Robust COVID-19 vaccination response after allogeneic stem cell transplantation using post transplantation cyclophosphamide conditioning

Dear Editor,

Since the rise of the COVID-19 pandemic, clinicians aim to understand the implications of this new infectious disease, enabling them to make evidence based clinical decisions for their specific patient populations. Despite increasing knowledge on the antibody response of SARS-CoV-2 vaccinations in hematological patients and more specifically in patients treated by means of an allogeneic stem cell transplantation, limited data are available on the impact of treatment with cyclophosphamide post transplantation (PTCy). Cyclophosphamide exerts its effect through specific deletion of proliferating alloreactive T-cells on day +3 and +4 after stem cell infusion, leaving the T-cell compartment responsible for immune reconstitution and resistance to infection, largely unaffected [1]. We hypothesize that this might preserve the ability to mount a robust antibody response against SARS-CoV-2, even in case of vaccination early after allogeneic stem cell transplantation.