Natural Killer Cells Recovery After Consolidation Chemotherapy in Elderly Patients with Acute Myeloid Leukemia (AML)

Human Natural Killer (NK) cells are able to kill abnormal cells while preserving normal cells. Accumulating clinical and experimental data point toward a key role of these cells in the control and clearance of most if not all hematologic malignancies. Recent insights into NK have stimulated studies of innate immunity in haematological malignancies, as the role of NK cells in allogeneic transplantation. Better knowledge of the deficiencies of these effector cells can allow elaborating new protocols of immunotherapy in order to directly enhance their capacity to eliminate tumor cells.

Hence, the mechanisms of recognition and killing of leukemic cells and their role in vivo have only been investigated very recently. Even though lysis of leukemic cells or leukemic cell lines by NK cells has been described in vitro, mechanisms underlying the interaction and destruction of these cells are not clearly defined. Some of these receptors are altered in AML patients at diagnosis and might be involved in the immune escape of AML blasts. However, the recovery of NK cells during consolidation chemotherapy treatment has not been studied. The present study monitored status of NK cells following patient's remission after chemotherapy in order to provide new targets for immunotherapy.

We enrolled 29 elderly patients (mean: 70-years old) with non promyelocytic AML in first CR following induction and pre-consolidation chemotherapy. Patient peripheral NK cells were analyzed at diagnosis, before consolidation chemotherapy and every two weeks after treatment for 8 weeks. 6-colors flow cytometry was performed to investigate the expression of MHC receptors (CD158a, b, e, i, CD85j and NKG2A), activating receptors (NKp30, NKp46, NKG2D, CD16, DNAM-1, 2B4) as well as their differentiation status (perforin and granzyme expression). Their function, as determined by cytotoxicity (⁵¹Cr release and CD107 expression) and cytokine production (intracellular staining of IFN-g), was analyzed using purified NK cells stimulated by K562, or in redirected assays using NKp30, NKp46 and CD16 mAbs. The recovery of these receptors was then correlated with PFS and OS.

NK cell counts were depressed after induction and pre-consolidation chemotherapy as compared to NK cell counts of age-matched controls; they were further depressed during the first 2 weeks post-consolidation chemotherapy, but were back to pre-consolidation chemotherapy level at 4 weeks. NKp30 and NKp46 expression was lower at diagnosis as compared to controls but their levels restored progressively after induction and consolidation chemotherapy.

NKG2D expression were depressed at pre-consolidation but increased after consolidation chemotherapy. For inhibitory receptors, CD158a or CD158b expressions were depressed at diagnosis, at post-induction and consolidation chemotherapy. In contrast, the NKG2A positive NK cell subsets increased progressively after consolidation chemotherapy. Moreover, sizes of perforin or granzyme positive NK cell subsets were increased in treated AML patients. K562 cytotoxicity was depressed after induction chemotherapy but increased after consolidation chemotherapy. In contrast, IFN-g secretion was decreased, at all time points.

Finally, we try to correlate the recovery of these different receptors with OS and PFS. NKp30 and NKG2D recovery seems to be correlated with better PFS and OS.

This study confirms that NK cells from AML patients displayed different phenotype and functional abnormalities at diagnosis. Chemotherapy seems to have different impact on the recovery of inhibitory or activatory NK receptors. The predominant data is that NK cells recovered rapidly after consolidation chemotherapy and seems to be more operational at that time. Immunotherapy of NK cells must be probably developed post consolidation chemotherapy when NK cells are ready and residual disease low. Antibodies to stimulate NK cells are actually evaluated in this setting.

Anfossi:Innate Pharma: Employment. Andre:Innate Pharma: Employment. Breso:Innate Pharma: Employment. Perri:Innate Pharma: Employment. Romagne:Innate Pharma: Employment.