Ongoing in vivo immunoglobulin class switch DNA recombination in chronic lymphocytic leukemia B cells.
Chronic lymphocytic leukemia (CLL) results from the expansion of malignant CD5(+) B cells that usually express IgD and IgM. These leukemic cells can give rise in vivo to clonally related IgG(+) or IgA(+) elements. The requirements and modalities of this process remain elusive. Here we show that leukemic B cells from 14 of 20 CLLs contain the hallmarks of ongoing Ig class switch DNA recombination (CSR), including extrachromosomal switch circular DNAs and circle transcripts generated by direct S micro -->Sgamma, S micro -->Salpha, and S micro -->Sepsilon as well as sequential Sgamma-->Salpha and Sgamma-->Sepsilon CSR. Similar CLL B cells express transcripts for activation-induced cytidine deaminase, a critical component of the CSR machinery, and contain germline I(H)-C(H) and mature V(H)DJ(H)-C(H) transcripts encoded by multiple Cgamma, Calpha, and Cepsilon genes. Ongoing CSR occurs in only a fraction of the CLL clone, as only small proportions of CD5(+)CD19(+) cells express surface IgG or IgA and lack IgM and IgD. In vivo class-switching CLL B cells down-regulate switch circles and circle transcripts in vitro unless exposed to exogenous CD40 ligand and IL-4. In addition, CLL B cells that do not class switch in vivo activate the CSR machinery and secrete IgG, IgA, or IgE upon in vitro exposure to CD40 ligand and IL-4. These findings indicate that in CLL at least some members of the malignant clone actively differentiate in vivo along a pathway that induces CSR. They also suggest that this process is elicited by external stimuli, including CD40 ligand and IL-4, provided by bystander immune cells.
Cerutti
Andrea
A
Division of Molecular Immunology, Department of Pathology, Weill Medical College of Cornell University, New York, New York 10021, USA. acerutti@med.cornell.edu
Zan
Hong
H
Kim
Edmund C
EC
Shah
Shefali
S
Schattner
Elaine J
EJ
Schaffer
András
A
Casali
Paolo
P
D001402:B-Lymphocytes / Q000187:drug effects / Q000201:enzymology / Q000276:immunology*; D001483:Base Sequence; D023201:CD40 Ligand / Q000494:pharmacology; D003564:Cytidine Deaminase / Q000378:metabolism; D004270:DNA, Circular / Q000235:genetics; D004273:DNA, Neoplasm / Q000235:genetics; D015536:Down-Regulation; D006801:Humans; D007070:Immunoglobulin A / Q000096:biosynthesis / Q000235:genetics; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000235:genetics; D007134:Immunoglobulin Switch Region; D066298:In Vitro Techniques; D015847:Interleukin-4 / Q000494:pharmacology; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology / Q000235:genetics* / Q000276:immunology*; D008969:Molecular Sequence Data; D010641:Phenotype; D011994:Recombinant Proteins / Q000494:pharmacology; D011995:Recombination, Genetic; D000098830:AICDA (Activation-Induced Cytidine Deaminase)
D004270:DNA, Circular; D004273:DNA, Neoplasm; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D011994:Recombinant Proteins; D023201:CD40 Ligand; D015847:Interleukin-4; D000098830:AICDA (Activation-Induced Cytidine Deaminase); D003564:Cytidine Deaminase