In the below video presentation from May, at the 7:30 minute...

In the below video presentation from May, at the 7:30 minute mark, Leslie mentioned that the study is at the "Phase1b study and it's a confirmation study whereby we are proving the proof of concept of the autologous CAR T failures into our Allogeneic CAR T". Maybe the formal and informal meetings that they have had with the FDA made them change from Phase 1/2a back to Phase 1/1b.
As highlighted in the study brief discussion summary, the study now includes both dose-escalation and dose-optimizationexpansion phases. Probably suggests a more thorough exploration of dosing regimens and including more patients (from 120 to 129, that's not much more compared to the original target). The focus has shifted to "identify a treatment regimen most likely to result in clinical efficacy while maintaining a favorable safety profile." This could imply that the earlier phase 2a portion may not have yielded the desired efficacy results or raised safety concerns.

Imugene (ASX:IMU) | JMM & éthica Capital Innovation & Investment Insights | May 2024 (youtube.com)