Abstract: The present invention provides an isolated and purified protein derived from Bacillus thuringiensis subspecies thuringiensis, having a molecular weight of approximately 20 kDa of SDS-PAGE, said protein having the partial amino acid sequence shown in SEQ ID No. 1, and wherein said protein displays cytotoxic effects against tumor cells. Also provided is a method of treating a neoplastic cell comprising administering a therapeutically effective dose of the composition of the present invention to said cell, and a method of activating macrophages, comprising administering a therapeutically effective dose of the composition of the present invention to said macrophages.