A tumor suppressor function for prosurvival BCL-2 proteins in the thymus.

BCL-2 family prosurvival proteins act as tumor suppressors in thymic cell-competition models, where Bcl2 loss or modest MCL-1/BCL-XL reduction accelerates T-ALL-like leukemia.

• Why it matters: Defective cell competition is linked to tumorigenesis in cancers such as T-ALL, but how prosurvival BCL-2 proteins shape this process in the thymus was unclear.
• What they did: The study measured elevated prosurvival BCL-2 in “new” thymic progenitors, then used a thymic transplant model with Bcl2 deletion and tested effects of reducing MCL-1 or BCL-XL; it also conditionally ablated Mcl1 early in thymic lymphopoiesis.
• The result: Bcl2 deletion accelerated leukemia onset in the transplant model without changing competitive outcomes, instead increasing apoptosis and IL-7-driven compensatory proliferation, which increased acquisition of oncogenic mutations; Mcl1 ablation caused profound thymocyte loss, elevated progenitor proliferation, and spontaneous T-ALL.

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