Fatal Severe Cytokine Release Syndrome Post-haploidentical Stem Cell Transplant With Post-transplant Cyclophosphamide in an Infant With Severe Combined Immunodeficiency and Disseminated Bacille Calmette-Guérin Infection

Introduction: Severe Combined Immunodeficiency (SCID) is a primary immunodeficiency disorder characterized by absent or dysfunctional T lymphocytes, leading to defective cellular and humoral immunity requiring urgent hematopoietic stem cell transplantation (HSCT). We report a case of SCID with disseminated Bacille Calmette-Guérin (BCG) infection who developed cytokine release syndrome (CRS) and possible Immune reconstitution inflammatory syndrome (IRIS) after Haploidentical HSCT with post-transplant cyclophosphamide. Methods: Data were retrospectively retrieved from electronic medical records. Result: A 5-month-old male infant was referred with fever, cough, and generalized maculopapular rash for 15 days, and had pallor without hepatosplenomegaly or lymphadenopathy. He had a history of previous male sibling death at 6 months of age due to pneumonia. Investigations: hemoglobin: 4.7 g/dL, TLC-6.37×10 3 /uL, absolute lymphocytes: 0.98×10 3 /uL, platelets: 319×10 3 /uL, bilateral patchy opacities in both lung fields, and low immunoglobulin levels. Lymphocyte subset analysis revealed T−, B+, NK− SCID. Genetic analysis showed a hemizygous mutation in IL2RG (c.314A>G). The child received intravenous (IV) antibiotics, antifungal, antitubercular drugs, irradiated blood products, and IV immunoglobulins. Urgent haploidentical HSCT from the mother was planned. Conditioning was Fludarabine-40 mg/m 2 /d for 4 days, cyclophosphamide: 14.5 mg/kg/d for 2 days. He received peripheral blood hematopoietic stem cells with CD34 − 15×10 6 cells/kg and CD3 − 805×10 6 cells/kg. Within 2 hours of stem cell infusion, he developed respiratory distress, fever, shock, and flaring of rash. Methylprednisolone was started in view of CRS. On day+2, he had sudden desaturation and bradycardia needing mechanical ventilation and inotropes. His inflammatory markers were elevated (Ferritin: 3640 ng/mL, IL-6:5000 pg/mL, CRP:255 mg/L). In view of high-grade CRS, he received an injection of tocilizumab 8 mg/kg on day +2 and day +4. He received post-transplant cyclophosphamide 5 mg/kg on day +3. The endotracheal secretion GeneXpert was positive for Mycobacterium supporting the diagnosis of disseminated tuberculosis. Our patient had disseminated BCG infection which could also be contributory in the initiation of IRIS as the mother was immunized with the BCG vaccine in childhood so she must be having cytotoxic T cells specific for BCG, which were transferred to the infant with peripheral blood stem cell product. He succumbed to severe acute respiratory distress syndrome and multiorgan dysfunction on day +5 post-transplant. Conclusions: In haploidentical HSCT of SCID, post-transplant course can be complicated by CRS and IRIS as these patients are inefficient in mounting any response to infused donor lymphocytes resulting in their unregulated growth.