Molecular Biology of Lymphoma

Dr Ramesh PurohitAcharya Tulsi Regional Cancer Treatment & Research

Centre, Bikaner

Lymphoma classification(based on 2001 WHO)

• B-cell neoplasms– Precursor B-cell neoplasms – Mature B-cell neoplasms – B-cell proliferations of uncertain malignant potential

• T-cell & NK-cell neoplasms– Precursor T-cell neoplasms – Mature T-cell and NK-cell neoplasms – T-cell proliferation of uncertain malignant potential

• Hodgkin lymphoma– Classical Hodgkin lymphomas – Nodular lymphocyte predominant Hodgkin lymphoma

Thirty diseases, one name:Try to imagine a single type of cell giving rise to nearly thirty different types of cancer - all with one name. Lymphoma - simply in the nodes, a mass in your brain, a disease of your stomach, or lesions all over your skin. It's not simply a matter of location. The behavior changes with the type and so does the treatment and the outcome.

The microscope isn't enough:Even a couple of decades back, what the pathologist saw under the microscope with simple stains was all that we had to identify the type of lymphoma. And there were only a few types of lymphoma that could be distinguished. However, it often turned out that the behavior of the same type of tumor was different in different individuals. Clearly, we were missing something.

The clue is in the molecules: MOLECULAR BIOLOGY (including Immunophenotyping and Genetic studies)

Use of Immunophenotyping and Genetic Studies in the Diagnosis of Lymphoid Neoplasms

The lymphoid neoplasms each have a characteristic morphology, which is sometimes sufficient to permit diagnosis and classification if well-prepared adequately sized sections are available.

However, there are many pitfalls in the histologic diagnosis of malignant lymphoma, immunophenotyping and genetic studies are extremely useful for resolving differential diagnostic problems.

Immunophenotyping and genetic studies are also developing key roles in patient management beyond diagnosis, including

• identification of prognostic molecules, • detection of minimal residual disease, and • assessment of appropriate molecules for targeted therapy.

Rule out other disorders associated with lymphocytosis

If lymphoproliferative disorder remains a significant possibility after clinical evaluation, cell surface phenotyping of lymphocytes should be performed.

Usually performed on peripheral blood using flow cytometry.

Technique provides percentage of lymphocytes positive for a particular antigen and density of antigens.

Normal peripheral blood lymphocytes consist of approximately 10% B-cells, 80% T-cells and 10% NK-cells

Need for Molecular Diagnosis

Flow Cytometry

to see markers on the surface of the cells.

This is a test that uses fluorescent antibodies to tag molecules on the surface of cells.

The flow cytometer has a teeny tube that allows the cells to flow one at a time past a laser beam.

In addition to telling what kinds of markers a cell has, you can also sort cells by size and complexity.

CD MarkersThe “CD” stands for “cluster designation / cluster of differentiation” It’s just a way of referring to the different molecules on the surface of cells so that instead of having all kinds of different names for these molecules, there is just one name (a number, actually) for each molecule.

It’s used for lots of different purposes, one of the most common (in hospital practice, anyway) being to find out what markers are on the surface of cells.e.g. In a g leukemia case, the cells expressed CD 13 and CD 33, you’d know the cells were myeloid, and that it was most likely an acute myeloid leukemia.

sometimes it’s the absence of a marker that helps you with the diagnosis. e.g. if you have a lymphoid neoplasm in which the cells are small and mature looking, and by flow those cells are CD5 positive but CD23 negative, you’d be able to rule out chronic lymphocytic leukemia and lean towards a diagnosis of mantle cell lymphoma.  Flow cytometry is super helpful with making a specific diagnosis.

CD Markers Most commonly used markers (CD = cluster designation)

B-cell – CD10, CD19, CD20, CD22, CD23, CD24, CD79b, CD103, Pax-5, kappa, lambda, CD200, cytoplasmic kappa, cytoplasmic lambda

T-cell – CD1, CD2, CD3, CD4, CD5, CD7, CD8, TCR α-β, TCR γ-δ, cytoplasmic CD3

Myeloid/monocyte – CD11b, CD13, CD14, CD14, CD15, CD33, CD64, CD117, myeloperoxidase

Miscellaneous – CD11c, CD16, CD25, CD30, CD34, CD38, CD41, CD42b, CD45, CD56, CD57, CD61, HLA-DR, glycophorin, TdT, bcl-2

