**1. Introduction**

[33] Sonneveld, P, Schmidt-wolf, I. G, Van Der Holt, B, et al. Bortezomib Induction and Maintenance Treatment in Patients with Newly Diagnosed Multiple Myeloma: Re‐ sults of the Randomized Phase III HOVON-65/ GMMG-HD4 trial. J Clin Oncol.

[34] Moreau, P, Pylypenko, H, Grosicki, S, et al. Subcutaneous Versus Intravenous Ad‐ ministration of Bortezomib in Patients with Relapsed Multiple Myeloma: a Rando‐

[35] Moreau, P, Richardson, P. G, Cavo, M, et al. Proteasome Inhibitors in Multiple Mye‐

[36] Hoering, A, Crowley, J, Shaughnessy, J. D, et al. Complete Remission in Multiple Myeloma Examined as Time-dependent Variable in Terms of Both Onset and Dura‐

[37] San-miguel, J. F, & Mateos, M. V. Can Multiple Myeloma Become a Curable Disease?

mised, Phase 3, Non-inferiority Study. Lancet Oncol. (2011). , 12, 431-40.

tion in Total Therapy Protocols. Blood (2009). , 114(7), 1299-1305.

loma: 10 Years Later. Blood (2012). , 120(5), 947-59.

Haematologica (2011). , 96(9), 1246-8.

(2012). , 30(24), 2946-55.

12 Multiple Myeloma - A Quick Reflection on the Fast Progress

Secretion of monoclonal immunoglobulins (M-Ig) may be associated with several malignant conditions, also called M-protein, paraprotein, or M-component they are produced by an abnormally expanded single (''mono-'') clone of plasma cells in an amount that can be detected in serum, urine, or rarely in other body fluids [1]. The M-Ig can be an intact immunoglobulin (Ig) (containing both heavy and light chains), or light chains in the absence of heavy chain (encountered in light chain myeloma, light chain deposition disease, AL amyloidosis), or rarely heavy chains in the absence of light chains only (heavy chain disease).

All intact Igs have the same structure, made up of mirror imaged identical light and heavy chains. There are five classes of heavy chain, γ, α, μ, δ and ε with two classes of light chain κ and λ. Igs are secreted by terminally differentiated B-lymphocytes and their normal function is to act as antibodies recognizing a specific antigen.

During B-cell maturation, the rearrangement of Ig heavy and light chain genes takes place early in pre-B-cell development and ends in memory B-cells or Ig producing plasma cells that have a unique heavy and light chain gene rearrangement, thus being selected to recognize a given antigen. During, oncogenic events which occur randomly during this process, the B cell may acquire a survival advantage, and proliferate into identical (clonal) daughter B-cells able to differentiate into Ig producing cells secreting a monoclonal component. With additional oncogenic events a mature B-cell neoplasm may develop, carrying the inherent ability to produce a monoclonal Ig. Multiple myeloma and Waldenstrom's macroglobulinaemia are architypical of Ig-secreting B-cell disorders.

© 2013 Kyrtsonis et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The purpose of this present chapter is to describe the properties of M-Igs and discuss the biologic, clinical and other implications of their presence in the course of B-cell disease entities.

reactive antibodies (Abs) [8]. The CD5 molecule negatively regulates BCR signals [9] and CD5

Monoclonal Immunoglobulin http://dx.doi.org/10.5772/55855 15

Lymph node (LN) colonization depends on the expression of L-selectin and integrin αLβ2 (LFA-1), while recruitment to mucosa-associated lymphoid tissues (MALT) depends on expression of L-selectin and integrin α4β7. Without antigenic stimulation, the naive B cells

Activation of mature naive B cells into Ig secreting plasma cells can be T-helper independent (TI) and antigen free, via invariant receptors (TI-1), or derives from crosslinking of the BCR by polyvalent Ags (TI-2). More frequently, it is performed in close collaboration with CD4 expressing T cells (T-helper dependant: TD), and results from a monovalent Ag aggression. MZ B cells of the spleen and other mucosal sites, mostly respond to TI-2 Ags, such as poly‐ saccharides of bacterial cell walls and other bacterial components, able to crosslink BCRs [11]. IgM+ MZ B cells that are CD27+ are memory cells while CD27- are naïve; their BCRs display

