In Vivo CAR-T: An Integrated Framework

In Vivo CAR-T: An Integrated Framework from Preclinical Development to Clinical Bioanalysis

Opportunities and Challenges in In Vivo CAR-T Development

In recent years, in vivo chimeric antigen receptor T-cell (in vivo CAR-T) therapy has emerged as a significant direction in oncology and, increasingly, in autoimmune diseases. Compared to conventional ex vivo CAR-T approaches, in vivo CAR-T directly engineers T cells within the patient’s body, substantially reducing manufacturing costs, shortening treatment timelines, and improving therapeutic accessibility. Driven by advances in targeted delivery technologies such as lipid nanoparticles (LNPs) and lentiviral vectors (LVVs), in vivo CAR-T is transitioning from concept to clinical translation. By bridging tumor immunology with advanced therapeutic modalities, this approach has gained considerable attention from both academic and industrial communities^1-2.

The core distinctions between the two approaches are summarized below (Figure 1):

• Ex vivo CAR-T: Requires extraction of patient T cells, ex vivo modification, cell expansion, and final infusion. This multi-step process results in several weeks of treatment and elevated costs.
• In vivo CAR-T: Delivers CAR constructs directly into the body via delivery systems, enabling in situ generation of CAR-T cells and rapid activation of the anti-tumor microenvironment.

Figure 1. Comparison of Ex Vivo and In Vivo CAR-T Therapies

This ‘in situ generation’ model confers significant advantages in production and application but also introduces substantial system complexity. From targeted delivery and gene expression to immune response and safety assessment, each step is challenging to isolate and validate independently, making preclinical research particularly demanding.

To address these challenges, WuXi Biology has established an integrated in vivo CAR-T research and evaluation framework. This standardized, seamless workflow spans from molecular design to in vivo validation, enhancing preclinical research efficiency and data interpretability while effectively supporting progression toward Investigational New Drug (IND) applications.

Integrated In Vivo CAR-T Preclinical Research Platform

WuXi Biology has constructed an integrated evaluation and research framework for in vivo CAR-T, emphasizing end-to-end continuity from initial design to in vivo validation. This ensures seamless connections between each stage, enabling more efficient and precise support for the overall advancement and systematic assessment of in vivo CAR-T products.

Aligned with the complete development pathway of in vivo CAR-T, WuXi has established three synergistic core modules (Figure 2):

1. Binder Screening and CAR Engineering Design
2. Delivery System Development and Evaluation
3. In Vitro and In Vivo Functional and Safety Validation

Figure 2. WuXi Biology’s End-to-End In Vivo CAR-T Preclinical Solution

Binder Screening and CAR Engineering Design: Improving Candidate Quality Early in Development

Leveraging mature antibody discovery platforms—including phage display, hybridoma technology, and single B-cell analysis—this module supports screening, identification, and characterization of diverse binders (e.g., scFv, VHH, DARPin) and CAR extracellular antigen-binding domains. This enables efficient acquisition of both high-affinity and high-specificity candidate molecules (Figure 3).

Figure 3. Binder and CAR scFv Screening, Identification, and Characterization

Furthermore, our team has implemented high-throughput CAR functional screening systems (e.g., Jurkat reporter assays) to evaluate CAR-mediated signal activation strength and specificity, along with quantitative analysis of basal immune cell signaling. This early-stage assessment facilitates identification of highly active candidates with low background noise, thereby enhancing developability from the source.

Delivery System Development and Evaluation: Bridging Design and Expression

For non-viral delivery systems (e.g., LNP-RNA platform), the team has established comprehensive capabilities spanning sequence design, molecular preparation, and functional validation. This includes linear and circular mRNA design and production, LNP formulation, and evaluation of targeting efficiency, transfection efficacy, and expression duration. Efficient and stable CAR expression can be achieved through mRNA sequence design and UTR optimization. Simultaneously, the targeting efficiency and safety of tLNPs can be enhanced through lipid screening, formulation optimization, coupling method validation, binder selection, and coupling density optimization. Through a systematic evaluation of both carrier and payload, we established correlations between delivery system design parameters and functional outcomes, providing key insights for optimizing in vivo studies and drug delivery strategies (Figure 4).

