Transitional B cell subsets-a convincing predictive biomarker for allograft loss?

In this issue, Cherukuri and colleagues describe a convincing association between the proportion of transitional B lymphocyte subsets in kidney transplant recipients and long-term outcomes, and present a biologically plausible mechanism, based on differential ability of T1 and T2 cells to regulate in vitro T cell responses to explain the link. Further work is clearly needed to validate their claim that measurement of T1/T2 ratios may represent a reliable and reproducible predictive biomarker of transplant outcomes.