Search

Despite an abundance of preclinical data, relatively little is known regarding the efficacy of DNA vaccination in humans. Here, we present results from a dose-escalation clinical trial of a dual expression plasmid encoding carcinoembryonic antigen (CEA) and hepatitis B surface antigen (HBsAg) in 17 patients with metastatic colorectal carcinoma. CEA was selected as a prototypic tumor-associated self-antigen, and the HBsAg cDNA was included as a positive control for immune response to the DNA vaccine without relying upon breaking tolerance to a self-antigen. Groups of 3 patients received escalating single i.m. doses of the DNA vaccine at 0.1, 0.3, and 1.0 mg. Subsequent groups of 3 patients received three repetitive 0.3- or 1.0-mg doses at 3-week intervals. A final group of 2 patients received three repetitive 2.0 mg doses at 3-week intervals. Toxicity was limited to transient grade 1 injection site tenderness, fatigue, and creatine kinase elevations, each affecting a minority of patients in a non-dose-related manner. Repetitive dosing of the DNA vaccine induced HBsAg antibodies in 6 of 8 patients, with protective antibody levels achieved in four of these patients. CEA-specific antibody responses were not observed, but 4 of 17 patients developed lymphoproliferative responses to CEA after vaccination. No objective clinical responses to the DNA vaccine were observed among this population of patients with widely metastatic colorectal carcinoma. Nevertheless, this pilot trial has provided encouraging human immune response data in support of this vaccine technology.

The principal objectives of this trial were twofold: (a) to examine the safety and relative efficacy of intradermal needle injection versus s.c. jet administration of a carcinoembryonic antigen (CEA)-encoding recombinant vaccinia virus (rV-CEA) over a limited dose range and (b) to evaluate CEA-specific immune responses or antitumor effects induced by rV-CEA vaccination. Patients were randomly assigned to one of two groups, depending upon the technique of vaccine administration. All 20 patients received two doses of 10(7) or 10(8) pfu of rV-CEA at a 4-week interval. Toxicity was limited to modest local inflammation at the inoculation site as well as low-grade fever and increased fatigue, each affecting fewer than 20% of the patients. No evidence of CEA-specific lymphoproliferation, interleukin 2 release, delayed-type hypersensitivity, or antibody response was observed. Thus, the efficacy comparison between the two administration techniques was based upon the induction of immune responses to the vaccinia virus vector. Both techniques induced vaccinia-specific lymphoproliferation, interleukin 2 release, and antibody responses of comparable magnitude and frequency as well as protected 80% of patients against pustule formation following vaccinia scarification. Thus, there is no compelling reason to recommend one administration technique over the other based upon toxicity or efficacy. We have selected s.c. jet injection for subsequent trials of rV-CEA based on the ability to accommodate larger injection volumes, enhanced standardization between clinicians, and avoidance of needles that could transmit the vaccine or blood-borne pathogens to health care workers. We recommend use of 10(8) pfu doses for subsequent trials of recombinant vaccinia virus vaccines based upon the favorable toxicity profile and more consistent local pustule formation indicative of an adequate inoculation of live virus. No objective clinical responses to the rV-CEA vaccine were observed among this population of patients with widely metastatic adenocarcinoma.

We have constructed a plasmid DNA encoding the full-length complementary DNA for human carcinoembryonic antigen (CEA) under transcriptional regulatory control of the cytomegalovirus early promoter/enhancer (pCEA) and demonstrated that this plasmid can function as a polynucleotide vaccine to elicit a CEA-specific immune response. This immune response protects against tumor challenge with syngeneic CEA-transduced colon carcinoma cells in mice. In the present work, the pCEA construct and purification method were modified to eliminate nonessential viral sequences, the ampicillin selectable marker, mutagens, and endotoxin to produce a reagent suitable for human clinical trials. The human use plasmid (pGT37) directs CEA expression at levels comparable with the original pCEA plasmid and can be propagated to yield large quantities of plasmid DNA based on kanamycin selection. A simple extraction technique greatly reduces contamination by endotoxin. Six weekly intramuscular injections of pGT37 elicited CEA-specific lymphoblastic transformation and antibody response in five of five mice and fully protected 10 of 10 mice against tumor challenge with syngeneic CEA-expressing colon cancer cells 42 days from the first plasmid injection. Thus, pGT37 encoding a tumor-associated antigen (CEA) has been shown to elicit cellular and humoral immune responses and mediate antitumor effects in vivo. This plasmid is suitable for human use and can be easily propagated in the laboratory.