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V Apostolopoulos

Publications and source records attributed to V Apostolopoulos.

At least 55 records · Page 3Linked to original sources
PubMed1998

Oxidised mannan antigen conjugates preferentially stimulate T1 type immune responses.

It is desirable to be able to produce either T1 or T2 responses and we have found that, in mice, mannose--coupled antigens stimulated T2 type responses antibodies and CTLs, whereas if oxidized, mannose--coupled antigens stimulated T1 responses little antibody and a potent CTL response. In addition, the cytokine profiles support the T1rT2 differentiation with these immunizations, in that oxidized mannan antigen gives IFNg, IL-2 and IL-12 production, whereas in the absence of oxidization, IL-4 and not the other cytokines is produced. A number of antigens have been examined--particularly Mucin 1 and the delivery method using mannose may be applicable to the other antigens.

Animals↗
PubMed1998

Parameters for using mannan-MUC1 fusion protein to induce cellular immunity.

We have previously reported preclinical studies in mice of the human mucin 1 (MUC1) antigen covalently linked to the yeast cell-wall mannan polysaccharide (MFP), and shown strong cellular responses of the T1 type using mice. We now describe the optimum parameters for administration of MFP to obtain cellular immunity [as measured by the cytotoxic T cell precursor (CTLp) frequency]. In dose/response studies, in which 1 microg-150 microg was given by the i.p. route, it was clear that doses of 1-7 microg led to cellular and not humoral immunity; at doses above 7 microg humoral immunity prevailed with little cellular immunity increasing doses giving greater amounts of antibody. The most favoured routes of administration were intraperitoneal or intradermal immunisation, which were substantially better than i.m., i.v.; s.c. administration was the worst. Three immunisations were necessary for a maximum cellular response, further immunisation decreasing the CTLp frequency. Six different adjuvants were used with MFP [complete and incomplete Freund's adjuvant (CFA, IFA) Alum, Adjuprime, muramyl dipeptide (MDP) and glutaminyl-muramyl dipeptide (GMDP)]; Alum, GMDP, MDP and IFA moderately increased the CTLp frequency, IFA being the best. Even though preclinical studies of the immunogen in mice may not necessarily mirror the behaviour of the immunogen in humans, these studies demonstrate the factors to be taken into account for phase I/II clinical trials.

Animals↗
PubMed1998

Peptide mimics of a tumor antigen induce functional cytotoxic T cells.

The ability to mimic peptide/peptide and/or peptide/carbohydrate structures may be important in generating cross-reactive antibodies for autoimmune and other diseases. We show that the peptide sequence DAHWESWL can mimic the conformation of the unrelated MUC1 peptide SAPDTRPAP(G). Mice immunized with mannan-MUC1-peptides make cytotoxic T lymphocytes (CTLs) and are protected from MUC1+ tumors. We show that the same specific anti-MUC1 responses can be produced by immunizing with the DAHWESWL peptide; furthermore, specific tumor protection is obtained in a manner similar to that with MUC1 immunization. The DAHWESWL peptide immunization leads to CTLs that recognize H2Dd and H2Ld but not H2b or human leukocyte antigens-group A (HLA-A) *0201 presented MUC1 peptides. However, mutation of the DAHWESWL peptide to a more HLA-A*0201-compatible structure with appropriate anchors (DLHWASWV), leads to the production of CTLs in HLA-A*0201 mice.

Amino Acid Sequence↗
PubMed1998

MUC1 cross-reactive Gal alpha(1,3)Gal antibodies in humans switch immune responses from cellular to humoral.