Figure 4. LNP-RNA Delivery System Production and Evaluation

In Vitro and In Vivo Functional and Safety Validation: Systematic Assessment from Mechanism to Holistic Effects

In Vitro Validation

At the in vitro level, our CAR-T biology platform possesses six distinct types of toolboxes, including short-term and long-term cytotoxicity, cell proliferation, phenotype profiling, cytokine analysis, specificity assessment, and antigen expression quantification, systematically characterizing cell therapy efficacy through a comprehensive suite of functional analyses. This testing platform processes upstream-prepared delivery system samples (spanning vector construction to formulation optimization) to perform quantitative evaluation of tLNP (targeted lipid nanoparticle) expression efficiency and targeting performance. Accumulated >50 ready-to-go dual-reporter cell lines enable high-throughput and accurate cytotoxicity screening for both kinetic and end-point purposes. Various assay models, including luciferase reporter systems, PBMC co-culture models, and primary cell assays with multi-parametric readouts provide robust functional and mechanistic insights. Multi-color flow cytometry panels quantitatively analyze CAR-T cell phenotype while multiplex cytokine profiling facilitates early assessment of Cytokine Release Syndrome (CRS) risk. These integrated assays generate clinically relevant endpoints to support CAR-T development from discovery through preclinical validation (Figure 5).

Figure 5. In Vitro Functional Validation

In Vivo Validation

To more faithfully recapitulate human immune microenvironments, the team has developed diverse humanized mouse models. These include humanized peripheral blood mononuclear cells (hPBMC) and humanized hematopoietic stem cells (hHSC) models, generated by injecting PBMCs or HSCs into tumor-bearing immunodeficient mice. These models enable systematic evaluation of CAR-T in vivo expansion, functionality, and immune responses across various immunological reconstitution contexts and tumor models.

WuXi Biology has established over 70 hPBMC models covering 23 cancer types, supporting diverse preclinical evaluation needs (Table 1).

Table 1. Humanized Tumor Models Established by WuXi Biology

For autoimmune indications, WuXi Biology has developed a pristane-induced systemic lupus erythematosus (SLE) model in CD34+ HSC humanized mice, designed to recapitulate key features of human SLE pathogenesis. This fully humanized SLE disease model is tailored specifically for supporting in vivo pharmacological evaluation of CAR-T therapies ^3-4 (Figure 6).

Figure 6. In Vivo CAR-T Efficacy Evaluation in SLE Model

Addressing the complexity and dynamic nature of in vivo CAR-T processes, the platform integrates pharmacokinetics (PK), biodistribution analysis, and comprehensive immunophenotyping to characterize CAR expression, cellular dynamics, and immune responses. This deepens mechanistic understanding and enhances data interpretability. Additionally, multidimensional safety assessments—including clinical observations, cytokine profiling, and histopathology—provide preliminary safety data to support the candidate for further development (Figure 7).

Figure 7. In Vivo Efficacy and Safety Evaluation

Clinical Bioanalytical Strategies for In Vivo CAR‑T Therapies

In vivo CAR‑T products possess dual regulatory attributes as both gene therapy products and cell therapy products generated in situ, requiring bioanalytical strategies that simultaneously comply with guidance for cell therapy products and in vivo gene therapy products ^[5,6]. A single analytical platform is insufficient to comprehensively characterize the in vivo behavior of such complex therapeutics. WuXi AppTec Bioanalytical Services (BAS) has established a multi-platform integrated analytical system covering LC–MS/MS, PCR, flow cytometry (FACS), ligand-binding assays (ELISA/MSD/Luminex/Simoa), and ELISpot to support the development of different CAR-T product types at the clinical stage (Figure 8).

