, male to-female sex mismatch, a primary diagnosis of AIH or biliary
disease and noncaucasian recipient race have been associated with an increased risk of
developing CR.

53. Pathogenesis
Class I MHC and
class II MHC antigens
are readily expressed
on biliary epithelial
cells
Chronic
ductopenic
rejection.
Direct
lymphocytotoxic
attack aimed at
MHC antigens

54. Endothelial
cells also express
HLA class I
antigens and
increased levels of
HLA class II
antigens during
inflammatory
processes
Vascular obliterative
lesions caused by intimal
proliferation and hyper-
trophy resulting from
repetitive endothelial
injury and repair
secretion of cytokines by
activated lymphocytes
Because the sole blood supply in
the biliary tract in human beings is
derived from hepatic artery
branches
Ischemic
damage to the
bile ducts

56. Banff criteria is
used for histologic
diagnosis of
chronic rejection
Foam cell
obliterative
arteriopathy
Diffuse biliary
epithelial senescence
changes with or
without bile duct loss
Bile duct loss
affecting greater than
50% of the portal
tracts

57. Proposed sequence of events leading to the development of chronic
rejection in liver transplantation
DSA, donor-specific antibody; IR, ischemia-reperfusion; TCMR, T-cell-mediated rejection.

58. Cellular site of action of the immunosuppressive agents

59. Summary
Liver is an
immunoprevileged
organ
The liver is more tolerogenic than other
solid organs, and matching of donor and
recipients is mainly limited to ABO
compatibility
Hyperacute rejection is an extremely
rare event despite the lack of MHC
matching which is not true of other
organ transplants
Acute liver allograft rejection does occur
in approx 50% to75% & majority are
readily reversed with immunosuppressive
approaches
Despite all immunosupressive
measures Chronic rejection
resulting in graft failure still
occurs in about 3% to 4%