Construction of a Vero Cell Line Expressing Human ICAM1 for the Development of Rhinovirus Vaccines

Human rhinoviruses (HRVs) are small non-enveloped RNA viruses that belong to the Enterovirus genus within the Picornaviridae family and are known for causing the common cold. Though symptoms are generally mild in healthy individuals, the economic burden associated with HRV infection is significant. A vaccine could prevent disease. The Vero-cell-based viral vaccine platform technology was considered for such vaccine development. Unfortunately, most HRV strains are unable to propagate on Vero cells due to a lack of the major receptor of HRV group A and B, intercellular adhesion molecule (ICAM1, also known as CD54). Therefore, stable human ICAM1 expressing Vero cell clones were generated by transfecting the ICAM1 gene in Vero cells and selecting clones that overexpressed ICAM1 on the cell surface. Cell banks were made and expression of ICAM1 was stable for at least 30 passages. The Vero_ICAM1 cells and parental Vero cells were infected with four HRV prototypes, B14, A16, B37 and A57. Replication of all four viruses was detected in Vero_ICAM1, but not in the parental Vero cells. Altogether, Vero cells expressing ICAM1 could efficiently propagate the tested HRV strains. Therefore, ICAM1-expressing cells could be a useful tool for the development and future production of polyvalent HRV vaccines or other viruses that use ICAM1 as a receptor.

Immunotherapy of metastatic melanoma by intratumoral injections of Vero cells producing human IL-2: phase II randomized study comparing two dose levels

BACKGROUND

Systemic IL-2 has shown some activity in metastatic melanoma, but its use is severely limited by toxicity. TG2001 is a product in which the human IL-2 cDNA was incorporated into the genome of Vero cells, a monkey fibroblast cell line. The goal of this intratumorally applied therapy was to create an antitumor immune response stimulated by xeno-antigens and local production of IL-2 in the close vicinity of tumor-specific antigens. TG2001 was reported to have a good safety profile in two previous dose-escalating phase I studies performed in 18 patients with various solid tumors, with encouraging clinical responses in three patients. The objectives of this study were to evaluate the tolerance and incidence of tumor regression in patients with metastatic melanoma, following repeated administration of Vero-IL-2 cells.

PATIENTS AND METHODS

This was on open-label, randomized phase II study comparing two doses of Vero-IL-2, 5x10(5) and 5x10(6) cells. Twenty-eight patients with metastatic melanoma were enrolled in the study, 14 in each treatment group. Patients received TG2001 by intratumoral injection on days 1, 3, and 5 every 4 weeks for four cycles, and every 8 weeks thereafter, until evidence of progressive disease (PD). Criteria for patient selection included histologically proven metastatic melanoma, with one tumor accessible for product administration, and at least another tumor site for response assessment. Evaluation included tumor measurements, humoral and T cell-mediated local and systemic immune response, humoral response to Vero cells, adverse events and standard laboratory parameters.

RESULTS

None of the patients achieved a confirmed objective response. Stable disease (SD) was seen in six (43%) and eight patients (57%) at the 5x10(5) and the 5x10(6) dose level, respectively. Two patients, one in each group, died during the study (i.e., within 1 month after the last injection) due to PD. Three patients exhibited antibody responses to Vero cells. T-cell immunity, serum cytokine levels and cytokine mRNA expression in tumor biopsies did not show meaningful alterations after therapy, except for a trend toward an increase in intratumoral TH2 cytokine (IL-4 and/or IL-10) levels. The study drug was well tolerated at both dose levels and side effects mainly consisted of injection site pain and erythema, and pyrexia.

CONCLUSION

The intratumoral administration of TG2001 was generally well tolerated in patients with metastatic melanoma, and transient disease stabilization was observed in 50% of patients.

Potency analysis of inactivated vaccines for Aujeszky's disease virus (ADV), strain RC/79: lymphocyte stimulation in immunized pigs

