Autoimmune cell therapy pauses expose stratification gaps

Novartis and Bristol Myers Squibb have paused multiple trials of their autoimmune cell therapies following inflammatory side effects. Novartis placed holds on its rap-cel program on 24 August after three cases of immune effector cell-associated hemophagocytic syndrome (IEC-HS), a rare and potentially life-threatening reaction, led to fatal outcomes in three participants.

Bristol Myers Squibb voluntarily paused enrollment in its zola-cel program after detecting transient and reversible inflammatory events during routine safety surveillance. One prior IEC-HS case had already been reported in a Phase 1 study.

What the pauses tell us about the field

Both companies are established cell-therapy developers. Novartis and Bristol Myers Squibb market cancer CAR-T products and are among the companies now redirecting cell therapy toward autoimmune disease. The rap-cel program alone spans eight immunology and neuroscience indications, including lupus, myasthenia gravis, and multiple sclerosis.

The expansion of cell therapy from oncology into autoimmune conditions reflects the considerable promise of the field. 

The recent safety events also underline how much there is still to learn as these therapies move into different patient populations.

One area of scrutiny is manufacturing. Both rap-cel and zola-cel use technologies intended to speed production compared with earlier CAR-T products. William Blair analyst Sami Corwin suggested that these approaches could be contributing to increased cell expansion and the reported toxicities, while cautioning that other factors may also be involved.

There may also be important biological differences between autoimmune and cancer populations. Jefferies analyst Roger Song observed that autoimmune diseases can involve greater baseline immune activation, raising the possibility that CAR-T treatment could amplify an already active immune response (BioPharma Dive).

The market reaction reflected the uncertainty. Shares in Kyverna, Cabaletta Bio, Allogene Therapeutics, CRISPR Therapeutics, and Fate Therapeutics fell sharply before recovering.

Why patient selection deserves more attention

It is too early to conclude what caused these events. Manufacturing, treatment design, underlying disease biology, patient characteristics, and clinical management all warrant scrutiny. The pauses also bring another question into sharper focus: how precisely can trials identify which patients are most appropriate for these therapies?

Autoimmune diseases are heterogeneous. Baseline immune activation, prior infections, disease severity, treatment history, biomarkers, and other patient characteristics may all influence how an individual responds to treatment.

The field's risk-mitigation strategies already incorporate some of this thinking through eligibility criteria. Some developers may be better positioned to avoid enrolling people at higher risk of serious immune reactions. Cabaletta, for example, excludes patients who have experienced certain recent infections or harmful inflammatory events.

These are, at their core, patient-selection decisions. As more clinical and biomarker data become available, eligibility may increasingly move beyond broad diagnostic criteria toward more sophisticated combinations of clinical, phenotypic, and molecular information.

That makes patient characterization relevant much earlier in trial planning. The question is not only whether sufficient patients exist, but whether researchers understand the subgroups within that population well enough to anticipate how eligibility criteria, biology, and treatment response might interact.

This challenge extends beyond cell therapy. Across autoimmune and inflammatory disease, heterogeneous populations continue to complicate the move toward more precise treatment. 

What the field should watch next

The first question is whether the observed safety events prove to be associated primarily with characteristics of the therapies themselves, their manufacturing approaches, particular patient characteristics, or some combination of these factors.

The second is whether eligibility criteria begin to evolve as safety and biomarker data accumulate. If researchers identify characteristics associated with greater risk or response, those signals could increasingly inform how future trials define and select their populations.

Different therapeutic approaches may also produce different safety profiles. Analysts assessing companies including Allogene and Fate have suggested that allogeneic approaches, made from donor cells, could carry different inflammatory risks because of differences in cellular composition. That remains a hypothesis to test as larger clinical datasets emerge.

Clinical management is also likely to improve as experience grows. Greater physician awareness of IEC-HS symptoms and appropriate treatment could improve management and outcomes over time.

None of this diminishes the therapeutic promise of autoimmune cell therapy. Rather, it reflects a field moving from compelling early signals toward the more difficult task of understanding how these therapies behave across larger and more varied patient populations.

As that happens, patient selection is likely to become an increasingly scientific discipline. Programs that can connect biological understanding, thoughtful eligibility design, and real-world patient characterization will be better positioned to generate evidence that is both compelling and interpretable.