Soluble CD4 enhances the efficacy of immunotoxins directed against gp41 of the human immunodeficiency virus.

Abstract

Monoclonal antibodies specific for the gpl20 or gp4l portions of the human immunodeficiency virus (HIV) envelope protein gpl60 were conjugated to ricin A chain, and their immunotoxic activities against HIV-infected cells were evaluated in the presence or absence of soluble CD4 (sCD4).Immunotoxin activity was measured in vitro as cytotoxicity and inhibition of secretion of infectious HIV. The efficacy of anti-gp4l immunotoxins was enhanced at least 30-fold in the presence of sCD4. This effect was specific for HIV-infected cells, but not for uninfected cells, and was seen at concentrations of sCD4 as low as 0.1 pg/mI. Anti-gpl20 immunotoxins were marginally inhibited at higher concentrations of sCD4. Flow cytometry analyses showed that sCD4 increased the expression of gp4l on the surface of infected cells and increased internalization of gpl20 and gp4l. These data suggest that sCD4 alters the cellular trafficking of HIV envelope proteins. These findings also have important implications for the therapeutic use of anti-HIV immunotoxins and may be generalizable to other immunotoxins as well.

In Vivo Efficacy of Anti-Glycoprotein 41, But Not Anti-Glycoprotein 120, Immunotoxins in a Mouse Model of HIV Infection

“…Anti-HIV ITs are highly effective antiviral agents when tested in vitro, with a therapeutic index of Ͼ10,000, far greater than that of any other antiviral agent tested (12). There have been reports that HIV may be eliminated from tissue cultures with ITs (11).…”

“…We have argued that CD4-PE40 is a flawed IT because of its short plasma residence time, high nonspecific toxicity, and targeting to gp120 rather than gp41 (17,18). We have further demonstrated that a combination of an anti-gp41 IT and a CD4-based protein demonstrates superior antiviral properties in vitro (10,12). In this manuscript we test the therapeutic potential of anti-gp120 and anti-gp41 ITs in a unique model of HIV infection, that is SCID mice injected with a mixture of HIVinfected and HIV-susceptible human CD4…”

“…Our laboratory has been involved in the development of anti-HIV ITs that are based on mAbs conjugated to RAC (9,10,12). Another IT, a chimera between CD4 and Pseudomonas exotoxin A, CD4-PE40, has been tested in clinical trials.…”

“…mAb 924 is a murine IgG1 Ab directed against the V3 loop of HIV gp120 and has greatest reactivity with strains of HIV derived from the IIIB isolate (8,9). mAbs 41.1 (9,12) and 7B2 are human IgG1 directed against the immunodominant region of gp41 (aa 598 -604).…”

“…In vitro studies have shown that anti-HIV ITs are among the most effective antiviral agents tested (11,12), with efficacy against multiple cell types, including macrophages (13), and against a variety of HIV isolates (10,14). The activity of anti-gp41 ITs, but not anti-gp120 ITs, can be enhanced 30-to 100-fold by the addition of soluble CD4 (sCD4) (10,12).…”