There is a ying/yang to most biological therapies, and the balance of efficacy versus toxicity is delicate and sometimes difficult to achieve in favor of the patients. When the therapeutic window is wide, these therapies can be used in the majority of patients, but when the therapeutic window is narrow, the decision to proceed must be carefully balanced with a thoughtful risk-benefit analysis. In this issue of the JCI, Ghosh et al. tackle one of the major obstacles in hematopoietic cell transplantation (HCT) technology: balancing the beneficial antitumor effect with the harmful anti-host effect.
