en Host-pathogen interactions and susceptibility factors Host-pathogen interactions and susceptibility factors Case Report Case Report Hematopoietic stem cell transplantation (HSCT) severely undermines the recipients' immune status and makes them prone to complications following viral infection. Here, we report a 3-year-old boy with mucopolysaccharidosis type VI who acquired SARS-CoV-2 infection after HSCT. The boy was diagnosed with SARS-CoV-2 during the post-transplant period (19 days after HSCT) when dealing with acute graft versus host disease (GVHD). He was successfully treated with remdesivir and tocilizumab and recovered. Well-timed treatment with tocilizumab might reduce the risk of invasive mechanical ventilation and death in patients with severe COVID-19 pneumonia in the early post HSCT period. Post Hematopoietic Stem Cell Transplantation, COVID-19, Mucopolysaccharidosis 225 229 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-361-1&slc_lang=en&sid=1 Tahereh Rostami trostami@sina.tums.ac.ir 0000-0003-3426-1332 No Department of Pediatric Cell Therapy, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Neda Alijani n-alijani@sina.tums.ac.ir 0000-0002-7506-811X No Department of Infectious Diseases, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Azadeh Kiumarsi akiumarsi@sina.tums.ac.ir 0000-0001-5492-8830 Yes Department of Pediatric Cell Therapy, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Soroush Rad 0000-0002-4230-3822 No Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Seied Amirhosein Mirhoseini amir.mir85@gmail.com No Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Mohammadreza Rostami mr.rostami2@gmail.com 0000-0002-6683-4783 No Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Amir Hesabi 0000-0003-1789-1500 No Department of Pediatric Cell Therapy, Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Seyed Ali Mousavi dr.seyyedalimousavi@yahoo.com No Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran Seied Asadollah Mousavi amir.hesabii@yahoo.com 0000-0001-7360-0064 No Research Institute for Oncology, Hematology and Cell Therapy, Tehran University of Medical Sciences, Tehran, Iran