Know when to say when: Serial assessment of apoptosis and lymphocyte infiltrates with combined intraprostatic autologous dendritic cell immunotherapy/radiation therapy in high-risk prostate cancer.

Abstract

149 Background: Previous work suggested combining local radiotherapy (XRT) with intratumoral syngeneic dendritic cell (DC) injection could result in apoptosis/cell death mediated induction of cytotoxic T lymphocytes (CTL) based anti-tumor immunity. However, the presence, timing, and effectiveness of effector CTL prior, during, and following combined XRT/intratumoral autologous DC injection in humans is unknown. Methods: Herein, we report on timing concerns of intraprostatic DC injection in vivo, in human; five HLA-A2+, high risk localized prostate cancer patients were treated on protocol using androgen suppression therapy (AS), external beam radiation therapy (EBRT, 45 Gy) followed by brachytherapy permanent interstitial implant with addition of autologous intraprostatic DC injections during EBRT, after fractions 5, 15, and 25 of 25. Multiple serial prostate biopsies were collected before initiation of treatment, during EBRT and at 3, 12, 24 and 36 months after completion of treatment. Biopsies were stained for CD3, CD4, CD8, and cleaved caspase 3, and evaluated in a blinded manner. Specific anti-tumor immunity was assessed via ELISpot IFN-gamma production by CTL stimulated by HLA-A2 peptides derived from sequences of proteins associated with prostate cancer. Results: Apheresis, DC injections, and biopsies were well tolerated. The pattern of distribution of CD8+ cells was consistent with prostate cancer antigen targeting, rather than non-specific organ infiltration. There was not immediate obvious intraprostratic infiltrate by CTL after DC injection in vivo, in humans. Measurable, induced increases in ELISpot titers in peripheral blood CTL were observed for some subjects and for some antigens, but non-specific immunity fluctuated. Conclusions: This initial translational experience demonstrates safety and timing of DC injection coordinated with combined AS and XRT. Design of future trials employing combination XRT and DC will consider timing concerns to match therapy-induced apoptosis/cell death. No significant financial relationships to disclose.