A major aim in immunology has been to understand how the immune system evokes characteristic responses to infection, foreign tissue grafts and tumours. The current view of immunoregulation is based mainly on studies of lymphocyte subsets, either in vitro or by adoptive transfer to irradiated recipients. Many reagents are available for defining T-cell subsets, but only recently have there been helper T-cell-specific antibodies against the mouse equivalent of the Leu3/T4 (man) and W3/25 (rat) antigens. It is clear that monoclonal antibodies will eventually replace antilymphocyte globulin for immunosuppression in organ grafting, but although there has been some clinical success, most monoclonal reagents cause only transient reductions in their target cells in vivo. This uncertainty in the potency of monoclonal antibodies has led some workers to consider them as targeting agents for such highly cytotoxic drugs as ricin A (ref. 21). We show here that unmodified monoclonal antibodies can be extremely effective at depleting cells in vivo and can be used for the selective manipulation of different aspects of the immune response.

Bivalent and bispecific antibodies and their fragments have immense potential for practical application.

HPV late gene expression is initiated as an infected basal cell migrates through the differentiating layers of the epidermis, resulting in the onset of vegetative viral DNA replication and the expression of viral late proteins. We have used a large synthetic immunoglobulin library displayed on phage (diversity 6.5 x 10(10) phage) to isolate three Fabs (TVG405, 406, and 407) which recognize distinct epitopes on the E4 late protein of HPV16. A C-terminal monoclonal (TVG404) was generated by hybridoma technology, and N-terminal polyclonal antiserum was prepared by peptide immunization (alpha N-term). The most potent antibody (TVG405) had an affinity for E4 of approximately 1.0 nM. All antibodies recognized the protein in paraffin-embedded archival material, allowing us to map events in the late stages of virus infection. Expression of E4 in vivo does not coincide with synthesis of the major virus coat protein L1, but precedes it by 1 or 2 cell layers in premalignant lesions caused by HPV16 and by up to 20 cell layers in HPV63-induced warts. In higher grade lesions associated with HPV16, E4 is produced in the absence of L1. By contrast, vegetative viral DNA replication and E4 expression correlate exactly and in some lesions begin as the infected epithelial cell leaves the basal layer. Differentiation markers such as filaggrin, loricrin, and certain keratins are not detectable in E4-positive cells, and nuclear degeneration is delayed. HPV16 E4 has a filamentous distribution in the lower epithelial layers, but associates with solitary perinuclear structures in more differentiated cells. Antibodies to the N-terminus of the protein stained these structures poorly. Our findings are compatible with a role for the HPV16 E4 protein in vegetative DNA replication or in modifying the phenotype of the infected cell to favor virus synthesis or virus release. The Fabs will be of value in the evaluation of model systems for mimicking HPV infection in vitro.

SUMMARYRat monoclonal antibodies were used to deplete selectively Lyt 2 (cytotoxic) and L3T4 (helper) T cell populations in vivo. These antibodies produced > 95 ~ depletion of the respective T cell subset as determined by fluorescent antibody and cytofluorographic analyses. Antibody-treated mice were infected in the ear pinna with herpes simplex virus (HSV) and the induction of virus-specific T cell and antibody responses were monitored during the acute infection. Lyt 2-deficient mice produced delayed hypersensitivity and HSV-specific antibodies comparable to those in untreated animals. However, major histocompatibility complex class I-restricted T cell killing was abolished. In contrast, L3T4-deficient animals failed to produce either primary delayed hypersensitivity response or specific antibodies to the virus, but cytotoxic T cell responses were induced and even augmented in comparison with infected, normal animals. This observation clearly demonstrates that Lyt 2 cytotoxic T cells can be induced in a helper T cell-deficient environment. The ability of T cell subset-deficient mice to clear infectious virus was investigated in the skin of the ear and the part of the nervous system innervating the site of infection. L3T4-deficient animals showed a markedly delayed clearance of virus from the ear and also had a more florid infection of the nervous system. However, Lyt 2-deficient mice cleared the infection in the ear normally, but a severe infection of the nervous system was still observed. The implication of these observations to the pathogenesis of this virus is discussed.

These results establish the following: the binding sites in HGF/SF for Met and for HSPGs can be dissociated by protein engineering; high-affinity binding of HGF/SF to HSPGs is not essential for signalling; one role of HSPG binding in the HGF/SF system appears to be sequestration and degradation of the growth factor; and HGF/SF mutants with decreased affinity for HSPGs exhibit enhanced activity in vivo.