Adoptive Cell Therapies (ACT): An Overview

Adoptive cell therapy (ACT) is a powerful immunotherapy strategy that uses a patient’s (autologous) or donor’s (allogeneic) immune cells. These cells are often expanded and genetically engineered outside the body (ex vivo) to target and eliminate cancer cells (Abodunrin et al., 2025). Several distinct ACT approaches have been developed, each with unique mechanisms and applications.

CAR T-cell therapy is one such approach. This is arguably the most prominent form of ACT. The process begins with collecting T-cells from the patient’s blood. These T cells are then genetically engineered in a laboratory to express chimeric antigen receptors (CARs) on their surface. A CAR consists of an extracellular antigen-binding domain, often derived from an antibody fragment (scFv), that recognizes a specific antigen on tumor cells (e.g., CD19 on B-cell malignancies). It also consists of intracellular signaling and co-stimulatory domains (e.g., CD3ζ, CD28, or 4-1BB), which activate the T cell upon antigen binding. After engineering, these CAR T cells are expanded in large numbers and infused back into the patient (CAR T Cells: Engineering Immune Cells to Treat Cancer — NCI, n.d.). Once in the body, the CARs guide the T cells to cancer cells that express the target antigen. This leads to T cell activation, proliferation, and the potent, targeted killing of cancer cells (D. Sun et al., 2024). This approach has been described as administering a “living drug” due to the cells’ ability to persist and expand within the patient (CAR T Cells: Engineering Immune Cells to Treat Cancer – NCI, n.d.).

CAR NK-Cell Therapy: Natural killer (NK) cells are a type of cytotoxic lymphocyte in the innate immune system that can recognize and kill cancer cells without prior sensitization or major histocompatibility complex (MHC) restriction. Similar to CAR T-cells, NK cells can be engineered to express chimeric antigen receptors (CARs), thereby enhancing their tumor-targeting specificity and cytotoxic potential (Morcillo-Martín-Romo et al., 2025). CAR-NK cell therapy has several potential advantages over CAR T-cell therapy. For example, it has a lower risk of inducing severe side effects, such as cytokine release syndrome (CRS) and neurotoxicity. Furthermore, NK cells can be sourced from allogeneic donors, which reduces the risk of graft-versus-host disease (GvHD) and opens the possibility of “off-the-shelf” therapies (Morcillo-Martín-Romo et al., 2025).

Engineered T Cell Receptor (TCR) Therapy: In this approach, T cells are genetically engineered to express specific T cell receptors (TCRs) that recognize tumor-associated antigens (Irvine et al., 2022). Unlike CARs, which typically target cell surface antigens, TCRs can recognize processed intracellular peptides presented on the cancer cell surface by major histocompatibility complex (MHC) molecules (Stephan, 2021). This significantly broadens the range of potential tumor antigens that can be targeted, including those derived from intracellular proteins, which constitute the vast majority of cellular proteins (AI Nanobots: Transforming Pharma’s Precision Medicine Landscape — Eularis, n.d.).

Tumor-Infiltrating Lymphocyte (TIL) Therapy: TIL therapy involves isolating T cells that have naturally infiltrated a patient’s tumor because these cells are often reactive against the cancer. These TILs are then activated and multiplied in large numbers outside the body before being reinfused into the patient (Greenberg, n.d.). The goal is to provide the patient with a large army of tumor-specific T cells capable of mediating an anti-tumor response.

Scientific Principles of Immune Cell Reprogramming

The ability to modify or reverse the fate of a cell experimentally is a cornerstone of engineered immune cell therapies (Abu Taha et al., 2025; Suma Sri Potti et al., 2025; Weerarathna et al., 2025). A cell’s identity is determined by its specific epigenetic and transcriptional landscape. Reprogramming involves altering these landscapes to generate a desired immune cell type or enhance its function. This can be achieved through several experimental approaches, including the enforced expression of specific transcription factors. For instance, introducing key lineage-specific transcription factors can convert one somatic cell type into another or even induce pluripotency (Team EMB, 2025). This principle is fundamental to genetic engineering processes, such as CAR T-cell or CAR-NK cell generation. In these processes, viral vectors or other gene delivery methods introduce genetic material encoding the CAR into target immune cells.

