Messenger RNA vaccines that are currently used for COVID-19 offer some protection against the disease including omicron, especially for individuals who have received boosters. But manufacturing cost of these vaccines and the need for ultra-cold refrigeration are some reasons for their low availability in low and middle-income countries.
This is where protein-based COVID-19 vaccines that are emerging could change the game. Two candidates of protein-based vaccines are developed at Boston Children’s Hospital.
From cost perspective, scale of manufacture of protein-based vaccines is potentially much cheaper than mRNA vaccines and may not require ultra-cold storage. This would help to provide vaccines to parts of the world such as Africa where vaccination rates is currently very low.
Currently used vaccines for COVID-19 are based on full SARS-CoV-2 spike protein. On the other hand, vaccine candidates developed at Boston Children’s Hospital use only a portion of the spike, called the receptor-binding domain (RBD).
The RBD part latches onto the angiotensin-converting enzyme receptors of our cells. But the two vaccines use very entirely different methods to stimulate immune responses.
The RBD protein segment is directly steered by this nanobody directly to antigen-presenting cells thereby stimulating a broader immune response.
Vaccines currently used for COVID-19 are presumed to trigger antigen-presenting cells, but only indirectly. Therefore, it is more efficient to remove the middleman and talk directly to antigen-presenting cells.
Meanwhile, to target antigen-presenting cells, the team carried out engineering of nanobodies to recognize and home to Class 2 major histocompatibility complex antigens on the surface of cells. The vaccine produced elicited strong immune response against SARS-CoV-2 and its variants in mice to stimulate to result in high quantity of counteracting antibodies against the RBD protein.