Biomedical subjects

W M Kast

Publications and source records attributed to W M Kast.

At least 55 records · Page 3Linked to original sources

PubMed1998

The biological activities of simian virus 40 large-T antigen and its possible oncogenic effects in humans.

Simian virus 40 (SV40) is an oncogenic virus which induces tumors in hamsters and transforms human cells in tissue culture. Between 1955 and 1963, polio vaccines and adenovaccines were contaminated with SV40; therefore, millions of people were exposed to this oncogenic virus. The SV40 proteins responsible for in vivo oncogenesis and in vitro cell transformation are encoded by the early region of the virus. These proteins are called T (tumor) antigens (Tags), because animals with tumors induced by SV40 have antibodies against these viral proteins. Recently, we and other research laboratories have found SV40 in specific types of human tumors: mesothelioma, ependymoma and choroid plexus tumors, osteosarcoma and sarcoma. The same tumor types will develop in hamsters which have been injected systemically with SV40. SV40 causes cell transformation in tissue culture and tumors in animals, because SV40 Tag binds and inactivates the cellular tumor suppressor gene products, Rb and p53. We found that SV40 Tag binds p53 and Rb in human mesotheliomas, possibly contributing to the malignant phenotype.

Animals↗

PubMed1998

The detection of simian virus 40 in human tumors by polymerase chain reaction.

Simian virus (SV) 40 is a deoxyribonucleic acid (DNA) virus that induces mesotheliomas, ependymomas, bone tumors, and lymphomas in hamsters. In recent years SV40 sequences have been detected in approximately 60% of mesotheliomas and ependymomas, in 33% of bone tumors and sarcomas, and in 13% of lymphomas. Because the amount of human specimens available for molecular studies is usually minimal, the method most commonly used to demonstrate SV40 in human specimens is the polymerase chain reaction (PCR). PCR is a highly sensitive and useful technique. In the PCR reaction, different sets of primers are used for targeting different regions of DNA. The regions of the SV40 genome targeted by PCR include the large T-antigen, the small t-antigen, the origin of replication, and viral protein-1 capsid protein. The use of these different sets of primers to test human tumor specimens for SV40 produce a different percentage of positive results. This is because these experiments revealed that some primers are more specific than others which may also detect sequences belonging to other DNA papovaviruses. Therefore, the combined use of different sets of primers is recommended when it is important to distinguish SV40 from other related papovaviruses such as BK and JC, which can also be occasionally present in human cells. Furthermore, these experiments demonstrated that polymerase chain reaction analyses for simian virus 40 can be performed better and easier when using deoxyribonucleic acid extracted from fresh and/or frozen tissue. Deoxyribonucleic acid from paraffin embedded specimens should not be used routinely for simian virus 40 testing because of the high risk of obtaining false negative results. However, these paraffin derived deoxyribonucleic acids can be used reliably in molecular laboratories specialized in these type of analyses. This paper describes the methods that we have developed to test simian virus 40 in human specimens.

Base Sequence↗

PubMed1998

Cellular immunity and immunotherapy against deoxyribonucleic acid virus-induced tumors.

An important role in the immune defense against deoxyribonucleic acid virus induced tumors is mediated by T-cells, as is evident from aetiological, animal model, and clinical data. In this review the most recent observations in this field are described for three prominent members of this family of viruses, namely human papillomavirus associated with human cervical cancer, human adenovirus associated with lung infections in humans and tumors in rodents, and simian virus 40 associated with rodent tumors and human mesothelioma, osteosarcoma and ependymoma.

Animals↗

PubMed1998

Evidence for and implications of SV40-like sequences in human mesotheliomas and osteosarcomas.

Pleural mesotheliomas and osteosarcomas develop in hamsters injected intracardially with SV40. Using primers specific for the RB-pocket binding domain of SV40 we analysed with the polymerase chain reaction frozen specimens from 48 human mesotheliomas and 145 human bone tumours. We found that 60% of human mesotheliomas and 33% of human bone tumours contained SV40-like DNA. Immunostaining, Western blot and RNA in situ hybridization experiments revealed SV40 Tag expression in human mesotheliomas. Osteosarcomas were not studied for Tag expression because not enough material was available. Finally, antibodies anti-Tag were detected in the sera collected from patients with mesothelioma. These data indicate that SV40, or a closely related virus, is/are present in human mesothelioma and osteosarcoma.

Animals↗

PubMed1998

Active immunization against cancer cells: impediments and advances.

