Pathophysiology of Hematologic Malignancies
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Transcript of Pathophysiology of Hematologic Malignancies
Pathophysiology of Hematologic Malignancies
Mehtap Kaçar Koçak M.D., PhD
Yeditepe University, Faculty of Medicine
WHO Classification of Hematopoietic and Lymphoid Tumors: B-cell Neoplasms
Indolent
• Chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma
• Lymphoplasmacytic/Waldenstrom’s macroglobulinemia (WM)
• Hairy cell leukemia
• Marginal zone lymphoma
– Extranodal mucosa-associated lymphoid tissue (MALT)
– Nodal
– Splenic
• Follicle center lymphoma, follicular, grade I-II
Aggressive
• Prolymphocytic leukemia
• Plasmacytoma/multiple myeloma
• Mantle cell
• Follicle center lymphoma, follicular, grade III
• Diffuse large B-cell lymphoma (DLBCL)
• Primary mediastinal large B-cell lymphoma
Very Aggressive
• Precursor B-lymphoblastic lymphoma/leukemia
• Burkitt lymphoma/ B-cell acute leukemia
• Plasma cell leukemia
Jaffe E, et al. IARC Press, World Health Organization, 2001.
Pathophysiology of Hematologic Malignancies: Relationship to Normal Hematopoiesis
Basic mechanisms of oncogenesis + extraordinary features of hematologic cells:
• Differentiation• Diverse and dynamic mechanisms of mobilization,
localization, activation, targeting• Biology of immune system/response• Stromal interactions• Interface with infectious diseases
Normal Immune System
• Innate
• Acquired
B cells – antibody production
T cells - detection of foreign peptide in setting of MHC
How do the lymphocytes that can recognize (and attack) the infectious/foreign material
become active?
Innate Immunity
• Innate immunity: immediately identifies the infectious or “dangerous”agent and attacks it; focuses on crude and general features of the agent that identify it as foreign or “dangerous”
Advances in Immunology: New England Journal of
MedicineDelves, Roitt, Medzhitov,
Janeway
CpGfmetLPSTeichoic acidmannan
MHC – window to the inside of the cell
Natural Killer CellsVirus
Virus
MHC
Acquired Immunity requires diversity of B and T cells to allow interaction with an
estimated 1014 epitopes
Diversity: B cells• The body makes new lymphocytes by jumbling the
recognition genes so that no 2 new lymphocytes that are made are identical:
Each lymphocyte recognizes something different
Gene rearrangements & mutations result in billions of new lymphocytes that
recognize unique objects
Diversity: T Cells (a spectrum of T cells, each with
different receptors that can bind to different peptides)
How do the T cells get smart enough to distinguish “self” from “foreign”?
Early steps in T-cell selection: Get rid of the bad ones
• T-cells leave BM• Undergo TCR gene
rearrangement & selection in thymus
• T-cells that have high level autoreactivity die
• T-cells that are not capable of reacting with foreign peptides + MHC also die
thymus
Bone marrow
Can’t react with self peptide & canreact with foreignpeptide
RIP
Immune Reaction
Germinal Center
Acquired Immune System: How to generate a specific immune response
Events Leading to GC Reaction• Once stimulated by foreign organism or cell, resident DC take up ag
and migrate to draining LN
• If pathogens enter blood – filtered by DC in spleen
• DCs directed towards T cell zones of secondary lymphoid tissue by CCR7 & chemokine ligands CCL19, CCL21
• DCs mature during migration – CD80, CD86 allowing presentation in MHC II to CD4+ cells (TCR [signal 1] & CD28 [signal 2]) with further maturation of T cells into Th
skin
antigen
Lymph node
T-cells that can react withantigen on cells survive;
others die
lymphatic
T-cells from thymus
RIP
Keeping the good T cells around:
• Th cells result in activation of ag-specific B cell responses
• Initial Th-B cell interactions occur in T cell zones adjacent to follicles
• B cell receptor binding to ag [signal 1] and CD40 ligation [signal 2] required for B cell activation
