Biotechnology · Cancer immunotherapy
Asher Bio
A South San Francisco company rebuilding interleukin-2 so it reaches only the killer T cells that attack tumors. Its lead molecule finished dose escalation in a Phase 1 trial and reported its first response numbers in May 2026.
Lafayette, Indiana, January 10, 2023
The first person ever to receive AB248 was treated at Horizon Oncology in Lafayette, Indiana, by an oncologist named Costantine Albany. Asher Bio named the doctor, the clinic and the date in a release a week later, which is unusual candor for a first-in-human dose.
What went into that patient was a piece of protein engineering: an antibody that grabs CD8 beta, a marker carried by cytotoxic T cells, fused to a deliberately weakened interleukin-2. On its own the cytokine barely signals. Tethered to a cell the antibody has already caught, it signals hard. Two handles on one cell, or nothing happens. The company calls this cis-targeting.
The cytokine that keeps breaking hearts
Interleukin-2 has the oldest and most frustrating record in cancer immunotherapy. High dose IL-2, sold as Proleukin, was the first modern immunotherapy to produce lasting complete responses in a minority of melanoma and kidney cancer patients. It was also close to unusable outside specialist centers, because of capillary leak syndrome and other toxicities.
A second generation followed, the not-alpha IL-2 drugs, engineered to skip the alpha receptor that stimulates regulatory T cells. The flagship was Nektar Therapeutics and Bristol Myers Squibb’s bempegaldesleukin, for which Bristol Myers committed up to $3.6 billion in 2018, the largest licensing deal in biotech history at the time.
On March 14, 2022, the Phase 3 PIVOT IO-001 trial in untreated advanced melanoma missed all three primary endpoints. Fierce Biotech reported 783 patients in the trial; Targeted Oncology reported 781 enrolled. Nektar stock fell 53% that morning to $4.97. William Blair analysts had called the study “the highest probability of success for the bempegaldesleukin franchise”.
That is the shadow Asher works in. Its argument is that the not-alpha designs fixed the wrong problem: they removed regulatory T cells but left natural killer cells, which the company says soak up drug and drive toxicity without helping kill tumors.
Two Pfizer scientists and a word for happy
Ivana Djuretic and Andy Yeung founded Asher in 2019 after leaving Pfizer, where Djuretic ran cytokine biology in the cancer immunology discovery unit. They went through Y Combinator that summer. The first Form D, filed in September 2019, lists the two of them as the only related persons, against a $3 million offering of which $490,000 had sold to eight investors.
Two academic co-founders joined: Ton Schumacher of the Netherlands Cancer Institute and Robert Schreiber of Washington University in St. Louis. Third Rock Ventures led a $55 million Series A announced in March 2021, with Craig Gibbs, previously chief business officer of Forty Seven, as chief executive. Gibbs told Fierce Biotech where the name came from: “Asher means happy or blessed in Yiddish”. By May 2026 Djuretic held the chief executive title herself.
Thirty four people out, three pharma partners in
In December 2023 the company “reduced its workforce by 60%, sending 34 employees on their way and pivoting to focus on a single immunotherapy”, as Fierce Biotech put it. AB821 and an infectious disease program went back on the shelf.
The bet paid off in capital. In April 2024 RA Capital led a $55 million Series C that brought AstraZeneca and Bristol Myers Squibb onto the cap table. In January 2025 both AstraZeneca and Amgen signed clinical supply agreements, for combinations with rilvegostomig and with tarlatamab in lung cancer. Asher keeps full ownership and supplies drug at no cost, so no upfront or milestone terms were disclosed. AB821 came off the shelf and entered the clinic at Yale in August 2025.
