Regulation of PD-L1 expression in stimulated antigen specific CD8+ T cells by immunoglobulin 4 (IgG4)

Abstract

Abstract Background Many studies have focused on finding a correlation between the responsiveness to immune checkpoint (IC) therapies and the expression level of IC markers. Here, we report the studies on the expression of co-inhibitory molecules on healthy donor peripheral mononuclear cells (PBMC). We co-cultured PBMCs from different donors with recall antigen peptide to analyze the responses to PD-1 blockade antibody treatment. We have used our previously reported optimized recall antigen assay in which the expanded antigen specific CD8+ T cells (TET+) were measured as a readout after the peptide stimulation. Interestingly, the IgG4 appears to reduce the TET+ cell population. To further study this potential effect of IgG4, we conducted a series of immune-profiling studies by comparing TET+ gated and TET− CD8+ gated T cells. Results and conclusion Healthy donor PBMCs were stimulated with recall peptide alone, or peptide plus either PD-1 blockade, or IgG4 and evaluated the PD-1, PD-L1, Tim-3, and Lag-3 expressions in either T cells or in monocytes. We then compared such expressions in TET+ and TET− CD8+ T cells. Unexpectedly, IgG4 isotype control treatment was associated with upregulated PD-L1 expression only in the TET+ CD8+ T cells. To confirm whether the decrease of TET+ population in our assay was caused by the up regulation of PD-L1, we blocked the PD-1 signal transduction pathway by treating the cells with a validated PD-1 blocking antibody. As a result of PD-1 blockade, the expansion of TET+ cell population was recovered by anti-PD-1 blocking treatment. Taken together, these results suggest that IgG4 treatment with recall peptide up regulates PD-L1 expression and therefore reduces the expansion of antigen specific CD8+ T cells in some donors.