Idiotype network components are involved in the murine immune response to simian virus 40 large tumor antigen

A role for antibodies in tumor immunity

Recent advances have demonstrated the clinical utility of specific monoclonal antibodies that recognize tumor-associated antigens on the surface of the tumor cell in the treatment of breast cancer and B cell lymphoma in humans. In addition to these studies, an experimental tumor model, where antibodies that recognize a viral-encoded tumor-specific antigen play a major role in tumor immunity, will be discussed. Together, these studies implicate antibodies as a means of providing tumor immunity against some cancers. The necessity for designing cancer vaccines that induce antibodies with specificity for antigens on the tumor cell will be discussed.

Emerging translational therapies for mesothelioma

Malignant pleural mesothelioma remains a therapeutic and diagnostic problem. Translational mechanisms for treatment of the disease are emerging from newly learned characteristics of the tumor on a molecular, cellular, and extracellular basis. Although slow to reach the clinical arena, these potential strategies do show proof of principle in the in vitro and in vivo settings, and some, including adenoviral molecular chemotherapy, have completed phase I testing. This review describes the rationale and status of these newer treatment ideas.

Nucleic acid vaccination against virally induced tumors

Plasmid DNA (pSV3-neo) encoding the large tumor antigen (T-ag) of simian virus 40 (SV40) was used to actively immunize mice to assess the induction of SV40 T-ag specific immunity. Mice were injected with naked DNA intramuscularly, and both the cellular and humoral immune responses were compared to those elicited in mice immunized with recombinant protein. Administration of recombinant SV40 T-ag elicited high titer antibodies reactive with SV40 T-ag, whereas inoculation with DNA failed to generate comparable levels of SV40 T-ag specific antibody. Conversely, antigen specific cytotoxic T lymphocyte activity was generated in mice immunized with pSV3-neo, but was not detected in mice immunized with the recombinant protein. Moreover, the cellular immunity generated by the injection of pSV3-neo DNA was protective against a lethal challenge with syngeneic SV40 transformed cells. Together, these data indicate that active immunization with genes encoding tumor specific antigens may be an efficacious strategy for the induction of cell-mediated mechanism(s) to prevent cancer.

Humoral immune response in a marsupial Monodelphis domestica: anti-isotypic and anti-idiotypic responses detected by species-specific monoclonal anti-immunoglobulin reagents

We examined the humoral immune response of the laboratory opossum (Monodelphis domestica) as a model marsupial species. To evaluate antibody responses, IgM and IgG preparations were purified from the sera of naïve Monodelphis. These two immunoglobulin (Ig) preparations were used to generate specific murine monoclonal antibodies for use in ELISA-based serology. Individual Monodelphis were then immunized with a multideterminant protein antigen, a murine monoclonal antibody (Mab) IgG preparation designated Pab 405. In contrast with the primary IgM response of eutherian mammals, the primary response of Monodelphis to mouse IgG involved both IgG and IgM. The specificity of this anti-mouse IgG response appeared isotypic in nature, specifically, the immune sera recognized Ig determinants common to both Pab 405 and a control IgG Mab. Further, to evaluate the antibody responses to mouse IgG, immune sera were adsorbed against a control IgG Mab to remove the anti-isotypic reactivity. The adsorbed Monodelphis sera recognized idiotope specificities expressed on Pab 405. Based on an inhibition ELISA, the anti-idiotype (anti-Id) response recognized an idiotope on Pab 405 associated with its antigen combining site. These results demonstrate that Monodelphis respond to a multideterminant protein antigen such as murine IgG, similarly but not identically to eutherian mammals, and can serve as a useful marsupial model for additional comparative immunological studies.

SV40 large tumor antigen associated synthetic peptides define native antigenic determinants and induce protective tumor immunity in mice

Synthetic peptides were utilized to define antigenic determinants on simian virus 40 (SV40) large tumor antigen (T-ag). Six synthetic peptides representing predicted B-cell epitopes on SV40 T-ag were used to immunize mice to compare the humoral immune responses and ascertain the ability of the peptide preparations to induce protective tumor immunity in vivo. Anti-peptide antibodies from BALB/c and C57BL/6 mice were examined for reactivity with SV40 T-ag by various immunologic assays. Antibodies from both strains to four of the peptides recognized recombinant SV40 T-ag by ELISA. However, T-ag recognition by anti-peptide antibodies differed when assessed by Western blot. Antibodies induced by the same four peptides in BALB/c mice recognized T-ag, whereas only three of the sex peptides induced antibodies in C57BL/6 mice capable of recognizing SV40 T-ag by Western blot. Flow cytometric analysis revealed that antibodies to peptides corresponding to T-ag amino acid residues 632-652 and 690-708 from BALB/c mice were able to recognize the surface of SV40 transformed cells, whereas five of the six peptides induced surface reactive antibodies in C57BL/6 mice. More important, peptides 632-652 and 690-708 elicited a protective immune response in BALB/c mice subsequently challenged with a lethal dose of syngeneic SV40 transformed cells. However, this tumor immunity was incomplete as only 50% of the mice survived the tumor challenge. These data indicate that antibodies induced by synthetic peptides corresponding to predicted B-cell epitopes on SV40 T-ag are capable of recognizing native and denatured determinants on T-ag. Furthermore, immune responses elicited by selected peptides partially protected BALB/c mice from a lethal tumor challenge.

