Phenotypical and functional characterization of Herpesvirus saimiri-immortalized human major histocompatibility complex class II-deficient T lymphocytes.

CD8+ T lymphocytes from two unrelated cases of MHC class II deficiency were immortalized in vitro using Herpesvirus saimiri. In both cases, a lack of expression of surface MHC class II molecules was ascertained, whereas variable defects were shown for MHC class I, CD74 (invariant chain) and LAG-3 (an MHC class II ligand). The functional analysis of both H. saimiri-immortalized T-cell lines revealed the existence of a proliferation impairment in response to anti-CD3 but not to other surface or transmembrane stimuli. Further characterization of this functional defect indicated that it was not associated with impaired early activation events (like calcium flux) but, rather, with certain late events, like the induction of IL-2. H. saimiri-immortalized T cells may be valuable in studying the biological role of MHC class II molecules in activated human T cells.