Objective and Importance. Cyclic neutropenia (CyN) is a rare autosomal dominant inherited disorder due to the mutation ELANE primarily affecting bone marrow stem cells and is characterized by recurrent neutropenia every 2 to 4 weeks. Symptoms vary from benign to severe, including death. Postulations on the cause of wide spectrum in symptom presentation include the possibility of other genetic mutations, such as MEFV. Recommended treatment for CyN is G-CSF to keep ANC higher to minimize risk of infection. Case. A 25-year-old male diagnosed with CyN, on G-CSF but worsening quality of life. Pretransplant investigations revealed ELANE mutation positive severe CyN along with familial Mediterranean fever (MEFV) mutation. Intervention. Bone marrow transplantation as treatment for dual mutation (ELANE and MEFV mutation) positive severe CyN. Conclusion. BMT may be considered as an alternative treatment for severe CyN in patients who are refractory to G-CSF. It is postulated that in our patient the combined mutations (CyN and MEFV) may have contributed to the severity of this individual's symptoms. We suggest CyN patients who present with severe symptoms have evaluation with ELANE mutation testing, Periodic Fever Syndromes Panel, and routine marrow assessment with FISH, conventional cytogenetics, and morphological evaluation for MDS/AML.
Myeloid-derived suppressor cells (MDSCs) are CD11b+Gr1+ cells that induce T-cell hyporesponsiveness, thus impairing antitumor immunity. We have previously reported that disruption of Pak2, a member of the p21-activated kinases (Paks), in hematopoietic stem/progenitor cells (HSPCs) induces myeloid lineage skewing and expansion of CD11bhighGr1high cells in mice. In this study, we confirmed that Pak2-KO CD11bhighGr1high cells suppressed T-cell proliferation, consistent with an MDSC phenotype. Loss of Pak2 function in HSPCs led to (1) increased hematopoietic progenitor cell sensitivity to granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling, (2) increased MDSC proliferation, (3) decreased MDSC sensitivity to both intrinsic and Fas-Fas ligand-mediated apoptosis, and (4) promotion of MDSCs by Pak2-deficient CD4+ T cells that produced more interferon γ, tumor necrosis factor α, and GM-CSF. Pak2 disruption activated STAT5 while downregulating the expression of IRF8, a well-described myeloid transcription factor. Together, our data reveal a previously unrecognized role of Pak2 in regulating MDSC development via both cell-intrinsic and extrinsic mechanisms. Our findings have potential translational implications, as the efficacy of targeting Paks in cancer therapeutics may be undermined by tumor escape from immune control and/or acceleration of tumorigenesis through MDSC expansion.
Advances in haploidentical bone marrow transplantation (h-BMT) have drastically broadened the treatment options for patients requiring BMT. The possibility of significantly reducing the complications resulting from graft-versus-host disease (GvHD) with the administration of post-transplant cyclophosphamide (PT-CY) has substantially improved the efficacy and applicability of T cell-replete h-BMT. However, higher frequency of disease recurrence remains a major challenge in h-BMT with PT-CY. There is a critical need to identify novel strategies to prevent GvHD while sparing the graft-versus-leukaemia (GvL) effect in h-BMT. To this end, we evaluated the impact of bendamustine (BEN), given post-transplant, on GvHD and GvL using clinically relevant murine h-BMT models. We provide results indicating that post-transplant bendamustine (PT-BEN) alleviates GvHD, significantly improving survival, while preserving engraftment and GvL effects. We further document that PT-BEN can mitigate GvHD even in the absence of Treg. Our results also indicate that PT-BEN is less myelosuppressive than PT-CY, significantly increasing the number and proportion of CD11b(+) Gr-1(hi) cells, while decreasing lymphoid cells. In vitro we observed that BEN enhances the suppressive function of myeloid-derived suppressor cells (MDSCs) while impairing the proliferation of T- and B-cells. These results advocate for the consideration of PT-BEN as a new therapeutic platform for clinical implementation in h-BMT.