A Phase I safety study of plasmid DNA immunization targeting carcinoembryonic antigen in colorectal cancer patients
Introduction
More than 1 million individuals are diagnosed with colorectal cancer (CRC) annually. About half a million deaths are reported [1]. The 5-year survival following surgery varies between 80 and 95% in American Joint Committee on Cancer (AJCC) stage I, 65–75% in stage II, 25–60% in stage III and less than 7% in metastatic or stage IV disease [2]. Despite that complete macroscopic tumor clearance is seen in 80% of CRC patients after resection, 50% of these patients develop recurrence [3]. Adjuvant chemotherapy reduces recurrence and cancer-related death by eradicating micrometastases. The role of adjuvant chemotherapy is still a subject of debate for stage II colon cancer while patients with stage III colon cancer have a survival benefit of adjuvant treatment of around 30% [4], [5]. In rectal cancer, adjuvant radiotherapy decreases the local recurrence rates by 50–60% compared to surgery alone and has become a standard procedure [6].
However, conventional chemotherapy and radiotherapy lack specificity and have an increased toxicity. Recent advances in immunology and molecular biology have opened new avenues for the clinical testing of therapeutic vaccination strategies against cancer, as a complementary treatment. Human carcinoembryonic antigen (CEA), over expressed by a large number of epithelial neoplasias, including CRC, gastric, pancreatic, breast, lung and ovarian carcinomas [7], fulfils criteria of a tumor associated antigen (TAA) for a therapeutic cancer vaccine, and has attracted considerable attention as a target for immunotherapy [8]. Targeting CEA in humans by different vaccination approaches has been shown to be safe, and induction of antigen-specific humoral, CD4+ helper T-cell as well as CD8+ cytotoxic T-cell (CTL) responses have been observed [9], [10]. In some cases, clinical and tumor marker responses have also been observed.
Antigen delivery of plasmid DNA, encoding tumor antigens, is an interesting approach for immunization for different diseases, including malignancies [11], [12]. Plasmid DNA vaccines can induce both humoral and CD4+ T-cell responses, and particularly elicit a strong CD8+ cytotoxic T-cell response (CTL) that is a unique feature of DNA vaccines, compared to protein or peptide vaccines [13], [14]. However, vaccinations with DNA alone or with recombinant vaccinia virus encoding CEA have shown low immunogenicity, with limited CEA-specific immune responses, when tested in human clinical trials [15], [16].
A plasmid DNA vaccine construct, encoding a modified CEA gene (lacking the N- and C-terminal signal sequences) fused to a promiscuous T helper epitope of the tetanus toxoid (CEA66 DNA) was shown to be strongly immunogenic in mice [17].
The present study aimed to evaluate CEA66 DNA immunization in CRC patients in the adjuvant setting. It was combined with granulocyte-macrophage colony-stimulating factor (GM-CSF) that was previously associated with induction of antibody to CEA [10]. Cyclophosphamide was given prior to start of immunotherapy treatment to reduce the number of regulatory T-cells [18], [19]. In addition, we evaluated an innovative needle-free jet injection delivery device (Biojector) in an attempt to further enhance the immunogenicity of the CEA66 vaccine.
Here we report safety data of this Phase I trial, which represents the first attempt to study a CEA66 DNA therapeutic vaccination strategy in humans.
Section snippets
Study design
The study was a single-centre, Phase I open label controlled trial. The primary objective was to evaluate safety and immunogenicity of a plasmid DNA CEA (CEA66 DNA) vaccine in combination with GM-CSF in CRC patients in the adjuvant setting. The secondary endpoints were to compare two routes of delivery of CEA66 DNA, (intradermal (ID) or intramuscular (IM) administration).
Patients
Ten patients were enrolled. Key inclusion criteria were age ≥18 years, histological confirmed AJCC stage II or III CRC,
Patient's enrolled and clinical outcome
Between September 2007 and October 2009 10 patients were enrolled, their clinical characteristics are shown in Table 1. Median age was 65 years (range 49–72), there were 4 females and 6 males. The median time from primary surgery to enrollment was 13 months, range 10–36 months. No CEA66 DNA injection was omitted. The median follow-up time was 72 weeks (range 30–124). The corresponding figures for Cohort A and B is 104 weeks (72–124) and 52 weeks (30–72), respectively.
All but two patients in
Adverse events
Safety and tolerability were evaluated in all ten patients that completed the intended vaccine schedule. No grade 3 or 4 adverse events possibly, probably or definitely associated with vaccination were reported. One SAE in patient no. 004/A was not considered related to the study drugs. He developed venous thrombosis in his not yet vaccinated arm. The thrombosis was considered to be related to a central venous access device at the same side.
Total numbers of AE related to vaccination including
Discussion
Despite the introduction of effective new drugs such as irinotecan and oxaliplatin, new treatment strategies are needed to optimize adjuvant therapy to improve the prognosis of patients with colorectal cancer, CRC. A number of clinical studies suggest that CRC might be an immunogenic tumor [21], justifying research to develop vaccine strategies. CEA might be a suitable target structure. In a previous Phase I clinical trial, we have demonstrated that immunization with recombinant CEA protein in
Acknowledgments
We thank the nurse staff (Kristina Edner, Anna-Lena Johansson, Maria Enkullen Moskovits, Mirjam Forsgren, Malin Backman, and Ylva Bodin) of the Karolinska University Hospital for excellent clinical work and Leila Relander for excellent secretarial help. We thank Vecura, Karolinska University Hospital, Huddinge, Sweden for production of the vaccine product and Bioject for providing the delivery device.
Conflict of interest: The authors report no conflicts of interest. The authors alone are
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