For eons, ticks have been drinking blood. Hookworms burrow into intestinal walls. Tapeworms coil through digestive tracts, sometimes for decades. And somehow—remarkably—the human immune system often lets them stay.
That evolutionary détente has caught the attention of a small San Francisco biotech called Ditto Biosciences, which is placing a rather audacious bet: that the molecular stealth tactics parasites use to evade destruction might be repurposed into drugs for rheumatoid arthritis, lupus, inflammatory bowel disease, and the sprawling constellation of autoimmune conditions that afflict somewhere between 23 million and 50 million Americans, depending on who's counting.
The founders—Adair Borges, who studied anti-CRISPR systems and parasitology at UCSF; Dennis Sun, with evolutionary biology credentials from Harvard and Berkeley; and Emily Weiss, a microbiologist who spent years at Illumina and DuPont—launched the company in 2025. They've been running AI screens on parasite proteins ever since, claiming to have analyzed more than a million candidates in their first seven months. Some of these, they say, bind to clinically validated human immune targets with affinities in the low nanomolar range, competitive with the antibody drugs already on the market.
It's an intellectually seductive premise. It's also completely unproven.
A Market Under Siege
The autoimmune therapeutics space is enormous—market size estimates vary widely depending on scope and definition, with some projections placing it at $271 billion in 2024 and pushing past $338 billion by decade's end, while others focused on specific treatment segments project more conservative growth from $107 billion in 2025 to $136 billion by 2035. It's also punishingly competitive. AbbVie alone pulled in nearly $27 billion from immunology products last year, anchored by Skyrizi, Rinvoq, and Humira, the latter still generating revenue despite a thicket of biosimilar competition. But the ground is shifting fast.
Biosimilars to Johnson & Johnson's Stelara (ustekinumab) hit the U.S. market in the past couple of years—Wezlana, Imuldosa, Starjemza, Steqeyma—with wholesale price cuts topping 80% in some cases, according to Samsung Bioepis. Formularies are flipping practically overnight. Medicare's Inflation Reduction Act has dragged a growing list of autoimmune biologics into price negotiations, squeezing margins that were once untouchable. And now CAR-T therapies, historically confined to blood cancers, are making early inroads into lupus and systemic sclerosis, hinting at a future where one-time cellular interventions could sideline chronic biologic infusions entirely.
For a startup entering this arena, incremental innovation won't cut it. "Me-too" antibodies with marginally better pharmacokinetics face skeptical payers and an FDA that's increasingly strict about demonstrating clinical differentiation. The message to new entrants is blunt: bring a genuinely novel mechanism, or prepare to fight on price.
Ditto's answer is parasites.
Evolutionary Immunologists
The core scientific idea isn't new. Academic labs have spent the better part of two decades cataloging the immunomodulatory proteins that parasites secrete to avoid getting killed. Evasins, for instance—tick-derived proteins that bind up chemokines and dampen inflammation—have been studied since at least 2008. A review in Frontiers last year called them "promising anti-inflammatory scaffolds," though no drug candidate has advanced beyond preclinical work. ES-62, a glycoprotein from filarial nematodes, suppresses Th17 pathways in mouse models of arthritis; one recent study even tied its effects to changes in gut microbiota. Hookworm proteins like AIP-2 have shown activity in asthma models.
But translation has been frustratingly slow, sometimes for reasons that have little to do with the science itself. Controlled infection trials—literally giving patients hookworms or pig whipworm eggs to modulate their immune systems—yielded mixed results in celiac disease and metabolic syndrome studies conducted in Australia over the past decade. The most notorious failure was Trichuris suis ova (TSO), which flopped in a Phase 2 Crohn's trial back in 2013. That setback, combined with FDA import restrictions on live helminths, effectively killed the idea of therapeutic parasitism via actual worms.
Ditto is doing something different, at least in theory. Rather than infecting anyone with anything, the company is hunting for individual proteins—biologics that can be isolated, engineered, manufactured at scale, and dosed like any antibody. The team has leaned heavily on AI structure prediction tools, including AlphaFold 3, which launched in mid-2024 and extended computational modeling to protein-ligand interactions. According to the company, thousands of candidates have emerged from these screens, some showing binding affinities around 1–2 nanomolar.
Emily Weiss noted on LinkedIn early this year that the team had stood up a wet lab and validation assays and identified "very promising molecules." The company is also assembling what it calls a tissue biobank, ostensibly to map human immune memory against parasite antigens—a preemptive strike against immunogenicity problems down the line.
Whether any of this translates to actual drugs remains an open question.
The Immunogenicity Problem
Here's the thing about parasite proteins: they're foreign. Deeply foreign. And the human immune system has spent evolutionary time learning to recognize and attack them.
