Not just a by‐product: circular DNA molecules derived from V(D)J recombination are linked to worse prognosis in B‐cell leukemia

Excised signal circles (ESC) are circular DNA molecules generated during T- and B-cell maturation. Previously considered biologically inert, recent work by Gao et al. now show that ESCs can replicate and accumulate in healthy lymphocytes. Moreover, the authors link higher levels of ESCs to an increased risk of relapse in B-cell leukemia patients and propose that this phenomenon is due to the unique ability of ESCs to induce genome instability.