BM: Bone Marrow, S: Spleen, B: Blood, LN-GC: Lymph Node-Germinal Center, MZL: Mantle Cell Lymphoma, MM: Multi‐ ple Myeloma, LPL: Lymphoplasmacytic Lymphoma, WM: Waldenstroms Macroglobulinaemia, FL: Follicular Lympho‐ ma, CLL: Chronic Lymphocytic Leukemia, BL: Burkitt Lymphoma, HCL: Hairy Cell Leukemia, DLBCL: Diffuse Large B Cell

T-helper-cell dependent (TD) B-cell activation takes place in germinal centers (GC) in response to the presence of free Ags, as part of immune complexes or at the surface of Ag presenting

Lymphoma, HD: Hodgkin Lymphoma, SHM: Somatic Hypermutations, CSR: Class Switch Recombination.

**Figure 1.** Schematic of B-cell Maturation and B-Lymphoproliferative Disorders Origin

B cells represent 50% of poly-/self-reactive cells [10].

recirculate again.

poly- and self- reactivity.

#### **2. Ontogeny of normal and monoclonal Ig-producing B-cells**

#### **2.1. B-cell development**

B-cell maturation is a complex process that comprises both cell differentiation into Ig secreting plasma cells and, in parallel, the rearrangement of the genes responsible for Ig synthesis. Furthermore it includes inherent risks of genetic derailment because it is associated with DNA remodellingwithintrinsicinstability,thuspresentingthepossibilityofmalignantdevelopment.

B cell development begins in the bone marrow (BM) from gestation week 18 and throughout life. The generation of pro-B cells from a common lymphoid progenitor cell depends on two main transcription factors, E12 and E47 and on the contribution of the transcriptional regula‐ tors EBF and Pax-5 [5]. During B-cell evolution the rearrangement of Ig heavy and light chain genes takes place [2]. The Ig heavy gene (IgH) is located on chromosome 14 while Ig light chain (IgL) genes are on chromosomes 2 and 22 for κ (1-40 vκ, 1-5 jκ and 1cκ) and λ (1-30 vλ, 1-4 jλ and 1-4cλ) light chain respectively. Rearrangement of IgH and IgL genes allows variable (V), diversity (D) and joining (J) gene segments rearrangement. V(D)J recombination starts in precursor B cells (pre B-I); recombinase activating genes 1 and 2 (RAG-1 and RAG-2), are essential for this step. The resulting IgVH is frequently not functional therefore the pre-B cell initiates V(D)J recombination at the other allele. If this is successful, the complete IgVH will be expressed as an Igμ H chain in the cytoplasm (Cy-Igμ) and on the membrane, together with a surrogate light chain, the pre B cell receptor complex (pre-BCR). Accordingly the pre-B-II cell proliferates, then looses its pre-BCR and re-express RAG proteins [7]. At that point, the Bcell is transformed into a small pre B-II cell that will subsequently rearrange the IgL variable gene segments and expresses a mature membrane BCR. If the BCR is not strongly self-reactive, the immature B cell leaves the BM as transitional B cell that evolves into naive B cell in the spleen; alternatively, it may mature in the periphery. However, if the immature B cell is still self-reactive, it will remain in the BM for additional IgVL recombination, replacing the selfreactive IgVL by another IgVL and so on. B cells producing self-reactive BCRs are removed from the repertoire during maturation by BM silencing mechanisms [3;4]. Splenic transitional B cells (CD27- CD5+ CD10+ CD24hi CD38hi and L-selectinlo) undergo differentiation into mature naive B2, also called follicular (FO) B cells, or marginal zone (MZ) B cells [5]. The aforemen‐ tioned B-cell population is characterized by limited proliferative capacity and survival upon BCR stimulation; it comprises less than 2% of the peripheral B cells [6]. While maturating in the spleen, transitional B cells loose CD10 and CD5 and start expressing higher levels of L selectin and CD44. Following which the B cell transforms into conventional naive B2 cells that recirculate via the blood to the secondary lymphoid tissues or organs [7]. MZ cells could represent the normal counterpart of marginal zone lymphoma cells and CD5+ B-cells the one of mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Blood also contains a small normal population of naive CD5+ CD27- cells that frequently produce poly-/selfreactive antibodies (Abs) [8]. The CD5 molecule negatively regulates BCR signals [9] and CD5 B cells represent 50% of poly-/self-reactive cells [10].

