Abstract
Background. The short synthetic peptide 302 has been shown to induce rapid membrane disruption of lymphoma cells in vitro and necrosis of local tumors in the A20 lymphoma model in Balb/c mice. In order to stimulate the immune system to generate an anti-tumor response we designed a model where intra-tumor injections of peptide 302 was combined with sc injections of the Toll-like receptor 9 binding synthetic oligonucleotide CpG 1826.
Methods. Balb/c mice were inoculated with A20 lymphoma cells sub-cutaneously (s.c.) on the abdomen. When the tumors reached a size of 5–7 mm, 302 peptide was administered directly into the tumors on days 1 and 6. CpG 1826 was injected s.c. on days 1–4 and 6–8. Tumor growth was measured repeatedly during follow-up. A20-specific T-cell responses were detected by culturing peripheral blood lymphocytes from treated animals for 24 hours with A20 lymphoma cells and analyzing for intracellular IFN-γ production by flow cytometry. To dissect the role of T-cell subtypes, the treatment was performed in animals depleted for CD4 or CD8 positive T-cells. In order to show A20 specific immunological memory, cured animals were re-challenged with the A20 lymphoma or the carcinoma cell line CT26.
Results. Combined treatment with peptide 302 and CpG 1826 cured 8 out of 10 mice, compared to only 2 out of 10 mice who received peptide 302 alone or CpG 1826 alone. Cured mice were followed for 9 weeks without relapsing. Similar results with the combination of peptide 302 and CpG were observed in a separate experiment. The highest cure rate was achieved when injecting CpG 1826 s.c. in the tumors draining lymph node area as compared to administration of CPG 1826 in a non-draining lymph node region or intra-peritoneal. Animals treated with peptide 302 + CpG 1826 or CpG 1826 alone developed CD8-specific IFN-γ responses against A20 cells. In one separate experiment CD8 knock-out mice did not respond to the treatment, unlike animals depleted for CD4+ cells and normal mice. Only 1 out of 10 cured animals re-challenged with the A20 lymphoma developed a new tumor, a result that was reproduced in a second experiment.
Conclusion: Treatment with intra-tumor injections of the anti-lymphoma peptide 302 in combination with CpG 1826 s.c. in the draining lymph node region cured established A20 tumors, induced tumor-specific CD8 positive tumor-reactive T-cells, and induced specific immunological memory. This principle represents a novel therapeutic vaccine approach.
Turning immunological memory into amnesia by depletion of dividing T cells