Redirecting coronavirus to a nonnative receptor through a virus-encoded targeting adapter.

Murine hepatitis coronavirus (MHV)-A59 infection depends on the interaction of its spike (S) protein with the cellular receptor mCEACAM1a present on murine cells. Human cells lack this receptor and are therefore not susceptible to MHV. Specific alleviation of the tropism barrier by redirecting MHV to a tumor-specific receptor could lead to a virus with appealing properties for tumor therapy. To demonstrate that MHV can be retargeted to a nonnative receptor on human cells, we produced bispecific adapter proteins composed of the N-terminal D1 domain of mCEACAM1a linked to a short targeting peptide, the six-amino-acid His tag. Preincubation of MHV with the adapter proteins and subsequent inoculation of human cells expressing an artificial His receptor resulted in infection of these otherwise nonsusceptible cells and led to subsequent production of progeny virus. To generate a self-targeted virus able to establish multiround infection of the target cells, we subsequently incorporated the gene encoding the bispecific adapter protein as an additional expression cassette into the MHV genome through targeted RNA recombination. When inoculated onto murine LR7 cells, the resulting recombinant virus indeed expressed the adapter protein. Furthermore, inoculation of human target cells with the virus resulted in a His receptor-specific infection that was multiround. Extensive cell-cell fusion and rapid cell killing of infected target cells was observed. Our results show that MHV can be genetically redirected via adapters composed of the S protein binding part of mCEACAM1a and a targeting peptide recognizing a nonnative receptor expressed on human cells, consequently leading to rapid cell death. The results provide interesting leads for further investigations of the use of coronaviruses as antitumor agents.