Postdoctoral Scholar, VIB - Flanders Institute for Biotechnology (Belgium) (2021)

Doctor of Philosophy, University of Oxford (UK) (2019)

Stanford Advisors

All Publications

  • Transitional dendritic cells are distinct from conventional DC2 precursors and mediate proinflammatory antiviral responses. Nature immunology Sulczewski, F. B., Maqueda-Alfaro, R. A., Alcantara-Hernandez, M., Perez, O. A., Saravanan, S., Yun, T. J., Seong, D., Arroyo Hornero, R., Raquer-McKay, H. M., Esteva, E., Lanzar, Z. R., Leylek, R. A., Adams, N. M., Das, A., Rahman, A. H., Gottfried-Blackmore, A., Reizis, B., Idoyaga, J. 2023


    High-dimensional approaches have revealed heterogeneity amongst dendritic cells (DCs), including a population of transitional DCs (tDCs) in mice and humans. However, the origin and relationship of tDCs to other DC subsets has been unclear. Here we show that tDCs are distinct from other well-characterized DCs and conventional DC precursors (pre-cDCs). We demonstrate that tDCs originate from bone marrow progenitors shared with plasmacytoid DCs (pDCs). In the periphery, tDCs contribute to the pool of ESAM+ type 2 DCs (DC2s), and these DC2s have pDC-related developmental features. Different from pre-cDCs, tDCs have less turnover, capture antigen, respond to stimuli and activate antigen-specific naive T cells, all characteristics of differentiated DCs. Different from pDCs, viral sensing by tDCs results in IL-1beta secretion and fatal immune pathology in a murine coronavirus model. Our findings suggest that tDCs are a distinct pDC-related subset with a DC2 differentiation potential and unique proinflammatory function during viral infections.

    View details for DOI 10.1038/s41590-023-01545-7

    View details for PubMedID 37414907

  • Rapid recruitment and IFN-I-mediated activation of monocytes dictate focal radiotherapy efficacy. Science immunology Tadepalli, S., Clements, D. R., Saravanan, S., Arroyo Hornero, R., Lüdtke, A., Blackmore, B., Paulo, J. A., Gottfried-Blackmore, A., Seong, D., Park, S., Chan, L., Kopecky, B. J., Liu, Z., Ginhoux, F., Lavine, K. J., Murphy, J. P., Mack, M., Graves, E. E., Idoyaga, J. 2023; 8 (84): eadd7446


    The recruitment of monocytes and their differentiation into immunosuppressive cells is associated with the low efficacy of preclinical nonconformal radiotherapy (RT) for tumors. However, nonconformal RT (non-CRT) does not mimic clinical practice, and little is known about the role of monocytes after RT modes used in patients, such as conformal RT (CRT). Here, we investigated the acute immune response induced by after CRT. Contrary to non-CRT approaches, we found that CRT induces a rapid and robust recruitment of monocytes to the tumor that minimally differentiate into tumor-associated macrophages or dendritic cells but instead up-regulate major histocompatibility complex II and costimulatory molecules. We found that these large numbers of infiltrating monocytes are responsible for activating effector polyfunctional CD8+ tumor-infiltrating lymphocytes that reduce tumor burden. Mechanistically, we show that monocyte-derived type I interferon is pivotal in promoting monocyte accumulation and immunostimulatory function in a positive feedback loop. We also demonstrate that monocyte accumulation in the tumor microenvironment is hindered when RT inadvertently affects healthy tissues, as occurs in non-CRT. Our results unravel the immunostimulatory function of monocytes during clinically relevant modes of RT and demonstrate that limiting the exposure of healthy tissues to radiation has a positive therapeutic effect on the overall antitumor immune response.

