Functional characterization of cooperating MGA mutations in RUNX1::RUNX1T1 acute myeloid leukemia

MGA (Max-gene associated) is a dual-specificity transcription factor that negatively regulates MYC-target genes to inhibit proliferation and promote differentiation. Loss-of-function mutations in MGA have been commonly identified in several hematological neoplasms, including acute myeloid leukemia (AML) with RUNX1::RUNX1T1, however, very little is known about the impact of these MGA alterations on normal hematopoiesis or disease progression. We show that representative MGA mutations identified in patient samples abolish protein-protein interactions and transcriptional activity. Using a series of human and mouse model systems, including a newly developed conditional knock-out mouse strain, we demonstrate that loss of MGA results in upregulation of MYC and E2F targets, cell cycle genes, mTOR signaling, and oxidative phosphorylation in normal hematopoietic cells, leading to enhanced proliferation. The loss of MGA induces an open chromatin state at promoters of genes involved in cell cycle and proliferation. RUNX1::RUNX1T1 expression in Mga-deficient murine hematopoietic cells leads to a more aggressive AML with a significantly shortened latency. These data show that MGA regulates multiple pro-proliferative pathways in hematopoietic cells and cooperates with the RUNX1::RUNX1T1 fusion oncoprotein to enhance leukemogenesis.

585. Safety and Immunogenicity of SARS-CoV-2 Vaccination in Children with a History of MIS-C

Background

Multisystem Inflammatory Syndrome in Children (MIS-C) is a rare sequela that typically develops 2–6 weeks after SARS-CoV-2 infection. According to CDC recommendations, children who recover from MIS-C should be vaccinated 90 days after diagnosis, but safety and immunogenicity data are lacking. Our aim was to evaluate the safety and immunogenicity of one dose of the BNT162b2 vaccine in children with a history of MIS-C.

Methods

We conducted a longitudinal study of children with MIS-C admitted to Monroe Carell Jr. Children's Hospital at Vanderbilt from 7/11/2020 to 3/23/2022. Children were eligible if they met CDC’s MIS-C criteria and had blood collected before and after SARS-CoV-2 vaccination. Clinical data were obtained from medical records and injection site and systemic reactions were recorded for a week following SARS-CoV-2 vaccination via memory aids. IgG against SARS-CoV-2 nucleocapsid (N), spike receptor-binding domain (RBD), and spike extracellular domain (ECD) was detected using an enzyme-linked immunosorbent assay. The first anti-RBD and anti-ECD levels prevaccination and postvaccination were compared using the paired-samples t-test.

Results

Seven children were included, of whom five were male and five were non-Hispanic White. The first blood sample was collected 3–44 days following admission. The median age at admission was 15.8 years (IQR, 10.5–14.7 years), and the median time from admission to vaccination was 7 months (IQR, 6–8 months). Five children each had injection site or systemic reactions (Figure 1); the majority were mild or moderate and occurred within 2 days of vaccination. Children were followed for a median of 5.6 months (4.3–6.2 months) postvaccination; none developed MIS-C recurrence. Following vaccination, mean anti-RBD and anti-ECD levels increased by 2.0 (1.2–2.9; p < 0.001) and 1.9 (1.2–2.6; p < 0.001) absorbance units, respectively (Figure 2). A sensitivity analysis excluding children with antibody evidence of reinfection (increase in anti-N level ≥ 0.5) showed similar results. Figure 1Safety of SARS-CoV-2 vaccination in children with a history of MIS-C.

Figure 2 Immunogenicity of SARS-CoV-2 vaccination in children with a history of MIS-C. The best-fit lines (LOESS) are indicated in black. The dashed line indicates the day of vaccination.

Conclusion

SARS-CoV-2 vaccination is safe and immunogenic in children with a history of MIS-C, with no documented recurrence of MIS-C–like illness. Further studies are needed to determine the optimal timing, safety, and immunogenicity of vaccination following MIS-C.

Disclosures

Natasha B. Halasa, MD, Quidel: Grant/Research Support|Quidel: equipment donation|Sanofi: Grant/Research Support|Sanofi: HAI testing and vaccine donation.