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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.

The purpose of the study was to identify factors that could predict good yields of peripheral blood stem cells (PBSC) in multiple myeloma (MM). Fifty-one MM patients, nine with refractory disease and 42 in plateau phase, were mobilized with high-dose cyclophosphamide (HD-Cy) at 4 g/m2 followed by granulocyte colony-stimulating factor (G-CSF) 5 microg/kg/day. Clinical and laboratory parameters at the time of mobilization were analyzed for correlations with the number of CD34+ cells collected, with the colony-forming unit granulocyte-macrophage (CFU-GM) count, and the mononuclear cell (MNC) count. In univariate analysis, low WBC count, low platelet count, prior exposure to melphalan, and an interval >6 months from the start of treatment correlated with poor yields of CD34+ cells. Low platelet count, prior exposure to melphalan or to radiotherapy, and an interval >6 months from the start of treatment were associated with a low CFU-GM count. On the basis of these data, we defined a scoring system able to predict the yield of the mobilizing procedure. According to this system, the presence of more than one risk factor (low WBC and platelet counts, prior exposure to melphalan, interval from first chemotherapy >6 months) was predictive of insufficient collections when a conventional combination of mobilizing measures are used.