• In addition to CD154, T cells also provide ICOS, a CD28-related protein that binds to B7-H2, a B7-like molecule constitutively expressed on B cells
Functional Characteristics of GC B Cells• GC - extensive B cell proliferation and
differentiation
• Doubling times of 6-10 hours
• Non-dividing GC B cells apparent towards the end of the first week
• Humans proliferating and nonproliferating B cells separate into distinct zones in the GC
– Centroblasts continue to expand in dark zone
– Centrocytes falling out of cycle segregate in light zones
• Molecular events of selection in GC: isotype switching, somatic hypermutation, affinity selection & apoptosis
• GC founder B cells • CD4+ Th• FDC networks support GC-B cell differentiation by
displaying immune complexed ag for extended periods of time and providing co-stimulation
• Distinct set of macrophages
becomes prominent and
ingest apoptotic B cells
resulting from failed selection
– “tingible bodies”
Cells Involved in the GC Reaction
a. Green – Ki67Red - IgM
b. Green – FDC M1Red – PNA (B cells)
c. Green – FDC M1Red - IgM
Kosco-Vilbois. Nature Immunol3:764.2003
• Somatic hypermutation (SHM) localized to GC– point mutations in variable regions of L and H chains– requires transcription; AID; uracil DNA glycosylase (UNG); error
prone DNA polymerases (); MSH2– most active in second and third week post-immunization– mutations first random [low replacement:silent ratio (R:S)]– change over time to selection of high affinity– immune complexes bound to FDC drive selection– low affinity (poor signaling through BCR) & autoreactive (signaling
by soluble ag) GC clones eliminated (similar to selection events in BM)
– GC B cells express high levels of Fas & Bax and low levels of bcl-2– 10-5 - 10 -3/base pair/division– base pair substitutions beginning -150-200 and extending 1.5 kb to
intronic enhancer, sparing C region– Sequence based “hot spots” – preferential targeting to
W(A/T)R(A/G)CY(T/C)– Transitions > transversions
Aberrant SHM
• Targets 5’ regions of BCL-6, FAS/CD95, C-MYC, PAX5, RhoH/TTF
• ? others
• Isotype switching – class switch recombination (CSR) – replacement
of with or constant regions
– cutting, looping/excision and joining process
– after challenge with T-dependent (TD) ag isotype switching is found in follicular and extra-follicular locations
– 3-4 d after immunization transcripts localized to areas of extrafollicular B cell activation resulting in “switched” short-lived AFC early in response
– isotype switching continues in GC
Immune cells that canbind to foreign materialtravel to lymph nodes
If there is anything to bindin the lymph node an editing processstarts; changing a few letters at a time to enhance binding
No/poor binding Lymphocyte death
High level bindingSURVIVAL(e.g after influenza vaccine only a lymphocyte that binds to flu lives) Editor
Follicular Dendritic Cells• FDC processes form strings of immune complex
coated bodies (iccosomes)• Trap and retain unprocessed ag
– FcRIIb (CD32)– FcRII (CD23)
• Immune complexed ag + DC + c’- >> stimulation of B cells than soluble ag
• Synapse + (GM1, BCR, phosphotyrosine containing proteins, PLC2, actin) – (CD45, CD22, SHP1)
• Interactions with FDC necessary to avert apoptosis – induction of FLIP; support ex vivo growth of NHL & H-RS cells
• CD32 inhibition – prevention of autoimmunity
Patient Question: How Did My Lymphoma Develop?
Mutations:the foundation of oncogenesis
Spontaneous mutation rate:1/1,000,000,000nucleotide/cell division
6 mistakes/cell division
>10,000,000,000 bone marrow and lymphocyte cell divisions/day
Nucleus DNA- 6,000,000,000 nucleotides (letters)
6 mutations
6 mutations6 mutations
6 mutations
6 mutations
“It was the best of dines,…”
“It was the best of diners,…”
“It was the best of dining,…”
+lymphoma
Normal rearrangement
Editor
Patient Question: What Did I Do Wrong?
