Active Specific Immunotherapy of Adenocarcinomas with Synthetic Tumor-Associated Antigens Conjugated to Keyhole Limpet Hemocyanin

摘要

We have been conducting phase II clinical trials for the treatment of various adenocarcinomas with synthetic carbohydrate epitope vaccines that utilized Keyhole Limpet Hemocyanin (KLH) as a carrier protein. To date, over 180 patients have been enrolled into these immunotherapy studies with the sialyl-Tn antigen conjugated to KLH. Objective tumor responses have been observed in these trials in both breast and ovarian cancer patients. The phase II studies have been designed to answer key questions towards optimizing the immunotherapeutic effects. The first question was to determine the optimal route (oral vs. intravenous) of low-dose cyclophosphamide that is used to overcome a state of tumor-induced immunosuppression. The antibody titer data from this study show a statistically significant increase in anti-STn IgG antibodies in the IV group. The second key question has been the optimal dose of antigen to use for the generation of a therapeutically beneficial immune response. This is in light of recent observations that low doses of antigens may favor a TH1 (cellular) immune response as opposed to a TH2 (antibody-based) immune response. We have shown that low doses (1 μg) of Theratope® STn-KLH vaccine but not high doses (25 μg) will induce a hapten-specific DTH response in CAF1 mice. In addition, a low dose of vaccine will cause greater T-cell proliferative activity in a popliteal lymph node cell population after footpad challenge. The supernatants of these antigen-stimulated cultures do indeed contain gamma-interferon in a relative absence of IL-10, thus confirming the TH1 nature of this response. We have investigated this low-dose T-cell response with other KLH conjugates and with KLH itself and this observation is consistent. Thus KLH conjugates, although frequently employed for optimizing an antibody response to T-cell-independent antigens, are capable of inducing TH1 immune responses, and do so optimally at lower doses. These effects are optimally seen with certain adjuvant formulations (DETOX TM-B, RIBI Immuno-chem). As a part of the immunologic monitoring of our ASI patients, we have performed in vitro antigen stimulations for hapten-specific blastogenesis and cytokine profiles. The data suggest that a TH1 immune response as measured by gamma-interferon production (without IL-10 production) is associated with disease stability and/or partial responses. These are the immunologic parameters by which the current dose range studies are being evaluated for the selection of an optimal therapeutic dose of Theratope® STn-