(703) Reverse Epitope Discovery of Asparaginase-Specific TCRs and Their Target Epitopes

Introduction/Rationale: Asparaginase (ASNase) is a crucial component of pediatric acute lymphoblastic leukemia (ALL) combination chemotherapy. However, its use is complicated by hypersensitivity reactions that necessitate switching from Escherichia coli-derived ASNase to Erwinia chrysanthemi ASNase to maintain therapy. While most hypersensitivity cases can be avoided by switching formulations, a subset of patients develop allergic responses to both. The role of ASNase-specific T cell responses in the development of ASNase hypersensitivity is poorly defined, and no bona fide ASNase-specific T cell receptors (TCR) have been identified.

Methods: We analyzed a large bulk TCR sequencing dataset of ALL patients with and without ASNase allergy and identified single chains significantly associated with allergy. To identify paired TCRs specific for ASNase, we deployed a novel, high-throughput, paired TCR sequencing method (TIRTL-Seq) on additional ALL patient samples with allergy and compared sequence features to the allergy-associated single chains.

Results: This yielded a list of candidate paired TCRs, 8 of which have been stably transduced into reporter cell lines for use in peptide library screens to validate their specificity and characterize their epitope recognition.

Conclusion: Understanding the T cell responses in ASNase hypersensitivity will provide insight into drug induced allergic responses and lay the foundation for optimization of ASNase formulations with reduced immunogenicity.