Successful tumor immunotherapy with peptides requires the induction of cytotoxic T lymphocytes (CTLs) rather than antibodies. Mice immunized with mannan conjugated to MUC1, a peptide found in large amounts in breast cancer, develop CTL responses. In contrast, immunized patients produce high antibodies with poor CTL responses to MUC1. Here, we provide evidence that this "switch" in the immune response is due to the fact that antibodies against the Gal alpha(1,3)Gal epitope, which are normally present in humans but not mice, cross-react with MUC1 peptides. In particular, mice that lack the gene for the epitope (and that produce anti-Gal antibodies) (Gal-/- mice) are like humans in their response to MUC1 immunization in that they develop antibody rather than CTL responses. After we exposed macrophages from Gal-/- mice in vitro to MUC1, in the absence of Gal antibody, and adoptively transferred them into the mice, Gal-/- mice produced a predominantly CTL response. The findings are of relevance for immunotherapy studies in humans and emphasize the differences seen in preclinical testing in rodents before clinical trials.

Animals↗
PubMed1998

Cyclophosphamide enhances the CTL precursor frequency in mice immunized with MUC1-mannan fusion protein (M-FP).

We have previously described the induction of murine CD8+ major histocompatibility complex class I restricted cytotoxic T cells to the 20 amino acid repeat region of human Mucin 1 (MUC1) variable number of tandem repeats region--a mucin greatly increased in expression in breast cancer and proposed as a target for immunotherapy. Mannan-MUC1 immunization protocol induces a high cytotoxic T lymphocyte (CTL) frequency, and some protection of mice against a tumor challenge. The CTL frequency can be substantially increased using cyclophosphamide (Cy), from 1/84,900 without Cy to 1/8,100 with Cy. Furthermore, in the presence of Cy, established tumors are rapidly eradicated, which does not happen in its absence. Cy clearly gives a major increase in the frequency of CTL precursors (CTLp) to MUC1 and could be of therapeutic value in patients.

Animals↗
PubMed1997

Antibody and T cell responses of patients with adenocarcinoma immunized with mannan-MUC1 fusion protein.

Mucin 1 (MUC1) is a large complex glycoprotein that is highly expressed in breast cancer, and as such could be a target for immunotherapy. In mice, human MUC1 is highly immunogenic, particularly when conjugated to mannan, where a high frequency of CD8(+) MHC-restricted cytotoxic T lymphocytes is induced, accompanied by tumor protection. On this basis, a clinical trial was performed in which 25 patients with advanced metastatic carcinoma of breast, colon, stomach, or rectum received mannan-MUC1 in increasing doses. After 4 to 8 injections, large amounts of IgG1 anti-MUC1 antibodies were produced in 13 out of 25 patients (with antibody titers by ELISA of 1/320-1/20,480). Most of the antibodies reacted to the epitopes STAPPAHG and PAPGSTAP. In addition, T cell proliferation was found in 4 out of 15 patients, and CTL responses were seen in 2 out of 10 patients. Mannan-MUC1 can immunize patients, particularly for antibody formation, and to a lesser extent, cellular responses. It remains to be seen whether such responses have antitumor activity.

Adenocarcinoma↗
PubMed1997

Induction of HLA-A2-restricted CTLs to the mucin 1 human breast cancer antigen.

HLA-A*0201/Kb transgenic mice were immunized with oxidized mannan-mucin 1 (MUC1) as a fusion protein (containing five repeats of the 20-amino-acid MUC1 VNTR (variable number of tandem repeats) that generated highly active CD8+ CTLs to MUC1 peptides. In a direct CTL assay, the MUC1 peptides could be presented specifically by both the transgenic murine HLA-A*0201/Kb and human HLA-A*0201 molecules. The 9-mer MUC1 peptide sequences (APDTRPA and STAPPAHGV) were presented by HLA-A*0201, although they did not contain L at P2 and L/V at P9, the preferred motifs; as a consequence, the binding was of relatively low affinity when compared with a high affinity-binding HIV peptide (ILKEPVHGV). In addition, when mice were immunized separately with the HLA-A*0201-binding peptides (STAPPAHGV or APDTRPAP-containing peptides-keyhole limpet hemocyanin-mannan), direct lysis of MCF-7 (HLA-A*0201+, MUC1+) also occurred. The findings are of interest for tumor immunotherapy, particularly as the CTLs generated to low affinity-binding peptides were highly active and could specifically lyse an HLA-A*0201+ human breast cancer cell line without further in vitro stimulation. The findings demonstrate that the range of peptides that can generate CTLs is broader than formerly considered.

