TECELRA® (afami-cel) is the first TCR-T cell therapy for solid tumors to be approved by the U.S. FDA

Dextramer® reagents were used to assess the transduction and monitor the cell phenotype of this ground-breaking drug

In August 2024, the U.S. Food & Drug Administration (FDA) granted afami-cel (TECELRA®) accelerated approval to treat adults with unresectable or metastatic synovial carcinoma.¹ The approval brings the first TCR-T cell therapy for a solid tumor to market. The decision was based on outcomes of the first cohort in Adaptimmune’s phase II SPEARHEAD-1 clinical trial.² Having demonstrated acceptable safety and promising efficacy in a phase I trial³, this study evaluated afami-cel (afamitresgene autoleucel) in patients with metastatic or unresectable synovial carcinoma (n = 44) and myxoid round cell liposarcoma (n = 8). The synovial sarcoma patients showed an overall response rate (ORR) of 39%², a remarkable improvement over treatment with a PD-1 inhibitor alone.⁴

Figure 1. MHC Dextramer® reagents afford highly sensitive detection of TCR-transduced T cells to determine transduction efficiency, infused cell phenotype, and product in vivo persistence to support safety assessments and release testing.

Insights from the phase I and phase II trials

In the phase I trial, Adaptimmune stained the manufactured product with a high-affinity MHC Dextramer® MAGE-A4 reagent, antibodies against CD3, CD4, CD8, and the canonical phenotype markers CD45RA and CCR7.³ Gating first for leukocytes (CD3⁺), among which they identified CD4⁺ and CD8⁺ cells, the researchers established that the T cell composition of afami-cel was mostly biased to CD4⁺. Further stratifying the product cell population, they showed that most of the transduced cells – whether CD4⁺ or CD8⁺ – had an effector memory or terminally differentiated effector memory phenotype.³

Longitudinal immunophenotyping of the infused cells using the same flow cytometry assay described above revealed that afami-cel presence peaked seven days after infusion in most patients.³ While the proportion of infused CD4⁺ and CD8⁺ cells with terminally differentiated effector memory phenotype remained relatively constant in patients showing partial response, stable disease, or progressive disease, the proportion of cells with stem cell memory phenotype increased gradually in all three patient groups. The effector memory phenotype showed a declining trend.³ Neither the CD4-to-CD8 cell ratio nor the immunophenotype of transduced and infused cells were associated with patient response.³

In the subsequent phase II study, transduction (reported median efficiency of 61.5%) was also evaluated with flow cytometry quantification of CD4⁺ and CD8⁺ expressing the engineered TCR defined as positive staining with the MHC Dextramer® reagent (supplementary information). Results show that afami-cel has a balanced proportion of transduced helper and cytotoxic T cells before infusion.² Similarly, the transduced T cells (i.e., Dextramer®-positive cells) were assessed for expression of CCD7 and CD45RA prior to infusion. CD4⁺ T cells predominantly showed both effector memory and T-cell effector memory phenotype. In contrast, the CD8⁺ T cell population was biased toward the T-cell effector memory phenotype and included more cells with naïve/stem cell memory phenotype (supplementary information).²

Get more details about the performed immunophenotyping here.

Quality reagents for every stage

Determining the number of viable cells expressing a transduced TCR and profiling the phenotype of cells in a manufactured product are just two workflows that benefit from the avidity and versatility of MHC Dextramer® reagents. In the case of the antigen MAGE-A4, Immudex offers reagents with different HLA haplotype-peptide pairings (see Table 1), several of which are already available as GMP. Our MHC Dextramer® GMP products meet all quality criteria and include an established shelf-life, expiry date, and certificate of analysis. The corresponding TCR monomers and TCR Dextramer® reagents are also available through our Custom Solutions and Services team.

MAGE-A4 related MHC Dextramer®

A selection of MHC Dextramer® reagents targeting MAGE-A4 available in our extensive product catalog.

^ HLA allele is mutated to enhance binding between MHC binding groove and peptide.

Just getting started with discovery research and assay design? Shorten your development time with RUO Dextramer® reagents for a smooth transition to GMP Dextramer® reagents for clinical trials and commercial manufacturing.

Learn more about Immudex products for the release testing of TCR-T cell therapies in this blog post.

References

¹ U.S. Food & Drug Administration. 2024. FDA grants accelerated approval to afamitresgene autoleucel for unresectable or metastatic synovial sarcoma. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-grants-accelerated-approval-afamitresgene-autoleucel-unresectable-or-metastatic-synovial-sarcoma (Accessed November 2024)
² D’Angelo, S. P. et al. 2024. The Lancet 403: 1460–1471. doi: 10.1016/S0140-6736(24)00319-2

³ Hong, D. S. et al. 2023. Nature Medicine 29: 104–114. doi: 10.1038/s41591-022-02128-z

⁴ Tawbi, H. A. et al. 2017. The Lancet Oncology 18: 1493–1501.

⁵ Sidaway, P. 2024. Nature Reviews Clinical Oncology 21: 401. doi: 10.1038/s41571-024-00894-y
⁶ CMC considerations for manufacturing gene-modified T cell products. Presentation at the CAR-TCR Europe Summit March 2023 by Alan Baer, PhD, Staff Fellow, Division of Cellular & Gene Therapies, Center for Biologics Evaluation and Research (CBER), U.S. Food and Drug Administration (FDA)
⁷ Iura, K. et al. 2017. Human Pathology 61: 130–139. Doi: 10.1016/j.humpath.2016.12.006
⁸ De Cock, L. et al. 2024. Translational Oncology 48: 102057. Doi: 10.1016/j.tranon.2024.102057