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Abstract: Treatment resistance of leukemia stem cells (LSCs) and suppression of the autologous immune system represent major challenges to achieve a cure in acute myeloid leukemia (AML). Although AML blasts generally retain high levels of surface CD38 (CD38pos), LSCs are frequently enriched in the CD34posCD38neg blast fraction. Here, we report that interferon gamma (IFN-γ) reduces LSCs clonogenic activity and induces CD38 upregulation in both CD38pos and CD38neg LSC-enriched blasts. IFN-γ-induced CD38 upregulation depends on interferon regulatory factor 1 transcriptional activation of the CD38 promoter. To leverage this observation, we created a novel compact, single-chain CD38-CD3 T-cell engager (BN-CD38) designed to promote an effective immunological synapse between CD38pos AML cells and both CD8pos and CD4pos T cells. We demonstrate that BN-CD38 engages autologous CD4pos and CD8pos T cells and CD38pos AML blasts, leading to T-cell activation and expansion and to the elimination of leukemia cells in an autologous setting. Importantly, BN-CD38 engagement induces the release of high levels of IFN-γ, driving the expression of CD38 on CD34posCD38neg LSC-enriched blasts and their subsequent elimination. Critically, although BN-CD38 showed significant in vivo efficacy across multiple disseminated AML cell lines and patient-derived xenograft models, it did not affect normal hematopoietic stem cell clonogenicity and the development of multilineage human immune cells in CD34pos humanized mice. Taken together, this study provides important insights to target and eliminate AML LSCs., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)

Background: Vaccines for SARS-CoV-2 have been considerably effective in reducing rates of infection and severe COVID-19. However, many patients, especially those who are immunocompromised due to cancer or other factors, as well as individuals who are unable to receive vaccines or are in resource-poor countries, will continue to be at risk for COVID-19. We describe clinical, therapeutic, and immunologic correlatives in two patients with cancer and severe COVID-19 who were treated with leflunomide after failing to respond to standard-of-care comprising remdesivir and dexamethasone. Both patients had breast cancer and were on therapy for the malignancy., Methods: The protocol is designed with the primary objective to assess the safety and tolerability of leflunomide in treating severe COVID-19 in patients with cancer. Leflunomide dosing consisted of a loading dose of 100 mg daily for the first three days, followed by daily dosing, at the assigned dose level (Dose Level 1: 40 mg, Dose Level -1, 20 mg; Dose Level 2, 60 mg), for an additional 11 days. At defined intervals, serial monitoring of blood samples for toxicity, pharmacokinetics, and immunologic correlative studies were performed, as well as nasopharyngeal swabs for PCR analysis of SARS-CoV-2., Results: Preclinically, leflunomide impaired viral RNA replication, and clinically, it led to a rapid improvement in the two patients discussed herein. Both patients completely recovered, with minimal toxicities; all adverse events experienced were considered unrelated to leflunomide. Single-cell mass-cytometry analysis showed that leflunomide increased levels of CD8+ cytotoxic and terminal effector T cells and decreased naïve and memory B cells., Conclusions: With ongoing COVID-19 transmission and occurrence of breakthrough infections in vaccinated individuals, including patients with cancer, therapeutic agents that target both the virus and host inflammatory response would be helpful despite the availability of currently approved anti-viral agents. Furthermore, from an access to care perspective, especially in resource-limited areas, an inexpensive, readily available, effective drug with existing safety data in humans is relevant in the real-world setting., Competing Interests: Conflict of Interest The authors declare that they have no competing interests that are relevant to this study.