Nothing: Many Mutations• 100,000,000,000,000,000
MUTATIONS IN EACH OF US FROM CONCEPTION-75 YEARS OLD
• ~ 94,608,000,000,000,000 SECONDS in 3 BILLION YEARS
•Mutations are random and most don’t significantly impact on the behavior of the cell;
What prevents the early uniform development of cancer ?
•Cancer occurs as a consequence of a series of very specific mutations in very specific cells at critical times in their development;
•Protective mechanisms: any cell can cause trouble; no single cell is criticalprogrammed cell death.
D. Hanahan & R.A. Weinberg. Cell (2000)
100:57-70
The The Hallmarks of Hallmarks of CancerCancer
B Cell Receptor• Survival of normal B cells
– Selection for for expression of BCR• Selection of pre-BCR in BM• Selection of functional non-autoreactive BCR in BM• Affinity selection in GC
– Mature resting B cells must express BCR to avert apoptosis
• BCR dependency of B-cell lymphomas– BCR expressed on nearly all B cell lymphomas– Translocations into non-productively rearranged
allele– Ongoing V region gene mutations during clonal
selection
BCR• Rare B cell lymphomas do not express
BCR– cHL (40% with EBV – ? LMP2A may
replace BCR signaling – but entire complex downregulated); downregulation of transcription factors, inactive chromatin
– PTLD– PEL– PMBCL
BCR• Antigen stimulation of BCR in NHL
– B-CLL• BCR binds autoantigens• HTLV-1• subgroups with similar VH and VL gene rearrangement
sequences
– PCNS lymphoma• 80% carry somatic V region mutations; same VH
region in ~50%
– FL• ongoing somatic mutation• ~ 80% FL & BL carry somatic mutations that result in
generation of carbohydrate linking motifs (<10% of nl B cells)
• Reciprocal translocations involving Ig loci– Bcl2-IgH associated with FL have breakpoints that are
directly adjacent to JH or DJH and loss of nucleotides at end of JH or DH - characteristic of VDJ recombination in BM
– Breakpoints within rearranged VDJ with somatically mutated V regions - translocation as a byproduct of SHM
– Breakpoints in IgH constant region switch point region – byproduct of class switch recombination
• Strand breaks in non-Ig genes: aberrant SHM– Bcl2 gene altered DNA structure recognized by RAG
nucleases
Transformation Events
Transformation Events• SHM
– Chromosomal translocations– Targeting of non-Ig genes
• Bcl-6 in normal and malignant GC B cells• Inactivating mutations of CD95• Myc
• Non reciprocal genetic alterations– P53 mutations, IkB mutations, genomic
amplification of Rel, API2-MALT1
• Infections– EBV, HHV-8
WHO SHM Ongoin
g SHMGCB
Mol Path Origin
SLL +/- - -
MCL - - - t(11;14) Pre GCB
BL + - + t(8;14); t(2;8), t(8;22)
GCB
DLCL GCB
+ + + bcl-2, bcl-6 GCB
DLCL ABC
+ - -
MZL + + - t(11;18); t(1;14); t(14;18)
Post GCB
Kwong Br J Haem 137:273.2007
Microenvironment• In vitro dependence upon stroma and
cytokines• Role of cellular microenvironment in cHL
Role of the Microenvironment in cHL
• Reactive cellular infiltrate– CD4+ lymphocytes – regulatory phenotype CTLA-4+
(CD4+CD10+ & CD4+CD25+)– Few CD4+Th1 & CD8+ CTL – production of IL-4, IL-13, IL-
10, TGF- by H-RS cells
• Eosinophils attracted by IL-5• Cytokines, chemokines & TNF R family members
– Cytokines: favor Treg cell formation; VEGF– Chemokines: TARC (CCL17) & MDC (CCL22) bind to
CCR4 on Th2 cells; eotaxin (CCL11); CCL28 – eosinophils & plasma cells
– TNF receptor family: CD30 & CD30L expression but CD30 induction of NFkB is CD30L independent; CD40 & RANK (autocrine RANK & RANKL)