Therefore, allogeneic NK cell transplantation from a healthy donor may be necessary during antibody treatment

Therefore, allogeneic NK cell transplantation from a healthy donor may be necessary during antibody treatment. == Results == All three cell lines were resistant to NK cell lysis, had some inhibitory KIR ligands and protease inhibitor-9, and expressed low levels of NKG2D activating ligands and adhesion molecules. After treatment with XmAb5574 or lintuzumab, MLL-rearranged leukemia cells were efficiently killed by NK cells. The addition of panmajor histocompatibility complex class I antibody, which Rabbit Polyclonal to SF3B4 blocked inhibitory KIR-HLA interaction, further augmented degranulation in all three KIR2DL1, KIR2DL2/3, and KIR3DL1 subsets of NK cells based on the rule of missing-self recognition. A mouse model showed a decreased rate of leukemia progression in vivo as monitored by bioluminescence imaging and longer survival after antibody treatment. == Conclusion == Our data support the use of a triple immunotherapy approach, including an antibody directed against tumor-associated antigen, KIR-mismatched NK cell transplantation, and inhibitory KIR blockade, for the treatment of NK cellresistant MLL-rearranged leukemias. Keywords:Antibody-dependent cell-mediated cytotoxicity, natural killer cells, killer-cell immunoglobulin-like receptors, mixed-lineage leukemia, targeted therapy == Introduction == Recurrent translocations that involve chromosome 11 band q23 have been observed in acute myeloid leukemia (AML), acute SPHINX31 lymphoblastic leukemia (ALL), and biphenotypic SPHINX31 (mixed lineage) leukemia; thus, the gene has been namedMLL(for myeloid/lymphoid, or mixed lineage, leukemia) (1). TheMLLgene is a member of the trithorax group and consists of 36 exons encoding a DNA-binding methyltransferase that contains 3,969 amino acids with a molecular weight of 430 kDa (2). The protein methylates histone H3 on lysine residue 4 (H3K4) for epigenetic control of early embryonic development and hematopoiesis (3,4). Chromosomal translocations during leukemogenesis usually involve an 8.3 kb breakpoint cluster region spanning exons 511 ofMLLwhich then join the amino terminal of MLL to the carboxy terminal of one of 70 partner proteins in frame (2,4). The common translocations include t(4;11) and t(11;19) in ALL and t(9;11) and t(6;11) in AML, resulting in the formation of fusion proteins, including MLL-AF4, MLL-ENL, MLL-AF9, and MLL-AF6, all of which have lost H3K4 methyltransferase activity (3). Instead, the chimeric fusion proteins lead to the aberrant expression of many downstream target genes, includingHOX, MEIS1, BCL2, C-MYC,andCDK6(2,5). MLL-rearranged leukemias have unique clinical features and are often associated with a poor prognosis (6). MLL rearrangements are found in approximately 80% of infant leukemias and in 10% of AML in adults (3). A very high proportion of patients with therapy-related acute leukemia after treatment with topoisomerase II inhibitors have MLL abnormalities involving AF4, AF9, and ENL, as well as CBP, that are characteristic of therapy-related AML (2,7). Patients with MLL-rearranged leukemia have a low probability of survival, in the 30% to 40% range, even with contemporary chemotherapy and hematopoietic stem cell transplantation (6,8). Because many MLL-rearranged leukemias express mixed-lineage or biphenotypic markers including B and myeloid antigens, targeted therapy using monoclonal antibodies against these antigens is an attractive alternative treatment. Rituximab is an FDA-approved chimeric antibody against human CD20, an antigen expressed beginning at the preB-cell stage. Unfortunately, most MLL-rearranged leukemias are stem-celllike and CD20-negative (3,4). Therefore, CD19 is a better target as a panB-cell antigen. XmAb5574 is SPHINX31 a humanized anti-CD19 antibody with its Fc domain engineered for higher affinity to FcRIIIa of effector cells and diminished non-specific binding to FcIIb. In chronic lymphoblastic leukemia, ALL, and mantle cell lymphoma, it may mediate SPHINX31 more effective antibody-dependent cell-mediated cytotoxicity (ADCC) than its parental counterpart as well as other therapeutic antibodies such as rituximab, ofatumumab and alemtuzumab (911). For pan-myeloid antigens, CD33 is an attractive target. Lintuzumab (also known as SGN-33 and huM195) is an anti-CD33 therapeutic antibody in clinical development (12). It was reported to promote survival in preclinical mouse models of AML (13,14). Natural killer (NK) cells are the primary lymphocytes that are involved in ADCC through the activation of high-affinity FcRIIIa (CD16) on their cell surfaces. Human NK cell transplantation has become feasible recently SPHINX31 and has therefore generated much interest in augmenting cancer antibody therapy (15). In a clinical study, NK cell therapy alone was found to be safe and beneficial in AML patients (16); however, NK cell transplantation may not always be effective, because immune escape is possible. Biologically, NK cell functions are regulated by two sets of surface molecules: activating and inhibitory receptors. Killer-cell immunoglobulin-like receptors (KIR) and NKG2D are two of the receptor families that are known to be important as inhibitory and activating receptors, respectively, in human leukemia cell recognition. Thus, leukemia cells may escape from NK cell immunosurveillance by upregulation of the expression of a KIR inhibitory ligand or downregulation of NKG2D activation signals. In this study, we characterized the NK cell ligand expression in MLL-rearranged leukemia and provided evidence that.