Even if a parasite protein has evolved to evade detection when it's being secreted in the context of an active infection—say, in the gut lining or a tick's saliva gland—that doesn't mean isolating it, injecting it subcutaneously, and repeating that injection every two weeks will go unnoticed. Anti-drug antibodies can neutralize efficacy, alter clearance rates, or trigger adverse reactions. FDA guidance dating back to 2014 lays out a risk-based framework for assessing immunogenicity: sequence similarity to human proteins, aggregation potential, T-cell epitope content, and longitudinal ADA monitoring in trials. The EMA's 2017 guidelines are similarly prescriptive.
Ditto's stated plan involves humanization—grafting the functional regions of parasite proteins onto human scaffolds—and computational epitope de-immunization, essentially shaving off the bits most likely to provoke an immune response. The tissue biobank presumably helps anticipate which patients might already have immune memory against certain parasite antigens, potentially accelerating ADA formation.
All of this sounds rational. None of it is validated. The company hasn't published preclinical data. No patents have surfaced in public databases. No specific molecules or targets have been named. For now, the pitch rests on founder credentials, some encouraging LinkedIn updates, and the fact that Y Combinator—historically a reliable signal in the tech world, though its life sciences track record is spottier—decided to back them.
A Sparse Competitive Landscape
Ditto isn't the only group chasing parasite-derived therapeutics, but the field is small and littered with stalled efforts. Macrobiome Therapeutics in Australia, spun out of James Cook University by parasitologists Alex Loukas and Paul Giacomin, is working on hookworm proteins for IBD and metabolic disease. Their programs appear to be preclinical, and public updates have been scarce. Paragen Bio, another Australian spinout, raised roughly A$6 million in 2018 with backing from AbbVie Ventures and OneVentures, then went quiet. No recent press. No pipeline disclosures. No obvious clinical milestones.
Academic labs continue tinkering with tick proteins—an ACS Nanoscience Au paper last year described evasin-based nanoparticles for vaccines—but therapeutic development seems stuck in the basic research phase.
Meanwhile, the broader autoimmune space isn't waiting. Apogee Therapeutics is advancing extended half-life antibodies targeting IL-13, IL-4Rα, and OX40L, aiming for quarterly dosing regimens that could upend treatment paradigms. Spyre Therapeutics is pushing next-generation TL1A antibodies for IBD and rheumatoid arthritis with similar ambitions. And then there's CAR-T, steadily creeping into autoimmune indications with fast-track designations and early safety signals in lupus nephritis and multiple sclerosis.
These competitors have established platforms, manufacturing know-how, and regulatory precedent on their side. Ditto is pioneering a new source of drug candidates entirely, which is either a defensible moat or a massive liability, depending on how the biology plays out.
What Ditto Has to Prove
The immediate task is straightforward, if daunting: validate the computational predictions. Show that the AI-predicted hits actually bind their targets in functional assays. Demonstrate that they modulate immune pathways in disease-relevant models—preferably humanized mice or ex vivo human tissue, not just rodent splenocytes. Engineer out immunogenicity without gutting potency, a balancing act that has tripped up more experienced teams. Then comes IND-enabling tox studies, Phase 1 safety trials in healthy volunteers, and proof-of-concept studies in actual patients.
Even under ideal conditions, that's a multi-year, multi-million-dollar slog.
The market opportunity is real enough. Autoimmune diseases are chronic, debilitating, and expensive to treat. Many patients cycle through multiple therapies, losing response to TNF inhibitors or IL-17 blockers and searching for alternatives. Payers are tightening budgets, true, but they're also hungry for innovation that justifies premium pricing—genuine mechanistic novelty, not just incremental improvements in half-life or subcutaneous formulation.
If Ditto can show that parasite-derived proteins offer meaningfully different biology—different cytokine modulation, different tissue distribution, different safety profiles than existing antibodies—there's a commercial path forward, perhaps partnering with a larger pharma player for late-stage development and commercialization.
But the burden of proof is steep. The field of helminth therapy has a track record of overpromising. TSO's failure is a cautionary tale, and controlled infection trials in Australia yielded results that were, at best, modest and inconsistent. Investors and potential pharma partners will want data, not just structure predictions and LinkedIn posts. They'll want pharmacokinetics in non-human primates. Efficacy in humanized disease models. A clear regulatory strategy for managing the immunogenicity risk that hangs over every non-human protein therapeutic.
Ditto's central wager is that evolution has already solved the hardest problems—that parasites, through millions of years of co-evolution with mammalian immune systems, have developed tricks that human drug designers are still fumbling toward. If that's true, and if the team can translate those tricks into manufacturable, safe, and effective biologics, the payoff could be substantial.
If not, Ditto joins the long list of intellectually compelling ideas that couldn't survive the translational valley between hypothesis and clinic.
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Note on Data Recency: This article references market projections, funding details, and clinical timelines that may reflect information available at the time of drafting. Readers should verify current figures and pipeline statuses independently, as the biotech landscape shifts rapidly.
