Therapeutic frontiers in macrophage-based cell therapies extend from neurodegenerative and cancerous disorders to regenerative and reconstructive treatments. In the context of autologous therapies, macrophage manufacturing represents one of many scenarios where industrial commercialization has not caught up to the latest scientific advances. Though monocyte to macrophage differentiation is well-characterized, its downstream processing continues to face significant administrative and operational hurdles, but not for much longer.
Monocyte-derived macrophages in adherent culture are a critical intermediate between leukapheresis and a therapeutic product available to the patient. © Green Elephant Biotech.
Macrophage-based cell therapies are advancing steadily from experimental concept to clinical reality. As highly heterogeneous, tissue-resident innate immune cells, macrophages are uniquely capable of adapting to local microenvironmental signals, with phagocytosis serving as their primary homeostatic function. These adaptive properties are now being actively leveraged in regenerative medicine, the treatment of solid tumors, and inflammatory conditions (1).
Nonetheless, the constraints common across today’s bioprocessing industry, including limited cell yield and insufficient quality consistency across therapy batches for larger patient cohorts, are equally present in macrophage manufacturing and the respective therapy development (2). A randomized controlled trial of the promising MAcrophage Therapy for liver CirrHosis (MATCH01), for example, encountered substantial variability in the efficiency of monocyte conversion to final product during manufacturing and ultimately failed to meet its primary endpoints (3).
A central driver of these challenges is the anchorage-dependent nature of macrophages. While certain macrophage populations of specific origin and maturation stage can proliferate in suspension, primary macrophages derived from bone marrow, peripheral blood, and tissues are strongly adherent (4). Providing sufficient surface contact to support survival and differentiation at scale, while enabling efficient and contamination-free harvesting, presents well-documented logistical and operational challenges across multiple adherent cell lines (2), including induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs).
Simultaneously, macrophage-related research tools, such as macrophage markers, are projected to grow at a compound annual rate of 6.7% between 2026 and 2033, reflecting persistent interest in chronic disease research and a clear pharmaceutical incentive to advance the field (5). This piece examines the promise of macrophage-based therapies through the lens of monocyte to macrophage differentiation or macrophage manufacturing at scale and the realities of translating that process from bench to clinic.
Monocyte to macrophage differentiation begins with adherence – a functional milestone
As noted above, monocytes are myeloid-derived precursor cells that circulate in the bloodstream and give rise to macrophages under precise conditions, such as tissue injury or inflammation. Their recruitment into tissues and subsequent differentiation are governed by chemokine gradients, most notably through C-C chemokine receptor type 2 (CCR2) which binds chemokine C-C motif ligand 2 (CCL2), secreted by nucleated cells in response to inflammatory stimuli (6). In clinical settings, monocytes are harvested from patients via leukapheresis, or white blood cell collection, a process also applied in chimeric antigen receptor (CAR)-T cell therapies.
Approximately 85% of circulating blood monocytes are classified as “classical” CD14⁺ cells, representing the principal population capable of differentiating into macrophages and dendritic cells (7). It is important to note that monocyte quality and quantity vary according to the patient’s health status, age, and prior treatment history. Sourcing monocytes even from healthy donors introduces its own complexities, with potential downstream implications for the final product’s safety and efficacy (2).
In vitro macrophage manufacturing protocols vary depending on the intended application, but robust processing typically requires the addition of macrophage colony-stimulating factor (M-CSF) to the culture system. Viability can be further improved by supplying agents that mimic the inflammatory microenvironment: interleukin (IL)-4, IL-10, and transforming growth factor (TGF)-β. Following approximately 6 days of incubation in a 5% CO₂ atmosphere at 37°C, cells are expected to display an adherent phenotype and require gentle detachment from the culture vessel. Adherence, in this context, functions as a practical indicator of successful monocyte to macrophage differentiation (8).
At this stage, M0 macrophages can be directed toward specific phenotypic and functional states in response to microenvironmental cues, depending on the target pathology and therapeutic strategy. M1 macrophages, induced by lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, IL-1β, and similar agents, exhibit pro-inflammatory behavior, actively phagocytosing and eliminating pathogens. M2 macrophages, promoted by IL-4, IL-13, and IL-10, favor an anti-inflammatory, tissue-regenerative mode (4). A compelling clinical illustration of the latter involves M2 macrophage transplantation in non-acute stroke patients, which produced a 75% improvement on the NIH Stroke Scale with no serious adverse events (9).
Legacy systems that work in the lab fall short in functionality and efficiency at scale
Conventional monocyte to macrophage differentiation relies on T-25 or T-75 tissue culture flasks, with potential scale-up into larger multi-layer stacking systems. In large-scale manufacturing, however, the number of vessels required per batch can reach into the hundreds, introducing variability and inconsistency, particularly in open-system environments. Macrophages are inherently sensitive to ex vivo manipulation, and each genetic modification, media exchange beyond the standard differentiation step, and expansion event represents an additional manufacturing risk (10).
