CHARACTERIZATION OF THE EXPRESSION AND IMMUNOGENICITY OF POLIOVIRUS REPLICONS THAT ENCODE SIMIAN IMMUNODEFICIENCY VIRUS SIV(MAC)239 GAG OR ENVELOPE SU PROTEINS

The effectiveness of the poliovirus vaccines to induce both systemic a nd mucosal immunity has prompted the development of this virus as a ve ctor in which to express foreign proteins. Our laboratory has previous ly reported on the construction and characterization of poliovirus gen omes that encode HIV-1 proteins (Porter DC, et al.: 3 Virol 1996;70:26 43-2649). To develop this system further, we have constructed poliovir us genomes, referred to as replicons, which encode the SIV(mac)239 Gag or Env SU in place of the poliovirus capsid gene (Pi). Since the repl icons do not encode capsid proteins, they are encapsidated into poliov irions by passage with a recombinant vaccinia virus, WP1, which provid es the poliovirus capsid proteins in trans. Using this system, we have derived stocks of the encapsidated replicons which encode the SIV(mac )239 Gag or Env SU protein. Infection of cells with the replicon that encodes SIV(mac)239 Gag resulted in the expression of a 55-kDa protein that was released from the infected cells. Analysis of the sedimentat ion of the released proteins by sucrose density gradient centrifugatio n revealed that the protein was released from the cell in the form of a virus-like particle. Infection of cells with the replicons encoding the SIV(mac)239 Env SU resulted in the expression of a 63-kDa protein, corresponding to the molecular mass predicted for the nonglycosylated SIV(mac)239 SU protein. A second protein with a molecular mass greate r than 160 kDa was also immunoprecipitated. After enzymatic deglycosyl ation, this protein migrated at a molecular mass consistent with that for an Env SU diner. Analysis of the medium from cells infected with t he replicon encoding SIV(mac)239 Env SU revealed the presence of a pro tein of molecular mass 85-90 kDa, possibly representing a fragment of the SIV(mac)239 Env SU protein. To determine the immunogenicity of the replicons encoding SIV(mac)239 Gag or Env SU, transgenic mice that ex press the human receptor for poliovirus, and are thus susceptible to p oliovirus, were immunized via the intramuscular route. A serum antibod y response to SIV envelope was detected following booster immunization , establishing that the encapsidated replicon was immunogenic. Finally , we demonstrate that the replicons have the capacity to infect periph eral blood mononuclear monocytes/macrophages, suggesting that this cel l is a possible target for in vivo infection. The results of our studi es, then, lend further support for the development and application of recombinant poliovirus replicons in a vaccine strategy.