The molecular hallmark of childhood ALL is characterized by recurrent, prognostic genetic alterations, many of which are cryptic by conventional cytogenetics. RNA-seq is a powerful next-generation sequencing technology with the ability to simultaneously identify cryptic gene rearrangements, sequence mutations and gene expression profiles in a single assay. We examined the feasibility and utility of incorporating RNA-seq into a prospective multi-center phase 3 clinical trial for children with newly-diagnosed ALL. Patients enrolled on the DFCI ALL Consortium Protocol 16-001 who consented to optional studies and had available material underwent RNA-seq. RNA-seq was performed in 173 ALL patients. RNA-seq identified at least one alteration in 157 (91%) patients. Fusion detection was 100% concordant with results obtained from conventional cytogenetic analyses. An additional 56 gene fusions were identified by RNA-seq, many of which confer prognostic or therapeutic significance. Gene expression profiling enabled further molecular classification into the following B-ALL subgroups: High hyperdiploid (n=36), ETV6-RUNX1/-like (n=31), TCF3-PBX1 (n=7), KMT2A-rearranged (n=5), iAMP21 (n=1), hypodiploid (n=1), BCR-ABL1/-like (n=16), DUX4-rearranged (n=11), PAX5 alterations (n=11), PAX5 P80R (n=1), ZNF384-rearranged (n=4), NUTM1-rearranged (n=1), MEF2D-rearranged (n=1) and Others (n=10). RNA-seq identified 141 nonsynonymous mutations in 93 (54%) patients; the most frequent were RAS-MAPK pathway mutations. Among 79 patients with both low-density array and RNA-seq data for the Ph-like gene signature prediction, results were concordant in 74 (94%) patients. In conclusion, RNA-seq identified several clinically-relevant genetic alterations not detected by conventional methods, supporting the integration of this technology in frontline pediatric ALL trials.

Variation of C-reactive protein (CRP) throughout the hospitalization course (blue line). COVID-19 test results are identified in green when positive and red when negative. The day of ALL diagnosis, the day of chemotherapy start (black arrows), the duration of hospitalization (red box), and the duration of symptoms (green box) are indicated. Induction chemotherapy includes methylprednisolone/prednisone (days 1-32), vincristine (days 4, 11, 18, and 25), PEG-asparaginase (day 7), and intrathecal cytarabine (days 1 and 18) CONFLICT OF INTEREST The authors declare that there is no conflict of interest.

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Background: Patients with sickle cell disease (SCD) are considered at higher risk of severe COVID-19 infection. However, morbidity and mortality rates are variable among countries. To date, there are no published reports that document outcomes of SCD patients with COVID-19 in Canada. Methods: A web-based registry was implemented in June 2020 capturing outcomes of SCD patients with COVID-19 from March 2020 to April 2022 and comparing them to the general population of Quebec, Canada. Results: After 24 months of the pandemic, 185 SCD patients with confirmed SARS-CoV-2 infection were included in the registry. Overall, the population was young (median age 12 years old) and had few comorbidities. No deaths were reported. Risk of hospitalization and admission to intensive care unit (ICU) because of COVID-19 was higher in patients with SCD than in the general population (relative risks (RR) 5.15 (95% confidence interval (95% CI) 3.84–6.91), p ˂ 0.001 and 4.56 (95% CI 2.09–9.93) p ˂ 0.001). A history of arterial hypertension or acute chest syndrome in the past 12 months was associated with a higher risk of severe disease (RR = 3.06 (95% CI 1.85–5.06) p = 0.008 and 2.27 (95% CI 1.35–3.83) p = 0.01). Hospitalized patients had lower hemoglobin F than non-hospitalized patients (12% vs. 17%, p = 0.02). For those who had access to vaccination at the time of infection, 25 out of 26 patients were adequately vaccinated and had mild disease. Conclusions: The SCD population is at higher risk of severe disease than the general population. However, we report favorable outcomes as no deaths occurred. Registries will continue to be critical to document the impact of novel COVID-19 specific therapy and vaccines for the SCD population.

