Vaccine Therapy of Colorectal Cancer Patients with Tumor Associated Antigens

Sammanfattning: In this thesis, two different vaccines were evaluated as adjuvant therapy for patients with colorectal cancer. The ability of the two candidate vaccines to generate antigen-specific cellular and humoral responses, respectively, was studied. The effectiveness of granulocyte colony stimulating factor (GM-CSF) as a cytokine adjuvant to augment the immune response was also examined.The first vaccination strategy involved immunization with the recombinant tumor-associated protein, carcinoembryonic antigen (CEA). Recombinant CEA was administered at 4 different dose levels 7 times during one year. Peripheral blood samples were regularly analyzed during 36 months. This vaccination regimen induced a strong immunoglobulin 1 (IgG1) and IgG4 response, a moderate IgG2 response and a weak IgG3 response against CEA. GM-CSF markedly augmented the effect on IgG1 and IgG4 as well as the T cell response. In contrast, dose of rCEA had no or modest effect on induced immune responses. The response gradually increased during the 12 months immunization period. Responses of all three IgG subclasses and of T cells were protracted up to 36 months. The anti-CEA IgG titers related significantly to survival. Functional HLA-DR epitopes of CEA could be defined. These major histocompatibility class II epitopes may serve as putative components of a peptide-based vaccination strategy. The other vaccine strategy consisted of the tumor-associated antigen epithelial cell adhesion molecule (Ep-Cam) expressed as a transgene in a viral vector, ALVAC. Patients were immunized subcutaneously/intradermally 3 times over 6 weeks and monitored for immune responses for 46 weeks. No anti-Ep-Cam specific humoral response was induced, but Ep-Cam specific type 1 T cells (interpheron-gamma production) were induced, mainly in the GM-CSF group. The cytotoxic cellular response appeared late, or a few months after the last immunization.Both vaccines were well tolerated. Since GM-CSF was an important component for both regimens, immungenicity of this cytokine was assessed. Multiple immunizations with low dose GM-CSF were associated with a low incidence of GM-CSF antibodies that did not neutralize the biological effect of GM-CSF. In conclusion, both vaccines are promising candidate vaccines. GM-CSF is necessary to induce a strong humoral and cellular immune response. Large clinical trials are urgently warranted to evaluate the clinical efficacy.