This is a literature report for the following literature source(s): "COVID-IRIS: Immune reconstitution after G-CSF administration for neutropenia during acute COVID-19 infection", Cancer Research, 2022; Vol:82. Abstract: Background: Immune reconstitution inflammatory syndrome (IRIS) is a rapid inflammatory response with immune recovery, most commonly observed following antiretroviral therapy initiation in people with HIV and underlying opportunistic infections. To date there is one reported case of COVID-associated IRIS in a neutropenic patient treated with granulocyte colony-stimulating factor (G-CSF). Here authors describe a second case of COVID-associated IRIS in a patient with history of follicular lymphoma who received G-CSF during acute COVID-19 infection. Case: A 64-year-old woman with history of follicular lymphoma and autologous stem cell transplant one year prior presented with dyspnea, diarrhea, and fever, and tested positive for SARS-CoV-2. She had received three doses of the Pfizer BioNTech vaccine. She was admitted to the hospital for acute hypoxic respiratory failure and treated with remdesivir 100mg, dexamethasone 6mg, and 2 L/min supplemental oxygen via nasal cannula for five days. Twelve days after discharge, the patient returned with persistent diarrhea, fatigue, fever, and an oxygen saturation of 87% on room air. She again tested positive for SARS-CoV-2 by PCR. She was admitted to the intensive care unit for high-flow nasal cannula (HFNC) with oxygen at 30 L/min and 50% FiO2 and treated with methylprednisolone 1 mg/kg daily. On admission, her D-dimer was 3943 ng/mL, C-reactive protein 136 mg/L, absolute neutrophil count (ANC) 767/mcL, platelets 84/mcL. Her chest CT scan was negative for pulmonary embolism but demonstrated bilateral ground glass opacities characteristic of COVID-19 pneumonia. Her ANC reached a nadir of 186 on day 3 at which point G-CSF (Filgrastim 300 mcg/day) was administered for three days with subsequent neutrophil recovery. On day 6, in light of a negative test for COVID antibodies, she received high-dose monoclonal antibodies through a compassionate use program. At that time, her oxygen requirements were stable and inflammatory markers had decreased to CRP 25 and D-Dimer 940. However, her oxygen requirements and inflammatory markers rapidly increased thereafter, with HFNC settings up to 60L/80%, D-dimer 27754, and CRP 135. After a repeat chest CT on day 8 showed worsened ground glass opacities throughout all lung fields, her steroid dose was increased to methylprednisolone 2 mg/kg daily out of concern for COVID-associated IRIS following G-CSF administration. Her oxygen requirement and inflammatory markers declined over the following 2-3 days and she was transferred out of the ICU. Discussion(s): Authors present here an unusual case of COVID-associated IRIS after G-CSF administration in a transplant patient with COVID-19 pneumonia. Given the increased risk of infection and severe illness in immunosuppressed patients despite vaccination, it is important for providers to be aware of complications associated with adjunct therapies such as G-CSF in this vulnerable population. No follow-up attempts are possible; information about lot/batch number cannot be obtained. No further information is expected. Sender's Comments: The efficacy of a drug varies from patient to patient and may be influenced by multiple factors, including the inherent disease condition, concurrent medical conditions, and concomitant medications; however, a contributory role of BNT162b2 to the reported drug ineffective and COVID-19 cannot be excluded. Case will be reassessed if additional information is received. Linked Report(s): US-PFIZER INC-202201065392 Same article/patient and different drug/event.