CRISPR platform HOMEBRED brings PCR-grade diagnostics to farms, clinics and homes

Diagnosing infectious disease and cancer has long depended on a paradox: the most accurate tests are locked inside laboratories. Polymerase chain reaction, the gold standard for reading genetic material, demands thermal cyclers, trained technicians and centralized infrastructure, resources that are scarce precisely where the burden of disease is heaviest. Only a single at-home nucleic acid test has ever cleared the U.S. Food and Drug Administration, a stark illustration of how difficult it remains to build molecular diagnostics that are simultaneously sensitive, specific and simple enough for anyone to run. A research team led by Adnan Asadbeigi and Mohammad Reza Bakhtiarizadeh at Tehran University of Medical Sciences now reports a platform that attacks this bottleneck head on, and the results, published in iScience, suggest that field-ready, PCR-quality genetic testing may finally be within practical reach.

The platform, named HOMEBRED for highly sensitive and specific omnipresent multiplex endonuclease-based reliable detection, is built on the SHERLOCK architecture that harnesses the CRISPR-associated protein Cas13a. When Cas13a finds the RNA sequence its guide molecule instructs it to find, it does not merely cut the target; it shreds any nearby RNA indiscriminately. This collateral cleavage activity is the engine of the assay. Synthetic RNA reporters carrying a fluorescent dye and a quencher float in the reaction; if the target is present, the reporters are cleaved, the fluorescence escapes, and the result can be read with the naked eye under an inexpensive handheld blue light or on paper-based lateral flow strips. No thermocycler, no sequencer, no fluorescence plate reader is required at any stage.

What separates HOMEBRED from earlier CRISPR diagnostics is the way its guide RNAs are chosen. Fragile crRNA target windows have been a chronic vulnerability in CRISPR-based tests, because a single mutation in the target sequence can silence the assay entirely, allowing an evolving pathogen to escape detection. The team addressed this with CaSilico, an automated computational pipeline that screens thousands of genome sequences to identify highly conserved, mutation-resistant regions. For foot-and-mouth disease virus, one of the most genetically variable livestock pathogens known, CaSilico analyzed 707 sequences of the conserved 3D gene across all seven serotypes, applying a 98 percent conservation threshold and yielding 41 candidate target sites from which two crRNAs were selected using stringent thermodynamic and specificity criteria.

That computational rigor proved consequential in practice. One of the two initial foot-and-mouth disease virus crRNAs, CR3D1, looked ideal on paper yet failed to detect the virus in the laboratory. When the researchers examined its predicted secondary structures in detail, they found that the centroid structure, not just the minimum free energy fold, deviated from the stable hairpin architecture that Cas13a requires for recognition. This failure mode has been observed by other groups, and the finding underscores a lesson increasingly clear in the field: guide RNA design must weigh thermodynamic structure predictions as carefully as sequence conservation. The redesigned guide, CR3D2, worked flawlessly, correctly classifying all 11 clinical samples in complete agreement with reference RT-qPCR, with detection limits reaching down to ten copies per microliter in both fluorescent and lateral flow formats.

Perhaps the most consequential demonstration involves brucellosis, a bacterial zoonosis that infects an estimated 300 million of the world’s 1.4 billion cattle and for which no human vaccine exists. Veterinary control programs face a stubborn problem known as DIVA, the inability to differentiate infected animals from vaccinated ones. A false positive in a vaccinated, high-breeding-value animal can trigger needless culling, while a missed infection lets the disease spread silently. HOMEBRED tackles this with a dual-crRNA architecture: one guide targets the conserved bcsp31 gene to detect the four major Brucella species, while a second exploits a deletion mutation in the narJ gene unique to the RB51 vaccine strain. In testing, the platform signaled every wild-type culture of B. melitensis, B. abortus and B. suis while remaining silent against the vaccine strain, achieving 100 percent concordance with reference PCR across all 14 samples tested.

