Background: Human telomerase reverse transcriptase (hTRT) is expressed in most human tumor cells (>90% of PC) but absent from most normal adult cells, identifying it as a potential immunotherapeutic target (PNAS 97:4796, 2000). We developed a new approach to induce T cell responses in vivo based on the injection of primary B lymphocytes genetically programmed to serve as antigen presenting cells with the dual function of antigen synthesis and presentation. This is done ex vivo by exploiting the phenomenon of spontaneous B cell transgenesis (Gene Therapy 11:42, 2003), using a plasmid with a modified immunoglobulin heavy chain gene incorporating 3 inserts: two HLA-A2-restricted hTRT peptides: p540 (PNAS 97:4796, 2000) in CDR 3, p572 (PNAS 99:12275, 2002) in CDR1; and a 12mer malarial peptide acting as a Th cell determinant in CDR2. Methods: HLA-A2(+) subjects had androgen-independent PC with (14) or without (1) overt metastases, PS<3, life expectancy >6 months, no current steroid treatment. Median pretreatment PSA=124. Prior treatment, except immunotherapy, was allowed. Mononuclear cells were separated from peripheral blood and incubated overnight with plasmid DNA. Nine subjects (3 in each of 3 cohorts) were reinfused once with 104, 105, or 106 autologous transgenic B cells. Six additional subjects were reinfused twice at a 4 week interval with 5x105 cells (3 fresh and 3 frozen boosters). Results: 12/15 subjects remain alive with followup of 17-69 weeks. No infusion-related events or dose-limiting toxicities were seen. No clinical or PSA responses were seen. Tetramer staining of hTRT-specific CD8 T lymphocytes was seen in all patients. Three patients developed CD8(+) T cells capable of killing hTRT expressing tumor cells in-vitro. Conclusions: single and double-dose TLI is feasible, safe and capable of inducing a T cell response against hTRT. Attempts to translate this immune response into clinical benefit by inhibiting T regulatory cells and targeting earlier stage patients are planned.
Phase I study of transgenic B lymphocyte immunization (TLI) against telomerase in androgen-indepedent prostate cancer (PC)
MONSURRO', Vladia;
2005-01-01
Abstract
Background: Human telomerase reverse transcriptase (hTRT) is expressed in most human tumor cells (>90% of PC) but absent from most normal adult cells, identifying it as a potential immunotherapeutic target (PNAS 97:4796, 2000). We developed a new approach to induce T cell responses in vivo based on the injection of primary B lymphocytes genetically programmed to serve as antigen presenting cells with the dual function of antigen synthesis and presentation. This is done ex vivo by exploiting the phenomenon of spontaneous B cell transgenesis (Gene Therapy 11:42, 2003), using a plasmid with a modified immunoglobulin heavy chain gene incorporating 3 inserts: two HLA-A2-restricted hTRT peptides: p540 (PNAS 97:4796, 2000) in CDR 3, p572 (PNAS 99:12275, 2002) in CDR1; and a 12mer malarial peptide acting as a Th cell determinant in CDR2. Methods: HLA-A2(+) subjects had androgen-independent PC with (14) or without (1) overt metastases, PS<3, life expectancy >6 months, no current steroid treatment. Median pretreatment PSA=124. Prior treatment, except immunotherapy, was allowed. Mononuclear cells were separated from peripheral blood and incubated overnight with plasmid DNA. Nine subjects (3 in each of 3 cohorts) were reinfused once with 104, 105, or 106 autologous transgenic B cells. Six additional subjects were reinfused twice at a 4 week interval with 5x105 cells (3 fresh and 3 frozen boosters). Results: 12/15 subjects remain alive with followup of 17-69 weeks. No infusion-related events or dose-limiting toxicities were seen. No clinical or PSA responses were seen. Tetramer staining of hTRT-specific CD8 T lymphocytes was seen in all patients. Three patients developed CD8(+) T cells capable of killing hTRT expressing tumor cells in-vitro. Conclusions: single and double-dose TLI is feasible, safe and capable of inducing a T cell response against hTRT. Attempts to translate this immune response into clinical benefit by inhibiting T regulatory cells and targeting earlier stage patients are planned.
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