{
  "abstract": "Objectives Systemic lupus erythematosus (SLE) patients have a 2–7-fold increased risk of hematologic malignancies, particularly B-cell non-Hodgkin lymphoma (B-NHL). Although germline susceptibility shared between SLE and B-NHL is minimal, somatic evolution of autoreactive B-cells has been implicated as a precursor to malignant transformation in autoimmune syndromes. We therefore aimed to characterize somatic alterations across SLE B-cell subsets, with an emphasis on double-negative (DN) B-cells, a central autoreactive population.Methods In a cohort of 35 SLE patients, we performed whole exome sequencing on FACS-isolated naïve (CD19+, IgD+), memory (MBC; CD19+, IgD-, CD27+), and DN (CD19+, IgD-, CD27-) from peripheral blood. Patient-matched buccal DNA was used to filter out germline variants, and somatic mutations detected by >=2 callers (Mutect2, Strelka2, and CaVEMan) were retained. Variant allele frequencies (VAFs) were compared across subsets to assess clonal dynamics. Associations with disease activity (SLEDAI-2KG), time since diagnosis, and age were evaluated. Pathway enrichment and lymphoma-associated mutations were interrogated in high-burden patients.Results DN and MBC proportions correlated with disease activity (rho=0.443, p=0.008; rho=0.354, p=0.037). DN and MBC had significantly higher somatic mutation burden than naïve cells (p=0.001 and p=0.017), consistent with expansion of antigen-experienced and/or autoreactive compartments under chronic inflammation ( figure 1A–B). Mutation burden in DN correlated with time since diagnosis, but not age, suggesting disease-associated acquisition and/or selective growth of mutated clones (figure 1C). Among mutations shared between MBC and DN, a disproportionate fraction expanded in DN (figure 1D). Shared mutations expanded in DN were enriched for B-cell activation and proliferation pathways, including NF-kB and B-cell receptor signalling (FDR<0.05; figure 1E). In patients with high mutation burden, both MBC and DN harboured non-synonymous variants in lymphoma-associated genes, including IGLL5 and CARD11 (figure 1F–H).Abstract LBS1:05 Figure 1Conclusions Our results identify DN B-cells as a clonally evolving population that acquires a high burden of somatic mutations under chronic inflammatory conditions, with some variants affecting genes and pathways relevant to malignant transformation. These results highlight DN cells as a plausible cell of origin for transformation in SLE and underscore the value of DN-focused molecular profiling to identify patients with high-risk clonal features and improve monitoring for progression and lymphoma transformation potential.",
  "authors": [
    {
      "affiliations": [
        "Princess Margaret Cancer Centre, Toronto, Canada"
      ],
      "name": "Loïc Caloren"
    },
    {
      "affiliations": [
        "Princess Margaret Cancer Centre, Toronto, Canada"
      ],
      "name": "Yumika Shiba"
    },
    {
      "affiliations": [
        "Princess Margaret Cancer Centre, Toronto, Canada"
      ],
      "name": "Pathum Kossinna"
    },
    {
      "affiliations": [
        "Princess Margaret Cancer Centre, Toronto, Canada"
      ],
      "name": "Xuyao Li"
    },
    {
      "affiliations": [
        "BC Cancer Research Institute, Vancouver, Canada"
      ],
      "name": "Lizzy Pijpers"
    },
    {
      "affiliations": [
        "University Health Network, Toronto, Canada"
      ],
      "name": "Dennisse Bonilla"
    },
    {
      "affiliations": [
        "University Health Network, Toronto, Canada"
      ],
      "name": "Zahi Touma"
    },
    {
      "affiliations": [
        "BC Cancer Research Institute, Vancouver, Canada"
      ],
      "name": "Leandro Venturutti"
    },
    {
      "affiliations": [
        "Princess Margaret Cancer Centre, Toronto, Canada"
      ],
      "name": "Federico Gaiti"
    }
  ],
  "title": "LBS1:05 B-cell subset somatic mutations reveal lymphoma-like pathways in systemic lupus erythematosus",
  "uid": "1dcd22f2-4467-564e-9ec8-f3d6df9fc945"
}