Editor's Note: In 2025, the highly anticipated 30th European Hematology Association (EHA) Annual Meeting was grandly held in Milan, Italy in a combination of online and offline formats. Professor Johanna Olweus from Oslo University Hospital delivered a compelling keynote speech, systematically elaborating on how T-Cell Receptor (TCR) T-cell therapy is overcoming the limitations of existing immunotherapies. By targeting shared neoantigens, mistranslated peptides, and an innovative strategy of "allogeneic presentation" of self-antigens, it brings revolutionary new hope for the treatment of hematological malignancies, especially acute leukemia.As a star in the current immunotherapy landscape, Chimeric Antigen Receptor T-Cell (CAR-T) therapy has achieved tremendous success in some hematological tumors. However, its limitations are becoming increasingly apparent. “Currently approved CAR-T cell therapies can only recognize cell surface molecules, and safe, tumor-specific targets of this kind are extremely rare,” Professor Olweus pointed out at the beginning of her report. In contrast, TCR-T cells can recognize intracellular antigen peptides presented by Human Leukocyte Antigen (HLA) molecules, making over 80% of the intracellular proteome a potential therapeutic target and greatly expanding the “targeting scope” of tumor immunotherapy.
Although TCR-T therapy has HLA-dependent restrictions, Professor Olweus emphasized that many HLA alleles are expressed at frequencies of 30% to 50% in major ethnic groups, giving them broad application potential. More importantly, the sensitivity of TCRs to their targets is far higher than that of antibodies, which is expected to reduce the risk of tumor immune escape and provide a solid theoretical basis for curing hematological malignancies.
New Target Discovery Strategy (1): Targeting Shared Neoantigens in Leukemia Stem Cells
The key to curing leukemia lies in eliminating Leukemia Stem Cells (LSCs), the root cause of disease relapse. Recurrent clonal mutations are among the most attractive targets in these cells. However, how can one find TCRs that accurately identify these mutations? Traditional methods rely on the patient’s own T-cell repertoire, but Professor Olweus noted that patient-derived T-cells are often functionally exhausted or tolerant due to long-term “co-existence with the tumor,” and their numbers are limited by prior treatments.
To address this, Professor Olweus’s team proposed the innovative concept of “Outsourcing Cancer Immunity,” which involves using the T-cell repertoires of healthy donors to screen for neoantigen-reactive TCRs. “We have demonstrated that T-cells from healthy donors can recognize up to five times more neoantigens compared to a patient’s tumor-infiltrating lymphocytes,” she shared.
Using this strategy, the team successfully screened a high-affinity TCR that recognizes the FLT3 D835Y mutation in Acute Myeloid Leukemia (AML). In a series of well-designed Patient-Derived Xenograft (PDX) models, this FLT3-TCR T-cell therapy demonstrated potent anti-tumor activity. Professor Olweus highlighted a key experiment: “We co-cultured patient-derived AML cells with FLT3-TCR T-cells for 48 hours before transplanting them into immunodeficient mice. During a follow-up of up to 7 months, all mice in the control group developed leukemic engraftment, while none in the TCR-T cell-treated group did, proving that TCR-T therapy targeting a single shared neoantigen is sufficient to eliminate leukemia-propagating cells.”
New Target Discovery Strategy (2): Mining for Tumor-Specific Antigens
Beyond genetic mutations, the abnormal protein translation process in cancer cells also provides a new source of targets for TCR-T therapy. Professor Olweus introduced a collaborative study with institutions like the Netherlands Cancer Institute, which found that interferon-gamma (IFN-γ) in the tumor microenvironment can cause tryptophan depletion. This, in turn, induces ribosomal frameshifting or amino acid substitutions, generating a large number of tumor-specific “substitutent peptides.”
Through immunopeptidomics, the team successfully identified a tryptophan-to-phenylalanine substitutent peptide shared across multiple cancer cell lines and screened for a TCR that could specifically recognize this peptide. Experimental data showed that under IFN-γ induction, various cancer cell lines could efficiently present this substitutent peptide and be precisely recognized and killed by the corresponding TCR-T cells. This discovery reveals peptides as a highly promising class of neoantigens that could potentially be used in combination with other therapies that induce IFN-γ (such as immune checkpoint inhibitors) to exert synergistic anti-cancer effects.
New Target Discovery Strategy (3): A Paradigm-Shifting Idea—Using Allogeneic HLA to Present Self-Antigens
The most striking part of the report was a paradigm-shifting targeting strategy. Conventional TCR therapy involves using a patient’s own TCR to recognize foreign peptides (neoantigens) presented on their own HLA. Professor Olweus’s team took the opposite approach, aiming to find TCRs that can recognize “self”-antigen peptides presented on “allogeneic” (non-self) HLA.
They selected Terminal deoxynucleotidyl Transferase (TdT) as an ideal self-antigen target. TdT is a highly lymphoid-specific protein, overexpressed in more than 90% of Acute Lymphoblastic Leukemia (ALL) cases but not in hematopoietic stem cells or mature lymphocytes, ensuring therapeutic safety.
By leveraging T-cells from healthy donors, the team successfully isolated a TCR that recognizes a TdT peptide presented by the common HLA-A2 allele. The in vitro experimental results were exciting: after co-culture with leukemia cells from B-ALL and T-ALL patients, the TdT-TCR T-cells almost completely eliminated the leukemia cells, with no significant effect on normal B-cells, T-cells, or CD34+ hematopoietic stem/progenitor cells, demonstrating outstanding killing specificity.
From Bench to Bedside: TdT-TCR Therapy Advances to First-in-Human Trial Building on solid basic research, Professor Olweus’s team has advanced this TdT-TCR T-cell therapy from the laboratory to the clinic. She announced excitedly, “We have submitted an application for an investigator-initiated Phase I/IIa, first-in-human clinical trial via the European Medicines Agency (EMA) central portal. It is planned for the treatment of pediatric and adult patients with relapsed/refractory T-cell or B-cell derived Acute Lymphoblastic Leukemia/Lymphoma.”
In the Q&A session, addressing clinical application questions, Professor Olweus responded that based on TdT overexpression in 90% of ALL patients and the fact that about 50% of patients are HLA-A2 positive, theoretically around 45% of patients would be eligible. Regarding concerns about fratricide, she explained that studies found the expression of TdT and HLA-A2 in normal thymocytes to be asynchronous, and animal models confirmed the therapy had no negative impact on the normal human hematopoietic system, showing a good safety profile.
Expert Opinions and Future Outlook
In summarizing her report, Professor Olweus presented three core points: first, the targets for TCR-T therapies currently in clinical development are still very limited; second, obtaining highly sensitive TCRs is key to ensuring efficacy, and the naïve T-cell repertoire of healthy donors is a rich source of such TCRs; finally, novel classes of targets, including shared neoantigens, mistranslated peptides, and self-antigens presented by allogeneic HLA, are constantly emerging.
Looking ahead, she mentioned that her team is participating in the “Cancer Grand Challenge” program, funded by Cancer Research UK (CRUK) and the U.S. National Institutes of Health (NIH). The project aims to use machine learning and structural biology to decode the cancer recognition code of TCRs, with the ultimate grand goal of predicting a TCR’s target directly from its sequence.
This report not only systematically showcased the cutting-edge progress in target discovery and clinical translation for TCR-T therapy but also provided tangible new strategies for conquering refractory hematological tumors through a series of innovative scientific ideas. The work of Professor Johanna Olweus and her team highlights the powerful driving force of translating basic research into clinical applications, filling us with greater expectations for the future of T-cell immunotherapy.
