I've done quite a bit of characterizing human xenografts (orthotopic and subQ) from a number of different tumors propogated in mice. I often culture pieces of xenograft tumor by various methods. After xenograft growth in a mouse, I found that the fibroblast componenet of the xeno stroma was made of mouse fibroblasts (host carcinoma associated fibroblasts).

For example, if I culture human primary tumor (not having seen a mouse background), I can recover human CAFs. If I culture a passage 1 human xeno from mice, I have only recovered host mouse CAFs. I can't say for certain that there are no human stromal cells remaining in the tumor stroma after xenografting, but I have never encountered them in dozens of xenografts examined. After xenografting, the only human component I've identified remaining have been the human tumor cells.

My impression is that the human stromal component of a xengrafted tumor is entirely replaced by host derived cells -- probably in the first passage through a mouse background.

Once we engaged a development that created surprise as well as need for carefulness: dog carcinoma cells (from cell line) were inoculated in nude mice, one of the tumors was isolated to produce a new in vitro cell line, which turned out to be mouse tumor (tested with dog DNA and mouse DNA hybridization).

Other readers ever experienced this?

Were the mouse cells found in the isolated canine tumor capable of establishing a tumor in nude mice?

Further, did you ever identify the type of mouse cell?

If tumorogenic, my hunch would be that it was a host mouse stromal cell possibly immortalized/transformed by interactions with canine carcinoma cells.

My experience with human pancreatic and colorectal xenografts is that all of the cells in the stroma of the tumor xenograft become host mouse cells after passage of the primary tumor in a mouse background.

The only human component I've recovered from such xenos is the human adenocarcinoma cells. The stromal component of the tumor has always been identified as host mouse.

We worked with several cell lines that had been passaged many times in culture, and one that was recultured after having produced a tumor in nude mice and proved to be tumorigenic if inoculated again in nude mice, was not canine but mice.

At the time we were glad to have this established, and excluded this cell line from the later article. No further studies done. But your suggested mechanism agrees with what we thought.

Has anybody every tried to identify the mouse stromal portion of the human xenograft tumor by IHC? I am looking for an antibody that only identifies the mouse component of the tumor.

Mr. French, how did you distinguish between the mouse and human cells from the xenograft?

I am also looking for a mouse specific antibody that does not cross-react with the human cells. The application is IHC. Can anyone recommend an antibody? This seems to be very hard to find.

Mr. French, I have the same question, how do you distinguish mouse fibroblast from human fibroblast?