An anti-CD4 (CDR3-loop) monoclonal antibody inhibits human immunodeficiency virus type 1 envelope glycoprotein-induced apoptosis

In Vitro Antitumoral Activity of Baculovirus-expressed Chimeric Recombinant Anti-CD4 Antibody 13B8.2 on T-cell Lymphomas

A baculovirus-expressed chimeric recombinant IgG1 (rIgG1) antibody, with Cgamma1 and Ckappa human constant domains, was derived from the murine monoclonal antibody 13B8.2, which is specific for the CDR3-like loop of the CD4 molecule. The recombinant IgG1 antibody 13B8.2 was previously shown to inhibit HIV-1 replication and to abrogate the one-way mixed-lymphocyte reaction and block proliferation of CD3-stimulated peripheral blood CD4 lymphocytes from healthy donors. Before testing this recombinant anti-CD4 antibody in in vivo preclinical trials, in vitro mechanisms of action of rIgG1 13B8.2 were assessed using various CD4 T-cell lymphomas. The baculovirus-expressed rIgG1 13B8.2 antibody led to 14% to 40% proliferation inhibition of the lymphoblastic leukaemia-derived SUP-T1, the acute T lymphoma-derived CCRF-CEM and Jurkat, and the cutaneous T-Cell lymphoma-derived HUT-78 cell lines, but it did not affect the cell cycle nor induce cell apoptosis. rIgG1 antibody 13B8.2 bound the C1q fraction, leading to 9% to 17% complement-mediated lysis of the HUT-78, H9, Sup-T1, and the CCRF-CEM cell lines. No correlation was observed between cell sensitivity to rIgG1 13B8.2-triggered complement-dependent lysis and CD35-, CD46-, CD55-, and CD59-surface expression on T lymphoma cells. Using fluorescence-activated cell sorter analysis, the antibody was shown to bind to FcgammaRI/CD64-transfected IIA1.6, FcgammaRII/CD32-transfected CDw32L, and FcgammaRIII/CD16-transfected Jurkat CD16 cell lines. In correlation with these findings, rIgG1 13B8.2 induced 11% to 31% antibody-dependent cell-mediated cytotoxicity of the CCRF-CEM, SUP-T1, A2.01 CD4, and Jurkat cell lines. These convincing results on the activity of the recombinant chimeric anti-CD4 antibody 13B8.2 have led us to perform in vivo preclinical study in a murine xenograft model of CD4 lymphomas.

Comparison of apoptosis and mortality measurements in peripheral blood mononuclear cells (PBMCs) using multiple methods

Death through apoptosis is the main process by which aged cells that have lost their function are eliminated. Apoptotic cells are usually detected microscopically by changes in their morphology. However, determination of early apoptotic events is important for in vitro (and ex vivo) studies. The main objective of the present study is to find the most sensitive method for apoptosis detection in human peripheral blood mononuclear cells (PBMCs) by comparing six different methods following five different means of immunological stimulation at 3 and 5 days. Each of six apoptosis quantification methods, except the trypan blue exclusion test, is a combination of two stains, one for the specific detection of apoptotic cells and the other for the unspecific detection of dead cells. Values for apoptosis and mortality were compared with a reference method. The choice of apoptosis detection method is more important following 3 days of stimulation than after 5 days of stimulation (P=2x10(-6) versus P=1x10(-2)). In contrast, we find mortality measurements following the different means of stimulation highly significant at both 3 and 5 days (F2.28=7.9, P=1.4x10(-6) at 3 days and F2.28=8.5, P=4.5x10(-7) at 5 days). Variation as a result of the combination of specific PBMC stimulation and the method used to detect apoptosis is reduced considerably with time (F1.58+3.7, P+3x10(-7) at 3 days to F=1.58=0.97, P=0.5 at 5 days). Based on Tukey's test, YO-PRO-1 is the most sensitive stain for apoptosis and, when combined with 7-AAD, provides an accurate measure of apoptosis and mortality. In conclusion, we propose YO-PRO-1/7-AAD as a new combination and low-cost alternative for the sensitive detection of early apoptosis.