CD Markers

CD1a, CD207: Langerhan cell histiocytosis cellsCD2, CD3, CD4, CD5, CD7, CD8: T cellsCD10: Early pre-B cells (immature B cells)CD11c, CD25, CD103, CD123: Hairy cell leukemia cellsCD13, CD33, CD117: Myeloid cellsCD14, CD64: Monocytic cells (positive in AML-M4 and AML-M5)CD15 :Reed-Sternberg cells, neutrophilsCD16, CD56: Natural killer cellsCD19, CD20, CD21, CD22 : B cellsCD23 and CD5 : Chronic lymphocytic leukemia/small lymphocytic

lymphomaCD23 negative and CD5 positive: Mantle cell lymphoma cells

CD Markers

CD30 and CD15: Reed-Sternberg cellsCD30 positive and CD15 negative: Anaplastic large cell lymphoma CD31: Endothelial cells (positive in angiosarcoma)CD33: Myeloid cells and precursorsCD34: Stem cells (also positive in angiosarcoma)CD41, CD61: Megakaryocytes and platelets (positive in AML-M7)CD45 : All leukocytes (except Reed-Sternberg cells!)CD45 RO: Memory T cellsCD45 RA: Naive T cellsCD68: Histiocytes (positive in malignant fibrous histiocytosis)CD99: Ewings sarcoma cellsCD117: Gastrointestinal stromal tumor (GIST) cells, mast cells (positive in mastocytosis), myeloid cells

Stages of Maturation/DifferentiationL

ineages

Lym

ph

oidM

yeloid

• cells are defined by lineage and stage of maturation/differentiation• regulated by signaling pathways and transcription factors•cell “identity” may be determined using morphology, immunophenotyping and molecular/genetic studies

AML

ALL CLL

CML

Lymphomas

Lymphomas

Lymphocyte Differentiation

B-Lineage LymphopoiesisMorphology / Immunophenotyping / Molecular Studies

Markers are helpful in determining:1. Lineage (ex. CD19)2. Maturation (ex. TdT, CD34, CD10)3. Both (ex. sIg)

Status of immunglobulin genes (i.e., germline, rearranged, somatic mutations) has implications for both

lineage and maturation.

B-cell lymphoproliferative disorders

Probable if immunoglobulin light chain restriction is demonstrated by surface typing of kappa or lambda B-cell CLL or mantle cell lymphomas (MCL) are suspected if CD5 is positive and

CD10 is negative Circulating MCL can be mistaken morphologically for B-cell CLL or B-cell prolymphocytic leukemia (B-PLL)

MCL considered in the followingCD20, CD19 – strong intensitySurface immunoglobulin – strongly expressedCD23 – absentDiagnosis

Molecular and FISH testingRequires t(11;14) translocation demonstration

CLL is more likely whenCD20 – weak intensitySurface immunoglobulins –  weakly expressedCD23 – presentCD200 – present

B-cell lymphoproliferative disordersCirculating germinal center cell-derived lymphoma is probable if CD10 is positive and CD5 is negative

Germinal center lymphomas – follicular, Burkitt lymphoma, diffuse large B-cell lymphoma (DLBCL)Diagnosis

Some cases can be confirmed by demonstration of  t(14;18) breakpoint by PCR or FISH testingPCR detects approximately 80% of t(14;18) translocations found in follicular lymphoma

FISH is more sensitive for this translocation in fixed tissueFISH can also detect an MYC or BCL6 rearrangement for BL or DLBCL

Marginal zone lymphoma should be considered if both CD5 and CD10 are negative

Hairy cell leukemia (HCL) has a characteristic phenotype that is CD5-, CD10-, CD11c+, CD22+, CD25+, and CD103+

CD103 antigen (also known as B-ly7) is present in virtually all casesCD11c and CD25 are less specific but present in almost all cases of hairy cell leukemiaHCL variant can be considered in otherwise typical cases of HCL when CD25-

T-cell lymphoproliferative disordersMost show abnormalities of pan T-cell antigens CD2, 3, 5, or CD7T-cell disorders

Proliferating lymphocytes are usually positive for CD3Most common form is large granular lymphocytosisUsually show rearrangement of TCR locusClonality assessed by flow cytometry, PCR or next generation sequencing (NGS)

