Peptide-MHC-directed expansion of antigen-responsive CD8 T cells using antigen-presenting scaffolds

The immunotherapeutic approach, adoptive cell transfer (ACT) have in malignant melanoma studies showed clinical durable responses in more than 50% of patients. However, the expansion of tumor infiltrating lymphocytes (TILs) requires extensive ex vivo culturing often at the cost of T cell differentiation and functional capacity.

Most current strategies involve non-specific expansion of bulk TILs, often providing growth preference to co-infiltrated virus-specific T cells and driving an exhausted phenotype of the T cell product. The aim of this thesis is to develop a new technology to expand tumor-reactive T cells, through use of Major histocompatibility complex (MHC)-loaded artificial antigen-presenting scaffolds (Ag-scaffold) to provide the T cells with specific functional stimulation to obtain phenotypic and functional properties to mediate tumor regression.

These scaffolds are built on a dextran-based polysaccharide backbone associated with streptavidin molecules where biotinylated peptide-MHC class I molecules are attached to govern the specific interaction with a specific T cell, and a combination of biotinylated cytokines and co-stimulatory molecules are co-attached to provide stimulation to the T cell to achieve increased functional properties.

The Ag-scaffolds interacts specifically with T cells based on recognition of the peptide-MHC molecule and effectively expand and functionally stimulate specific T cells, while leaving all other T cell specificities untouched. We found that the Ag-scaffold expansion strategy support antigen directed T cell proliferation while retaining a favorable functional profile of the expanded T cells, as the T cells express a multifunctional cytokine profile upon antigen challenge, high CD28 expression, and reduced PD-1 expression.

Importantly, numerous different antigen-specific CD8 T cell populations can be stimulated in a single culture, as each T cell specificity is expanded with individual Ag-scaffolds carrying MHC class I molecules comprising one peptide specificity. In this way, broad tumor target recognition can be obtained, leading to a T cell product with increased tumor-cell killing potential.

This expansion technology could with great advantage be used in ACT, to increase the anti-tumor effect of the transferred T cell product, as all of the achieved T cell characteristics are of significant importance for in vivo tumor cell recognition following ACT of expanded T cell products.