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Introduction and Approach to
Transplantation Pathology
Disclosures
• Omnyx – Clinical development team and
potential for eventual equity shares
• Wyeth - Consultant
• Bristol-Myers Squibb - Consultant
• DCL/Novartis - Consultant
Transplant Pathology
General Considerations
• Allograft pathology (and reporting) is the same as native
organ pathology, except for syndromes unique to the
allograft:
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Preservation/reperfusion injury
Rejection
Opportunistic viruses
Malignancies
GVHD
• Final diagnosis is based on extensive clinicopathologic
diagnosis
• More than one insult can contribute to the injury and
diagnostic hierarchy should be assigned, if possible.
• Pathophysiologic approach usually trumps morphological
approach, but combination is best
Rejection is a Process
not a specific type of immune response!
• Immune system redundancy and complexity
enables many different pathways for organ
damage/destruction
• Similarities among individuals enables gross
classification into T-cell mediated and AMR
• Various immunologic effector mechanisms are
more or less accentuated in individual patients
• Changes in immunosuppressive therapy:
– Affect the timing, severity, or histopathologic quality
of rejection
– Newer “biologically-based” IS agents are creating
unique immunologic conditions and deficiencies
(unusual infections at unusual sites).
Leukocyte Migration
Peripheral and Central Recognition
(Demetris et al Early events in liver allograft rejection: Am J Pathol 1991; 138: 609)
– Donor leukocytes travel to recipient
lymphoid tissues
• Immunologic “imprint” varies with
organ
– Recipient leukocytes infiltrate organ
– Genetic non-identity triggers
proliferation and apoptosis
• Leads to:
– Acute rejection
– Regulatory responses
• Treg, apoptosis, etc.
Adaptive Immunity and T Lymphocytes
• Naïve T lymphocytes (CD45RA)
– Longer response time, might require central
lymphoid tissue, less potent effector functions
• Memory T lymphocytes (CD45RO)
– Shorter response time, activated in organs, more
potent effector functions
– Generated by:
• Previous exposure to alloantigen
– Blood transfusion or other tissue tx; pregnancy
• Infection/molecular mimicry
– Pathogen-specific T cells cross-react with alloantigens
• Homeostatic Proliferation
– Natural or iatrogenic lymphopenia induces proliferation of
residual cells, many of which have Tm phenotype
Immunosuppression Strategies
Steroid bolus
P.R.N.
Prednisone
Tacrolimus
Ab-depletion Rx
Immune Responses
Irreversible
Rejection
More Agspecific
clonal
deletion
Pretreatment
Tx
Epitope
spreading
Homeostatic
proliferation
Classification of Rejection
• Antibody-mediated Rejection (AMR)
– Early after Tx can be catastrophic (hyperacute)
– Later onset usually associated with activation of
development of memory cells, poorer response to therapy
and diminished survival
– Major contributor to chronic rejection
• Acute or T Cell-Mediated
– Most episodes occur within 6 months; later in inadequately
immunosuppressed patients.
– Sub-classified by severity and whether there is overlap
with antibody-mediated rejection
• Chronic Rejection
– Usually occurs more than 6 months after Tx; except for
liver
– Generally irreversible except for liver
– Staging is important to help approach further therapy
Antibody-Mediated Rejection
• Antibodies may be preformed or develop after
transplantation
– Anti-endothelial cells most deleterious (ABO,
lymphocytotoxic)
– Susceptibility = kidney > heart > intestine > lung >
liver
– Increased risk in multiparous women, previous blood,
or tissue exposure
• Recognized histopathologically as microvascular
endothelial “activation”, leukocyte margination,
injury and congestion, lymphocytic and
necrotizing arteritis
• Definitive diagnosis usually requires clinical
dysfunction, typical histopathologic changes and
evidence of antibody-mediate injury and
circulating anti-donor antibodies.
Acute “Cellular” or T Cell Mediated Rejection
• Mediated primarily by inflammatory cells
– T lymphocytes, macrophages, B cells, eosinophils, and
neutrophils
• Most active period is during the first 6 months after
Tx unless Ab-depletion therapy used
– Later episodes:
• inadequate immunosuppression
• Immune reconstitution
• Grading Used to Help Guide Therapeutic
Intervention
– Indeterminate/minimal/borderline, mild, moderate,
and severe
Basis for Histopathologic Grading of Acute
Rejection
• Severity and Distribution of Inflammation
– Localized or diffuse
– Estimate of amount of tissue injury
• Direct or Indirect Evidence of Microvascular or
Arterial Injury and Ischemia
– Inflammatory or necrotizing arteritis
– Interstitial hemorrhage w/o necrosis
– Confluent necrosis
Chronic Rejection
Risk Factors
• Immune Factors – Primary
– Number and severity of acute cellular and AMR
episodes
– Matching
• MHC, Sex, Race
– Infections
• CMV, Polyoma virus, bronchiolitis
• “Non-immune” - Secondary
– older donors, cold ischemia, donor
atherosclerosis, inadequate functional capacity
Major Problem in Transplantation
Immune graft damage
Fibrosis
Chronic Rejection
DM, ↑BP,
Renal failure
Opport. Infections
Tumors
CPC Conferences Keep Amplitude
of Drift Low
Rejection
Rejection
Infection
Infection
Special Procedures Needed
• Specialized stains used for native kidney, liver,
lung, pancreas, and small intestinal biopsies
• IPEX or IF staining for IgGs and C (esp. C4d)
• IPEX staining and/or ISH for viruses that
commonly affect allograft recipients:
– BK/Polyoma, EBV, CMV, HSV, VZ, Adenovirus,
HHV-6, HBV,
• Genetic analysis for origin of tissue:
– XY ISH, specific anti MHC Abs, genetic identity
testing
• Electron Microscopy: F/U of renal allograft
biopsies
Use of Gene Arrays in Transplantation
Purvesh Khatria and Minnie M. Sarwal
Current Opinion in Organ Transplantation 2009, 14:34–39
• The current standard in allograft dysfunction
diagnosis is histopathology, which is subjective,
non-quantitative, and does not offer any
insights into rejection mechanisms. On the
contrary, gene expression profiling using
microarray can provide objective, quantitative
gene expression, which in turn can provide
mechanistic insights into pathogenesis of
transplant rejection.
Limitations of Microarrays
• Loss of spatial and temporal relationships
• Deconvoluting gene signatures
– Effects of multiple conflicting factors
• Age, sex, medications, circumstances of biopsy
• Expensive and requires time to complete
• Post translational events not included
• Multiple gene assays limits dynamic range of
MA compared to real time PCR
• Overwhelming amount of data generated on
infinite variations
Reporting on Allograft Biopsies
• Final diagnosis should be based on extensive
clinicopathologic correlation
• More than one insult can contribute to the injury and
diagnostic hierarchy should be assigned, if possible.
• Provide Value in Your Report!
• Liver Allograft, Needle Biopsy:
– Negative for acute cellular and chronic rejection (RAI = 0/9).
– Chronic hepatitis, recurrent HCV, mildly active (mHAI =
6/18).
– Mild to moderate portal/periportal fibrosis (Fibrosis stage =
2/6).
– Compared to the previous biopsy of 01/01/2009 the current
biopsy shows increased fibrosis and architectural distortion.
Conclusions
• Antigen migration/lymphoid trafficking early
after transplantation important concept
• Working knowledge of immunologic events and
mechanisms greatly assists clinical practice and
research
• Final interpretation should be based on complete
clinicopathologic correlation
• Specialized staining procedures needed for
complete specimen evaluation
• Reporting should be complete, hierarchical, if
needed, and answer clinical questions/concerns