Large granular lymphocytosis is suspected if percentage of CD16+, CD56+, or CD57+ T cells is >50% or if absolute count of these cells >2,000/µL

Angioimmunoblastic lymphoma has characteristic CD10+ and CD4+, and CD52-, CD56-, and CD16-

Anaplastic large cell lymphoma – CD30+ and ALK(+)Some pan T-cell antigens are frequently deleted

Sézary syndrome should be considered if CD4+, CD7-, and CD26-

Hodgkin’s Lymphoma

NLPHL is immunophenotypically distinct from other types of HL. The lymphocytic and histiocytic (L&H) cells usually express

• LCA (CD45), • immunoglobulin J chain, • B-cell antigens (CD19, CD20, CD22, CD79A, and BCL-6), • and epithelial membrane antigen (EMA) and are negative for CD15 and CD30 (Fig. 7-1 C and D ). These results suggest that the L&H cells are B cells that arise from the germinal center.

The L&H cells are negative for T-cell antigens but are often surrounded by a rosette of small, reactive T cells that may be positive for pan–T-cell antigens and CD57. Epstein-Barr virus (EBV) is almost always absent in the L&H cells of NLPHL

Immunophenotyping in Hodgkin’s Lymphoma

Immunophenotypic Findings in Classical Hodgkin's Lymphoma

positive for CD15 and CD30 and

negative for LCA (CD45) and EMA .

B-cell antigens—such as CD20, CD79A, PAX-5/BSAP, and

MUM1/IRF4—are expressed in a subset of cases.

CD20 expression is often weak.

T-cell antigens are usually not expressed by the neoplastic cells.

BCL-2 is positive in up to half the cases and has been correlated

with poorer prognosis.

EBV is common in the Reed-Sternberg and Hodgkin cells of

classic HL

Hodgkin's Lymphoma and Cell Lineage both NLPHL and classical types of HL, the neoplastic cells arise from B-cell precursors .

neoplastic cells of HL carry monoclonal immunoglobulin (Ig) gene rearrangements. In NLPHL, the Ig gene rearrangements are usually functional, and Ig mRNA transcripts can be identified in most L&H cells. The Ig gene variable regions also carry somatic mutations. As the process of somatic mutation is restricted to the germinal center of secondary lymphoid follicles, the presence of somatic mutations suggests that NLPHL arises from germinal center B cells.

In classical HL, over 95% of cases carry monoclonal Ig gene rearrangements, with somatic mutations in the variable regions suggesting germinal center B-cell origin. However, unlike the case in NLPHL, there are defects in Ig transcription, and thus Ig mRNA transcripts are often absent. In 25% of cases, the mutations are extensive or involve stop codons, so-called "crippling mutations.”

NHL

Follicular Lymphoma FL is a neoplasm of mature B-cell lineage

Most grade 1 and 2 tumors express immunoglobulin, but a subset of FLs, mostly grade 3, may be immunoglobulin-negative.

All FLs express pan–B-cell markers, and typically express immunoglobulin and B-cell antigens at high density ("bright" immunofluorescence by flow cytometry).

These neoplasms also express the germinal center-associated markers CD10 and BCL-6 and are negative for T-cell antigens.

BCL-2 is expressed in 80 to 90% of FLs and is most often negative in grade 3 neoplasms.

As BCL-2 is negative in reactive germinal centers, this marker is helpful in differential diagnosis

The cytogenetic hallmark of FL is the t(14;18)(q32;q21), which is identified in 80 to 90% of neoplasms.

However, a small subset of FLs lack the t(14;18) including • grade 3B nodal FL• FLs arising in extranodal sites, such as skin, • and FLs occurring in children.

Other cytogenetic abnormalities have been reported in FL. Of these, trisomy 7 and 18, abnormalities of 3q27-28 and 6q23-26, and 17p deletions are most frequent.

Abnormalities of 3q27-28 involve the bcl-6 gene and most often occur in the form of translocations .

Follicular Lymphoma

DLBCLs are of mature B-cell lineage. Approximately two-thirds of cases express monotypic immunoglobulin (Ig);

approximately one-third of DLBCLs are Ig-negative.

These tumors express pan-B-cell antigens, 60 to 70% express BCL-2, and a subset is positive for CD10 and BCL-6.

Most DLBCLs have a high proliferation rate.

