In recent years, “cancer immunotherapy” has been progressing rapidly, and the treatment has attracted much attention as the fourth cancer treatment after surgery, chemotherapy and radiation therapy. In 2018 and 2019, this cancer immunotherapy had two big topics around the world. One is the “immune checkpoint inhibitor” that brought Professor Honjou, Kyoto University the Nobel Prize in Medicine and Physiology, and the other was a new leukemia treatment by which expensive treatment costs became a hot topic in Japan. It is a cancer cell therapy “Kymriah”. “Immune checkpoint inhibitors” and “Kymriah” have shown significant effects on cancers that have been ineffective with previous therapies, and revolutionizing cancer treatment. However, these treatments are not effective for all cancer patients, and their high cost and side effect have been pointed out.
Kymriah is a cancer-specific cell therapy called chimeric receptor T cell (CAR-T) therapy that expresses antibody molecules on the surface of killer T cells that can kill target cells. The antibody of the therapy target antigen molecules that show selective expression on the surface of cancer cells. Antigen molecules expressed on cancer cells include “cancer antigens” expressed only on cancer cells and “cancer-related antigen” which is expressed on cancer cells and normal cells but whose expression is much higher on cancer cells, and hundreds of the antigens have been identified so far. However, most of the cancer antigens and cancer-related antigens are expressed only inside cells but not on the cell surface, so they cannot be used as target molecules for CAR-T therapy that act from outside the cells. On the other hand, the T cell receptor (TCR) can recognize molecules expressed in cells, so it can target cancer molecules existing in cells. Therefore, TCR-T therapy using antigen-specific T cell receptor (TCR) therapy has attracted attention and researches have been conducted, but the progress has not been made so much. In particular, the development of TCR-T therapy for HLA type, which is common in Japanese, has not been advanced. The main reason for this is considered to be the weak binding of TCR. Normally, TCRs have much lower binding affinity than that of antibodies so that activation of killer T cells via TCRs is not easy.
Under such circumstances, we have developed a method for obtaining antibody genes from individual antigen-specific B cells in as short as 7 days, and have been conducting researches on antibodies and CAR-T using the antibodies. At the same time, we have applied this technology to develop a technology to efficiently obtain TCR genes from individual T cells in 10 days, and have analyzed cancer cell-specific TCRs in many cancer patients.
In this research, we will conduct development of hybrid T cells utilizing the strengths of CAR-T therapy and TCR-T therapy, applying the basic technologies developed in our previous research. Concretely speaking, we will reduce the effects of CAR while retaining its cancer specificity and have CAR support TCR to activate killer T cell. This is expected to enhance the effect while maintaining the target specificity of TCR. On the other hand, by using TCR as the main component of this hybrid T cell, reduction of side effects, which is a disadvantage of CAR, can be expected. Therefore, this research on the development of hybrid T cells is expected to lead to an effective treatment with fewer side effects.