Analysis Finds Link Between Ibrutinib’s Effect on CAR T-Cell Expansion, Toxicity in Mantle Cell Lymphoma

An fresh look at trial results that propelled the only FDA approval of a chimeric antigen receptor (CAR) T-cell therapy for mantle cell lymphoma (MCL) shows prior treatment with ibrutinib, a first-generation Bruton tyrosine kinase (BTK) inhibitor, can improve outcomes—but at a price.¹

Patient data from ZUMA-2 (NCT02601313), a single-arm trial of 74 patients with relapsed or refractory MCL previously treated with chemotherapy, an anti-CD20 antibody, and BTK inhibitor, led to the 2020 approval of brexucabtagene autoleucel (brexu-cel), a CD-19 directed therapy sold as Tecartus (Gilead). The overall response rate for brexu-cel was 87%, with a complete remission (CR) rate of 62%.²

A remaining question—and one of importance today—is how patients fared based on what treatment they received prior to brexu-cel. Authors from Dana Farber Cancer Institute, Massachusetts General Hospital, and Harvard Medical School, led by Eli P. Darnell, MD, sought to address this question through a series of tests involving blood samples from patients in ZUMA-2, comparing cell behavior and clinical outcomes for patients treated with ibrutinib (Imbruvica; Pharmacyclics/Janssen) and acalabrutinib (Calquence; AstraZeneca), a second-generation BTK inhibitor. Findings are to be published in the February 24, 2026, issue of Blood Advances.¹

Sequencing of therapies has becoming increasingly challenging in the treatment of MCL and other blood cancers, as the growing number of options and therapeutic classes invites debate: which to give first, and to which patients?

All patients in ZUMA-2 had received prior treatment with a BTK inhibitor. Of 68 evaluable patients in cohort 1, 52 received ibrutinib only, 10 received acalabrutinib only, and 6 received both agents. To isolate BTK inhibitor-specific effects, patients who received both drugs were excluded from the analysis. Baseline characteristics were generally similar across groups, although the ibrutinib cohort had higher rates of confirmed bone marrow involvement (54% vs 30%) and extranodal involvement (60% vs 30%).¹

Those Exposed to Ibrutinib See Superior PFS

Patients previously treated with ibrutinib had superior progression-free survival (PFS), with a median of 26.51 months after brexu-cel, compared with 6.57 months for those exposed to acalabrutinib (P = .0067). At 24 months post-infusion, 53% of ibrutinib-treated patients were progression-free vs only 23% of those treated with acalabrutinib. Baseline measurements showed this could not be attributed to tumor burden. However, there was no difference in overall survival between the 2 groups.

The authors note that their findings differ from recent real-world data presented by the Center for International Blood and Marrow Transplant Research, which analyzed outcomes for 361 patients with MCL who received brexu-cel; this group included 171 treated with ibrutinib, 137 with acalabrutinib, and 53 with zanubrutinib (Brukinsa; BeOne Medicines). Although that study revealed trends toward improved response rates and survival in patients exposed to ibrutinib, the differences did not reach statistical significance.³

“This data set differs from the ZUMA-2 cohort because it largely reflects standard-of-care treatment of a heterogenous group of nonrandomized patients,” the authors wrote. “Ultimately these findings do not definitively show superiority for a particular BTK [inhibitor] ahead of brexu-cel, and randomized prospective trials are needed to determine whether there is a clinical benefit to ibrutinib exposure vs other BTK [inhibitors] before brexu-cel therapy.”

Enhanced CAR T-Cell Expansion, Along With CRS

Ibrutinib was a breakthrough when it was first approved to treat R/R MCL in 2013 and a year later for patients with at least 1 prior treatment for chronic lymphocytic leukemia. However, its off-target effects became well-known, which developers of second-generation therapies, including acalabrutinib and zanubrutinib, sought to address.

In April 2023, ibrutinib was voluntarily pulled from the market for treatment of previously treated MCL when confirmatory trials did not meet standards for full approval, although this action did not affect the drug’s status in other indications.

The Dana-Farber investigators evaluating patients from ZUMA-2 found that the ibrutinib group had greater peripheral blood CAR T-cell expansion, with a median peak of 92 cells per microliter (µl) compared with 14 cells per µl in the acalabrutinib group (P =.007). This was accompanied by higher levels of inflammatory cytokines, which in turn corresponded with higher rates of CAR T-cell-related toxicities.

Incidents of cytokine release syndrome (CRS) of grade 2 or higher and neurologic events occurred more frequently in ibrutinib-exposed patients, with this trend continuing for events of grade 3 or higher. Patients with neurologic events of at least grade 2 had higher CAR T-cell expansion than those events of grade 1 or less (P = .004). This authors observed that this suggests a direct relationship between expansion and the severity of toxicity.

