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Previous phase I DNA‑vaccine based clinical trials using Mammaglobin‑A (Mam‑A), a human breast tumor associated antigen (TAA), demonstrated that this agent was safe and efficient at treating patients with stage IV breast cancer. The long‑term success of cancer vaccines is limited by the diminished expression of human leukocyte antigen (HLA) class I molecules in the tumor microenvironment. The current study assessed the impact of various selenocompounds on the expression of HLA class I molecules in THP‑1 cells, an apparent proficient antigen that presents a human monocyte‑like cell line, and their eventual activation of MamA2.1 (HLA‑A2 immunodominant epitope of Mam‑A) specific cytotoxic CD8+ T lymphocytes (CTLs). The results revealed that, following treatment with methylselenol producing compounds [methylselenic acid (MSA) and dimethylselenide (DMDSe)], the expression of HLA class‑I was increased and components involved with the antigen presentation machinery of THP‑1 cells were upregulated. Furthermore, CTLs activated by MamA2.1 peptide presenting THP‑1 cells, pre‑treated with MSA and DMDSe, demonstrated an enhanced cytotoxicity in HLA‑A2+/Mam‑A+ AU565 and UACC‑812 breast cancer cell lines when compared with CTLs activated by THP‑1 cells without drug treatment. However, no significant cytotoxicity was observed under similar conditions in HLA‑A2+/Mam‑A‑ MCF‑7 and MDA‑MB‑231 breast cancer cell lines. The results indicated that treatment with methylselenol producing compounds retained antigen‑dependent activation of CD8+ T cells. The data of the current study demonstrated that MSA and DMDSe potentiated effector cytotoxic responses following TAA specific activation of CTLs, indicating their future role as vaccine adjuvants in cancer immunotherapy.