Effect of Aging on NK Cell Population and Their Proliferation at Ex Vivo Culture Condition by Gounder, Sellamuthu Subbanna, Abdullah, Basri Johan Jeet, Radzuanb, Nur Ezzati Izyan Mohd, Zain, Farah Dalila Mohd, Sait, Nurhidayah Mohamad, Chua, Corine, Subramani, Baskar