Chisako Iriyama

Inhibitory FcγRIIb (CD32b) becomes activated by therapeutic mAb in both cis and trans and drives internalization according to antibody specificity

A major feature that distinguishes type I from type II anti-CD20 monoclonal antibodies (mAbs) and reduces their therapeutic efficacy is the tendency to internalize from the cell surface. We have shown previously that the extent of internalization correlates with the capacity of type I mAb to simultaneously engage both CD20 and the inhibitory Fcγ receptor, FcγRIIb, in a bipolar configuration. Here, we investigated whether mAbs directed at other B-cell surface receptors also engaged FcγRIIb and whether this interaction promoted internalization. Most mAbs engaged and activated FcγRIIb, with the strength of activation related to the level of mAb bound to the cell surface. However, engagement did not affect internalization of most mAb-ligated receptors, either in cell lines or primary chronic lymphocytic leukemia cells with the exception of CD19 and CD38. Furthermore, at high cell concentrations/density both cis and trans interactions between cell-surface bound mAb and FcγRIIb were evident, but trans interactions did not inhibit type I anti-CD20 mAb-mediated internalization. These data identify that FcγRIIb is engaged by many mAbs in both cis and trans configurations, triggering its activation, but that internalization via FcγRIIb occurs for only a select subset. These findings have implications when designing new antibody-based therapeutics.

Fcγ receptors: genetic variation, function, and disease

Fcγ receptors (FcγRs) are key immune receptors responsible for the effective control of both humoral and innate immunity and are central to maintaining the balance between generating appropriate responses to infection and preventing autoimmunity. When this balance is lost, pathology results in increased susceptibility to cancer, autoimmunity, and infection. In contrast, optimal FcγR engagement facilitates effective disease resolution and response to monoclonal antibody immunotherapy. The underlying genetics of the FcγR gene family are a central component of this careful balance. Complex in humans and generated through ancestral duplication events, here we review the evolution of the gene family in mammals, the potential importance of copy number, and functionally relevant single nucleotide polymorphisms, as well as discussing current approaches and limitations when exploring genetic variation in this region.

Cloning and sequencing of a novel human gene which encodes a putative hydroxylase

AbstractUsing a conventional two-hybrid technique with MAWD as bait protein, a novel full-length cDNA was isolated and sequenced from a human liver cDNA library. This cDNA consists of 2575 base pairs and has a predicted open reading frame encoding 255 amino acids. Overall, it is similar to the catalytic enzyme PHZF, catalyzing the hydroxylation of phenazine-1-carboxylic acid to 2-hydroxy-phenazine-1-carboxylic acid. Polymerase chain reaction-based mapping with both a monochromosomal hybrid panel and radiation hybrid cell panels placed the gene to human chromosome 10q21.1 near the marker D10S210.

Cloning and sequencing of a novel human gene that encodes a putative target protein of Nesh-SH3.

AbstractBy using a conventional two-hybrid technique with an Src homology 3 (SH3) domain of Nesh as the bait protein, a novel full-length cDNA was isolated and sequenced from a human placenta cDNA library. This cDNA consists of 3023 bp and has a predicted open reading frame that encodes 486 amino acids. It possesses an SH3 binding motif, a nuclear targeting sequence, and no catalytic domain. Overall, it has no similarity to known molecules involved in a signaling cascade. Polymerase Chair reaction-based mapping with both a monochromosomal hybrid panel and radiation hybrid cell panels localized the gene on human chromosome 3q12 near the marker D3S1271.

De novo diffuse large B-cell lymphoma with a CD20 immunohistochemistry-positive and flow cytometry-negative phenotype: molecular mechanisms and correlation with rituximab sensitivity.