The immune system’s primary role is to detect and eliminate pathogens, foreign particles, and aberrant cells, including tumor cells, in order to maintain homeostasis (T. Sun et al., 2024). Immune engineering seeks to leverage and enhance these natural capabilities. This field focuses on applying fundamental immunological discoveries to engineer innovative strategies for disease prevention, detection, and treatment by precisely modulating immune activity. This modulation can involve bolstering defenses or tempering overactive responses (Greenbaum et al., 2021; Logesh et al., 2024; Pires et al., 2019).

Current Successes and Prevailing Limitations

Adoptive cell therapies, particularly CAR T-cell therapies, have achieved remarkable success in transforming the treatment landscape for several hematological malignancies. As of April 2023, six CAR T-cell products had received regulatory approval, showing unparalleled effectiveness in treating patients with relapsed or refractory B-cell leukemias, lymphomas, and multiple myeloma. For example, CAR T cells targeting the CD19 antigen have induced long-lasting remissions in a significant proportion of patients with B-cell acute lymphoblastic leukemia (B-ALL) and B-cell non-Hodgkin lymphoma (B-NHL) (D. Sun et al., 2024). CAR-NK cells have also shown promise in early clinical trials, demonstrating favorable safety profiles and encouraging efficacy (Morcillo-Martín-Romo et al., 2025).

Despite these triumphs, significant limitations persist. One major challenge is the limited efficacy of current ACTs in treating solid tumors (D. Sun et al., 2024). Solid tumors present a formidable barrier due to factors such as inefficient infiltration of engineered cells into the tumor mass, heterogeneous expression of target antigens, and a profoundly immunosuppressive tumor microenvironment (TME) (Irvine et al., 2022). The TME can actively inhibit the function of infused immune cells through various mechanisms, including the presence of immunosuppressive cells (e.g., regulatory T cells and myeloid-derived suppressor cells), physical barriers such as a dense extracellular matrix, and metabolic challenges.

Toxicity remains a serious concern, especially with CAR T-cell therapies. Cytokine release syndrome (CRS), which is a systemic inflammatory response resulting from the rapid activation and proliferation of CAR T cells, and immune effector cell-associated neurotoxicity syndrome (ICANS) can be life-threatening. Antigen escape, in which tumor cells downregulate or lose the target antigen, can lead to relapse following an initial response. Furthermore, the ex vivo manufacturing process for autologous cell therapies is complex, expensive, and time-consuming. It typically takes several weeks from T-cell collection to product infusion (D. Sun et al., 2024). This “one patient, one batch” approach limits scalability and accessibility (Stephan, 2021). Engineered T-cells can also become dysfunctional or “exhausted” after prolonged antigen exposure within the tumor microenvironment (TME) (Irvine et al., 2022). Finally, on-target, off-tumor toxicity can occur if the target antigen is also expressed in healthy tissues, causing unintended damage (D. Sun et al., 2024). General immunotherapy side effects, such as flu-like symptoms, skin reactions, and gastrointestinal issues, can impact patients’ quality of life (Booth & Roland, 2024).

The Rationale for In Vivo Immune Cell Reprogramming

The limitations of conventional ex vivo engineered cell therapies have spurred research into in vivo immune cell reprogramming strategies. The basic concept involves delivering the genetic engineering machinery directly to patients to program immune cells within their natural physiological context (Stephan, 2021). This approach offers several potential advantages that could address many prevailing challenges.

First, in vivo programming could significantly simplify the manufacturing process. Rather than using complex, individualized ex vivo cell culture and genetic modification, in vivo strategies could use “off-the-shelf” reagents, such as nanoparticles carrying genetic payloads. These reagents can be mass-produced, stored, and administered more like conventional pharmaceuticals. This simplification could reduce costs, shorten the time to treatment, and expand patient access beyond specialized treatment centers (Stephan, 2021).

Secondly, programming immune cells within their physiological environment may result in cells that are more functional and persistent. Ex vivo culture conditions often involve supraphysiological levels of cytokines and can alter cell phenotypes or lead to exhaustion before the cells are infused into the patient (Stephan, 2021).

In vivo programming avoids these artificial conditions, enabling immune cells to be engineered in their native environment and potentially resulting in more robust and durable anti-tumor responses. Additionally, in vivo methods usually do not require lymphodepleting preconditioning regimens for recipients, which are often necessary for ex vivo therapies to make space for infused cells (Stephan, 2021).