Immunotherapy of cancer is still mainly an experimental treatment. Some monoclonal antibodies have been approved for adjuvant therapy of cancer in patients, but active immunization strategies have not yet matured to this stage. The fact that vaccination against viral diseases is effective has primed high expectations for successful vaccination against cancer as well. Indeed, in some animal models, therapeutic results could be obtained against short-term established tumors, which paved the way for clinical trials. However, the first results with active immunization in cancer patients were disappointing and this led to a careful examination of current protocols and the search for more effective approaches. Evaluation of the available data suggests that cancer patients may not be comparable in their immune response to cancer vaccines with healthy persons. Furthermore, the tumor seems to be able to develop several immune-escape mechanisms, which either inactivate the specific immune cells or prevent activation of potential effector mechanisms against the tumor. Here, we review the impediments that have been identified in murine models and clinical trials for immunotherapy of cancer. It will be important to study the hurdles to come to a better understanding of the immune evasion of tumors and to achieve efficient activation of the immune system in cancer patients against the tumor. This knowledge will open new possibilities for active immunization against cancer.

Animals↗

PubMed1997

Targeting of cytotoxic T cells against leukemic B cells by bispecific antibody (aCD3 x aCD19) does not distract the T cell from its primary target.

Bispecific Abs (BsAb) represent a novel format of immunotherapy, recognizing immune effector cells (e.g., T cells), on the one hand, and target cells (e.g., tumor cells), on the other hand. To be successful, cross-linking of the two cell types is necessary for effector cell activation and subsequent killing of the malignant target cells. We asked the question, whether CTL that were incubated with the BsAb aCD3 x aCD19 and malignant B cells and activated to kill the malignant B cells were still able to eliminate their natural target cells (e.g., virus-infected autologous body cells). To test this, HLA-A*0201-restricted, influenza-specific CTL were incubated with BsAb- and HLA-A*0201-positive B lymphoid tumor cells in combination with HLA-A*0201-positive, virus-infected non-B lymphoid cells as natural target cells. The results showed that even in the presence of BsAb and high amounts of tumor B cells, CTL were still capable of eliminating the virus-infected non-B lymphoid target cells; actually, CTL recognized and eliminated the homologous original target cells preferentially.

Antibodies, Bispecific↗

PubMed1997

HIV-1 reverse transcriptase-specific CTL against conserved epitopes do not protect against progression to AIDS.

A small group of HIV-1-infected subjects who either do not progress to AIDS or progress only slowly have sustained HIV-1-specific CTL responses. It has been suggested that the specificities of these responses differ from the CTL responses of rapid progressors due to recognition of epitopes that are under structural or functional constraints. We have, in this respect, studied the CTL response to reverse transcriptase (RT) in long term survivors (LTS) and in HIV-1-infected individuals who progressed to AIDS within 3 to 6 yr. Both LTS and progressors displayed vigorous RT-specific CTL responses of comparable magnitude during the asymptomatic phase. From each individual at least two CTL lines were obtained from blood samples drawn at different time points during follow-up. A total of 19 CTL lines recognized nine different RT-derived epitopes. CTL obtained from progressors recognized epitopes with a similar degree of amino acid conservation as epitopes targeted by CTL from LTS. Furthermore, five of seven epitopes were recognized by both LTS and progressors. Moreover, one of the epitopes recognized by progressors contained the highly conserved YMDD motif that is essential for RT activity. In conclusion, our data imply that neither the magnitude nor the specificity of HIV-1-specific CTL against RT is a major cause of a more protracted course of disease.

Acquired Immunodeficiency Syndrome↗

PubMed1997

Identification of HLA-A*0201-restricted CTL epitopes encoded by the tumor-specific MAGE-2 gene product.

MAGE-2 is expressed in many tumors, including melanoma, laryngeal tumors, lung tumors and sarcomas, but not in healthy tissue, with the exception of testis. Thus, MAGE-2-derived peptides that bind to HLA class I molecules and elicit cytotoxic T lymphocyte (CTL) responses could be of significant therapeutic importance. In this study, we show that several MAGE-2-derived peptides bind with high affinity to HLA-A*0201. Three of them form complexes with HLA-A*0201 that are stable at 37 degrees C and are immunogenic in HLA-A*0201Kb transgenic mice. Moreover, CTLs against 2 of them (M2 112-120, and M2 157-166) specifically recognize cells that express both the MAGE-2 protein and HLA-A*0201Kb. These 2 peptides are processed and presented in the context of HLA-A*0201. Therefore, these peptides are candidate components in peptide-based vaccines for the treatment and prevention of several types of MAGE-2-expressing cancers.

