In vivo CRISPR/Cas9 editing of the TTR gene with NTLA-2001 in patients with transthyretin amyloidosis- dose selection considerations

Background and aims: Waning SARS-CoV-2 specific antibody (Ab) responses and high infection rates has led to the widespread use of 3rd/4th vaccine doses (V3/V4) in vulnerable patients.However, the immune response to V4 in patients with suboptimal prior vaccine responses is unexplored.We recruited liver transplant recipients (LT) and autoimmune hepatitis patients (AIH) to assess the immune responses to V4, including to SARS-CoV-2 omicron (B.1.1.529)variant.Method: Anti-spike (S) and anti-nucleocapsid (N) IgG titres were assessed (Roche assay) after V4 (24 Pfizer BNT162b2, 8 Moderna mRNA-1273) in 32 immunosuppressed patients, including 23 with liver disease (15 LT, 8 AIH) and 9 inflammatory bowel disease (IBD) patients.All patients had absent (13/32 (41%); 11 LT, 2 AIH) or low Ab responses (19/32 (59%); 4 LT, 6 AIH, 9 IBD) after 2 vaccines (V2) defined as anti-S IgG level <400 AU/ml.Anti-S and anti-N IgG titres performed after V2/V3.WT and omicron specific T cell responses were assessed by IFN-γ ELISpot assay in 30/32 patients using peptide pools covering whole-S and minipools of S-specific mutated peptides.Results: There were significant increases in anti-S IgG titres following V3 in all groups, stratified by those with absent and low anti-S Abs post V2 (Fig. 1A).All patients with a low post V2 response had a significant increase in anti-S Ab responses after V3 that was sustained (but not further enhanced) after V4.In liver patients with no anti-S Ab responses after V2, 7/13 (54%) developed anti-S Abs after V3 (0.41 AU/ml vs. 126.72AU/ml; p = 0.016), and importantly these responses were further significantly enhanced following V4 (126.72 AU/ml vs. 3212.90AU/ml; p = 0.002).However, 3/13 (23%) with absent anti-S Abs after V2 remained nonresponsive after V3 and V4.T cell responses to full-S WT and omicron peptides were heterogenous, but generally of high magnitude and detectable in 29/30 patients (Fig. 1B).There was a loss against Omicron (51.8%) when T cell responses were assessed using the variant mini pools (Fig. 1B).LT had significantly reduced response compared to IBD against omicron (mean 796.3 SFC/10 6 vs. 1589 SFC/10 6 ; p = 0.0294) and WT (mean 897.6 SFC/10 6 vs. 1817 SFC/10 6 ; p = 0.0274) (Fig. 1B).Importantly, the 3 seronegative patients after V4, mounted a robust T cell response to WT (mean 882.5 SFC/10 6 ) and omicron (mean 2280 SFC/10 6 ).There was no correlation between humoral and cellular responses (R 2 = 0.01). Conclusion:In liver and IBD patients, low anti-S Ab responses after 2 COVID19 vaccines may be enhanced by V3 and sustained by V4.Patients with absent anti-S Ab responses after 2 doses may have a significant increase in anti-S Ab titres after both V3 and V4.However, a small subset remain non-responsive and should be prioritised for prophylactic strategies.Importantly, immunosuppressed liver patients develop robust T cell responses to WT and omicron independent of anti-S Ab titres.