Figure 8. WuXi AppTec BAS CAR-T clinical bioanalysis platform

LNP lipid component pharmacokinetic analysis (LC–MS/MS)

In LNP‑mediated in vivo CAR‑T studies, LC–MS/MS can quantify ionizable lipids, PEGylated lipids, and other formulation‑specific components to characterize systemic exposure, tissue distribution, and clearance of LNP lipid components. Notably, the pharmacokinetics of a single lipid component cannot fully represent the in vivo fate of the intact LNP or its delivery efficiency to T cells; results should therefore be interpreted together with mRNA quantitation, CAR expression, and CAR‑positive cell data.

Major challenges include interference from endogenous lipids in biological matrices and difficulty in quantitative correction when stable isotope internal standards are lacking. Sample pretreatment should be optimized according to the physicochemical properties of different lipids, matrix type, and sensitivity requirements, with options including protein precipitation, liquid–liquid extraction, solid‑phase extraction, or combined strategies to improve cleanup and reduce matrix effects.

CAR‑Encoding Nucleic Acid and Vector‑Related Nucleic Acid Analysis (qPCR/ddPCR)

For pharmacokinetic analysis of in vivo CAR‑T, whether the vector is LNP or lentivirus, PCR remains the dominant technology for nucleic acid detection.

For LNP vectors delivering mRNA, CAR mRNA exposure is measured primarily by RT‑qPCR; the core challenge is the extreme lability of RNA, as ubiquitous environmental RNases pose a lethal threat, necessitating specialized RNA‑protective blood collection tubes or RNA preservatives added during clinical sample collection ^[7].

For lentiviral vectors, genomic DNA must be extracted and copy number quantitated at the DNA level, as this represents the gold standard for assessing long‑term persistence of in vivo CAR‑T cells. Regulatory expectations require qPCR or digital PCR (ddPCR) sensitivity to reach at least 50 copies per microgram gDNA (Figure 9).

Figure 9. Nucleic Acid Detection Analysis on the PCR Platform

CAR+ T Cell Enumeration and Cellular Kinetics Analysis (FACS)

Flow cytometry can monitor absolute counts of CAR+ T cells per blood volume to plot the classic in vivo CAR‑T expansion–contraction curve for efficacy and toxicity assessment. Generally, greater early expansion may correlate with improved efficacy but may also increase toxicity risk.

Practically, PK samples are stained for T cell markers and anti‑CAR antibodies and analyzed using absolute counting beads to obtain absolute counts of T cells and CAR‑T cells. Anti‑CAR reagents can be purchased, synthesized, or supplied by sponsors per requirements.

During method development and validation, key parameters should be verified according to product characteristics, typically including specificity of the anti‑CAR reagent, linear range and lower limit of detection, intra‑ and inter‑batch precision, and storage and handling conditions before sample processing.

A persistent challenge is developing anti-idiotype antibodies with high affinity and high interference resistance. Using specific anti‑CAR reagents combined with T cell surface markers (CD3/CD4/CD8) is recommended.

Pharmacodynamics Analysis (FACS)

Pharmacodynamic (PD) indicators for in vivo CAR‑T can be measured by flow cytometry (FACS); the most direct PD endpoint is whether target cells are effectively cleared. Appropriate panels are designed to evaluate drug efficacy by analyzing changes in target cell counts and proportions. For the common target B cells, detailed B cell panels (e.g., CD19, CD20, CD22) are used. Using CD19 as a B-cell marker, peripheral blood B cell counts are monitored at multiple time points (Figure 10) ^[8]. By dynamically tracking the rapid decline in peripheral blood B‑cell counts after dosing and their subsequent reconstitution, drug efficacy is assessed.  Sustained B‑cell depletion (B‑cell aplasia) is often a clinical surrogate endpoint for persistent CAR‑T activity.

Figure 10. Assess Drug Effect by Analyzing Changes in Target B Cell Counts and Proportions^[8]

Humoral Immunogenicity Analysis (ELISA/MSD)

Humoral immunogenicity assessment for in vivo CAR‑T must consider both the delivery system and CAR‑expressed products. For LNP delivery systems, anti‑PEG antibodies should be monitored because pre‑existing anti‑PEG antibodies may exist in healthy populations; clinical studies should include pre‑dose baseline testing to distinguish pre‑existing antibodies from treatment‑induced or boosted responses ^[9]. Detection can be performed using ELISA or MSD platforms (Figure 11), and assay reagents (e.g., PEG lipids or appropriate PEGylated compounds) should be selected according to formulation composition.

