The clinical problem is formidable. Bone defects caused by trauma, infection, tumour resection and congenital abnormalities are common, and while small injuries heal spontaneously, defects exceeding the local regenerative capacity, so-called critical-sized defects, often fail to close on their own. Autologous bone grafting remains the gold standard because it delivers osteogenic cells, inductive growth factors and a conductive matrix simultaneously, but it is limited by donor-site morbidity and restricted availability. Allografts are more available yet carry risks of immune rejection, infection and variable efficacy. What is needed, the review contends, are regenerative strategies that remain stable and reproducible inside the messy, inflamed microenvironment of a real defect.

Bioprinting offers an unusual degree of control over that environment. Unlike conventional fabrication, printing allows multiple materials, cells and bioactive signals to be arranged in three dimensions with defined pore architecture, compositional gradients and localised mechanical properties. Composite bioinks built from printable hydrogels such as gelatin methacryloyl (GelMA), alginate and hyaluronic acid methacrylate can be blended with inorganic phases including calcium phosphate, hydroxyapatite, beta-tricalcium phosphate and bioactive glass, balancing printability with an osteogenic milieu. Crucially, these same components release ions and present surface chemistry that shape the earliest host immune recognition of the implant, making the printer a tool for immunology as much as for structural engineering.

The biological rationale comes from the now well-established field of osteoimmunology. Bone repair unfolds in overlapping phases: an inflammatory phase dominated by neutrophils and pro-inflammatory M1-like macrophages that clear debris and pathogens; a proliferative phase in which macrophages shift toward reparative M2-like states, releasing factors such as TGF-beta and VEGF that recruit mesenchymal stem cells and drive angiogenesis; and a remodeling phase in which osteoblasts and osteoclasts, governed by the RANKL/OPG axis, convert woven bone into mechanically adapted lamellar bone. Simply suppressing the early inflammatory burst, the review stresses, can starve the repair process of the very signals that initiate cell recruitment and vascularisation. The goal instead is controlled, resolvable inflammation.

Material composition is one of the three main levers the authors identify. Strontium-substituted calcium silicate hydrate nanowires incorporated into a GelMA bioink, for example, released Sr, Ca and Si ions that nudged macrophages toward a repair-associated phenotype while supporting bone marrow stromal cell differentiation, producing substantial regeneration in rat critical-sized calvarial defects. Silicon-substituted calcium phosphate combined with methacrylated bone-derived extracellular matrix showed a striking temporal immune transition in vivo, from early pro-inflammatory activation to later anti-inflammatory resolution, linked to suppression of p38 MAPK signalling. Zinc-releasing ZIF-8 metal-organic framework particles delivered the anti-inflammatory polyphenol luteolin alongside Zn2+ ions, integrating immunomodulation, antioxidation and antibacterial action in a single printed construct.

Geometry itself can be immunologically active. Using digital light processing, researchers fabricated hydroxyapatite scaffolds identical in composition but differing only in pore size, and found that 600-micrometre pores best regulated macrophage behaviour through IFN-beta and HIF-1alpha-related signalling while improving vascularisation and bone formation. Even curvature matters: beta-tricalcium phosphate scaffolds engineered with negative Gaussian curvature suppressed macrophage Ras-MAPK/HIF-1alpha signalling and increased secretion of BMP-2 and VEGF, promoting vascularised bone ingrowth in a rabbit segmental defect model. Melt electrowriting adds another dimension, with ordered PCL microfibres and calcium phosphate coatings steering macrophages toward repair-associated states via PI3K/AKT and cAMP-PKA signalling, demonstrating that physical microarchitecture can substitute for exogenous drugs.

The most sophisticated strategies deliver bioactive cargo in stage-matched sequences. One printed system used coaxial bioprinting with sequential crosslinking to release interferon-gamma first, preserving the early inflammatory activation needed for repair initiation, before Laponite-derived magnesium and silicon ions gradually drove macrophages toward a reparative state, ultimately enhancing vascularised bone regeneration in calvarial defects. Interleukin-4 delivered from graphene oxide/black phosphorus nanointerfaces promoted CD206-positive macrophages while the materials themselves supported angiogenesis and osteogenesis. Exosome-based approaches add further nuance: macrophage-derived vesicles from mixed functional states outperformed those from purely M2-like macrophages in stimulating osteogenic signalling, underscoring the review’s warning that the simplified M1/M2 dichotomy cannot capture the continuum of immune states that real healing involves.

