SION: Highlights from the RBC Healthcare Conference

Research evidence excerpt

SION: Highlights from the RBC Healthcare Conference

EQUITY RESEARCH QUICK TAKE

RBC Capital Markets, LLC

Brian Abrahams, M.D. (Head of Global

Healthcare Research)

Nevin Varghese, Ph.D. (Analyst)

Kevin Meli, Ph.D. (Senior Associate)

May 20, 2026

Sionna Therapeutics Inc.

Highlights from the RBC Healthcare Conference

NASDAQ: SION | USD 39.50 | Underperform | Speculative Risk | Price Target USD 23.00

Sentiment: Neutral

CFO Elena Ridloff presented; mgmt continues to sound confident in the translation from the HBE assay to upcoming clinical data

from '719 add-on trial, where they maintain a 10mmol SwCl bar, and cited strategic flexibility to pursue various permutations

with their agents (wholly-owned dual combo or add-on to Trikafta) depending on data. We acknowledge they have demonstrated

engagement of a novel CFTR target and that CF is a large market opportunity if they are successful - we just think too much market

cap is stemming from a historically challenging preclinical assay. We are Underperform, Speculative Risk.

• '719 + SoC and '451 dual combo remain on track for summer '26 readout; mgmt continues to expect to show at least a 10mmol

SwCl benefit on top of SoC in the '719 add-on trial, supported by ph.I PK/exposure work. They believe this level of SwCl change

should ultimately translate to ~3% improvement in FEV1, though reiterated that this initial study is not powered for FEV1 given

its small size and short duration, and the high variability within the measurement.

• In the '451 HV study with '2222 or '109, SION is assessing PK to determine which dual combo to advance and mgmt maintained

that the dual combo is the priority over an add-on path, though the add-on strategy for '719 remains an option to pursue, such