Stefania Massari

Investigating the role of STAT5 in ALCL pathogenesis

Medizinische Universität Wien

Supervisor: Lukas KENNER

Research objectives:

Preliminary data from our group demonstrates that deletion of platelet derived growth factor receptor beta (PDGFRβ), in a murine mimic of anaplastic large cell lymphoma (ALCL), the CD4/NPM-ALK transgenic mouse significantly increases survival rates.

Both STAT3 and STAT5 have been implicated in ALK+ ALCL progression, although the oncogenic contribution of STAT5 is less conclusive. Interestingly, deletion of PDGFRβ in vivo results in a reduction of the total levels of STAT5 in tumours suggesting that PDGFRβ regulates STAT5 representing a major signalling pathway in ALCL pathology and a potential therapeutic target. As such, this pathway will be investigated further in ALCL model systems to understand how it affects the biology of the tumours and survival rates and to explore whether this signalling axis represents a therapeutic target in both treatment naïve and relapsed disease.

To further elucidate the importance of the PDGFRβ-STAT5 axis in ALCL and its clinical relevance, it is essential to analyse the effects of dual PDGFRβ and STAT5 deletion in vivo. For this purpose, we will breed the established CD4/NPM-ALK mouse expressing or lacking PDGFRβ to a Stat5a/b floxed mouse model, in which both Stat5 genes are flanked by loxP sites for T cell or stromal cell-specific deletion.

We hypothesise that deleting STAT5a/b in the PDGFRβ knock-out mouse model will further increase the survival rate of these animals by decreasing tumour burden, as our in vitro results suggest that STAT5 represents the major downstream signalling molecule in the PDGFRβ pathway.

We propose to analyse in which way Stat5a/b gene expression is responsible for ALK+ ALCL growth by scRNAseq profiling and track its role for clonal evolution by comparing it with whole exome sequencing (WES) of those tumours.

Finally, we will analyse whether our results show relevance to humans by staining a large cohort of ALK+ ALCL patient samples with antibodies against PDGFRß and stat5a/b and will correlate the expression data with clinical endpoints.

Expected results:

We will analyse the effects of Stat5a/b deletion in NPM-ALK driven tumour cells in vivo and determine whether this signalling axis represents a therapeutic target in ALCL. In addition, we will determine if inhibition of PDGFRß and/or Stat5a/b improves survival in vivo and if Stat5a/b expression is of prognostic significance.

Planned secondments:

Year 1: Universitätsklinikum Freiburg: Analysis of immune cell profiles in the mouse model through learning the methodology that has been developed in the host lab (5 months)

Year 2: MLL Leukaemia lab: Conduct and analyse scRNAseq using equipment and expertise available at the MLL lab who will provide specific training (3 months)