Per Johan Klasse

Human and murine monoclonal antibodies directed against a conserved sequence from gp41 (aa583–599) of human immunodeficiency virus type 1

Human spleen cells from an HIV-seropositive donor were immunized in vitro with the aa583-599 peptide conjugated to an heptalysyl core. This sequence was derived from the putatively HIV-immunosuppressive region of HIV1 gp41. The same conjugated peptide was used to immunize mice. One human and one mouse IgM monoclonal antibody (mAb) directed against the aa583-599 peptide were obtained. The two mAb had distinct patterns of reactivity against a panel of 42 peptides with modified sequences. Neither of the mAb inhibited the immunosuppressive effect of aa583-599 octopus-lys-conjugated peptide on anti-CD3 Ab-induced lymphoproliferation. In addition, both mAb did not neutralize cell-free virus transmission or enhance HIV infection. However, HmAb inhibited formation of syncytia between HIV1-infected (but not HIV2-infected cells) and non-infected target cells at concentrations above 20 micrograms/ml, whereas MmAb did not have any effect. The degree of conservation of the aa583-599 region makes HmAb a candidate for use as a group-specific reagent in future HIV1 passive immunotherapy protocols.

A cluster of continuous antigenic structures in the transmembrane protein of HIV-1: Individual patterns of reactivity in human sera

We investigated the antigenicity of a highly conserved region in the transmembrane protein of the human immunodeficiency virus type 1 (HIV-1). In order to identify antigenically important residues, amino-acid sequences of synthetic peptides representing this region were varied systematically: single residues were omitted from the sequence of HIV-env 583-599; threonines were substituted for pairs of residues in HIV-env 581-599; the sequences of heptadeca-peptides were shifted by single residues. The peptides were tested in an enzyme immuno-assay against fourteen HIV-1 antibody-positive human sera, which were previously found to react with HIV-env 583-599, and against rabbit antisera to the peptides HIV-env 583-599 and 586-606. Substitutions as well as deletions in the sequence 589-596 (AVERYLKD) aborgated the antigenicity of the peptides with most of the human sera. Changes outside this sequence affected the reactivities differentially. Six overlapping dodeca-peptides, shifted in the sequence by single residues, lacked antigenicity in a competition assay, suggesting antigenic dependence on an ordered peptide conformation, which the longer peptides may preferentially assume. 19- and 21-mers with overlapping sequences competed to different extents with each other for binding to the antibodies of 3 human sera, illustrating that more than one antigenic structure in this narrow region can be recognized by a single polyclonal serum.

Three-dimensional structure and antigenicity of transmembrane-protein peptides of the human immunodeficiency virus type 1: Effects of a neutralization-escape substitution

A point mutation (Ala‐589 to Thr) in the transmembrane protein of the human immunodeficiency virus type 1 (HIV‐1) has been shown to decrease the sensitivity of the virus to the neutralizing effect of human HIV‐1 specific antibodies [(1990) J. Virol. 64, 3240‐3248]. Here 17‐residue peptides with the parental and mutant sequences were compared: the parental peptide bound antibodies of sera from HIV‐1 infected persons more frequently and with higher affinity than the mutant peptide. However, according to circular dichroism (CD), NMR spectroscopy and molecular modelling the peptides have indistinguishable backbone conformations under a variety of experimental conditions. These techniques showed for both peptides that no ordered helix was present in water solution. However, for both peptides in alcohol‐water solutions approximately 60% α‐helix coula be induced. The three‐dimensional structures of these peptides provide a basis for understanding how this mutation in the transmembrane protein may affect the interaction with both the outer envelope glycoprotein and with antibodies.

Cross-Reactivity with SIVmac in East African HIV-1-Positive Sera: Evidence against Double Infection with HIV-1 and a SIVmac/HIV-2-like Virus

IgG antibodies reactive with simian immunodeficiency virus isolated from a rhesus monkey suffering from simian acquired immunodeficiency syndrome (SIVmac, strain 239, a virus which is very closely related to human immunodeficiency virus type 2-HIV-2) were found in 18 of 120 Swedish and 8 of 11 east African confirmed HIV-1 antibody positive (HIV-1 ab+) sera, both by enzyme immunoassay and electrophoretic immunoblotting (p = 1 x 10(-6). In electrophoretic immunoblotting most of the cross-reactivity of SIVmac-reactive sera occurred on p27, the major gag protein of SIVmac. The possibility that SIVmac antibody reactivity could be due to double infection with HIV-1 and a SIVmac-related virus was eliminated by the results of absorptions between sera of Swedish and west and east African origin and viral antigens (SIVmac and North American or African/Haitian strains of HIV-1) coupled to agarose beads. HIV-2 ab+ and SIVmac reactive west African sera recognized SIVmac epitopes unrelated to HIV-1, whereas HIV-1 ab+, SIVmac reactive east African, and Swedish sera recognized SIVmac epitopes cross-reactive with epitopes present in both African and North American HIV-1 strains. No unique SIVmac-reactive African HIV-1 epitopes could thus be defined. Neither did absorption of Swedish and African HIV-1-positive sera with different HIV-1 strains (1 Haitian, 2 Zairian, and 1 North American) give evidence for unique epitopes.