What is proven, and what is still claimed
| Evidence | What the record shows | Source type |
|---|---|---|
| Peer-reviewed preclinical | Two companion papers in Cancer Discovery, July 1, 2024, volume 14 issue 7: one from Asher with Schumacher and Schreiber on the design of AB248, one from the Netherlands Cancer Institute testing it on human tumor tissue. Also Science Translational Medicine, January 10, 2024, on hepatitis B, and Transplantation and Cellular Therapy, July 30, 2026, on engineered T cells. | Public record |
| Lead trial, as registered | NCT05653882 (AB248-101), Phase 1, started January 4, 2023, 552 participants estimated, 20 US sites, Merck Sharp & Dohme a collaborator. Active, not recruiting. All five primary outcome measures are safety measures. Primary completion estimated August 2026. | Public record |
| First efficacy numbers | In a May 21, 2026 release ahead of ASCO abstract 2616: responses in 2 of 11 cutaneous melanoma patients on monotherapy at 0.3 to 0.5 mg/kg, an 18% objective response rate; 7 of 30 responses in checkpoint-refractory melanoma on the pembrolizumab combination, 30% at 0.3 mg/kg. About 20-fold CD8 T cell expansion, no maximum tolerated dose reached. | Company-stated |
| Peer review of clinical data | None found as of September 2026. The efficacy figures exist as conference posters and company releases. | Not found |
| Selectivity, which number | Three figures for one property: “over 500-fold preference for CD8+ T cells compared to other cell types” in the 2024 publication release, “approximately 1,000-fold preference for the activation of CD8+ T cells over NK cells and Tregs” in company boilerplate, and a 2021 chief executive claim of 1,000 to 10,000 fold. | Figures differ |
| Partner-run trials | NCT07037758 (DeLLphi-311), Amgen sponsor, Phase 1b of tarlatamab plus AB248 in small cell lung cancer, started September 16, 2025, 380 estimated. NCT07027488, Yale sponsor, Phase 1 of AB821, started August 5, 2025, 50 estimated. NCT07300475, Washington University, vaccine plus AB248 in triple negative breast cancer, 30 estimated, not yet recruiting. | Public record |
| AstraZeneca combination | Announced January 7, 2025 as a global Phase 1b/2 in first-line lung cancer with rilvegostomig. No matching study appears on ClinicalTrials.gov as of September 2026. | Not found |
| Approvals | None. Every use of AB248 and AB821 is investigational. | Public record |
Read plainly: the preclinical case for cis-targeting is unusually well documented, in strong journals, with well-known academics as co-authors. The clinical case is one step behind. A first-in-human trial whose registered primary endpoints are all safety measures has produced response rates in the teens and twenties in patients who had already failed checkpoint inhibitors. That is a real signal, not a proven benefit. Asher has never run a randomized trial, and bempegaldesleukin looked good in Phase 1 too.
What to watch
- Primary completion of AB248-101, estimated August 2026, and whether the response rates hold as the melanoma cohorts fill.
- A peer-reviewed paper on the clinical data. Everything published so far is preclinical.
- Whether the AstraZeneca study ever registers. It was announced in January 2025.
- The AB821 amendment the company says is in development, testing IL-21 and IL-2 together.
- A new Form D. The last one was filed April 16, 2024.
In their words
“We first identify the immune cell subtype we want to target, next we attenuate the affinity of the immunomodulator towards receptors across all cell-types, then we create a fusion protein to direct the therapy only to the desired immune cell type, and finally we optimize the pharmacological properties.”
Andy Yeung, co-founder and chief technology officer, Series A release, 2021 · Company release
“significantly de-risks the program and shows that we have a very clear therapeutic index that hasn’t been seen before with previous IL-2 therapies, so that gave us a lot of confidence that we could be more aggressive about developing AB248”
Craig Gibbs, then chief executive, on a 2021 toxicity study, to Fierce Biotech · Interview
“While immune checkpoint inhibitors are an incredibly powerful tool for treating certain cancers, many tumors don’t respond, underscoring the need for new agents that can reinvigorate exhausted T cells and make them susceptible to PD-1 blockade”
Daniela Thommen, Netherlands Cancer Institute, senior author on the second Cancer Discovery paper, 2024 · Company release
“This exciting agreement with AstraZeneca is a reflection of the emerging clinical data from our Phase 1 study of etakafusp alfa.”
Don O’Sullivan, chief business officer, January 2025 release · Company release
“AB248 and AB821 were each designed to address historical limitations of cytokine therapy by selectively activating CD8+ T cells while avoiding the broader immune activation associated with conventional cytokines”
Ivana Djuretic, chief executive and co-founder, May 2026 release · Company release
“These data are particularly encouraging given that patients enrolled in the melanoma cohorts had received extensive prior immunotherapy, including prior checkpoint inhibitor doublets”
Harriet Kluger, Yale School of Medicine, quoted in the May 2026 release · Company release
Related companies
Sources
- Public recordClinicalTrials.gov NCT05653882, AB248-101
- Public recordClinicalTrials.gov NCT07027488, NCT07037758, NCT07300475
- Public recordTwo AB248 papers in Cancer Discovery, pages 1206 and 1226
- Public recordCD8 cis-targeted IL-2 drives potent antiviral activity against hepatitis B virus
- Public recordCis-targeted IL-2 Mutein to Augment the Antitumor Activity of Engineered T Cells
- Public recordForm D filings, CIK 0001787260
- IndependentAsher Bio snags $108M series B for immunotherapy programs
- IndependentAsher drops 60% of staff as immunotherapy biotech zeroes in on lead candidate
- IndependentAsher Bio’s encouraging early data sparks $108M financing
- IndependentAsher Bio launches with $55 million in funding
- IndependentBMS-Nektar’s Opdivo combo fails phase 3
- IndependentBempegaldesleukin Plus Nivolumab Not Effective
- CompanyAsher Bio Launches with $55 Million Series A Financing
- CompanyAsher Bio Closes $108 Million Series B Financing
- CompanyDosing of First Patient in Phase 1a/1b Clinical Trial of AB248
- CompanyAsher Bio Closes $55 Million Series C Financing
- CompanyClinical supply agreements with AstraZeneca and with Amgen
- CompanyTwo Presentations at the ASCO 2026 Annual Meeting
- CompanyAsher Bio website: home, about, pipeline, contact
Profile researched and written by Healthcare Discovery. Last updated September 29, 2026.