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Introduction Approximately 1500 people live with sickle cell disease (SCD) in the province of Quebec, Canada. Public health has recognized these patients as immunocompromised. SCD patients may be at higher risk of developing severe COVID-19 infection due to their underlying pro-inflammatory and thrombogenic state, splenic dysfunction and secondary organopathies. Descriptions about disease severity and mortality rates in SCD vary widely. From the SECURE-SCD registry, Mucalo et al. recently reported a 0.3% and 4.7% mortality rate in children and adults, respectively. In the French registry, Arlet and colleagues reported a 2.4% death rate among those hospitalized with COVID-19 and SCD, not different from the general population. As a result, the COVID-19 morbidity and mortality rates among the SCD population remain uncertain. Objectives The primary objectives of our study are to describe the epidemiology, baseline characteristics and clinical outcomes of SCD patients with COVID-19 infection in the province of Quebec. In addition, we aim to identify risk factors for hospitalization and severe forms of COVID-19. Methods We built a web-based SCD-COVID-19 registry regrouping 7 adult and 4 paediatric tertiary care hospitals in the province of Quebec in June 2020. All SCD patients with a confirmed SARS-CoV-2 infection by PCR test were included in the study. We compared the prevalence of infection and hospitalization rates of SCD patients to the general population of Quebec using the epidemiological data from the INSPQ (National Institute of Public Health of Quebec) public database. We retrospectively analyzed data included between March 11, 2020 to March 1, 2021. Relative risk was calculated using bilateral association measures (exact fisher, mid-p or chi-squared tests, as appropriate) to compare the incidence of infection and hospitalization of SCD patients to the population of Quebec and to assess risk factors of hospitalization among SCD patients. Results During the first 12 months of the pandemic, 74 patients were included in the registry. The male to female ratio was 1:1.12. Median age was 23 years, ranging from 8 months to 68 years old. SS-Sbeta 0 genotypes were present in 51% of cases, while 49% were SC or Sbeta +. The majority of patients were on disease modifying therapy: 54% were on hydroxyurea and 17.5% on exchange transfusion therapy. The incidence of reported COVID-19 infection was significantly higher in SCD patients compared to the general population (4.9% vs. 3.5% p=0,002) (Table 1). Even more strikingly, SCD had rate of hospitalization 10-times greater than the general population (33.8 vs 3.2%, p<0,001). Nevertheless, the risk of admission to the intensive care unit was similar between SCD patients and the general population (24.0% vs. 24.1%, p=0.99). No death was recorded amongst SCD patients with COVID-19 compared to a death rate in the general population in Quebec of less than 70 years old of 48-78 for 100 000 infections (male-female). A history of acute chest syndrome (ACS) in the last year (OR 2.6 [1.5-4.6], p=0.04) and arterial hypertension (OR 3.3 [2.3-4.8], p=0.01) were associated with a higher risk of hospitalization (Table 2). On the other hand, there was no statistically significant association with age, sex, genotype, ABO blood group, baseline SCD therapy, or other comorbidities (chronic renal disease, obesity, pulmonary hypertension, chronic lung disease and previous admission to ICU) in our cohort. Conclusions Similar to other reports, we found that SCD patients were at much greater risk of hospitalization compared to the general population. We however found no increased risk of mortality or disease complication. This contrasts with results from other registries. A history of ACS and hypertension were associated with a higher risk of hospitalization. Whether social determinants of health could explain some of the outcome variability between different countries merit further investigation. Furthermore, we believe that registries are critical to monitor the impact of preventive measures. As vaccination is ongoing, it will be important to consider its impact on hospitalization and death rate among SCD population. Recruitment to the registry is ongoing and updated data will be presented at the meeting. Figure 1 Figure 1. Disclosures Soulieres: BMS: Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding. Forté: Novartis: Honoraria; Canadian Hematology Society: Research Funding; Pfizer: Research Funding.

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Introduction: Thrombo-embolic event (TE) is a frequent complication of childhood acute lymphoblastic leukemia (cALL) and is associated with reduced survival. Overexpression of podoplanin or coagulome genes and coagulation pathway activation have been identified in cancer-induced TE but the role of leukemia environment in TE occurrence has not been fully elucidated in ALL. We assessed whether leukemia gene expression (GE) signature at diagnosis was associated with TE development in cALL. Methods: We included children aged 0-18 years old (y.o.), from two hospitals, with newly diagnosed ALL and available RNA sequencing data from bone marrow at diagnosis. The primary outcome was the occurrence of grade ≥2 TE during ALL therapy using the Ponte Di Legno Working Group classification. TEs were classified as early (ET) if they occurred within 6 weeks from treatment start, or late (LT) otherwise. We compared differential gene expression (DE) in children with and without TE, adjusted for age (<10 or ≥10 y.o.) and ALL type (T or B-ALL). A secondary analysis stratified children between ET, LT and no TE. Gene set enrichment analysis (GSEA) was performed on KEGG and gene ontology (GO) databases. DE with absolute fold change ≥2 and p-values <0.05 were considered significant. Results: We included 80 patients (median age: 5 years [interquartile range, IQR: 3-11 years], 53% male, 83% precursor B-cell ALL) of whom 19 (23.8%) developed a TE (7 ET and 12 LT) at a median of 76 days (IQR: 31-133 days) following cancer diagnosis. Patients with TE were more likely to be ≥10 y.o., while other demographic and clinical characteristics were similar. No genes from the coagulome, podoplanin or Hallmark coagulation pathways were differentially expressed in children with and without TE. The KEGG Ribosome pathway was the most upregulated pathway in the group with TE (normalized enrichment score (NES) = 2.35, adjusted p-value= 0.012) and ET (NES = 2.63, adjusted p-value < 0.001). LT was not significantly associated with ribosome pathway dysregulation. Interestingly, prior reports identified functional enrichment in ribosomal pathway as a biomarker for venous TE. A heatmap classification for ribosomal genes revealed 3 distinct signatures: ribosomal downregulation, moderate and high ribosomal activation. High ribosomal activation profile was seen in 6/7 ET and 9/12 LT, corresponding to a positive and negative predictive value of 0.55 and 0.92 for TE, respectively. Conclusion: TEs in cALL were not associated with dysregulation in coagulation pathways or podoplanin gene at the RNA level. However, ribosomal translational pathway was highly upregulated in the group with thrombosis, particularly with ET. Dysregulation of posttranscriptional machinery might explain the pro-thrombotic effect of leukemia environment in cALL and warrants further investigation including proteomic exploration. Citation Format: Marie-Claude Pelland-Marcotte, Meredith Michelle Rémy, Yan Ma, Jessica Liu, Camille Jimenez-Cortes, Thomas Sontag, Maxime Caron, Pascal Saint-Onge, Sylvie Langlois, Charles Joly-Beauparlant, Daniel Sinnett, Arnaud Droit, Thai Hoa Tran, Raoul Santiago. Ribosomal translational regulation is a potential mechanism for leukemia-related thrombo-embolic event in childhood acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3897.