Molecular and Clinical Features of B Cell Chronic Lymphocytic Leukemia (CLL) Carrying Stereotyped B Cell Receptors: An Italian Experience.
Authors: Bomben Riccardo , Dal-Bo Michele , Capello Daniela , Forconi Francesco , Zucchetto Antonella , Maffei Rossana , Laurenti Luca , Bertoni Francesco , Bulian Pietro , Rossi Davide , Del-Principe Maria Ilaria , Ilariucci Fiorella , Sozzi Elisa , Zucca Emanuele , Degan Massimo , Lauria Francesco , Del-Poeta Giovanni , Efremov Dimitar G. , Marasca Roberto , Gaidano Gianluca , Gattei Valter 
Published: October 2019

Abstract
CLL subsets with stereotyped HCDR3 and IGH/IGK-L gene combinations have been reported among cases with both mutated (M) and unmutated (UM) IGHV gene status. Here we evaluated the characteristics of stereotyped combinations in 1428 IG sequences (848 M and 580 UM) from 1399 CLL patients ordered according to a HCDR3-driven clustering, performed aligning HCDR3 amino acid sequences (codons 107–117 IMGT) by the multiple sequence alignment software ClustalX (1.83). Clusters with stereotyped HCDR3 were selected for having a mean alignment score>60/100. We identified 73 different clusters with stereotyped HCDR3, 32/73 with >3 cases (range 3–32) for a total of 247 cases (17.4%), 81 with M and 166 with UM IGHV genes; 17/32 clusters (200 cases) were previous described, while 15 (47 cases) were novel. Seventeen/32 clusters (156 cases) were composed by UM cases (UM/M = 153/3), 14/32 clusters (59 cases) were of M cases (UM/M = 3/53), and a single cluster (32 IGHV3-21 cases) was a mixed one (UM/M=10/22). In our series, 64% of cases (158/247) utilized four specific IGHV genes, i.e. 1–69 (60/169 cases, all UM, split into 6 clusters), 3–21 (32/55 cases, all in a single cluster), 4–34 (19/129 cases, 17 M and 2 UM, split into 2 clusters), 4–39 (17/55 cases, 14 M and 3 UM, split into 3 clusters) or mixed IGHV genes of the IGHV1 family/clan (IGHV1-2/1-3/1-18/1-46/7-4), all in a single cluster (30/153 cases, all UM). Clinical data (time-to-treatment, TTT) were available for 637/1399 patients. UM cases (251) had significantly shorter TTT (p<0.00001), as compared to M (386) cases. Similarly, TTT were significantly shorter (p<0.0005) in 113 CLL patients belonging to clusters (Hom) as compared to 492 CLL patients not belonging to clusters (Het), although these differences were no longer observed when TTT of Hom vs. Het cases were compared in the context of M (Hom/Het = 34/336) and UM (Hom/Het = 79/156) CLL. Patients belonging to the IGHV3-21 cluster had TTT similar to 241 UM cases and significantly shorter (p<0.0001) than 370 M CLL. Shorter TTT were also documented in 15 cases belonging to the IGHV3-21 cluster when compared to 13 IGHV3-21-expressing Het cases either considered altogether or split into M and UM cases (p=0.03). Finally, patients belonging to the IGHV1-2/1-3/1-18/1-46/7-4 mixed cluster had shorter TTT in comparison either with all the other M and UM cases, or with the cases expressing the same IGHV genes but with Het HCDR3 gene, even if this latter group was split in M and UM cases (p = 0.002). The identification of stereotyped HCDR3 CLL suggests a role of specific antigen(s) in defining the biological and clinical features of this disease.