While emerging therapies such as gene therapy are being explored, allogenic hematopoietic stem cell transplantation (HSCT) remains the most established curative treatment for sickle cell anemia (SCA). Yet its application is limited by toxicity risks, donor availability, and socioeconomic factors. In pediatric cases, myeloablative HSCT from an HLA-matched related donor (HLA-MRD), following either Busulfan or Treosulfan-based conditioning regimen yields SCA-free survival rates surpassing 90%, along with minimal occurrences of graft-versus-host disease (GVHD).^1-4 However, the optimal timing of transplantation remains debated due to concerns about fertility impairment, incidence of GVHD and transplant-related mortality at older ages.² While current literature suggests that outcomes generally improve with younger age (10–16 years), extensive toxicities associated with HSCT in SCA are not well-characterized. This analysis, aims to address this gap by providing a comprehensive assessment of acute toxicities associated with pediatric HSCT from HLA-MRD in the treatment of SCA, with a comparison between two age groups.

This study included 97 SCA patients under 18 years of age who underwent HLA-MRD transplantation following myeloablative conditioning (MAC) regimen with antithymocyte globulin (ATG) between January 2005 and December 2019. Of these, 78 patients were under 13 years old, while 19 were aged 13–18 years. Median age at transplantation was 9 years [6; 12]. Patient and transplant characteristics are detailed in Table 1. The primary indications for HSCT were recurrent vaso-occlusive events, acute chest syndrome, and cerebral vasculopathy. Before transplantation, patients aged 13–18 years exhibited higher incidence of bacterial infections (68% vs. 35%, p = .01). All patients received a MAC regimen, based on IV busulfan (16 mg/kg, adjusted to drug monitoring when available with a targeted AUC of 900–1300 μmol min/L), combined with either cyclophosphamide (n = 91, total dose of 200 mg/kg) or fludarabine (n = 6, total dose of 160 mg/m²). In vivo T-cell depletion was achieved using rabbit ATG (total dose of 20 mg/kg). Cyclosporin A (CSA) was used for GVHD prophylaxis alone (n = 7), or combined with methotrexate (n = 58) or mycophenolate mofetil (n = 28) (conditioning regimens are detailed in Table S1). Bone marrow (BM) was the primary stem cell source (n = 84), while cord blood was exclusively used in patients below 13 years (p = .07), either as a unique source (n = 13, 17%) or in combination with BM (n = 7, 9%). The median infused CD34+ cell count was significantly higher in patients under 13 years (6.0 × 10⁶ CD34⁺/kg [3; 8] vs. 4.5 × 10⁶ CD34⁺/kg [3; 5], p = .034).

All patients achieved engraftment, and no cases of secondary rejection or recurrence of SCA symptoms were observed. However, two patients over 13 years required a secondary infusion of CD34+ selected cells due to poor graft function (p = .037). Both patients exhibited persistent hypoplastic marrow function at 2 months (first patient) and 8 months (second patient) post-HSCT, despite repeated whole blood chimerism assessments confirming complete donor chimerism. The need for additional cell infusions may be attributed to concomitant infections and/or the low quantity of the initial graft. Interestingly, the median duration to achieve platelet recovery was shorter for patients under 13 years (30 vs. 35 days, p = .028). Five-year overall survival (OS) and disease-free survival (DFS) were comparable, reaching 97% (CI95, 94%–100%) in patients aged <13 years and 95% (CI95, 85%–100%) for those aged 13–18 (p = .5), with a median follow-up of 53 months [36; 79]. These excellent results align with published cohorts, consistently demonstrating survival rates exceeding 95% in pediatric SCA recipients undergoing HLA-MRD transplant.^{1, 2} The main outcomes of HSCT are summarized in Table S2 and Figure S1.

