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The generation of cytotoxic effector T cells requires delivery of two signals, one derived from a specific antigenic epitope and one from a costimulatory molecule. A phase I clinical trial was conducted with a non-replicating canarypoxvirus (ALVAC) constructed to express both human carcinoembryonic antigen (CEA) and the B7.1 costimulatory molecule. This was the first study in cancer patients to determine if the delivery of costimulation with a tumor vaccine was feasible and improved immune responses. Three cohorts of six patients, each with advanced CEA-expressing adenocarcinomas, were treated with increasing doses of an ALVAC-CEA-B7.1 vaccine (4.5 x 10(6), 4.5 x 10(7), and 4.5 x 10(8) plaque-forming units, PFU). Patients were vaccinated by intramuscular injection every 4 weeks for 3 months and monitored for side-effects, tumor growth and anti-CEA immune responses. ALVAC-CEA-B7.1 at doses up to 4.5 x 10(8) PFU was given without evidence of significant toxicity or autoimmune reactions. Three patients experienced clinically stable disease that correlated with increasing CEA-specific precursor T cells, as shown by in vitro interferon-gamma enzyme-linked immunoassay spot tests (ELISPOT). These three patients underwent repeated vaccination resulting in augmented CEA-specific T cell responses. This study represents the first use of costimulation to enhance antitumor vaccines in cancer patients. This approach resulted in CEA-specific immunity associated with stable diseases in three patients. This study also demonstrated that CEA-specific T cell responses could be sustained by repeated vaccinations. Although the number of patients was small, the addition of B7.1 to virus-based vaccines may improve immunological and stable diseases to vaccination against tumor-associated antigens with tolerable toxicity.

Interleukin-10 (IL-10) has a wide range of in vivo biological activities and is a key regulatory cytokine of immune-mediated inflammation. The authors found that murine IL-10 given 12 hours after a recombinant vaccinia virus (rVV) containing the LacZ gene significantly enhanced the treatment of mice bearing 3-day-old pulmonary metastases expressing beta-galactosidase. Because IL-10 has been shown to inhibit the functions of key elements of both innate and acquired immune responses, the authors hypothesized that IL-10 might act by inhibiting clearance of the rVV, thus prolonging exposure to the experimental antigen. However, evidence that IL-10 was not acting primarily through such negative regulatory mechanisms included the following: (a) IL-10 also enhanced the therapeutic effectiveness of a recombinant fowlpox virus, which cannot replicate in mammalian cells; (b) Titers of rVV in immunized mice were lower, not higher; and (c) Although IL-10 did not alter levels of anti-vaccinia anti-bodies or natural killer cell activity, rVV-primed mice treated with IL-10 had enhanced vaccinia-specific cytotoxic T-lymphocyte activity. Thus, IL-10 enhanced the function of a recombinant poxvirus-based anti-cancer vaccine and may represent a potential adjuvant in the vaccination against human cancers using recombinant poxvirus-based vaccines.

Background: The inadequacy of systemic treatments of advanced colorectal cancer has aroused interest in biologic therapy. Recent animal models have demonstrated the efficacy and safety of a recombinant vaccine that contains vaccinia and the gene for carcinoembryonic antigen (rV-CEA)., Methods: A phase I clinical trial of rV-CEA was conducted to assess vaccine toxicities, the maximum tolerated dosage, resulting immune activities, and tumour responses. A dose-escalation protocol was devised for three concentrations. Six patients per dosage were each to receive three vaccinations., Results: Seventeen patients with advanced colorectal cancer received a total of 44 vaccinations. Mild local and systemic reactions-comparable to those seen with vaccinia alone-were observed and were typically associated with the first vaccination. No significant complications or deaths were caused by the rV-CEA. In particular, no autoimmune colitis developed, nor did leukopenia occur, despite some homology between CEA and leukocyte antigens. All three vaccine concentrations were equally well tolerated. Most patients demonstrated tumor progression by clinical and radiographic parameters and by CEA levels. Immune assays are pending., Conclusions: This phase I trial demonstrated the safety of rV-CEA in patients with advanced colorectal cancer. Future clinical studies are warranted and will likely be influenced by investigations of the immune responses to the vaccine.