The family of Paramyxoviruses includes common disease agents such as measles, mumps and parainfluenza. Live recombinant vaccines against these diseases have greatly contributed to their reduction, especially in developed countries. The use of live recombinant viruses in vaccines thus represents a well-established method of conferring immunity against the pathogen.

With the advent of reverse genetics these viruses can also be used to introduce foreign genes, encoding foreign antigens, into their recombinant genome. For instance, insertion of an RNA segment into the recombinant measles genome encoding for an immune stimulatory protein derived from Plasmodium falciparum or HIV antigens could result in immune responses that could protect against malaria and AIDS. In such cases, because the recombinant viruses retain their high immunogenic properties, they induce a strong humoral and cellular response against both their own (measles) and the foreign (malaria or HIV) proteins. Crucell holds the exclusive rights to a patented cloning technique to engineer paramyxoviruses.

A plasmid and cell-line based system was developed to allow the easy insertion of heterologous genes into the measles virus (MV) vaccine genome and rescue of replication competent live recombinant vaccine candidate. The plasmids can accommodate single or multiple gene insertions before the recombinant viruses are rescued using quality-controlled mammalian cells. Additionally, a routine in-house developed method for small- and large-scale production of the recombinant measles vaccine is available.