Managing infections during immunosuppressive therapy is crucial yet challenging in terms of diagnosis and treatment. Documentation of such outcomes in SCA recipients post-HSCT, especially in younger cohorts, is scarce despite infections being the leading cause of mortality.^{1, 2} Consistent with this observation, all three deaths in our study (2 patients <13 years (3%) and 1 patient aged 13–18 (5%)) were infection-related, occurring at 2-, 5- and 10-months post HSCT, while under immunosuppressive therapy. This underscores the need to carefully managing infection indicators in HSCT for SCA.

Specific treatment for cytomegalovirus (CMV), Epstein Barr Virus (EBV), BK virus and adenovirus replication was required in 28%, 16%, 11% and 4% of cases respectively (Table 1). Antiviral prophylaxis during our study relied on acyclovir or valacyclovir, initiated with the MAC regimen and continued until CD4+ levels reached at least 0.25 × 10⁹/L. Notably, no EBV-related post-transplant lymphoproliferative disease or CMV disease occurred. BK virus and adenovirus replications were successfully treated with cidofovir, administered either systemically or via bladder infusion, and brincidofovir, administered systemically. BK virus replication requiring treatment was significantly more frequent in patients aged 13–18 (26% vs. 8%, p = .037), marking the first instance of such an observation in recipients with SCA. The incidence in our cohort surpassed the rarely described rates found in existing literature⁵ and can be attributed to the tight monitoring and proactive treatment of viruria in our centers. This approach is supported by the high severity of symptoms, as 36% of affected individuals needed an indwelling catheter to prevent acute urinary retention. Additionally, endovascular lesions caused by SCA itself might sustain this phenomenon and warrant consideration.

In our cohort, 31% of patients developed bacterial infections requiring systemic antibiotics, with no significant association with prior splenectomy (p = .6). Gram-positive bacteria were the predominant pathogens, accounting for 50% of these infections. Notably, adolescents aged 13–18 had a significantly higher infection incidence than younger patients (53% vs. 26%, p = .029). Yet neutrophil reconstitution was similar across age groups, suggesting that factors such as bacterial carriage or antibiotic resistance from previous exposures might contribute to this disparity and need further investigations. Additionally, 10 patients (10%) were treated for probable or proven fungal infection (Candida sp. (n = 7), Aspergillus (n = 3)), with similar incidence between age groups. In univariate analysis, patients with infections requiring systemic treatment were older (10 [7; 12] vs. 8 [5; 9], p = .008) and received lower stem cell doses (4 × 10⁶ CD34⁺/kg [3; 6] vs. 7 × 10⁶ CD34⁺/kg [5; 9], p < .001) (Table S3). Interestingly, viral replication and bacteremia rates seem to be less frequent in SCA patients receiving reduced-intensity regimens,⁵ highlighting the need for further prospective studies on conditioning regimen intensity, especially in adolescents.

Older patients in our cohort demonstrated a greater prevalence of acute Grade III–IV skin toxicity (10% vs. 0%, p = .037), all linked to busulfan administration, as diffuse toxic erythema associated with pruritus and/or oral or genital erosion. These symptoms resolved spontaneously without steroid treatment, underscoring their distinctive nature compared to acute GVHD. Following mucositis (53% incidence), neurological impairment was the second most prevalent Grade III–IV acute organ toxicity in our study, affecting 12% of patients. Occurrences were consistent across age groups and not influenced by prior cerebral vasculopathy, with all cases resolving favorably. This was primarily characterized by acute encephalitis in a septic context (n = 2) or seizures and posterior reversible encephalopathy syndrome (PRES; n = 10). PRES occurred early, with a median time of 17 days post-HSCT (5–28), and were associated with CSA treatment. Switching to mycophenolate mofetil and maintaining strict blood pressure control led to positive outcomes. The incidence of PRES in our cohort was notably higher than reported in the literature.³ All patients received anticonvulsant prophylaxis during busulfan administration and CSA therapy (Table S1). However recent years have seen enhanced management strategies, focusing on precise control of arterial hypertension, prompt correction of magnesium deficiency, and maintenance of hemoglobin levels above 9 g/dL and platelet counts above 50 × 10⁹/L. Additionally, eight patients (8%) experienced significant acute endothelial toxicity, manifesting as thrombotic microangiopathy and capillary leak syndrome. Three patients (3%) developed Grade III–IV acute cardiac toxicity, all presenting with pericardial effusion. Concurrent infections (Adenovirus or Candida sp.) were identified in two cases without definitive evidence for infectious causality.

