A new study published in Nature Communications reports that MHS552, an engineered antibody carrying a modified form of the immune-signaling molecule interleukin-2, selectively expands functional regulatory T cells in nonclinical models and in healthy human participants. The work, led by I. Radanović, M. DiDonato, A.C. Meijs and colleagues, focuses on a longstanding challenge in immunology: how to strengthen the immune system’s natural braking mechanisms without broadly suppressing protective immunity. Regulatory T cells, commonly called Tregs, are central to that balance. By restraining excessive activation of other immune cells, they help prevent the immune system from attacking the body’s own tissues.
Interleukin-2, or IL-2, is a cytokine that controls the growth, survival and activity of several lymphocyte populations. Although IL-2 can promote the expansion of Tregs, it also stimulates conventional effector T cells and natural killer cells, which are important for antimicrobial and antiviral defense but can contribute to inflammation when activated inappropriately. This dual activity has limited the precision of conventional IL-2 therapies. The scientific objective behind MHS552 is to alter that biological distribution, using an engineered IL-2 variant, known as a mutein, and an antibody framework intended to deliver the signal in a more selective manner.
A mutein is a protein whose amino-acid sequence has been deliberately changed to modify its biological properties. In cytokine engineering, these changes can affect receptor binding, signaling strength, circulation time or the types of cells that respond to the molecule. MHS552 combines this principle with antibody-based targeting. Rather than allowing a modified cytokine to circulate as an independent signal, the therapeutic design attaches or “engrafts” the IL-2 mutein to an antibody scaffold. This creates a multifunctional molecule in which the antibody and cytokine components work together to influence where and how the immune signal is presented.
The strategy is particularly relevant to the biology of Tregs because these cells are highly responsive to IL-2. Tregs depend on signaling through the high-affinity IL-2 receptor, a molecular complex that includes the alpha chain CD25 along with signaling receptor components. Many conventional T cells can also respond to IL-2, but differences in receptor expression, cellular state and signal integration may create opportunities for selective expansion. A carefully engineered IL-2 signal could therefore favor Tregs while reducing unwanted activation of other lymphocytes. The study’s central finding, as indicated by its title, is that MHS552 achieved this selective expansion while preserving the functional properties of the regulatory cells.
Expansion alone, however, is not enough to establish an effective immune therapy. A larger population of Tregs would be therapeutically meaningful only if the cells remained capable of suppressing inappropriate immune responses. The researchers therefore assessed not simply whether Treg numbers increased, but whether the expanded cells retained functional characteristics. This distinction is technically important because cytokine-driven proliferation can, in some circumstances, alter cellular identity or produce cells that are numerically abundant but biologically ineffective. The reported results indicate that MHS552 expanded Tregs that remained functional in the experimental systems examined.
The research included nonclinical models as well as healthy human participants, providing evidence across more than one stage of development. Nonclinical studies allow investigators to examine pharmacology, immune-cell responses and biological activity under controlled conditions before or alongside human testing. Studies in healthy participants are essential because immune signaling can differ substantially between laboratory models and people. Evidence of selective Treg expansion in healthy individuals suggests that the engineered molecule can influence human immune biology as intended, although it does not by itself demonstrate benefit in patients with autoimmune disease, inflammatory disorders or transplant complications.
The therapeutic rationale reaches beyond cell counts and into the architecture of immune regulation. Tregs suppress immune activation through several mechanisms, including inhibitory cytokines, modulation of antigen-presenting cells and direct interactions with other lymphocytes. When Treg activity is inadequate or poorly balanced, immune responses may become chronic or misdirected. A therapy that increases the number of competent Tregs could, in principle, help restore tolerance while avoiding the generalized immunosuppression associated with many older treatments. That possibility is especially significant for diseases in which the immune system must be restrained without eliminating its ability to respond to infections.
The findings may also be relevant to viral immunology, although MHS552 is not presented as an antiviral drug. During viral infection, immune activation is necessary to control replication, but excessive or prolonged responses can damage tissues and contribute to immunopathology. Tregs participate in this tension by limiting inflammation while sometimes influencing the durability and strength of antiviral immunity. A selective Treg-expanding therapy would therefore need to be evaluated carefully in the context of infection risk, viral clearance and vaccine responses. The current study provides a platform for that discussion, but it does not establish how MHS552 affects active viral infections or immunity to specific viruses.
One of the most important technical questions for the field will be whether the selectivity observed in the study remains consistent across different tissues, disease states and treatment schedules. Immune-cell composition varies between blood and organs, and Tregs themselves are not a uniform population. Their phenotype, stability and suppressive activity can depend on the inflammatory environment and the tissues in which they reside. Future clinical research will need to determine how long the expanded cells persist, whether they accumulate at relevant sites of disease, how the treatment influences other immune populations and whether the therapeutic window is wide enough to limit infectious or other immune-related risks.
MHS552 illustrates a broader shift in drug development from broad immune stimulation toward engineered control of cytokine signaling. By combining protein engineering with antibody-based delivery, researchers are attempting to make powerful biological signals more predictable and cell-selective. The study in Nature Communications adds evidence that an IL-2 mutein-engrafted antibody can expand functional regulatory T cells in experimental settings and in healthy people. The next test will be clinical: whether this controlled increase in immune regulation can translate into meaningful treatment for patients while preserving the protective responses required to confront pathogens, including viruses.
Subject of Research: Selective expansion of functional regulatory T cells using the IL-2 mutein-engrafted antibody MHS552.
Article Title: IL-2 mutein-engrafted antibody MHS552 selectively expands functional regulatory T cells in nonclinical models and healthy participants.
Article References: Radanović, I., DiDonato, M., Meijs, A.C. et al. “IL-2 mutein-engrafted antibody MHS552 selectively expands functional regulatory T cells in nonclinical models and healthy participants.” Nature Communications (2026). https://doi.org/10.1038/s41467-026-76491-7
Image Credits: AI Generated
DOI: 10.1038/s41467-026-76491-7
Keywords: MHS552, interleukin-2, IL-2 mutein, regulatory T cells, Tregs, immunotherapy, cytokine engineering, antibody therapeutics, immune tolerance, viral immunology
Tags: antibody-based immune therapeuticscytokine engineeringcytokine signaling modificationengineered IL-2 antibody therapyimmune balance in autoimmune diseasesimmune system balancing strategiesimmune system modulationimmunotherapy for immune regulationnonclinical and human clinical modelsregulatory T cell expansionselective immune regulationTreg cell therapy
