X4 Pharmaceuticals Inc

Neutrophil functionality assessment sub-study

•X4 also announcednew findings from a sub-study comparing the mean percentage of functional neutrophils in samples from healthy donors (n=5) to participants from the Phase 2 CN study (n=9) using two common study methods. These results demonstrated that the mean percentage offunctional circulating neutrophils in CN participants in this sub-study was comparable to that of healthy donors after six months of mavorixafor dosing.

◦The subset of participants with congenital neutropenia (n=4 of 9) also had mean percentage of functional neutrophils comparable to those of healthy donors.

◦This is the first clinical demonstration of the functionality of neutrophils mobilized by mavorixafor, and further increases the company’s confidence in achieving success in the ongoing pivotal Phase 3 4WARD clinical trial.