Generation of Recombinant Rotaviruses Expressing Human Norovirus Capsid Proteins.

Rotavirus, a segmented double-stranded RNA virus of the family, is a primary cause of acute gastroenteritis in young children. In countries where rotavirus vaccines are widely used, norovirus (NoV) has emerged as the major cause of acute gastroenteritis. Towards the goal of creating a combined rotavirus-NoV vaccine, we explored the possibility of generating recombinant rotaviruses (rRVs) expressing all or portions of the NoV GII.4 VP1 capsid protein. This was accomplished by replacing the segment 7 NSP3 open reading frame with a cassette encoding, sequentially, NSP3, a 2A stop-restart translation element, and all or portions (P, P2) of NoV VP1. In addition to successfully recovering rRVs with modified SA11 segment 7 RNAs encoding NoV capsid proteins, analogous rRVs were recovered through modification of the segment 7 RNA of the RIX4414 vaccine strain. An immunoblot assay confirmed that rRVs expressed NoV capsid proteins as independent products. Moreover, VP1 expressed by rRVs underwent dimerization and was recognized by conformational-dependent anti-VP1 antibodies. Serially passaged rRVs that expressed the NoV P and P2 were genetically stable, retaining additional sequences of up to 1.1 kbp without change. However, serially passaged rRVs containing the longer 1.6-kb VP1 sequence were less stable and gave rise to virus populations with segment 7 RNAs lacking VP1 coding sequences. Together, these studies suggest that it may be possible to develop combined rotavirus-NoV vaccines using modified segment 7 RNA to express NoV P or P2. In contrast, development of potential rotavirus-NoV vaccines expressing NoV VP1 will need additional efforts to improve genetic stability. Rotavirus (RV) and norovirus (NoV) are the two most important causes of acute viral gastroenteritis (AGE) in infants and young children. While the incidence of RV AGE has been brought under control in many countries through the introduction of universal mass vaccination with live attenuated RV vaccines, similar highly effective NoV vaccines are not available. To pursue the development of a combined RV-NoV vaccine, we examined the potential of using RV as an expression vector of all or portions of the NoV capsid protein VP1. Our results showed that by replacing the NSP3 open reading frame in RV genome segment 7 RNA with a coding cassette for NSP3, a 2A stop-restart translation element, and VP1, recombinant RVs can be generated that express NoV capsid proteins. These findings raise the possibility of developing new generations of RV-based combination vaccines that provide protection against a second enteric pathogen, such as NoV.