Connections Between BTK Inhibitors and CAR T-Cell Phenotypes

Analyses of comprehensive phenotypes revealed distinct differences in CAR T-cell characteristics based on prior treatment with the 2 BTK inhibitors. Single-cell profiling, using 4 samples from each BTK inhibitor group, demonstrated that brexu-cel products from ibrutinib-exposed patients were enriched for genes associated with cytotoxicity (IFN-γ, GZMA, GZMB, GNLY, PRF1, TNF) and effector function, while products from acalabrutinib-exposed patients showed increased expression of memory and naive phenotype markers (CCR7, SELL, TAP1).

“We identified a significant enrichment in genes related to T-cell cytotoxicity (P = .03) in product samples from ibrutinib-exposed patients compared with acalabrutinib-exposed patients,” the authors wrote. “The ibrutinib group trended toward a higher T-cell exhaustion gene set score, and the acalabrutinib group had an increase in naive gene set score.”

Flow cytometry confirmed these patterns, revealing that ibrutinib-exposed patients had increased frequencies of T helper 17 (Th17) and Th17.1 cells in their brexu-cel products. The Th17.1 phenotype—a subset that produces IFN-γ and has been implicated in inflammatory and autoimmune disorders—was particularly notable, as it independently correlated with increased CAR T-cell toxicity in the ibrutinib group.

Finally, the investigators looked at the CAR T cells 7 days post-infusion, and found that ibrutinib-exposed patients showed more pronounced effector memory (EM) differentiation, while acalabrutinib-exposed patients retained more central memory (CM) phenotypes. Of note, higher CD4+ and CD8+ EM:CM ratios on day 7 proved to be independent predictors of clinical response to brexu-cel across all patients, regardless of BTK inhibitor exposure.

“This suggests that ibrutinib exposure could prime CAR T cells toward effector phenotypes after antigen exposure, which may lead to an improved PFS in the ibrutinib group,” they wrote. “Increased frequency of CM in CAR T-cell products has historically been associated with better outcomes in refractory lymphoma.”

What the Findings Mean for Clinical Practice

The authors write that the differences likely stem from ibrutinib's dual inhibition of both BTK and the T-cell-specific kinase ITK, whereas acalabrutinib selectively targets BTK without affecting ITK. Meanwhile, they write, ITK inhibition has been shown to have a modulating effect on T-cell function.

“This may indicate an ibrutinib-driven Th17 polarizing effect on T cells. Th17 T cells have been shown to harbor antitumor effect, and efforts have been made to harness their phenotype for immunotherapy and cellular therapies,” they write. “Furthermore, Th17 cells are the inflammatory counterpart to the suppressive regulatory T cells (Treg) with which they share a lineage pathway.”

While second-generation BTK inhibitors, acalabrutinib and zanubrutinib, are increasingly prescribed to avoid toxicity, this analysis suggests there may be downstream effects on CAR T-cell therapy use. But given the small size of the ZUMA-2 population and especially the very small size of the acalabrutinib group relative to the ibrutinib group, the Dana Farber authors call for more research into this question.

“Prospective study of the effect of specific BTK [inhibitor] exposure before brexu-cel is needed to determine if our findings should inform clinical practice,” they wrote.

Noting current trends in clinical practice, they conclude, “Although introduction of brexu-cel in earlier lines of treatment for BTK [inhibitor]-naive patients is anticipated to improve clinical outcomes, determining the optimal selection of BTK [inhibitor] for MCL is important, as most patients will be exposed to a BTK [inhibitor] in a line of therapy before CAR T-cell therapy in the current treatment landscape.”

References

1. Darnell EP, Gallagher KME, Kanska J, et al. Ibrutinib exposure correlates with improved efficacy of CAR T cells in patients with mantle cell lymphoma. Blood Adv. 2026;10(4):1023-1034. doi: 10.1182/bloodadvances.2025018137
2. FDA approves brexucabtagene autoleucel for relapsed or refractory mantle cell lymphoma. News release. FDA. Updated July 27, 2020. February 13, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-brexucabtagene-autoleucel-relapsed-or-refractory-mantle-cell-lymphoma
3. Ahmed N, Thiruvengadam S, Hamadani M, et al. Real-world outcomes of brexucabtagene autoleucel for relapsed or refractory mantle cell lymphoma: a CIBMTR analysis. Blood Adv. 2025;9(20):5382-5396. doi:10.1182/bloodadvances.2024015014.