Amino Acid Sequence↗
PubMed1997

MUC1 peptide epitopes associated with five different H-2 class I molecules.

We have previously described the induction of murine CD8+ major histocompatibility complex (MHC) class I-restricted cytotoxic T cells (CTL) recognizing the 20-amino acid repeat region of the human mucin 1 (MUC1) variable number of tandem repeats region (VNTR), a mucin greatly increased in expression in breast cancer and proposed as a target for immunotherapy. In that study, CTL could detect MUC1 peptides associated with the MHC of all nine strains examined, and we now report the different epitopes presented by five different MHC class I molecules. The epitopes were defined in CTL assays using peptide-pulsed phytohemagglutinin blasts or MHC class I-transfected L cells as targets; in addition, peptide binding assays and T cell proliferation studies were performed. Within the 20-amino acid VNTR, nine potential epitopes could be defined. The epitopes for the four MHC class I molecules [Kb (three epitopes), Dd, Ld and Kk] were closely related, all containing the amino acids PDTRPAP. For Db, three epitopes were identified, all containing APGSTAP. Most of the epitopes did not contain a consensus motif for the particular MHC class I allele, and bound with low 'affinity', compared with known high-affinity peptides. CD8+ T cell proliferation also occurred to the same MHC class I-presented epitopes. Finally, when conventional anchor residues were introduced into the peptides, peptide binding increased, whereas CTL recognition was either retained (Kb) or lost (Db) depending on the epitope.

Amino Acid Sequence↗
PubMed1997

Induction of T1 (cytotoxic lymphocyte) and/or T2 (antibody) responses to a mucin-1 tumour antigen.

Effective vaccination-based control of intracellular pathogens or parasites and various tumours is dependent upon induction of cytotoxic lymphocytes and other mechanisms of cellular immunity. Such responses are usually described as being antagonistic to an antibody-based immune response. This paper elaborates on previous studies that have demonstrated that conjugation of a fusion protein (FP, incorporating copies of the variable number of tandem repeat sequence of human mucin-1 (MUC1)) to oxidized mannan results in a significant shift from a type-2 response towards a type-1 response. This response induces complete protection upon challenge of immunized mice with MUC1 expressing tumour cells. This report details experiments in which the balance between type-1 and type-2 anti-MUC1 responses is manipulated by altering the dose of mannan-FP (M-FP) delivered. It is also shown that type-1 and type-2 responses may be induced simultaneously by administration of both forms of the antigen (FP/M-FP). Further, when a type-2 response is induced after FP immunization, a type-1 response can also be established by subsequent immunization with M-FP without adversely affecting the initial response. The converse also applies when M-FP is used for the initial immunizations, followed by FP administration. Delivery of interleukin-1 beta as a cytokine adjuvant with M-FP immunizations also enhanced antibody responses to levels fourfold that induced by M-FP alone without adversely affecting the cytotoxic activity induced by M-FP immunization. Contrary to the type-1/type-2 paradigm, cellular and antibody responses to MUC1 were not antagonistic. These results have important implications for the development of vaccination strategies against pathogens for which both the cellular and humoral compartments of the immune response contribute to protection.

Adjuvants, Immunologic↗
PubMed1996

Cell-mediated immune responses to MUC1 fusion protein coupled to mannan.

The immunotherapy of cancer requires the definition of a suitable target for and the induction of a CD8+ cytotoxic lymphocyte reaction. In breast cancer, particularly mucins (MUC1) of the variable number of tandem repeat sequence may be a suitable target, but there has been a problem in inducing a cytotoxic response. MUC1 peptides, conjugated to carriers (keyhole-limpet hemocyanin or diphtheria toxoid) induce a humoral response and give poor tumor protection in mice and there is little cellular immunity. However, when MUC1 fusion protein is conjugated to mannan under oxidizing conditions, a cellular immune response is induced, with significant tumor protection, cytotoxic T lymphocytes and little antibody. The procedure may also be useful for other antigens.