    View details for DOI 10.1126/sciimmunol.add7446

    View details for PubMedID 37294749

  • Plasmacytoid dendritic cells: A dendritic cell in disguise. Molecular immunology Arroyo Hornero, R., Idoyaga, J. 2023; 159: 38-45


    Since their discovery, the identity of plasmacytoid dendritic cells (pDCs) has been at the center of a continuous dispute in the field, and their classification as dendritic cells (DCs) has been recently re-challenged. pDCs are different enough from the rest of the DC family members to be considered a lineage of cells on their own. Unlike the exclusive myeloid ontogeny of cDCs, pDCs may have dual origin developing from myeloid and lymphoid progenitors. Moreover, pDCs have the unique ability to quickly secrete abundant levels of type I interferon (IFN-I) in response to viral infections. In addition, pDCs undergo a differentiation process after pathogen recognition that allows them to activate T cells, a feature that has been shown to be independent of presumed contaminating cells. Here, we aim to provide an overview of the historic and current understanding of pDCs and argue that their classification as either lymphoid or myeloid may be an oversimplification. Instead, we propose that the capacity of pDCs to link the innate and adaptive immune response by directly sensing pathogens and activating adaptive immune responses justify their inclusion within the DC network.

    View details for DOI 10.1016/j.molimm.2023.05.007

    View details for PubMedID 37269733

  • Sodium perturbs mitochondrial respiration and induces dysfunctional Tregs CELL METABOLISM Corte-Real, B. F., Hamad, I., Hornero, R., Geisberger, S., Roels, J., Van Zeebroeck, L., Dyczko, A., van Gisbergen, M. W., Kurniawan, H., Wagner, A., Yoset, N., Weiss, S. Y., Schmetterer, K. G., Schroeder, A., Krampert, L., Haase, S., Bartolomaeus, H., Hellings, N., Saeys, Y., Dubois, L. J., Brenner, D., Kempa, S., Hafler, D. A., Stegbauer, J., Linker, R. A., Jantsch, J., Mueller, D. N., Kleinewietfeld, M. 2023; 35 (2): 299-+


    FOXP3+ regulatory T cells (Tregs) are central for peripheral tolerance, and their deregulation is associated with autoimmunity. Dysfunctional autoimmune Tregs display pro-inflammatory features and altered mitochondrial metabolism, but contributing factors remain elusive. High salt (HS) has been identified to alter immune function and to promote autoimmunity. By investigating longitudinal transcriptional changes of human Tregs, we identified that HS induces metabolic reprogramming, recapitulating features of autoimmune Tregs. Mechanistically, extracellular HS raises intracellular Na+, perturbing mitochondrial respiration by interfering with the electron transport chain (ETC). Metabolic disturbance by a temporary HS encounter or complex III blockade rapidly induces a pro-inflammatory signature and FOXP3 downregulation, leading to long-term dysfunction in vitro and in vivo. The HS-induced effect could be reversed by inhibition of mitochondrial Na+/Ca2+ exchanger (NCLX). Our results indicate that salt could contribute to metabolic reprogramming and that short-term HS encounter perturb metabolic fitness and long-term function of human Tregs with important implications for autoimmunity.

    View details for DOI 10.1016/j.cmet.2023.01.009

    View details for Web of Science ID 001041611700001

    View details for PubMedID 36754020

  • Dissecting the role of CSF2RB expression in human regulatory T cells FRONTIERS IN IMMUNOLOGY Corte-Real, B. F., Hornero, R., Dyczko, A., Hamad, I., Kleinewietfeld, M. 2022; 13: 1005965


    Colony stimulating factor 2 receptor subunit beta (CSF2RB; CD131) is the common subunit of the type I cytokine receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-3 and IL-5. Interestingly, FOXP3+ regulatory T cells (Tregs), which play a pivotal role in prevention of autoimmunity have been demonstrated to highly overexpress CSF2RB and genome-wide association studies (GWAS) identified CSF2RB as being linked to autoimmune diseases like multiple sclerosis (MS). However, the exact biological role of CD131 in human Tregs has not been defined yet. Here we investigated CD131 importance on Treg phenotype and function in a broad range of in vitro studies. Although we could not recognize a specific function of CSF2RB; CD131 in human Tregs, our data show that CD131 expression is vastly restricted to Tregs even under stimulatory conditions, indicating that CD131 could aid as a potential marker to identify Treg subpopulations from pools of activated CD4+ T cells. Importantly, our analysis further demonstrate the overexpression of CSF2RB in Tregs of patients with autoimmune diseases like MS and systemic lupus erythematosus (SLE) in comparison to healthy controls, thereby indicating that CSF2RB expression in Tregs could serve as a potential novel biomarker for disease.

