Cell-surface display of E7 antigen from human papillomavirus type-16 in Lactococcus lactis and in Lactobacillus plantarum using a new cell-wall anchor from lactobacilli

The human papillomavirus type-16 (HPV-16) E7 protein is considered a major viral oncoprotein involved in cervical cancer (CxCa) and a potential candidate for the development of a vaccine against this neoplasia. Here, two lactic acid bacteria (the model one Lactococcus lactis and a probiotic one Lactobacillus plantarum) were engineered to deliver an E7 mutant protein (E7mm), which has a reduced transforming activity and consequently, could fit better to therapeutic use in humans than the native form of E7. An efficient cell-surface display of E7mm was obtained in L. lactis using an expression cassette encoding a precursor composed of (i) the signal peptide and the first 15 amino acids of the mature part of the lactococcal Usp45 protein; (ii) E7mm and (iii) the cell-wall anchor of the Streptococcus pyogenes M6 protein (CWA_M6). This hybrid precursor was produced but not cell-wall anchored in Lb. plantarum. We thus replaced CWA_M6 by the cell-wall anchor of a Lb. plantarum protein which allows an efficient cell-wall anchoring of E7mm in this bacterium. The E7mm production and cell-surface display in both L. lactis and a probiotic bacterium, Lb. plantarum, represent one more step towards the development of a safe and effective treatment against CxCa.