BACKGROUND: Suppressing inhibitory molecules such as signal transducer and activator of transcription (STAT) 3 in dendritic cells (DCs) and eliciting an effective immune response via T cells against antigens (Ags) produced exclusively by malignant cells represents the major method in the process of DC-based vaccines. Pyrimethamine (Pyri), a potential STAT3 inhibitor, is an antimalarial drug that is employed for ameliorating various cancers, including breast cancer. The present study aimed to investigate T cell-mediated responses after DCs and T cells co-culturing using breast cancer lysate (BCL) and Pyri to inhibit STAT3 protein in the DCs for the first time. METHOD: Employing the Magnetic Activated Cell Sorting (MACS) technique, monocytes were separated from peripheral blood mononuclear cells (PBMCs). After monocytes were differentiated into DCs, they were divided into two groups: mature dendritic cells (mDCs) (received lipopolysaccharide (LPS) and BCL) and Pyrimethamine-treated mature dendritic cells (Pyri-mDCs) (incubated with LPS, BCL, and Pyri). Flow cytometry was used to examine the surface markers related to DC phenotype in both groups of DCs. Consequently, RT-PCR was employed to investigate the expression of genes linked to inflammatory and anti-inflammatory cytokines in mDCs and Pyri-mDCs as well as related genes to T cell response after DC/T cell co-culturing. RESULTS: Our outcomes revealed that Pyri-mediated STAT3 inhibition in DCs upregulates and downregulates the expression of inflammatory and anti-inflammatory cytokines' genes. Furthermore, co-culture of Pyri-mDCs with autologous T cells downregulated T helper (Th) 2 and regulatory T cell (Treg) responses and augmented Th1 activation compared to T cell cultured along with mDCs. CONCLUSION: Overall, our research points to Pyri-mediated STAT3 suppression in DCs loaded with BCL as a potentially effective therapeutic method for inducing effective T cell responses
nevertheless, additional investigation is required to evaluate the effectiveness of this approach especially in pre-clinical settings.