The potential of in vivo programming to democratize access to advanced cell therapies is particularly compelling. Current ex vivo adoptive cell therapies (ACTs), such as CAR T-cell therapy, are logistically demanding and expensive, largely confining their availability to well-resourced academic medical centers (D. Sun et al., 2024). The shift towards

In vivo reprogramming using readily manufacturable nanomedicines could drastically reduce the specialized infrastructure and personnel required. This could make these powerful treatments accessible to a much larger global patient population, similar to how monoclonal antibody therapies became widely available after their initial complex development phases. Table 1 provides a comparative overview of ex vivo versus in vivo immune cell programming strategies, highlighting these key differentiators.

The development of nanorobots for medical applications marks a significant advancement in the precision of engineering at the cellular and molecular levels. These sophisticated nanoscale entities are designed to perform complex tasks within the human body, opening new avenues for diagnosis and therapy (Suma Sri Potti, 2025).

Design, Materials, and Construction of Medical Nanorobots

Medical nanorobots are typically defined as autonomous structures at the nanoscale, ranging from approximately 1-100 nm (Immunotherapy Side Effects, 2019; Program for Immune Engineering, n.d.; Naik et al., 2024) to 0.1-10 µm (Weerarathna et al., 2025). These nanorobots are engineered to perform specific medical interventions. This size range enables interaction with biological components at a fundamental level. The design and construction of these nanorobots involve the careful selection of materials to ensure biocompatibility, functionality, and stability within the physiological environment (Fu et al., 2025).

A variety of materials are employed in nanorobot fabrication:

• The presence of biocompatible organic components is indicated by the following: Lipids are frequently utilized in the fabrication of nanocarriers, such as liposomes, while polymers can provide structural frameworks or form nanoparticles for drug encapsulation (Onkar et al., 2024). In the field of nanotechnology, DNA is utilized as a structural material in a process known as “DNA origami,” which enables the precise fabrication of nanoscale structures with programmable functionalities (Naik et al., 2024).
• The following categories comprise inorganic materials: Carbon, frequently in the form of nanotubes or diamond-like coatings, is valued for its inertness, strength, and thermal conductivity (Naik et al., 2024). Gold nanoparticles are utilized for their unique optical properties in imaging or photothermal therapy, and some designs even propose mechanical disruption of cells using gold nanostructures (Naik et al., 2024). Silica is another inorganic material that is utilized due to its stability and ease of surface functionalization (Onkar et al., 2024).
• The following components are of a biological nature: An innovative approach involves the incorporation of biological entities into the design of nanorobots, encompassing the utilization of biological components as integral components of the nanorobot or as a constituent part of its operational functionality. This encompasses genetically modified bacteria, including non-pathogenic strains of Salmonella, which can be engineered to target tumors and deliver therapeutic payloads (Naik et al., 2024). Viruses are of particular interest in this regard due to their intrinsic capacity to facilitate the delivery of genetic material. Consequently, they have emerged as a source of inspiration for the design of nanorobots (Aggarwal & Kumar, 2022; Glécia Virgolino da Silva Luz et al., 2016).

The construction techniques for nanorobots include molecular self-assembly, wherein components spontaneously organize into the desired structures, as well as more direct fabrication methods such as electron beam lithography and chemical vapor deposition (Team EMB, 2025). The bottom-up assembly of nanostructures is also facilitated by nanomanipulation using scanning probe microscopes (SPMs) (Naik et al., 2024). Key design principles emphasize the optimization of size for navigation through biological barriers, the selection of appropriate shapes for specific functions, the capacity to bear a payload, and, crucially, biocompatibility to avert adverse immune responses (Fu et al., 2025).

Translational and Technical Challenges of AI-Guided Nanorobots

Notwithstanding the encouraging outlook, several substantial challenges must be addressed before AI-guided nanorobots can be translated into clinical practice. First, the real-time decision-making by AI systems in vivo necessitates ultra-compact, biocompatible processing units. However, these units currently face constraints related to power, miniaturization, and thermal dissipation. Secondly, biosafety concerns encompass nanoparticle-induced toxicity, immunogenicity, and the potential for chronic accumulation in vital organs such as the liver and spleen. Thirdly, the potential for off-target effects, wherein nanorobots may interact with non-cancerous cells or tissues due to non-specific surface markers or biodistribution variability, persists as a substantial impediment. Furthermore, the ethical landscape is intricate; the implementation of autonomous therapeutic systems within the human body gives rise to inquiries concerning control, consent, and liability. These considerations necessitate meticulous long-term preclinical evaluation, standardized safety metrics, and regulatory frameworks to guide subsequent human trials (Huhulea et al., 2025).