ICML 2025 | Interim results from the MorningSun study: mosunetuzumab for high-tumor burden FL

So the Phase II MorningSun study is actually a basket study with many different expansion cohorts. The one that I presented is this interim analysis from a Phase II expansion cohort in patients with newly diagnosed untreated follicular lymphoma. They all have to have high-tumor burden per GELF criteria and all these patients that were enrolled from 55 different sites in the United States but 45 or 55 are community sites so most of these are really with the aim to recruit patients from the community sites. So in this study, mosunetuzumab was a CD20xCD3 bispecific antibody that was given subcutaneously as a monotherapy and there’s step-up dosing in cycle one but from cycle two and on it’s one dose every three weeks so it’s pretty convenient and steroids as pre-medication also as a way to mitigate cytokine release syndrome was only given in the first cycle and cycle two so only for four doses and other subsequent doses there’s no need for steroids. So what we have seen with all these patients, a total of 102 of them, the overall response rate is 87%. And complete response rate we’re seeing in 61% of these patients. When we look at the progression-free survival, the median progression-free survival was not reached, 12 months progression-free survival was 83%. So it’s quite encouraging. When we look at the safety profile, the most common adverse event is really injection site reaction which is low grade or resolved. And the one that is of interest is cytokine release syndrome which is also pretty much matched what we’re seeing with using mosunetuzumab in a subcutaneous fashion in a relapsed/refractory setting. The total CRS rate is 34% but most are grade 1 and some are grade 2. There’s no grade 3 or above CRS. And all CRS except one case occurred during cycle one and are resolved. So therefore, this is a first expansion Phase II study looking at mosunetuzumab subcutaneous injection in untreated follicular lymphoma patients who need treatment per GELF criteria. And we see very encouraging efficacy using this single dose. And also we see a very manageable safety profile. And this is also given in the outpatient setting. So further study really looking at giving this in a more expanded cohort with a focus in community setting really warrants further study.