Stable integration and expression of the Plasmodium falciparum circumsporozoite protein coding sequence in mycobacteria.

The DNA coding for the circumsporozoite protein of Plasmodium falciparum (CSP; aa 1-412) has been placed under the control of the mycobacterial promoter derived from the gene encoding the 64-kDa antigen of Mycobacterium bovis-BCG. This expression cassette was cloned into pJRD184, an Escherichia coli multicloning site vector, together with the kanamycin resistance gene from Tn903 and the attachment site and integrase gene from the temperate mycobacteriophage FRAT1. One of the resulting plasmids, pNIV2173, introduced by electroporation into both Mycobacterium smegmatis and M. bovis-BCG, integrated at a specific site in the genome of each recipient. Recombinants expressed immunoreactive polypeptides, ranging in size from 62 to 43 kDa, at a level of about 1% of total soluble proteins. Part of this material was present in the culture medium indicating that mycobacterial recombinants were able to secrete the CSP. The M. smegmatis and M. bovis-BCG recombinants, transformed with pNIV2173 and grown in absence of antibiotic, were followed for more than 400 and 50 generations respectively. Over this time span, neither DNA rearrangement nor loss of expression was observed. Inoculation of the recombinant BCG to mice did not induce humoral response to CSP nor proliferative response to CSP Th2R CD4+ T lymphocyte epitope.