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Antigenic sites on human T cell leukemia virus type I (HTLV-I) gp46 and gp21 envelope glycoproteins that are immunogenic in man were studied with envelope gene (env)-encoded synthetic peptides and a mAb to HTLV-I gp46 envelope glycoprotein. Antibodies in 78% of sera from HTLV-I seropositive subjects reacted with synthetic peptide 4A (amino acids 190 to 209) from a central region of HTLV-I gp46. Human anti-HTLV-I antibodies also bound to synthetic peptides 6 (29% of sera) and 7 (18% of sera) from a C-terminal region of gp46 (amino acids 296 to 312) and an N-terminal region of gp21 (amino acids 374 to 392), respectively. mAb 1C11 raised to affinity-purified HTLV-I gp46 reacted with gp46 external envelope glycoprotein and gp63 envelope precursor in immunoblot assay and also bound to the surface of HTLV-I+ cells lines HUT-102 and MT-2. Antibody 1C11 did not react with HTLV-II or HIV-infected cells or with a broad panel of normal human tissues or cell lines. In competitive RIA, anti-gp46 antibody 1C11 was inhibited from binding to gp46 either by antibodies from HTLV-I seropositive subjects or by HTLV-I env-encoded synthetic peptide 4A, indicating that 1C11 bound to or near a site on gp46 within amino acids 190 to 209 also recognized by antibodies from HTLV-I-seropositive individuals. When tested in syncytium inhibition assay, mAb 1C11 did not neutralize the infectivity of HTLV-I. Thus, HTLV-I infection in man is associated with a major antibody response to a region of gp46 within amino acids 190 to 209 that is on the surface of virus-infected cells.

Murine tumor cells frequently express retroviral protein p15E, a protein with antiinflammatory activity. This has led to the hypothesis that p15E expression allows nascent tumor cells to escape host immunologic defenses. To evaluate the role of p15E expression in tumorigenesis, NIH3T3 cells transformed by various oncogenes and BALB/c lines transformed by carcinogens or SV40 were examined for p15E expression and tumorigenicity. All of the NIH3T3 transformants and most of the BALB/c transformants did not express p15E, indicating that transformation per se does not inevitably induce the expression of p15E. Although not expressing p15E, some of these transformants were capable of forming tumors in immune competent hosts, indicating that p15E is not universally required for tumor growth. Four of the transformed cell lines negative for p15E expression and deficient in tumor-forming capacity were transfected with a gene coding for Moloney retroviral p15E. Despite the expression of p15E, there was no augmentation of their tumorigenic capacity, showing that p15E is not sufficient to ensure tumor formation by a transformed cell. These results argue against a general role for retroviral p15E expression in tumorigenesis.

In an attempt to understand the mechanisms of immunodeficiency induced by human T lymphotropic virus type I (HTLV-I), HSV-specific CD4+ human multifunctional T cell clones were infected with HTLV-I in vitro. Early after HTLV-I infection, when their growth was still IL-2-dependent, clones were found to have almost completely lost their cytotoxic activity. At that time, their HSV-Ag-induced proliferative response and helper function for anti-HSV antibody production by B cells were only partially impaired. After this initial phase, the HTLV-I-infected clone became IL-2-independent, and the helper function was also completely lost. IL-2-dependent HTLV-I-infected clones showed degrees of proliferative response and elevation of intracellular free Ca2+ concentration induced by anti-CD3 mAb equivalent to those of HTLV-I-uninfected clones. On the other hand, during the IL-2-independent stage, expression of CD3-TCR complex on the cell surface was markedly decreased, and no significant elevation of intracellular free Ca2+ concentration was detected in response to anti-CD3 mAb. These data indicated that the loss of cytotoxic activity of HSV-specific T cell clones observed early after HTLV-I infection was not the result of impaired antigen recognition via the CD3-TCR complex, but might be due to dysfunction in the effector phase. On the other hand, the dysfunction of helper activity found late after HTLV-I infection might have mainly occurred in the recognition phase due to the decreased expression of CD3-TCR complex. The present data appear to suggest certain aspects of the pathogenesis of the immunodeficiency occurring in HTLV-I infection.

A murine mAb, STEGI 1, was generated against a 30-kDa raf protein purified from an Escherichia coli expression vector. Immunoblot analysis confirmed that this antibody recognized the original immunizing protein as well as a 44- to 48-kDa protein from several raf-transformed cell lines. Immunoprecipitation experiments isolated a 48-kDa protein from a cell line transfected with a c-raf construct as well as from normal NIH 3T3 fibroblasts. Parallel experiments with polyvalent antiserum prepared against E. coli-derived v-raf (C terminus)-precipitated proteins with apparent Mr of 48 and 74 kDa, as had been described previously. Immunofluorescence flow cytometry of raf-transformed cell lines revealed intense intracytoplasmic staining. This staining was specifically inhibited by preincubation of STEGI 1 with purified raf 30-kDa protein. It should now be possible to more easily assess the role of the raf oncogene product in malignant transformation.