The incidence of veno-occlusive disease (VOD) in the cohort was 12% (n = 12), displaying comparability between age groups (Table 1). Individuals aged 13–18 years exclusively manifested mild forms of VOD, while younger patients experienced moderate and severe VOD in 5% and 3% of cases, respectively. The median time to onset was 13.5 days (9–21). Importantly, no cases of very severe VOD were observed, consistent with previous literature.

Grade III–IV acute GVHD occurred in 11% of the cohort (n = 11), aligning with previous findings in comparable cohorts,^{1, 2} and all cases resolved favorably. There was no significant difference between the age groups. The skin was the predominantly affected organ (88%), before gut (19%) and liver (11%). Of note, no risk factors of Grade III/IV acute GVHD nor acute organ toxicity were identified.

This study corroborates HSCT excellent outcomes in young HLA-MRD recipients in SCA. While large adult and pediatric series have demonstrated that older transplant age is associated with reduced OS/DFS or increased GVHD incidence, our findings align with Bernaudin et al.³ and indicate that this trend does not persist in younger cohorts. Yet, our study emphasizes a notable association between older age at transplantation and increased infection rates, suggesting interests of reduced-intensity conditioning in adolescents. Future prospective studies examining alternative therapies (gene therapy or exagamglogene autotemcel),⁶ as well as other conditioning regimens and transplantation approaches are essential to improve quality of life, and reduce both acute and long-term toxicity in SCA patients transplanted at ages older than 13.

虽然正在探索基因疗法等新兴疗法，但同种异体造血干细胞移植 （HSCT） 仍然是镰状细胞贫血 （SCA） 最成熟的治疗方法。然而，其应用受到毒性风险、供体可用性和社会经济因素的限制。在儿科病例中，来自 HLA 匹配的亲缘供体 （HLA-MRD） 的清髓性 HSCT，遵循基于白消安或特利奥万的预处理方案，无 SCA 生存率超过 90%，并且移植物抗宿主病 （GVHD） 的发生率最低。^1-4 然而，由于担心生育能力受损、GVHD 的发生率和老年人移植相关死亡率，移植的最佳时机仍然存在争议。² 虽然目前的文献表明，结果通常随着年龄的增长而改善（10-16 岁），但与 SCA 中 HSCT 相关的广泛毒性尚未得到充分表征。本分析旨在通过对 HLA-MRD 治疗 SCA 中与儿科 HSCT 相关的急性毒性进行全面评估，并在两个年龄组之间进行比较，从而填补这一差距。

本研究包括 97 例 18 岁以下的 SCA 患者，这些患者在 2005 年 1 月至 2019 年 12 月期间接受了清髓性预处理 （MAC） 方案和抗胸腺细胞球蛋白 （ATG） 的 HLA-MRD 移植。其中，78 名患者年龄在 13 岁以下，而 19 名患者年龄在 13-18 岁之间。移植时的中位年龄为 9 岁 [6; 12]。患者和移植特征详见表 1。HSCT 的主要适应证是复发性血管闭塞事件、急性胸部综合征和脑血管病变。移植前，13-18 岁患者细菌感染的发生率较高 （68% vs. 35%，p = .01）。所有患者均接受基于静脉白消安 （16 mg/kg，目标 AUC 为 900-1300 μmol min/L 时调整为药物监测）的 MAC 方案，联合环磷酰胺 （n = 91，总剂量 200 mg/kg） 或氟达拉滨 （n = 6，总剂量 160 mg/m²）。使用兔 ATG （总剂量为 20 mg/kg） 实现体内 T 细胞耗竭。环孢菌素 A （CSA） 单独用于 GVHD 预防 （n = 7），或与甲氨蝶呤 （n = 58） 或吗替麦考酚酯 （n = 28） 联合使用（预处理方案详见表 S1）。骨髓 （BM） 是主要的干细胞来源 （n = 84），而脐带血专门用于 13 岁以下的患者 （p = .07），作为独特的来源 （n = 13， 17%） 或与 BM 联合使用 （n = 7， 9%）。13 岁以下患者的中位输注 CD34+ 细胞计数显著升高 （6.0 ×^{10 6} CD34⁺/kg [3; 8] vs. 4.5 × 10⁶ CD34⁺/kg [3; 5]，p = .034）。

