CD28 and diffuse large B-cell lymphoma: In a phase Ib study of patients with refractory or relapsed DLBCL after failure of anti-CD19 CAR T therapy, a single infusion of CAR T cells co-expressing a PD-1-CD28 fusion protein induced a potent anti-tumor response (3/6 complete response and 1/6 stable disease) demonstrating the potential of anti-CD19 CAR-PD-1-CD28 T cells as salvage treatment, when first CAR T therapy proves ineffective or the disease is resistant to such approach [41].