Quick immunology refresher.

Regulatory T cells (Tregs) are basically the immune system’s brake pedal.

Mess up the brakes, you get autoimmune disease.

Restore them, you might cure it.

For the last 20 years, almost every Treg-focused biotech has targeted CD4 Tregs. That’s where the science lived and its where all the money flowed.

Mozart Therapeutics went the other way.

They’re building drugs around CD8 Tregs, a separate regulatory T cell population that Stanford’s Mark Davis laid out a decade ago as its own thing. These cells don’t suppress broadly. They hunt down and eliminate specific pathogenic immune cells driving autoimmunity.

Fix the right cell, fix the disease.

Mozart just reported interim Phase 1b data for MTX-101, their lead bispecific, in adults with Stage 3 type 1 diabetes.

The mechanism is clever.

MTX-101 binds CD8 on one arm and KIR (an inhibitory receptor) on the other, which simultaneously targets CD8 Tregs and releases the brake that’s keeping them inactive. The idea is to let these cells do what they’re supposed to do: kill the autoreactive T cells attacking pancreatic beta cells.

In the interim data, treated patients showed CD8 Treg expansion, reduction in pathogenic T cell populations, and decreased autoantigen responses. Higher-dose cohorts showed stabilization or increases in C-peptide over roughly 20 weeks, which is the key biomarker for preserved beta cell function.

No p-values, no patient counts. Interim readout caveats apply.

Here’s the context that makes this interesting.

The same day Mozart reported these data, SAB Biotherapeutics dropped Phase 1 data on SAB-142, a fully human anti-thymocyte globulin (made in cows, which is its own story), showing C-peptide preservation in four T1D patients.

The T1D disease-modification race is suddenly very real.

Sanofi has teplizumab approved. Diamyd is running a Phase 3 with retogatein.

Sana is preparing its IND for hypoimmune islets.

Century Therapeutics raised $135 million for a beta islet program.

Even BreezeBio raised a $60M Series B for mRNA-based tolerance induction.

Everyone is chasing the same biomarker: C-peptide preservation.

Mozart’s angle is that they’re the only one trying to fix T1D by waking up a specific regulatory T cell population, not broadly suppressing the immune system or replacing beta cells. If MTX-101 can hold C-peptide for two years instead of 20 weeks, the CD8 Treg thesis becomes a platform, not just a drug. And Mozart has an IL-15 mutein program behind MTX-101 doing similar CD8 Treg expansion work preclinically.

The company has raised $80 million from a who’s who of life sciences funds. They’ve cleared Phase 1a. They have signal in Phase 1b. And they’re targeting the modality that nobody else in autoimmune has bothered with.

Next milestone to watch: full Phase 1b readout and whether the C-peptide signal holds past the 20-week mark. If it does, Mozart just became a lot more interesting to anyone building autoimmune pipelines.