POOR RESPONSE TO FIRST BNT162B2 SARS-COV-2 VACCINE DOSE IN RECIPIENTS OF ALLOGENEIC HEMATOPOIETIC STEM CELL TRANSPLANT.

On March 2021, the Italian National COVID-19 vaccination campaign was extended to patients with high risk chronic medical conditions, including recipients of allogeneic stem cell transplant (allo-SCT). In the present study, we prospectively assessed serological response following the first BNT162b2 SARS-CoV-2 vaccine dose in recipients of allo-SCT in our centre. Inclusion criteria for the participation in this study included: (1) age above 18 years; (2) allo-SCT for any hematological disease; (3) eligibility for vaccination. Patient serum was collected on day 1 (D1; before the first BNT162b2 dose), and on day 21 (D21; before the second dose of the vaccine). IgG antibodies to the receptor binding domain (RBD) of the S1 subunit of the spike protein of SARS-CoV-2 were analyzed by CMIA assay. The study population included 34 recipients of allo-SCT (22 males/12 females; median age: 59 years, range 28-70 years). Patients characteristics are depicted in Table 1. Thirty-one patients were evaluable for serological assessments on D1 and D21. On D1, only 1 patient with known previous exposure to SARS-CoV-2 had detectable anti-S and anti-N IgG antibodies. After the first dose of vaccine, on D21, 4/31 (13%) patients had detectable anti-S IgG antibodies above the cut-off of 7,1 BAU, excluding the patient who had experienced natural infection. Median anti-S IgG titer of responders was 121,6 BAU (range 32,8-481). Interestingly, all these four patients were receiving tyrosine kinase (TKI) inhibitors for an ongoing cGVHD (Ruxolitinib, 2 pts; Imatinib, 2 pts) at the time of vaccination. Median time from transplant to vaccination was 51 months (range 32-74) in responders, as compared to 10 months (range 4-142) in non responders. In fact, no patients who had undergone allo-SCT from less than 2 years showed an antibody response. Our preliminary data suggest that the first dose of BNT162b2 vaccine leads to production of SARS-CoV-2 IgG antibodies in a minority of recipients of allogeneic stem cell transplant. Further, patients who received vaccination later after transplant seem more likely to show antibody production