HLA class II molecules presenting IDO1-derived peptides (IDO1-HLA-II complex)

HLA class II molecules presenting IDO1-derived peptides represent a specialized immune target consisting of the major histocompatibility complex (MHC) class II proteins (HLA-DR, HLA-DQ, or HLA-DP) bound to specific peptide fragments derived from the indoleamine 2,3-dioxygenase 1 (IDO1) enzyme. IDO1 is an intracellular enzyme that catalyzes the rate-limiting step of tryptophan degradation into kynurenine, a process that creates a profoundly immunosuppressive tumor microenvironment by depleting essential nutrients for T cells and producing toxic metabolites (NIH, 2015). While IDO1 itself is an intracellular enzyme, its peptides are processed and presented on the cell surface via HLA class II molecules, particularly in response to interferon-gamma (IFN-γ) stimulation (Andersen et al., 2015). This presentation allows the immune system, specifically CD4+ T helper cells, to recognize and target IDO1-expressing cells, which include both malignant tumor cells and regulatory immune cells like myeloid-derived suppressor cells (MDSCs) and dendritic cells (IO Biotech, 2024). Therapeutic strategies, such as the peptide vaccine imsapepimut (IO-102), aim to exploit this target by inducing a robust T-cell response that can eliminate these immunosuppressive hubs within the tumor, thereby enhancing the efficacy of other immunotherapies like PD-1/PD-L1 inhibitors (Kjeldsen et al., 2021).

Other names

IDO1-MHC-II complexIDO1-derived peptide-HLA class II complexIDO1-HLA-DR complexIDO1-HLA-DQ complexIDO1-HLA-DP complexIDO-specific T-cell target

Vaccination with IDO1-derived peptides (e.g., imsapepimut) stimulates the expansion of CD4+ T helper cells that specifically recognize IDO1-derived peptides presented by HLA class II molecules on the surface of IDO1-expressing cells. This recognition leads to the direct lysis of tumor cells and immunosuppressive immune cells (such as dendritic cells and macrophages) and the release of pro-inflammatory cytokines, thereby reversing the immunosuppressive tumor microenvironment and enhancing overall anti-tumor immunity (Andersen et al., 2015; Kjeldsen et al., 2021).