Molecular characterization of immunoglobulin variable regions from murine monoclonal antibodies specific for simian virus 40 large tumour antigen

In this report we compare the immunoglobulin variable (IgV) region function and structure relationships of murine monoclonal antibodies that recognize simian virus 40 (SV40) large tumour antigen (T ag). Comparison of monoclonal antibody V region function is based on SV40 T ag epitope recognition and idiotype (Id) expression. Structural comparisons are based on V region gene sequence determination. The data presented herein, suggests that a high degree of homology within both the V kappa and VH regions, along with minor differences within V kappa complementarity determining regions (CDR) may result in the detection of similar SV40 T ag epitopes by the monoclonal anti-SV40 T ag preparations. The expression of a cross-reactive Id also appears to be based on the high degree of homology within both V kappa and VH regions and depends on conformational interactions imparted by both regions.

Fine specificity of the murine immune response to SV40 large tumour antigen utilizing synthetic peptides that define selected epitopes

Baculovirus-derived recombinant simian virus 40 large tumour antigen (SV40 T-ag) was used to immunize BALB/c, C57Bl/6 and CB6/F1 mice and their anti-SV40 T-ag antibody responses were examined for the ability to bind synthetic peptides representing six predicted B cell epitopes on SV40 T-ag. In C57Bl/6 mice, anti-SV40 T-ag antibodies failed to bind any of the six SV40 T-ag peptides. However, the antibody responses induced in both BALB/c and CB6/F1 mice recognized synthetic peptides corresponding to two distinct epitopes (amino acids 690-708 and 660-679, respectively) associated with the carboxyl-terminal half of SV40 T-ag. In addition, murine MoAbs (BALB/c) generated to native SV40 T-ag, and previously characterized as recognizing the carboxyl-terminus of SV40 T-ag by deletion mutant analysis, also bound the synthetic peptide (residues 690-708) defining the carboxyl-terminus of SV40 T-ag. These data indicate that the antibody responses induced in BALB/c and CB6/F1 mice by immunization with baculovirus-derived recombinant SV40 T-ag are capable of recognizing sequential carboxyl-terminal epitopes on SV40 T-ag defined by peptides 690-708 and 660-679, respectively. No statistically significant differences in anti-SV40 T-ag antibody titres were observed between the three inbred mouse strains. These data suggested that the fine specificities of the anti-SV40 T-ag responses as assessed by synthetic peptide binding were different in the three inbred strains of mice examined. Finally, in vivo tumour challenge studies comparing recombinant SV40 T-ag with the two carboxyl-terminus peptide epitopes indicated that some tumour immunity was induced in BALB/c, but not CB6/F1 mice, by immunization with peptide 690-708 conjugated to a carrier protein. These studies suggest that the carboxyl-terminal region of SV40 T-ag represents a continuous sequential epitope involved in both the antibody response to SV40 T-ag and tumour immunity in BALB/c mice.

Comparison of the murine humoral immune response to recombinant simian virus 40 large tumor antigen: epitope specificity and idiotype expression

Baculovirus-derived recombinant simian virus 40 (SV40) large tumor antigen (SV40 T-Ag) was used to immunize inbred strains of mice to compare the humoral immune responses. Specifically we examined the epitope specificities and idiotype (Id) expression on anti-(SV40 T-Ag) responses induced in BALB/c and C57BL/6 inbred strains of mice. The predominant SV40 T-Ag epitopes recognized by the anti-(SV40 T-Ag) responses appeared to differ between these two inbred strains, this being based on the ability of sera to inhibit the binding of several murine monoclonal antibodies specific for SV40 T-Ag. In addition, anti-(SV40 T-Ag) responses produced in C57BL/6 mice failed to express a previously described cross-reactive Id expressed in the anti-(SV40 T-Ag) response in BALB/c mice. This cross-reactive Id is detected by a mouse monoclonal anti-Id, designated 58D, which has been shown to represent a potential focal point for manipulating the humoral immune response to SV40-induced tumors in BALB/c mice. Together, these data indicate that the functional duality of the humoral immune response, as assessed by epitope recognition and Id expression, differs between these two inbred strains of mice when immunized with a recombinant SV40 T-Ag.