An analysis of three clinical trials of tisagenlecleucel found that levels of chimeric antigen receptor (CAR) transgene (or the gene that is artificially introduced into a patient’s genome) are highly variable in patients with relapsed/refractory acute lymphocytic leukemia (ALL) and diffuse large B-cell lymphoma (DLBCL), suggesting that transgene levels are not a reliable biomarker for guiding clinical decisions in these patients.
Rakesh Awasthi, PhD, senior scientist at Novartis, which manufactures tisagenlecleucel, presented these findings at the 2019 American Association for Cancer Research Annual Meeting.
“With the emerging data, it is important to improve our current understanding regarding the significance of in vivo expansion and persistence of CAR T cells as it relates to response,” Dr. Awasthi told ASH Clinical News. “The transgene levels associated with maximal expansion and at later time points showed high variability among both responders and nonresponders [with ALL and DLBCL]. Based on the data presented, a definitive cut point predicting response could not be ascertained.”
Of the three included trials, two studied tisagenlecleucel in pediatric or young adult patients with ALL: ELIANA, which enrolled 75 patients, and ENSIGN, which enrolled 29 patients. The JULIET trial enrolled 93 adult patients with DLBCL. All participants received a single infusion of tisagenlecleucel.
To investigate the relationship between transgene persistence and clinical response, the researchers examined CAR transgene levels with quantitative polymerase chain reaction.
They found that responders and nonresponders in both patient cohorts had detectable CAR transgene levels, with a median time to maximal transgene level of nine to 10 days (range not provided). While there was a similar geometric mean maximal expansion between responders and nonresponders with DLBCL, there was a 1.7-fold difference in patients with ALL (p values not reported).
The investigators observed high interindividual variability in transgene levels in both disease cohorts. CAR T-cell expansion levels were lower in the blood of patients with DLBCL, which the researchers suggest may be “due to partitioning of functional CAR T cells to target sites including lymph nodes.”
Compared with nonresponders, responders in both disease cohorts had longer median time to their last quantifiable transgene level and longer transgene half-life – two markers of T-cell persistence. Despite this observation, “in some cases, transgene levels were not detectable at later timepoints in patients with continued response,” Dr. Awasthi noted. He added that a smaller proportion of patients still demonstrated a favorable clinical response following a reduction in levels to below the level of quantification.
“We have shown that pediatric patients with ALL can maintain durable responses despite loss of transgene,” Dr. Awasthi commented. “In certain patients, one potential reason for this observation is that the initial expansion and persistence sufficiently eradicated the tumor.”
He added that, in the DLBCL cohort, the expansion was similar between responders and nonresponders according to data from peripheral blood samples. “In addition, quantifiable transgene levels were observed in some patients with DLBCL at the time of relapse. These findings underscore the importance of characterizing and understanding trafficking of CAR transgene to the tumor site by obtaining post-treatment and progression biopsies,” he concluded.
The study’s implications are limited by the small number of patients enrolled in these trials. It also is unknown whether these results will be generalizable to other approved or investigational CAR T-cell therapies.
The authors report relationships with Novartis, which sponsored both trials included in this analysis.
Awasthi R, Mueller KT, Yanik GA, et al. Evaluation of in vivo chimeric antigen receptor (CAR) transgene levels in patients (pts) treated with tisagenlecleucel. Abstract #CT237. Presented at the American Association for Cancer Research Annual Meeting, April 2, 2019; Atlanta, GA.