    View details for DOI 10.3389/fimmu.2022.1005965

    View details for Web of Science ID 000899046100001

    View details for PubMedID 36532080

    View details for PubMedCentralID PMC9755334

  • The Charcot-Leyden crystal protein Galectin-10 is not a major determinant of human regulatory T-cell function ALLERGY Arroyo-Hornero, R., Aegerter, H., Hamad, I., Corte-Real, B., Staes, K., van Der Woning, B., Verstraete, K., Savvides, S. N., Lambrecht, B. N., Kleinewietfeld, M. 2022; 77 (9): 2818-2821

    View details for DOI 10.1111/all.15332

    View details for Web of Science ID 000801014400001

    View details for PubMedID 35491437

  • Fast and Efficient Genome Editing of Human FOXP3(+) Regulatory T Cells FRONTIERS IN IMMUNOLOGY Van Zeebroeck, L., Hornero, R., Corte-Real, B. F., Hamad, I., Meissner, T. B., Kleinewietfeld, M. 2021; 12: 655122


    FOXP3+ regulatory T cells (Tregs) are central for maintaining peripheral tolerance and immune homeostasis. Because of their immunosuppressive characteristics, Tregs are a potential therapeutic target in various diseases such as autoimmunity, transplantation and infectious diseases like COVID-19. Numerous studies are currently exploring the potential of adoptive Treg therapy in different disease settings and novel genome editing techniques like CRISPR/Cas will likely widen possibilities to strengthen its efficacy. However, robust and expeditious protocols for genome editing of human Tregs are limited. Here, we describe a rapid and effective protocol for reaching high genome editing efficiencies in human Tregs without compromising cell integrity, suitable for potential therapeutic applications. By deletion of IL2RA encoding for IL-2 receptor α-chain (CD25) in Tregs, we demonstrated the applicability of the method for downstream functional assays and highlighted the importance for CD25 for in vitro suppressive function of human Tregs. Moreover, deletion of IL6RA (CD126) in human Tregs elicits cytokine unresponsiveness and thus may prevent IL-6-mediated instability of Tregs, making it an attractive target to potentially boost functionality in settings of adoptive Treg therapies to contain overreaching inflammation or autoimmunity. Thus, our rapid and efficient protocol for genome editing in human Tregs may advance possibilities for Treg-based cellular therapies.

    View details for DOI 10.3389/fimmu.2021.655122

    View details for Web of Science ID 000691310000001

    View details for PubMedID 34408743

    View details for PubMedCentralID PMC8365355

  • CD70 expression determines the therapeutic efficacy of expanded human regulatory T cells COMMUNICATIONS BIOLOGY Hornero, R., Georgiadis, C., Hua, P., Trzupek, D., He, L., Qasim, W., Todd, J. A., Ferreira, R. C., Wood, K. J., Issa, F., Hester, J. 2020; 3 (1): 375


    Regulatory T cells (Tregs) are critical mediators of immune homeostasis. The co-stimulatory molecule CD27 is a marker of highly suppressive Tregs, although the role of the CD27-CD70 receptor-ligand interaction in Tregs is not clear. Here we show that after prolonged in vitro stimulation, a significant proportion of human Tregs gain stable CD70 expression while losing CD27. The expression of CD70 in expanded Tregs is associated with a profound loss of regulatory function and an unusual ability to provide CD70-directed co-stimulation to TCR-activated conventional T cells. Genetic deletion of CD70 or its blockade prevents Tregs from delivering this co-stimulatory signal, thus maintaining their regulatory activity. High resolution targeted single-cell RNA sequencing of human peripheral blood confirms the presence of CD27-CD70+ Treg cells. These findings have important implications for Treg-based clinical studies where cells are expanded over extended periods in order to achieve sufficient treatment doses.

