Role of Next Generation Immune Checkpoint Inhibitor (ICI) Therapy in Philadelphia negative Classic Myeloproliferative neoplasm (MPN): Review of the Literature
Authors: Yadav Ruchi , Hakobyan Narek , Wang Jen Chin 
Published: July 2023

The classic, chronic Philadelphia chromosome-negative (Ph-) myeloproliferative neoplasms (MPN)- mainly essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF)&mdash; represent a heterogeneous group of stem cell disorders characterized by clonal proliferation of one or more hematopoietic cell lineages with organomegaly and constitutional symptoms. Several studies have shown that the presence of chronic inflammation and a dysregulated immune system play indisputable roles in the pathogenesis of these diseases. Lately, the treatment of cancer including hematological malignancy has progressed on the agents targeting the immune system, cytokine milieu, immunomodulatory agents, and targeted immune therapy. Immune checkpoints are the molecules that regulate T cells function in the tumor microenvironment (TME). The fully unraveled primary immune checkpoints are programmed cell death-1 (PD-1)/programmed cell death ligand-1 (PD-L1), and cytotoxic T-lymphocyte antigen-4 (CTLA-4). Immune checkpoint inhibitor therapy (ICIT) is based on blocking the inhibitory pathways in T cells to promote anti-tumor immune responses and has revolutionized cancer treatment paradigms. Despite the impressive clinical success of ICIT, tumor intrinsic resistance remains a daunting challenge for oncologists leading to a low response rate in solid tumors and hematological malignancies. A phase II trial on Nivolumab for patients with Primary Myelofibrosis, post-Essential thrombocythemia myelofibrosis, or post- Polycythemia myelofibrosis has been performed (ClinicalTrials.gov Identifier: NCT02421354). This clinical trial, on the efficacy of PD-1 blockade using the monoclonal antibody Nivolumab, was prematurely terminated due to a lack of efficacy and adverse events. A multicenter, open-label, phase 2, single-arm study was conducted including pembrolizumab in patients with Dynamic International Prognostic Scoring System category of intermediate-2 or greater primary, post-essential thrombocythemia or post-polycythemia vera myelofibrosis that were ineligible for or were previously treated with Ruxolitinib. Pembrolizumab treatment was well tolerated, but there were no objective clinical responses, so the study closed after the first stage was completed. To permit more patients to benefit from immunotherapy, the focus has changed to targeting alternative novel immune checkpoints in the tumor microenvironment such as lymphocyte activation gene-3 (LAG-3), T cell immunoglobulin, and mucin domain 3 (TIM-3), V-domain immunoglobulin-containing suppressor of T-cell activation (VISTA), T cell immunoglobulin and ITIM domain (TIGIT) and human endogenous retrovirus-H long terminal repeat-associating protein 2 (HHLA2) forming the basis of next-generation ICIT. Our article aims at emphasizing and discovering the role of next-generation ICIT in MPN as targeted immunotherapy involving monoclonal antibodies, checkpoint inhibitors, or therapeutic vaccines against selected MPN epitopes that could further enhance tumor-specific immune responses. Immunotherapeutic approaches are expanding and hopefully will extend the therapeutic armamentarium in patients with myeloproliferative neoplasms. Preliminary studies from our laboratory showed over-expressed MDSC and over-expressed VISTA in MDSC, and in progenitor and immune cells directing the need for more clinical trials using next-generation ICI in the treatment of MPN.