Myelofibrosis Patients with <em>CALR</em>, <em>MPL</em>, or Other Clonal Mutations Exhibit Dysfunctional NK Cells with Increased KIR2DL1 Inhibition — ASN Events
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  3. Myelofibrosis Patients with CALR, MPL, or Other Clonal Mutations Exhibit Dysfunctional NK Cells with Increased KIR2DL1 Inhibition

Myelofibrosis Patients with CALR, MPL, or Other Clonal Mutations Exhibit Dysfunctional NK Cells with Increased KIR2DL1 Inhibition (#196)

Mariana Medeiros 1 2 , Camila Araújo Bernardino Garcia 1 2 , Larissa Sarri Binelli 1 2 , Allana Guimarães de Carvalho 1 2 , Priscila Santos Scheucher 1 , Josiane Lílian dos Santos Schiavinato 1 , Leonardo Carvalho Palma 1 , Pedro Manoel Marques Garibaldi 1 , Lorena Lôbo de Figueiredo-Pontes 1 2
  1. Hematology Division, Department of Medical Imaging, Hematology, and Clinical Oncology, Ribeirao Preto Medical School at University of Sao Paulo, Ribeirão Preto, Sao Paulo, Brasil
  2. Ribeirão Preto Blood Center Foundation, University of São Paulo, Ribeirão Preto, Sao Paulo, Brasil

Myelofibrosis (MF), driven by JAK-STAT signaling mutations in hematopoietic stem cells, has the worst survival rates among myeloproliferative neoplasms (MPNs), worsening from JAK2 mutated (JAK2+) to JAK2 not mutated (JAK2-), including patients with mutations in CALR, MPL or other clonal mutations. The JAK-STAT pathway is pivotal for natural killer (NK) cell development, maturation, and function. These mutations may disrupt NK cell-mediated immune surveillance, contributing to disease progression. To characterize the cytotoxic immune cells of MF patients, peripheral blood mononuclear cells (PBMC) from 15 JAK2+ and 9 JAK2- (5 CALR+, 1 MPL+, 3 others) and 5 healthy donors (controls: CT) were analyzed by flow cytometry to profile: NK cell frequency and subtypes (CD45hiCD3-CD19-CD56brightCD16-; CD45hiCD3-CD19-CD56dimCD16+; NK maturation stages [CD57+ hypermature; CD11b-CD27- tolerant (DN), CD27+CD11b- immature secretory (IS), CD27+CD11b+ mature secretory (MS), CD11b+CD27- cytotoxic]; NK receptors (NKG2A, KIR2DL1, and NKp46). NK cytotoxic capacity was measured by quantifying dead/K562 target cells after PBMC co-culture. No significant differences were observed in total and hypermature NK cell frequency between JAK2⁺ and JAK2⁻ patient groups. JAK2⁻ patients exhibited an increased proportion of cytotoxic NK cells (CD11b⁺CD27⁻; 82.79±6.6 vs. 71,54±16, p=0.034). However, they exhibited higher inhibitory signaling via KIR2DL1 (28.08±23 vs. 10.56±12.54, p=0.027) and a trend towards lower activating signaling via NKp46 (40.12±27.9 vs. 70.18±32, p=0.12). On the other hand, JAK2⁻ group showed a higher expression of NKG2D activating receptor (82.09±16.6 vs. 59±31.7, p=0.037). Indeed, when cytotoxic capacity was evaluated, NK cells from JAK2⁻ patients showed a reduced capacity to induce K562 lysis compared to healthy donors (28.9±8.3 vs. 81.7±4.3, p=0.035) and JAK2+ patients (28.9±8.3 vs. 33.8; statistical analysis was not performed due to small sample size: JAK2+ n=1). These findings suggest that non-JAK2 mutations shape an inhibitory NK cell phenotype, impairing its cytotoxic function and contributing to immune evasion, with potential implications for immunotherapeutic strategies in myelofibrosis.