Abstract 2934: Increased type-2 T cell rates and coincidence of Th17 spikes with autoimmune events and PSA declines upon combined prostate GVAX and anti-CTLA4 immunotherapy
Authors: Stam Anita GM , Santegoets Saskia JAM , Scheper Rik J. , Lougheed Sinead M. , Gall Helen , Jooss Karin , Sacks Natalie , Hege Kristen , Lowy Israel , Gerritsen Winald R. , van den Eertwegh Alfons JM , de Gruijl Tanja D. 
Published: February 2011

The effects of a GM-CSF-secreting allogeneic prostate cancer vaccine (Prostate GVAX) and the anti-CTLA4 antibody Ipilimumab were investigated in a Phase I dose escalation/expansion trial of patients with metastatic, hormone-refractory prostate cancer (mHRPC). All patients received a 500 million cell priming dose of GVAX on day 1 followed by bi-weekly intradermal treatments of 300 million cells over a 24-week period. Ipilimumab was administered every 4 wks from day 1 during the same period. Initially, 12 patients were enrolled in cohorts of 3 and each cohort was assigned an escalating dose of Ipilimumab at 0.3, 1, 3 or 5 mg/kg. 16 additional patients were enrolled in the expansion cohort of 3 mg/kg Ipilimumab. Results showed that the GVAX and Ipilimumab combination was active in mHRPC patients. PSA declines of more than 50% (Partial Response, PR) were observed in 5 of 22 patients in the 3-5 mg/kg Ipilimumab doses, and were associated with Autoimmune Breakthrough Events (ABE), including Grade 2 or 3 hypophysitis and Grade 3 alveolitis. PSA stabilizations (Stable Disease, SD) were observed in 1/3 pts in lower (0.3 and 1 mg/kg), and in 7 of 22 in the higher (3-5 mg/kg) dose levels.

In this study, cytokine profiles of peripheral blood-derived T cells were determined ex vivo and after in vitro stimulation with PMA and ionomycin by intracellular staining for IL-2, −4, −5, −10, TNF-α, IFN-γ and IL-17A. Of these cytokines, only IL-4 was detectable ex vivo in CD4+ and CD8+ T cells; post-treatment increases were detectable in the higher (3-5 mg/kg) but not in the lower (0.3-1 mg/kg) Ipilimumab dose levels. After PMA/ionomycin stimulation, no consistent changes were observed in the frequencies of IFN-γ, IL-2 and TNF-α-producing type-1 T cells compared to pre-treatment values. In contrast, significantly increased rates of IL-4 and IL-5 producing CD4+ and CD8+ T cells were found upon treatment (visit 1 versus visit 5) at higher (3-5 mg/kg) Ipilimumab dose levels. Overall these data clearly demonstrate a shift in favor of a Type-2 cytokine profile due to the GVAX/Ipilimumab administration. The frequencies of IL-17A producing CD4+ T (Th17) cells increased over the course of treatment in 5 of 18 patients. Of note, in 3 (PR) out of 5 of these patients this increase of the Th17 subset coincided with onset of hypophysitis and/or adrenal insufficiencies, as well as the onset of PSA decline. The two patients with increased Th17 rates without these pituitary or adrenal-related ABE showed SD. In summary, our results show that combined GVAX/Ipilimumab administration gives rise to Type-2/Th17 cytokine profiles in mHRPC patients, but that only increases in Th17 show a relation to ABE and PSA responses.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2934.