ALBERT

Description: Introduction: Acute graft-versus-host disease (aGVHD) is a major limitation of allogeneic stem cell transplantation (alloSCT) due to associated morbidity and mortality. A search for biomarkers that predict its occurrence is continuously evolving. Regulatory T cells (T regs) have been shown to suppress the early expansion of alloreactive donor T cells and limit the capacity to induce GVHD without minimizing the graft-versus-leukemia (GVL) effect. Recently, the role of regulatory B cells (B reg) in GHVD was demonstrated, with exacerbation of GVHD in both donor and host mice lacking functional regulatory B cells. Semaphorin 3A (Sema3A) is an immunoregulatory molecule secreted by activated B, T and antigen presenting cells. It enhances suppressor ability of B and T regulatory cells by increased secretion of interleukin-10 (IL-10) and transforming growth factor β (TGF-β). The aim of the present study was to explore whether Sema3A expression on B reg and T reg cells from donors and/or recipients pre- or early post-transplantation can predict occurrence of aGVHD. Methods: Thirty four consecutive patients referred to alloSCT were included in the first study cohort. Additionally, 10 donor/recipient (D/R) pairs were enrolled. All participants signed informed consent. 20 cc of fresh peripheral blood were drawn from recipients at day -7 pre-alloSCT and upon WBC engraftment, as well as from their corresponding donors. Mononuclear cells were isolated using ficoll gradient separation and subjected to FACS analysis using monoclonal antibodies evaluating the level of Sema3A expression on B reg cells (CD19/CD25high/ Sema3A), T reg cells (CD4/CD25high/Sema3A) and natural killer (NK) cells (CD3/CD56). Cutoff for positive expression of Sema3A on regulatory cells was considered only if ≥20% of cells expressed the above phenotype of T, B cell and NK population. The FACS results correlated with occurrence of clinical aGVHD grade II-IV. Descriptive statistical analysis and student t test are used to describe results. Results: Overall, 44 recipients were analyzed. Median age at transplant was 49.9 (18-69), 34 were diagnosed with acute leukemia/MDS, 8 - lymphoproliferative and 2 - myeloproliferative diseases. All patients received peripheral mobilized stem cells. Myeloablative conditioning was administered to 33 and reduced intensity to 11 patients. GVHD prophylaxis consisted of standard cyclosporine and methotrexate. Twenty patients developed aGVHD grade II-IV, mostly grade II –III (80%). Recipient expression of Sema3A on B cells pre-transplant was higher in patients without aGVHD versus those with aGVHD (79.9% vs 69.5%, respectively; p