Circulating CD3⁺HLA-DR⁺ Extracellular Vesicles as a Marker for Th1/Tc1-Type Immune Responses

Extracellular vesicles (EVs) are known to contain unique proteins that reflect the cells of origins. Activated T cells are reported to secrete various EVs. To establish T cell subset-specific biomarkers, we performed proteomic analysis with Th1- and Th2-derived EVs and identified HLA-DR as a Th1-dominated EV membrane protein. We designed a measurement system for CD3⁺CD4⁺, CD3⁺CD8⁺, and CD3⁺HLA-DR⁺ EVs to specifically determine EV subpopulations derived from CD4⁺, CD8⁺, and Th1-type T cells, respectively. In vitro analysis showed that CD3⁺CD4⁺ EVs and CD3⁺CD8⁺ EVs were selectively secreted from activated CD4⁺ and CD8⁺ T cells, respectively, and that CD3⁺HLA-DR⁺ EVs were actively secreted from not only Th1 but also activated CD8⁺ T (probably mostly Tc1) cells. To evaluate the clinical usefulness of these EVs, we measured the serum levels in patients with inflammatory diseases, including Epstein-Barr virus (EBV, n = 13) infection, atopic dermatitis (AD, n = 10), rheumatoid arthritis (RA, n = 20), and osteoarthritis (OA, n = 20) and compared the levels with those of healthy adults (n = 20). CD3 CD4 EVs were significantly higher in all of EBV infection, AD, RA, and OA while CD3⁺CD8⁺ EVs were higher in EBV infection, lower in RA, and not different in AD and OA relative to the control. The levels of CD3⁺HLA-DR⁺ EVs were markedly higher in EBV infection and significantly lower in AD. The results suggest that these EV subpopulations reflect in vivo activation status of total CD4⁺, total CD8⁺, and Th1/Tc1-type T cells, respectively, and may be helpful in T cell-related clinical settings, such as cancer immunotherapy and treatment of chronic infection, autoimmune diseases, and graft-versus-host disease.