Monoclonal anti-idiotypic antibody mimics the CD 4 receptor and binds human immunodeficiency virus ( acquired immunodeficiency syndrome / receptor mimicry / T-lymphocyte surface molecule )

A monoclonal anti-idiotypic (anti-Id) antibody, HF1.7, was generated against anti-Leu-3a, a mouse monoclonal antibody (mAb) specific for the CD4 molecule on human helper/inducer T lymphocytes. The anti-Id nature of HF1.7 was demonstrated by the following properties. (i) It reacted in a solid-phase immunoassay with anti-Leu-3a and not with a panel of irrelevant mouse mAbs. (ii) It partially inhibited the binding of anti-Leu-3a to CD4+ T cells. (iii) It detected a common idiotype present on various anti-CD4 mAbs. Because the CD4 molecule represents the receptor site for human immunodeficiency virus (HIV), the etiologic viral agent of acquired immunodeficiency syndrome, we examined the ability of the anti-Id mAb HF1.7 to mimic CD4 and bind HIV. This anti-Id mAb reacted with HIV antigens in commercial HIV ELISAs and recognized HIV-infected human T cells but not uninfected cells when analyzed by flow cytofluorometry. Attesting further to the HIV specificity, the anti-Id mAb reacted with a recombinant gp160 peptide and a molecule of Mr 110,000-120,000 in immunoblot analysis of HIV-infected cell lysates. The anti-Id mAb also partially neutralized HIV infection of human T cells in vitro. These results strongly suggest that this anti-Id mAb mimics the CD4 antigenic determinants involved in binding to HIV. Acquired immunodeficiency syndrome (AIDS) is a devastating disease resulting from infection of many cellular components vital for the maintenance of immune homeostasis. Human immunodeficiency virus [HIV; also called human T-lymphotropic virus type III (HTLV-III), lymphadenopathy-associated virus (LAV), and AIDS-associated retrovirus (ARV)], the etiological agent of AIDS, is lymphotropic for cells expressing the CD4 molecule. HIV has been shown to infedt not only the helper/inducer subset of T lymphocytes but also cells of the monocyte/macrophage lineage (1-4). In vitro infection by HIV can be effectively blocked by monoclonal antibodies (mAbs), such as anti-Leu-3a and OKT4A, directed against the CD4 target molecule (4-6). It has been shown recently (7) that HIV binds to the CD4 molecule via an envelope glycoprotein of Mr 110,000. These results imply that the CD4 antigenic determinants recognized by anti-Leu3a and OKT4A either represent the site of attachment ofHIV or are closely associated with it. Based on Jerne's idiotype network hypothesis (8), anti-idiotype (anti-Id, or Ab-2) against anti-Leu-3a or OKT4A (Ab-1) bearing the internal image should mimic the antigen (CD4) and bind to HIV envelope glycoprotein. This interaction in turn may inhibit the binding ofHIV to CD4 on target cells and therefore could lead to viral inactivation. A monoclonal anti-Id antibody, termed HF1.7, was generated against mAb anti-Leu-3a. HF1.7 exhibited the following properties. (i) It reacted in solid-phase enzyme-linked immunosorbent assay (ELISA) with anti-Leu-3a and not with a panel ofirrelevant mouse mAbs. (ii) It partially inhibited the binding of anti-Leu-3a to CD4' T cells. (iii) It reacted with HIV antigens in commercial HTLV-III and LAV ELISAs. (iv) It reacted by viable membrane immunofluorescence assay with HIV-infected human T cells but not uninfected cells. (v) It bound to a molecule of M, 110,000-120,000 in immunoblot analysis of HIV-infected-cell lysate. (vi) It bound a recombinant gpl60 peptide by a double-antibody radioimmunoassay (RIA). (vii) The binding of anti-Leu-3a to its anti-Id mAb was inhibited by mAbs against CD4 but not by irrelevant mAbs. (viii) It partially neutralized HIV infection of human T cells in vitro. These results strongly suggest that mAb HF1.7 reacts with an idiotypic (Id) determinant on anti-Leu-3a and mimics part(s) of the CD4 molecule that represents the viral receptor for HIV and binds to HIV envelope glycoprotein. This binding may prevent the virus from attaching to target cells, resulting in viral neutralization. mAb HF1.7 may be an important reagent in the understanding of the molecular mechanism of HIV pathogenicity and in the development of diagnostic and therapeutic strategies. MATERIALS AND METHODS mAbs. The CD4-specific mAbs anti-Leu-3a (Becton Dickinson), OKT4A (Ortho Diagnostics), and anti-T4 (Coulter Immunology) were purchased from their manufacturer as purified immunoglobulins or were the gift of G. Thorton (Johnson and Johnson Biotechnology Center, La Jolla, CA). mAbs that recognize other lymphocyte phenotypic markers (Leu-1, Leu-2a, Leu-5b, Leu-8, Leu-M1) were purchased as purified immunoglobulins from Becton Dickinson. Generation of Monoclonal Anti-Id Antibodies. Threeto five-week-old BALB/c mice were immunized intravenously with purified anti-Leu-3a mAb (30 ,ug per mouse) in 0.9% NaCl. Six injections were given at weekly intervals. Three days after the last injection, the mice were killed and their spleen cells were fused with the mouse myeloma cell line NS-1 as described previously (9). Supernatant fluids from wells with hybrid growth were screened for reactivity against HIV or anti-Leu-3a by an ELISA described below. ELISAs. The HTLV-III ELISA (Electro-Nucleonics, Silver Spring, MD) and the LAV EIA (Genetic Systems, Seattle, WA) were done according to the manufacturers' specifications. Horseradish peroxidase-conjugated goat antimouse IgG antibodies (Vector Laboratories, Burlingame, CA) were substituted for goat anti-human IgG enzyme Abbreviations: AIDS, acquired immunodeficiency syndrome; FITC, fluorescein isothiocyanate; HIV, human immunodeficiency virus; Id, idiotype (idiotypic); mAb, monoclonal antibody; SV40 T antigen, simian virus 40 large tumor antigen; TCIDm, 50% tissue culture infective dose. *To whom reprint requests should be addressed at: Department of Virology and Immunology, Southwest Foundation for Biomedical Research, P.O. Box 28147, San Antonio, TX 78284. 3891 The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 3892 Medical Sciences: Chanh et al. Table 1. Reactivity of mAb HF1.7 with HIV antigens in ELISA