The purpose of this present chapter is to describe the properties of M-Igs and discuss the biologic, clinical and other implications of their presence in the course of B-cell disease entities.

B-cell maturation is a complex process that comprises both cell differentiation into Ig secreting plasma cells and, in parallel, the rearrangement of the genes responsible for Ig synthesis. Furthermore it includes inherent risks of genetic derailment because it is associated with DNA remodellingwithintrinsicinstability,thuspresentingthepossibilityofmalignantdevelopment.

B cell development begins in the bone marrow (BM) from gestation week 18 and throughout life. The generation of pro-B cells from a common lymphoid progenitor cell depends on two main transcription factors, E12 and E47 and on the contribution of the transcriptional regula‐ tors EBF and Pax-5 [5]. During B-cell evolution the rearrangement of Ig heavy and light chain genes takes place [2]. The Ig heavy gene (IgH) is located on chromosome 14 while Ig light chain (IgL) genes are on chromosomes 2 and 22 for κ (1-40 vκ, 1-5 jκ and 1cκ) and λ (1-30 vλ, 1-4 jλ and 1-4cλ) light chain respectively. Rearrangement of IgH and IgL genes allows variable (V), diversity (D) and joining (J) gene segments rearrangement. V(D)J recombination starts in precursor B cells (pre B-I); recombinase activating genes 1 and 2 (RAG-1 and RAG-2), are essential for this step. The resulting IgVH is frequently not functional therefore the pre-B cell initiates V(D)J recombination at the other allele. If this is successful, the complete IgVH will be expressed as an Igμ H chain in the cytoplasm (Cy-Igμ) and on the membrane, together with a surrogate light chain, the pre B cell receptor complex (pre-BCR). Accordingly the pre-B-II cell proliferates, then looses its pre-BCR and re-express RAG proteins [7]. At that point, the Bcell is transformed into a small pre B-II cell that will subsequently rearrange the IgL variable gene segments and expresses a mature membrane BCR. If the BCR is not strongly self-reactive, the immature B cell leaves the BM as transitional B cell that evolves into naive B cell in the spleen; alternatively, it may mature in the periphery. However, if the immature B cell is still self-reactive, it will remain in the BM for additional IgVL recombination, replacing the selfreactive IgVL by another IgVL and so on. B cells producing self-reactive BCRs are removed from the repertoire during maturation by BM silencing mechanisms [3;4]. Splenic transitional B cells (CD27- CD5+ CD10+ CD24hi CD38hi and L-selectinlo) undergo differentiation into mature naive B2, also called follicular (FO) B cells, or marginal zone (MZ) B cells [5]. The aforemen‐ tioned B-cell population is characterized by limited proliferative capacity and survival upon BCR stimulation; it comprises less than 2% of the peripheral B cells [6]. While maturating in the spleen, transitional B cells loose CD10 and CD5 and start expressing higher levels of L selectin and CD44. Following which the B cell transforms into conventional naive B2 cells that recirculate via the blood to the secondary lymphoid tissues or organs [7]. MZ cells could represent the normal counterpart of marginal zone lymphoma cells and CD5+ B-cells the one of mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). Blood also contains a small normal population of naive CD5+ CD27- cells that frequently produce poly-/self-

**2. Ontogeny of normal and monoclonal Ig-producing B-cells**

**2.1. B-cell development**

14 Multiple Myeloma - A Quick Reflection on the Fast Progress

Lymph node (LN) colonization depends on the expression of L-selectin and integrin αLβ2 (LFA-1), while recruitment to mucosa-associated lymphoid tissues (MALT) depends on expression of L-selectin and integrin α4β7. Without antigenic stimulation, the naive B cells recirculate again.