Figure 11. CAR-T Immunogenicity ADA Assay – PEG

For CAR‑expressed products, the CAR extracellular domain or scFv can be used as the capture antigen to develop bridging ELISA or MSD assays for anti‑CAR antibodies ^[10]. If viral vectors are used, antibodies against vector components such as envelope or capsid proteins should be evaluated according to vector type, and neutralizing antibody assays should be performed when necessary (Figure 12).

Figure 12. CAR-T Immunogenicity ADA Assay – CAR, P24

Method development should emphasize evaluating sensitivity, specificity, matrix effects, and drug tolerance. When soluble antigen, residual vector components, or other related substances in samples interfere with ADA detection, pretreatment strategies such as acid dissociation or solid‑phase extraction combined with acid dissociation (SPEAD) may reduce interference and improve ADA detection capability ^[11].

CAR-T Cellular Immunoassay (ELISpot)

ELISpot is the gold standard for assessing T cell function at the single‑cell level. Antigen peptide libraries are co‑cultured with patient PBMCs, and cytokines secreted by stimulated T cells (e.g., IFN‑γ) are captured in situ by antibodies on the plate, forming visible spots used to evaluate whether induced CAR‑T cells possess actual effector function (Figure 13)^[12].

Figure 13. Schematic outlining the workflow for detecting antigen-reactive T cells by ELISpot^[12]

Summary

In vivo CAR-T holds transformative potential, but its inherent complexity—spanning delivery, expression, functionality, and safety—demands a systematic and continuous research paradigm.

WuXi AppTec’s integrated platform unifies molecular design, delivery system development, humanized model establishment, and comprehensive in vitro/in vivo validation into a single, seamless workflow. This end-to-end solution transforms fragmented experiments into cohesive, data-rich research, significantly enhancing R&D efficiency and delivering robust, submission-ready evidence to accelerate IND filings and clinical translation.

References

1. Xu, J., Chen, Z., Su, L., Ren, A. & Mei, H. In vivo CAR cell therapy: from bench to bedside. J Hematol Oncol 18, 105, doi:10.1186/s13045-025-01759-2 (2025).
2. Bot, A., Scharenberg, A., Friedman, K. et al. In vivo chimeric antigen receptor (CAR)-T cell therapy. Nat Rev Drug Discov 25, 116-137 (2026). https://doi.org/10.1038/s41573-025-01291-5
3. Müller, F. et al. CD19 CAR T-cell therapy in autoimmune disease—a case series with follow up. N. Engl. J. Med. 390, 687-700 (2024).
4. Mougiakakos, D. et al. CD19-targeted CAR T cells in refractory systemic lupus erythematosus. N. Engl. J. Med. 385, 567-569 (2021).
5. NMPA. Guidelines for Research and Evaluation of Cell Therapy Products. 2021.
6. NMPA. Guidelines for Pharmaceutical Research and Evaluation of In Vivo Gene Therapy Products. 2022.
7. FDA. Guidance for Industry: Long Term Follow-Up After Administration of Human Gene Therapy Products. 2020.
8. Wang Q, et al. In Vivo CD19 CAR T-Cell Therapy for Refractory Systemic Lupus Erythematosus. N Engl J Med. 393, 1542-1544 (2025)
9. FDA. Immunogenicity Testing of Therapeutic Protein Products – Developing and Validating Assays for Anti-Drug Antibody Detection. 2019.
10. NMPA. Guidelines for Immunogenicity Studies of Drugs. 2020.
11. Neelapu SS. CAR-T failure: immune escape and T-cell exhaustion. Blood. 2019;134(23):1999-2001.
12. Charlesworth CT. et al. Identification of preexisting adaptive immunity to Cas9 proteins in humans. Nat Med. 25(2), 249-254 (2019).