    View details for DOI 10.1038/s42003-020-1097-8

    View details for Web of Science ID 000553151500001

    View details for PubMedID 32665635

    View details for PubMedCentralID PMC7360768

  • The Impact of Dietary Components on Regulatory T Cells and Disease FRONTIERS IN IMMUNOLOGY Hornero, R., Hamad, I., Corte-Real, B., Kleinewietfeld, M. 2020; 11: 253


    The rise in the prevalence of autoimmune diseases in developed societies has been associated with a change in lifestyle patterns. Among other factors, increased consumption of certain dietary components, such as table salt and fatty acids and excessive caloric intake has been associated with defective immunological tolerance. Dietary nutrients have shown to modulate the immune response by a direct effect on the function of immune cells or, indirectly, by acting on the microbiome of the gastrointestinal tract. FOXP3+ regulatory T cells (Tregs) suppress immune responses and are critical for maintaining peripheral tolerance and immune homeostasis, modulating chronic tissue inflammation and autoimmune disease. It is now well-recognized that Tregs show certain degree of plasticity and can gain effector functions to adapt their regulatory function to different physiological situations during an immune response. However, plasticity of Tregs might also result in conversion into effector T cells that may contribute to autoimmune pathogenesis. Yet, which environmental cues regulate Treg plasticity and function is currently poorly understood, but it is of significant importance for therapeutic purposes. Here we review the current understanding on the effect of certain dietary nutrients that characterize Western diets in Treg metabolism, stability, and function. Moreover, we will discuss the role of Tregs linking diet and autoimmunity and the potential of dietary-based interventions to modulate Treg function in disease.

    View details for DOI 10.3389/fimmu.2020.00253

    View details for Web of Science ID 000523705000001

    View details for PubMedID 32153577

    View details for PubMedCentralID PMC7047770

  • CD45RA Distinguishes CD4(+)CD25(+)CD127(-/low) TSDR Demethylated Regulatory T Cell Subpopulations With Differential Stability and Susceptibility to Tacrolimus-Mediated Inhibition of Suppression TRANSPLANTATION Hornero, R., Betts, G. J., Sawitzki, B., Vogt, K., Harden, P. N., Wood, K. J. 2017; 101 (2): 302-309


    Adoptive transfer of forkhead box protein (FOX)3 regulatory T (Treg) cells offers a promising strategy to reduce damage to an allograft by the recipient's immune system. Identification of cell surface markers sufficient to purify Treg cells expanded ex vivo to remove cellular contaminants requires optimization. Furthermore, the expanded Treg must be able to survive, expand, and suppress in allograft recipients exposed to immunosuppressants, such as tacrolimus (TAC). Reduced CD127 expression enhances identification of Treg in the human CD4CD25 population. CD45RA expression identifies naive CD4CD25 Treg with an enhanced stability of Treg phenotype.We combine an analysis of CD45RA, CD25, and CD127 expression to identify subpopulations of CD4CD127CD25 cells. Regulatory T cells were sorted according to expression of CD25 and CD45RA and expanded in the presence of a physiological relevant concentration of TAC. Regulatory T cell-specific demethylation region (TSDR) demethylation, FOXP3 expression, and suppression were analyzed.CD4CD127CD25CD45RA Treg cells had a stable TSDR demethylated FOXP3 phenotype after expansion whereas CD4CD127CD25CD45RA Treg cell lost the TSDR demethylated phenotype. CD45RA Treg had a greater capacity to suppress after expansion with TAC.Although CD45RA Treg retained a greater suppressive capacity when expanded with TAC, the marked loss of the TSDR demethylated status highlights the potential for loss of stability of these cells in transplant recipients treated with TAC based immunosuppression. We show that a population of CD4CD127CD45RA Regulatory T cell may offer the best compromise between susceptibility to loss of suppression when exposed to TAC and maintenance of a TSDR demethylated phenotype following in vitro expansion.

    View details for DOI 10.1097/TP.0000000000001278

    View details for Web of Science ID 000393647400024

    View details for PubMedID 28118317

    View details for PubMedCentralID PMC5265687