所有患者均实现了植入，未观察到继发性排斥反应或 SCA 症状复发的病例。然而，由于移植物功能不佳，两名 13 岁以上的患者需要二次输注 CD34 + 选定的细胞 （p = .037）。尽管反复的全血嵌合体评估证实了完整的供体嵌合体，但两名患者在 HSCT 后 2 个月 （第一名患者） 和 8 个月 （第二名患者） 都表现出持续的骨髓发育不良功能。需要额外的细胞输注可能归因于伴随的感染和/或初始移植物的数量少。有趣的是，13 岁以下患者实现血小板恢复的中位持续时间较短 （30 天对 35 天，p = .028）。5 年总生存期 （OS） 和无病生存期 （DFS） 相当，<13 岁患者达到 97% （CI95， 94%–100%），13-18 岁患者达到 95% （CI95， 85%–100%） （p = .5），中位随访时间为 53 个月 [36; 79]。这些出色的结果与已发表的队列一致，一致表明接受 HLA-MRD 移植的儿科 SCA 受者的生存率超过 95%。^1、2HSCT 的主要结局总结于表 S2 和图 S1 中。

免疫抑制治疗期间的感染管理至关重要，但在诊断和治疗方面也具有挑战性。尽管感染是导致死亡的主要原因，但 HSCT 后 SCA 受者的此类结果的记录很少，尤其是在年轻群体中。^1、2与这一观察结果一致，我们研究中的所有 3 例死亡 （2 例患者 <13 岁 （3%） 和 1 例 13-18 岁患者 （5%） ）都与感染相关，发生在 HSCT 后 2 个月、 5 个月和 10 个月，同时接受免疫抑制治疗。这强调了仔细管理 HSCT 中 SCA 感染指标的必要性。

分别有 28%、16%、11% 和 4% 的病例需要对巨细胞病毒 （CMV）、EB 病毒 （EBV）、BK 病毒和腺病毒复制进行特异性治疗（表 1）。我们研究期间的抗病毒预防依赖于阿昔洛韦或伐昔洛韦，从 MAC 方案开始，一直持续到 CD4+ 水平至少达到 0.25 × 10⁹/L。值得注意的是，没有发生与 EBV 相关的移植后淋巴组织增生性疾病或 CMV 疾病。BK 病毒和腺病毒复制用全身或膀胱输注 cidofovir 和全身给药 brincidofovir 成功治疗。在 13-18 岁的患者中，需要治疗的 BK 病毒复制显着更频繁 （26% vs. 8%，p = .037），这标志着在 SCA 受者中首次出现此类观察。我们队列的发病率超过了现有文献中很少描述的发生率⁵，这可归因于我们中心对病毒尿的严格监测和积极治疗。这种方法得到了症状高度严重的支持，因为 36% 的受影响个体需要留置导管来防止急性尿潴留。此外，由 SCA 本身引起的血管内病变可能会维持这种现象并值得考虑。