CD20 is expressed in most B‐cell lymphomas and is a critical molecular target of rituximab. Some B‐cell lymphomas show aberrant CD20 expression, and rituximab use in these patients is controversial. Here we show both the molecular mechanisms and the clinical significance of de novo diffuse large B‐cell lymphomas (DLBCL) that show a CD20 immunohistochemistry (IHC)‐positive and flow cytometry (FCM)‐ negative (IHC[+]/FCM[−]) phenotype. Both IHC and FCM using anti‐CD20 antibodies L26 and B1, respectively, were analyzed in 37 of the 106 cases of de novo DLBCL; 8 (22%) of these cases were CD79a(+)/CD20(+) with IHC and CD19(+)/CD20(−) with FCM. CD20 (MS4A1) mRNA expression was significantly lower in IHC(+)/FCM(−) cells than in IHC(+)/FCM(+) cells (P = 0.0005). No genetic mutations were detected in MS4A1 promoter and coding regions. Rituximab‐mediated cytotoxicity in the CDC assay using IHC(+)/FCM(−) primary cells was significantly lower than in IHC(+)/FCM(+) cells (P < 0.05); however, partial effectiveness was confirmed. FCM using rituximab detected CD20 more efficiently than B1. No significant difference was observed between IHC(+)/FCM(−) and IHC(+)/FCM(+) patients in overall survival (P = 0.664). Thus, lower expression of CD20 mRNA is critical for the CD20 IHC(+)/FCM(−) phenotype. Lower CD20 expression with FCM does not rule out rituximab use in these patients if expression is confirmed with IHC. FCM using rituximab may be more informative than B1 for predicting rituximab effectiveness in IHC(+)/FCM(−) cases.

A novel insertion mutation of K294RGG within BCR - ABL kinase domain confers imatinib resistance: sequential analysis of the clonal evolution in a patient with chronic myeloid leukemia in blast crisis

BCR-ABL kinase domain mutations were sequentially analyzed in a patient with chronic myeloid leukemia (CML) who exhibited repeated B-lymphoid blast crisis (CML-BC) during treatment with imatinib and dasatinib. We first identified five mutant BCR-ABL clones: Y253H, G250E, F311L, F317L and K294RGG, which was generated by two-nucleotide mutations and six-nucleotide insertion, at the third BC during the imatinib treatment, and retrospectively found that three of them (Y253H, G250E, K294RGG) were already present at the second BC. The in vitro analysis using K294RGG mutant BCR-ABL-expressing 32D cells revealed that K294RGG mutation was imatinib resistant but dasatinib sensitive. Consistent with the in vitro data, the clone with K294RGG mutation was eliminated by the dasatinib treatment in this patient. During the imatinib treatment, several mutant clones emerged and expanded, while additional mutations on the same allele were not acquired. However, after the dasatinib treatment, wild-type BCR-ABL clone disappeared and T315I or F317L mutation was acquired in G250E and Y253H mutant clones on the same allele without the emergence of each sole mutant clone. Cytogenetic and immunoglobulin heavy chain gene rearrangement analysis revealed that all mutant clones that appeared in this patient might be derived from the same CML clone.

Using peripheral blood circulating DNAs to detect CpG global methylation status and genetic mutations in patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a hematopoietic stem cell disorder. Several genetic/epigenetic abnormalities are deeply associated with the pathogenesis of MDS. Although bone marrow (BM) aspiration is a common strategy to obtain MDS cells for evaluating their genetic/epigenetic abnormalities, BM aspiration is difficult to perform repeatedly to obtain serial samples because of pain and safety concerns. Here, we report that circulating cell-free DNAs from plasma and serum of patients with MDS can be used to detect genetic/epigenetic abnormalities. The plasma DNA concentration was found to be relatively high in patients with higher blast cell counts in BM, and accumulation of DNA fragments from mono-/di-nucleosomes was confirmed. Using serial peripheral blood (PB) samples from patients treated with hypomethylating agents, global methylation analysis using bisulfite pyrosequencing was performed at the specific CpG sites of the LINE-1 promoter. The results confirmed a decrease of the methylation percentage after treatment with azacitidine (days 3-9) using DNAs from plasma, serum, and PB mono-nuclear cells (PBMNC). Plasma DNA tends to show more rapid change at days 3 and 6 compared with serum DNA and PBMNC. Furthermore, the TET2 gene mutation in DNAs from plasma, serum, and BM cells was quantitated by pyrosequencing analysis. The existence ratio of mutated genes in plasma and serum DNA showed almost equivalent level with that in the CD34+/38- stem cell population in BM. These data suggest that genetic/epigenetic analyses using PB circulating DNA can be a safer and painless alternative to using BM cells.

Peripheral blood cell-free DNA is an alternative tumor DNA source reflecting disease status in myelodysplastic syndromes.