This sensitivity has direct implications for polarization stability as well. M1- and M2-like macrophages can revert toward an unpolarized phenotype if the culture medium is not appropriately supplemented. One study reported a 50% reduction in M2-like cells following 6 days of culture in polarizing agent-free medium. This high phenotypic responsiveness also constrains harvesting options. Mechanical methods, including scraping, or enzymatic approaches like trypsin treatment of adherent macrophages, can compromise both viability and function. Multiple studies have demonstrated that trypsin exposure alters macrophage membrane protein composition and permeability — properties, critical to the cell’s therapeutic capacity (11).
As with the majority of cell-based therapies, commercializing macrophage formulations requires strict good manufacturing practice (GMP) compliance. These conditions are notoriously difficult to replicate in a flask-based environment, where manual harvesting and environmental exposure remain unavoidable. Donor-to-donor variability in monocyte starting material, combined with the demand for GMP-grade cytokines and culture media, further complicates production standardization and reproducibility, constraining developers’ ability to bring potentially life-saving therapies to patients (2, 10).
While PSC-derived macrophages are sometimes proposed as a solution to challenges of limited proliferative capacity and short cultivation windows, this approach carries its own trade-offs. Although PSC-derived macrophages share functional and transcriptomic similarities with their monocyte-derived counterparts, the phenotype of tissue-resident macrophages remains distinct and may be more clinically relevant in specific indications. One emerging application of PSC-derived macrophages gaining increased attention is the Monocyte Activation Test (MAT), a pyrogen detection assay used in the quality control of biologics and therapeutics, driven by the growing imperative to move away from animal-based testing models (12). Generating PSC-derived macrophages in a bioreactor may appear operationally simpler, but this approach does not resolve the fundamental tension between scalability and cell integrity described earlier (2, 13).
Large-scale macrophage manufacturing will move forward outside the flask paradigm
In the United States alone, patent applications for macrophage-based therapies have more than doubled since 2015, with similar growth trends observed in Europe and Japan, reflecting sustained interest in macrophage manufacturing as a platform for treating oncological and inflammatory diseases. Does this research momentum translate into clinical activity? By 2021, approximately 606 registered clinical trials with no signs of declining research activity support that statement (14).
The commercial reality, however, is more sobering. With 74% of FDA Complete Response Letters in the cell and gene therapy field attributed to manufacturing and quality deficiencies, a significant proportion of ongoing clinical trials are at risk of failing to meet endpoints in larger patient cohorts, as illustrated by MATCH01. The tendency to prioritize clinical speed over manufacturing maturity is a well-documented factor, though its root causes are clear and addressable (15).
Closed bioprocessing and manufacturing automation represent 2 of the most actionable strategies for producing reproducible, GMP-compliant cell therapies without sacrificing biological quality. Quality by design and proactive regulatory engagement may appear to slow the path to commercialization, but they do not — particularly when eliminating the need for repeated process revalidation. Automated workflows integrated into pre-optimized processes have been shown to deliver a 74% reduction in manufacturing costs and a 100-fold improvement in facility throughput, as demonstrated by Multiply Labs (15).
Approaches to monocyte to macrophage differentiation scale-up will undoubtedly vary by context, but the biology and functional characteristics of these cells demand that current process-level failures be addressed directly. Rather than introducing the heterogeneity and complex standardization requirements of stem cell-derived systems, next-generation culture vessels must be designed to preserve the macrophage’s native adherent biology while enabling high-yield reproducible harvesting without multiplying process complexity (15). The flask is where macrophage manufacturing begins, but this does not mean that this is where the process should end.
Macrophage cell therapy is no longer constrained by biology. The differentiation process is well-characterized, the polarization toolbox is mature, and the clinical rationale across various indications is being established. What continues to limit macrophage manufacture and clinical programs is infrastructure — more specifically, the absence of culture systems designed to support adherent immune cell manufacturing at scale.
As seen throughout this entry, macrophage manufacturing challenges in cell therapy are solvable process challenges. One of the paths forward lies in closed and automated bioprocessing platforms that respect the macrophage’s native adherent biology, while delivering the GMP compliance that clinical and commercial programs demand. The same strategy that underlies macrophage manufacturing could benefit a wider adoption of essential patient safety techniques, such as MAT, across cell therapy and vaccine production. To close the gap between validated biological concepts and the therapies that will reach their respective patient cohorts requires purpose-built systems, not adapted culture flask workflows.
Addressing the manufacturing gap: CellScrew® and Archimedes® One
Escape the vessel proliferation paradox that makes macrophage manufacturing unmanageable at scale with CellScrew®. A single compact vessel geometry supports the surface-attachment requirements of differentiating macrophages and significantly reduces handling steps, along with the spatial footprint of the process. With harvest efficiencies above 90% for adherent cell lineages, CellScrew® represents a familiar system outside of the flask paradigm.
Ready to upgrade towards automated process control and GMP-grade closed fluid management? Dynamic adherent bioreactor, Archimedes® One, extends the CellScrew® cultivation platform to full bioprocess integration. Integrated monitoring and control of pH, DO, and temperature provide the process visibility that flask-based systems simply cannot offer, enabling consistent differentiation conditions across batches without extensive manual handling.
More details surrounding clinical manufacturing and Early Access Program are available on our website!
References:
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- Rodgers, DT, Novobrantseva, T, Barcia, RN, Smart Cell Therapy: an industry perspective on macrophages as living drugs (2025), Cytotherapy 27: 849-63. doi: 10.1016/j.jcyt.2024.12.002.
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