Tyrosine kinase inhibitors, such as imatinib mesylate (Gleevec, Novartis, formerly known as STI571) are confirmed to be the first line treatment of Chronic Myelogenous Leukemia (CML) and of a rare form of gastroenteric stromal cancer. It has been reported that in the latter case, the response to the drug in vivo is mainly due to immunocompetent cells, able to produce cytokines with antineoplastic activity. In this study, peripheral blood and bone marrow of 20 CML patients were studied, prior and during treatment with imatinib, to assess morphologic, phenotypic, cytogenetic and biomolecular patterns. Plasma from BM and PB was also tested to evaluate (by ELISPOT and real time polymerase chain reaction) cytokines able to induce B lymphocytes differentiation, and/or proliferation, such as interleukin (IL)-4, IL-6 (ligand for CD126), IL-3, IL-10 or IL-21 together with chemokines MCP-1, SDF-1, IP-10 and IL-8. In 14 out of 20 CML patients a significant increase in the percentage of BM lymphoplasmocytoid cells was observed on imatinib treatment with >10% (range 8–12%) of CD20+CD126+cells. Among this population, two third of cells coexpressed IgM and one third was IgD+, moreover a lower fraction of IgM+CD126+CD20− (3–4%) or IgD+CD126+CD20− (2–3%) cells was found too. In all these patients SDF1 increased in the BM plasma after imatinib (from 10–80pg/ml to 150–450pg/ml) and its receptor CXCR4 was up-regulated on CD20+CD126+cells. In 4 patients the amount of IP-10 in BM plasma and the expression of its receptor CXCR3 were also increased. No significant modification in transcription and secretion of IL-3, IL-4, IL-6, IL-10, IL-21, IL-8 or MCP1 were observed. The lasting 6 patients had<5% of CD20 +CD126+ lymphocytes (range2–4%), 2/3 coexpressing IgM and 1/3 coexpressing IgD. Every patients with increased number of CD126+ B lymphocytes achieved hemathologic remission, 7 of them complete cytogenetic and biomolecular remission. On the other hand, among the patients with low or undetectable CD20+CD126+cells, 2 obtained only hemathological remission. In the 2 relapsed patients, BM CD20+CD126+ lymphocytes decreased from 11% and 8% to 7 and 5%, respectively, with undetectable IgM+ CD126+CD20− or IgD+ CD126+CD20− cells. The increased production of SDF-1, following imatinib administration, might increase BM lymphoplasmocitoid cells, thanks to the double proliferative/chemotactic effect of the cytokine on B cells, with redistribution and in situ differentiation of CD20+ CD126+ lymphocytes. These findings shed some light on the possibility that, even in CML, immunological events may play a role in disease control;moreover they could be useful in monitoring disease outcome.

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