CD28 and B-cell chronic lymphocytic leukemia: Shortly thereafter, impressive responses for CLL patients were reported in a separate Phase I trial, where 3 patients were treated with a 2nd generation anti-CD19 CAR that differed from the NIH construct in both the costimulatory domain (4-1BB in contrast to CD28) and the virus used for transduction (lentivirus as opposed to retrovirus)[80, 134].