Bedeutung der Helicobacter-pylori-Infektion für die Pathogenese und Therapie von MALT-Lymphomen des Magens

Seit 1983 ist das Konzept des Mukosa-assoziierten lymphatischen Gewebes (MALT) im Magen auf dem Boden einer chronischen Helicobacter(H.)-pylori-Infektion bekannt. Viele epidemiologische, biologische und molekulargenetische Studien haben die Rolle von H. pylori in der Lymphomgenese unterstützt. Bis heute wurden weltweit mehr als 650 Patienten mit gastralem MALT-Lymphom und H.-pylori-Infektion antibiotisch behandelt. Bei etwa 75% der Fälle kann mit Hilfe dieser Therapie eine komplette Lymphomremission induziert werden. Klinische prädiktive Faktoren helfen dabei, Patienten bezüglich ihres Risikos besser zu stratifizieren und damit die Probabilität des Ansprechens zu verbessern. Neue zytogenetische Erkenntnisse haben zudem dazu beigetragen, ein besseres Verständnis der Lymphomgenese zu erlangen. Mit der kürzlich beschrieben Translokation t(11;18) (q21;q21) könnte in Zukunft ein prädiktiver genetischer Faktor verfügbar sein.The Role of Helicobacter pylori Infection for the Development and Treatment of Gastric MALT Lymphomas Since 1983, it is well known that mucosa-associated lymphoid tissue (MALT)-type lymphoma of the stomach is due to chronic Helicobacter pylori (H. pylori) infection. Many epidemiological, biological, and moleculargenetic studies have implicated the role of H. pylori in lymphomagenesis. Nowadays, more than 650 patients with gastric MALT lymphoma worldwide have been treated with antibiotics for H. pylori infection, achieving a complete remission in about 75% of cases. Clinical predictive factors help to stratify patients into risk groups, and help to predict the probability of lymphoma remission. New insights into cytogenetics have also contributed to the understanding of lymphomagenesis, and with the newly identified translocation t(11;18)(q21;q21) we might have also a genetic factor at hand to predict treatment response.Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Somatic hypermutation and B-cell lymphoma.

During the B-cell response to T-cell-dependent antigens, the B cells undergo a rapid proliferative phase in the germinal centre. This is accompanied by the introduction of mutations into the immunoglobulin (Ig) variable region (V) genes. The B cells are then selected according to the affinity of the encoded immunoglobulin for antigen, resulting in affinity maturation of the response. Analysis of mutations in IgV genes has given insight into the history of individual B cells and their malignancies. In most cases, analysis of mutations confirms classifications of B-cell lineage designated by studies of cellular morphology and surface antigen expression. However, of particular interest is the subdivision of groups of malignancies by analysis of somatic hypermutation. It is now apparent that there are two subsets of chronic lymphocytic leukaemia (CLL), one with a low load of mutations and poor prognosis. and one with a heavy load of mutations with a much more favourable prognosis. In addition, in Burkitt's lymphoma, sporadic and endemic subtypes are now considered possibly to have a different pathogenesis, reflected in differences in the numbers of mutations. Hodgkin's disease, which was a mystery for many years, has now been shown to be a B-cell tumour. Although in many cases the Ig genes are crippled by somatic hypermutation, it is thought that failure to express Ig is more likely to be associated with problems of transcription. It has been proposed that the distribution of mutations in a B-cell lymphoma can be used to determine whether a lymphoma is selected. We have investigated the load and distribution of mutations in one group of lymphomas--marginal zone B-cell lymphomas of mucosa-associated lymphoid tissues (MALT-type lymphoma), which are dependent on Helicobacter pylori for disease progression, to investigate the limits of information that can be derived from such studies. Comparison of the load of mutations demonstrates that these tumours have approximately the same load of mutations as normal mucosal marginal zone B cells from the Peyer's patches and mucosal plasma cells. This is consistent with the origin of these cells from mucosal marginal zone B cells with plasma cell differentiation. To investigate selection in MALT lymphomas we compared a region of the framework region three in ten MALT lymphomas which use the V(H4) family, with the same codons in groups of V(H4) genes that are out of frame between V and J. The latter accumulate mutations but are not used and are not selected. A group of V(H4) genes are in-frame between V and J were also included for comparison. There were no obvious differences in the distribution of mutations between the groups of genes; the same hot spots and cold spots were apparent in each. In the MALT lymphomas, selection was apparent in the framework regions only and the tendency was to conserve. We therefore feel that there is selection to conserve antibody structure and that this does not reflect selection for antigen. We do not believe that antigen selection can be deduced reliably from sequence information alone. It is possible that somatic hypermutation could be a cause of malignancy since it has been shown that the process may generate DNA strand breaks and is known to be able to generate insertions and deletions. Such events may mediate the translocation of genes--a process that is pivotal in the evolution of many lymphomas