CD4-IgG2 is a novel fusion protein comprising human IgG2 in which the Fv portions of both heavy and light chains have been replaced by the V1 and V2 domains of human CD4. This tetrameric protein is being developed as an immunoprophylactic agent to reduce the probability of infection following HIV-1 exposure, in settings such as occupational or perinatal exposure to the virus. CD4-IgG2 has been expressed in Chinese hamster ovary cells and is secreted as a fully assembled heterotetramer. The protein binds with nanomolar affinity to purified gp120 from both a laboratory-adapted strain and a primary isolate of HIV-1. Pharmacokinetic studies in rabbits demonstrated that CD4-IgG2 has a plasma terminal half-life greater than 1 day, compared with 15 min for soluble CD4 (sCD4). CD4-IgG2 does not bind to Fc receptors on the surface of U937 monocyte/macrophage cells. Compared to molecules that incorporate the Fc portion of IgG1, CD4-IgG2 has less potential to mediate functions such as antibody-dependent enhancement of infection or transplacental transmission of HIV-1. When tested in a virus-free HIV-1 envelope glycoprotein-mediated cell fusion assay, the tetrameric CD4-IgG2 molecule inhibited syncytium formation more effectively than monomeric sCD4 or a dimeric CD4-gamma 2 fusion protein. This suggests the protein will block cell-to-cell transmission of HIV-1. Moreover, CD4-IgG2 effectively neutralized a panel of laboratory-adapted strains and primary isolates of HIV-1, including strains with different tropisms and isolated from different stages of the disease, at concentrations that should be readily achieved in vivo.

Abstract. Unexplained, generalized lymphadenopathy in homosexual men, which can be a prodrome to the acquired immunodeficiency syndrome, is associated with impaired cell-mediated immunity, a low ratio of T helper-inducer to T suppressor-cytotoxic cells (defined by the T4 and T8 monoclonal antibodies), and hypergammaglobulinemia. We performed double-marker studies on T cells by using a panel of monoclonal antibodies (Ia, T 17, TQ 1, and Leu-8), which reportedly detect activation or functional subsets of the T4 and T8 T cell populations.The T4:TQI-or T4:Leu-8-subset, which is the major helper subset for B cell responses, is normally represented in lymphadenopathy patients. A depression in the reciprocal subset, T4:TQ1+ or T4:Leu-8', accounts for the T4 T cell defect. Similarly, the TQ1 and Leu-8 markers delineate the abnormality of T8 T cells: the T8:TQ l-or T8:Leu-8-subset is elevated, whereas the T8:TQ1+ or T8:Leu-8' subset is normally represented. We found no evidence of excessive activation of T4 T cells by using the T17 or Ia monoclonal antibodies. We did find an overall increase in Ia-positive T cells; however, this was due to increased T8:Ia+ cells.In functional studies, immunoglobulin production induced by pokeweed was subnormal. Most lymphadenopathy patients had normal T helper cell function when combined with normal B cells. The dampened pokeweed responses could be partially explained by depression of the T4:TQ1+ (or T4:Leu-8+) subset (which has minor

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Immune complex assays (and other immunologic tests) were performed on sera from 162 patients with the acquired immunodeficiency syndrome (AIDS) and 275 AIDS-related subjects. Immune complexes were detected in 89% of AIDS patients and 93% of homosexual men with lymphadenopathy. Immune complex levels in AIDS patients were not associated with a particular risk group or with types of opportunistic infection or malignancy; however, they correlated with other laboratory features of the immune defect (depression in T helper cells and T helper/suppressor-cell ratio, and IgG levels). Immune complexes were also detected in a lesser proportion of risk-group controls (homosexual men, hemophiliacs, Haitians). In risk-group controls, immune complex levels were associated with certain features reflecting sexual practice, blood product exposure, or infection, but these features did not account for the higher levels found in AIDS patients. In appropriate situations, immune complex assays may be of value as screening tests or, possibly, as prognostic indicators for AIDS or AIDS-related syndromes.

We have studied the distribution of Leu8 and Ia on T cells of the helper (T4) and suppressor (T8) phenotype in homosexual men with chronic unexplained lymphadenopathy, homosexual men with the acquired immunodeficiency syndrome (AIDS), and homosexual and heterosexual controls. Decreased numbers of helper T cells in lymphadenopathy patients are due to a decrease in the T4:Leu8+ subset, whereas in AIDS patients, both the T4:Leu8+ and the T4:Leu8- subsets were decreased.