Large Granular Lymphocyte (LGL) Expansions Comprising Oligoclonal T Cell or NK Cell Populations in Dasatinib Treated Patients Are Associated with HLA-A*0201, CMV Reactivation and Enhanced Anti-Leukemic Control.

Immunosuppressive effects of the second generation tyrosine kinase inhibitor dasatinib (Sprycel®) on T cells and NK cells have been described in vitro. In contrast, in some CML or Ph⁺ ALL patients receiving dasatinib, the development of a chronic, oscillating lymphocytosis has been observed in vivo. We previously showed that dasatinib-induced lymphocytosis typically comprises of oligoclonal NK or CD8⁺ cytotoxic T cell large granular lymphocyte (LGL) expansions and was associated with HLA-A*0201, CMV reactivation and enhanced, long-lasting therapy responses in patients with advanced leukemia.

To further elucidate the mechanisms underlying LGL expansions during dasatinib, we analyzed T cell and NK cell effector functions directly ex vivo. Specifically, we evaluated activation, proliferation, cytotoxic activity, cytokine secretion, degranulation, KIR expression profile and apoptosis/necrosis susceptibility.

We observed decreased NK cell cytotoxic activity against the cell line K562 only in patients with NK cell expansions, potentially due to exhaustion based on excessive in vivo proliferation. This reduced lytic ability was restored after pre-treatment with IL-2 for 18h. No correlation between functionality and KIR expression profile was found. Furthermore, patients with LGL expansions exhibited elevated IP10/RANTES levels in the plasma compared to non-LGL patients and healthy controls. Strikingly, within the CD8⁺ T cell population specific for the CMV epitope NLVPMVATV (pp65, residues 495-503) restricted by HLA-A*0201, we observed distinct CD8high and CD8low fractions in patients with LGL expansions (n=5) but not in patients without LGL expansions (n=4) or in healthy controls (n=3). The CD8high subpopulation was more resistant to inhibition by dasatinib compared to other cell fractions; in addition, dasatinib effectively abrogated down-regulation of both TCR and CD8 in the CD8high subpopulation in vitro.

Thus, we hypothesize that CMV reactivation is intimately linked to the observed LGL expansions in dasatinib-treated patients. The expanded cytotoxic cells may target both CMV-infected and leukemic cells by virtue of epitope sharing and thus explain the enhanced anti-leukemic control we observed. Further investigations based on the application of polychromatic flow cytometry and analysis of T cell clonality are underway to establish the nature of this association in more detail. Dasatinib and derivatives may prove to be useful in modulating anti-leukemic/anti-host immune responses in vivo.

Mustjoki:BMS: Honoraria. Ekblom:BMS: Honoraria. Porkka:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Seggewiss:BMS: Honoraria.