Enhancing Efficacy of TCR-engineered CD4 + T Cells Via Coexpression of CD8α

Engineered PD-L1 co-expression in PD-1 knockout and MAGE-C2-targeting TCR-T cells augments the cytotoxic efficacy toward target cancer cells

Expression of the PD-1 protein by tumor cells is relatively common and has been shown to exert proliferation-inhibitory effects across various tumor types, including T-cell malignancies, non-small cell lung cancer, and colon cancer. However, harnessing this tumor suppressor pathway is challenging because PD-1 activation by PD-L1 also suppresses normal T-cell function. We hypothesized that cancer antigen-specific TCR-T cells engineered to express PD-L1 could selectively activate the PD-1 pathway in tumor cells while simultaneously preventing self-inhibition by knocking out intrinsic PD-1 expression in TCR-T cells. To test this hypothesis, we co-expressed a MAGE-C2-specific recombinant TCR and the PD-L1-encoding CD274 gene in normal human T cells in which the PDCD1 gene was knocked out. These engineered TCR-T cells targeted MAGE-C2-expressing malignant cells, activating PD-1 signaling to suppress tumor proliferation while maintaining suppressed PD-1 signaling in the TCR-T cells themselves. To evaluate the tumor-suppressive potential of this approach, we compared the efficacy of PDL1-MC2-TCR-TPD1⁻ cells against subtypes lacking PD-L1 expression, PD-1 knockout, or both. Our findings demonstrated that this TCR-T model exhibited significantly enhanced cytotoxic efficacy compared to other subtypes in vitro, ex vivo, and in vivo. These results suggest that the targeted activation of intrinsic PD-1 signaling in T-cell malignancies inhibits tumor proliferation and, when combined with PD-1 inhibition in TCR-T cells, synergistically enhances their cancer-suppressing efficacy. This study provides a foundation for novel cancer treatment strategies.

Melanoma-associated antigen A4: A cancer/testis antigen as a target for adoptive T-cell receptor T-cell therapy

T-cell receptor (TCR) T-cell therapies are adoptive cell therapies in which patient cells are engineered to express TCRs targeting specific cancer antigens and infused back into the patient. Since TCR recognition depends on antigen presentation by the human leukocyte antigen system, TCRs can respond to intracellular antigens. Cancer/testis antigens (CTAs) are a large family of proteins, many of which are only expressed in cancerous tissue and immune-privileged germline sites. Melanoma-associated antigen A4 (MAGE-A4) is an intracellular CTA expressed in healthy testis and placenta, and in a range of cancers, including esophageal, head and neck, gastric, ovarian, colorectal, lung, endometrial, cervical, bladder, breast and prostate cancers; soft tissue sarcomas; urothelial and hepatocellular carcinomas; osteosarcoma; and melanoma. This expression pattern, along with the immunogenicity and potential role in tumorigenesis of MAGE-A4 make it a prime target for TCR T-cell therapy. We outline the preclinical and clinical development of TCR T-cell therapies targeting CTAs for treatment of solid tumors, highlighting the need for extensive preclinical characterization of putative off-target, and potential on-target but off-tumor, effects. We identified ten clinical trials assessing TCR T-cell therapies targeting MAGE-A4. Overall, manageable safety profiles and signals of efficacy have been observed, especially in patients with advanced synovial sarcoma, myxoid/round cell liposarcoma, ovarian, head and neck, and urothelial cancers, with one TCR T-cell therapy approved by the US Food and Drug Administration in August 2024. We also review the limitations, and strategies to enhance efficacy and improve safety, of these therapies, and summarize related immunotherapies targeting MAGE-A4.

Adoptive T Cell Therapy Targeting MAGE-A4

MAGE A4 (Melanoma Antigen Gene A4) is a cancer testis antigen (CTA) that is expressed normally in germline cells (testis/embryonic tissues) but absent in somatic cells. The MAGE A4 CTA is expressed in a variety of tumor types, like synovial sarcoma, ovarian cancer and non-small cell lung cancer. Having its expression profile limited to germline cells has made MAGE A4 a sought-after immunotherapeutic target in certain malignancies. In this review, we focus on MAGE-A4's function and expression, current clinical trials involving targeted immunotherapy approaches, and challenges and opportunities facing MAGE-A4's targeted therapeutics.

