Relationship between Clinical/Hematological Response and Increase of Plamacells in the Bone Marrow of Patients with Chronic Myelogenous Leukemia Imatinib Mesylate Treatment (631).

Tyrosine kinase inhibitors, such as imatinib mesylate (Gleevec, Novartis, formerly known as STI571) are the first line treatment of Chronic Myelogenous Leukemia (CML) and of a rare form of gastroenteric stromal cancer. It has been recently reported that in the latter case, tumor cells are refractory to imatinib antiproliferative effect in vitro and the response to the drug in vivo is due to immunocompetent cells, able to produce cytokines with antineoplastic activity. In this study, 20 CML patients, prior and during treatment with imatinib mesylate, underwent bone marrow (BM) aspirates every 6 months, including: morphologic and phenotypic analysis, cytogenetic and biomolecular evaluation, compared to peripheral blood. Plasma from BM and peripheral blood was also recovered for cytokyne-chemokine dosage. We report that in 12 out of 20 CML patients a significant increase in the percentage of BM lymphoplasmocytoid cells was observed upon treatment with imatinib mesylate, with >10% (range 10–16%) of CD20+CD126+cells. Among this population, two third of cells coexpressed IgM and one third was IgD+, while a smaller fraction of IgM+CD126+CD20– (3–4%) or IgD+CD126+CD20- (2–3%) cells was also found. The lasting 8 patients had<5% of CD20 +CD126+ lymphocytes (range2–4%), 2/3 coexpressing IgM and 1/3 coexpressing IgD. All patients with increased number of CD126+ B lymphocytes underwent hematologic remission, 7 of them with complete molecular and cytogenetic remission. On the other hand, among the patients with low or undetectable CD20+CD126+cells, only 4 underwent hemathological remission and none of them displayed stable cytogenetyc and molecular remission. In two patients relapsed after six months of treatment, the fraction of BM CD20+CD126+ lymphocytes decreased from 16% and 11% to 7 and 5%, respectively, with undetectable IgM+ CD126+CD20- or IgD+ CD126+CD20- cells. These data suggest that this population of lymphoplasmocytoid B cells depends on or contribute to the pharmacological response; by the way, this phenomenon might help in monitoring the outcome of disease and the response to treatment. To check this item and understand the biochemical mechanisms substaining the observed increase in BM lymphoplasmocitoid cells on imatinib treatment, we wonder if the production of cytokines able to induce B lymphocytes differentiation, such as interleukin (IL)-4, IL-6 (whose receptor is CD126), IL-3, IL10 or IL-21 was affected by imatinib administration. To this aim, both soluble cytokines (by ELISPOT) and their mRNA (by real time polymerase chain reaction) were evaluated in the BM of these patients: moreover, the expression of MCP-1, SDF-1, IP-10 and IL-8 were also measured, to verify whether the increse in BM CD20+ CD126+ lymphocytes was due to a redistribution rather than to “in situ” differentiation. Preliminary results seem to indicate that the latter hypothesis is unlikely; in addition, when CD20+ CD126+ were increased in the BM, they also raised in the peripheral blood. These immunological events might have a role in the response to tyrosine kinase inhibitor and need further investigations.