CD19 is a pan B-cell surface receptor expressed from pro-B-cell development until its down-regulation during terminal differentiation into plasma cells. CD19 represents an attractive immunotherapy target for cancers of lymphoid origin due to its high expression levels on the vast majority of non-Hodgkin's lymphomas and some leukemias. A humanized anti-CD19 antibody with an engineered Fc domain (XmAb5574) was generated to increase binding to Fc; receptors on immune cells and thus increase Fc-mediated effector functions. In vitro, XmAb5574 enhanced antibodydependent cell-mediated cytotoxicity 100-fold to 1,000-fold relative to an anti-CD19 IgG1 analogue against a broad range of B-lymphoma and leukemia cell lines. Furthermore, XmAb5574 conferred antibody-dependent cell-mediated cytotoxicity against patient-derived acute lymphoblastic leukemia and mantle cell lymphoma cells, whereas the IgG1 analogue was inactive. XmAb5574 also increased antibody-dependent cellular phagocytosis and apoptosis. In vivo, XmAb5574 significantly inhibited lymphoma growth in prophylactic and established mouse xenograft models, and showed more potent antitumor activity than its IgG1 analogue. Comparisons with a variant incapable of Fc; receptor binding showed that engagement of these receptors is critical for optimal antitumor efficacy. These results suggest that XmAb5574 exhibits potent tumor cytotoxicity via direct and indirect effector functions and thus warrants clinical evaluation as an immunotherapeutic for CD19 + hematologic malignancies.

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Engagement of the low-affinity Ab receptor FcγRIIb downregulates B cell activation, and its dysfunction is associated with autoimmunity in mice and humans. We engineered the Fc domain of an anti-human CD19 Ab to bind FcγRIIb with high affinity, promoting the coengagement of FcγRIIb with the BCR complex. This Ab (XmAb5871) stimulated phosphorylation of the ITIM of FcγRIIb and suppressed BCR-induced calcium mobilization, proliferation, and costimulatory molecule expression of human B cells from healthy volunteers and systemic lupus erythematosus (SLE) patients, as well as B cell proliferation induced by LPS, IL-4, or BAFF. XmAb5871 suppressed humoral immunity against tetanus toxoid and reduced serum IgM, IgG, and IgE levels in SCID mice engrafted with SLE or healthy human PBMC. XmAb5871 treatment also increased survival of mice engrafted with PBMC from a unique SLE patient. Unlike anti-CD20 Ab, coengagement of FcγRIIb and BCR complex did not promote B cell depletion in human PBMC cultures or in mice. Thus, amplification of the FcγRIIb inhibitory pathway in activated B cells may represent a novel B cell-targeted immunosuppressive therapeutic approach for SLE and other autoimmune diseases that should avoid the complications associated with B cell depletion.

Bispecific antibodies based on full-length antibody structures are more optimal than fragment-based formats because they benefit from the favorable properties of the Fc region. However, the homodimeric nature of Fc effectively imposes bivalent binding on all current full-length bispecific antibodies, an attribute that can result in nonspecific activation of cross-linked receptors. We engineered a novel bispecific format, referred to as mAb-Fv, that utilizes a heterodimeric Fc region to enable monovalent co-engagement of a second target antigen in a full-length context. mAb-Fv constructs co-targeting CD16 and CD3 were expressed and purified as heterodimeric species, bound selectively to their co-target antigens, and mediated potent cytotoxic activity by NK cells and T cells, respectively. The capacity to co-engage distinct target antigens simultaneously with different valencies is an improved feature for bispecific antibodies with promising therapeutic implications.