Activation of mature naive B cells into Ig secreting plasma cells can be T-helper independent (TI) and antigen free, via invariant receptors (TI-1), or derives from crosslinking of the BCR by polyvalent Ags (TI-2). More frequently, it is performed in close collaboration with CD4 expressing T cells (T-helper dependant: TD), and results from a monovalent Ag aggression. MZ B cells of the spleen and other mucosal sites, mostly respond to TI-2 Ags, such as poly‐ saccharides of bacterial cell walls and other bacterial components, able to crosslink BCRs [11]. IgM+ MZ B cells that are CD27+ are memory cells while CD27- are naïve; their BCRs display poly- and self- reactivity.

BM: Bone Marrow, S: Spleen, B: Blood, LN-GC: Lymph Node-Germinal Center, MZL: Mantle Cell Lymphoma, MM: Multi‐ ple Myeloma, LPL: Lymphoplasmacytic Lymphoma, WM: Waldenstroms Macroglobulinaemia, FL: Follicular Lympho‐ ma, CLL: Chronic Lymphocytic Leukemia, BL: Burkitt Lymphoma, HCL: Hairy Cell Leukemia, DLBCL: Diffuse Large B Cell Lymphoma, HD: Hodgkin Lymphoma, SHM: Somatic Hypermutations, CSR: Class Switch Recombination.

**Figure 1.** Schematic of B-cell Maturation and B-Lymphoproliferative Disorders Origin

T-helper-cell dependent (TD) B-cell activation takes place in germinal centers (GC) in response to the presence of free Ags, as part of immune complexes or at the surface of Ag presenting cells (APC). B-cells then differentiate into short-lived, Ab-forming plasma cells or proliferate as centroblasts expressing CD10+, CD38+ and BCL-6. These centroblasts express low amounts of the BCR at their surface and undergo somatic hypermutations (SHM), by accumulating nucleotide substitutions in their Ig variable (*IgV*) genes [12;13]. GC activated B-cells are meant to be short-lived, except for the few with a high affinity IgV region (BCR) for the Ag. These high-affinity B cells are selected in the GC light zone, and may undergo class switch recom‐ bination (CSR), switching the IgM/IgD sequence with any of the other downstream region sequences [14]. Igs formed early in the context of normal response to an Ag aggression are of IgM and IgD isotypes; these are located on the B-cell surface as recognition receptors. Then activated B cells divide, and class switching from the IgD and IgM heavy chains to IgG, IgE or IgA classes takes place [15;16]. The process is regulated by various cytokines [16] while both SHM and CSR depend on the B-cell-specific enzyme activation-induced cytidine deaminase (AID) which is highly expressed by GC B cells [17]. Cytokines and costimulatory soluble factors stimulate the transcriptional activation of individual I promoters and determine the S region and Ig isotype involved in the CSR event. SHM depends on transcription of the variable (IgVH and IgVL) regions and leads to point mutations and, to a lower extent, insertions and deletions. The rate of SHM is about 1 mutation on 1000 nucleotides per cell division. CSR consists on transcription of the S regions that started upstream of an I exon that is located 5' of each S region, giving rise to non-coding germline transcripts that span the I exon, the S region and downstream CH exons [7].

elling. Thus, the initiating steps of the malignant B-cell transformation concern erroneous V(D)J rearrangement. Recurrent translocations involving the IgH or IgL locus and observed in B-cell lymphoproliferative disorders are shown in table 1, in relation to their biologic

Regulator of CDKs

G1→S

renewal

CDK4/CDK6 required for cell cycle transition

Monoclonal Immunoglobulin http://dx.doi.org/10.5772/55855 17

proliferation regulation & differentiation

Transcription factor, cell proliferation, differentiation, apoptosis, stem cell self

hematopoiesis regulation

of tumor & stromal cells

**Disease Entity IgH Translocation Gene Involved Biologic Consequences**

MM t(6;14) Cyclin D3 Cell cycle: G1→S transition

FL t(14;18) Bcl2 Antiapoptotic

by CCND1

MM t(14;20) MAFB Transcription factor, lineage specific

MM t(4;14) FGFR3 Signal transduction, pathways activation, cell

MM t(14;16) c-MAF Cell cycle Stimulation. Promote interactions

Monoclonal gammopathy of undetermined significance (MGUS) is a pro-neoplastic condition that may evolve into multiple myeloma (MM) or other B-cell lymphoproliferative disorders. MGUS represent a first step in the development of monoclonal diseases while the progression of MGUS to MM or other entities may be secondary to a random second genetic event. Several studies indicate that the majority of IgH locus aberrations reported in MM are already present in MGUS, favoring the hypothesis that these are early genetic events in the progression leading

