The human immunodeficiency virus (HIV-1) has been established as the primary etiologic agent in the pathogenesis of acquired immunodeficiency syndrome (AIDS) and related disorders. ( Barre-Sinoussi, et al.  Science (1983) 220:868-871; Gallo, et al.,  Science (1984) 224:500-503; Levy, et al.,  Science (1984) 225:840-842). 
The CD4+ cells play a central role in HIV infection. ( Fauci, Science (1988) 239:617-622).  CD4 is a molecule present on the surface of certain lymphocytes and, to a lesser degree, macrophages.  The CD4 molecule plays a significant role in the function of T4 helper lymphocytes and serves as a marker for such cells. ( Gallo, R. C. and Montagnier, L., Scientific American (1988) 259:41-48.)  The virus uses the CD4 receptor to gain entry into a number of cells. ( Dalgleish, et al.,  Nature (1984) 312:763-767).  The envelope glycoprotein, gp160, is the precursor to the gp120, which specifically binds to the surface receptor (CD4) of CD4+ cells, and the gp41, the transmembrane (TM) glycoprotein which initiates cell-membrane fusion, leading to the formation of multinucleated giant cells commonly called syncytia. ( Kowalski, Science (1987) 237:1351-1355).  Fusion leads to the death of the syncytial cells.  While HIV-1 may also cause cell death through mechanisms independent of cell fusion, data suggest that the formation of syncytia contributes to the progressive depletion of CD4+ cells (T4 helper lymphocytes), quantitatively and functionally. ( Lifson, et al.,  Nature (1986) 323:725-728).  This is the most profound hematologic feature and hallmark associated with acquired immunodeficiency syndrome (AIDS) (Broder, S. M. and Gallo, R. C., N. Eng.  J. Med. ( 1984) 311:1292-1297), as demonstrated by impaired cell-mediated immunity. 
Infection of humans with HIV-1 leads to a humoral immune response by B lymphocytes resulting in the production of antibodies directed against most of the viral structural antigens.  A particular subset of antibodies is directed against HIV envelope antigens (gp120 and gp41) which may be involved in induction of active immunity. ( Matthews, et al.,  AIDS Research and Human Retroviruses (1987) 3:197-206).  Neutralization assays with sera from HIV-infected individuals (Robert-Guroff, et al.,  Nature (1985) 316:72-74; Rasheed, et al.,  Virology (1986) 150:1-9) or from immunized animals, suggest that the envelope glycoprotein contains epitope(s) that elicit antibodies capable of neutralizing HIV infection in vitro.  As an in vivo corollary, it has been demonstrated that high neutralizing antibody titers correlated with a better clinical outcome, and low or decreasing neutralizing antibody titer signaled poor prognosis. ( Robert-Guroff, et al.,  AIDS Research and Human Retroviruses (1988) 4:343-350).  A decrease in average antibody titers has been clinically observed in late stages of infection, particularly with regard to antibodies directed against the HIV envelope epitopes and specifically against the TM gp41 region containing the amino acid sequence against which the herein described human monoclonal antibody is biologically reactive. ( Shafferman, et al.,  AIDS Research and Human Retroviruses (1989) 5:33-39; Chiodi, et al.,  J. Med.  Virol. ( 1987) 23:1-9; McPhee, et al.,  FEBS Lett. ( 1988) 233:393-396). 
Measures capable of boosting the neutralizing antibody titer of individuals already infected with the virus, eliciting high-titer neutralizing antibodies (i.e., active immunotherapy), or increasing neutralizing antibodies (i.e., passive immunotherapy) in individuals at risk would prove beneficial in controlling viral spread in vivo or in preventing new infection. ( Robert-Guroff, et al.,  AIDS Research and Human Retroviruses (1988) 3:343-350). 
The present invention makes possible the measures cited above.  Any attempts at passive immunotherapy will require the production of large quantities of antibody on a routine basis.  The development of a continuous cell line accommodates this.  The monoclonality of the antibody enables the administration of reactive physiological amounts of the antibody since all of the antibody being administered is directed against the biologically active epitope of the virus, unlike polyclonal serums which contain antibodies against other structural proteins as well.  The potential immunogenicity of the peptide sequence of this epitope, as evidenced by the immunogenicity of a peptide of similar sequence, will enable safe and effective vaccination of individuals, thereby avoiding the great risks involved in immunizing with attenuated or even killed viruses. 
The present invention is further directed to a kit and a method for detecting the presence and determining concentration of an antibody that inhibits HIV-1 fusion-associated epitope, a peptide on gp41 with the amino acid sequence represented by GCSGKLIC (SEQ NO:1).  The detection and quantitation method includes an enzyme-linked immunosorbent assay (ELISA). 
The determination of the concentration of the antibody that inhibits HIV-1 fusion-associated epitope on gp41, present in body fluids of a patient seropositive for HIV-1 antibodies, provides the physician with an objective means to form a prognosis for each individual case and assists the clinician therefore in determining the appropriateness to initiate medical intervention or change therapy.