Regulatory T cells are not a strong predictor of survival for patients with glioblastoma

Immunotherapy is emerging as an effective new treatment for many cancers,1 but it has yet to translate into a proven clinical benefit for patients with glioblastoma.2 A purported limitation of applying immunotherapy to gliomas is the tumor-induced impairment of the immune response, especially within the tumor microenvironment.3 Regulatory T cells (Tregs), a subpopulation of CD4+ T cells, characterized by the expression of the unique transcription factor Forkhead box protein 3 (FoxP3), depress immune function. Expression of Helios, a member of the Ikaros transcription factor family, is a marker for thymic or natural Tregs (nTregs).4 Although Tregs share functionality and suppression mechanisms across cancers, an increasing number of reports indicate tumor-specific variability in the proportion of Tregs in peripheral blood and in the tumor microenvironment. There are even reports where elevated numbers of Tregs inversely correlate with patient survival and/or response to immune therapies.5–7 The association between glioblastoma and immunosuppression suggests that accurately assessing immune competency could help to predict survival and identify patients most likely to benefit from immunotherapy. Severe CD4+ lymphopenia early in treatment correlates with shorter survival,8 while extensive lymphocytic infiltration of glioblastoma improves survival.9,10 In patients with glioblastoma, the percentage of Tregs in peripheral blood has been reported to be increased compared with normal controls.11,12 In tumor tissue, the number of Tregs correlates with persistent tumor burden and poor immune antitumor response.13 Several recent studies examining the prognostic implications of Tregs in patients with glioblastoma have reported inconsistent results. Heimberger et al14 and Lohr et al9 found no association between Tregs and prognosis in patients with glioblastoma, while Jacobs et al15 reported a moderate, although not statistically significant, inverse association between tumor Tregs and survival. In contrast, Yue et al16 found a significant association between the density of Tregs infiltrating glioblastoma and poor prognosis. Comparing measurements of Tregs from immunohistochemistry (IHC) and flow cytometry across studies is challenging because there are variations in surface and intracellular markers measured and differences in the parent population used to quantify Treg proportions. In this prospective study, we used epigenetic quantitative (q)PCR, a novel methodology to more accurately measure lymphocyte populations, to determine the association between Tregs measured in tumor tissue and peripheral blood and overall survival (OS) in patients with newly diagnosed glioblastoma.