Autologous hematopoietic stem cell transplantation in lymphoma patients is associated with a decrease in the double strand break repair capacity of peripheral blood lymphocytes

Patients who undergo autologous hematopoietic stem cell transplantation (aHCT) for treatment of a relapsed or refractory lymphoma are at risk of developing therapy related- myelodysplasia/acute myeloid leukemia (t-MDS/AML). Part of the risk likely resides in inherent interindividual differences in their DNA repair capacity (DRC), which is thought to influence the effect chemotherapeutic treatments have on the patient’s stem cells prior to aHCT. Measuring DRC involves identifying small differences in repair proficiency among individuals. Initially, we investigated the cell model in healthy individuals (primary lymphocytes and/or lymphoblastoid cell lines) that would be appropriate to measure genetically determined DRC using host-cell reactivation assays. We present evidence that interindividual differences in DRC double-strand break repair (by non-homologous end-joining [NHEJ] or single-strand annealing [SSA]) are better preserved in non-induced primary lymphocytes. In contrast, lymphocytes induced to proliferate are required to assay base excision (BER) or nucleotide excision repair (NER). We established that both NHEJ and SSA DRCs in lymphocytes of healthy individuals were inversely correlated with the age of the donor, indicating that DSB repair in lymphocytes is likely not a constant feature but rather something that decreases with age (~0.37% NHEJ DRC/year). To investigate the predictive value of pre-aHCT DRC on outcome in patients, we then applied the optimized assays to the analysis of primary lymphocytes from lymphoma patients and found that individuals who later developed t-MDS/AML (cases) were indistinguishable in their DRC from controls who never developed t-MDS/AML. However, when DRC was investigated shortly after aHCT in the same individuals (21.6 months later on average), aHCT patients (both cases and controls) showed a significant decrease in DSB repair measurements. The average decrease of 6.9% in NHEJ DRC observed among aHCT patients was much higher than the 0.65% predicted for such a short time frame, based on ageing results for healthy individuals.接受自体造血干细胞移植（autologous hematopoietic stem cell transplantation, aHCT）治疗复发或难治性淋巴瘤的患者，存在罹患治疗相关骨髓增生异常综合征/急性髓系白血病（therapy-related myelodysplasia/acute myeloid leukemia, t-MDS/AML）的风险。该风险的部分诱因可能源于个体间DNA修复能力（DNA repair capacity, DRC）的固有差异，而DRC被认为会影响造血干细胞移植前化疗对患者干细胞的作用效果。检测DRC需要识别个体间修复能力的细微差异。本研究首先针对健康个体的原代淋巴细胞及/或淋巴母细胞系，探索了适用于通过宿主细胞复活实验（host-cell reactivation assays）测定遗传决定型DRC的细胞模型。本研究证实，健康个体中双链断裂修复（double-strand break repair, DSB repair，包括非同源末端连接[non-homologous end-joining, NHEJ]或单链退火[single-strand annealing, SSA]）的个体间差异在未诱导增殖的原代淋巴细胞中保留得更为完好。与之相反，检测碱基切除修复（base excision repair, BER）或核苷酸切除修复（nucleotide excision repair, NER）则需要使用经增殖诱导的淋巴细胞。本研究确定，健康个体淋巴细胞中的NHEJ与SSA DRC均与供者年龄呈负相关，这提示淋巴细胞中的DSB修复并非恒定特征，而是会随年龄增长而降低（每年约降低0.37%的NHEJ DRC）。为探究造血干细胞移植前DRC对患者预后的预测价值，本研究随后将优化后的实验方法应用于淋巴瘤患者的原代淋巴细胞分析。结果发现，后续罹患t-MDS/AML的患者（病例组），其DRC与从未发生t-MDS/AML的对照人群并无显著差异。然而，当在造血干细胞移植后不久（平均为移植后21.6个月）对同一批个体进行DRC检测时，造血干细胞移植患者（包括病例组与对照组）的DSB修复检测值均出现显著下降。造血干细胞移植患者中观测到的NHEJ DRC平均下降幅度达6.9%，远高于基于健康个体的衰老研究结果所预测的该短时间区间内0.65%的下降幅度。