The genetic engineering of immune cells has become one of the most promising directions in modern medicine, offering new therapeutic possibilities for the treatment of cancer. Among these, chimeric antigen receptor T cell (CAR-T) therapy has achieved remarkable outcomes in haematological malignancies by genetically engineering a patient's own T cells to recognise and eliminate tumour cells. However, the complexity and high cost of manufacturing CAR-T cells outside the body have encouraged the exploration of a fundamentally different approach: delivering genetic material directly into circulating T cells in vivo, bypassing the need for cell extraction and manipulation. Synthetic mRNA has gained considerable attention as a therapeutic cargo for this purpose, offering transient, non-integrating gene expression without the safety concerns associated with viral vectors.