双靶点嵌合抗原受体T细胞治疗CD19抗原表位缺失急性B淋巴细胞白血病一例报告并文献复习 Translated title: CD19 antigen loss after treatment of Bispecific T-cell Engager and effective response to salvage bispecific CAR-T therapy in B cell acute lymphoblastic leukemia: a case report and literature review

Abstract

目的

了解CD19异构体对双特异性T细胞衔接器（BiTE）治疗的反应，进一步探讨BiTE治疗无效的相关机制及相应的解决方案。

方法

通过半定量RT-PCR的方法检测1例CD19 ⁺急性B淋巴细胞白血病（B-ALL）患者BiTE治疗前后CD19异构体mRNA表达量的情况，Sanger测序对相应的异构体序列进行分析，流式细胞术及转录组测序分析治疗前后谱系特异性分子的表达情况。

结果

患者初诊时即存在2号外显子缺失型CD19异构体的表达，BiTE治疗后患者未缓解，流式细胞术检测发现CD19抗原表达转阴，但2号外显子缺失型CD19异构体的表达量并无增加，且细胞表型及转录组测序均未见谱系转化的发生。外显子可变剪接引起的缺失型CD19异构体的表达及谱系转化并非该患者CD19抗原表位缺失的机制。该例患者在疾病进展退出BiTE治疗组之后，采用中国医学科学院血液病医院自主研发的CD22及CD19 CAR-T序贯治疗后完全缓解。

结论

该例患者CD19抗原-缺失导致BiTE治疗无效，其缺失并非由可变剪接或谱系转换所致，更换为CD22、CD19双靶点CAR-T细胞治疗有效。

Translated abstract

Objective

To analyze the influence of CD19 isoforms to the efficacy of CD19/CD3 Bispecific T-cell Engager (BiTE) antibody, and explore the resistance mechanism of BiTE immunotherapy.

Methods

Semi-quantitative RT-PCR (qRT-PCR) was used to detect the expression of CD19 mRNA isoforms before and after BiTE treatment in a patient with CD19 ⁺ B cell acute lymphoblastic leukemia (ALL). CD19 isoforms were analyzed by Sanger sequencing. Flow cytometry and transcriptome sequencing were performed to analyze the expression of cell lineage specific molecules before and after BiTE treatment.

Results

The expression of CD19 isoform with exon 2 deletion was identified at diagnosis. After relapsed and treatment of BiTE antibody, the patient did not achieve remission and CD19 antigen on leukemic cells turned negative detected by flow cytometry after BiTE treatment. However the expression ratio of CD19 isoform with exon 2 deletion was not increased. Flow cytometry phenotype and transcriptome sequencing confirmed that no linage switching developed, which suggested the expression of CD19 isoform caused by exon alternative splicing and lineage switching was not related to CD19 epitope loss in this patient. This patient achieved complete remission by sequential administration of self-developed CD22 CAR-T and CD19 CAR-T after disease progression.

Conclusion

Targeting or combining an alternative antigen specific CAR-T may be a promising treatment option after losing CD19 expression in relapsed ALL.