The platform also ventures into oncology. BCR-ABL1 fusion transcripts, produced when chromosomes 9 and 22 break and rejoin, are the hallmark of chronic myeloid leukemia, and the specific transcript isoform a patient carries influences response to tyrosine kinase inhibitor therapy. HOMEBRED distinguished the e13a2, e14a2 and e1a2 isoforms using isoform-specific guide RNAs and recombinase polymerase amplification primers sharing a common reverse primer on the ABL1 gene. Validated against the KCL-22 and K-562 leukemia cell lines and 14 clinical samples, the assay matched Sanger sequencing in specificity and exceeded RT-qPCR in sensitivity. Strikingly, three samples that reference RT-qPCR had called negative were positive by HOMEBRED, and two patients were found to co-express two transcript types simultaneously, findings with direct implications for treatment selection and minimal residual disease monitoring.

Two reaction formats were compared head to head. The two-step assay runs amplification and detection in separate tubes, while the single-step format folds both into one pot, reducing handling time and contamination risk. For Brucella, the one-pot version matched the two-step version perfectly, but for foot-and-mouth disease virus it dropped to 77 percent agreement, missing three positives and losing roughly an order of magnitude in detection limit. The authors conclude that the two-step format remains the safer default when sensitivity is paramount, reserving the single-step format for targets where its performance is proven. All duplicate reactions across both formats achieved 100 percent qualitative concordance, 111 out of 111 pairs, a reproducibility figure that speaks to careful optimization.

The extraction-free capability is where HOMEBRED pushes furthest past the existing literature. Traditional purification, when skipped, usually devastates sensitivity because crude biological matrices carry enzymatic inhibitors such as hemin and polysaccharides. The team paired their assay with HUDSON, a method that heats samples with chemical reducers to destroy nucleases and release genetic material, and applied it directly to vesicular fluid and epithelial tissue from foot-and-mouth disease cases. Without any nucleic acid extraction, the workflow detected viral seedstock down to 3.23 times ten to the fourth plaque-forming units per milliliter by colorimetric readout and 3.23 times ten to the third by fluorescence, an improvement of up to two orders of magnitude over comparable extraction-free CRISPR assays. The strategic choice of epithelial tissue, which proves far more chemically compatible with the HUDSON reaction than blood or feces, appears central to this performance.

Robustness against real-world genetic drift was verified by sequencing. Sanger analysis of foot-and-mouth disease virus samples confirmed that the computationally designed target region stayed fully conserved across strains, with a single substitution in one sample that failed to impair detection. Two leukemia clinical samples harbored point mutations inside the protospacer region, and HOMEBRED still called both correctly with no signal loss. The choice of Cas13a over the Cas12a enzymes used in several rival platforms also matters here: Cas13a requires no protospacer adjacent motif, freeing guide design from target-site constraints that are particularly restrictive when isolating the narrow junctions of fusion transcripts, and its vigorous trans-cleavage activity sustains signal generation even at suboptimal temperatures.

The authors acknowledge limits. Clinical isolates of B. canis could not be physically tested due to regional availability, so the team verified the assay against synthetic DNA carrying the identical conserved bcsp31 target domain, supported by sequence alignments showing 100 percent identity. No accessible cell line expressing the minor e1a2 transcript was available for extended in vitro benchmarking. Future work, they write, should prioritize lyophilized reagent formulations to round out farm-level deployment. Even with those caveats, HOMEBRED demonstrates that a single CRISPR platform, guided by automated conserved-region design and read by nothing more sophisticated than a handheld blue light, can deliver sensitivity on par with PCR across livestock pathogens, zoonotic bacteria, respiratory viruses and leukemia biomarkers, a convergence that could materially narrow the diagnostic gap between well-resourced laboratories and the places where early detection matters most.

Subject of Research: A CRISPR-Cas13a diagnostic platform enabling instrument-free detection of infectious agents and oncogenic mutations

Article Title: HOMEBRED: A unified CRISPR platform for field-ready shadowing of infectious agents and oncogenic mutations

Article References: Asadbeigi, A., Fazilaty, H., Saffari, M., Shirkoohi, R., Modarressi, M. H., Salehi, A., & Bakhtiarizadeh, M. R. (2026). HOMEBRED: A unified CRISPR platform for field-ready shadowing of infectious agents and oncogenic mutations. iScience, 29(10), Article 117532. https://doi.org/10.1016/j.isci.2026.117532

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117532

Keywords: CRISPR diagnostics, Cas13a, SHERLOCK, HOMEBRED, foot-and-mouth disease virus, brucellosis, SARS-CoV-2, BCR-ABL1, chronic myeloid leukemia, recombinase polymerase amplification, DIVA, point-of-care testing