In MM, the most frequent partners in reciprocal translocations involving the IgH locus on chromosome 14q32, are 11q13 (15%), 4p16 (5%), 16q23 (5%), 21q12 (2%) and 6p21 (2%); two additional partners are also found rarely 12p13 (<1%) and 8q24 (<1%). Thus, the aforemen‐ tioned translocations may deregulate seven oncogenes involved, CCND1, CCND2, CCND3, MAF, MAFB, MAFA and FGFR3/MMSET [24]. The overall rate of 14q32 translocations increases with disease progression and reaches 90% in advanced tumors. Light chain translo‐ cations are rather rare in MM, particularly Igκ, which seem to be very infrequent [25]. Changes in the expression of gene subsets could be partly responsible for disease heterogeneity, as well as for further disease transformation. Moreover, with the 11q13 partner, constitutive upregu‐ lation of cyclin D1 results, deregulating the cell cycle [26]; t(11;14) is accompanied with a higher frequency of CD20 expression, hyposecretory disease and λ light chain usage. This subtype is increasingly encountered in AL amyloidosis, with or without MM, and in the rare IgM MM

repercussions in disease entities concerned.

BL/MM t(8;14) myc

to MM [23].

**Table 1.** Main Recurrent Translocations Involving The IgH Locus

MCL/MM t(11;14) Cyclin D1 encoded

Terminally differentiated B cells become either Ab-producing mature plasma cells that home to the bone marrow or memory cells [18]. Memory B cells (CD27+) are Ag-selected B cells, derived from TD GC responses and usually express either IgM- IgD- or IgM+ IgD+, comprising about 20% of all peripheral B cells. A small percentage of IgM only (IgM+ IgD-) and IgD only (IgM- IgD+) also exists. IgD-only B cells have undergone a Cμ deletion due to a non-canonical CSR event, express Igλ, contain extremely high levels of somatic IgV mutations [19] and show a strongly biased V3-30 IgVH gene usage [20], that can be seen in some malignant B-cell disorders [2]. Memory B-cells are long-lived, prone to Ig class switch (to IgG, IgA or IgE) and contain hypermutated IgV genes. Following stimulation, they present a competitive advantage over naive B cells in rapidly transforming themselves into plasma cells producing high affinity, class switched, IgG/IgA Abs [21]. They may hide in BM niches and recirculate numerous times. It is believed that in most indolent B-cell lymphoproliferative disorders, a proneoplastic condition precedes where the precursor neoplastic B-cell circulates and recirculates as a memory cell.

#### **2.2. Malignant transformation**

Where one or more oncogenic events occur during B-cell maturation, the resulting daughter cell will be identical and, if it has the ability to differentiate into an Ig producing cell, it will secrete a monoclonal component. Consequently, all B-cell mature neoplasms [22] have a common origin as well as the inherent ability to produce a monoclonal Ig.

Malignant B-cell Non-Hodgkin's lymphoma (NHL) possibly develops because risks for genetic derailment are increased during SHM and CSR that are associated with DNA remod‐ elling. Thus, the initiating steps of the malignant B-cell transformation concern erroneous V(D)J rearrangement. Recurrent translocations involving the IgH or IgL locus and observed in B-cell lymphoproliferative disorders are shown in table 1, in relation to their biologic repercussions in disease entities concerned.


