Long‐term clinical and immunological effects of p53‐SLP® vaccine in patients with ovarian cancer

Vaccine-induced p53-specific immune responses were previously reported to be associated with improved response to secondary chemotherapy in patients with small cell lung cancer. We investigated long-term clinical and immunological effects of the p53-synthetic long peptide (p53-SLP®) vaccine in patients with recurrent ovarian cancer. Twenty patients were immunized with the p53-SLP® vaccine between July 2006 and August 2007. Follow-up information on patients was obtained. Clinical responses to secondary chemotherapy after p53-SLP® immunizations were determined by computerized tomography and/or tumor marker levels (CA125). Disease-specific survival was compared to a matched historical control group. Immune responses were analyzed by flow cytometry, proliferation assay, interferon gamma (IFN-γ) ELISPOT and/or cytokine bead array. Lymphocytes cultured from skin biopsy were analyzed by flow cytometry and proliferation assay. Of 20 patients treated with the p53-SLP® vaccine, 17 were subsequently treated with chemotherapy. Eight of these patients volunteered another blood sample. No differences in clinical response rates to secondary chemotherapy or disease-specific survival were observed between immunized patients and historical controls (p = 0.925, resp. p = 0.601). p53-specific proliferative responses were observed in 5/8 patients and IFN-γ production in 2/7 patients. Lymphocytes cultured from a prior injection site showing inflammation during chemotherapy did not recognize p53-SLP®. Thus, treatment with the p53-SLP® vaccine does not affect responses to secondary chemotherapy or survival, although p53-specific T-cells do survive chemotherapy.