Researchers are using a detailed biomarker strategy to understand how a new class of immune therapies can essentially "reset" the immune system in patients with autoimmune diseases like lupus and rheumatoid arthritis. Rather than relying on a single blood test, doctors are now measuring multiple biological markers over time to track whether treatment is working, how long the benefit lasts, and whether it's safe. This comprehensive approach is helping scientists understand a promising new therapy called CLN-978, which targets and eliminates harmful B cells while allowing the immune system to rebuild itself.

What Is Immune Reset and Why Does It Matter?

Immune reset is a concept that sounds like rebooting a computer. In autoimmune diseases, the immune system mistakenly attacks the body's own tissues. The goal of immune reset is to eliminate the B cells that produce harmful antibodies while preserving the immune cells that protect against infection. If successful, patients could experience long-lasting disease control without needing to take immunosuppressive drugs indefinitely.

CLN-978 is a bispecific T cell engager, a type of therapy that acts like a bridge between two types of immune cells. It connects T cells (which kill infected or abnormal cells) directly to B cells that are causing disease. Once connected, the T cells destroy the harmful B cells. The therapy is delivered as a subcutaneous injection, meaning patients can receive it in an outpatient clinic rather than a hospital.

What Do the Initial Clinical Results Show?

Early clinical data from 29 patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) demonstrates encouraging results. In the lupus group, 71% of patients showed significant improvement in disease activity after a single dose, and 5 patients achieved complete remission. In the rheumatoid arthritis group, disease activity improved in 71% of patients, with one patient reaching remission.

The therapy achieved deep B cell depletion in both blood and tissue. In the lupus patients, 82% showed a reduction in peripheral blood B cells of more than 80% from baseline. In the rheumatoid arthritis patients, 67% of those receiving higher doses achieved B cell counts below the limit of detection. Importantly, the therapy reduced disease-driving autoantibodies without affecting protective vaccine immunity, suggesting the immune system retained its ability to fight infections.

How Are Doctors Measuring Success Beyond Clinical Symptoms?

Biomarkers are biological measurements that help doctors understand what's happening inside the body at a molecular level. Rather than waiting weeks or months to see if a patient feels better, biomarkers provide early signals of whether the treatment is working. The research team uses a suite of biomarkers measured over time, including:

• B cell counts in blood: Serial blood samples track how deeply B cells are depleted and how quickly they return, revealing the depth and durability of the treatment effect.
• B cells in inflamed tissues: When feasible, tissue biopsies from lymph nodes and joints show whether B cell depletion extends beyond the bloodstream to where inflammation actually occurs.
• Autoantibody levels: These disease-driving antibodies are relatively easy to measure and often correlate with improvements in inflammation and clinical symptoms.
• Cytokine levels: Cytokines are small proteins that immune cells use to communicate with each other, and measuring them helps ensure the immune system is activating appropriately and provides early safety signals.

This multi-layered approach allows researchers to connect the dose of therapy, the biological changes it causes, and the clinical improvements patients experience. No single biomarker tells the whole story; instead, doctors interpret all the data together to build a complete picture of how the immune system is responding.

What Safety Concerns Have Emerged?

The therapy showed a favorable safety profile across most dose levels tested. Most adverse events related to immune activation were mild (Grade 1), occurring primarily after the first dose. However, one patient receiving the highest dose tested (45 micrograms) experienced a more serious cytokine release syndrome, a condition where immune activation becomes too intense. This led researchers to pause enrollment in that dose cohort and plan to implement more gradual dose escalation in future multi-dose regimens. Importantly, no cases of immune effector cell-associated neurotoxicity syndrome, a serious neurological complication, were observed.

How Does This Approach Differ From Current Autoimmune Treatments?

Most current autoimmune treatments require patients to take medications continuously to suppress the immune system. This approach carries the risk of infections and other complications from long-term immunosuppression. CLN-978 offers a different strategy: a short course of treatment designed to reset the immune system, with the possibility of redosing months or years later if disease activity returns. This could mean fewer medications, fewer doctor visits, and better quality of life for patients.

"Following a single target dose of CLN-978, patients with refractory SLE and difficult-to-treat RA demonstrated clinical benefit, including remissions. These initial Phase 1 data demonstrate the deep and dose-dependent B cell depletion achievable with CLN-978 and reinforce our belief that it has strong potential as a disease-modifying treatment in multiple challenging-to-treat autoimmune conditions," said Jeffrey Jones, MD, MBA, Chief Medical Officer at Cullinan Therapeutics.

Jeffrey Jones, MD, MBA, Chief Medical Officer, Cullinan Therapeutics

What Are the Next Steps in Development?

The research team is currently studying multi-dose regimens to determine whether repeated doses can provide even more durable disease control. The OUTRACE clinical trials are ongoing and actively recruiting patients with lupus and rheumatoid arthritis who have not responded to other treatments. Cullinan Therapeutics is also developing a second T cell engager called velinotamig, which targets a different B cell marker, suggesting this therapeutic approach may work across multiple autoimmune conditions.

The comprehensive biomarker framework being used in these studies is expected to inform how these therapies are ultimately used in clinical practice and may accelerate the development of similar immune-resetting approaches for other autoimmune diseases. For patients living with lupus, rheumatoid arthritis, and related conditions, this research represents a potential shift toward shorter, more targeted treatments that work with the immune system rather than simply suppressing it.