Interleukin-15 (IL-15)

Overview

Interleukin-15 (IL15) is a pleiotropic cytokine that plays a critical role in promoting survival, proliferation, and effector differentiation of lymphocytes, particularly T cells and natural killer cell. As a proinflammatory cytokine, IL15 is a key mediator of adaptive and innate immune responses, functioning through both autocrine and paracrine signaling pathways. In contemporary immunotherapeutic applications, IL15 has emerged as a strategic component in engineered cellular therapies, where its capacity to enhance immune cell fitness, proliferative capacity, and persistence has positioned it as a valuable augmentation factor in chimeric antigen receptor (CAR) T cell and CAR-NK cell platforms. The ability to deliver IL15 through multiple modalities—including direct cytokine co-expression, mRNA-based therapies, and gene transfer vectors—has expanded its therapeutic utility in treating hematologic and solid malignancies characterized by immunosuppressive tumor microenvironments.

Recent Publications Summary

Recent publications highlight IL-15 as both a biomarker-associated protein and a functional immunotherapy payload across cancer and autoimmune research. In a prospective plasma proteomics study in advanced gastric cancer/gastroesophageal junction cancer, responders to PD-1-based immunochemotherapy had significantly lower baseline IL-15 levels, and IL-15 was incorporated into a composite risk model that helped predict treatment response 42412320Jul. In systemic lupus erythematosus, IL-15 was identified among a cost-optimized 5-protein diagnostic panel that retained good accuracy while substantially reducing assay cost, supporting its potential use in protein-based disease detection 42490652Jul.

Several studies used IL-15 to enhance cellular immunotherapies by improving persistence, activation, and antitumor function. In ALPPL2-specific human CAR T cells, coexpression of IL15 promoted effector differentiation and sustained proliferative capacity, consistent with a role for IL-15 in supporting T-cell fitness in the tumor microenvironment 41860794Mar. In GPC3-targeted CAR-T cells for liver cancer, an in silico cytokine-optimization platform identified IL-15 as the most effective cytokine enhancer, particularly in the setting of low antigen density, and this prediction guided generation of cytokine-armored CAR-T cells for experimental testing 42387611Jul. Similarly, a compact genome-regulation platform was used to activate endogenous CXCL9, IL-15, and IFN-γ, with the resulting immune-activation regimen enhancing T-cell migration and killing of cancer cells and patient-derived organoids, and showing synergy with anti-PD-1 therapy in humanized mice 41917051Mar.

IL-15 was also incorporated into NK-cell and multi-cytokine strategies aimed at overcoming tumor immunosuppression. A next-generation engineered NK-cell platform included endogenous soluble IL15 production together with PD-L1 and HLA-E targeting to improve recruitment, activation, cytolytic function, survival, and metabolic fitness in the tumor microenvironment 42425951Jul. In B-cell lymphoma, the off-the-shelf CD19 CAR NK-cell therapy TAK-007, which expresses IL-15, showed encouraging response rates, rapid availability, and an excellent safety profile in heavily pretreated patients, although durability remained limited 41996826Apr. Beyond cell therapy, an intraperitoneal mRNA-based approach for ovarian cancer delivered a combination of single-chain interleukins including IL-12, IL-15, and pro-IL-18/Caspase-1 in lipid nanoparticle to reprogram the peritoneal tumor microenvironment in a syngeneic mouse model 42116169May.

What Changes, What Holds

1. IL-15 is emerging as a clinically useful biomarker as well as a therapeutic factor
NEW DIRECTION Plasma and protein-panel studies extend IL-15 beyond its established immune-stimulatory role into disease stratification and response prediction. That does not displace its cytokine biology, but it does add a practical diagnostic dimension in cancer and autoimmunity. The evidence is still early and correlative, so whether IL-15 is independently actionable or mainly a component of broader protein signatures remains unsettled 42412320Jul42490652Jul.

2. IL-15 coexpression can materially strengthen engineered T-cell therapies
REINFORCES These studies sharpen the existing view that IL-15 is a fitness factor for adoptive cellular therapy by showing benefit in persistence, activation, and antitumor function across different CAR-T engineering strategies. The work does not change what IL-15 is understood to do; it broadens the experimental support for using it as an armored payload, including in settings where antigen density is low and immune activation must be sustained 41860794Mar42387611Jul.

3. IL-15 is being used as part of broader immune-activation programs, not only as a standalone cytokine
NEW DIRECTION Endogenous activation of IL-15 alongside chemokine and interferon programs suggests a more networked way to deploy IL-15 than the Overview’s direct co-expression and gene-transfer framing. The established cytokine role stands, but the new work points to IL-15 as one node in coordinated transcriptional reprogramming that may improve trafficking and checkpoint synergy. Whether this is superior to simpler IL-15 delivery remains open 41917051Mar.

4. IL-15 expression in NK-cell therapies is being paired with additional immune-evasion countermeasures
REINFORCES The NK-cell and mRNA studies reinforce the idea that IL-15 is useful as an augmentation factor in hostile tumor microenvironments, especially when persistence and metabolic fitness are limiting. They do not overturn the baseline; instead, they show that IL-15 is increasingly being embedded in multi-pronged designs rather than used alone. The durability of benefit and the relative contribution of IL-15 versus the other engineered elements remain unresolved 42425951Jul42116169May.

Overview update candidates: IL-15 as a biomarker-associated protein; IL-15 as part of coordinated immune-activation programs; IL-15 embedded in multi-component engineered cell and mRNA therapies.