**Table 1.** Main Recurrent Translocations Involving The IgH Locus

cells (APC). B-cells then differentiate into short-lived, Ab-forming plasma cells or proliferate as centroblasts expressing CD10+, CD38+ and BCL-6. These centroblasts express low amounts of the BCR at their surface and undergo somatic hypermutations (SHM), by accumulating nucleotide substitutions in their Ig variable (*IgV*) genes [12;13]. GC activated B-cells are meant to be short-lived, except for the few with a high affinity IgV region (BCR) for the Ag. These high-affinity B cells are selected in the GC light zone, and may undergo class switch recom‐ bination (CSR), switching the IgM/IgD sequence with any of the other downstream region sequences [14]. Igs formed early in the context of normal response to an Ag aggression are of IgM and IgD isotypes; these are located on the B-cell surface as recognition receptors. Then activated B cells divide, and class switching from the IgD and IgM heavy chains to IgG, IgE or IgA classes takes place [15;16]. The process is regulated by various cytokines [16] while both SHM and CSR depend on the B-cell-specific enzyme activation-induced cytidine deaminase (AID) which is highly expressed by GC B cells [17]. Cytokines and costimulatory soluble factors stimulate the transcriptional activation of individual I promoters and determine the S region and Ig isotype involved in the CSR event. SHM depends on transcription of the variable (IgVH and IgVL) regions and leads to point mutations and, to a lower extent, insertions and deletions. The rate of SHM is about 1 mutation on 1000 nucleotides per cell division. CSR consists on transcription of the S regions that started upstream of an I exon that is located 5' of each S region, giving rise to non-coding germline transcripts that span the I exon, the S region and

Terminally differentiated B cells become either Ab-producing mature plasma cells that home to the bone marrow or memory cells [18]. Memory B cells (CD27+) are Ag-selected B cells, derived from TD GC responses and usually express either IgM- IgD- or IgM+ IgD+, comprising about 20% of all peripheral B cells. A small percentage of IgM only (IgM+ IgD-) and IgD only (IgM- IgD+) also exists. IgD-only B cells have undergone a Cμ deletion due to a non-canonical CSR event, express Igλ, contain extremely high levels of somatic IgV mutations [19] and show a strongly biased V3-30 IgVH gene usage [20], that can be seen in some malignant B-cell disorders [2]. Memory B-cells are long-lived, prone to Ig class switch (to IgG, IgA or IgE) and contain hypermutated IgV genes. Following stimulation, they present a competitive advantage over naive B cells in rapidly transforming themselves into plasma cells producing high affinity, class switched, IgG/IgA Abs [21]. They may hide in BM niches and recirculate numerous times. It is believed that in most indolent B-cell lymphoproliferative disorders, a proneoplastic condition precedes where the precursor neoplastic B-cell circulates and recirculates as a

Where one or more oncogenic events occur during B-cell maturation, the resulting daughter cell will be identical and, if it has the ability to differentiate into an Ig producing cell, it will secrete a monoclonal component. Consequently, all B-cell mature neoplasms [22] have a

Malignant B-cell Non-Hodgkin's lymphoma (NHL) possibly develops because risks for genetic derailment are increased during SHM and CSR that are associated with DNA remod‐

common origin as well as the inherent ability to produce a monoclonal Ig.

downstream CH exons [7].

16 Multiple Myeloma - A Quick Reflection on the Fast Progress

memory cell.

**2.2. Malignant transformation**

Monoclonal gammopathy of undetermined significance (MGUS) is a pro-neoplastic condition that may evolve into multiple myeloma (MM) or other B-cell lymphoproliferative disorders. MGUS represent a first step in the development of monoclonal diseases while the progression of MGUS to MM or other entities may be secondary to a random second genetic event. Several studies indicate that the majority of IgH locus aberrations reported in MM are already present in MGUS, favoring the hypothesis that these are early genetic events in the progression leading to MM [23].

