ABSTRACT
For long-term attack on tumor cells in patients with prostate cancer, induction of cytolytic T cells is desirable. Several lineage-specific target proteins are known and algorithms have identified candidate MHC class I-binding peptides, particularly for HLA-A*0201. We have designed tolerance-breaking DNA fusion vaccines incorporating a domain of tetanus toxin fused to candidate tumor-derived peptide sequences. Using three separate peptide sequences from prostate-specific membrane antigen (PSMA) (peptides PSMA(27) , PSMA(663) , and PSMA(711) ), this vaccine design induced high levels of CD8(+) T cells against each peptide in a HLA-A(*) 0201 preclinical model. In contrast, the full-length PSMA sequence containing all three epitopes was poorly immunogenic. Induced T cells were cytotoxic against peptide-loaded tumor cells, but only those against PSMA(27) or PSMA(663) peptides, and not PSMA(711) , were able to kill tumor cells expressing endogenous PSMA. Cytotoxicity was also evident in vivo. The preclinical model provides a powerful tool for generating CD8(+) T cells able to predict whether target cells can process and present peptides, essential for planning peptide vaccine-based clinical trials.
Subject(s)
Antigens, Surface/immunology , Cancer Vaccines/immunology , Glutamate Carboxypeptidase II/immunology , Peptides/immunology , T-Lymphocytes, Cytotoxic/immunology , Vaccines, DNA/immunology , Amino Acid Sequence , Animals , Antigens, Surface/chemistry , Antigens, Surface/genetics , CD8-Positive T-Lymphocytes/immunology , CD8-Positive T-Lymphocytes/metabolism , Cancer Vaccines/administration & dosage , Cancer Vaccines/genetics , Cell Line, Tumor , Cytotoxicity, Immunologic/immunology , Enzyme-Linked Immunosorbent Assay , Epitopes, T-Lymphocyte/immunology , Glutamate Carboxypeptidase II/chemistry , Glutamate Carboxypeptidase II/genetics , HLA-A Antigens/immunology , HLA-A2 Antigen , Humans , Interferon-gamma/immunology , Interferon-gamma/metabolism , Male , Mice , Mice, Inbred C57BL , Molecular Sequence Data , Peptides/genetics , Prostatic Neoplasms/immunology , Prostatic Neoplasms/pathology , Prostatic Neoplasms/therapy , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/immunology , T-Lymphocytes, Cytotoxic/metabolism , Tetanus Toxin/genetics , Tetanus Toxin/immunology , Vaccination/methods , Vaccines, DNA/administration & dosage , Vaccines, DNA/geneticsABSTRACT
The Wilms tumor antigen, WT1, is associated with several human cancers, including leukemia. We evaluated WT1 as an immunotherapeutic target using our proven DNA fusion vaccine design, p.DOM-peptide, encoding a minimal tumor-derived major histocompatibility complex (MHC) class I-binding epitope downstream of a foreign sequence of tetanus toxin. Three p.DOM-peptide vaccines, each encoding a different WT1-derived, HLA-A2-restricted epitope, induced cytotoxic T lymphocytes (CTLs) in humanized transgenic mice expressing chimeric HLA-A2, without affecting hematopoietic stem cells. Mouse CTLs killed human leukemia cells in vitro, indicating peptide processing/presentation. Low numbers of T cells specific for these epitopes have been described in cancer patients. Expanded human T cells specific for each epitope were lytic in vitro. Focusing on human WT1(37-45)-specific cells, the most avid of the murine responses, we demonstrated lysis of primary leukemias, underscoring their clinical relevance. Finally, we showed that these human CTL kill target cells transfected with the relevant p.DOM-peptide DNA vaccine, confirming that WT1-derived epitopes are presented to T cells similarly by tumors and following DNA vaccination. Together, these data link mouse and human studies to suggest that rationally designed DNA vaccines encoding WT1-derived epitopes, particularly WT1(37-45), have the potential to induce/expand functional tumor-specific cytotoxic responses in cancer patients.
