Human cytomegalovirus (CMV), a herpesvirus that causes congenital disease and opportunistic infections in immunocompromised individuals, encodes functions that facilitate efficient viral propagation by altering host cell behavior. Here we show that CMV blocks apoptosis mediated by death receptors and encodes a mitochondria-localized inhibitor of apoptosis, denoted vMIA, capable of suppressing apoptosis induced by diverse stimuli. vMIA, a product of the viral UL37 gene, inhibits Fas-mediated apoptosis at a point downstream of caspase-8 activation and Bid cleavage but upstream of cytochrome c release, while residing in mitochondria and associating with adenine nucleotide translocator. These functional properties resemble those ascribed to Bcl-2; however, the absence of sequence similarity to Bcl-2 or any other known cell death suppressors suggests that vMIA defines a previously undescribed class of anti-apoptotic proteins.

We have identified a human cytomegalovirus cell-death suppressor, denoted vICA, encoded by the viral UL36 gene. vICA inhibits Fas-mediated apoptosis by binding to the pro-domain of caspase-8 and preventing its activation. vICA does not share significant sequence homology with FLIPs or other known suppressors of apoptosis, suggesting that this protein represents a new class of cell-death suppressors. Notably, resistance to Fas-mediated apoptosis is delayed in fibroblasts infected with viruses that encode mutant vICA, suggesting that vICA suppresses death-receptorinduced cell death in the context of viral infection. Although vICA is dispensable for viral replication in vitro, the common targeting of caspase-8 activation by diverse herpesviruses argues for an important role for this antiapoptotic mechanism in the pathogenesis of viral infection in the host, most likely in avoiding immune clearance by cytotoxic lymphocytes and natural killer cells.

Purpose: The CD38 cell surface antigen is expressed in diverse hematologic malignancies including multiple myeloma, B-cell non-Hodgkin lymphoma (NHL), B-cell chronic lymphocytic leukemia, B-cell acute lymphoblastic leukemia (ALL), and T-cell ALL. Here, we assessed the antitumor activity of the anti-CD38 antibody SAR650984.Experimental Design: Activity of SAR650984 was examined on lymphoma, leukemia and multiple myeloma cell lines, primary multiple myeloma samples, and multiple myeloma xenograft models in immunodeficient mice.Results: We identified a humanized anti-CD38 antibody with strong proapoptotic activity independent of cross-linking agents, and potent effector functions including complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and antibody-dependent cellular phagocytosis (ADCP), equivalent in vitro to rituximab in CD20 þ and CD38 þ models. This unique antibody, termed SAR650984, inhibited the ADP-ribosyl cyclase activity of CD38, likely through an allosteric antagonism as suggested by 3D structure analysis of the complex. In vivo, SAR650984 was active in diverse NHL, ALL, and multiple myeloma CD38 þ tumor xenograft models. SAR650984 demonstrated single-agent activity comparable with rituximab or cyclophosphamide in Daudi or SU-DHL-8 lymphoma xenograft models with induction of the proapoptotic marker cleaved capase-7. In addition, SAR650984 had more potent antitumor activity than bortezomib in NCI-H929 and Molp-8 multiple myeloma xenograft studies.

We report that the cytomegalovirus-encoded cell death suppressor vMIA binds Bax and prevents Bax-mediated mitochondrial membrane permeabilization by sequestering Bax at mitochondria in the form of a vMIA–Bax complex. vMIA mutants with a defective mitochondria-targeting domain retain their Bax-binding function but not their ability to suppress mitochondrial membrane permeabilization or cell death. vMIA does not seem to either specifically associate with Bak or suppress Bak-mediated mitochondrial membrane permeabilization. Recent evidence suggests that the contribution of Bax and Bak in the mitochondrial apoptotic signaling pathway depends on the distinct phenotypes of cells, and it appears from our data that vMIA is capable of suppressing apoptosis in cells in which this pathway is dominated by Bax, but not in cells where Bak also plays a role.

The viral mitochondria-localized inhibitor of apoptosis (vMIA), encoded by the UL37 gene of human cytomegalovirus, inhibits apoptosis-associated mitochondrial membrane permeabilization by a mechanism different from that of Bcl-2. Here we show that vMIA induces several changes in Bax that resemble those found in apoptotic cells yet take place in unstimulated, nonapoptotic vMIA-expressing cells. These changes include the constitutive localization of Bax at mitochondria, where it associates tightly with the mitochondrial membrane, forming high molecular weight aggregates that contain vMIA. vMIA recruits Bax to mitochondria but delays relocation of caspase-8-activated truncated Bidgreen fluorescent protein (GFP) (t-Bid-GFP) to mitochondria. The ability of vMIA and its deletion mutants to associate with Bax and to induce relocation of Bax to mitochondria correlates with their anti-apoptotic activity and with their ability to suppress mitochondrial membrane permeabilization. Taken together, our data indicate that vMIA blocks apoptosis via its interaction with Bax. vMIA neutralizes Bax by recruiting it to mitochondria and "freezing" its pro-apoptotic activity. These data unravel a novel strategy of subverting an intrinsic pathway of apoptotic signaling.Apoptosis is mediated through two main pathways, the extrinsic (death receptor) pathway and the intrinsic (mitochondrial) pathway. The extrinsic pathway is initiated by ligation of a plasma membrane death receptor, which results in a stepwise recruitment of adaptors and initiator caspases (in particular, caspase-8) into the death-inducing signaling complex.

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The human cytomegalovirus UL37 exon 1 gene encodes the immediate early protein pUL37x1 that has antiapoptotic and regulatory activities. Deletion mutagenesis analysis of the open reading frame of UL37x1 identified two domains that are necessary and sufficient for its antiapoptotic activity. These domains are confined within the segments between amino acids 5 to 34, and 118 to 147, respectively. The first domain provides the targeting of the protein to mitochondria. Direct PCR sequencing of UL37 exon 1 amplified from 26 primary strains of human cytomegalovirus demonstrated that the promoter, polyadenylation signal, and the two segments of pUL37x1 required for its antiapoptotic function were invariant in all sequenced strains and identical to those in AD169 pUL37x1. In total, UL37 exon 1 varies between 0.0 and 1.6% at the nucleotide level from strain AD169. Only 11 amino acids were found to vary in one or more viral strains, and these variations occurred only in the domains of pUL37x1 dispensable for its antiapoptotic function. We infer from this remarkable conservation of pUL37x1 in primary strains that this protein and, probably, its antiapoptotic function are required for productive replication of human cytomegalovirus in humans.

A majority of ovarian and non-small cell lung adenocarcinoma cancers overexpress folate receptor a (FRa). Here, we report the development of an anti-FRa antibody-drug conjugate (ADC), consisting of a FRa-binding antibody attached to a highly potent maytansinoid that induces cell-cycle arrest and cell death by targeting microtubules. From screening a large panel of anti-FRa monoclonal antibodies, we selected the humanized antibody M9346A as the best antibody for targeted delivery of a maytansinoid payload into FRa-positive cells. We compared M9346A conjugates with various linker/maytansinoid combinations, and found that a conjugate, now denoted as IMGN853, with the N-succinimidyl 4-(2-pyridyldithio)-2-sulfobutanoate (sulfo-SPDB) linker and N