In MM, the most frequent partners in reciprocal translocations involving the IgH locus on chromosome 14q32, are 11q13 (15%), 4p16 (5%), 16q23 (5%), 21q12 (2%) and 6p21 (2%); two additional partners are also found rarely 12p13 (<1%) and 8q24 (<1%). Thus, the aforemen‐ tioned translocations may deregulate seven oncogenes involved, CCND1, CCND2, CCND3, MAF, MAFB, MAFA and FGFR3/MMSET [24]. The overall rate of 14q32 translocations increases with disease progression and reaches 90% in advanced tumors. Light chain translo‐ cations are rather rare in MM, particularly Igκ, which seem to be very infrequent [25]. Changes in the expression of gene subsets could be partly responsible for disease heterogeneity, as well as for further disease transformation. Moreover, with the 11q13 partner, constitutive upregu‐ lation of cyclin D1 results, deregulating the cell cycle [26]; t(11;14) is accompanied with a higher frequency of CD20 expression, hyposecretory disease and λ light chain usage. This subtype is increasingly encountered in AL amyloidosis, with or without MM, and in the rare IgM MM and is associated with favorable outcome. Translocation t(4;14)(p16;q32), is cryptic because of its telomeric location [27] and has been associated with IgA isotype, λ chain usage, deletion or monosomy of chromosome 13, immature plasma morphology, more aggressive disease and shortened survival. It leads to deregulation of fibroblast growth factor receptor 3 (FGFR3) gene on der(14) and of Multiple Myeloma SET (MMSET) domain gene on der(4); the latter may be a critical transforming event. t(4;14) was found characterized by deregulation of chromatin organization, actin filament and microfilament movement [28].

applies for cyclins D2 and D3). Under normal conditions, cyclin D1 acts through its interaction with cyclin dependent kinases (CDKs). CDKs are enzymes that add phosphate groups to protein-targets in order to make them inactive. The resulting complexes CDK4-D1 and CDK6- D3, promote the progress to cell cycle phase S, resulting in an uncontrolled proliferation.

Follicular lymphoma (FL) is characterized by the presence of chromosomal translocation t(14;18), which promotes protein bcl2 overexpression that in turn, leads to the suspension of apoptosis and survival increment of B cells that harbor the translocation. Less commonly, bcl2 is deregulated by translocation to the Igκ t(2;8) and Igλ t(8;22) loci [35]. The t(14;18) is appa‐ rently mediated by the RAG recombinase proteins, which cleave at J segments in the IgH locus and at an unusual non B form DNA structure in bcl2. These B cells undergo an epigenetic reprogramming which, in conjunction with the acquisition of additional events, leads to FL development. The t(14;18)(q32;q21) may also be observed in diffuse large B cell lymphoma (DLBCL) [36] and in non-gastric MALT lymphomas. It brings the MALT1 gene under the

The IgH locus contains a region of 40-50 functional variable (VH), 27 diversity (DH) and 6 joining (JH) gene segments which is flanked by exons encoding the Ig constant regions (Cμ, Cδ, Cγ3, Cγ1, Cα1, Cγ2, Cγ4, Cε and Cα2). The Igκ locus contains 34-38 functional Vκ and 5 Jκ gene segments and one exon encoding the constant region of Igκ (Cκ). The Igλ locus comprises 29-30 functional Vλ and 4 functional Jλ-Cλ combinations [16]. Consequently, one of about fifty functional VH, another of thirty D, and one of six JH genes and, in the same way, one of thirty VL and one of four JL genes will be used. It appears that there are nearly 200 functional heavy and light chain gene segments that give rise to combinations of gene products,

antigen combining sites [15;38;39]. Independently of the initiating stimulus, partly due to the aberrant Ig locus translocations and the putative activation or silencing of genes in monoclonal diseases, the cell starts to synthesize Ig following the variable domain rearrangement. On the coding DNA strand, the gene segments for the formation of the variable and the constant domains of the heavy chain are in order 5´ VDJ-μ-δ-γ3-γ1-α1-γ2-γ4-ε-α2- 3´. The RNA polymer‐ ase binds to the template strand of DNA and starts reading in 3´ to 5´ direction adding nucleotides to the 3´end of pre-mRNA transcript. Alternative splicing of the pre- mRNA brings together the VDJ variable domain and constant domain segments leading to the formation of the mRNA heavy Ig chain. As this procedure occurs in order, initially VDJs will get together with μ constant domain leading to the synthesis of heavy IgM component. This will bind with a light chain forming an IgM molecule. Thus, in order, cells make at first IgM, then IgD, IgG3, IgG1, IgA1, IgG2, IgG4, IgE and IgA2 that consist of the same variable domains but different constant domains due to alternative splicing and giving them different specific properties [40].

antibodies with different unique variable end

Monoclonal Immunoglobulin http://dx.doi.org/10.5772/55855 19

control of the IGH enhancer [37].