Tumor Regression Following Engineered Polyomavirus-Specific T Cell Therapy in Immune Checkpoint Inhibitor-Refractory Merkel Cell Carcinoma

Although immune check-point inhibitors (CPIs) revolutionized treatment of Merkel cell carcinoma (MCC), patients with CPI-refractory MCC lack effective therapy. More than 80% of MCC express T-antigens encoded by Merkel cell polyomavirus, which is an ideal target for T-cell receptor (TCR)-based immunotherapy. However, MCC often repress HLA expression, requiring additional strategies to reverse the downregulation for allowing T cells to recognize their targets. We identified TCRMCC1 that recognizes a T-antigen epitope restricted to human leukocyte antigen (HLA)-A*02:01. Seven CPI-refractory metastatic MCC patients received CD4 and CD8 T cells transduced with TCRMCC1 (TTCR-MCC1) preceded either by lymphodepleting chemotherapy or an HLA-upregulating regimen (single-fraction radiation therapy (SFRT) or systemic interferon gamma (IFNγ)) with concurrent avelumab. Two patients who received preceding SFRT and IFNγ respectively experienced tumor regression. One experienced regression of 13/14 subcutaneous lesions with 1 'escape' lesion and the other had delayed tumor regression in all lesions after initial progression. Although TTCR-MCC1 cells with an activated phenotype infiltrated tumors including the 'escape' lesion, all progressing lesions transcriptionally lacked HLA expression. While SFRT/IFNγ did not immediately upregulate tumor HLA expression, a secondary endogenous antigen-specific T cell infiltrate was detected in one of the regressing tumors and associated with HLA upregulation, indicating in situ immune responses have the potential to reverse HLA downregulation. Indeed, supplying a strong co-stimulatory signal via a CD200R-CD28 switch receptor allows TTCR-MCC1 cells to control HLA-downregulated MCC cells in a xenograft mouse model, upregulating HLA expression. Our results demonstrate the potential of TCR gene therapy for metastatic MCC and propose a next strategy for overcoming epigenetic downregulation of HLA in MCC.

Cancer testis antigens: Emerging therapeutic targets leveraging genomic instability in cancer

Cancer care has witnessed remarkable progress in recent decades, with a wide array of targeted therapies and immune-based interventions being added to the traditional treatment options such as surgery, chemotherapy, and radiotherapy. However, despite these advancements, the challenge of achieving high tumor specificity while minimizing adverse side effects continues to dictate the benefit-risk balance of cancer therapy, guiding clinical decision making. As such, the targeting of cancer testis antigens (CTAs) offers exciting new opportunities for therapeutic intervention of cancer since they display highly tumor specific expression patterns, natural immunogenicity and play pivotal roles in various biological processes that are critical for tumor cellular fitness. In this review, we delve deeper into how CTAs contribute to the regulation and maintenance of genomic integrity in cancer, and how these mechanisms can be exploited to specifically target and eradicate tumor cells. We review the current clinical trials targeting aforementioned CTAs, highlight promising pre-clinical data and discuss current challenges and future perspectives for future development of CTA-based strategies that exploit tumor genomic instability.

The screening, identification, design and clinical application of tumor-specific neoantigens for TCR-T cells

Recent advances in neoantigen research have accelerated the development of tumor immunotherapies, including adoptive cell therapies (ACTs), cancer vaccines and antibody-based therapies, particularly for solid tumors. With the development of next-generation sequencing and bioinformatics technology, the rapid identification and prediction of tumor-specific antigens (TSAs) has become possible. Compared with tumor-associated antigens (TAAs), highly immunogenic TSAs provide new targets for personalized tumor immunotherapy and can be used as prospective indicators for predicting tumor patient survival, prognosis, and immune checkpoint blockade response. Here, the identification and characterization of neoantigens and the clinical application of neoantigen-based TCR-T immunotherapy strategies are summarized, and the current status, inherent challenges, and clinical translational potential of these strategies are discussed.