Engineered Exosomes Expressing HLA and Co-Stimulatory Molecules to Generate Antigen-Specific CD8+ T Cells for Adoptive Cell Therapy

S.K and H.-J.S. contributed equally for this works

Dendritic cell-derived exosome (DEX) has been known as an efficient stimulator of T cells. However, the production of sufficient DEX remains a barrier to broad utility for immunotherapy. In this study, we engineered K562 cells expressing triple-co-stimulatory signals (CD80, 4-1BBL, and CD83) with HLA-A2 as an AAPC. Specifically, CD137L (4-1BBL) is an ideal signaling molecule for long-term propagation of CD8+ T cells, and the addition of other co-stimulatory molecules, such as CD80 and CD83, is used to support the expansion of naive T cell subsets. DC-derived exosomes display immunologically important molecules such as HLA and co-stimulatory molecules. Likewise, CoEX-A2 expressed high levels of HLA-A2, CD80, CD83, and CD137L (41BBL) and mediate strong, antigen-specific CD8+ T lymphocyte activation. The stimulation of freshly isolated peripheral CD8+ T cells with the appropriate antigen specificity observed here was likely made possible by the use of the sensitive ELISPOT assay. Viral or tumor protein-pulsed exosomes can directly stimulate CD8+ T cell proliferation and differentiation into CTLs in vitro. In addition, exosomes can be taken up by both CD8+ T cells and K562 cells. Meanwhile, K562 cells that have taken up exosomes can also stimulate CD8+ T cells, which may be due to the higher levels of HLA-A2, CD80, CD83, and 41BBL expression observed on exosomes. Therefore, the CD8+ T cell antigen-specific expansion observed in our cultures is likely the result of coated CoEX-A2s working directly or in a cross-dressed manner. The results suggest that these novel exosomes may provide a crucial source to generate antigen-specific CD8+ T cells for adoptive cell therapy against viral infection and tumors.