The invention provides placental perfusate cells, CD56+, CD16- placental intermediate natural killer cells, and combinations of natural killer cells isolated from placental perfusate and natural killer cells isolated from umbilical cord blood which is isolated from the placenta from which said placental perfusate is obtained. Further provided herein are such cells and cell combinations for use in a method of suppressing the proliferation of tumor cells, in particular for the treatment of an individual having a tumor. Also provided herein are composition comprising isolated CD56+, CD16- natural killer cells which are isolated from placental perfusate and wherein the natural killer cells comprise at least 50% of cells in the composition.
