NKG2A Down-Regulation by Dasatinib Enhances Natural Killer Cytotoxicity and Accelerates Effective Treatment Responses in Patients With Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a hematological malignancy characterized by the presence of t(9;22) chromosomal translocation that results in BCR-ABL fusion gene. ABL tyrosine kinase inhibitors (TKIs), such as imatinib, nilotinib, and dasatinib, are currently the front-line treatment options for CML. Recently, natural killer (NK) cell activation and expansion have been shown to be associated with optimal treatment responses for CML. To investigate the effects and mechanisms of these TKIs on NK cells, here we characterized activating and inhibitory NK receptors in CD3−CD16+CD56dim NK cells isolated from CML patients in chronic phase (CP). The expressions of activating NK receptors, such as NKG2D, natural cytotoxicity receptor (NCR) and DNAM-1, rebounded after successful TKI treatments for CML. In contrast, among the three surveyed inhibitory receptors (NKG2A, KIR2DL1, and KIR3DL1), only the expression of NKG2A was reverted and suppressed to a very low level by dasatinib, and not by imatinib or nilotinib. CML patients treated with dasatinib indeed expressed fewer NKG2A+ NK cells, which send negative signals for induction of NK cytotoxicity. For these dasatinib-treated patients, the duration to reach major molecular response (MMR) was shorter, and significantly correlated with individual's NKG2A+ NK cell number. This clinical relevance to NKG2A was not observed in treatments with imatinib or nilotinib. In line with dasatinib-specific down-regulation of NKG2A, NK cytotoxicity evaluated by the killing assay was also significantly higher in patients treated with dasatinib than in those treated with imatinib or nilotinib. The lower NK cytotoxicity from imatinib or nilotinib treatments could be reverted by NKG2A blockade using anti-NKG2A antibody. Further in vitro experiments revealed mechanistically that dasatinib could inactivate p38 mitogen-activated protein kinase (MAPK), and consequently affect nuclear import of GATA-3 and GATA-3 transcriptional activities for NKG2A. Our results highlight the dual effects of dasatinib in direct inhibition of ABL kinase and in immunomodulation through NKG2A down-regulation, contributing to accelerated molecular responses (MR) in CML

DNA-based vaccines against cancer

Efficient antigen expression in vivo is an essential step in eliciting anti-tumour immunity by DNA vaccines.  In this study we showed that inclusion of either Intron A of the human cytomegalovirus immediate early gene promoter or the SV40 promoter/enhancer in the vaccine vectors could increase the expression of an idiotypic (Id) Ig-FrC fusion construct in vitro, and incorporation of both components resulted in the highest expression level.  Vaccination studies in mice showed that the levels of antigen expression in vitro correlated with the antibody responses in vivo.  Importantly, higher antibody responses appeared to confer better protection against tumour challenge.  Furthermore, higher level of antigen expression could also improve CD8+ T cell responses and provide better tumour protection when a DNA vaccine encoding that AH1 CTL epitope (pDOM-AH1) was tested.  Together, the data strongly suggest that increasing antigen expression is an effective approach to augmenting the potency of DNA tumour vaccines. One strategy for enhancing the efficacy of tumour vaccines is to link to tumour antigen to a pathogen-derived antigen that can activate potent cognate CD+ T cell help. In this study, we explored the utilities of the B subunit of Escherichia coli heat-labile enterotoxin (EtxB).  EtxB is not only a highly immunogenic molecule itself, but also can act as a potent adjuvant or carrier to increase immune responses to other antigens.  Fusion of EtxB to a tumour antigen should provide linked CD4+ T cell help.  Moreover, EtxB can directly exert potent immuno-modulatory activities on lymphocytes and antigen presenting cells.  A further attraction is its potential to enhance activation of T cell responses by enhancing antigen via receptor-mediated mechanism.</p

DNA-based vaccines against cancer

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