In a clinical trial of CAR T therapy for multiple myeloma, a higher CD4+/CD3+ ratio was associated with improved clinical outcomes.[41] In CAR T therapy for solid tumors, we also found that a higher CD4+/CD3+ ratio was associated with better therapeutic outcomes by analyzing public scRNA‐seq data[33, 42] (Figure 5n; Figure S8b, Supporting Information). Here, CD4 is linked to AL amyloidosis.