Active Specific Immunotherapy with a -Human Chorionic Gonadotropin Peptide Vaccine in Patients with Metastatic Colorectal Cancer: Antibody Response Is Associated with Improved Survival

Purpose: Human chorionic gonadotropin (hCG) is produced by colorectal cancers and may play a role in its progression. The clinical and immunological effects of a synthetic vaccine targeting -hCG composed of the COOH terminal peptide of -hCG (CTP37) conjugated to diphtheria toxoid (DT) was investigated in patients with metastatic colorectal cancer. Experimental Design: Seventy-seven patients from 12 centers were randomly divided into two vaccine dose groups. CTP37-DT was formulated in an emulsion and administered i.m. on days 0, 28, and 70. Patients were evaluated for toxicity, overall survival, and antibody response to hCG and to DT. Results: Immunizations were well tolerated with no patients requiring cessation of the injections. Anti-hCG antibody was detected in 56 of the 77 patients treated. Significant differences in antibody response and survival were not observed between the two dose groups. An intention-to-treat analysis of all vaccinated patients showed a median survival of 34 weeks. Patients who developed anti-hCG antibody levels higher than or equal to the median value exhibited a median survival of 45 weeks compared with 24 weeks for patients who developed anti-hCG antibody levels lower than the median (P 0.0002). In contrast, no significant difference was observed when comparing survival based upon the level of DT antibody that developed (P 0.80). Conclusions: Vaccination with CTP37-DT induced antihCG antibodies in most patients with advanced colorectal cancer. Anti-hCG antibody induction was associated with longer overall survival. CTP37-DT has an excellent safety profile and warrants further study in patients with colorectal cancer.