A peptide recognized by human cytolytic T lymphocytes on HLA-A2 melanomas is encoded by an intron sequence of the N-acetylglucosaminyltransferase V gene

Human monocyte-derived macrophages and dendritic cells are comparably effective in vitro in presenting HLA class I-restricted exogenous peptides

Recent experimental data have shown that mice could be immunized efficiently, in particular against cancer, by the injection of antigen-loaded dendritic cells (DC) or macrophages (MPH). In the present work, these two antigen-presenting cells (APC) were prepared in humans from circulating mononuclear cells (MNC). MPH were obtained from MNC that were cultured in hydrophobic plastic bags and purified by elutriation. DC were from the culture of adherent elutriation-purified monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). The two APC were prepared in parallel from the same donors and their phenotype and antigen-presenting capacity were compared. DC differed from MPH by a higher expression of HLA-DR and CD23 and a lower expression of CD14, CD64 and of adhesion molecules. DC and MPH were comparably effective in (a) enhancing the mitotic response of autologous lymphocytes to immobilized anti-CD3 (accessory function); (b) presenting melanoma peptides to specific cytotoxic T lymphocyte (CTL) clones; and (c) stimulating the generation of CTL directed against a myxovirus influenza peptide. However, DC were more effective than MPH in inducing the mitotic response of allogeneic peripheral blood leucocytes (PBL), possibly because of their higher expression of HLA class II molecules. In conclusion, DC and MPH prepared from blood MNC did not differ substantially in their ability to activate HLA class I-restricted T-cell responses by exogenous peptide presentation.

Multi-epitope DNA vaccines

The evolution of vaccine strategies has seen a move from whole organisms to recombinant proteins, and further towards the ultimate in minimalist vaccinology, the epitope. The epitope-based approach is clearly compelling as only a relatively tiny, but immunologically relevant, sequence is often capable of inducing protective immunity against a large and complex pathogen. The post-reductionist era in epitope-based vaccinology has seen a quest to re-construct complexity and design vaccines containing many epitopes. The hope is that such multi-epitope vaccines might induce immunity against multiple antigenic targets, multiple strain variants, and/or even multiple pathogens. The ability of DNA vaccination to co-deliver a series of antibody and/or CD4 T cell epitopes remains largely unexplored. Successful viral vector and DNA-based experimental vaccines coding for multiple contiguous CD8 CTL epitopes have, however, recently been described. This simple CTL poly-epitope (or polytope) strategy may find application in the design of vaccines against several diseases including EBV, HIV and cancer.

Identification of genes coding for tumor antigens recognized by cytolytic T lymphocytes

Strategies have been developed to characterize tumor antigens recognized by cytolytic T lymphocytes (CTL). We use a genetic approach based on the transfection of HLA genes and cDNA libraries in COS cells to isolate the gene producing the antigenic peptide. The tumor-specific expression of this gene can be evaluated by cDNA synthesis and quantitative PCR amplification. Transfection of fragments of the isolated gene allows the identification of the region encoding the antigenic peptide. Peptides are synthesized and tested for their ability to sensitize target cells to lysis by the CTL.

Histocompatibility leukocyte antigen-A2402-restricted cytotoxic T lymphocytes recognizing adenocarcinoma in tumor-infiltrating lymphocytes of patients with colon cancer

To cast light on T cell-mediated specific immunity at the tumor site of colon cancer, we investigated whether interleukin-2 (IL-2)-activated tumor-infiltrating lymphocytes (TIL) from colon cancer show histocompatibility leukocyte antigen (HLA)-class I-restricted cytotoxicity against adenocarcinoma. IL 2-activated TIL from all four HLA-A24 patients examined lysed HLA-A2402+ adenocarcinomas, but not HLA-A2402- tumors. Those of two of the four cases also lysed HLA-A2402+ squamous cell carcinomas. CD8+ cytotoxic T lymphocyte (CTL) clones recognizing HLA-A2402+ adenocarcinomas were established from one CTL line. This CTL line produced IFN-gamma upon recognition of an HLA-A2402- adenocarcinoma transfected with HLA-A2402 cDNA. These results suggest the presence of HLA-A2402-restricted CTL recognizing adenocarcinoma at the tumor site of colon cancer. Furthermore, HLA-A31-restricted CTL activity was found in IL-2-activated TIL from one of two HLA-A31+ patients, suggesting the existence of HLA-class I-restricted CTL involving an allele other than A24.

Transcription of the gene encoding melanoma-associated antigen gp100 in tissues and cell lines other than those of the melanocytic lineage

The expression of the gp100 antigen is generally thought to be confined to cells of the melanocytic lineage, which makes the protein a suitable melanoma-specific marker. Strikingly, after screening a panel of normal tissues, tumour samples and cell lines of non-melanocytic origin, we found transcripts encoding gp100 in virtually every tissue and cell line tested. In contrast, tyrosinase and MART-1/MelanA transcripts were detected only in cells of the melanocytic lineage. However, no gp100 protein could be detected by either Western blotting or cytotoxicity assays. Therefore, at the protein level, gp100 remains exclusive for cells of melanocytic origin despite its transcription in many cell types. The major implication of this finding is that screening of patient material for gp100 expression should preferrably be performed by antibody staining. Reverse transcriptase polymerase chain reaction (RT-PCR) can be employed, provided that it is performed in a tightly controlled, semiquantitative setting.

Costimulation, tolerance and ignorance of cytolytic T lymphocytes in immune responses to tumor antigens

Despite the fact that many tumors express MHC class I molecules presenting "foreign" peptide antigens, a vigorous tumor-destructing immune response is seldom detected. A possible explanation is that tumors cannot provide adequate costimulatory signals as provided by professional antigen presenting cells. CD28, upon interacting with B7, triggers costimulatory signals critical for the T-cell response. Transfection of tumor cells with B7 augments the immunogenicity of the tumor so that an anti-tumor immune response can be amplified. When B7-CD28 costimulation is provided CTL specific for otherwise silent epitopes can be activated. Therefore, unresponsiveness of T cells to many tumor antigens should be considered as ignorance rather than tolerance. Immunological ignorance may thus contribute to the failure of the immune system to respond against the tumor antigens.

Tumor antigens recognized by T lymphocytes

In the last five years, knowledge of human tumor antigens recognized by autologous cytolytic T lymphocytes (CTL) has increased considerably. So far, genetic and biochemical approaches have led to the molecular identification of three classes of antigens. Most of these antigens consist of peptides that are presented to T cells by HLA molecules. The first class comprises antigens encoded by genes such as MAGE, BAGE, and GAGE, which are expressed in various tumors of different histological origins, but not in normal tissues other than testis. The second class represents differentiation antigens encoded by genes that are only expressed in melanoma and normal melanocytes like tyrosinase, Melan-A/MART-1, gp100 and gp75. The third class includes antigens produced by unique point mutations in genes that are ubiquitously expressed. In most cases, the antigenic peptide is encoded by the mutated region of the gene. A number of these antigens provide promising targets for new protocols of specific cancer immunotherapy.