The killing activity of cord blood mononuclear cells (cMNC) against cytomegalovirus (CMV)-uninfected and -infected fibroblasts was comparable to that of adult peripheral blood mononuclear cells (aPBMC). The killing activity of cMNC against K562 cells was significantly lower compared with that of aPBMC. Treatment of cMNC and aPBMC with interleukin-2 (IL-2), IL-12 or IL-15 significantly enhanced killing activity against K562 cells and CMV-uninfected and -infected cells. By comparison of cMNC with aPBMC, killing activity against the K562 cells of cMNC was augmented to the level of aPBMC when cultured with IL-2, IL-12 or IL-15. The killing activity of cMNC against CMV-uninfected and -infected fibroblasts did not increase to the level of adult PBMC by treatment with IL-2, IL-12 or IL-15. These data suggest that cord blood contains a functionally different NK cell subpopulation than that among adult NK cells.

These data suggest that lymphocytes cultured with IL-2 or IL-12 mediate killing against HHV-6-infected cells and killing of HHV-6-infected cells was through apoptosis. Fas-Fas ligand interaction is one pathway by which HHV-6-infected cells are killed. Killing of HHV-6-infected cells by NK cells activated by cytokines may play a role in the recovery from HHV-6 infection in vitro.