Differential expression of CD8 defines phenotypically distinct cytotoxic T cells in cancer and multiple sclerosis

Abstract

Background: Cytotoxic T lymphocytes take on a leading role in many immune-related diseases. They function as key effector immune cells fighting cancer cells, but they are also considerably involved in autoimmune diseases. Common to both situations, CD8⁺ T cells need to adapt their metabolism and effector function to the harsh and nutrient-deprived conditions of the disease-associated microenvironment.

Methods: We used an in vitro starvation as well as rapamycin treatment protocol mimicking nutrient deprivation to generate CD8^Low versus CD8^High T cells and performed FACS-Sorting followed by transcriptomic profiling of the cytotoxic T cell subsets. Prominent markers identified in the CD8^Low versus the CD8^High T cells were then used to investigate the presence of these cell subsets in immune-related human diseases. Employing cancer tissue microarrays and PhenOptics multispectral imaging as well as flow cytometry, we studied these CD8⁺ T cell subsets in cancer and relapsing-remitting multiple sclerosis patients.

Results: Starvation induced a decreased expression of CD8, yielding a CD8^Low T cell subpopulation with an altered transcriptomic signature and reduced effector function. CD8^Low T cell showed enhanced ST2L and IL6ST (CD130) expression compared to CD8^High T cells which expressed elevated KLRD1 (CD94) and granzyme B levels within the tumour microenvironment (TME). Spatial analysis revealed the presence of CD8^High T cells in close proximity to tumour cells, while the CD8^Low T cells resided at the tumour boundaries. Importantly, the number of tumour-infiltrating CD8^Low T lymphocytes correlated with a poor prognosis as well as with enhanced cancer progression in human mammary carcinoma. We also found a reduced frequency of CD8^Low T lymphocytes in a cohort of relapse (disease active) multiple sclerosis patients compared to healthy subjects during immune cell starvation in vitro.

Conclusions: In summary, our data show that functionally distinct cytotoxic T lymphocytes can be identified based on their expression of CD8. Indicating a more general role in CD8 T cell immunity, these cells may play opposing roles in the TME, and also in the pathophysiology of autoimmune diseases such as multiple sclerosis.

Keywords: CD8+ T cells; mTOR; multiple sclerosis; multispectral imaging; tumour immunity.