Lymphocyte-mediated cytotoxicity in humans during revaccination with vaccinia virus

Fifteen healthy human volunteers were revaccinated with vaccinia virus. Blood samples (4 to 7) were obtained during the 3 weeks after revaccination. Peripheral blood lymphocytes were washed extensively and tested for cytotoxicity against vaccinia-infected autologous and/or homologous skin fibroblasts. Without addition of antibodies, peak levels of killing were observed on days 7 to 9. The killing did not depend on common HLA markers. On days with peak activity, extensively washed lymphocytes showed higher levels of killing than normally washed lymphocytes. By cell separation experiments, the cell most active in killing proved to be a nonadherent, non-phagocytizing lymphocyte with Fc receptors. Serum antibodies tested in two sensitive serological assays peaked on days 14 to 17. The question of whether the killing observed is dependent on or independent of antibodies is not clarified in the present study.