Fernando Plata

Retrovirus antigens recognized by cytolytic T lymphocytes activate tumor rejection in vivo

We have initiated the molecular definition of the antigens recognized by Gross MuLV-specific cytolytic T lymphocytes on the surface of Gross MuLV-induced tumor cells. A panel of target cells was obtained by the double transfection and expression of a retrovirus gene and a foreign H-2 gene in recipient mouse fibroblasts. Our results show that class I H-2 transplantation antigens have a directive influence in determining the antigenicity of proteins encoded by the gag and env MuLV genes. Genes not linked to H-2 influence the intensity and the specificity of the cytolytic T lymphocyte response to Gross MuLV-induced tumors. Finally, MuLV-induced antigens expressed by transfected fibroblasts induce tumor immunity and lead to accelerated tumor rejection in vivo.

Immune resistance to Trypanosoma cruzi: Synergy of specific antibodies and recombinant interferon gamma in vivo

The protective effects of interferon gamma (IFN-gamma) against infection by Trypanosoma cruzi were studied in vitro and in vivo in a murine model of infection. The possible synergy between IFN-gamma and trypomastigote-specific antibodies in the rejection of the parasite was also considered. Our results in vitro indicate that IFN-gamma activates macrophages to reject the parasite and this mechanism may lead to a decrease in parasitaemia in vivo. Finally, IFN production in vivo after infection by T. cruzi was compared among mice from different genetic backgrounds. Reduced parasitaemia and extended survival correlated with the early production of circulating IFN-gamma and anti-trypomastigote antibodies after infection. The appearance of an unusual type of circulating IFN in response to infection by T. cruzi was also detected; this IFN was resistant to neutralization by antibodies to IFN-alpha/beta and to IFN-gamma.

Enhancement of HIV-specific cytotoxic T lymphocyte responses by zidovudine (AZT) treatment

Zidovudine or 3′‐azido‐2′‐3′‐dideoxy‐thymidine (AZT) is an antiviral drug widely used to treat HIV‐infected patients. Because cytotoxic T lymphocytes (CTL) are thought to contribute actively to resistance against HIV‐induced disease, we studied sequentially 10 HIV‐infected individuals under zidovudine treatment for a period of 6–12 months. For a given patient all lymphocyte suspensions corresponding to the complete zidovudine therapy period were tested on the same day and on the same target cells. Patients were selected for expression of HLA‐A2 and/or HLA‐A3 class I transplantation antigen. HLA‐restricted cytotoxicity specific for env, gag and nef HIV proteins was quantified for each patient at 6 week intervals. The data clearly indicated that zidovudine has a beneficial effect on the CTL response during the first 6–12 weeks of treatment, inducing cytotoxicity levels up to 100‐fold stronger than base line. This effect was usually short lived. However, patients who maintained strong levels of cytotoxicity had better clinical and survival outlook than patients who had lost all detectable cytotoxic lymphocytes. It is proposed that AZT, among other effects, delays the onset of disease in HIV‐infected patients by contributing to the stimulation of the HIV specific CTL response.

HIV-specific cytotoxic T lymphocytes directed against alveolar macrophages in HIV-infected patients

A CD8+ lymphocytic infiltration of the lungs is frequently observed in HIV-infected patients, even prior to the onset of opportunistic infections. In such patients, we could demonstrate that most of these CD8+ alveolar T lymphocytes displayed the D44 marker and were functional cytolytic T lymphocytes directed against autologous HIV-infected alveolar macrophages. This primary cytolytic activity was HLA-restricted and, at least partially, specific for the HIV envelope protein, since HLA-A2 alveolar T lymphocytes could specifically lyse cell lines expressing both the HLA-A2 and Env antigens. In contrast to data obtained in peripheral blood, no ADCC activity was observed against the Env antigen. HIV-specific alveolar T-lymphocyte cytolytic activity decreased with progression towards AIDS as shown by studies of a series of 40 patients. Functional abnormalities of the lung epithelium could be associated with the specific lysis of alveolar macrophages, suggesting that local tissue injury could result from the in vivo immune conflict between alveolar HIV-specific CTL and HIV-infected macrophages.