Mitogenic and antigenic lymphocyte stimulation was examined in pigs that had been immunized with 2 inactivated vaccines which had been prepared with Aujesky's disease virus (ADV), strain RC/79. One vaccine was partially purified by ultra-centrifugation (Vaccine A) the other one was not (Vaccine B). A second dose of vaccine had no influence over the blastogenic response when the lymphocytes were stimulated with phytohemoagglutinin (PHA). Lymphocyte response to the ADV antigen in the immunized pigs was significantly higher at day 30 post inoculation than at day 0 indicating that it was highly specific. Cellular antigens contained in the viral cultures produced a slight non-specific response as shown by a low increase in the levels of lymphocyte blastic transformation (LBT) in the control group at day 30 p.i., this group only received a non infected Vero cell suspension. This was the case in pigs that received vaccine A as well as in those that were vaccinated with vaccine B. Vaccine B contains a greater quantity of contaminating cellular antigens, since it is an impure vaccine. Such antigens could act as non-specific immunomodulators, potentiating cell-mediated immunity (CMI). This assay demonstrated that inactivated vaccines produced with VPR-RC/79, partially purified and unpurified are capable of inducing a humoral immune response. The blastogenic reaction of the peripheral blood lymphocytes to antigens of ADV strain RC/79, indicated that the employed immunogens also induced the CMI. Results indicate that the analyzed immunogens could be considered for the possible implementation of epidemiological measures, which imply the use of vaccines to prevent pseudo-rabies in Argentina.

Novel mechanism of antibody-independent complement neutralization of herpes simplex virus type 1

The envelope surface glycoprotein C (gC) of HSV-1 interferes with the complement cascade by binding C3 and activation products C3b, iC3b, and C3c, and by blocking the interaction of C5 and properdin with C3b. Wild-type HSV-1 is resistant to Ab-independent complement neutralization; however, HSV-1 mutant virus lacking gC is highly susceptible to complement resulting in > or =100-fold reduction in virus titer. We evaluated the mechanisms by which complement inhibits HSV-1 gC null virus to better understand how gC protects against complement-mediated neutralization. C8-depleted serum prepared from an HSV-1 and -2 Ab-negative donor neutralized gC null virus comparable to complement-intact serum, indicating that C8 and terminal lytic activity are not required. In contrast, C5-depleted serum from the same donor failed to neutralize gC null virus, supporting a requirement for C5. EDTA-treated serum did not neutralize gC null virus, indicating that complement activation is required. Factor D-depleted and C6-depleted sera neutralized virus, suggesting that the alternative complement pathway and complement components beyond C5 are not required. Complement did not aggregate virus or block attachment to cells. However, complement inhibited infection before early viral gene expression, indicating that complement affects one or more of the following steps in virus replication: virus entry, uncoating, DNA transport to the nucleus, or immediate early gene expression. Therefore, in the absence of gC, HSV-1 is readily inhibited by complement by a C5-dependent mechanism that does not require viral lysis, aggregation, or blocking virus attachment.

Gene therapy with cytokine-transfected xenogenic cells (Vero-IL-2) in patients with metastatic solid tumors: mechanism(s) of elimination of the transgene-carrying cells

Eleven patients with advanced cancer were treated in a clinical gene therapy trial by repeated intra- tumoral injections with different doses of xenogenic fibroblasts secreting high amounts of human interleukin-2 (Vero-IL2). Treatments in a total of 14 courses were well tolerated and resulted in clinical responses and measurable biological effects. Together with increases in serum interleukin-2 (IL-2), modifications of the V-beta T cell receptor repertoire and induction of intratumoral T-cell infiltration were observed. When the intratumoral expression of endogenous cytokine genes and the persistence of the IL-2 transgene at the application site and in peripheral blood were investigated, rapid disappearance of the transgene at the application site appeared to be the most prominent biological effect. Tests detecting a single Vero-IL2 cell against a background of 10(5) non-transfected cells were not able to demonstrate significant expression of exogenous IL-2 (i.e. the transgene or transgene-carrying cells) in tumor biopsies or blood at different times. Therefore, further studies were performed to evaluate the mechanism(s) involved in the rapid disappearance of xenogenic carrier cells in more detail. We show here that significant in vitro cytotoxicity against transgene-carrying Vero cells can be observed in peripheral blood of all the patients before treatment as well as in healthy controls. "Cold" target inhibition shows that significant killing of Vero-IL2 cells is mediated by natural killer (NK) cells. This was confirmed by showing that established CD3(-)/CD16(+)/CD56(+) peripheral blood NK cell clones kill both K562 and Vero-IL2 target cells. The failure of other mechanisms (complement, antibody-dependent cell cytotoxicity or cytotoxic T lymphocytes) to destroy xenogenic, histoincompatible Vero cells in vitro suggests that NK cells also might be responsible for the killing of Vero-IL2 in vivo and for the failure to detect the transgene at the application site. These results might also be of importance for some aspects of the current discussion of xenotransplantation.

