Structural and diffusion weighted MRI demonstrates responses to ibrutinib in a mouse model of follicular helper (Tfh) T-cell lymphoma

Recent analyses of the genetics of peripheral T-cell lymphoma (PTCL) have shown that a large proportion of cases are derived from normal follicular helper (Tfh) T-cells. The sanroque mouse strain bears a mutation that increases Tfh cell number and heterozygous animals (Roquin^san/+) develop lymphomas similar to human Tfh lymphoma. Here we demonstrate the usefulness of Roquin^san/+ animals as a pre-clinical model of Tfh lymphoma. Long latency of development and incomplete penetrance in this strain suggests the lymphomas are genetically diverse. We carried out preliminary genetic characterisation by whole exome sequencing and detected tumor specific mutations in Hsp90ab1, Ccnb3 and RhoA. Interleukin-2-inducible kinase (ITK) is expressed in Tfh lymphoma and is a potential therapeutic agent. A preclinical study of ibrutinib, a small molecule inhibitor of mouse and human ITK, in established lymphoma was carried out and showed lymphoma regression in 8/12 (67%) mice. Using T2-weighted MRI to assess lymph node volume and diffusion weighted MRI scanning as a measure of function, we showed that treatment increased mean apparent diffusion coefficient (ADC) suggesting cell death, and that change in ADC following treatment correlated with change in lymphoma volume. We suggest that heterozygous sanroque mice are a useful model of Tfh cell derived lymphomas in an immunocompetent animal.

Synthetic Lethal Screen Demonstrates That a JAK2 Inhibitor Suppresses a BCL6-dependent IL10RA/JAK2/STAT3 Pathway in High Grade B-cell Lymphoma

We demonstrate the usefulness of synthetic lethal screening of a conditionally BCL6-deficient Burkitt lymphoma cell line, DG75-AB7, with a library of small molecules to determine survival pathways suppressed by BCL6 and suggest mechanism-based treatments for lymphoma. Lestaurtinib, a JAK2 inhibitor and one of the hits from the screen, repressed survival of BCL6-deficient cells in vitro and reduced growth and proliferation of xenografts in vivo BCL6 deficiency in DG75-AB7 induced JAK2 mRNA and protein expression and STAT3 phosphorylation. Surface IL10RA was elevated by BCL6 deficiency, and blockade of IL10RA repressed STAT3 phosphorylation. Therefore, we define an IL10RA/JAK2/STAT3 pathway each component of which is repressed by BCL6. We also show for the first time that JAK2 is a direct BCL6 target gene; BCL6 bound to the JAK2 promoter in vitro and was enriched by ChIP-seq. The place of JAK2 inhibitors in the treatment of diffuse large B-cell lymphoma has not been defined; we suggest that JAK2 inhibitors might be most effective in poor prognosis ABC-DLBCL, which shows higher levels of IL10RA, JAK2, and STAT3 but lower levels of BCL6 than GC-DLBCL and might be usefully combined with novel approaches such as inhibition of IL10RA.

Follicular helper T-cells: expanding roles in T-cell lymphoma and targets for treatment

Follicular helper T-cells (Tfh cells) are a subset of CD4(+) T-cells that are essential for normal production of high affinity antibodies. Tfh cells characteristically produce IL21 and IL4 and show high expression of surface markers CXCR5, ICOS, PDCD1 (PD-1) and the chemokine CXCL13. In this review we will focus on the emerging links between Tfh cells and subtypes of T-cell non-Hodgkin lymphoma: angioimmunoblastic T-cell lymphoma (AITL) and ~20% of peripheral T-cell lymphoma not otherwise specified (PTCL-NOS) have surface marker features of Tfh cells and share a spectrum of genetic abnormalities. The recurrent genetic abnormalities associated with AITL include mutations in epigenetic modifiers such as TET2 and DNMT3A and the motility and adhesion gene, RHOA, is mutated in up to 70% of cases. ~20% of PTCL-NOS demonstrate RHOA mutations and have other characteristics suggesting an origin in Tfh cells. The recognition that specific genetic and surface markers are associated with malignant Tfh cells suggests that the next few years will bring major changes in diagnostic and treatment possibilities. For example, antibodies against IL21, PDCD1 and ICOS are already in clinical trials for autoimmune disease or other malignancies and antibodies against CXCL13 are in pre-clinical development.