Unintentional transduction of a single leukemic B cell appears to have induced resistance to CTL019 (tisagenlecleucel, Kymriah) therapy, a recent case study suggests.
A total of 9 months after receiving a seemingly successful CD19-targeted chimeric antigen receptor (CAR) T-cell (CTL019; tisagenlecleucel) infusion, a 20-year-old man with B-cell acute lymphoblastic leukemia (B-ALL) had a frank relapse, with more than 90% bone marrow infiltration of CAR-transduced B-cell leukemia cells. Further investigation showed that the CAR gene had unintentionally been added to a solitary leukemic B cell during the CAR T-cell manufacturing process, reported, of the University of Pennsylvania, Philadelphia.
“The transduction of a single leukemic cell with an anti-CD19 CAR lentivirus during CTL019 manufacturing is sufficient to mediate resistance through masking of the CD19 epitope. This is a rare event, as this is the only case out of 369 patients reported worldwide at the time of publication. ... These findings illustrate the need for improved manufacturing technologies that can purge residual contaminating tumor cells from engineered T cells,” the authors wrote in.
The findings also confirm the cancer stem cell hypothesis in humans, “given that clonal analysis indicated that the relapse and subsequent death of the patient were attributed to the progeny of a single leukemic blast cell with extensive replicative capacity, both in culture and in vivo,” they wrote.
Initially, “the infused CTL019 cells displayed the typical pattern of in vivo engraftment and expansion by CAR19-specific flow cytometry, followed by decline to an undetectable level in the peripheral blood” of the affected patient, the authors wrote. “The expansion and contraction phases and long-term persistence of CAR T cells were confirmed via qPCR using CAR-specific primers.” The patient was in complete remission at day 28.
However, they added, routine peripheral blood monitoring with quantitative polymerase chain reaction for CAR-specific sequences identified “the emergence of a second expansion phase of CAR cells starting at day 252, which did not correlate with re-expansion of CAR + T cells by flow cytometry.” Frank relapse soon followed.
Analysis confirmed “that the lack of detection of CD19 by flow cytometry was due to CAR19 binding in cis to CD19 on the surface of leukemic blasts, thus masking the epitope from detection by standard flow cytometry,” the authors wrote.
Study funding was provided by Bristol-Myers Squibb, Novartis, the National Institutes of Health, and others. Dr. Ruella and several of his colleagues work under a research collaboration involving the University of Pennsylvania and the Novartis Institutes of Biomedical Research and are inventors of intellectual property licensed by the University of Pennsylvania to Novartis.
SOURCE: Ruella M et al. Nat Med. 2018 Oct 1.