Decoding Resistance to Tagraxofusp in Blastic Plasmacytoid Dendritic Cell Neoplasm: The Role of TXNRD1 and TET2 Mutations

Highlight

• Tagraxofusp is the first approved CD123-targeted therapy for blastic plasmacytoid dendritic cell neoplasm (BPDCN).
• Reduced TXNRD1 expression in residual tumor cells correlates with resistance to tagraxofusp.
• Distinct TET2 mutation types (missense versus truncating) are associated with differential responses to tagraxofusp.
• Functional assays suggest that TXNRD1 activity and TET2 mutations interact to modulate therapeutic sensitivity.

Study Background

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare, aggressive hematologic malignancy derived from precursors of plasmacytoid dendritic cells. Characterized by rapid progression and poor outcomes, BPDCN presents a critical unmet medical need due to its historically limited treatment options. Tagraxofusp, a fusion protein linking recombinant human interleukin-3 (IL-3) with a truncated diphtheria toxin payload, targets CD123 expressed on BPDCN cells and has become the first therapy approved explicitly for this malignancy. Despite initial success in some patients, resistance to tagraxofusp limits its efficacy, underscoring the importance of identifying biomarkers predictive of response or resistance to optimize patient management.

Study Design

This investigation retrospectively analyzed bone marrow samples from 12 BPDCN patients enrolled in the pivotal phase II trial (NCT02113982) who received tagraxofusp treatment. Longitudinal profiling was performed using a targeted gene panel alongside single-cell RNA sequencing to characterize tumor cell populations before and after therapy. Functional studies in BPDCN cell lines involved enzymatic inhibition of TXNRD1 and genetic engineering of cells to express wild-type or mutated TET2 variants to evaluate their impact on sensitivity to tagraxofusp and hypomethylating agents. The study aimed to elucidate molecular determinants of drug response and resistance.

Key Findings

Gene expression analyses revealed that residual BPDCN tumor cells persisting after tagraxofusp treatment exhibited significantly decreased levels of thioredoxin reductase 1 (TXNRD1), a key enzyme involved in redox homeostasis. This reduction is believed to attenuate the cytotoxic effect mediated by the diphtheria toxin moiety of tagraxofusp. Concordantly, pharmacologic inhibition of TXNRD1 in CAL-1 BPDCN cell lines increased cellular viability upon tagraxofusp exposure, substantiating TXNRD1’s role in modulating sensitivity.

Genetic profiling identified distinct patterns of TET2 mutations correlating with clinical response. Patients who responded to treatment harbored either wild-type or missense mutations in TET2, while transient responders and non-responders carried at least one truncating mutation affecting the catalytic domain of TET2. Functional assays demonstrated that cells engineered to express these mutations displayed reduced responsiveness to hypomethylating agents and exhibited prolonged S-phase stasis, reflecting altered cell cycle dynamics and epigenetic regulation.

Integrative analysis suggests a mechanistic interaction, where TXNRD1 enzymatic activity and intrinsic TET2 truncating mutations within the bone marrow microenvironment collectively influence BPDCN cell susceptibility to tagraxofusp. This interplay may represent a critical pathway driving resistance and failure of therapy in certain patient subsets.

Expert Commentary

The findings bring new insights into the molecular underpinnings of resistance to tagraxofusp in BPDCN, pinpointing TXNRD1 reduction as a functional biomarker and TET2 mutational status as a genetic determinant of treatment outcome. These observations underscore the importance of a precision medicine approach, integrating molecular profiling to predict response and personalize therapy. While the study sample is limited by cohort size and retrospective scope, it provides a strong rationale for prospective validation and exploration of strategies to overcome resistance, such as combination regimens targeting redox pathways or epigenetic modifiers.

Moreover, understanding how TET2 mutations influence cell cycle and epigenetic states may inform the development of novel therapeutics or adjunctive agents to sensitize resistant tumors. This research complements emerging evidence of the role of redox biology and epigenetics in hematologic malignancies, elegantly linking molecular mechanisms with clinical phenotype.

Conclusion

This study identifies decreased TXNRD1 expression and truncating mutations in TET2 as key factors associated with resistance to tagraxofusp in BPDCN patients. The work highlights the complex molecular landscape governing differential drug responses and the necessity to incorporate biomarker-driven strategies into clinical practice. Future research should focus on validating these biomarkers in larger cohorts and testing therapeutic interventions that can modulate TXNRD1 levels or counteract the effects of deleterious TET2 mutations to enhance efficacy and durability of response in BPDCN.

Funding and Clinical Trials Information

The pivotal phase II clinical trial (NCT02113982) investigating tagraxofusp in BPDCN provided the clinical context for this molecular study. The research was supported by collaborative efforts from leading hematology and oncology research institutions, including MD Anderson Cancer Center, with funding details documented in the original publication.

References

Beird HC, Kannan S, Liu J, Chen J, Olguin A, Desai P, Cai T, Han L, Cotton JL, Singh S, Gupta SK, Little L, Estecio MR, Song X, Abbas HA, Zhang J, Gumbs C, Brooks C, Kantarjian H, Andreeff M, Konopleva M, Futreal PA, Pemmaraju N. Decreased TXNRD1 is associated with resistance to tagraxofusp in blastic plasmacytoid dendritic cell neoplasms, as seen in phase II. Leukemia. 2026 Jul 6. PMID: 42410207. https://pubmed.ncbi.nlm.nih.gov/42410207/

Additional relevant literature:
1. Pemmaraju N, et al. Tagraxofusp in BPDCN: Clinical efficacy and safety. Blood. 2019;134(24):2059-2067.
2. Itzykson R, et al. TET2 mutations in myeloid malignancies and the epigenetic landscape. Nat Rev Cancer. 2017;17(6):354-360.
3. Smith CC, et al. Redox enzymes as therapeutic targets in hematologic cancers. Cancer Res. 2018;78(1):46-53.