More than two decades ago, a sick infant was treated for a severe immunodeficiency disorder at the Ulm University Medical Centre. Later, an unusual mutation in his DNA is discovered. Is there a correlation? As the researchers in Ulm hear of similar cases, an international project is born. The “Ulm patient” is no longer alone. From this point on, more than a hundred scientists, spread out across four continents, start pooling their research. And they discover that a spontaneous point mutation in the transcription factor IRF4 leads to the failure of B and T cells, thus weakening the immune system. Their results have been published in the highly renowned journal Science Immunology.

At the turn of the millennium, a boy who is just under a year old is admitted to the Department of Paediatric and Adolescent Medicine at the Ulm University Medical Centre. He displays signs of a massive immunodeficiency disorder: repeated respiratory tract infections, pneumonia triggered by a fungus, fungal infections on the hands and feet and an alarmingly low level of antibodies.

Fortunately, the treatment with antibiotics and mycostatics is successful, but the cause of the illness remains a mystery for a long time. It is not until many years later that researchers at the Institute for Transfusion Medicine at Ulm University and the Institute for Transfusion Medicine and Immunogenetics Ulm (Institut für Klinische Transfusionsmedizin und Immunognetik, IKT) at the German Red Cross Blood Donation Service finally find out the cause of the boy’s life-threatening immunodeficiency disorder. With modern methods of genetic sequencing, the researchers from Ulm uncover a spontaneous genetic mutation affecting the transcription factor IRF4. “Transcription factors bind to the DNA and control the activity of the genes, specific to each cell. IRF4 is known for playing a key role in training the adaptive immune system. We suspected that there would be a connection here, but we weren’t able to prove it at that time”, explains Professor Hubert Schrezenmeier, medical director of the IKT and the Institute for Transfusion Medicine.

In the course of discussions with international cooperation partners, the researchers from Ulm learn of another six cases in five families, spread across the world. The majority of these children have identical, and the rest very similar, clinical symptoms to those of the patient from Ulm, and all of them carry the identical spontaneously occurring mutation in the gene of the transcription factor IRF4. An international research consortium is established, consisting of specialists in the fields of paediatrics, human genetics, transfusion medicine, molecular biology and immunology. More than a hundred scientists from Europe, the USA, Canada, China and Australia are involved. “The transcontinental cooperation spans six time zones, from Vancouver to Shanghai to Canberra”, reports Dr Klaus Schwarz, who heads the Department of Molecular Diagnostics at the IKT and is one of the eight coordinators of the study. At the Ulm site alone, there are researchers involved from the Institute for Transfusion Medicine and the Department of Paediatric and Adolescent Medicine as well as the Institutes of Biophysics, Physiological Chemistry and Pathology.

Years of effort pay off

The research team not only identifies the common genetic features of the seven children with immunodeficiency disorders, they also succeed in uncovering the biochemical and cell-biological mechanisms that trigger the immune deficiency: in the course of a genetic point mutation, the amino acid threonine was replaced by arginine in the DNA-binding domain of the transcription factor IRF4, more specifically in position 95. The mutation is only present on one allele and it is dominant. “The dominance of a genetic variant is rare in congenital immunodeficiency disorders. The fact that the mutation appeared in the children and not in their parents is very, very unusual”, explains private instructor Dr Ulrich Pannicke from the Institute for Transfusion Medicine, who is one of the eight first authors of the study published in Science Immunology.

The effects of the mutation, which the researchers categorise as “multimorphic,” are also unusual. Typically, mutations lead to biological functions either being lost, amplified or added. The case with this unusual T95R mutation in the transcription factor IRF4 is that all of these things occur at once. “It is the first time that this unique phenomenon has been observed”, says Dr Pannicke. Bioinformatic analyses carried out at the Max Delbrück Centre for Molecular Medicine in Berlin, among other places, have demonstrated that the mutated IRF4 protein not only binds to the previously known DNA binding sites – either in a stronger or weaker fashion, depending on context– but also to sites on the genome, where it shouldn’t be binding at all.

The failure of the B and T cells is ultimately the reason for the immunodeficiency disorder

The unusual binding behaviour of the mutated transcription factor IRF4 is not without consequence to the organism, in particular the adaptive immune system. The B cells do not mature properly and are not able to produce antibodies. For the T cells, it was observed that even though they divide normally, they also display maturation and functional disorders. Among other things, specific cytokines are not released. These regulatory proteins convey immune reactions and control inflammation processes; they have an intercellular alarm function, so to speak. The failure of B and T cells is ultimately the reason for the immune deficiency and explains the pathological susceptibility to infection in children with IRF4 point mutation. Researchers were able to verify this molecular genetic mechanism in mouse models.

So what does this all mean for the afflicted children, who have in the meantime matured into adolescents and young adults? The researchers hope that, in the future, these new findings will not only have diagnostic value, but also therapeutic benefits. Until that time, the conventional forms of treatment are also still available. Some of the patients have been successfully treated with stem cell transplants. Others receive lifelong injections with antibodies, including the patient from Ulm.

Text and mediacontact: Andrea Weber-Tuckermann
Translation: Kate Gaugler

Publication reference:
A multimorphic mutation in IRF4 causes human autosomal dominant combined immunodeficiency. IRF4 International Consortium; Fornes O, Jia A, Kuehn HS, Min Q, Pannicke U, Schleussner N, Thouenon R, Yu Z, de Los Angeles Astbury M, Biggs CM, Galicchio M, Garcia-Campos JA, Gismondi S, Gonzalez Villarreal G, Hildebrand KJ, Hönig M, Hou J, Moshous D, Pittaluga S, Qian X, Rozmus J, Schulz AS, Staines-Boone AT, Sun B, Sun J, Uwe S, Venegas-Montoya E, Wang W, Wang X, Ying W, Zhai X, Zhou Q, Akalin A, André I, Barth TFE, Baumann B, Brüstle A, Burgio G, Bustamante JC, Casanova JL, Casarotto MG, Cavazzana M, Chentout L, Cockburn IA, Costanza M, Cui C, Daumke O, Del Bel KL, Eibel H, Feng X, Franke V, Gebhardt JCM, Götz A, Grunwald S, Hoareau B, Hughes TR, Jacobsen EM, Janz M, Jolma A, Lagresle-Peyrou C, Lai N, Li Y, Lin S, Lu HY, Lugo-Reyes SO, Meng X, Möller P, Moreno-Corona N, Niemela JE, Novakovsky G, Perez-Caraballo JJ, Picard C, Poggi L, Puig-Lombardi ME, Randall KL, Reisser A, Schmitt Y, Seneviratne S, Sharma M, Stoddard J, Sundararaj S, Sutton H, Tran LQ, Wang Y, Wasserman WW, Wen Z, Winkler W, Xiong E, Yang AWH, Yu M, Zhang L, Zhang H, Zhao Q, Zhen X, Enders A, Kracker S, Martinez-Barricarte R, Mathas S, Rosenzweig SD, Schwarz K, Turvey SE, Wang JY. Science Immunology 2023 Jan 20; 8(79): eade7953. DOI: 10.1126/sciimmunol.ade7953. Epub 2023 Jan 20. PMID: 36662884.

Further information:
PD Dr. Ulrich Pannicke, Abteilung für Molekulare Diagnostik, Institut für Transfusionsmedizin, Universität Ulm, E-Mail: ulrich.pannicke(at)uni-ulm.de