IGHV-unmutated and IGHV-mutated chronic lymphocytic leukemia cells produce activation-induced deaminase protein with a full range of biologic functions

Abstract

IntroductionChronic lymphocytic leukemia (CLL) follows either an indolent or an aggressive course 1 and clinical decompensation is often accompanied by the appearance of new or increasing numbers of genetic aberrations associated with shorter survival, "clonal evolution." 2 The mechanism(s) responsible for the generation of these genetic abnormalities are not defined in CLL, which is not the case in certain other human cancers, especially lymphoid malignancies of germinal center (GC) origin, in which activation-induced deaminase (AID) appears to be pathogenic. [3][4][5] AID is required for the beneficial generation of Ab diversity in normal B lymphocytes by inducing IGV somatic hypermutation (SHM) and helps in the development of protective effector mechanisms by mediating IGH class-switch recombination (CSR). 6,7 These beneficial on-target AID activities occur primarily during a GC reaction and involve conversion of cytidine to uridine on single-stranded DNA at the IG locus. Such on-target actions in CLL B cells have been a matter of interest for several years, primarily because the presence or absence of IGHV mutations (which require AID) in CLL cells is closely linked to clinical outcome. Patients with leukemic clones with minimal (Ͻ 2% difference from germline) or no mutation in the IGHV (unmutated CLL [U-CLL]) have a far worse prognosis than patients with IGHV-mutated CLL (M-CLL). 8,9 Despite this SHM-based subcategorization of CLL cases, some clones exhibit ongoing IGHV diversification in vivo and in vitro, [10][11][12] with an antigen-driven pattern present in some cases, 13 and up to 50% of patients exhibit molecular evidence for intraclonal isotype CSR. [14][15][16][17][18] AID activity focused elsewhere 19 ) can lead to mutations, deletions, or translocations outside of the IG locus, as in GC-derived lymphomas. [3][4][5] However, such a role for AID in CLL has been questioned for several reasons: (1) although circulating CLL cells can express AID mRNA, [20][21][22] the number of such cells is exceedingly low (0.01%-0.2%) 22 ; (2) AID protein synthesis by these same cells has not been demonstrated 18,[20][21][22][23] ; (3) demonstration of the full range of AID functions is lacking in CLL, for example, by failure of cells to demonstrate SHM, especially for U-CLL clones, even on stimulation and induction of AID mRNA, 21 thereby creating the apparent paradox that U-CLL patients express more AID mRNA than M-CLL patients yet exhibit no or minimal SHM; and (4) despite association with several prognostic markers, 20,21,[24][25][26] no prospective analysis linking AID expression and disease severity has been performed.In the present study, we aimed to address these issues as a means of determining whether AID could be involved in the evolution of CLL to a more aggressive disease. We report that CLL cells are able to produce AID protein, but synthesis is The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by page charge payment. Therefore, and...

Generation of a poor prognostic chronic lymphocytic leukemia-like disease model: PKC subversion induces up-regulation of PKC II expression in B lymphocytes

“…18 PKCa-KR cells also exhibited an elevated proliferative capacity compared with control B cells, both in vitro and in vivo ( Figure 3D,E). Supporting this, aicda expression, which has been associated with increased CLL cell proliferation, 19,20 was significantly increased in GFP + CD19 + cells expressing PKCa-KR at the later stages of culture compared to MIEV-expressing cells ( Figure 3F). We previously demonstrated that PKCa-KR-transduced cells exhibited reduced PKC activity during the early stages of the OP9 co-culture, as expected ( Figure 4A, left).…”

“…48 Indeed, up-regulation of activationinduced deaminase has been associated with elevated double-strand DNA breaks in CLL cells, promoting the generation of genetic aberrations. 20 Therapies that reduce proliferation do, therefore, offer an important treatment option for progressive CLL. Our findings support the development of clinical studies with ruboxistaurin and sotrastaurin in CLL, given the recent promising data assessing the clinical efficacy of BCR-targeting inhibitors such as the Btk inhibitor ibrutinib.…”

Immunogenetic Studies of Chronic Lymphocytic Leukemia: Revelations and Speculations about Ontogeny and Clinical Evolution

“…Initially, this was thought to indicate functional inactivation of AID or defects in other yet unidentified factors critical for SHM. However, more recently, AID was shown to be expressed in both M-CLL and U-CLL at both the mRNA and protein level, and more particularly within the small proportion of cells that are undergoing or have recently undergone division (22). AID was capable of inducing SHM and CSR after in vitro stimulation with CD40 and IL4, a system, in essence, mimicking costimulatory signals provided by T cells in vivo.…”

“…AID was capable of inducing SHM and CSR after in vitro stimulation with CD40 and IL4, a system, in essence, mimicking costimulatory signals provided by T cells in vivo. On these grounds, it was proposed that the lack of SHM in U-CLL clones in vivo is not due to an intrinsic AID defect, but rather due to active inhibition (22).…”

IgG-Switched CLL Has a Distinct Immunogenetic Signature from the Common MD Variant: Ontogenetic Implications

“…4,5). Activation-induced cytidine deaminase (AID), which is normally required for both SHM and CSR, is expressed in a small proliferative compartment within the CLL clone, irrespective of the immunoglobulin heavy variable (IGHV) gene mutational status, and can be functionally induced in vitro under conditions that mimic T-cell help (6). Furthermore, ongoing CSR and high AID expression define a subgroup of U-CLL displaying even worse prognosis, underscoring the importance of intense (micro) environmental stimulation for shaping clonal behavior and eventual clinical outcome (7).…”