New (type of) CoViD vaccine

The protective effect of established COVID-19 vaccines is initially very robust, but wanes relatively quickly. This limitation imposes a need for periodic booster shots, which drives vaccine hesitation.

In contrast, an innovative vector vaccine developed at the Helmholtz Center for Infection Research (HZI) presents a compelling alternative. It elicits prolonged immune response in animal models, and maintains its efficacy over extended time.

The concept employs an animal cytomegalovirus (MCMV; murine cytomegalovirus) as the vector that expresses and delivers the coronavirus spike protein information. Crucially, this vector poses no threat to humans, enhancing the vaccine's safety profile.

In 2022, researchers from the department Viral Immunology headed by Prof. Luka Cicin-Sain at the Helmholtz Center for Infection Research reported on the novel vector vaccine for the first time. The promising immunogenic profile of the MCMV-based vaccine has now been shown to protect against disease.

A recent publication with the involvement of national and international research partner institutions, such as the Max Delbrück Center in Berlin and the University of Rijeka in Croatia, demonstrates lasting and broad immune responses and antiviral protection in the mouse model. The work is published in the journal Frontiers in Immunology.

Using an animal cytomegalovirus that cannot replicate in human cells as a vector is a clever move, because it combines high immunogenicity of a natural infection with the safety of a non-replicating vector.

In vector vaccines, viruses are used as vehicles to introduce building blocks of the pathogen against which the vaccination is directed into the human body. In vaccines against COVID-19, the gene for the blueprint of the spike protein that anchors the coronavirus to the host cells is integrated into the vector viruses.

Murine CMV is considered safe for humans

There are reasonable concerns about the safety of vaccines based on some vector viruses. Human viruses that are used as vectors have to be attenuated by genetic modifications. The MCMV, however, can be used as is, because cytomegaloviruses are highly host-selective.

This means that the MCMV can only replicate in mouse cells, but not in human ones, as two of the first authors, Dr. Kristin Metzdorf and Dr. Henning Jacobsen explain. For this reason, among others, MCMV is ideal as a vector for vaccines.