I am working on trafficking of MDSCs to tumor xenograft (LLC-1 cells at the moment). I am adaptively transfer MDSC from tumor bearing mice to recipient tumor bearing mice and thereafter I track them to different organs and study their bio-distribution, especially tumor. 

However, I have noticed that the size of tumor (tumor microenvironment) affects the cells recruitment to the tumor as well other organs.

I would very appreciate if anyone knows more about it and how it affects? Especially, how does it affects the ratio between PMN and M-MDSC? And how the size or tumor microenvironment affects the bio-distribution? Also a relevant paper would be very nice!

I know that the ration is around 7, means PMN migrate around 7 times more than M-MDSC. However, I have noticed some times, in LLC-1 tumors, this ratio is one to one, which came very very strange to me because many other times in my experiments this ratio is one M-MDSC (Ly6C hi) to 5 to 7 PMN-MDSC (Ly6G hi) cells!  would the size affects this ratio? Also what other factors may change this?

How the size of tumor xenograft affect the recruitment of MDSCs (specifically M-MDSC and PMN-MDSC) to the tumor?