PE Associate to MBB Consultant Possible Without MBA?

Hi all,

Is it possible for someone to lateral into a "Post-MBA Consultant" role at MBB without going to business school after they finish their 2-3 year associate role in PE? I am referring to people who have 4-6 years of front office work experience (i.e., 2/3 years in IB + 2/3 years in PE).

Or would MBB not give you the time of day without an MBA if you were looking to join long-term? I believe the MBB work experience is invaluable if one wanted to work their way up at a company, but is B-School the only way to get your foot in the door at MBB in the first place (assuming you didn't join out of undergrad)?