Abstract 4302: Long term monitoring of circulating regulatory T cells (Treg), myeloid derived suppressor cella (MDSC) and type I effector T cells in melanoma patients treated with neoadjuvant ipilimumab

Abstract

Abstract Background: Patients with regionally advanced melanoma were treated with neoadjuvant ipilimumab in a previously reported study (Tarhini. PLOS One 2014) where significant changes in circulating Treg, MDSC and peptide specific type I CD4+ and CD8+ T cells were observed early on-treatment (6 weeks) that correlated with clinical outcome. Methods: Patients were treated with ipilimumab (10 mg/kg IV every 3 weeks x 2 doses) bracketing surgery. Blood (serum / peripheral blood mononuclear cells) specimens were collected at baseline and during treatment for up to 9 months. We conducted longer term monitoring in patients with available specimens at 3 (n = 28), 6 (n = 22) and 9 (n = 13) months utilizing multicolor flow cytometry. We compared the frequencies of circulating suppressive Treg and MDSC on-study to baseline levels, as well as frequencies of CD4+ and CD8+ T cells specific to shared tumor-associated antigens (Gp-100, MART-1, NY-ESO-1) utilizing overlapping peptide libraries (15-mer peptides overlapping by 4). The prognostic value of cell frequencies in relation to the probability of the event of progression at 9 months was tested. Results: Baseline levels of Treg (CD4+/CD25hi+/CD39+) were significantly associated with 9 months progression free survival (PFS) (p = 0.04). A significant increase in Treg (CD4+CD25hi+Foxp3+ and CD4+/CD25hi+/CD39+) frequencies reported previously at 6 weeks after initiation of ipilimumab appears to have reversed starting 3 months as no significant changes were seen at this or any of the later time points compared to baseline. However, in monitoring the time dependent change over time in circulating Treg there was a trend towards an association with PFS (p = 0.09). Unlike what we had observed and reported at 6 weeks, no significant decrease in MDSC levels was seen at 3 months or later time points compared to baseline. We detected evidence of spontaneous in vivo cross presentation resulting in type I (interferon-γ producing), fully activated (CD69+) CD4+ and CD8+ antigen-specific T-cell immunity against cancer-testis (NY-ESO-1) as well as melanocytic lineage (MART-1, gp100) antigens in the absence of therapeutic vaccination. These responses were significantly potentiated at 6 weeks and persisted at 3, 6 and 9 months following the initiation of ipilimumab. Conclusions: Neoadjuvant ipilimumab significantly modulates the levels of cellular mediators of immune suppression (Treg and MDSC) early on-treatment with less significant changes seen on long term follow up. Significant potentiation of the type I effector T cell response is seen early and persists on long term monitoring. These biomarkers warrant further investigation in relation to the mechanism of action of ipilimumab and for their potential prognostic and therapeutic predictive value. (Supported by NIH award P50CA121973 and BMS) Citation Format: Janet Retseck, Amanda Gillespie-Twardy, Alexis Nasr, Hui-Min Lin, Yan Lin, John Kirkwood, Lisa H. Butterfield, Haris Zahoor, Cindy Sander, Ahmad A. Tarhini. Long term monitoring of circulating regulatory T cells (Treg), myeloid derived suppressor cella (MDSC) and type I effector T cells in melanoma patients treated with neoadjuvant ipilimumab. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4302. doi:10.1158/1538-7445.AM2015-4302