Induction of T cell tolerance to a protein expressed in the cytoplasm through retroviral-mediated gene transfer.

Abstract

Host immune responses to foreign gene products have been shown to lead to the elimination of genetically modified cells, and are a major barrier to successful therapeutic gene therapy. We have shown that immunological tolerance to retrovirally transduced cell surface proteins can be induced by expressing the gene encoding these products in bone marrow derived cells. Here, we investigate if expression of foreign gene products in bone marrow derived cells can be used to induce tolerance to cytoplasmic proteins. Balb/c mice were reconstituted with syngeneic bone marrow cells transduced with retrovirus carrying the gene encoding enhanced green fluorescent protein (eGFP), or mock-transduced bone marrow cells. After reconstitution, mice were immunized with cells expressing eGFP, and T cells were tested for the ability to kill eGFP-expressing targets in in vitro cytotoxic T lymphocyte (CTL) assays. T cells from Balb/c mice reconstituted with mock-transduced bone marrow were able to kill target cells expressing eGFP. In contrast, T cells from mice reconstituted with eGFP-transduced bone marrow were unable to kill targets expressing eGFP. In addition, we observed that T cell responses to eGFP in C57BL/6 mice were minimal even under highly immunogenic conditions. These data suggest that expression of foreign gene products in bone marrow derived cells is capable of inducing T cell tolerance to proteins expressed exclusively in the cytoplasm.