Biomedical subjects

W M Kast

Publications and source records attributed to W M Kast.

At least 19 recordsLinked to original sources

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↗

PubMed1996

Peptide-based cancer vaccines.

The application of molecularly defined vaccines composed of a limited number of tumor-specific T cell epitopes has resulted in protective antitumor T cell immunity in several mouse tumor models. The first encouraging results with such vaccines have been obtained in human beings. The development of the next generation of rationally designed vaccines that are both effective and safe for application in a clinical setting requires comparison of different modes of delivery of tumor-associated T cell epitopes in multiple epitope constructs.

Animals↗

PubMed1996

The current status of therapeutic HPV vaccine.

Cervical carcinoma is the second most common cause of cancer-related deaths in women worldwide. Recurrences occur in 15% of the patients after optimal treatment of low-risk early-stage disease. Treatment results of recurrent disease are relatively poor and for this reason new therapeutic strategies are warranted. Viral infection with human papillomavirus seems to have an essential part in the aetiology of cervical carcinoma. Evidence for the assumption that cervical carcinoma, among other malignancies such as melanomas, renal malignancies and Kaposi sarcoma, are immunogenic is provided by the fact that these malignancies grow more rapidly in the presence of systemic immunosuppression. Spontaneous regression for these tumour types is also described and immunohistochemical studies show extensive infiltrates in the tumour, consisting of immunocompetent cells. It is thus postulated that cellular immunity, and mainly the T-cell system plays an important role in the antitumour defence in cervical carcinoma. This review describes the rationale for the use of immunotherapy as treatment for cervical carcinoma as well as the results of recent developments in tumour immunology and its implications for the clinical use of immunotherapeutical approaches.

Animals↗

PubMed1995

Antigen capture and major histocompatibility class II compartments of freshly isolated and cultured human blood dendritic cells.

Dendritic cells (DC) represent potent antigen-presenting cells for the induction of T cell-dependent immune responses. Previous work on antigen uptake and presentation by human DC is based largely on studies of blood DC that have been cultured for various periods of time before analysis. These cultured cells may therefore have undergone a maturation process from precursors that have different capacities for antigen capture and presentation. We have now used immunoelectron microscopy and antigen presentation assays to compare freshly isolated DC (f-DC) and cultured DC (c-DC). f-DC display a round appearance, whereas c-DC display characteristic long processes. c-DC express much more cell surface major histocompatibility complex (MHC) class II than f-DC. The uptake of colloidal gold-labeled bovine serum albumin (BSA), however, is greater in f-DC, as is the presentation of 65-kD heat shock protein to T cell clones. The most striking discovery is that the majority of MHC class II molecules in both f-DC and c-DC occur in intracellular vacuoles with a complex shape (multivesicular and multilaminar). These MHC class II enriched compartments (MIIC) represent the site to which BSA is transported within 30 min. Although MIIC appear as more dense structures with less MHC class II molecules in f-DC than c-DC, the marker characteristics are very similar. The MIIC in both types of DC are acidic, contain invariant chain, and express the recently described HLA-DM molecule that can contribute to antigen presentation. CD19+ peripheral blood B cells have fewer MIIC and surface MHC class II expression than DCs, while monocytes had low levels of MIIC and surface MHC class II. These results demonstrate in dendritic cells the elaborate development of MIIC expressing several of the components that are required for efficient antigen presentation.

Animals↗

PubMed1995

Eradication of large human B cell tumors in nude mice with unconjugated CD20 monoclonal antibodies and interleukin 2.

Since antibody-dependent cellular cytotoxicity is considered an important mechanism by which mAbs may exert their antitumor effects, it seems likely that these antitumor effects can be enhanced by the activation of the appropriate effector cell populations. We have used nude mice xenografted with human Daudi tumor cells as a model to compare the antilymphoma effects of unconjugated CD19 (CLB-CD19) and CD20 (BCA-B20) mAbs (IgG2a subclass) alone or in combination with recombinant human interleukin 2 (rhIL-2) or recombinant mouse granulocyte-macrophage-colony-stimulating factor (rmGM-CSF). Treatment of established tumors with BCA-B20 or rhIL-2 or rmGM-CSF as a single agent, all resulted in highly significant decreases of tumor growth rates, but did not increase the number of complete regressions. The combination of CLB-CD19 or BCA-B20 mAbs with rhIL-2 or rmGM-CSF resulted in larger decreases of growth rates than either of the agents alone. Complete eradication of large Daudi tumors could be achieved when treatment with BCA-B20 mAbs was combined with rhIL-2, but not with the combination of CLB-CD19 mAbs and rhIL-2 nor with the combination of BCA-B20 mAbs and rmGM-CSF. Cured animals kept for 2-3 months after complete regression of the tumors were still tumor free. Regression of tumors was correlated with the infiltration of lymphocytes as well as macrophages into the tumor. This is the first report to show that unconjugated CD20 mAbs are to be preferred over unconjugated CD19 mAbs, and interleukin 2 over GM-CSF in the combinational treatment of large B cell tumors.

