Immunoglobulin Heavy Chain (IGH) Gene Rearrangement In Waldenström Macroglobulinemia and Other Monoclonal IgM Disorders
Authors: Varettoni Marzia , Zibellini Silvia , Arcaini Luca , Orlandi Ester , Pascutto Cristiana , Boveri Emanuela , Corso Alessandro , Passamonti Francesco , Mangiacavalli Silvia , Rizzi Silvia , Pochintesta Lara , Paulli Marco , Morra Enrica , Lazzarino Mario 
Published: October 2019

Abstract
Abstract 4139

Background.
The presence of a serum IgM monoclonal component is associated with a spectrum of lymphoid disorders including Waldenström Macroglobulinemia (WM), IgM monoclonal gammopathy of undetermined significance (MGUS) and IgM-related disorders (IgM-RD). Limited information is available on immunoglobulin heavy chain (IGH) gene rearrangement in this setting.

Purpose.
The aim of this study was to analyze IGHV-D-J rearrangements in a large series of patients (pts) and to compare the gene usage across different monoclonal IgM disorders.

Patients and methods.
We analyzed 107 pts including 52 WM, 47 IgM MGUS and 8 IgM-RD. Diagnosis was made according to the consensus criteria proposed at the 2nd International Workshop on WM. Mononuclear cells were obtained from bone marrow in all pts. IGHV-D-J rearrangements were amplified and directly sequenced from cDNA using primers specific for each of the leader sequences of HV1-6 subgroups in combination with a joining heavy chain (JH) consensus primer or cμ constant region primer. Sequences were aligned to ImMunoGeneTics sequence directory using the IMGT V-QUEST analysis software.

Results.
A complete productive monoclonal IGHV-D-J rearrangement was obtained in 84/107 cases (78%). Using a homology cut-off value of 98% to the nearest germline gene, we observed mutated IGHV in 79/84 pts (94%) and unmutated IGHV in 5 (6%). The frequency of IGHV, IGHD and IGHJ gene usage is shown in the table. The most common IGHV subgroup was IGHV3, which was found in 69/84 cases (82%). The individual IGHV genes most frequently used were IGHV3-23 (20/84, 24%) and IGHV3-7 (10/84, 12%). IGHD segments were assignable in 83 out of 84 rearrangements. The most represented IGHD subgroups were IGHD3 (23/83, 28%), IGHD6 (16/83, 19%) and IGHD2 (15/83, 18%). The most common individual IGHD genes were IGHD6-19 (10/83, 12%) and IGHD2-2 (8/83, 10%). The analysis of IGHJ genes showed a preferential usage of IGHJ4 gene (56/84, 67%) and IGHJ4*02 allele (54/84, 64%). The median HCDR3 length was 13 amino acids (range: 5–29). We found an association between IGHV3 and IGHJ4 subgroups (p=0.01), while no association was found between IGHV and IGHD (p=0.8), and between IGHD and IGHJ subgroups (p=0.8).
We compared IGH rearrangement features in pts with WM, MGUS and IgM-RD. A complete productive monoclonal IGHV-D-J rearrangement was detected in a higher percentage of WM pts (47/52, 90%) as compared to MGUS (31/47, 66%) and IgM-RD pts (6/8, 75%) (p=0.01). The proportion of mutated IGHV cases was similar in the three groups (p=0.6). Regarding specific gene usage, there was a trend toward a higher usage of IGHV3-23 gene in WM (14/47, 30%) as compared to MGUS (4/31, 13%) (p=0.07). On the contrary, there was no difference in distribution of IGHD subgroups (p=0.13) and IGHJ genes (p=0.5). The median HCDR3 length was similar in WM, MGUS and IgM-RD (p=0.6).
We also compared IGHV usage with clinical characteristics of pts. Interestingly, we found that autoimmune manifestations were more frequently observed in pts carrying IGHV4-34 gene (3/4, 75%) as compared to pts using alternative genes (8/80 pts, 10%) (p=0.006). Autoimmune phenomena associated with IGHV4-34 gene were represented by cold agglutinin haemolytic anemia in 2 pts with IgM-RD and 1 with WM.

Conclusions:
the identification of a monoclonal IGHV-D-J rearrangement seems more feasible in WM as compared to MGUS and IgM-RD. In all three groups, the majority of cases are mutated, confirming the derivation of the clone from a post-germinal center cell. This study shows a preferential usage of VH3 subgroup and in particular of VH3-23 gene, with a trend for a higher usage in WM as compared to other IgM disorders. A higher prevalence of autoimmune manifestations was observed in pts carrying VH4-34 gene.

Disclosures:
No relevant conflicts of interest to declare.