Amino Acid Sequence↗
PubMed1996

Breast cancer immunotherapy: current status and future prospects.

The development of an immunotherapeutic approach to cancer is the concern for many immunologists, but despite the impressive progress over the past decade, such as the identification of tumour antigens and antigenic peptides as potential targets, there are still many obstacles in eliciting an effective immune response to eradicate cancer. Mucins have attracted interest as potential targets for immunotherapy in the development of vaccines for cancers expressing Mucin1 (MUC1; e.g. breast, pancreas, ovary etc.). All of the identified targets for cancer, including MUC1, are normal proteins; however MUC1 expressed on tumours can be considered as tumour specific due to their overexpression, altered glycosylation and its ubiquitous distribution on the cell surface rather than at the secretory pole in adenocarcinomas. These observations have led to the development of several different approaches to immunize against breast cancer using synthetic carbohydrates or peptides conjugated to carriers and given together with a variety of adjuvants to elicit the appropriate immune response. Mannan, a polymannose carbohydrate isolated from the cell wall of yeast, is an appropriate and effective protein carrier for eliciting a cellular (T1-type) or humoral (T2-type) immune response depending on the mode of conjugation (oxidized or reduced). In addition, mannan holds promise and opens many avenues as a carrier for vaccine development for other antigens. Several clinical trials are in progress to evaluate the immunogenicity of MUC1 and its suitability as to use for immunotherapy/vaccine for breast cancer.

Animals↗
PubMed1995

CTL in mice immunized with human mucin 1 are MHC-restricted.

CTLs that recognize tumor Ags have been described in mice and humans, particularly for melanoma. These CTLs are CD8+, which is MHC-restricted. In contrast, in human carcinomas of the breast, pancreas, or ovary, and in multiple myeloma, CD8+ CTLs have been described that lyse targets expressing human MUC1 in a non-MHC-restricted manner. On the basis of these observations, we immunized mice with conjugates of mannan-human fusion protein, human mucin 1 (MUC1), which produced CD8+ CTLs. In contrast to the human anti-MUC1 CTLs found in cancer patients, the murine anti-MUC1 CTLs were clearly MHC-restricted, e.g., in inbred mice of the H-2-b, d, k, s, or z haplotypes; the H-2 restriction was also confirmed in H-2 congenic strains. Tests of H-2 recombinant strains demonstrated that MUC1 peptides were able to associate with D or K class I molecules of the b, d, or k haplotypes. Mice lacking MHC-class I molecules made weak CTL responses that were H-2Db-restricted, and in the class I H-2Kbm1 mutant strain, CTL restriction was also shown. Finally, cold target inhibition studies demonstrated that Kb and Db are recognized similarly, but Kk is less well recognized. Thus, anti-MUC1 CTLs induced by immunization of mice are different from those obtained from patients. The immunization of cancer patients with MUC1 peptides is now undergoing clinical trials and it will be of interest to observe whether the CTLs induced are HLA-restricted, not restricted, or whether both types of CTLs are produced.

Animals↗
PubMed1995

Oxidative/reductive conjugation of mannan to antigen selects for T1 or T2 immune responses.

The induction of CD8+ cytotoxic T lymphocytes (CTLs) is desirable for immunization against many diseases, and recombinant-synthetic peptide antigens are now favored agents to use. However, a major problem is how to induce CTLs, which requires a T1-type response to such synthetic antigens. We report that T1-type (generating high CTL, low antibody) or T2-type (the reciprocal) responses can be induced by conjugation of the antigen to the carbohydrate polymer mannan: T1 responses are selected by using oxidizing conditions; T2 responses are selected by using reducing conditions for the conjugation. Using human MUC1 as a model antigen in mice, immunization with oxidized mannan-MUC1 fusion protein (ox-M-FP) led to complete tumor protection (challenge up to 5 x 10(7) MUC1+ tumor cells), CTLs, and a high CTL precursor (CTLp) frequency (1/6900), whereas immunization with reduced mannan-MUC1 FP (red-M-FP) led to poor protection after challenge with only 10(6) MUC1+ tumor cells, no CTLs, and a low CTLp frequency (1/87,800). Ox-M-FP selects for a T1 response (mediated here by CD8+ cells) with high interferon gamma (IFN-gamma) secretion, no interleukin 4 (IL-4), and a predominant IgG2a antibody response; red-M-FP selects for a T2-type response with IL-4 production and a high predominant IgG1 antibody response but no IFN-gamma.