The authors are candid about translational hurdles. Every added component, whether living cells, recombinant cytokines, exosomes or decellularised matrix, increases batch variability, manufacturing complexity and regulatory burden. Sterilisation methods can silently alter hydrogel mechanics and even macrophage gene expression, while endotoxin contamination at low levels can confound the interpretation of a material’s intrinsic immunological effects. Degradation kinetics must be synchronised with tissue ingrowth: too fast and the scaffold loses support prematurely, too slow and the foreign-body response persists. The review advocates defining critical quality attributes that reflect immunomodulatory potency, not just scaffold geometry and compressive strength, and pursuing standardised platforms with patient-specific variation confined to a validated design space.

Looking forward, the field is moving toward spatiotemporal and even intelligent regulation. Microenvironment-responsive hydrogels that release therapeutic ions only under pathological acidity or oxidative stress, four-dimensional printing that changes scaffold architecture over time, and machine-learning frameworks that optimise bioink composition against immune as well as mechanical endpoints all feature in the review’s roadmap. Pathology-specific design receives particular emphasis: infected defects need preserved antimicrobial inflammation before resolution, diabetic defects require correction of hyperglycaemia-driven oxidative stress, and aged or osteoporotic bone demands restoration of senescence-impaired immune function rather than generic osteogenic stimulation. The overarching message is that the next generation of bone scaffolds should not simply contain more ingredients, but should speak the immune system’s own temporal language, guiding inflammation, vascularisation and remodeling in the order that nature intended.

Subject of Research: Immunoregulatory biomaterials and 3D bioprinting strategies for bone regeneration

Article Title: Advances in 3D bioprinting of immunoregulatory biomaterials for bone regeneration

Article References: Wang, X., & Zhang, A. (2026). Advances in 3D bioprinting of immunoregulatory biomaterials for bone regeneration. Materials Today Bio, 41, Article 103714. https://doi.org/10.1016/j.mtbio.2026.103714

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103714

Keywords: 3D bioprinting, bone regeneration, osteoimmunology, macrophage polarization, bioinks, GelMA, biomaterials, critical-sized bone defects, exosomes, cytokine delivery, scaffold architecture, tissue engineering

The central problem the researchers set out to solve is well known to anyone following the CAR-T field. Engineered T cells have produced remarkable results in certain blood cancers, but solid tumors present a hostile microenvironment that wears these cells down. In pancreatic cancer specifically, mesothelin-targeted CAR-T therapy—a promising approach because mesothelin is abundantly expressed on pancreatic tumor cells—has been limited by insufficient persistence, progressive T-cell exhaustion, and metabolic dysfunction. CAR-T cells that enter the tumor find themselves starved of nutrients, bathed in suppressive signals, and deprived of the cytokine support they need to keep proliferating and killing. Within days, many of them become dysfunctional ghosts of their former selves.

Interleukin-2 is the classic T-cell growth cytokine, and systemic administration of recombinant IL-2 has long been known to boost T-cell responses. But giving IL-2 intravenously at doses high enough to support CAR-T cells triggers severe toxicity, including vascular leak syndrome and dangerous expansion of regulatory T cells, which paradoxically suppress antitumor immunity. The study’s solution is elegant in its localization: the team engineered second-generation MSLN-targeted CAR-T cells to secrete an IgG1 Fc-fused IL-2(C125S) variant, creating what they call MSLN-IL2m CAR-T cells. The Fc fusion extends the cytokine’s half-life, while the C125S mutation disables a site associated with preferential expansion of regulatory T cells, aiming the growth signal preferentially at the CAR-T cells themselves rather than at their suppressive counterparts.

The experimental design was deliberately rigorous. The researchers generated CAR-T cells from five independent healthy donors, ensuring that their findings were not an artifact of a single donor’s immune system. They tested these cells against pancreatic ductal adenocarcinoma cell lines expressing different levels of mesothelin, subjected them to serial antigen-stimulation assays that mimic the repeated encounters CAR-T cells face inside a tumor, and challenged them with suppressive-stress models designed to reproduce the hostile conditions of the pancreatic tumor microenvironment. Phenotypic and functional analyses tracked exhaustion markers and memory phenotypes, while metabolic-flux assays measured the cells’ mitochondrial performance in real time.

