Addition of interferon-a to the p53-SLP V R vaccine results in increased production of interferon-c in vaccinated colorectal cancer patients: A phase I/II clinical trial Eliane C.M. Zeestraten 1 *, Frank M. Speetjens 1 *, Marij J.P. Welters 2 *, Sepideh Saadatmand 1 , Linda F.M. Stynenbosch 2 , Rogier Jongen 2 , Ellen Kapiteijn 2 , Hans Gelderblom 2 , Hans W. Nijman 3 , A. Rob P.M. Valentijn 4 , Jaap Oostendorp 4 , Lorraine M. Fathers 4 , Jan W. Drijfhout 5 , Cornelis J.H. van de Velde 1 , Peter J.K. Kuppen 1 , Sjoerd H. van der Burg 2 and Cornelis J.M. Melief 5,6 1 Department of Surgery, Leiden University Medical Center, Leiden, The Netherlands 2 Department of Clinical Oncology, Leiden University Medical Center, Leiden, The Netherlands 3 Department of Gynecology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands 4 Department of Clinical Pharmacy and Toxicology, Leiden University Medical Center, Leiden, The Netherlands 5 Department of Immunohematology and Blood Transfusion, Leiden University Medical Center, Leiden, The Netherlands 6 ISA Pharmaceuticals B.V., Leiden, The Netherlands We previously established safety and immunogenicity of a p53 synthetic long peptides (p53-SLP V R ) vaccine. In the current trial, we investigated whether combination of interferon-alpha (IFN-a) with p53-SLP V R is both safe and able to improve the induced p53- specific IFN-c response. Eleven colorectal cancer patients successfully treated for metastatic disease were enrolled in this study. Of these, nine patients completed follow-up after two injections with p53-SLP V R together with IFN-a. Safety and p53-specific immune responses were determined before and after vaccination. Furthermore, cryopreserved PBMCs were compared head-to-head to cryopreserved PBMCs obtained in our previous trial with p53-SLP V R only. Toxicity of p53-SLP V R vaccination in combination with IFN-a was limited to Grade 1 or 2, with predominantly small ongoing swellings at the vaccination site. All patients harbored p53-specific T cells after vaccination and most patients showed p53-specific antibodies. Compared to the previous trial, addition of IFN-a significantly improved the frequency of p53-specific T cells in IFN-c ELISPOT. Moreover, in this trial, p53-specific T cells were detectable in blood samples of all patients in a direct ex vivo multiparameter flowcytometric assay, opposed to only 2 of 10 patients vaccinated with p53-SLP V R only. Finally, patients in this trial displayed a broader p53-specific immunoglobulin-G response, indicating an overall better p53-specific T-helper response. Our study shows that p53-SLP V R vaccination combined with IFN-a injection is safe and capable of inducing p53-specific immunity. When compared to a similar trial with p53-SLP V R vaccination alone the combination was found to induce significantly more IFN-c producing p53-specific T cells. The modest to poor prognosis of colorectal cancer patients treated with curative intent, calls for additional treatment modalities such as immunotherapy. 1 p53 is one of the most frequently used tumor-associated antigens in tumor directed vaccination studies. 2 Because of a mutation, p53 is inactivated and overexpressed in 34–45% of colorectal tumors, while Key words: p53, immunotherapy, colon, colorectal, cancer, vaccine, synthetic long peptides, immune monitoring, therapeutic, IFN-a Additional Supporting Information may be found in the online version of this article Conflict of Interest: This study was conducted by the Leiden University Medical Center (LUMC), which holds a patent on the use of synthetic long peptides as vaccine (U.S. patent number 7,202,034). The LUMC does not share the financial benefit from this patent with its employees. ISA Pharmaceuticals, a biotechnology company, has licensed the patent from the LUMC. Dr. Melief is a full-time employee of ISA Pharmaceuticals B.V., reports having a stock-appreciation right that is the equivalent of a stock option in 1% of the issued share capital of ISA Pharmaceuticals and being named as an inventor on the patent for the use of synthetic long peptides as vaccine and serving as a member of the steering committee of ISA Pharmaceuticals; Drs. Oostendorp and Drijfhout, serving as nonpaid members of the strategy team of ISA Pharmaceuticals and holding no financial interest in the company; Dr. van der Burg, being named as one of the inventors on the patent for the use of synthetic long peptides as vaccine but holding no financial interest and serving as a nonpaid member of the steering committee of ISA Pharmaceuticals. No other potential conflict of interest relevant to this article was reported *E.C.M.Z., F.M.S., and M.J.P.W. contributed equally to this work Grant sponsor: The Netherlands Organization for Health Research and Development; Grant number: 92003509 DOI: 10.1002/ijc.27819 History: Received 15 May 2012; Accepted 9 Aug 2012; Online 5 Sep 2012 Correspondence to: Cornelis J.M. Melief, ISA Pharmaceuticals, Niels Bohrweg 11-13, 2333 CA, Leiden, The Netherlands, E-mail: melief@ isa-pharma.com Tumor Immunology Int. J. Cancer: 132, 1581–1591 (2013) V C 2012 UICC International Journal of Cancer IJC