Animals↗

PubMed1997

Tumor eradication by wild-type p53-specific cytotoxic T lymphocytes.

The tumor suppressor protein p53 is overexpressed in close to 50% of all human malignancies. The p53 protein is therefore an attractive target for immunotherapy. Cytotoxic T lymphocytes (CTLs) recognizing a murine wild-type p53 peptide, presented by the major histocompatibility complex class I molecule H-2Kb, were generated by immunizing p53 gene deficient (p53 -/-) C57BL/6 mice with syngeneic p53-overexpressing tumor cells. Adoptive transfer of these CTLs into tumor-bearing p53 +/+ nude mice caused complete and permanent tumor eradication. Importantly, this occurred in the absence of any demonstrable damage to normal tissue. When transferred into p53 +/+ immunocompetent C57BL/6 mice, the CTLs persisted for weeks in the absence of immunopathology and were capable of preventing tumor outgrowth. Wild-type p53-specific CTLs can apparently discriminate between p53-overexpressing tumor cells and normal tissue, indicating that widely expressed autologous molecules such as p53 can serve as a target for CTL-mediated immunotherapy of tumors.

Adoptive Transfer↗

PubMed1997

Autoantibodies to p53 in ovarian cancer patients and healthy women: a comparison between whole p53 protein and 18-mer peptides for screening purposes.

Autoantibodies against complete p53 protein and 18-mer peptides of p53 in ovarian cancer patients and healthy women were examined. Sera from 9% (4/46) of ovarian cancer patients but none (0/51) of healthy women recognized complete p53 protein. The antibodies were mainly of the IgG1 isotype. Two patients had also IgG2 antibodies. Sera from 28% (13/46) of cancer patients and 21% (11/52) of healthy women contained either IgM, or IgM plus IgG2 antibodies against 18-mer p53 peptides. Screening against complete p53 protein instead of peptides seems necessary for identifying patients with tumor-related antibodies. IgG2 antibodies against p53 suggest p53-specific CD4+ T helper 1 cell activity in some of the ovarian cancer patients.

Autoantibodies↗

PubMed1997

Activation or frustration of anti-tumor responses by T-cell-based immune modulation.

Many types of tumors (e.g. virus-induced tumors, melanomas, tumors over-expressing certain oncogenes) often express antigens that can induce T-cell-mediated tumor-specific immune responses. Nonetheless, many such tumors manage to circumvent the induction of an effective anti-tumor T-cell response, as is apparent from the many tumor-bearing patients. Therefore, optimally designed vaccination protocols may evoke a more powerful and competent T-cell-mediated anti-tumor response, allowing the host to effectively deal with at least some cancers. These vaccination approaches might include immunization with whole (tumor) cell-based vaccines, entire tumor antigens or selected T-cell epitopes derived from tumor antigens. This survey is an update of several anti-tumor vaccination approaches employed, and on novel possibilities to target the anti-tumor immune response to preselected tumor-derived T-cell epitopes.

Adenoviridae↗

PubMed1996

Peptide specificity of alloreactive CD4 positive T lymphocytes directed against a major histocompatibility complex class I disparity.

The mouse strains C57BL/6 (B6, H2b) and Kbm1 mutant bm1 have a defined difference of three amino acids at position 152, 155, and 156 in the MHC class I K molecule. This causes a change in the side and the bottom of the antigen presenting groove of the K molecule resulting in strong allogeneic responses in vitro and in vivo. Here we report on the peptide specificity of CD4+ T cells of B6 origin directed against the Kbm1 mutant and speculate on the peptide specificity of CD8+ bm1-specific T lymphocytes of B6 origin. Bm1-specific CD4+ T helper cells recognized a peptide derived from the Kbm1 molecule encompassing the three mutations, presented by MHC class II molecules on syngeneic cells. The ability of this peptide to bind to MHC class II resulted from amino acid mutations at positions 155 and 156. Furthermore, the recognition of the natural peptide derived from the Kbm1 molecule presented by MHC class II I-Ab molecules on cells of bml origin could be blocked by addition of an MHC class II I-Ab binding competitor peptide. Thus, due to the mutations in an MHC class I molecule, indirect presentation via MHC class II molecules and MHC class II-restricted recognition of a peptide derived from such a MHC class I molecule is demonstrable.