HIV-specific cytotoxic T lymphocytes against alveolar macrophages: specificities and downregulation.

To analyse the evolution of alveolar-lymphocyte-mediated cytotoxic activity directed against autologous alveolar macrophages (AM), cytotoxic assays against various HIV+ target cells were performed in a cohort of 75 patients with HIV-associated lymphoid interstitial pneumonitis (LIP) studied at distinct stages of HIV infection. Our data confirm that alveolar HIV-specific cytotoxic T lymphocytes (CTL) against AM were detectable before AIDS in patients with CD8+ LIP. Mild CD8+ lymphocytic alveolitis occurs silently in 62% of stage II and III patients with no respiratory symptoms. In these cases, the lack of spontaneous alveolar-lymphocyte-mediated cytotoxic activity against autologous AM may contrast with the detection of primary alveolar CTL specific for HIV proteins such as nef. In AIDS patients, the alveolar CTL lytic efficiency against both AM- and HIV-antigen-expressing cells can be inhibited by a suppressor factor produced by alveolar CD8+ CD57+ cells. Therefore, spontaneous CTL lysis of AM may be (1) limited to a subgroup of patients with active LIP and (2) controlled by distinct mechanisms, including suppressor phenomenons, and HIV replication levels in AM.

Implications of HIV specific cytotoxic T lymphocytes in AIDS

The immune response to HIV in infected humans leads to the production of HIV specific cytotoxic T lymphocytes (CTL) which circulate in high frequencies. The presence of these CTL and their eventual protective activities have been studied by various laboratories, and correlations have been made with certain immunopathological manifestations of HIV infections. It seems probable that HIV-immune CTL participate in the induction of certain disorders by initiating inflammatory reactions in the lungs, central nervous system, and lymph nodes. Various virus antigens recognized by HIV-immune CTL on the surface of the infected cell have been identified, and the molecular definition of the epitopes recognized is well under way. Likewise, numerous HLA transplantation antigens that regulate HIV antigen recognition by CTL have been identified. These data are discussed in view of the development of an eventual vaccine and of functional immunotherapies. They are compared with results obtained in animal experimental systems.

MOLECULAR DEFINITION OF RETROVIRUS‐INDUCED ANTIGENS RECOGNIZED BY TUMOUR‐SPECIFIC H‐2‐RESTRICTED CYTOLYTIC T LYMPHOCYTES

The antigenic specificities of H‐2‐restricted, tumour‐specific cytolytic T lymphocytes (CTL) were studied at the molecular level using CTL from BALB.B and C57BL/6 (H‐2b) mice sensitized to an H‐2b Gross murine leukaemia virus (MuLV)‐induced tumour. Target cells were produced by the double trans‐fection of mouse L cells (H‐29 with the cloned H‐2Kb or H‐2P gene and retro‐viral DNA derived from a molecular clone of Akv MuLV (closely related to Gross MuLV). Doubly transfected L cells which express either H‐2Kb or H‐2Db antigen and retroviral antigens are lysed in a virus‐specific manner by Gross MuLV‐immune CTL. The existence of two independent Gross MuLV‐immune CTL subpopulations, one restricted by H‐2Kb and the other by H‐2Db, is thus confirmed. Gross MuLV‐immune CTL from both BALB.B and C57BL/6 mice killed L cells that express Akv MuLV gag gene products and H‐2Kb or H‐2Db antigen. In contrast, only CTL from C57BL/6 mice killed L cells that express Akv MuLV env gene products and H‐2Kb or H‐2Db. This indicates that specific recognition of MuLV‐induced antigens by CTL can be selective and varies according to the origin of the CTL.

Progess in Antimicrobial Immunity

The presented papers dealt with the interactions of viral, bacterial and parasitic infectious agents with the immune system in animal models and in man. Three main approaches were undertaken : (a) immunogenetic control of host resistance to infection; (b) the role of T cell-mediated reactions in host protection and pathology; and (c) modulation of the host’s immune functions by microbial infection.