How the discovery of a mutation in a young Spanish girl with severe lupus is forging the path for new treatments

How the discovery of a mutation in a young Spanish girl with severe lupus is forging the path for new treatments

A team of scientists from different parts of the world came together to investigate the cause of an unusually severe case of lupus in a seven-year-old Spanish girl. Whole genome sequencing uncovered a single genetic glitch – a point mutation in the TLR7 gene – as the putative cause of the disease. When this mutation was introduced into mice, mutant mice developed lupus-like symptoms, confirming that the point mutation they discovered was in fact causative (1). What does this mean for patients like the little Spanish girl suffering from this chronic disease? Are new targeted therapies on the horizon?

Lupus – epidemiology, symptoms, and current treatments

Systemic lupus erythematosus (SLE), commonly referred to as lupus, is a devastating autoimmune disease affecting around 3.41 million people globally. It disproportionately affects women, with approximately 3.04 million cases compared to 0.36 million in men (2). A complex interplay between genetic factors and adaptive and innate immune system dysregulation leads to inflammation and tissue damage in lupus patients (3). Symptoms vary from person to person and can include skin rashes, notably the “butterfly rash,” as well as muscle and joint pain, anemia, fatigue, hair loss, and kidney problems (4).

Due to the clinical heterogeneity of the disease, the diagnosis and treatment of lupus is often challenging. Treatment responses can be diverse and unpredictable. Thanks to earlier diagnosis and better disease management, survival has improved considerably in the last five decades (3). Current treatments include antimalarials, typically hydroxychloroquine, chronic steroids, high-dose chemotherapeutic regimens, and more recently targeted biologic therapy (3). Despite this progress, many underlying mechanisms leading to lupus remain elusive, roadblocking the development of more effective treatments and possibly a cure.

Toll-like receptors (TLRs) in lupus

Toll-like receptors (TLRs) play a pivotal role in the development of lupus. TLRs, known for recognizing patterns in pathogens, are key components in both innate and adaptive immune responses. Specifically, the dysregulation of TLR7 and TLR9 signaling in B cells has been implicated in lupus’s pathogenesis (5). Genome-wide association studies have linked several TLR7 polymorphisms to lupus (6). In mice models, TLR7 overexpression causes severe lupus, whereas TLR7 deletion prevents or alleviates the disease (1,7,8).

The case of a seven-year-old Spanish girl with severe lupus

In 2022, Brown and colleagues identified a gain-of-function point mutation in the TLR7 gene as the underlying cause of lupus in a seven-year-old Spanish girl with severe symptoms. Whole genome sequencing followed by bioinformatics analysis of the patient revealed a de novo, TLR7 p.Tyr264His (Y264H) missense variant. Figure 1A-B shows the TLR7 variants in the patient’s family identified by Sanger sequencing using the Big Dye Terminator Cycle sequencing kit v3.1 on the 3730 DNA Analyze system (1).

To determine whether the identified genetic variant – TLR7^Y264H – causes lupus, the investigators the mutation in mice through CRISPR–Cas9 editing. The mutant mice developed autoimmune symptoms and end organ damage. This was the first instance where a TLR7 genetic variations were identified as the cause of lupus in humans (1).

Figure 1: TLR7 variants in the family of a Spanish child diagnosed with severe lupus at the age of seven (A) identified by Sanger sequencing using the Big Dye Terminator Cycle sequencing kit v3.1 (Applied Biosystems) on the 3730 DNA Analyze (Applied Biosystems) system (B). Sanger sequencing workflow (C).

From discovery to clinic – TLR inhibition as an emerging treatment modality

In 2023, Hawtin et al. published preclinical characterization of MHV370, an orally-administered TLR7/8 antagonist, for lupus therapy. They showed that in human and mouse cells, MHV370 inhibits TLR7/8-dependent production of cytokines, in particular interferon-α, a known contributor to autoimmune diseases (9).

For example, the team showed that MHV370 suppresses chronic TLR7-dependent immune activation in in vivo mouse models (9). Transcriptomic profiling via amplicon sequencing (Ion AmpliSeq Transcriptome Mouse Gene Expression Kit, Thermo Fisher Scientific) using blood obtained from three groups of mice [(1) naïve, (2) 14 days R848-treated (TLR7 agonist), (3) 14 days R848-treated + MHV370 from day seven onwards] showed MHV370 suppression of chronic TLR7-dependent immune activation in mice.  In the R848-only group, several inflammatory pathways were shown to be activated. In the group treated with R848 and MHV370 from day seven onwards, the activated inflammatory pathways were downregulated, demonstrating that MHV370 can normalize pro-inflammatory parameters in a state of chronic TLR7 activation (see data here:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10213863/figure/fig3/)

The team further showed that MHV370 prevented and halted the development of the disease in a mouse model of lupus. The results from this preclinical study establish TLR7/8 inhibition as a promising treatment modality for lupus (9). A phase 2 study is underway evaluating MHV370’s safety, tolerability, and efficacy in two other autoimmune diseases (10).

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References:

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4. Lupus symptoms: https://www.cdc.gov/lupus/basics/symptoms.htm
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6. Celhar T, Fairhurst AM. Toll-like receptors in systemic lupus erythematosus: potential for personalized treatment. Front Pharmacol. 2014 Dec 8;5:265. doi: 10.3389/fphar.2014.00265. PMID: 25538618; PMCID: PMC4258990.
7. Pisitkun P, Deane JA, Difilippantonio MJ, Tarasenko T, Satterthwaite AB, Bolland S. Autoreactive B cell responses to RNA-related antigens due to TLR7 gene duplication. Science. 2006 Jun 16;312(5780):1669-72. doi: 10.1126/science.1124978. Epub 2006 May 18. PMID: 16709748.
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9. Hawtin S, André C, Collignon-Zipfel G, Appenzeller S, Bannert B, Baumgartner L, Beck D, Betschart C, Boulay T, Brunner HI, Ceci M, Deane J, Feifel R, Ferrero E, Kyburz D, Lafossas F, Loetscher P, Merz-Stoeckle C, Michellys P, Nuesslein-Hildesheim B, Raulf F, Rush JS, Ruzzante G, Stein T, Zaharevitz S, Wieczorek G, Siegel R, Gergely P, Shisha T, Junt T. Preclinical characterization of the Toll-like receptor 7/8 antagonist MHV370 for lupus therapy. Cell Rep Med. 2023 May 16;4(5):101036. doi: 10.1016/j.xcrm.2023.101036. PMID: 37196635; PMCID: PMC10213863.
10. A study to evaluate the safety, tolerability and efficacy of MHV370 in participants with Sjogren’s Syndrome (SjS) or Mixed Connective Tissue Disease (MCTD): https://classic.clinicaltrials.gov/ct2/show/NCT04988087