TNFRII may play key role in CTCL, speaker says

“So we are currently doing FISH studies to confirm that this receptor is actually amplified in as many as half of cases of MF, suggesting that maybe, between mutation and amplification, this is an important driver of CTCL.”

Therapeutic possibilities

The researchers also thought that, if TNFRII is an important driver of CTCL, there would be some kind of transcriptional mark on the lymphoma cells. So they performed gene set enrichment analyses on 24 CTCL samples that had undergone 3-seq.

By comparing tumors expressing high levels of TNFRII and those expressing low levels of TNFRII, the team identified an expression signature that corresponds to the receptor’s known effects on RNA levels in T cells.

When they searched publicly available datasets, the researchers found this signature in 63 cases of MF (Shin et al, Blood 2007). And results of control experiments suggested the signature is specific to CTCL.

“If TNFRII is more active [in CTCL] and the mutation that we found is a hyperactivating mutation, we would expect this pathway to show increased activity downstream; namely, you would expect more processing of p100 to p52,” Dr Ungewickell said.

To investigate this possibility, the researchers generated Jurkat cells expressing empty vector, wild-type TNFRII, or mutant TNFRII and looked at NF-κB processing. They did see an increase in processing with the mutant receptor, compared to the wild-type receptor or empty vector.

“We also found, somewhat surprisingly, increases in phospho-ERK with the mutant receptor, as well as phospho-MEK,” Dr Ungewickell said.

“And to our knowledge, the RAS/MAP kinase pathway has not previously been linked to TNFRII signaling, suggesting that there is some kind of direct or indirect cross-talk between these pathways. We think it’s very interesting, since there are KRAS mutations that activate the RAS/MAP kinase pathway in a subset of these cases, suggesting some kind of synergy.”

Introducing the mutant receptor into primary CD4+ T cells had an effect similar to that observed in the Jurkat cells. The researchers did western blotting for NF-kB processing, and they saw an increase in p100 to p52 processing.

“This is a preliminary experiment, but we’re actually quite excited about this, since Jurkat cells have many abnormalities, due to the fact that they’re a leukemia line, and primary T cells will have the rest of the genome intact,” Dr Ungewickell said.

Now, he and his colleagues are conducting several studies to identify the changes that occur in primary T cells when mutant TNFRII is expressed. They also want to see if they can recapitulate CTCL and identify the transcriptional signature they previously found in patient biopsies and cells.

Lastly, the researchers are performing functional assays to evaluate proliferation, apoptosis, and pharmacological information, with the goal of identifying therapies that might be effective in patients with TNFRII mutation or amplification.

“Patients who have increased TNFRII signaling might respond to proteasome inhibitors, since p100 and p52 processing requires the proteasome,” Dr Ungewickell said. “And given that cross-talk with the RAS/MAP kinase signaling, as well as the KRAS mutations, we also think . . . that MEK inhibitors might be effective in the treatment of CTCL.”