3T3 Cells↗
PubMed1995

The immunogenicity of MUC1 peptides and fusion protein.

Mucin 1 (MUC1) is highly expressed in breast cancer, has an ubiquitous distribution and, due to altered glycosylation, peptides within the VNTR are exposed. These peptides are the target for anti-MUC1 antibodies, which give a differential reaction on cancer compared with normal tissue. The amino acids, APDTR or adjacent amino acids, are highly immunogenic in mice for antibody production (after immunisation with either breast cancer cells, human milk fat globule (HMFG) or the VNTR peptide). In addition, human studies show that this region of the MUC1 VNTR functions as target epitopes for cytotoxic T cells. We have performed preclinical and clinical studies to examine the immune responses to MUC1 in mice and humans: (a) MUC1+ 3T3 or P815+ 3T3 cells in syngeneic mice are rejected, with the generation of both cytotoxic T lymphocyte (CTL) and DTH responses and a weak antibody response and a weak antibody responses; this type of immunity gives rise to total resistance to re-challenge with high doses of these tumors; (b) immunisation with peptides (VNTR x 2), a fusion protein (VNTR x 5), or HMFG leads to no CTLs, DTH, good antibody production and weak tumour protection (to 10(6) cells, but not 5 x 10(6) cells) (possibly a TH2 type response); (c) immunisation with mannan-fusion protein (MFP) gives rise to good protection (resistance to 50 x 10(6) cells), CTL and DTH responses and weak antibody responses (possibly a TH1 type response, similar in magnitude to that obtained after tumor rejection); (d) established tumors can be rapidly rejected by delayed treatment of MFP; (e) the CTL responses are MHC restricted (in contrast to the human studies); (f) APDTR appears not to be the T cell reactive epitope in mice. On the basis of these findings, two clinical trials are in progress: (a) VNTR x 2 (diphtheria toxoid) which gives rise to some T cell proliferation, DTH and antibody responses in some patients and (b) an MFP trial. The ability to alter the immune response towards cellular immunity with mannan or to humoral immunity with peptides, allows the immune response to be selectively manipulated.

Animals↗
PubMed1994

Murine immune response to cells transfected with human MUC1: immunization with cellular and synthetic antigens.

Humans with breast cancer have T-cells in their lymph nodes which recognize a peptide sequence within the variable number of tandem repeats of the mammary mucin, MUC1, which is overexpressed in breast cancer. To find means of making this recognition event into a potent immune response to breast cancer, we used a murine tumor model and have examined the parameters of the immune response to human mucin (MUC1) expressed in murine BALB/c 3T3 cells. We then sought to boost this response with MUC1-containing synthetic peptides, fusion proteins, and natural mucin (HMFG). MUC1+3T3 cells were found to be rejected by BALB/c mice by day 15 due to a cellular [CD3+, Ly2+ (CD8+)] response. The cellular rejection response was accompanied by the generation of CD8+ cytotoxic T-cells, CD4+ delayed-type hypersensitivity, and little anti-MUC1 antibody. This immune response is presumably of the TH1 type (which occurs in CD8 as well as CD4 cells) of CD8+ cytotoxic cells. By contrast, mice immunized with the MUC1 synthetic peptide, a fusion protein, or HMFG have good antibody responses, a delayed-type hypersensitivity reaction, but no cytotoxic T-cells and less tumor protection, possibly a TH2 type response. We conclude that CD8+ cytotoxic anti-mucin cells can produce significant antitumor responses in vivo to a human "tumor" antigen expressed in murine cells; immunization with soluble synthetic or native materials leads to the "humoral" (TH2) type of immunity, and efforts need to be made to convert this to a TH1-type response.

3T3 Cells↗