Diffuse large B-cell lymphomas are heterogeneous at the molecular level. A subset of cases carries the t(14;18) involving the bcl-2 gene,

Diffuse large B-cell lymphoma

Another subset of DLBCLs has translocations or other abnormalities involving the bcl-6 gene at chromosome 3q27.

The bcl-6 gene is rearranged in approximately 20 to 40% of DLBCLs, more often in tumors arising in extranodal sites

Gene-expression profiling studies performed in recent years have suggested that DLBCLs can be divided into three groups:

o germinal center cell type, o activated B-cell type, and a third, o noncharacteristic group.

Patients with the germinal center type of DLBCL have a better prognosis independent of the IPI

Diffuse large B-cell lymphoma

Mantle cell lymphoma Immunophenotypic studies have shown that MCLs express monotypic Ig light chain (more often Ig λ), IgM, IgD, pan-B-cell antigens, BCL-2, alkaline phosphatase, and CD5 (23).

Unlike CLL/SLL, MCL is often positive for CD79B and FMC-7 and typically is negative for CD10, CD23, and BCL-6. However, approximately 10% of MCLs can be CD23-positive.

The t(11;14)(q13;q32) is present in virtually all cases of MCL (100). In this translocation the ccnd-1 gene (also known as PRAD1 and bcl-1) on 11q13 is juxtaposed with the Ig heavy chain gene on 14q32, resulting in overexpression of cyclin D1. Cyclin D1 facilitates cell cycle transition from G1 to S phase (101).

Although the t(11;14) is central to the pathogenesis of MCL, the t(11;14) is not sufficient to cause lymphomagenesis. Other molecular abnormalities are also required like mutations in the atm, p16, and p53 genes.

Burkitt lymphomaBurkitt's lymphomas of endemic, sporadic, and AIDS-associated types are of mature B-cell lineage

They express Ig, pan-B-cell antigens, CD10, and BCL-6.

Burkitt's lymphomas have a very high proliferation rate, >99%, using an antibody specific for Ki-67.

These tumors are negative for IgD, CD21, CD23, lymphocyte homing receptors, and T-cell antigens. They are usually negative for BCL-2.

Burkitt lymphoma C-myc translocations are characteristic of Burkitt's lymphoma.

Approximately 80% of cases carry the t(8;14)(q24;q32),

the remaining cases having one of two variant translocations, t(2;8)(p11;q24) or t(8;22)(q24;q11).

Common to each of these translocations is involvement of chromosome region 8q24, the site of the c-myc gene, which is deregulated.

Via these translocations, c-myc is juxtaposed with the Ig heavy

chain on the derivative chromosome 14, or with the Ig κ and Ig λ genes on the derivative chromosome 8.

stemcell

lymphoidprecursor

progenitor-B

pre-B

immatureB-cell

maturenaiveB-cell

germinalcenterB-cell

memoryB-cell

plasma cell

DLBCL,FL, BL, HL

LBL, ALL

CLLMCL

MM

MZLCLL

Genetic alterations Infection Antigen stimulation Immunosuppression

NHL: A heterogeneous group of diseases deriving from

Mature B cells 85% and T cells 15%.

Among B-NHL, most histologic subtypes arise from germinal center (GC) or post-

GC B cells,

In contrast with neoplasms of precursor lymphoid cells, chromosomal translocations associated with mature B and T-cell malignancies do not generally lead to coding fusions between two genes.

They juxtapose the proto-oncogene to heterologous regulatory sequences derived from the partner chromosome.

REG = regulatory sequence.

Proto-oncogene

Proto-oncogene

TRANSCRIPTIONALDEREGULATION

FUSIONPROTEIN

TRANSLOCATION TRANSLOCATION

REG

REG REG

REG

REG REGCODING CODING

COD

CODING CODING

CODING ING

Two exceptions to the deregulation model of NHL

translocations:

t(2;5) of T-cell anaplastic large cell lymphoma and

t(11;18) of MALT lymphoma,

These cause gene fusions coding for chimeric proteins.

Oncogene Protein Translocation Disease

bcl-1 Cyclin D1 t(11;14) MCL

bcl-2BCL2

(antiapoptosis)t(14;18) FL

myc Transcription factor t(8;14) Burkitt’s NHL

bcl-6Zinc-finger

transcription factort(3;14) DLBCL

.