**3. Monoclonal immunoglobulins charateristics**

**3.1. Ig synthesis, secretion and metabolism**

allowing the production of more than 5 × 107

The t(14;16)(q32;q23) leads to the dysregulation of the c-maf oncogene; it is more frequently encountered in IgA isotope and is associated with chromosome 13 deletion whereas t(14;20) (q32;q11) results in maf-B deregulation that like c-maf is a basic zipper transcription factor. The clinical significance of these rare IgH translocations is unknown and under investigation. However, the oncogenic process is continually going on during disease course and secondary IgH translocations can be observed such as those involving the myc oncogene (8q24), that are associated with advanced and aggressive disease. Especially in patients with cytogenetically high-risk disease, more changes are observed, including heterogeneous clonal mixtures with shifting predominant competitive clones [29].

It is interesting to observe that the abnormalities observed are not disease specific and can occur in different B-cell disorders in which they may confer different phenotypes, suggesting a role for additional factors [24].

A hallmark of Burkitt lymphoma (BL) is the expression of the myc oncogene, which has an essential role in cell proliferation, cell growth, protein synthesis, metabolism and apoptosis [30]. myc deregulated expression arises from t(8;14)(q24;q32), juxtaposing myc to the IgH locus, in 80% of cases, whereas in the remaining, myc is translocated to the κ- (2p12), or λ- (22q11) light chain respectively. In endemic BL, most myc/IgH breakpoints originate from aberrant somatic hypermutation, in contrast to sporadic cases where the translocation mostly involves the Ig switch regions of the IgH locus at 14q32. The discrepancies are perhaps due to differences in Epstein Bar Virus positivity between endemic and sporadic forms [31]. myc translocations are not completely specific for BL and have been reported in other B-cell entities.

Almost 70% of mantle cell lymphoma (MCL) patients are genetically characterized by the chromosomal translocation t(11;14). In several cases, patients also have point mutations and / or deletion of the ATM (ataxia telangiectasia mutated) gene. In addition, blastic forms or subtypes with more aggressive clinical behavior, may have additional mutations in genes that act as negative regulators of the cell cycle such as p16, p18 and p53 [32]. Rarer MCL cases are negative for cyclin D1, lack t(11; 14) and stand out of the usual clinical picture of MCL [33]; in such cases, cyclin D2 or cyclin D3 are overexpressed, a different permutation t(2; 12) (p12; p13) which connects cyclin D2 to the IgL-k locus may be present; it does not cause loss or quanti‐ tative disorder of genetic material, but at a molecular level, reconnecting two chromosomal regions can disrupt important genetic sequences, causing inactivation or gene mutation. Moreover, in this permutation, the protooncogene PRAD1 (Parathyroid Adenomatosis 1, or bcl1) which is normally found on chromosome 11, is swapped in the heavy chain Ig gene on chromosome 14 [34]. The resulting oncogene bcl1/IGH encodes cyclin D1 that is an important cell cycle regulator, particularly during the transition from the G1 to the S phase (the same applies for cyclins D2 and D3). Under normal conditions, cyclin D1 acts through its interaction with cyclin dependent kinases (CDKs). CDKs are enzymes that add phosphate groups to protein-targets in order to make them inactive. The resulting complexes CDK4-D1 and CDK6- D3, promote the progress to cell cycle phase S, resulting in an uncontrolled proliferation.

Follicular lymphoma (FL) is characterized by the presence of chromosomal translocation t(14;18), which promotes protein bcl2 overexpression that in turn, leads to the suspension of apoptosis and survival increment of B cells that harbor the translocation. Less commonly, bcl2 is deregulated by translocation to the Igκ t(2;8) and Igλ t(8;22) loci [35]. The t(14;18) is appa‐ rently mediated by the RAG recombinase proteins, which cleave at J segments in the IgH locus and at an unusual non B form DNA structure in bcl2. These B cells undergo an epigenetic reprogramming which, in conjunction with the acquisition of additional events, leads to FL development. The t(14;18)(q32;q21) may also be observed in diffuse large B cell lymphoma (DLBCL) [36] and in non-gastric MALT lymphomas. It brings the MALT1 gene under the control of the IGH enhancer [37].
