Feasibility of Autologous Tumor Cell-TLR9 Agonist Vaccination for Metastatic Colorectal Cancer

Current therapies for metastatic colorectal cancer only prolong life for approximately 2 years. A more innovative therapy that prolongs life significantly or even cures is needed. Bone marrow transplantation is a curative therapy for patients with leukemias and lymphomas. Tumor eradication in the case of transplantation of the patient's own marrow (autologous transplantation) is based on the intensive chemotherapy and/or radiotherapy used for conditioning. Tumor eradication in the case of transplantation using the marrow of a normal donor is based on both tumor reduction from conditioning and the immune elimination of tumor cells by T cells in the donor transplant that recognize the foreign tissue antigens expressed by the tumor cells and kill these cells. The use of bone marrow transplantation to treat tumors other than leukemia and lymphoma has been limited, and studies of transplantation of the patient's own marrow for the treatment of advanced /metastatic breast cancer have not conclusively shown benefit beyond conventional therapy. Recently, the Strober lab developed a preclinical model that effectively treated colon cancer in mice by combining immunotherapy and autologous bone marrow transplantation in order to markedly augment the anti-tumor potency of immunotherapy. They used the CT26 colon cancer as the therapeutic target either as a single subcutaneous tumor nodule, as a disseminated tumor in the lungs and peritoneum, or as a metastatic tumor in the liver depending on the route of administration of the tumor cells in BALB/c mice. Mice were vaccinated mice with established primary tumors or disseminated/ metastatic disease with irradiated tumor cells mixed with the adjuvant CpG, and found that vaccination alone had no effect on tumor growth. Similarly radiation conditioning of tumor bearing hosts followed by transplantation of bone marrow and spleen cells or purified T cells and hematopoietic stem cells from unvaccinated donors of the same strain had no effect. In contrast, radiation conditioning of mice followed by transplantation of hematopoietic and immune cells from donors of the same strain vaccinated with tumor cells and CpG cured almost all subcutaneous primary as well as disseminated and metastatic tumors in the hosts. A similar result was obtained after autologous transplantation of hematopoietic and immune cells from tumor bearing mice that had been vaccinated after tumor establishment. Investigation of tumor infiltrating cells showed that the injected donor T cells do not accumulate in the tumors unless the host has been irradiated before injection. Based on this model, we have assembled a team of Stanford University faculty members with expertise in gastrointestinal cancers, immunotherapy, radiation oncology, and bone marrow transplantation in the Departments of Medicine and Pathology to translate the preclinical findings into a Phase I safety and feasibility clinical study for the treatment of 10 patients with metastatic colorectal cancer. Resected tumor cells will be irradiated and mixed with CpG to create a vaccine. Patients will receive subcutaneous vaccination at weeks 1 and 2 after resection. Six weeks later, immune T cells and then G-CSF "mobilized" purified blood progenitor cells will be harvested from the blood and cryopreserved. If needed patients will receive chemotherapy for tumor reduction. When disease is controlled off chemotherapy, patients will receive a conditioning regimen of fludarabine (30mg/m2 daily x 3 days) followed by intensive fractionated total body irradiation. The dose of fTBI will be escalated using a 3+3 design to ensure safety and will range from 400 to 800 gray. The patient will then undergo hematopoietic and immune cell rescue. They will undergo a third vaccination within 7-14 days after transplant. Thereafter, serial monitoring of tumor burden will continue. Immune monitoring will occur before and after vaccination as well as after transplantation. Tests will include in vitro anti-tumor immune responses of T cells (proliferation, cytotoxicity, cytokine secretion etc.) to stimulation with whole tumor cells and tumor cell lysates pulsed on to antigen presenting cells, anti-tumor antibody responses, and immune reconstitution after transplantation.