Causes of CAR T-cell therapy inefficacy: therapy inefficacy for patients with MM receiving CAR T-cell therapy can be due to disease- or patient-related factors, although logistical concerns relating to product manufacturing and cost/availability are also significant. Therapy-related toxicity can also represent a challenge even in patients with strong responses. CAR-HLH, Chimeric antigen receptor T cell-related hemophagocytic lymphohistiocytosis.