Molecular Testing in Lymphoma

1. Establishing a diagnosis of lymphoma•What is the significance of clonality?

2. Classification of lymphoma

3. Discovery and future developments•Refining prognostic and diagnostic categories•Developing new therapeutic regimens

B

T

BB

B

B

In the presence of antigen T- and B-lymphocytes combine to produce:

Plasma cells/specific antibody

An expanded clone of memory B-cells

A reactive lymphocyte proliferation is polyclonal;Each expanded clone has different gene re-arrangement

A neoplastic lymphocyte proliferation is clonal

•Same gene rearrangement•Same chromosomal abnormality

Polymerase Chain Reaction for IGH chain gene (and TCR gene) re-arrangement can be used to determine pattern of clonality within a lymphoid infiltrate

•Implication: clonality = malignancy

primers

Products: Same size in monoclonal populationDifferent sizes in polyclonal population

Limitations and Pitfalls of Molecular Clonality Studies

1. Limited sensitivity

2. Clonality does not equate with malignancy

3. Ig & TCR re-arrangements are not markers of lineage

4. Pseudoclonality

5. Oligoclonality

6. False positive results

7. False negative results

Disruption of TS loci in NHL: leads to biallelic inactivation, through deletion of one allele and mutation the

other.

The TS genes in NHL: p53, p16, and ATM.

IGH gene rearrangement

No encounter with antigen

DEATH

Encounter with appropriate antigen

SURVIVAL

Naïve B-cell

CD34+

Progenitor B cell

Pre-B cell

Mature B cell: IgM+/IgD+

Immature B cell: IgM+/IgD-

IGK+/-L gene rearrangement

Immunoglobulin gene rearrangements

Pre-B Early B Mature B Plasmacytoid B

Type of B cell lymphoma is a function of:

1) Where the cell was in development/maturation when it went “bad”

2) What molecular derangement occurred

PlasmaActivated BStem cell

Burkitts, FL, DLBCL WM MMMCL, CLLALL

Germinal center

B-cell Lymphoma

Type CD5 CD10 CD19 CD20 CD22 CD23 CD43 CD79a sIg cIgFollicular 1 3 4 4 4 2 1 4 4 0Nodal marginal zone

1 1 4 4 4 1 2 4M4, D1

2

MALT 1 1 4 4 4 1 2 4 M4 2Splenic Marginal zone

1 1 4 4 4 1 0 4 M4 2

CLL/SLL 4 0 4 4 4 4 4 4 D3 2

Lymphoplasmacytic Waldenstroms

1 1 4 4 4 0 3 4M4, D2

4

Mantle Cell 4 1 4 4 4 1 4 4M&D

40

Precursor B-cell(lymphoblastic)

4 3 4 4 4 0 0 4 0 0

Diffuse large B-cell

2 2 4 4 4 0 1 4    

Mediastinal large cell

2                  

Burkitt's 1 4                

Footnote: 0 = negative, 1 = <10% positive, 2 10-50% positivity, 3 = 50-90% positivity and 4 = >90% positive

T-cell CD markersType CD3 CD5 CD7 CD4 CD8 CD30

NK16/56

T-prolymphocytic leukaemia + - + +(-) -(+) - -

T-large granular lymphoproliferative

+ - + - + - +(-)

Mycosis Fungoides + + + - -(+) -(+) -

Cutaneous ALCL + +(-) +(-) +(-) - ++-(+)/-(+)

Primary systemic ALCL +(-) +(-) +(-) -(+) -(+) ++ -

Peripheral T-cell lymphoma, unspecified

+(-) +(-) -(+) +(-) -(+) -(+)-(+)/-(+)

Subcutaneous panniculitis-like T-cell

+ + + -(+) +(-) -(+) -/-(+)

Hepatosplenic T-cell lymphoma + - + - - - +/+(-)

Angioimmunoblastic T-cell lymphoma

+ + - +(-) -(+) - -

Extranodal NK/Tcell lymphoma S -, C + - -(+) -(+) - - -/+

Enteropathy-associated T-cell lymphoma

+ + + -(+) +(-) +(-) -

Adult T-cell leukaemia/lymphoma

+ + - +(-) -(+) +(-) -

Footnote: + = >90% positive:  +(-) = >50% positive;  -(+) = <50% positive;  - = <10% positive.ALCL-Anaplastic large cell lymphoma;  C=Cytoplasmic;  S-Surface.

Question: Identify the disease by this IHC report