Natural killer cell mediated cytotoxicity against VERO target cells; the suppressive effect of pentoxifylline

The K-562 cell line is widely known and used as a NK cell target. In this study we report that VERO (African green monkey kidney epithelial cell line) is an excellent target of the human NK cell cytotoxicity. Considerable cytotoxicity was observed in a 4 h 51Cr release assay with nonadherent and immunomagnetically separated CD56+ NK cells from PBMC. On the contrary, adding K-562 cells as cold target to the assay the cytotoxicity significantly decreased. Using a standard chromium-release assay the NK cell activity (NKCA) against VERO cells was investigated in a population of healthy volunteers (mean value of cytotoxicity was 26.6%) and compared with the values of cytotoxicity against K-562 target cells (32.6%). The difference was not significant (P > 0.05). The suppressive effect of PTX on in vitro NK cell activity was observed at concentration of 100 microg/ml using VERO target cells as well as K-562 cells. Our studies provide the first evidence that the NK cell activity is suppressed in vitro by PTX using VERO cells as NK target cells.

Efficacy of a food plant-based oral cholera toxin B subunit vaccine

Transgenic potatoes were engineered to synthesize a cholera toxin B subunit (CTB) pentamer with affinity for GMI-ganglioside. Both serum and intestinal CTB-specific antibodies were induced in orally immunized mice. Mucosal antibody titers declined gradually after the last immunization but were restored following an oral booster of transgenic potato. The cytopathic effect of cholera holotoxin (CT) on Vero cells was neutralized by serum from mice immunized with transgenic potato tissues. Following intraileal injection with CT, the plant-immunized mice showed up to a 60% reduction in diarrheal fluid accumulation in the small intestine. Protection against CT was based on inhibition of enterotoxin binding to the cell-surface receptor GMI-ganglioside. These results demonstrate the ability of transgenic food plants to generate protective immunity in mice against a bacterial enterotoxin.

Gene therapy of spontaneous canine melanoma and feline fibrosarcoma by intratumoral administration of histoincompatible cells expressing human interleukin-2

The production of human interleukin-2 (hIL-2) local to the tumor site by engineered histoincompatible cells has been shown in various murine models to promote a strong immune response leading to tumor growth inhibition or rejection. To assess whether this strategy would be similarly applicable for treatment of primary neoplastic cells, two naturally occurring tumors were used as preclinical models; the highly metastatic melanoma of the dog and the low metastatic fibrosarcoma of the cat. We demonstrate that both cats and dogs when treated by tumor surgery, radiotherapy and repeated local injections of xenogeneic Vero cells secreting high levels of hIL-2 relapse less frequently and survive longer than control animals treated by surgery and radiotherapy alone. Local secretion of hIL-2 by the xenogeneic cells is shown to be necessary for the induction of an optimal antitumor effect. Moreover, the safety of the procedure was demonstrated in both animal models and through extensive toxicological analysis performed in rats. These results confirm for the first time to our knowledge the safety and therapeutic potential of a gene transfer strategy in animals with spontaneous metastatic and nonmetastatic tumors.

Biological characterization of clones derived from the Edmonston strain of measles virus in comparison with Schwarz and CAM-70 vaccine strains

Four virus clones were derived from the Edmonston strain of measles virus by repeated plaque purification. These clones were compared with the vaccine strains Schwarz and CAM-70 in terms of biological activities including plaque formation, hemagglutination, hemolysis and replication in Vero cells and chick embryo fibroblasts (CEF). Two clones of intermediate plaque yielded mixed plaque populations on subcultivation whereas the other two, showing small and large plaque sizes, showed stable plaque phenotypes. The vaccine strains showed consistent homogeneous plaque populations. All the Edmonston clones showed agglutination of monkey erythrocytes in isotonic solution while both vaccine strains hemagglutinated only in the presence of high salt concentrations. Variation in the hemolytic activity was observed among the four clones but no hemolytic activity was detected for the vaccine virus strains. Vaccine strains replicated efficiently both in Vero cells and CEF. All four clones showed efficient replication in Vero cells but different replication profiles in CEF. Two of them replicated efficiently, one was of intermediate efficiency and the other showed no replication in CEF. Two of the clones showed characteristics similar to vaccine strains. One in terms of size and homogeneity of plaques, the other for a low hemolytic activity and both for the efficiency of propagation in CEF.

[Ebola virus reproduction in cell cultures]

Ebola-Zaire virus production in Vero and BGM cells was studied. The CPE developed in both cell cultures. The cell monolayer destruction by 80-90% was seen at a low multiplicity of infection in 7-8 days after virus inoculation. An overlay composition was developed for virus titration using plaque assay. The plaque production was shown to be directly proportional to the virus dose. The curve of Ebola virus production in Vero cell culture fluid was determined. At a multiplicity of infection of 0.01 PFU/cell, the maximum virus titer of 10(6.4) PFU/ml was reached in 7 days postinfection. Specific antisera were generated by inoculation of guinea pigs. Indirect immunofluorescent assay was used for testing of virus-specific antigen and antibody.

