Whole-virus vaccine development by continuous culture on a complementing host.

We have evaluated an adaptive strategy for generating whole-virus vaccines using a bacteriophage model. Wildtype phage T7 was cultivated in a two-stage continuous stirred-tank reactor (CSTR) utilizing a recombinant E. coli host that constitutively expressed T7 RNA polymerase, an essential enzyme of the early viral metabolism. Over the course of 180 generations a diversity of phage variants emerged, outgrew the wildtype, and were subsequently eclipsed by yet fitter variants, based on host-ranges, restriction patterns, and one-step growth responses of isolated clones. The fittest variant, which required complementation by the recombinant host in order to grow, deleted at least 12 percent of its genome and replicated twice as fast as the wildtype. Moreover, this variant was immunogenically indistinguishable from the wildtype, based on cross-reactivities of antisera raised against both. These results suggest the feasibility of the proposed strategy for the development of safe whole-virus vaccines.