And that is because DCVAX is a lysate of the tumor, whereas the MRK vaccine uses an analysis of SELECTED tumor antigens MRNA.
MRNA starts with tissue samples, including a biopsy, and then undertake next generation sequencing (WES and RNA, as well as HLA typing) to design to the vaccine. The results for each patient are provided as inputs to their proprietary bioinformatics algorithm. Up to 34 neoantigens are selected using that. The mRNA encoding those is then encapsulated in lipid nanoparticles.
both of which are presented to antigen presenting cells (mostly) such as Dendritic Cells.
After intramuscular injection of MRNA's vaccine, healthy cells uptake the lipid nanoparticles that encode the mRNA for the neoantigens and it is translated and processed, before being presented to the immune system.