Mitochondrial DNA copy number plays opposing roles in T-lymphocyte infiltration of colorectal cancer based on mismatch repair status: new directions for immunotherapy?

Abstract

Researchers have previously reported that mitochondrial DNA copy number (mtDNA-CN) can play different roles in microsatellite instable/mismatch repair-deficient (MSI/dMMR) and microsatellite stable/mismatch repair-proficient (MSS/pMMR) colorectal cancer (CRC). To support malignancy, dMMR CRC relies on glycolysis, while pMMR CRC favors oxidative phosphorylation. However, it is unclear whether mtDNA-CN changes are related to T cell infiltration in CRC. The mtDNA-CN was detected by qRT-PCR in 532 patients, and the expression of CD3 and CD8 in 485 patients was detected by immunohistochemistry. The correlation between mtDNA-CN and the prognosis of CRC patients was further analyzed, and the correlation between mtDNA-CN and T lymphocyte infiltration was also analyzed. Biopsy specimens from the immune checkpoint inhibitors (ICIs) treatment cohort were obtained to verify the correlation between mtDNA-CN and the efficacy of ICIs. The effects of mtDNA-CN and MMR status on gene expression were analyzed by RNA-seq. Our results show that mtDNA-CN has inverse relationships to CRC prognosis in cases with different MMR statuses, potentially inducing the U-shaped association in CRC. The opposing correlations between mtDNA-CN and T lymphocyte infiltration in cases of dMMR CRC and pMMR CRC further suggest that mtDNA-CN might play an important role in CRC development. More importantly, cases of pMMR CRC with lower mtDNA-CN and of dMMR CRC with higher mtDNA-CN can benefit more dramatically from ICIs. Furthermore, RNA-seq revealed a link between the level of mtDNA-CN and T lymphocyte infiltration in CRC cases with different MMR statuses. Our study found a potential relationship between mtDNA-CN and CRC development that differs by MMR status, potentially providing a rationale for the use of mtDNA-CN as both a predictive biomarker and a therapeutic target for ICIs.