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IntroductionIn the past decade, monoclonal antibodies directed against B-cell antigens have proven beneficial for patients with B-lineage neoplasms. Approved immunotherapeutics include the anti-CD52 antibody alemtuzumab (Campath-1H), 1 2 anti-CD20 antibodies, rituximab (Rituxan) 2 and most recently ofatumumab (Arzerra), 3 and 2 anti-CD20 conjugates carrying radioactive isotopes, 90 Yibritumomab tiuxetan (Zevalin) 4 and 131 I-tositumomab (Bexxar). 5 In particular, when used as a single agent or in combination with chemotherapy, rituximab has shown efficacy and relative safety in many B-cell non-Hodgkin lymphomas (NHLs) and some B-cell leukemias. 2,6 However, some patients do not respond to rituximab, and many of those that do will relapse. 2 In addition, some B-cell tumors either lack CD20 expression or lose it during rituximab treatment. 7 Thus, antibodies targeting other B-cell antigens are warranted, and several are being explored, including those targeting CD40, a 45-to 50-kDa transmembrane glycoprotein belonging to the tumor necrosis factor receptor family.CD40 is broadly expressed on hematologic cells, including B cells and on several types of epithelial and endothelial cells. [8][9][10] The ligand of CD40, CD40L (CD154), is preferentially expressed on activated T cells but has also been found on other hematologic cell types. Signaling via the CD40 pathway plays a key role in defining cellular and humoral immune responses. 10 CD40 is overexpressed by the malignant counterparts to Blineage cells and is found on most mature B-cell malignancies, including NHL, Hodgkin disease, and chronic lymphocytic leukemia (CLL), and on some early acute lymphocytic leukemias (ALL) 8,11,12 ; it is also expressed on multiple myeloma (MM) cells. 13 Many solid tumors express CD40, including melanoma and carcinomas of the kidney, bladder, lung, pancreas, colon, prostate, ovary, breast, head, and neck. 14 CD40 agonists have been shown to trigger immune responses against various tumors 15,16 and to inhibit the growth of different neoplastic cells, both in vitro and in vivo. 17,18 Broad stimulation of the immune system and expression on a wide range of malignancies make CD40 an attractive target for antibody-based immunotherapy. Over the past 2 decades, several CD40-specific antibodies have been tested against B-lineage malignancies in vitro and in animal models, yielding various degrees of success. [19][20][21][22][23] Recently, 2 humanized antibodies have emerged for further development: a mild CD40 agonist, 20,24,25 and a CD40 antagonist, HCD122 (CHIR-12.12). 21,23 These agents were evaluated in phase 1 and 2 trials in patients with relapsed MM, NHL, and CLL. Thus far, they have demonstrated a favorable safety profile and have shown some antitumor activity in NHL and MM. [26][27][28] In addition, a strongly agonistic anti-CD40 antibody, CP-870,893, evaluated in phase 1 trials in patients with melanoma and other solid tumors, was found to be well tolerated and to have antitumor activity. 29 Therefore, preclinical and early clinic...

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As an important regulator in Wnt-signaling pathway, the APC gene is involved in apoptosis and cell cycle arrest. The loss of APC function is observed in most familial adenomatous polyposis-associated and sporadic colorectal cancer. APC gene is frequently inactivated by DNA mutations. However, hypermethylation in APC gene promoter was also observed in different cancers. In this study, by analyzing the methylation status of APC promoter in 22 colorectal cancer cell lines with different APC expression levels, we identified Regions A and B in the promoter, where the methylation of CpG sites was invariably correlated with the loss of gene expression. By nuclease accessibility assay, we also observed a correlation between the closed chromatin conformation in APC promoter and loss of gene expression. When the nonexpressing cell lines were treated with a DNA methyltransferase inhibitor, 5-Aza-2-Deoxycytidine, the APC expression in these cells was induced, CpG sites were demethylated, and closed chromatin conformation was opened. However, when these cell lines were treated with a histone deacetylase inhibitor, Trichostatin A, no significant changes in APC expression, methylation status, and chromatin conformation were observed. Using transient transfection assay, a CCAAT box located in Region B was identified, which was involved in up-regulation of APC expression. Methylation of CpG sites around the CCAAT box resulted in a significant inhibition in the gene expression. The specific binding of a transcription factor CCAAT-binding factor (CBF) to the CCAAT box was determined by electrophoretic mobility shift analysis. The binding was inhibited after CpG sites close to the CCAAT box were methylated, indicating that DNA methylation can silence gene expression through interfering with the binding of transcription factors to the promoter. The biological function of CBF in APC gene regulation was further indicated by the decrease of luciferase activities in cells cotransfected with a plasmid carrying APC promoter/luciferase gene and a plasmid expressing dominant negative CBF mutant. In summary, methylation of CpG sites around CCAAT box in APC promoter inhibits the gene expression by changing the chromatin conformation and interfering with the binding of transcription factor CBF to CCAAT box.