Hematopoietic stem cell transplantation is a highly specialized and unique medical procedure. Autologous transplantation allows the administration of high-dose chemotherapy without prolonged bone marrow aplasia. In allogeneic transplantation, donor-derived stem cells provide alloimmunity that enables a graft-versus-tumor effect to eradicate residual disease and prevent relapse. The first allogeneic transplantation was performed by E. Donnall Thomas in 1957. Since then the field has evolved and expanded worldwide. New indications beside acute leukemia and aplastic anemia have been constantly explored and now include congenital disorders of the hematopoietic system, metabolic disorders, and autoimmune disease. The use of matched unrelated donors, umbilical cord blood units, and partially matched related donors has dramatically extended the availability of allogeneic transplantation. Transplant-related mortality has decreased due to improved supportive care, including better strategies to prevent severe infections and with the incorporation of reduced-intensity conditioning protocols that lowered the toxicity and allowed for transplantation in older patients. However, disease relapse and graft-versus-host disease remain the two major causes of mortality with unsatisfactory progress. Intense research aiming to improve adoptive immunotherapy and increase graft-versus-leukemia response while decreasing graft-versus-host response might bring the next breakthrough in allogeneic transplantation. Strategies of graft manipulation, tumor-associated antigen vaccinations, monoclonal antibodies, and adoptive cellular immunotherapy have already proved clinically efficient. In the following years, allogeneic transplantation is likely to become more complex, more individualized, and more efficient.

Outcomes of allogeneic hematopoietic stem cell transplantation (allo- HSCT) have improved in the recent decade; however, infections and graft-versus-host disease remain two leading complications significantly contributing to early transplant-related mortality. In past years, the human intestinal microbial composition (microbiota) has been found to be associated with various disease states, including cancer, response to cancer immunotherapy and to modulate the gut innate and adaptive immune response. In the setting of allo-HSCT, the intestinal microbiota diversity and composition appear to have an impact on infection risk, mortality and overall survival. Microbial metabolites have been shown to contribute to the health and integrity of intestinal epithelial cells during inflammation, thus mitigating graft-versus-host disease in animal models. While the cause-andeffect relationship between the intestinal microbiota and transplant-associated complications has not yet been fully elucidated, the above findings have already resulted in the implementation of various interventions aiming to restore the intestinal microbiota diversity and composition. Among others, these interventions include the administration of fecal microbiota transplantation. The present review, based on published data, is intended to define the role of the latter approach in the setting of allo-HSCT.

This national Israeli multicenter retrospective study aimed to characterize the clinical course of COVID-19 infection among patients with hematological malignancies, with special emphasis on treatment efficacy and outcome. Clinical and laboratory data from haemato-oncological patients diagnosed with COVID-19 from 16 medical centers were centrally reported. Multivariate regression analyses were used to determine variables associated with severe disease, hospitalization, and mortality. In total, 313 patients were included: 103 (35.7%) developed severe/critical respiratory infection, 178 (61.4%) were hospitalized, and 60 (20.0%) died. Age > 70 years was associated with severe/critical disease (p = 0.036) and mortality (p = 0.023), hypertension with severe/critical disease (p = 0.046) and hospitalization (p = 0.001), active haemato-oncological treatment with hospitalization (p = 0.009), and remdesivir treatment was associated with decreased mortality (p = 0.021). Convalescent plasma, enoxaparin, and corticosteroids resulted in no clinical benefit. In conclusion, COVID-19 infection seems particularly severe in patients with hematological malignancies, and of all examined therapies, remdesivir appears to be the most effective.