Biomarkers of Cellular-Therapy Persistence and Functional Activity After Administration

Abstract

Cellular therapies, including chimeric antigen receptor (CAR) T-cell and other adoptive cell therapies, have revolutionized the management of various hematologic and solid malignancies. However, therapeutic efficacy is closely linked to the persistence and sustained functional activity of administered cells. Biomarkers that accurately reflect both the in vivo persistence and activity of these cellular products are critical for clinical decision-making, early detection of relapse, and optimization of treatment protocols. This review critically appraises current and emerging biomarkers for monitoring cellular-therapy persistence and function, integrating recent evidence and guideline-based recommendations to inform clinical practice.

Introduction

The advent of cellular therapies marks a paradigm shift in the treatment of cancer and immune-mediated diseases. Their clinical effectiveness hinges not only on immediate cytotoxicity but also on long-term persistence and functional activity of the infused cells. The ability to accurately monitor these parameters using robust biomarkers is fundamental for optimizing patient outcomes, guiding retreatment, and informing next-generation therapeutic designs. This review synthesizes recent advances in biomarker discovery, discusses their clinical and mechanistic relevance, and evaluates implications for practice and future research.

Epidemiology / Disease Burden

Cellular therapies have gained rapid adoption, particularly in hematologic malignancies such as B-cell acute lymphoblastic leukemia (ALL), diffuse large B-cell lymphoma (DLBCL), and multiple myeloma, where conventional therapies often fail. The global burden of relapsed/refractory disease in these populations underscores the need for therapies capable of inducing durable remissions. Real-world data indicate that loss of cellular-therapy persistence is a major contributor to relapse, heightening the clinical imperative for reliable biomarkers that can predict and monitor therapeutic durability.

Pathophysiology

The success of cellular therapies relies on the complex interplay between the infused cells and the host microenvironment. Post-infusion, cell persistence is influenced by factors such as antigen availability, host immune rejection, exhaustion phenotypes, and the cytokine milieu. Functional activity is not only defined by cytotoxic potential but also by proliferative capacity and immune modulation. Biomarkers reflecting these mechanistic underpinnings—such as cell surface markers (CD19, CD22), cytokine profiles (IL-2, IFN-γ), and exhaustion markers (PD-1, LAG-3, TIM-3)—provide windows into the biological fate and efficacy of the administered cells.

Risk Factors

Several patient- and therapy-specific factors modulate cellular-therapy persistence and function. Host factors include immunogenicity, prior therapies, disease burden, and the presence of immunosuppressive elements in the tumor microenvironment. Therapy-related determinants encompass cell dose, lymphodepletion regimen, transgene construct, and manufacturing variables. Understanding these risk factors is essential for interpreting biomarker kinetics and identifying patients at risk for early loss of therapeutic benefit.

Clinical Features

Clinically, loss of cellular-therapy persistence often precedes disease relapse. Symptoms may be non-specific or overlap with other post-treatment sequelae. Early identification relies on laboratory and imaging-based monitoring rather than overt clinical presentation. Functional activity loss can manifest as suboptimal response or recurrence of disease markers. Thus, the integration of biomarker-driven surveillance into routine follow-up is paramount for timely intervention.

Diagnosis

Diagnostic strategies for monitoring cellular-therapy persistence and function leverage both direct and indirect biomarkers. Quantitative polymerase chain reaction (qPCR) and flow cytometry are widely used to track circulating engineered cells via transgene detection or surface markers. Functional assays—such as cytokine release profiling, cytotoxicity studies, and single-cell transcriptomics—provide complementary insights into cell potency. Imaging biomarkers, including PET/CT with radiolabeled probes, are emerging as non-invasive tools for in vivo tracking. Multiparametric approaches, combining cellular and soluble biomarkers, enhance diagnostic accuracy and prognostic value.

Treatment & Management

Biomarker-guided management strategies are increasingly integral to optimizing cellular-therapy outcomes. Persistent detection of therapeutic cells correlates with durable remission, prompting extension or modulation of surveillance intervals. Conversely, rapid decline or loss of cellular biomarkers may trigger early salvage interventions, such as additional cell infusions or adjunctive immunomodulation. Monitoring functional biomarkers allows for risk stratification of cytokine release syndrome or neurotoxicity, informing preemptive or reactive management protocols in line with current guidelines.

Recent Advances / Emerging Therapies

Recent advances in biomarker discovery have yielded several promising candidates. Next-generation sequencing enables sensitive detection of clonal T-cell receptor rearrangements, while digital droplet PCR offers quantitative precision. Novel surface and intracellular markers, such as TIGIT and TOX, are being explored for their association with cell exhaustion and functional decline. Single-cell multi-omics platforms are elucidating the heterogeneity within infused cell populations, paving the way for personalized biomarker panels. Additionally, circulating extracellular vesicles and metabolic signatures are under investigation as surrogates for cellular-therapy activity. These innovations promise to enhance real-time monitoring and improve therapeutic refinement.

Guideline Recommendations

Professional bodies, including the American Society for Transplantation and Cellular Therapy (ASTCT) and the European Society for Blood and Marrow Transplantation (EBMT), endorse the use of serial biomarker assessments to guide post-infusion monitoring. Recommendations include periodic quantification of cellular products via molecular and immunophenotypic methods, functional assessment through cytokine profiling, and integration of clinical data for comprehensive management. Emphasis is placed on standardized assays and harmonized reporting to facilitate cross-trial comparison and real-world applicability.

Conclusion

Biomarkers of cellular-therapy persistence and functional activity are central to maximizing the clinical benefit of these transformative treatments. Advances in assay technology and mechanistic understanding are expanding the biomarker repertoire, enabling more precise, individualized monitoring. Incorporation of these biomarkers into routine clinical practice supports timely therapeutic adjustments, early relapse detection, and improved patient outcomes. Ongoing research and guideline evolution will continue to refine biomarker utility, fostering the next era of personalized cellular therapy.