Functional Analysis of Killer Ig-Like Receptor-Expressing Cytomegalovirus-Specific CD8(+) T Cells

Killer Ig-like receptors (KIR) are expressed by human NK cells and T cells. Although Ag-specific cytolytic activity and cytokine production of KIR+ T cells can be inhibited by KIR ligation, the effect of KIR on proliferation is unclear. KIR+ T cells have been reported to have a general proliferative defect. To investigate whether KIR+ T cells represent end-stage dysfunctional T cells, we characterized KIR+ CMV-specific T cells in allogeneic stem cell transplantation patients and healthy donors. In both patients and healthy donors, a significant percentage KIR+ T cells was detected at various time points. All stem cell transplantation patients studied showed KIR expression on CMV-specific T cells, while not all donors had KIR-expressing CMV-specific T cells. From two of the patients and one donor KIR+ CMV-specific T clones were isolated and analyzed functionally. T cells were detected that expressed KIR that could not encounter their corresponding KIR ligands in vivo, illustrating that KIR expression by these T cells was not based on functional selection but a random process. Our data demonstrate that KIR+ T cells are fully functional T cells that are only restricted in effector functions and proliferation upon KIR ligation. The level of KIR-mediated inhibition of the effector functions and proliferation depended on the strength of TCR stimulation. We observed no diminished general proliferative capacity and therefore we conclude that these T cells do not represent end-stage dysfunctional T cells. The Journal of Immunology, 2009, 182: 92-101.