The Moderna and Pfizer vaccines inject mRNA with the code to create the COVID19 spike protein encapsulated by a fatty, lipid bubble. This bubble will bump into a cell and fuse with it, and the mRNA will enter the cell's cytoplasm. The ribosomes of the cell will read the instructions in coding and start making the spike protein.
The J&J vaccine injects a weakened cold virus that has been altered to contain DNA with the coding to make the COVID19 spike protein. This virus enters a cell and then the DNA will enter the cell's nucleus. The DNA will then encode the mRNA strands with these same instructions that will then exit the nucleus and go into the cytoplasm of the cell and the ribosomes will read the instructions from the mRNA to produce the spike protein. AstraZeneca is similar but uses the cell of chimpanzee.
There is no other way for the ribosomes of a cell to receive and carry out instructions to make spike protein if mRNA is not involved. All of the vaccines use mRNA to get the cells to produce the spike protein - the method of how the mRNA gets there is how they differ.