ALBERT

Description: Delayed T cell reconstitution after allogeneic hematopoietic stem cell transplant (allo-HSCT) is an important contributor to transplant-related morbidity and mortality due to infection and malignant relapse. Optimal T cell recovery requires a functional thymus, and strategies to enhance T cell reconstitution have the potential to improve overall outcome in allo-HSCT recipients, however, at the present time such strategies are limited. Hence one of the most significant clinical challenges is the need for rapid regeneration of thymopoiesis following induced immunodepletion and transplantation. Zinc is the second most abundant trace metal in the body, binding to more than 300 proteins involved in DNA synthesis and repair, gene transcription, cell proliferation as well as differentiation and apoptosis. Zinc deficiency (ZD) is a clinical condition causing immunosuppression and thymic atrophy with a consequent reduction in the number of circulating recent thymic emigrants (RTEs). Furthermore, mild ZD is one of the causes of the reduction in thymic function in the elderly and the role of zinc in tissue regeneration after damage has been clearly demonstrated in liver, skin, and intestinal diseases. In a pilot clinical trial, we demonstrated that patients receiving oral zinc supplementation after autologous HSCT showed increased thymic-dependent T cell reconstitution in the absence of adverse clinical events (Iovino 2018, Leuk Res). Although a clear clinical benefit was observed, the mechanisms underlying this process are poorly understood. Thus, we used a murine model to evaluate the effect of zinc supplementation in thymic reconstitution after acute damage. Using a model of thymic damage caused by sub-lethal total body irradiation (SL-TBI, 550 cGy), we found that mice that received zinc supplementation demonstrated increased thymic cellularity when compared to untreated age-matched mice (Fig. 1a). Importantly, this finding was also confirmed in a clinically-applicable model of MHC-matched allogeneic HSCT (Fig. 1b). We have previously demonstrated endothelial cells (EC), which are extremely resistant to damaged, are able to trigger thymic endogenous reconstitution after damage by producing regenerative factors such as BMP4, which targets thymic epithelial cells (TECs), a key population crucial for T cell development (Wertheimer 2018, Science Immunol). Interestingly, in our model of zinc administration, we found an increase in the number of regeneration-initiating ECs (Fig. 1c), and increased proliferation of TECs (Fig. 1d), which can occur in response to BMP4. Consistent with the hypothesis that zinc supplementation is activating the BMP4 pathway, when stimulated in vitro for 24 hours with supraphysiological doses of zinc sulfate, ex vivo propagated ECs (exECs) were directly induced to produce BMP4 (Fig. 1e), suggesting a likely mechanism by which zinc supplementation promotes thymic reconstitution. In conclusion, we demonstrate a mechanism by which zinc supplementation can improve thymic function and offers an innovative therapeutic strategy to improve T cell reconstitution in patients receiving allo-HSCT. Figure 1. Figure 1. Disclosures No relevant conflicts of interest to declare.

Description: INTRODUCTION Multiple myeloma (MM) is considered an incurable disease. Despite the introduction of novel agents allowed deeper response, high-dose chemotherapy and autologous stem cell transplantation (ASCT) remain the standard of care for patients (pts) in good clinical conditions. The most used strategies to mobilize stem cells from bone marrow (BM) into peripheral blood are high-dose cyclophosphamide (HD-CTX) plus G-CSF and G-CSF plus plerixafor (G-CSF+P). The goal of this retrospective study is to investigate whether the two different mobilization strategies have an impact on the clearance of monoclonal PCs in the apheresis products and on pts' outcome. PATIENTS AND METHODS We analyzed 62 pts (median age 61, range 41-75, 37 males and 25 women) diagnosed with MM and treated with ASCT between Mar 2014 and Mar 2018 at our Hematology Division (Pisa, Italy). All pts received induction therapy with at least 4 cycles of bortezomib, thalidomide and dexamethasone (VTD). 9/62 pts obtained a less than partial response (PR) and received lenalidomide-based regimens. After induction, 8 (12,9%) pts achieved complete remission (CR), 26 (41,9%) were in PR, 28 (45,2%) obtained a very good partial response (VGPR). 43/62 fit pts received HD-CTX (2-3 g/sqm) on day 1 followed by G-CSF (30 MU/day) started on day 4 until day 7, increased to 60 MU/day from day 8 until the end of apheresis. In 19/62 pts, after 4 days of G-CSF (60 MU/day) administration and not sufficient mobilization, we added plerixafor (0,24 mg/kgbw) for up to 4 consecutive days. In 43/62 pts we collected apheresis samples (10μl) analyzed through flow citometry to enumerate clonal residual PCs. The panel used to asses clonality included: CD138 Per-Cp, CD38 APC, CD19 PE-Cy7, CD45 APC-Cy7, cytoplasmic immunoglobulin K chain and L chain. RESULTS At the end of the peripheral blood stem cell (PBSC) collection, pts treated with HD-CTX presented a higher CD34+ absolute count (p=0.0489) and achieved the threshold of 5x106 CD34+ cells/kgbw in a significantly (p=0.006) higher percentage. We found a nearly significant (p=0.0517) lower count of CD34+ PBSCs in pts who received lenalidomide-based regimens before the mobilization. Performing flow citometry on apheresis samples, we observed that the number of the harvested clonal PCs showed a significant correlation (p=0.0115) with the occurrence of post-ASCT relapse. ROC curve analysis investigating the predictive effect of the number of pathological PCs on disease relapse showed an area under the curve of 0,6978 (95% CI 0.5392-0.8564; p=0.0267). Neither BM residual PCs detectable on BM biopsies performed before apheresis (r=-0.1323; p=0.609) nor the type of mobilization scheme (p=0.707) had an impact on the proportion of clonal PCs in the graft. Additionally, we did not observe any statistically significant difference in progression free- (PFS) (p=0.8276) and overall survival (OS) (p=0.2475) between the HD-CTX and G-CSF+P groups. DISCUSSION PBSC mobilization has a succession rate 〉 85%. Despite the use of HD-CTX to increase PBSC yields and decrease tumor burden, there is not clear evidence of a superior mobilization strategy. Additionally, HD-CTX has a not negligible toxicity and approximately 10% of the pts require hospitalization. Conversely, G-CSF+P is a safe and effective approach also in poor mobilizers. In our study, we observed a significative difference in the apheresis yields (p=0.0489) and in the percentage of pts who achieved the threshold of 5x106 CD34+ cells/kgbw (p=0.006) in favor of HD-CTX. Additionally, the detection of harvested residual clonal PCs could be a promising strategy to recognise pts more likely to relapse after ASCT. Nonetheless, we failed to demonstrate a superior effect of HD-CTX in the clearance of harvested clonal PCs, in agreement with the absence of a different pts' outcome amongst the two mobilization strategies. In conclusion, the choice between the two regimens is challenging and requires careful consideration of multiple factors. Overall, young fit pts, especially in the high-risk setting, should be treated with all appropriate modalities including chemiomobilization followed by double-ASCT. Conversely, in pts candidate to a single-ASCT it is reasonable to use G-CSF+P, since HD-CTX does not improve PFS and OS and add toxicity. The absence of an in-vivo purging effect on apheresis products of chemiomobilization further strengthens a chemotherapy-free mobilization. Disclosures Galimberti: Roche: Speakers Bureau; Celgene: Speakers Bureau; Novartis: Speakers Bureau.

Description: A mini review of the toxicity of Thallium (Tl) at low doses is herein presented. Thallium has severe toxicity. Although its acute biological effects have been widely investigated and are well known, its biological effects on human health and in cell cultures at low doses (