Effect of the novel therapeutic cancer vaccine formulation DPX-0907 on multifunctional T-cell responses in ovarian, breast, and prostate cancer patients.

Abstract

2588 Background: To increase the efficacy of peptide cancer vaccines, we developed a novel vaccine platform called DepoVax, an adjuvanted water-free depot formulation with the ability to generate enhanced immune responses. Naturally processed HLA-A2 restricted peptides that are selectively presented by breast, ovarian and prostate cancer cell lines, but not by normal HLA-A2+ cells, were used as antigens with a proprietary adjuvant and a T helper peptide epitope to create a therapeutic cancer vaccine, DPX-0907. Methods: A phase I clinical study was designed to examine the safety and immune activating potential of DPX-0907 in advanced stage breast, ovarian and prostate cancer patients. A total of 23 late stage cancer patients were recruited and were divided into two dose volume cohorts in a three immunization clinical protocol. Results: DPX-0907 proved to be safe with no serious adverse effects related to the vaccine reported. Of those evaluable for immunogenicity, all breast cancer patients (3/3), most of ovarian (5/6) and one third of prostate (3/9) cancer patients demonstrated immune response to one or more of seven antigenic peptides, resulting in a 61% response rate. Immune responses correlated with achievement of CR, PR or SD to last treatment. No difference in immune response rate or magnitude was seen between the two dose groups. DPX-0907 displayed strong immune induction potential, with 73% of immune responders showing responses with just one dose of vaccine. In 83% of responders, immune responses were detected at ≥2 time points post vaccination and 64% had a persistent immune response at one month post last vaccination. Immune monitoring showed peptide-specific CD8 T cells, and these T cells were able to secrete multiple Th1 cytokines indicating their multifunctionality, a feature attributable to cells that mediate protective responses. Conclusions: These data support the ability of DPX-0907 to elicit Th1 dominated, specific immunity and support the rationale for further testing in immunologically competent cancer patients. The novel DepoVax formulation may promote multifunctional memory responses with peptides from other tumor associated antigens.