T-Cell and B-Cell Responses After Vaccination against Influenza Virus and Pneumococcus in Chronic Phase CML Patients Treated with Tyrosine Kinase Inhibitors.

Abstract 2214

Poster Board II-191

Imatinib (IM), nilotinib and dasatinib are remarkably effective as single-agent treatments for chronic myeloid leukemia (CML) in chronic phase (CP). However little is known on their potential impact on the immune system and to date no human in vivo data are available. Data from in vitro and animal studies on the effects of IM on the immune response have been contradictory ranging from impaired antigen-specific T-cell response to enhanced stimulation of tolerant T cells. In addition few data are available to assess potential immunomodulatory effects of the second-generation tyrosine kinase inhibitors (TKIs) nilotinib and dasatinib. Dasatinib has inhibitory activity against a broader range of protein kinases than imatinib including the Src family kinases Lck and Fyn, both of which are associated with T-cell receptor primary signal transduction pathways. Dasatinib may also inhibit B cell signaling through the Lyn pathway which may have potential implications for immunotherapeutic strategies. An understanding of the effects of different TKIs on the immune response will have implications for the development of immunotherapeutic strategies. The aim of this study was to prospectively analyze humoral and cellular immune responses to vaccination against influenza virus (Flu) and Pneumococcus in CP-CML patients treated with IM, dasatinib or nilotinib compared to healthy controls.

Fifty CP-CML patients on standard dose TKIs (IM, n=22; dasatinib, n=15; nilotinib, n=13) and 15 healthy controls were vaccinated against Flu (Inflenza vaccine Ph. Eur. 2008/2009, CSL biotherapies) and pneumococcus (Pneumovax II, Sanofi Pasteur MSD). Samples were taken pre and at 1 and 3 months post-vaccination. Titers of IgM and IgG anti-pneumococcal were determined using ELISA technology. A positive response was defined as an IgM serum titer >100 U/ml at 1 month; IgG response was considered positive for IgG >200 U/ml at 1 or 3 months. To investigate possible correlation between B cell subsets and the pneumococcal humoral response we evaluated IgM memory B cells (CD19⁺ CD27⁺ IgM^high IgD^low) and switched memory B cell (CD19⁺ CD27⁺ IgM^- IgD^-) subsets using flow cytometry. We analyzed the immunological T-cell response to influenza virus both quantitatively and qualitatively using flow cytometry for intracellular TNF-α, IFN-gamma and IL2 and the cytotoxicity marker CD107a. A response was considered positive if there was a minimum of 0.10% Flu-specific TNF-α producing T-cells and the percentage of antigen-specific TNF-α producing T-cells was 2-fold or higher compared to pre-vaccination level.

Preliminary results on 28 patients and 11 healthy controls have been analyzed thus far. Significantly fewer patients on TKIs mounted an anti-pneumococcal IgM response (IgM serum titer > 100 U/ml) compared to healthy controls (9/28 versus 8/11, p=0.033). An anti-pneumococcal IgM response was detected in 20%, 37.5% and 40% of CML patients on dasatinib, nilotinib and IM respectively, and in 73% of the healthy controls. Moreover, patients on TKI had significantly lower levels of anti-pneumococcal IgM at 1 month compared to healthy controls (median, 84.5 U/ml, range 5 to 200 vs 200 U/ml, range 15 to 200, p=0.006). At 1 month the median levels of IgM in patients on dasatinib, nilotinib and IM were 55 U/ml (range, 12 to 172), 87 U/ml (range, 8-138) and 90 U/ml (range, 5 to 200) respectively.

We have so far analyzed CD8 and CD4 T cell responses to Flu vaccination in 15 patients on TKI and 5 healthy controls. Prior to vaccination, T cell responses against Flu were detected in 4/15 patients on TKI and 1/5 healthy controls, indicating pre-existing memory T cell responses to Flu. In these subjects the T-cell response to Flu did not increase significantly after vaccination and as such the response was defined as negative. A significant T-cell response to Flu was seen in 7/15 patients on TKI (median 0.28% TNF-α⁺CD4⁺ T cells, range 0.10–2.25%) and in 3/5 healthy control (median 0.79% TNF-α⁺CD4⁺T cells, range 0.12–1.34%).

These preliminary results suggest that in patients with CML on TKIs the IgM B cell response to vaccination with Pneumovax is significantly impaired compared to healthy controls. We have as yet not detected a significant difference in T-cell response following vaccination with Flu in CML patients on TKIs compared to healthy controls. We are in the process of analyzing the remaining samples.