Animals↗

PubMed1996

Protective antitumor immunity induced by immunization with completely allogeneic tumor cells.

We have shown previously that immunization of B6 mice (H-2b) with tumor cells of B6 origin transformed by the human adenovirus type 5 early region 1 (Ad5E1) induces an H-2Db-restricted CTL response against an E1B-encoded CTL epitope. We now report that immunization of B6 mice with Ad5E1-transformed tumor cells of BALB/c origin (H-2d), apart from inducing a B6 anti-BALB/c allo-response, also induces a strong CTL response against the E1B-encoded H-2Db-presented CTL epitope. BALB/c Ad5E1-transformed tumor cells are not recognized by E1B-specific CTLs, indicating that nontumor cells have processed the E1B-encoded CTL antigen and have presented the E1B peptide to E1B-specific CTLs. These data also show that the B6 anti-BALB/c allo-response does not overwhelm the anti-E1B response induced by the allogeneic tumor cell vaccination. Moreover, B6 mice immunized with allogeneic BALB/c Ad5E1 cells are, in contrast to mice vaccinated with untransformed BALB/c cells, protected against a subsequent challenge with B6 Ad5E1-expressing tumor cells. These data show that immunization with completely allogeneic tumor cells can lead to protective syngeneic antitumor immunity, indicating that completely allogeneic tumor cell vaccines can be used for the induction of antitumor immunity.

Animals↗

PubMed1996

Peptide vaccination can lead to enhanced tumor growth through specific T-cell tolerance induction.

Vaccination with synthetic peptides representing cytotoxic T lymphocyte (CTL) epitopes can lead to a protective CTL-mediated immunity against tumors or viruses. We now report that vaccination with a CTL epitope derived from the human adenovirus type 5 E1A-region (Ad5E1A234-243), which can serve as a target for tumor-eradicating CTL, enhances rather than inhibits the growth of Ad5E1A-expressing tumors. This adverse effect of peptide vaccination was rapidly evoked, required low doses of peptide (10 micrograms), and was achieved by a mode of peptide delivery that induces protective T-cell-mediated immunity in other models. Ad5E1A-specific CTL activity could no longer be isolated from mice after injection of Ad5E1A-peptide, indicating that tolerization of Ad5E1A-specific CTL activity causes the enhanced tumor outgrowth. In contrast to peptide vaccination, immunization with adenovirus, expressing Ad5E1A, induced Ad5E1A-specific immunity and prevented the outgrowth of Ad5E1A-expressing tumors. These results show that immunization with synthetic peptides can lead to the elimination of anti-tumor CTL responses. These findings are important for the design of safe peptide-based vaccines against tumors, allogeneic organ transplants, and T-cell-mediated autoimmune diseases.

Adenovirus E1A Proteins↗

PubMed1996

Efficient tumor eradication by adoptively transferred cytotoxic T-cell clones in allogeneic hosts.

Tumor-specific cytotoxic T cells (CTLs) can play an important role against cancer as illustrated by the observation that adoptive transfer of tumor-specific CTLs can mediate potent anti-tumor effects. Although such CTLs can be detected at the tumor site, relatively little is known about the mechanisms by which they enter the tumor. In this study, the role of major histocompatibility complex (MHC) class 1 molecules on vascular endothelium in the tumor in entry of, and tumor eradication by, tumor-specific CTL was investigated. Two H-2Db-restricted CTL clones recognizing peptide VNIRNCCYI on human adenovirus type 5 early region 1-(Ad5E1)-induced tumors were used to test whether CTLs were able to cross the vascular endothelium lacking the restricting MHC molecule. One CTL clone recognizes peptide VNIRNCCYI in the context of both H-2Db and H-2Dbm14 molecules. The other CTL clone recognizes this peptide only in the context of H-2Db. Adoptive transfer of these CTLs leads to eradication of Ad5E 1-induced, H-2Db-expressing tumors in B6(H-2Db+) and Bm14(H-2Db-) nude mice. Our data show that presentation of tumor-derived peptides by MHC molecules on endothelial cells of blood vessels in a tumor do not play a major role in eradication of tumors by adoptively transferred CTL in combination with interleukin-2. Moreover, our data show that successful adoptive CTL immunotherapy is possible across allogeneic barriers, without inducing severe side effects, provided the tumor expresses the MHC class 1-peptide complex recognized by the CTLs.

