“The therapeutic potential of multiclonal tumoricidal T cells derived from tumor infiltrating lymphocyte-derived iPS cells”
The significance of this research
A research team led by Professor Shin Kaneko at the Center for iPS Cell Research and Application (CiRA), Kyoto University, has succeeded in extracting T cells that attack only tumors (tumor-specific T cells) from lymphocytes proliferating in human colon cancer (tumor-infiltrating lymphocytes: TILs), generating iPS cells (iPSCs) from the TILs, and regenerating tumor-specific T cells from the iPSCs. These regenerated T cells were confirmed to be qualitatively and functionally better than the original TILs and could be a promising cell resource for immunotherapy using TILs in the future.
Conventional immunotherapy using TILs
TILs contain T cells that selectively attack tumors. T cells are a type of immune cell that recognize antigenic proteins on the surface of cells such as virus-infected cells or cancer cells and proliferate to attack them. Since each T cell expresses one type of receptor, it can recognize only one type of antigen (antigen specificity). TILs contain many kinds of tumor-specific T cells with different receptors, and thus can respond to many kinds of tumor antigens. These tumor-specific T cells mainly recognize neoantigens resulting from genetic mutations in cancer cells. The efficacy of immunotherapy using TILs has been shown in malignancies with high mutation burden such as melanoma.
Issues of conventional immunotherapy using TILs
To obtain a better therapeutic effect, a higher number of TILs in a less differentiated state is necessary. However, it is practically difficult to prepare ideal cells, because the main populations in TIL are often senescent and fairly differentiated and the number of them is limited.
Immunotherapy with TIL-derived iPSCs
iPSC technology makes it possible to initialize cells to a less differentiated state and allow them to proliferate almost indefinitely. In addition, T cells regenerated from T-cell-derived iPSCs take over the same receptors as the original T cells. Therefore, it should be possible to generate a large number of young T cells that retain antigen specificity against tumors by using TIL-derived iPSCs. However, there have been no reports of the regeneration of T cells from TIL-derived iPSCs.
Results of this study
The research team obtained TILs from surgically resected human colon cancers. They also cultured the cancer cells in three dimensions and established spheroids, which are spherical tissues. These spheroids and TILs were then co-cultured and enriched into tumor infiltrating-cytotoxic T lymphocytes（TI-CTLs）which are tumor-reactive. Some of the enriched TI-CTLs respond to tumors regardless of T cell receptor (TCR) antigen specificity, so they extracted TCR-dependent TI-CTLs by selecting only TI-CTLs whose responses were inhibited by HLA class I blocking antibodies. In addition, they divided TI-CTLs by TCR type (T cell receptor β-chain variable region). They then established iPSCs (TIL-iPSCs) from each of these TI-CTLs and regenerated T cells (TIL-iPS-T) from the TIL-iPSCs.
Next, they compared the function of TIL-iPS-T with that of TI-CTL and found that the proliferative capacity of TIL-iPS-T was improved. Moreover, the telomere length, which is an indicator of cellular senescence, was extended in TIL-iPS-T, indicating that those cells were rejuvenated.
They finally characterized TIL-iPS-T in vivo using patient-derived spheroids xenograft mice. TIL-iPS-T containing all types of TCRs obtained in the experiment (n = 3) and TI-CTL (n = 3) were transplanted subcutaneously together with cancer spheroids and followed for 3 weeks, and the results showed that TIL-iPS-T accumulated more in the tumor and stayed there longer than TI-CTL.
Additional information for researchers
This study was conducted on human colorectal cancers containing both DNA mismatch repair profiles: deficient (MMR-D) and proficient (MMR-P). The killing activity levels of TIL-iPS-T against cancer spheroids were similar to TI-CTL for MMR-D, and increased killing activity was found in TIL-iPS-T for MMR-P. This is due to the fact that TIL-iPS-T utilized TCR-independent cytotoxicity in addition to the ordinal TCR-dependent mechanism. Since TIL-iPS-T did not show killing activity against spheroids derived from non-cancerous areas or adverse effects on mice, it was concluded that TCR-independent cytotoxicity does not necessarily interfere with therapy.