The present invention provides a method for enhancing the immune function of leukocytes in a subject, which comprises the steps of: (a) isolating leukocytes from the subject; (b) treating the leukocytes obtained from step (a) with an inhibitor of the endoplasmic reticulum calcium ion pump; and (c) administrating the treated leukocytes obtained from step (b) back to the subject. A pharmaceutical composition for enhancing the immune function of leukocytes in a subject and a method for preparing said pharmaceutical composition are also provided.