Animals↗

PubMed1995

Human CTL epitopes encoded by human papillomavirus type 16 E6 and E7 identified through in vivo and in vitro immunogenicity studies of HLA-A*0201-binding peptides.

Human papillomavirus type 16 (HPV16) is strongly associated with cervical carcinogenesis. The HPV16 E6 and E7 oncoproteins are constitutively expressed in the majority of cervical tumor cells and are, therefore, attractive targets for CTL-mediated immunotherapy. In mice, the outgrowth of a lethal dose of HPV16-induced tumor cells has been prevented by vaccination with a CTL epitope encoded by HPV16 E7, indicating the feasibility of peptide immunization to obtain antitumor CTL responses. In the present study, the immunogenicity of 9 HLA-A*0201-binding peptides encoded by HPV16 E6 and E7 was analyzed in vivo in HLA-A*0201Kb transgenic mice and in vitro in CTL cultures induced from PBMC of HLA-A*0201+ healthy donors. Four peptides with a good binding affinity were immunogenic in HLA-A*0201Kb transgenic mice, and three of them were also highly immunogenic in CTL induction experiments with PBMC of HLA-A*0201+ healthy donors. Human CTL clones specific for these three peptides were capable of lysing the HPV16 E7-containing HLA-A*0201+ cervical carcinoma cell line CaSki. These E7-derived peptides (11-20, YMLDLQPETT; 82-90, LLMGTLGIV; 86-93, TLGIVCPI), therefore, are likely to represent naturally processed human CTL epitopes of HPV16. Additionally, these three HPV16-encoded peptides have the highest affinity of binding to the HLA-A*0201 molecule. In this study, peptides with a lower binding affinity were less immunogenic. Therefore, our data illustrate that the HLA-binding affinity of a peptide has a major impact on its immunogenicity. In conclusion, we have identified immunogenic peptides encoded by HPV16 E6 and E7 that could be used in vaccines for the prevention and treatment of cervical carcinoma.

Amino Acid Sequence↗

PubMed1995

MHC class II compartments and the kinetics of antigen presentation in activated mouse spleen dendritic cells.

MHC class II (MHC-II) molecules bind fragments of exogenous Ags in an intracellular endocytotic compartment. In view of divergent data on the MHC-II distribution in different cell lines, it was of interest to localize MHC-II molecules in a natural and the most potent APC type, the dendritic cell (DC). By using immunogold labeling of ultrathin cryosections of cultured mouse spleen DC, we found that MHC-II molecules were present abundantly at the plasma membrane and in intracellular compartments containing internal membrane vesicles and/or membrane sheets. The majority of these compartments was situated late in the endocytotic route, as demonstrated by the late appearance (after a lag of 30 min) of internalized exogenous tracer. These compartments contained the lysosomal enzymes cathepsin D and beta-hexosaminidase, but lacked the late endosomal marker cation-dependent mannose-6-phosphate receptor. We conclude that most of the intracellular MHC-II molecules in cultured spleen DC reside in a compartment with (pre)lysosomal characteristics, resembling the so-called MHC-II-enriched compartments (MIIC), originally described in B cells. We also investigated whether the presence of MHC-II molecules in endocytotic compartments was related to the kinetics of Ag processing and presentation by these cells. Pulse-chase endocytosis experiments with hen egg lysozyme (HEL) as a model Ag showed that activated spleen DC were able to efficiently process and present this Ag to an HEL-specific T hybridoma cell line. However, presentation started only after a lag of 2 h and was maximal after 6 h. The difference in time between the arrival of Ag in proteolytic endocytotic compartments, in particular MIIC, and effective Ag presentation is discussed in the context of DC maturation.

Animals↗