Molecular evidence for antigen drive in the natural history of mantle cell lymphoma.

To further our understanding about antigen involvement in mantle cell lymphoma (MCL), we analyzed the expression levels of activation-induced cytidine deaminase (AID), a key player in B-cell responses to antigen triggering, in 133 MCL cases; assessed the functionality of AID by evaluating in vivo class switch recombination in 52 MCL cases; and sought for indications of ongoing antigen interactions by exploring intraclonal diversification within 14 MCL cases. The AID full-length transcript and the most frequent splice variants (AID-ΔE4a, AID-ΔE) were detected in 128 (96.2%), 96 (72.2%), and 130 cases (97.7%), respectively. Higher AID full-length transcript levels were significantly associated (P < 0.001) with lack of somatic hypermutation within the clonotypic immunoglobulin heavy variable (IGHV) genes. Median AID transcript levels were higher in lymph node material compared to cases in which peripheral blood was analyzed, implying that clonal behavior is influenced by the microenvironment. Switched tumor-derived IGHV-IGHD-IGHJ transcripts were identified in 5 of 52 cases (9.6%), all of which displayed somatic hypermutation and AID-mRNA expression. Finally, although most cases exhibited low levels of intraclonal diversification, analysis of the mutational activity revealed a precise targeting of somatic hypermutation indicative of an active, ongoing interaction with antigen(s). Collectively, these findings strongly allude to antigen involvement in the natural history of MCL, further challenging the notion of antigen naivety.

Analysis of expressed and non-expressed IGK locus rearrangements in chronic lymphocytic leukemia.

Immunoglobulin kappa (IGK) locus rearrangements were analyzed in parallel on cDNA/genomic DNA in 188 kappa- and 103 lambda-chronic lymphocytic leukemia (CLL) cases. IGKV-KDE and IGKJ-C-intron-KDE rearrangements were also analyzed on genomic DNA. In kappa-CLL, only 3 of 188 cases carried double in-frame IGKV-J transcripts: in such cases, the possibility that leukemic cells expressed more than one kappa chain cannot be excluded. Twenty-eight kappa-CLL cases also carried nonexpressed (nontranscribed and/or out-of-frame) IGKV-J rearrangements. Taking IGKV-J, IGKV-KDE, and IGKJ-C-intron-KDE rearrangements together, 38% of kappa-CLL cases carried biallelic IGK locus rearrangements. In lambda-CLL, 69 IGKV-J rearrangements were detected in 64 of 103 cases (62%); 24 rearrangements (38.2%) were in-frame. Four cases carried in-frame IGKV-J transcripts but retained monotypic light-chain expression, suggesting posttranscriptional regulation of allelic exclusion. In all, taking IGKV-J, IGKV-KDE, and IGKJ-C-intron-KDE rearrangements together, 97% of lambda-CLL cases had at least 1 rearranged IGK allele, in keeping with normal cells. IG repertoire comparisons in kappa- versus lambda-CLL revealed that CLL precursor cells tried many rearrangements on the same IGK allele before they became lambda producers. Thirteen of 28 and 26 of 69 non-expressed sequences in, respectively, kappa- or lambda-CLL had < 100% homology to germline. This finding might be considered as evidence for secondary rearrangements occurring after the onset of somatic hypermutation, at least in some cases. The inactivation of potentially functional IGKV-J joints by secondary rearrangements indicates active receptor editing in CLL and provides further evidence for the role of antigen in CLL immunopathogenesis.