[Use of various cell culture antigens in the indirect fluorescent antibody test for the detection of antinuclear antibodies]

Cell culture antigens were prepared from Vero, BHK-21 and Hep-2 cells which were propagated on slide, for detection antinuclear antibody (ANA) in sera with indirect fluorescent antibody test (IFAT). ANA were investigated in 55 sera which were positive at 1/20 titer with KB IFAT ANA test kits (Virgo), by using these cell culture antigens. 50 sera (91%) with Vero antigens, 46 sera (83%) with BHK-21 antigens and 44 sera (80%) with Hep-2 antigens were found positive at 1/20 titer. As conclusion Vero cell culture which is propagated on slide can be used as antigen for detection of ANA with IFAT.

Elevation of the levels of SmB, B' and D proteins but not that of the La (SS-B) antigen during HSV infections

Three Sm proteins, B, B' and D, which are highly immunoreactive in systemic lupus erythematosus (SLE), increase in abundance in Vero cells infected with laboratory strains and clinical isolates of herpes simplex virus (HSV) types 1 and 2. The autoimmune antigen La (SS-B) does not accumulate in identical infections. The significance of the Sm antigen accumulation is discussed in terms of its possible role in HSV infection and in connection with the origin of autoantibodies in SLE.

Combined estimation of tetanus and diphtheria antitoxin in human sera by the in vitro Toxin-Binding Inhibition (ToBI) test

The use of the principle of inhibition of toxin binding to an antitoxin coated immunoassay plate as described in a previous paper for tetanus antitoxin titration, was adapted for the estimation of diphtheria antitoxin in human sera. With a few modifications, a Toxin-Binding Inhibition (ToBI) test was developed which could be used for a combined estimation of both tetanus and diphtheria antitoxin levels. The application of streptavidin-biotinylated peroxidase complex when using small serum samples (less than 50 microliters) is discussed. Antitoxin titres (both diphtheria and tetanus) of 0.002 IU ml-1 were detectable by the ToBI test, this being far below the level considered to be protective in man. Sera from 140 adults with different vaccination histories were titrated for both tetanus and diphtheria antitoxin. Good correlations were found between the estimates obtained by the ToBI test and those obtained by the toxin-neutralization (TN) test in mice (tetanus antitoxin) and those obtained in the in vitro neutralization test in VERO cells (diphtheria antitoxin). It is concluded that the ToBI test is a simple and reliable alternative to the functional models currently in use for the estimation of diphtheria and tetanus antitoxin levels. In addition, the ToBI test eliminates the need for laboratory-animal or cell-culture facilities and can be performed with small quantities of serum as required in field trials.

Comparative study of the safety and protective value, in pre-exposure use, of rabies vaccine cultivated on human diploid cells (HDCV) and of the new vaccine grown on Vero cells

The object of the study is to compare the tolerance and the efficacy of a new inactivated rabies vaccine grown on Vero cells (PVRV), with the vaccine cultivated on human diploid cells (HDCV), using the schedule recommended by WHO for pre-exposure on days 0, 7 and 21. Of students exposed to a risk of rabies at Alfort Veterinary School, 144 volunteers received either HDCV or PVRV vaccine. No student received a booster between the first blood sample before immunization on day 0 and the last antibody titration 21 months after the beginning of immunization. No serious side-effect occurred with either vaccine, although some vaccinees complained of redness, induration or local pain and, exceptionally, of fever. The study indicates the excellent immunogenicity of both HDCV and PVRV vaccines in all vaccinees. The geometric mean of antibody titres shows a higher titre in the PVRV group and a rapid decline in immune response with both vaccines, four months after the first injection, followed by a stabilization of the antibody level throughout the rest of the study. It should be noted, however, that very few individuals were found to be seronegative 21 months after the first injection.

