A novel tumor antigen derived from enhanced degradation of bax protein in human cancers

Area of Science:

• Immunology
• Oncology
• Molecular Biology

Background:

• Cancer cells often evade apoptosis, leading to increased survival and resistance to chemotherapy.
• Defects in Bax protein expression, due to mutations or proteasomal degradation, limit apoptosis in cancer cells.

Purpose of the Study:

• To investigate if Bax peptides, resulting from abnormal proteasomal degradation in cancer, can be presented by HLA class I molecules to CD8(+) T cells.
• To identify and characterize T cell responses against such Bax-derived tumor antigens.

Main Methods:

• Generation of T cells from healthy donors against pooled Bax peptides.
• Isolation and characterization of specific CD8(+) T cell clones, including their peptide and HLA restriction.
• Testing the reactivity of isolated T cell clones against various cancer cells and normal cells.

Main Results:

• A CD8(+) T cell clone (KSIVB17) was isolated, recognizing the Bax(136-144) peptide presented by HLA-A*0201.
• KSIVB17 effectively recognized and killed HLA-matched cancer cells, including chronic lymphocytic leukemia (CLL) cells, but not normal cells.
• T cell reactivity correlated with observed Bax protein degradation patterns in cancer cells.

Conclusions:

• Abnormally degraded Bax peptides can serve as tumor antigens for T cell-mediated cancer recognition.
• Bax degradation products represent potential immune targets, particularly in cancers like CLL where enhanced degradation is linked to poor prognosis.
• This suggests a novel strategy for tumor antigen discovery based on regulatory proteins with altered degradation in cancer.