Antibody Response to Sars-Cov-2 Vaccination in Patients Following Allogeneic Hematopoietic Cell Transplantation

Background: Vaccines against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have been approved rapidly. However, pivotal studies have been conducted in healthy volunteers, while recipients of allogeneic hematopoietic cell transplantations (allo-HCT) may have different dynamics and patterns of response to the vaccine and data in this cohort is lacking. Methods: Here, we examined longitudinal antibody (AB) titers to SARS-CoV-2 vaccination with BNT162b (Comirnaty ®) or mRNA-1273 (Moderna Covid-19 Vaccine ®) in allo-HCT recipients who had undergone allo-HCT >3months (m) ago and in healthy controls (hospital employers). Serial AB titers (prior to (T0); 1m after 1 (st) dose (T1); 1m (T2), 3m (T3), 6m (T4) post 2 (nd) dose) were measured with an in-house developed multiplex Antibody CORonavirus Assay (ABCORA) that measures SARS-CoV-2 IgG, IgA, and IgM reactivities against RBD (receptor binding domain), S1 (subunit 1 of the spike protein), S2 (subunit 2 of the spike protein) and N (nucleoprotein), thereby allowing to differentiate immunity after vaccination versus immunity after infection. As neutralization activity correlates well with S1 AB binding, the potency of the AB response was defined as the sum of S1 IgG, IgA and IgM reactivities (cumulative S1 (cS1)). Based on computational methods high neutralization potency was predicted above a cS1 threshold of 17. Results: We enrolled 114 allo-HCT patients (median age 57y (range 18y-74y)) between March 9th 2021 and May 31st 2021 at the University Hospital Zurich, Switzerland. Currently, AB responses at T1, T2, and T3 are available for 99, 95 and 89 patients, respectively. Patients were grouped into those (A) 3-6m post-HCT (T1: n=25 at, T2: n=23, T3: n=20); (B) 6-12m post-HCT (T1: n=13, T2: n=13, T3: n=12); and (C) >12m post-HCT (T1: n=61, T2: n=59, T3: n=57). In addition, AB responses are available for healthy controls (median age 35y (range 23y-64y)) (T1: n=75, T2: n=69, T3: n=48). There were 10 patients and 5 healthy subjects with a reported or detected SARS-CoV-2 infection. There was a statistically significant difference of cS1 AB levels between the 4 groups at T1, T2, and T3 (ANOVA p-values (p) <0.001, respectively, Fig 1) with the lowest AB response in group A (cS1 median value 0.957 at T1, 5.22 at T2, 1.90 at T3) and B (cS1 median value 0.973 at T1, 4.76 at T2, 11.9 at T3) compared to group C (cS1 median value 6.21 at T1, 199 at T2, 76.4 at T3) and healthy controls (cS1 median value 54.9 at T1, 228 at T2, 91.1 at T3). Using a multivariate linear regression analysis adjusted on age and gender, we found that patients in groups A and B had significantly lower cS1 levels than groups C and healthy subjects (p<0.001, p<0.001, p=0.034 of healthy versus groups A, B, C respectively at T2, and p<0.001, p=0.004, p=0.12 at T3), and that preinfected patients had higher cS1 levels at T2 and T3 respectively (p=0.003 and 0.006). The dynamics of the AB response were more diverse in allo-HCT recipients. In a multivariate linear regression analysis (Fig 2) assessing factors associated with humoral immune responses in allo-HCT recipients, we found consistently lower cS1 responses in patients early post-HCT (group A+B (p=0.002)) and higher cS1 levels in those who had been preinfected with SARS-CoV-2 (p=0.012). Patients under immunosuppressive treatment (IST) and those who had relapsed disease post-HCT showed significantly lower cS1 immune responses (p=0.028 and 0.005, respectively). The presence of moderate or severe chronic GVHD was not a statistically significant factor influencing AB levels. This may be explained by (i) the heterogeneity of the condition of chronic GVHD and low patient numbers; (ii) the late time point >12m post-HCT with generally higher AB levels. Consistent with other reports age >65y was also associated with lower cS1 responses (p=0.03). Conclusion: Allo-HCT recipients early post-transplant, those of older age, and those given IST displayed insufficient AB titers to the vaccine. Such knowledge is of critical importance to transplant recipients and their physicians to guide treatment decisions regarding re-vaccination, and social behavior during this pandemic. Monitoring AB development in all allo-HCT recipients and vulnerable patients with other immunocompromising conditions may be crucial to determine those at increased risk for infection and for the timing of booster vaccines. [Figure: see text] DISCLOSURES: Manz: CDR-Life Inc: Consultancy, Current holder of stock options in a privately-held company; University of Zurich: Patents & Royalties: CD117xCD3 TEA.