Defining the transcriptional and functional heterogeneity of CD4 T cells in the Bone Marrow of Clonal Haematopoiesis and myeloid malignancies.

Clonal Haematopoiesis of Indeterminate Potential (CHIP) is a phenomenon present in 10-20% of the population aged >65-years and is characterized by the expansion of immune cells harbouring somatic mutations in genes associated with myeloid malignancies (i.e. DNMT3A, TET2, TP53)1. These clonally expanded cells can transform and give rise to myeloid malignancies such as Myeloid Dysplastic Syndromes and Acute Myeloid Leukaemia, but their presence has also been linked with an increased risk of developing chronic inflammatory disease.

A better understanding of the cellular mechanism associated with progression or preventing the expansion of these mutated cells might help to develop biomarker and therapeutic strategies to treat or prevent the diseases associated with Clonal Haematopoiesis.

To this aim, Dr Napolitani's team is carrying out deep immune profiling of the peripheral blood and the bone marrow of a longitudinal cohort of patients undergoing hip replacement. In an interim analysis, his team observed a higher proportion of effector and cytotoxic CD4+ T cells in individuals with a low frequency of mutated cells, compared to individuals without mutations.

Conversely, the frequency of these cells dropped in individuals with large, expanded clones. This observation supports the hypothesis that CD4 T cells might limit the expansion of mutated clones and that individuals with a low frequency of these cells might be more susceptible to developing CHIP.

CHIP clones harbouring mutations in genes involved in the DNA Damage Response pathway (DDRp) pathway, such as TP53, have a high risk of transforming into malignant clones and leading to Acute Myeloid Leukemia. Notably, AML patients with DDRp driver mutations are characterized by an increased immune infiltration (Rutella). Interestingly, CHIP patients with DDRp mutations also showed an elevated frequency of effector and cytotoxic CD4+ T cells.

This suggests that CD4 T cells might be ineffective in controlling the expansion of clones harbouring DDRP mutations compared to mutation conferring a lower risk of transformation, such as DNMT3A and TET2. A better understanding of the cellular mechanisms associated with progression or preventing the expansion of clones harbouring CHIP mutation might help to develop biomarker and therapeutic strategies to harness T cell immunity in CHIP and myeloid malignancies.

This PhD project aims to explore the potential involvement of CD4 T cells in regulating clonal expansion within the context of Clonal Haematopoiesis. Additionally, it aims to investigate whether and how TP53 mutations confer expanding CHIP clones with the ability to evade CD4 T cell-mediated responses.

Aim 1) Define the heterogeneity of CD4 T cells in the Bone Marrow of individuals with CHIP and myeloid malignancies. Aim 2) Functional characterization of the interplay between distinct bone marrow CD4 T cells subsets and mutated HSPCs

Aim 3) Identification of T cells specific for mutated clones in the Bone Marrow of individuals harbouring DNMT3A and TP53 CHIP mutations.