The results were striking across the board. MSLN-IL2m CAR-T cells showed enhanced expansion and stronger activation of STAT5, the transcription factor that serves as the primary downstream messenger for the IL-2 receptor, while maintaining CAR expression and viability comparable to conventional cells. When repeatedly stimulated with antigen, the cytokine-secreting cells demonstrated stronger antigen-dependent cytotoxicity, greater proliferation, more robust cytokine production, and markedly better functional persistence. Just as importantly, they displayed reduced expression of exhaustion-associated markers and preserved memory-associated phenotypes—the immunological hallmarks of cells that can keep fighting rather than burn out.

The metabolic findings may be the most novel aspect of the study. Under PDAC-associated suppressive conditions, MSLN-IL2m CAR-T cells maintained greater mitochondrial membrane potential, greater spare respiratory capacity, and higher ATP production than their conventional counterparts. They also expressed higher levels of PPARGC1A, the master regulator of mitochondrial biogenesis, and CPT1A, a key enzyme in fatty acid oxidation, while showing a lower mitochondrial superoxide-associated signal, indicating less oxidative damage. In the metabolic language of modern immunology, these cells remained oxidative, resilient powerhouses instead of collapsing into the glycolytically exhausted state that characterizes dysfunctional tumor-infiltrating T cells.

To confirm that these advantages actually flowed through the IL-2 receptor pathway, the researchers used pharmacological STAT5 inhibition and IL-2Rα blockade. Both interventions partially attenuated the functional, phenotypic, and metabolic advantages of the engineered cells, supporting an important—but notably non-exclusive—contribution of IL-2Rα–STAT5 signaling. This partial dependence suggests that the Fc-fused cytokine may also act through additional mechanisms, such as autocrine and paracrine effects on other IL-2 receptor configurations, and leaves room for further mechanistic dissection in future work.

The in vivo results provided the crucial translational validation. In an AsPC-1 xenograft model of pancreatic cancer, MSLN-IL2m CAR-T cells showed greater intratumoral accumulation, improved tumor control, and reduced bioluminescent tumor burden compared with conventional MSLN CAR-T cells, and the treated animals survived significantly longer. Tolerability assessments revealed no major abnormalities in hepatic, renal, or hematologic parameters, and body weight remained stable—early reassurance that localized cytokine delivery does not reproduce the systemic toxicity that has plagued recombinant IL-2 therapy, though the authors are careful to note that comprehensive safety evaluation remains necessary.

The implications for the field are considerable. Armoring CAR-T cells with autocrine cytokine support has been attempted before, but the specific combination of an Fc fusion for extended half-life and the C125S mutation for reduced regulatory T-cell preference represents a refined iteration of the concept. By coupling the cytokine’s production directly to the CAR-T cells themselves, the approach ensures that the growth signal is delivered exactly where it is needed—at the tumor site, in the midst of antigen stimulation—rather than systemically. The metabolic data add an important dimension, suggesting that the cytokine support does not merely keep cells alive but actively preserves their mitochondrial machinery and oxidative metabolism under stress.

Cautions remain, as they must in any preclinical study. The xenograft model used, while standard for the field, does not fully recapitulate the immunosuppressive complexity of human pancreatic tumors, and the authors explicitly call for validation in clinically relevant models and comprehensive safety assessment before the approach moves toward patients. Questions about the long-term behavior of cytokine-secreting cells, the risk of uncontrolled autonomous growth, and the behavior of the construct in humans all await answers. Still, the study delivers a clear and encouraging message: when CAR-T cells are engineered to carry their own metabolic and survival support into the tumor battlefield, they fight longer, stay fitter, and kill better—a combination that pancreatic cancer patients, who have waited too long for immunotherapy to work for them, will be watching closely.

Subject of Research: Engineering mesothelin-targeted CAR-T cells to secrete Fc-fused IL-2(C125S) to improve persistence and antitumor activity in pancreatic cancer

Article Title: Fc-fused IL-2(C125S) improves MSLN-targeted CAR-T cell persistence, metabolic fitness, and antitumor activity

Article References: Quan, H., Yao, J., Zhang, Y., Zhan, F., & Wang, Y. (2026). Fc-fused IL-2(C125S) improves MSLN-targeted CAR-T cell persistence, metabolic fitness, and antitumor activity. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-09016-x

Image Credits: AI Generated

DOI: 10.1186/s12967-026-09016-x

Keywords: CAR-T cells, pancreatic ductal adenocarcinoma, mesothelin, interleukin-2, T-cell exhaustion, mitochondrial fitness, immunometabolism, STAT5 signaling, solid tumors, cytokine delivery, preclinical study, Journal of Translational Medicine