Amino Acid Sequence↗

PubMed1996

Enhanced tumor outgrowth after peptide vaccination. Functional deletion of tumor-specific CTL induced by peptide vaccination can lead to the inability to reject tumors.

CTL can play an important role in the defense against tumors. Protective CTL-mediated immunity can be established in animal tumor models after vaccination with synthetic peptides representing CTL epitopes. We now report that immunization with synthetic peptides can also lead to CTL tolerance associated with the inability to reject tumors. B6 tumor cells transformed by the human adenovirus early region 1 (Ad5E1) present an Ad5E1A- and an Ad5E1B-encoded CTL epitope to the immune system. CTL clones directed against either of these epitopes are able to eradicate established Ad5E1-induced tumors, showing that these CTL epitopes are targets of CTL that can mediate tumor regression. Here, we show that protective immunity against Ad5E1-expressing tumor cells can be established by immunization with Ad5E1-transformed cells and with an adenovirus vector containing the Ad5E1 region. Protective immunity, in either case, is associated with specific CTL memory. To test whether vaccination with synthetic peptides leads to protection against Ad5E1-expressing tumor cells, we vaccinated mice s.c. with a low dose of the Ad5E1B peptide. This peptide was chosen because the CTL response against the Ad5E1B-encoded CTL epitope contributes most to the antitumor response in B6 mice after vaccination with Ad5E1-transformed cells. Ad5E1B peptide-vaccinated mice were not protected against the outgrowth of Ad5E1-expressing tumor cells, but instead were no longer able to reject a tumor inoculum that was rejected by nonvaccinated mice. Moreover, the protection induced by tumor cell vaccination against Ad5E1B-expressing tumors was gone when the Ad5E1B-encoded CTL epitope was injected a few days before tumor challenge. This is associated with peptide-induced tolerance of Ad5E1B-specific CTL activity. These findings are relevant for the design of therapeutic approaches against both malignancies and T cell-mediated autoimmune diseases.

Adenovirus E1A Proteins↗

PubMed1996

Immunogenicity of peptides bound to MHC class I molecules depends on the MHC-peptide complex stability.

The impact of the MHC class I peptide binding stability on the immunogenicity of particular peptide Ags in class I-restricted cytotoxic T lymphocyte responses is not clearly established. Therefore, we have determined the dissociation rate of each peptide from MHC class I at 37 degrees C and compared this to that of a consensus CTL epitope. Newly defined immunogenic peptides formed relatively stable MHC-peptide complexes as shown by their low dissociation rates, whereas nonimmunogenic peptides displayed high dissociation rates. In addition virtually all previously described HLA-A*0201-restricted T cell epitopes showed low dissociation rates. Furthermore, we show that the immunogenicity of HIV-1-derived peptides can be predicted more accurately by their dissociation rate than by the MHC class I binding affinity. Selection of peptides based on affinity and their dissociation rate leads to a more precise identification of candidate CTL epitopes than selection based on affinity alone. These results help to understand why some peptides are recognized by CTL and, along with detailed knowledge of protein processing rules, therefore have important implications for the selection of peptides in peptide-based vaccines.

Amino Acid Sequence↗

PubMed1996

Occasional memory cytotoxic T-cell responses of patients with human papillomavirus type 16-positive cervical lesions against a human leukocyte antigen-A *0201-restricted E7-encoded epitope.

Most cervical carcinoma (Cxca) cells constitutively express human papillomavirus type 16 (HPV16) E6 and E7 oncoproteins. These proteins are, therefore, attractive targets for T cell-based immunotherapy. Previously, we identified HVP16 E7-encoded CTL epitopes. In patients with cervical intraepithelial neoplasia or Cxca, little is known concerning T-cell activity against viruses in general and against HPV16 in particular. Here, we have screened the blood of 10 healthy donor controls and of 22 patients with HPV16+ cervical lesions for the presence of CTLs directed against HPV16 E7- and control influenza virus matrix-derived epitopes presented by HLA-A *0201. We detected influenza virus-specific CTLs in all donors and in the majority of patients, indicating that most patients have functioning T-cell responses despite their lesions or therapeutic interventions. Moreover, we show that patients with HPV16+ lesions occasionally have memory CTLs against a HPV16 E7-encoded epitope (sequence YMLD-LQPETT), providing evidence for natural CTL immunity against HPV16 in patients with cervical lesions. Combined, these findings raise possibilities for vaccination with HPV16 E7-encoded peptides to induce or augment CTL responses for treatment or prevention of Cxca.

Amino Acid Sequence↗