Genetic alterations in myelodysplastic syndromes (MDS) are critical for pathogenesis. We previously showed that peripheral blood cell‐free DNA (PBcfDNA) may be more sensitive for genetic/epigenetic analyses than whole bone marrow (BM) cells and mononuclear cells in peripheral blood (PB). Here we analyzed the detailed features of PBcfDNA and its utility in genetic analyses in MDS. The plasma‐PBcfDNA concentration in MDS and related diseases (N = 33) was significantly higher than that in healthy donors (N = 14; P = 0.041) and in International Prognostic Scoring System higher‐risk groups than that in lower‐risk groups (P = 0.034). The concentration of plasma‐/serum‐PBcfDNA was significantly correlated with the serum lactate dehydrogenase level (both P < 0.0001) and the blast cell count in PB (P = 0.034 and 0.025, respectively). One nanogram of PBcfDNA was sufficient for one assay of Sanger sequencing using optimized primer sets to amplify approximately 160‐bp PCR products. PBcfDNA (approximately 50 ng) can also be utilized for targeted sequencing. Almost all mutations detected in BM‐DNA were also detected using corresponding PBcfDNA. Analyses using serially harvested PBcfDNA from an RAEB‐2 patient showed that the somatic mutations and a single nucleotide polymorphism that were detected before allogeneic transplantation were undetectable after transplantation, indicating that PBcfDNA likely comes from MDS clones that reflect the disease status. PBcfDNA may be a safer and easier alternative to obtain tumor DNA in MDS.

Emetine elicits apoptosis of intractable B-cell lymphoma cells with MYC rearrangement through inhibition of glycolytic metabolism

Despite improved clinical outcomes of diffuse large B-cell lymphoma, a certain proportion of patients still develop a primary refractory disease. To overcome these lymphomas that are intractable to existing treatment strategies, the tumor microenvironment has been identified as a potential therapeutic target. Here we describe our search for effective drugs for primary refractory lymphoma cells with MYC rearrangement. Through the drug screening of 3,440 known compounds, we identified a unique compound, emetine. This compound was effective against lymphoma cells with MYC rearrangement from two different patients that were co-cultured with cancer associated fibroblasts. Emetine induced the death of these cells with a half maximal inhibitory concentration of 312 nM and 506 nM, respectively. Subsequent analyses of the mechanism of action of emetine showed that the drug induced apoptosis of tumor cells via alteration of glucose metabolism through inhibition of hypoxia inducible factor-1α. Moreover, emetine inhibited the potential of cancer associated fibroblasts to support tumor cell viability in vitro and demonstrated significant inhibition of tumor growth in in vivo analyses. Emetine also induced cell death in other primary refractory lymphoma cells with MYC rearrangement. Our combined data indicate that emetine is a potential promising drug for the treatment of intractable lymphomas, which targets both the tumor and its microenvironment.

Evaluation of High-Throughput Genomic Assays for the Fc Gamma Receptor Locus

Cancer immunotherapy has been revolutionised by the use monoclonal antibodies (mAb) that function through their interaction with Fc gamma receptors (FcγRs). The low-affinity FcγR genes are highly homologous, map to a complex locus at 1p23 and harbour single nucleotide polymorphisms (SNPs) and copy number variation (CNV) that can impact on receptor function and response to therapeutic mAbs. This complexity can hinder accurate characterisation of the locus. We therefore evaluated and optimised a suite of assays for the genomic analysis of the FcγR locus amenable to peripheral blood mononuclear cells and formalin-fixed paraffin-embedded (FFPE) material that can be employed in a high-throughput manner. Assessment of TaqMan genotyping for FCGR2A-131H/R, FCGR3A-158F/V and FCGR2B-232I/T SNPs demonstrated the need for additional methods to discriminate genotypes for the FCGR3A-158F/V and FCGR2B-232I/T SNPs due to sequence homology and CNV in the region. A multiplex ligation-dependent probe amplification assay provided high quality SNP and CNV data in PBMC cases, but there was greater data variability in FFPE material in a manner that was predicted by the BIOMED-2 multiplex PCR protocol. In conclusion, we have evaluated a suite of assays for the genomic analysis of the FcγR locus that are scalable for application in large clinical trials of mAb therapy. These assays will ultimately help establish the importance of FcγR genetics in predicting response to antibody therapeutics.