DR. APPLEBAUM: [Question off microphone] The question I have is about the insertion of the suppressor mutation, would that have to occur in every single transgenic cell?

DR. LOOK: I kind of lost the question. That is why it doesn't work in the mouse. If you were going to do an insertional screen, of course, in the mouse -- this is kind of a very abbreviated version of my talk, so I need to mention, all the advantages of mouse models of cancer and leukemia, in particular.

So, in the mouse model, one can do insertional mutagenesis to screen for mutations that accelerate the onset, and we all know about this work of Copeland and Jenkins and others.

In the fish, since every cell in the fish is the product of a mutated parent, it will have the suppressor mutation.

Then you can look for a delayed onset, where normally you had always had the faster progressing cells from one clone would over-grow any that grew slower. Is that clear?

DR. APPLEBAUM: [Question off microphone].

DR. LOOK: No, the Myc is already there. So, what you do is, you mutagenize the males and breed it with females harboring the transgene.

So, when you get the mutation, it will be a dominant. So, you will look for influence of the mutation on the transgene, you will look for either acceleration or delay. The diagram is pretty mind boggling.

DR. LINKER: Were you surprised you only saw T cell tumors in this model?

DR. LOOK: Yes, because of course, we should have seen B cell tumors also. So, I recently started -- when I moved to Dana Farber from St. Jude, I started on the zebra fish model, and Lynn Zon has been enormously helpful.

So, first, I wanted to look at B lineage ALL, and he told me immediately, don't even go there, because the B cells in the fish are very difficult to identify.

They certainly develop. The fish have immunoglobulin, but they are buried deep in the pancreas, they develop quite late in life, and the whole ontogeny is quite uncertain, now, in fish.

In the T cells, by contrast, the thymus is very peripheral, and stays lateral. So, you can observe it throughout, very early in development, and also throughout the life of the fish.

DR. LINKER: Do you think that the fish don't survive long enough to see B cell tumors or other problems?

DR. LOOK: So far we haven't. It may be the problem that they get the T cell tumors so early that if the B cells don't develop until three weeks of life, then of course, they will already have T cell ALL.

We are not really clear how to get around it. You might use an E-mu type promoter, I would think, to try to target them specifically.

DR. YU: My questions have to do with, is every leukemia developed from the fish identical in genetic expression?

Do you see subgroups that may express the HOX-11 and another group that expresses HOX-11 L2 and so forth?

DR. LOOK: David wants me to mention that data as preliminary because he has only looked at a few. We have hundreds of tumors now. So, he is going through all of them, but so far we don't see HOX-11 yet, only SCL, LMO2, and almost all of them seem to mis-express those two genes in particular.

As you know, the HOX-11 group seems to be a very good risk subset in children, somewhat larger in adults. In both children and adults, the SCL LMO2 variant of T cell ALL is the most common and includes the high risk cases.

DR. GAYNON: You said that there is clinical heterogeneity in the TAL1 group. There must be some other factor that distinguishes those that are good and those that are bad. Do you have any insight into what that might be?

DR. LOOK: No, and so I think maybe Cheryl and I will talk maybe after the meeting. We haven't been able to get enough cases.

Steve Sallan is here. Certainly I think the DFCI regimen, along with the current COG regimen, with high dose asparaginase and anthracycline is very effective for T cell ALL in children, but there is still a problem with early failures, either induction failure or failure early in treatment.

I think probably for the most immediate future, the array approach would be the most likely to pick out genes like G0 that will identify those cases. Maybe Cheryl has already done it.

DR. CARROLL: Our next speaker is Michael Andreeff from the M.D. Anderson Cancer Center. He is going to talk about apoptosis in ALL, significance and exploitation.

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