Abstract
BackgroundWe previously reported early on-treatment significant modulation in circulating regulatory T cell (Treg), myeloid derived suppressor cells (MDSC) and antigen-specific type I CD4+ and CD8+ T cells that correlated with clinical outcome in regionally advanced melanoma patients treated with neoadjuvant ipilimumab. Here, we investigated the long term immunologic impact of CTLA4 blockade.MethodsPatients were treated with ipilimumab given at 10 mg/kg IV every 3 weeks for 2 doses bracketing surgery. Blood specimens were collected at baseline and during treatment for up to 9 months. We tested immune responses at 3, 6, and 9 months utilizing multicolor flow cytometry. We compared frequencies of circulating 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).ResultsLevels of Treg significantly increased when measured at 6 weeks following ipilimumab but returned to baseline by 3 months, with no significant difference in Treg levels between relapsed and relapse-free groups at 3, 6 or 9 months. However, lower baseline levels of circulating Treg (CD4+CD25hi+CD39+) were significantly associated with better relapse free survival (RFS) (p = 0.04). Levels of circulating monocytic HLA-DR+/loCD14+ MDSC were lower at baseline in the relapse-free group and further decreased at 6 weeks, though the differences did not reach statistical significance including measurements at 3, 6 or 9 months. We detected evidence of type I (interferon-γ producing), 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 boosted at 6 weeks and persisted at 3, 6 and 9 months following the initiation of ipilimumab.ConclusionsLower Treg levels at baseline are significantly associated with RFS and increased Treg frequency after CTLA4 blockade was only transient. Lower MDSC was also associated with RFS and MDSC levels were further decreased after ipilimumab. Tumor specific effector immune responses are boosted with CTLA4 blockade and tend to be durable.Trial registration ClinicalTrials.gov Identifier: NCT00972933
Highlights
We previously reported early on-treatment significant modulation in circulating regulatory T cell (Treg), myeloid derived suppressor cells (MDSC) and antigen-specific type I CD4+ and CD8+ T cells that correlated with clinical outcome in regionally advanced melanoma patients treated with neoadjuvant ipilimumab
Levels of Treg significantly increased when measured at 6 weeks following ipilimumab but almost returned to baseline levels by 3 months, with no significant difference in Treg levels between relapsed and relapse-free groups at 3, 6 or 9 months
There were no significant differences in Fox3p+ Treg levels between the two groups at later time points
Summary
We previously reported early on-treatment significant modulation in circulating regulatory T cell (Treg), myeloid derived suppressor cells (MDSC) and antigen-specific type I CD4+ and CD8+ T cells that correlated with clinical outcome in regionally advanced melanoma patients treated with neoadjuvant ipilimumab. Detectable locally and regionally advanced melanoma has a 5-year relapse rate that exceeds 70% at 5 years [1,2,3,4]. In the Melanoma Intergroup Surgical Trial, a local recurrence was associated with 5 and 10 year survival rates of 9–11% and 5%, respectively [6]. Interferon-alfa (IFN), ipilimumab (ipi) and nivolumab have achieved regulatory approvals for the adjuvant treatment of high-risk melanoma following surgical management, while the combination of dabrafenib and trametinib was granted a breakthrough therapy designation by the Food and Drug Administration for stage III melanoma with a BRAF V600 mutation [1]. Adjuvant ipilimumab at 10 mg/kg was approved by the FDA in 2015 after improved RFS compared to placebo in stage III melanoma was demonstrated in EORTC 18071 trial [11]. A recent update from this trial has reported a significant OS benefit [12]
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