Monoclonal antibodies against Vero cells that protect against diphtheria toxin

Mice were immunized with a cell line (Vero) that possesses a high number of membrane receptors for diphtheria toxin. Spleen cells from these mice were fused with SP2/0-Ag14 cells and two cell lines (1A2 and 2D2) isolated by screening for the ability of their secreted antibodies to inhibit binding of radiolabeled diphtheria toxin to Vero cells. These antibodies protected Vero cells from the inhibition of protein synthesis mediated by diphtheria toxin. The antibodies were purified, iodinated, and their binding characteristics investigated. At 4 degrees C, the association of 1A2 and 2D2 with Vero cells was saturable (KD approximately 10(-8) M) and indicated about 10(6) binding sites/cell. Diphtheria toxin did not inhibit the binding of either radiolabeled antibody. Monoclonal antibody 1A2 completely inhibited 125I-2D2 binding and vice versa. Trypsin or phospholipase C treatment of Vero cells had no effect on the ability of the monoclonal antibodies to bind to the cells. These findings suggest that: (1) the two monoclonal antibodies recognize the same or closely related epitopes and (2) the antibodies bind a domain distinct from the toxin binding site or to a subcomponent of the diphtheria toxin receptor that is present at many other cell surface sites. These antibodies offer a powerful tool to study the structure, processing and mode of action of diphtheria toxin receptors.

HSV-specific IgA from tears blocks virus attachment to the cell membrane

The results of this investigation demonstrate that the IgA antibody in tears inhibits the attachment of herpes simplex virus (HSV) to cells and implicate immunoglobulin A (IgA) isotype antibody in the protection of the ocular surface. Tears were collected from the eyes of infected and uninfected rabbits and tested for the presence of infectious virus, for viral neutralization titer, and in an enzyme-linked immunoassay (ELISA) for antibody to HSV. Neither the tears from the uninfected rabbits nor the tears from the infected rabbits produced viral cytopathic effects on indicator cells in vitro. Tears from uninfected rabbits had no virus neutralization capacity while the tears from infected rabbits had titers of 1:10 to 1:40. Tears collected from HSV-1 infected rabbits, but not uninfected rabbits, had anti-HSV antibody titers as determined by the enzyme-linked immunosorbent assay. Lectin affinity column enrichment of IgA from the tears of uninfected and infected rabbits was examined for the capacity to block viral adsorption to cells using 32P-labeled virus. It was found that exposure of the radio-actively-labeled virus to the purified IgA fraction of tears from infected rabbits reduced the amount of virus binding to Vero cells, whereas the purified IgA obtained from uninfected tears had minimal activity. These results may imply a role for the IgA-containing fraction of tears from HSV-infected animals in preventing viral attachment to cells and suggest that antibody of this isotype plays a protective role at the ocular surface.

Veto cell H-2 antigens: veto cell activity is restricted by determinants encoded by K, D, and I MHC regions

Responder cells from primary syngeneic and allogeneic one-way mixed-lymphocyte cultures (MLC) specifically inhibit the development of cytotoxic T lymphocytes (CTL) directed against the major histocompatibility complex (MHC) antigens of the MLC responder cells. This special kind of suppressor activity is known as veto suppression. Ia+ cells with veto activity obtained from H-2 recombinant mouse strains were shown to downregulate alloantigen (class II)-specific helper activity for class I-specific CTL development in a primary MLC provided that the veto cells expressed the same I-E alpha subregion as the MLC stimulator cells. The veto-induced suppression of allo-help was prevented by the addition of supernatant from concanavalin A-stimulated spleen cells (Con A-SN) and was inhibited considerably by very high amounts of recombinant interleukin-2 (IL-2). In the presence of Con A-SN, CTL precursors recognizing either the K end or the D end of the veto cell MHC were found to be inactivated. Thus, our results indicate that MLC responder cells include active veto cells expressing Ia region-encoded restriction elements for allospecific T helper cells, as well as K- or D-encoded restriction elements for allospecific T cytotoxic cells.

Persistent infection of Vero cells by paramyxoviruses. A morphological and immunoelectron microscopic investigation

Two Vero cell lines persistently infected with canine distemper virus (CDV) or with both CDV and canine parainfluenza (CPI) viruses were investigated. Cells in the CPI-CDV cell line were 90-100% positive for CPI antigen and exhibited 10-80% CPI hemadsorption. Cytoplasmic CDV antigen expressed in both singly and dually infected monolayers varied weekly from 1 to 100%. Numerous cytolytic crises were observed in both cell lines. Cell replication was severely depressed in both cell lines when compared with uninfected Vero cells. Infrequent interfering activity against lytic CPI virus was present in the CPI-CDV cell line but not between lytic CDV and progeny virus from the CDV or the CPI-CDV cell line. Ultrastructurally, Vero cells persistently infected with both paramyxoviruses contained two types of viral nucleocapsids (NC). By immunoelectron microscopy, smooth NC were identified as CPI virus and rough NC were of CDV origin. The viral NC never intermingled but rather were restricted to discrete cytoplasmic areas containing either one type of NC or the other.