Tyrosine Kinase Inhibitor Therapy Induced Changes in Humoral Immunity in Patients with Chronic Myeloid Leukemia

By affecting not only BCR-ABL1 but also a wide variety of other tyrosine kinases, tyrosine kinase inhibitors (TKIs) have potential impact on the immune defense system. As patients could use TKIs even for decades, immunological off-target effects may be of significance in clinical practice. The aim of this project was to study the effects of TKI therapy on B-cell-mediated immunity in vivo in CML patients.

Peripheral blood (PB) and bone marrow (BM) samples were collected from newly diagnosed chronic phase CML patients and follow-up samples were obtained during TKI therapy at 1, 3, 6, and 12 months after therapy start (imatinib n=21, dasatinib n=15 and nilotinib n=7). Samples from healthy volunteers served as controls (n=10). Plasma immunoglobulin (Ig) levels were measured with an immunoturbidometric method and BM and PB lymphocyte subclasses were analyzed with multicolor flow cytometry. Ig heavy chain rearrangement PCR according to BIOMED-2 protocol was used to identify clonal B-cell populations among sorted CD19^pos B lymphocytes.

At diagnosis, before TKI therapy, plasma Ig levels were similar to healthy controls. During imatinib treatment IgA and IgG levels decreased continuously and were significantly lower at 12 months compared either to diagnostic samples or to healthy controls: median IgA level at 12 months 1.22 vs. 1.51 g/l at diagnosis (p=0.040) or vs. 1.61 g/L in healthy controls (p=0.023); median IgG at 12 months 7.00 vs. 8.80 g/l at diagnosis (p=0.009) or vs. 8.55 g/l in healthy controls (p=0.009). Similarly plasma IgM levels decreased: 0.59 g/ at 12 months vs. 1.06 g/l at diagnosis (p=0.0002), but did not differ significantly from healthy controls (0.75 g/l, p=0.331). Positive correlation was found between plasma IgG and IgM levels at 3 months (r=0.678, p=0.045). One imatinib patient developed severe constant hypogammaglobulinemia, which was first noticed at 3 months, and imatinib was discontinued at 15 months due to recurrent respiratory infections.

In dasatinib-treated patients, only plasma IgM levels decreased notably, and at 12 months, they were significantly lower (0.39 g/l) compared to diagnosis (0.86 g/l, p=0.011) or healthy controls (0.75 g/l, p=0.037).

No statistically significant changes were observed in nilotinib-treated patients, possibly due to small number of patients.

The CD45 expression analyzed by flow cytometry was used to detect different B-cell subclasses (CD45^high as mature B-cells, CD45^intermediate as maturating B-cells and CD45^low as immature B-cells). In imatinib treated patients the proportion of mature B-cells in BM from all CD19+ cells was significantly lower at 3 months than in dasatinib group (55% vs. 84%, p<0.05), whereas the proportion of maturating B-cells was higher (34% vs. 12%, p<0.05). This could be related to the observed low plasma Ig levels in imatinib patients, as only mature B-cells are capable of secreting immunoglobulins. BM B-cell profile of nilotinib patients resembled that of imatinib patients.

Although clonal T-cells are found in the majority of CML patients (Kreutzman et al. Blood 2010), Ig heavy chain rearrangement analysis did not reveal any clonal B-cell populations in CML patients at diagnosis (n=2) or during imatinib (n=2) or dasatinib (n=9) treatment. Similarly, no marked abnormalities were observed in serum electrophoresis or immunofixation analysis.

Imatinib-treated patients have reduced plasma Ig levels and the proportion of mature immunoglobulin-secreting B-cells was lower in BM. Unexpectedly, dasatinib-induced changes were much less prominent, although dasatinib inhibits a broader spectrum of kinases, some of which are clearly involved in B lymphocyte biology, such as the Lyn-kinase. Further studies are needed to understand which kinase inhibition plays the major role in imatinib-induced reduction of Ig levels. However, the measurement of plasma Ig levels is warranted in patients with recurrent respiratory infections and possibility of hypogammaglobulinemia needs to be taken into account.

Koskela:Novartis: Honoraria. Richter:Bristol-Myers Squibb: Honoraria; Novartis: Honoraria. Hjorth-Hansen:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria. Porkka:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria. Mustjoki:Novartis: Honoraria; Bristol-Myers Squibb: Honoraria.