The NK and NKT Cell Compartment Is Suppressed in CML Patients before and after Imatinib Treatment.

In CML patients, lymphocyte subsets have been shown to be disturbed. NK cells as well as CD8+ T cells have been shown to be significantly lower in patients with relapse after BMT than without relapse (Jiang et al., 1996). After successful treatment (IFN- α and BMT/SCT), MHC-restricted CD8+ T cells as well as MHC-unrestricted cytotoxic NK and lymphokine activated killer (LAK) cells play an important role in controlling the disease (Meseri et al., 1993, de Castro et al., 2003, Molldrem et al., 2000), which can lead not only to hematological, but also cytogenetic responses. The development of imatinib mesylate, a selective inhibitor of the bcr/abl tyrosine kinase, as a first-line therapy enormously enhanced treatment options for CML patients, and has led to hematologic, and occasionally cytogenetic, responses at various stages of disease. To explore, if CML patients, who develop clinical responses with imatinib mesylate treatment, have normalization of their lymphocyte subsets with restoration of CD8+ and NK cells, we studied peripheral blood T cell, B cell, and NK cell subpopulations in patients in chronic or accelerated phase before and after treatment with imatinib mesylate. In 5 CML patients, 8-color flow cytometry was applied to investigate the lymphocyte subsets using anti-CD3, anti-CD4, anti-CD8, anti-CD19, anti-CD56, anti-CD25, anti-CD27, and anti-CD45RA antibodies. 5 healthy donors served as controls. There was no significant difference in CD19+ B cells or CD3+ T cells as well as its CD4+ and CD8+ subsets between CML patients and healthy controls. T regulatory cells (CD4+CD25+) were also similar in patients in comparison to the healthy controls (0.6% – 3% vs 2.3%). In contrast, CD3–CD56+ NK cells (4% vs 14%, p<0.05) as well as NK T cells (CD3+CD56+ 1% vs 14%, p<0.02; CD8+CD56+ 2% vs 17%, p<0.03) were profoundly decreased in CML patients compared to the healthy controls prior to treatment with imatinib mesylate. Importantly, these abnormalities persisted even during treatment and following hematological responses (range 10 months – 35 months) (CD3-CD56+ 4–8%, CD3+CD56+ 0.5–5.5%, CD8+CD56+ 2.7–7%). On further analysis, these NK and NKT cells were mostly effector (CD45RA+CD27−, 50–80%) or memory (CD45RA-CD27+, 10–30%) cells. These results suggest, that CML not only disturbs the myeloid and the lymphoid compartment before treatment, but persistently impairs the MHC-unrestricted cytotoxic NK cells and NKT cells after treatment with imatinib mesylate, even in patients in hematological (and cytogenetic) remission with normal white cell counts (2.0 – 8.0/nl). Further investigations are required to better understand the mechanism of the prolonged and specific NK and NKT cell suppression in imatinib mesylate treated patients, and its impact on the course of the disease.