Acquired Resistance to Anti-PD-1 Therapy Induced by Mutant PSMB5 Down-Regulation Antigen Processing and Presentation in Non-Small Cell Lung Cancer

Objective To explore the role of mutant PSMB5 in required resistance to immunotherapy in non-small cell lung cancer (NSCLC).

Methods Comparison of RNA expression was performed on six pairs of pre- and post-treatment tumor tissues from patients who received immunotherapy. CD8 expression levels were detected by immunohistochemistry in paired tumor samples. PD-1⁺CD8⁺ T cells were sorted through flow cytometry for TCR sequencing. Cell-free DNA (cfDNA) was extracted for genetic analysis. We co-cultured tumor cells with mutant or wide PSMB5 with T cells to explore the impact of PSMB5 on the immune response.

Results Gene set enrichment analysis (GSEA) showed that the antigen presentation ability of mutant PSMB5 from baseline was lower than wild-type PSMB5 after resistance to immunotherapy, as well as the cytolytic activity score of the tumor microenvironment. The immunohistochemical results showed that CD8 expression in mutant PSMB5 tumors was significantly reduced compared with wild type. Clonal analysis of dynamic cfDNA and PD-1⁺CD8⁺ TCR showed immune ignoring with the emergence of PSMB5 clones. In vitro coculture of immune cells with mutant or wide-type PSMB5 tumor cells showed the mutant PSMB5 failed to stimulate the expansion of T cells, following flow cytometry analysis indicated a lower proportion of 4-1BB in the mutant PSMB5 stimulated CD8 T cells.

Conclusions We identified that mutant PSMB5 was associated with the dysfunction of the proteasome B5 subunit and impaired the function and quantity of lymphocytes in the tumor microenvironment.