USC turns immature immune cells into a renewable cancer-fighting platform
Scientists at the University of Southern California have built a renewable immune-cell platform that could change how cellular immunotherapies are manufactured and delivered. Instead of starting with mature macrophages, which are difficult to expand and fragile outside the body, the team worked with granulocyte-monocyte progenitors, or GMPs, an earlier stage of blood-cell development that can still generate functional immune defenders.
The result is a system that can be expanded in the laboratory, genetically engineered, and then used to produce replacement immune cells after administration. In mouse experiments, the engineered progenitors established themselves in bone marrow, generated new immune cells, and slowed the progression of blood cancers and solid tumors. The work also showed activity in a mouse model of chronic granulomatous disease, where the cells restored bacterial killing capacity.
A single developmental choice changed the entire therapy concept. By moving one step earlier in the immune-cell lineage, the investigators gained the ability to manufacture a continuing supply of therapeutic cells rather than relying on a one-time infusion of mature effectors.
Why progenitor cells may solve a manufacturing problem in cell therapy
Cell therapy has repeatedly run into the same bottleneck: enough therapeutic cells are hard to make, hard to preserve, and often hard to keep active long enough to matter. Mature macrophages are attractive because they naturally migrate into tissues and can infiltrate tumors, including solid tumors that often resist T-cell-based strategies. Yet once these cells fully mature, they are difficult to multiply in large quantities, harder to genetically modify, and vulnerable to damage during freezing and storage.
After infusion, mature macrophages can also accumulate in organs such as the lungs and liver rather than dispersing widely. Their relatively short persistence further limits how long any antitumor effect can last. The USC strategy addresses those constraints by expanding progenitor cells first, then engineering them before terminal differentiation.
The biological logic is straightforward. Progenitors can be grown in larger numbers while still retaining the ability to become functional macrophages and related immune cells. If those progenitors survive in the recipient and keep producing descendants, the therapy gains a built-in source of replenishment instead of depending on cells that may disappear quickly.
GMPs retained identity and could be expanded for extended periods
The team focused on a carefully defined chemical environment that allowed GMPs to survive and multiply for long periods in the laboratory without prematurely maturing. Even after extensive expansion, the cells maintained the molecular features that defined their identity and preserved the capacity to develop into functional immune cells when prompted.
That matters because the usual assumption in blood biology has been that long-term self-renewal belongs primarily to hematopoietic stem cells, the upstream source of all blood and immune lineages. Progenitor cells are typically viewed as more committed and less durable. This work showed that, under controlled laboratory conditions, GMPs can also self-renew while retaining lineage potential.
The finding carries both therapeutic and biological implications. On the therapeutic side, it creates a scalable starting population for engineering cell products. On the biology side, it suggests that developmental stage can be more flexible than traditionally assumed when cells are placed in the right environment.
CAR engineering extended the antitumor effect
The progenitors were not only expanded; they were also engineered with a chimeric antigen receptor, or CAR, so the cells could recognize a chosen molecular marker on cancer cells. CAR technology has already transformed certain blood cancer treatments by redirecting T cells against malignant targets. The USC team tested whether a similar concept could be applied earlier in the myeloid lineage.
Some cells carried an additional immune-activating signal designed to recruit and stimulate nearby immune cells, including T cells. In the mouse studies, that added signal strengthened the antitumor response beyond what was seen with CAR engineering alone. The broader immune activation also retained activity even when donor and recipient immune characteristics did not match, raising the possibility of off-the-shelf manufacturing.
Off-the-shelf therapy would be a major practical shift. Rather than preparing a custom product for each patient, a donor-derived cell source could potentially be expanded, engineered, and distributed in advance. The study does not establish clinical feasibility in people, but it does provide a credible framework for how such a product might be built.
Mouse studies showed activity against blood cancers, solid tumors, and infection
In mice, the engineered GMPs took up residence in bone marrow and other blood-forming sites, where they generated additional engineered macrophages and related immune cells. That continuing source of replacement cells appears to have been central to the observed effect, since it reduces reliance on a single bolus of mature cells.
The progenitor-based approach slowed progression in both blood cancers and solid tumors. Solid tumors are especially important in this context because they have been harder to treat with existing engineered T-cell strategies. Macrophages can reach tissue compartments that T cells may struggle to penetrate, so a renewable macrophage lineage could offer a different route into the tumor microenvironment.
A separate experiment extended the concept beyond oncology. In mice with chronic granulomatous disease, the infused GMPs restored the ability to fight bacterial infection. That result points to possible future use in inherited immune deficiency, where a durable supply of functional immune cells could replace a defective arm of host defense.
The next hurdle is human safety, durability, and control
The work remains preclinical, and that limitation is central. A therapy designed to persist and keep generating immune cells could be powerful, but it also raises questions about duration of effect, control of cell growth, and safety if the cells survive longer than intended. Any transition into human testing will need to show that engineered GMPs can be made consistently, remain controlled in vivo, and avoid unintended immune consequences.
The study also leaves open how the approach would behave across different cancer types, tumor microenvironments, and donor-recipient combinations. Mouse success does not guarantee that the same lineage flexibility, trafficking patterns, or antitumor potency will translate cleanly to patients.
Even so, the work provides a concrete new manufacturing strategy for cellular immunotherapy. Rather than treating cell expansion and immune engineering as separate technical hurdles, the USC team linked them in a single progenitor-based platform. If the approach survives human testing, the field may gain a way to build longer-lasting, more scalable cellular therapies from a cell type that was previously viewed as too committed to serve as a renewable starting point.