Molecular Monitoring After CAR T-Cell Therapy in Follicular Lymphoma
How integrating tumor-informed ctDNA, PET/CT and CAR T-cell kinetics helps characterize response after cellular therapy
CAR T-cell therapy has expanded treatment options for patients with relapsed or refractory follicular lymphoma (FL), inducing deep responses even in heavily pretreated patients. But once a patient responds, a key question remains: how can clinicians determine whether that response is truly durable, especially when metabolic activity on imaging doesn't always represent active lymphoma?
Follicular Lymphoma in the CAR T-Cell Era
FL is an indolent B-cell malignancy marked by cycles of response and relapse. Anti-CD19 CAR T-cell therapy has changed outcomes for relapsed/refractory patients, but inflammatory changes after immunotherapy can complicate PET/CT interpretation — raising the question of whether longitudinal molecular monitoring can add information beyond imaging.
A New Monitoring Challenge: Tumor, Therapy and Imaging
CAR T-cell therapy is a living cellular product that expands, peaks, and contracts after infusion — while clinicians simultaneously need to track whether the lymphoma-derived molecular signal is clearing, persisting, or returning. A prospective study combined personalized ctDNA, serial PET/CT, and CAR T-cell quantification by flow cytometry and qPCR to address this directly.
Study Overview and Scientific Collaboration
Led by Dr. Ana Jiménez-Ubieto and Dr. Santiago Barrio at Hospital Universitario 12 de Octubre in Madrid, the study followed 10 evaluable patients with relapsed/refractory FL (nine POD24, median three prior treatment lines) over a median follow-up of 36 months, integrating ctDNA MRD, PET/CT with Deauville scoring, and CAR T-cell kinetics.
Personalized Molecular Monitoring: From Tumor Profiling to LiqBio-MRD
Baseline lymph node DNA was screened with a 56-gene lymphoma panel, identifying trackable mutations in all evaluable patients (CREBBP, KMT2D and EP300 most frequent). An individualized multiplex mini-panel was built per patient, with follow-up cfDNA sequenced at ~500,000× depth and an average of 4.5 mutations tracked per patient across 45 evaluable samples.
Molecular Response After CAR T: Timing Matters
Early ctDNA positivity was common — all six day+7 samples remained positive, even in patients who later achieved durable remission. What mattered was the trajectory: all durable responders cleared ctDNA at or around month 3, while the two patients who progressed had detectable ctDNA at or before radiographic relapse.
When PET/CT and ctDNA Tell Different Stories
All 14 PET/CT-negative assessments were also ctDNA-negative. The most informative cases were discordant ones: two of four PET-positive assessments were ctDNA-negative and did not correspond to progression — including one patient whose new lymph node finding two years post-infusion was ultimately excluded as lymphoma by biopsy after repeated molecular negativity.
CAR T-Cell Kinetics: Monitoring the Therapy Itself
CAR T-cell expansion, measured by flow cytometry and qPCR, peaked around day+7 and became undetectable by month 3 in most patients. The one patient with poor CAR T-cell expansion was also a progressor — a biologically interesting observation, though the cohort is too small to establish this as a predictive relationship.
From Published Evidence to an Integrated Altum Monitoring Framework
The tumor-informed, patient-specific principle used in the study aligns with Altum TRACKseq, while the therapeutic-cell kinetics approach mirrors Altum DUALseq — together offering a framework to monitor both the tumor and the therapy, interpreted alongside clinical and imaging context.
Clinical and Translational Implications
Molecular trajectories may be more informative than isolated early measurements. ctDNA can add molecular context to equivocal or unexpectedly positive PET/CT findings after immunotherapy, and tumor response together with treatment kinetics can be studied as complementary longitudinal biomarkers in translational and clinical development programs.
Limitations and Future Directions
The central lesson isn't that one technology should replace another: response after cellular therapy is best understood through complementary signals — the tumor, the therapy, and the clinical/imaging context. The optimal molecular response window after CAR T-cell therapy in FL remains to be defined prospectively.
Download the Full Whitepaper
Our new whitepaper, Molecular Monitoring After CAR T-Cell Therapy in Follicular Lymphoma, explores how tumor-informed MRD and therapeutic-cell kinetics can be integrated into longitudinal clinical and translational studies.
Are you developing a CAR T-cell or cellular therapy program? Talk to Altum Sequencing about molecular monitoring strategies for cellular therapy development.
Altum Sequencing is a Madrid-based precision oncology company spun off from Hospital Universitario 12 de Octubre, developing ctDNA-based liquid biopsy technology for cancer monitoring and MRD detection.
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