Peripheral blood-derived virus-specific memory stem T cells mature to functional effector memory subsets with self-renewal potency.

Memory T cells expressing stem cell-like properties have been described recently. The capacity of self-renewal and differentiation into various memory/effector subsets make them attractive for adoptive T cell therapy to combat severe virus infections and tumors. The very few reports on human memory stem T cells (T(SCM)) are restricted to analyses on polyclonal T cells, but extensive data on Ag-specific T(SCM )are missing. This might be due to their very low frequency limiting their enrichment and characterization. In this article, we provide functional and phenotypic data on human viral-specific T(SCM), defined as CD8(+)CD45RA(+)CCR7(+)CD127(+)CD95(+). Whereas <1% of total T cells express the T(SCM) phenotype, human CMV-specific T(SCM) can be detected at frequencies similar to those seen in other subsets, resulting in ∼ 1 /10,000 human CMV-specific T(SCM). A new virus-specific expansion protocol of sort-purified T(SCM) reveals both upregulation of various T cell subset markers and preservation of their stem cell phenotype in a significant proportion, indicating both self-renewal and differentiation potency of virus-specific T cells sharing their TCR repertoire. Furthermore, we describe a simplified culture protocol that allows fast expansion of virus-specific T(SCM) starting from a mixed naive T/T(SCM) pool of PBLs. Due to the clinical-grade compatibility, this might be the basis for novel cell therapeutic options in life-threatening courses of viral and tumor disease.