Analysis of rearranged immunoglobulin genes indicating a process of clonal evolution in chronic lymphocytic leukaemia

Most immunoglobulin heavy chain switch mu rearrangements in B-cell chronic lymphocytic leukemia are internal deletions

We investigated 38 cases of B-cell chronic lymphocytic leukemia (B-CLL) for the presence of non-productive rearrangements in the S(mu) regions and defined for the first time the molecular nature of these rearrangements. Southern blot analysis revealed S(mu) region rearrangements in 13 cases (34%) and polymerase chain reactions (PCRs) indicated that these rearrangements consisted of internal deletions of the S(mu) region. Long-distance PCRs localized the S(mu) deletions in the V(H)DJ(H) rearranged allele in most cases. We investigated if S(mu) deletions were related to V(H) somatic mutations that, together with isotype switch recombination, are indicative of the B-cell maturation stage. No significant correlation between the presence of S(mu) deletions and V(H) somatic mutations was found, indicating that the two processes are independent in B-CLL. Moreover no significant correlation between S(mu) deletions and prognosis was observed. Having shown that S(mu) internal deletions are not chromosome translocations rules out their involvement in the onset of malignancy, while their localization in the V(H)DJ(H) rearranged alleles suggests a possible role in the stabilization of the isotype of the expressed immunoglobulin.

Secondary abnormalities of chromosome 6q in B-cell chronic lymphocytic leukemia: a sequential study of karyotypic instability in 51 patients

Although karyotypic abnormalities are well documented in B-cell chronic lymphocytic leukemia (B-CLL), few sequential cytogenetic studies have been done. In this study, peripheral blood lymphocytes from fifty-one patients with B-CLL were sequentially karyotyped over a mean interval of 13.8 months (range, one to 51 months). Cytogenetic clones were detected in 33/51 patients (66%) on initial study, including 17 patients with structural abnormalities of chromosome 13q14, and three patients with trisomy 12. Karyotypic evolution was documented in 22/51 patients (43%). The most common secondarily acquired chromosome aberrations were structural abnormalities of the long arm of chromosome 6 involving the region of 6q21-q24 (six patients). Four patients each had acquired structural abnormalities of 1q, 3p, 12q, and 13q. Disease progression, as measured by advance in Rai stage or death from the disease, was observed more often in the clonal evolution group than in the karyotypically stable group (11/22 vs. 5/29; P = 0.017). Patients with secondary abnormalities of 6q had a significantly decreased progression-free survival interval compared with other patients in the study (P = .023). The authors conclude that clonal karyotypic evolution is common in B-CLL, and that clonal evolution correlates with clinical disease progression. Furthermore, the poor outcomes previously attributed to CLL with 6q abnormalities may be related to the clonal acquisition of these abnormalities over time. Future studies should focus on the relevant genetic events underlying the clinical progression observed with karyotypic evolution of B-CLL.

The pathology of the chronic lymphoid leukaemias

The chronic lymphoid leukaemias, though they all possess relatively mature lymphoid phenotypes, are a diverse group of diseases at the clinical, morphological, immunophenotypical, and biological levels. Generally accepted entities within this category include B-cell chronic lymphocytic leukaemia of classical and mixed-cell types, B-cell and T-cell prolymphocytic leukaemia, hairy-cell leukaemia and hairy-cell variant, splenic lymphoma with circulating villous lymphocytes, large granular lymphocytic leukaemia, adult T-cell leukaemia/lymphoma syndrome, and leukaemic phases of malignant lymphomas of both B-cell and T-cell types. Recent advances have helped to differentiate these diseases, allowing the development of more specific therapy and more accurate prognostication. In this article, we review the pathological aspects of these diseases.