A transformative innovation in immunotherapy has been unveiled whereby chimeric antigen receptor (CAR) T cells can be generated directly within patients rather than ex vivo. By utilizing lipid nanoparticles engineered with ionizable lipids conjugated to antibodies targeting the T cell surface protein CD5, mRNA encoding CAR constructs is delivered specifically to T cells in vivo. This approach leverages the advantages of mRNA over DNA-based vectors, reducing integration risks and enabling rapid reprogramming of the immune system to combat cancer and autoimmune diseases. The methodology holds significant promise to streamline manufacturing processes and expand patient access to cellular immunotherapies.