The goal of this observational study is to learn how the immune system responds to myeloproliferative neoplasms (MPN) in adults with known or suspected MPN. Researchers also want to identify immune cells that could help develop future immune-based treatments for MPN.

The main questions it aims to answer are:

• Are there T cells in the bone marrow that can recognize MPN cells?
• Which targets (antigens) on MPN cells are recognized by these immune cells?
• Can researchers identify T cell receptors (TCRs) that may be used in future TCR-based therapies?

Researchers will study samples from adults with polycythemia vera (PV), essential thrombocythemia (ET), primary myelofibrosis (PMF), post-PMF, or unclassifiable MPN. Samples from healthy donors without blood disorders will also be included for comparison.

By providing blood and bone marrow samples, participants will:

• Allow researchers to study immune cells and genetic material from these samples
• Allow researchers to perform laboratory tests to study how immune cells recognize MPN cells

Researchers will use laboratory methods such as genetic sequencing, cell analysis, and cell culture experiments to better understand immune responses in MPN.

Participants will not receive direct medical benefit from this study. The results may help researchers better understand MPN and support the future development of immune-based therapies.

Inclusion Criteria:

• Patients previously diagnosed or suspected of having PV, ET, pre-PMF, overt PMF, or an unclassifiable MPN.
• Patients not previously diagnosed with a haematological disease as controls

Exclusion Criteria:

• Patients with any other hematological malignancy.

(i) Adult patients previously diagnosed with or suspected of having PV, ET, pre-PMF, overt PMF, or an unclassifiable MPN.

(ii) Healthy controls undergoing hip replacement surgery, that have not been diagnosed with any hematological disease.