Binding of human immunodeficiency virus type 1 gp120 to CXCR4 induces mitochondrial transmembrane depolarization and cytochrome c-mediated apoptosis independently of Fas signaling

Apoptosis of CD4(+) T lymphocytes, induced by contact between human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein (gp120) and its receptors, could contribute to the cell depletion observed in HIV-infected individuals. CXCR4 appears to play an important role in gp120-induced cell death, but the mechanisms involved in this apoptotic process remain poorly understood. To get insight into the signal transduction pathways connecting CXCR4 to apoptosis following gp120 binding, we used different cell lines expressing wild-type CXCR4 and a truncated form of CD4 that binds gp120 but lacks the ability to transduce signals. The present study demonstrates that (i) the interaction of cell-associated gp120 with CXCR4-expressing target cells triggers a rapid dissipation of the mitochondrial transmembrane potential resulting in the cytosolic release of cytochrome c from the mitochondria to cytosol, concurrent with activation of caspase-9 and -3; (ii) this apoptotic process is independent of Fas signaling; and (iii) cooperation with a CD4 signal is not required. In addition, following coculture with cells expressing gp120, a Fas-independent apoptosis involving mitochondria and caspase activation is also observed in primary umbilical cord blood CD4(+) T lymphocytes expressing high levels of CXCR4. Thus, this gp120-mediated apoptotic pathway may contribute to CD4(+) T-cell depletion in AIDS.

Syncytium formation amplifies apoptotic signals: a new view on apoptosis in HIV infection in vitro

Infection of CD4+ cells with HIV in vitro causes extensive cytopathology. The mechanism that underlies this process is unclear and conflicting data exist regarding whether cytotoxicity is due to necrosis or apoptosis. It was previously reported and is shown here that the coculture of HIV glycoprotein-expressing cells with CD4+ cells results in apoptosis within several hours. This study demonstrates that apoptosis did not occur in single cells and was mediated neither by CD4 nor by coreceptor signaling, indicating that apoptosis was not induced by intra- or intercellular glycoprotein-receptor interaction. Detection of apoptosis required cell-to-cell fusion and undetectable levels of apoptotic cell death were substantially amplified upon syncytium formation. Similar results were obtained with syncytium-forming cultures of measles virus glycoprotein-expressing cells. These findings indicate that the apoptotic cell death observed in cultures of HIV and other syncytium-forming viruses is primarily due to amplification of background apoptosis in the wake of cell-to-cell fusion.

The synthetic CD4 exocyclic CDR3.AME(82-89) inhibits NF-kappaB nuclear translocation, HIV-1 promoter activation, and viral gene expression

We have previously shown that the synthetic aromatically modified exocyclic (AME) analog (CDR3.AME(82-89), derived from the CDR3 (residues 82-89) region of CD4 domain 1, inhibits replication of human immunodeficiency virus type 1 (HIV-1) in infected cells. In this work, we investigated the mechanism by which this inhibition is achieved. Although cells exposed to HIV-1 and treated with the CDR3.AME(82-89) peptide did not release viral particles for more than a week and kept surface expression of CD4, viral DNA was found in those cells 24 h after virus exposure, indicating that the CDR3.AME(82-89) analog does not prevent virus entry. However, virus transcription remained extremely low in infected cells, as demonstrated by the study of spliced HIV-1 mRNA in cultures treated with CDR3.AME(82-89) 72 h postinfection. Finally, the CDR3.AME(82-89) peptide was found to be a potent inhibitor of HIV-1 promoter activity and nuclear factor-kappaB translocation, indicating that the antiviral property of this peptide is, at least in part, linked with the ability of the molecule to prevent HIV-1 transcription.

Apoptosis: an innate immune response to virus infection

Viruses can induce apoptosis of infected cells either directly, to assist virus dissemination, or by inadvertently triggering cellular sensors that initiate cell death. Cellular checkpoints that can function as 'alarm bells' to transmit pro-apoptotic signals in response to virus infections include death receptors, protein kinase R, mitochondrial membrane potential, p53 and the endoplasmic reticulum.