AbCellera Walks Away From ABCL575 as OX40/OX40L Setbacks Mount
AbCellera has joined the growing list of drug developers backing away from OX40-pathway immunology, ending plans to move ABCL575 beyond phase 1. The antibody targets OX40 ligand and was being developed for atopic dermatitis and other autoimmune diseases, but the company now says it does not plan to continue the program past its first clinical study.
The phase 1 results themselves were not the problem. AbCellera said the study met all of its endpoints, with a favorable tolerability profile and pharmacokinetic behavior that supports an extended dosing interval. In a clinical setting, that combination usually means the drug can be given less often without obvious early safety concerns, a property that would normally strengthen the case for deeper development.
Instead, the company made a strategic retreat in response to external developments across the OX40/OX40L class.
A Mechanism Under Pressure After Multiple Late-Stage Reversals
The abandonment of ABCL575 lands in a year that has been unusually harsh for this immunology target. OX40 sits on activated T cells and helps sustain immune signaling; its ligand is part of the costimulatory machinery that can amplify inflammatory responses. In diseases such as atopic dermatitis, that biology made the pathway attractive because dampening overactive T-cell activity could, in theory, reduce the persistent skin inflammation that drives itch, erythema, and barrier disruption.
The scientific logic was clear enough to draw sustained investment. What has become clear instead is that the class has not translated cleanly from mechanism to clinically decisive benefit. In March, Kyowa Kirin shut down clinical studies of rocatinlimab, its Amgen-partnered anti-OX40 monoclonal antibody, after emerging concerns about malignancies with possible viral or immune-related links. Four months later, Sanofi halted plans to submit amlitelimab, an anti-OX40 ligand antibody, for atopic dermatitis after concluding it would not represent a meaningful improvement over existing treatments.
Those decisions changed the calculus around the entire target family. A program can look chemically sound and still fail in the market if competing therapies deliver better efficacy, more durable responses, or a cleaner safety profile. In immunology, that threshold is especially unforgiving because patients and prescribers already have biologics and advanced systemic therapies that set a high bar for both benefit and tolerability.
AbCellera did not describe a safety problem with ABCL575. The decision reads as a response to a shrinking strategic window rather than a failure of the molecule itself. Even so, when multiple companies begin stepping away from the same pathway in close succession, the signal is hard to ignore.
Why Extended Dosing Was Not Enough to Keep the Program Alive
The pharmacokinetic profile matters because chronic inflammatory disease programs rarely survive on convenience alone. An extended dosing interval can support adherence and lower treatment burden, especially in diseases like atopic dermatitis where long-term therapy is common. But convenience does not rescue a drug class if the therapeutic effect is modest or uncertain relative to the alternatives already on the market.
That tension appears to have shaped the decision here. A phase 1 study can establish whether a therapy is tolerable, how it behaves in the body, and whether exposure levels support dosing flexibility. It cannot answer the more consequential question of whether the mechanism will produce a meaningful clinical advantage once tested in larger, more heterogeneous patient populations.
OX40/OX40L programs face a particularly difficult benchmark because the pathway sits upstream in immune activation, where the margin between useful immunomodulation and unwanted immune disturbance can be thin. If the biology is too weakly suppressed, efficacy may not justify development. If the pathway is suppressed too broadly, safety concerns can emerge, especially in chronic use. That is the trap that has caught more than one immunology program in recent years.
The Class Still Has Defenders, but the Evidence Is Fragmenting
The picture is not uniformly bleak. In September, Inhibrx Biosciences reported phase 2 data for its hexavalent OX40 agonist INBRX-106 in combination with Keytruda in treatment-naïve, PD-L1 positive metastatic or unresectable recurrent head and neck squamous cell carcinoma. The study showed a 48.3% confirmed objective response rate, and company leadership said the findings strengthened its conviction in OX40-mediated T-cell costimulation.
That result points to a different side of the same biology: instead of suppressing OX40 signaling in autoimmunity, it attempts to stimulate the pathway in cancer to improve antitumor immune activity. The fact that one arm of the class may still be viable in oncology while another is losing support in autoimmune disease reflects how context-dependent immune modulation can be. A target that looks promising in one indication may fail in another because the desired direction of immune change is opposite, the clinical endpoint differs, and the acceptable risk profile changes completely.
For AbCellera, the practical decision is to conserve resources for assets with clearer commercial and clinical momentum. The company pointed to ABCL635, its neurokinin 3 receptor-targeting antibody for menopausal hot flashes, as a recent phase 2 winner. Executives have described that program as a potential best-in-class non-hormonal therapy with strong differentiation versus approved NK3R competitors.
What ABCL575’s Exit Signals for Autoimmune Drug Development
ABCL575’s exit does not prove the OX40/OX40L pathway is biologically dead. It does show how quickly enthusiasm can erode when efficacy expectations, safety concerns, and competitive pressure begin to point in different directions. In autoimmune drug development, especially for atopic dermatitis, companies now need more than proof of tolerability and workable pharmacokinetics. They need evidence that a new mechanism can outperform entrenched standards in a disease area where patients and clinicians already have several credible options.
The next tests of the pathway will matter less for theory than for durability of response, magnitude of benefit, and immune safety over time. Until those questions are answered convincingly, developers may continue to see OX40 as a target worth exploring in the laboratory but too unstable to carry deep into the clinic.