在我们的队列中，31% 的患者发生需要全身性抗生素的细菌感染，与既往脾切除术无显著关联 （p = .6）。革兰氏阳性菌是主要的病原体，占这些感染的 50%。值得注意的是，13-18 岁青少年的感染率明显高于年轻患者 （53% vs. 26%，p = .029）。然而，不同年龄组的中性粒细胞重建相似，这表明细菌携带或先前暴露的抗生素耐药性等因素可能导致这种差异，需要进一步调查。此外，10 例患者 （10%） 接受了可能或确诊的真菌感染 （念珠菌属 （n = 7）、曲霉菌 （n = 3）） 的治疗，年龄组间发病率相似。在单变量分析中，需要全身治疗的感染患者年龄较大 （10 [7; 12] vs. 8 [5; 9]，p = .008），接受的干细胞剂量较低 （4 × 10⁶ CD34⁺/kg [3;6] vs. 7 × 10⁶ CD34⁺/kg [5;9]，p < .001）（表 S3）。有趣的是，在接受低强度方案的 SCA 患者中，病毒复制和菌血症率似乎较少，⁵ 这凸显了对预处理方案强度进行进一步前瞻性研究的必要性，尤其是在青少年中。

我们队列中的老年患者表现出急性 III-IV 级皮肤毒性的患病率更高 （10% vs. 0%，p = .037），所有这些都与白消安给药有关，因为与瘙痒和/或口腔或生殖器糜烂相关的弥漫性毒性红斑。这些症状无需类固醇治疗即可自发消退，与急性 GVHD 相比，强调了它们的独特性质。在我们的研究中，继粘膜炎（53% 发生率）之后，神经功能障碍是第二普遍的 III-IV 级急性器官毒性，影响了 12% 的患者。各年龄组的发生率是一致的，不受既往脑血管病变的影响，所有病例均得到良好解决。这主要以脓毒症情况下的急性脑炎 （n = 2） 或癫痫发作和后部可逆性脑病综合征 （PRES;n = 10）。PRES 发生较早，HSCT 后中位时间为 17 天 （5-28），并且与 CSA 治疗相关。改用吗替麦考酚酯并保持严格的血压控制导致了积极的结果。我们队列中 PRES 的发生率明显高于文献中报道的发病率。³ 所有患者在白消安给药和 CSA 治疗期间接受了抗惊厥预防 （表 S1）。然而，近年来加强了管理策略，重点是精确控制动脉高血压，及时纠正镁缺乏，以及维持血红蛋白水平高于 9 g/dL 和血小板计数高于 50 ×^{10 9}/L。此外，8 例患者 （8%） 出现明显的急性内皮毒性，表现为血栓性微血管病和毛细血管渗漏综合征。 3 例患者 （3%） 出现 III-IV 级急性心脏毒性，均表现为心包积液。在 2 例病例中确定了并发感染 （腺病毒或念珠菌属），但没有明确的感染因果关系证据。

队列中静脉闭塞性疾病 （VOD） 的发生率为 12% （n = 12），显示出年龄组之间的可比性（表 1）。13-18 岁的个体仅表现出轻度 VOD，而年轻患者分别在 5% 和 3% 的病例中出现中度和重度 VOD。中位发病时间为 13.5 天 （9-21）。重要的是，没有观察到非常严重的 VOD 病例，这与以前的文献一致。

III-IV 级急性 GVHD 发生在 11% 的队列中 （n = 11），与先前在类似队列中的发现一致，^1、2 并且所有病例均得到良好解决。年龄组间无显著差异。皮肤是主要受影响的器官 （88%），其次是肠道 （19%） 和肝脏 （11%）。值得注意的是，未发现 III/IV 级急性 GVHD 的危险因素或急性器官毒性。

本研究证实了 HSCT 在 SCA 年轻 HLA-MRD 受者中的优异结果。虽然大型成人和儿科系列研究表明，移植年龄较大与 OS/DFS 降低或 GVHD 发病率增加相关，但我们的研究结果与 Bernaudin 等人3 一致，并表明这种趋势在年轻群体中不会持续存在。然而，我们的研究强调了移植年龄较大与感染率增加之间的显着关联，这表明对青少年降低强度条件反射感兴趣。未来前瞻性研究将检查替代疗法（基因治疗或 exagamglogene autotemcel）⁶ 以及其他预处理方案和移植方法，这对于改善 13 岁以上移植的 SCA 患者的生活质量和减少急性和长期毒性至关重要。