Actually - cohorts do tend to fill slowly! I think they've been pretty speedy in comparison to other trials I've watched. They are taking end-stage people. These folks have already suffered much treatment. Modern oncology treatments hurt heart/kidneys/liver/blood. And to effectively study this drug, the company needs people with moderately well functioning heart/kidneys/liver/blood. Cancer therapies also leave recipient open to bacterial and fungal infections - and those people have to be excluded too. So - the patients need to be treatment flunkies with at least 3 months left and minimal to moderate (but no severe) injury to those major organs from prior treatment. This is much harder to find than you'd think.

So they're not actually slow. This is normal. Not what we want to see - but still totally normal.