Due to genetic mutations in the cells, the cells proliferate and differentiate uncontrollably, and eventually, develop into malignant tumors. There are many abnormal proteins encoded by the mutant genes on the surface of cancer cells. It stands to reason that these abnormal proteins should be recognized by the body's immune system in time. It triggers an immune response to clear the cancer cells in one fell swoop. However, due to the rapid development of tumor cells, they are extremely camouflaged and constantly mutate. In the face of fierce and witty tumor cells, the originally powerful immune cells also seem to be "inadequate", and they may even Some tumor cells are "ignoring". The immunosuppression formed in the tumor microenvironment has even paralyzed the immune system. Based on the above information, which of the following studies may be helpful in the development of effective antitumor drugs? ['Researchers sequence the DNA of tumor cells and healthy cells from each patient to identify tumor-specific mutations and identify related abnormal proteins.', 'Scientists use immunotherapy to try to transform immune cells that are "unsuspecting" to tumor cells and return them to the battlefield.', 'Scientists compare the lifestyle and personality characteristics of patients with malignant tumors and healthy people to find out the risk factors that induce tumors.', 'Scientists use mice to test, inject the extracted tumor abnormal protein as a vaccine into mice to stimulate and enhance their immune response.']