Background Checkpoint proteins regulate the immune system. Breast cancer (BC) cells exploit the up-regulation or down-regulation of these proteins to evade anti-tumor immune responses. Soluble forms of immune checkpoint molecules (ICM) can be measured in human plasma. However, their biological and clinical significance remains mostly unknown. The aim of the present analysis was to measure the levels of pre-treatment ICM in newly diagnosed BC patients (pts) and compare them to healthy controls.
Methods Soluble forms of ICM, as well as cytokines and chemokines, were measured using Multiplex® bead array and ELISA technologies. Plasma samples from 98 BC pts and 45 healthy controls were analyzed for each protein. Data was prospectively obtained. Measured levels were compared between BC pts and healthy controls using a non-parametric test (Mann-Whitney).
Results Soluble stimulatory molecules GITR (p < 0.000002), GITRL (p < 0.007), CD27 (p < 0.002), CD28 (p < 0.003), CD40 (p < 0.003), CD80 (p < 0.009), ICOS (p < 0.0006) as well as inhibitory molecules PD-L1 (p < 0.0000001), CTLA-4 (p < 0.005), TIM-3 (p < 0.00006), HVEM (p < 0.00002) and TLR-2 (p < 0.05) levels were significantly lower in early BC pts compared to healthy controls. When analyzed according to BC characteristics (TNBC vs. non-TNBC, tumor size, stage, nodal status and age) no significant difference was detected between the soluble levels of these ICM and between the different subsets. Additionally, serum levels of CXCL5 (p < 0.000001), CCL23 (p < 0.04), IL-16 (p < 0.00005), interferon-a (p < 0.03) and IL1-RA (p < 0.03) were significantly lower compared to healthy controls. Serum CX3CL1 or fractalkine (p < 0.024465) was significantly higher compared to healthy controls.
Conclusions In the current study, we identified low levels of both stimulatory and inhibitory soluble immune checkpoint molecules in newly diagnosed, non-metastatic BC pts compared to healthy controls. These results indicate that early BC is associated with a down-regulation of both soluble stimulatory and inhibitory immune-checkpoint pathways. Newly diagnosed early BC pts have a generalized immune-suppression independent of subtype and stage, which, to our knowledge, is the first study to describe soluble immune checkpoints in early BC pts.
Trial Registration N/A
Ethics Approval The study was approved by The Research Ethics Committee, Faculty Health Sciences, University of Pretoria, approval number 517/2017.
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