Chronic graft vs. host disease and hypogammaglobulinemia predict a lower immunological response to the BNT162b2 mRNA COVID-19 vaccine after allogeneic hematopoietic stem cell transplantation.

Objective: Due to the high mortality rate of COVID-19, the assessment of BNT162b2 SARS-CoV-2 mRNA vaccine (Pfizer-BioNTech) efficacy in allogeneic hematopoietic stem cell transplant (HSCT) recipients is mandatory.
Patients and Methods: We conducted a single-center pilot study with the main objective of evaluating the immunogenicity of the BNT162b2 mRNA vaccine in 31 hematological patients who underwent hematopoietic stem cell transplantation within the previous 12 months and/or were affected by chronic graft-vs.-host-disease (cGVHD), by the assessment of antibody levels at 30-45 days after the second dose of vaccine.
Results: After the second dose of vaccine, 23 out of 31 patients (74%) showed a positive immune response. The presence of severe cGVHD or Ig deficiency identified 7 out of 8 (85%) of non-responders. The median absolute cluster of differentiation 19 (CD19) count was significantly lower in non-responders vs. responders (109/µl vs. 351/µl). Underlying pathology, comorbidities, type of donor, time intervals from transplant and cluster of differentiation 3/cluster of differentiation 4/cluster of differentiation 8 (CD3/CD4/CD8) subsets were not significantly associated with an effective immune response to vaccination.
Conclusions: Despite the limited sample of patients enrolled, our findings suggest that hypogammaglobulinemia and cGVHD could be associated with poor humoral response to the BNT162b2.