18The current study highlights for the first time cloning, overexpression, purification, and assessing 19 the cytotxcity of the novel interferon epsilon (IFN ), from the Arabian camel Camelus 20 dromedarius, against two human breast cancer cell lines MDA-MB-231 and MCF-7. Full-length 21 cDNA encoding interferon epsilon (IFN) was isolated and cloned from the liver of the Arabian 22 camel, C. dromedarius using reverse transcription-polymerase chain reaction. The sequence 23 analysis of the camel IFN cDNA showed a 582-bp open reading frame encoding a protein of 193 24 amino acids with an estimated molecular weight of 22.953 kDa. A BLAST search analysis revealed 25 that the C. dromedarius IFN shared high sequence identity with the IFN genes of other species, 26 such as Camelus ferus, Vicugna pacos, and Homo sapiens. Expression of the camel IFN cDNA in 27 Escherichia coli gave a fusion protein band of 22.73 kDa after induction with either isopropyl β-D-28 1-thiogalactopyranoside or lactose for 5 h. Recombinant IFN protein was overexpressed in the 29 form of inclusion bodies that were easily solubilized and refolded using SDS and KCl. The 30 solubilized inclusion bodies were purified to apparent homogeneity using nickel affinity 31 chromatography. We examined the effect of IFN on two breast cancer cell lines MDA-MB-231 32 and MCF-7. In both cell lines, IFN inhibited cell survival in a dose dependent manner as observed 33 by MTT assay, morphological changes and apoptosis assay. Caspase-3 expression level was found 34 to be increased in MDA-MB-231 treated cells as compared to untreated cells.35 36 37 virally infected chick cells, and they called it interferon (IFN), a substance that interferes with 43 influenza and vaccinia virus replication [1]. Since then, the efforts to discover, characterize, and 44 develop new interferons as major therapeutic proteins have continued for over 60 years [2]. IFNs 45 are members of a large cytokine family of evolutionarily conserved pleiotropic regulators of cellular 46 functions; they are relatively low-molecular weight signaling proteins (20-25 kDa) usually 47 glycosylated and produced by a variety of cells, such as epithelia, endothelia, stroma, and cells of 48 the immune system [3-5]. The expression of IFNs is induced by a variety of different stimuli 49 associated with viral infections, bacteria, parasites, inflammation, and tumorigenesis [6]. IFNs, 50 therefore, induce a diverse range of biological functions and responses, including cell proliferation 51 and differentiation, inflammation, chemotaxis, immune cell (natural killer cells and macrophages) 52 activation, and apoptosis [7, 8]. The key to understanding these regulatory proteins lies in the 53 recognition of their pleiotropism, overlapping activities, functional redundancies, and side effects 54 [3]. Based on the type of receptors they interact with for signal transduction, IFNs are classified into 55 three major types namely, type I, II, and III, which have different gene and protein structures and 56 biological a...