The slower antibody response in myelofibrosis patients after two doses of mRNA SARS-CoV-2 vaccine calls for a third dose

Immunization with mRNA SARS-CoV-2 vaccines has been highly recommended and prioritized in fragile categories with higher risk of mortality after COVID-19 disease compared to healthy people, including patients with myelofibrosis (MF). Available data on the vaccine immune response developed by MF patients, and the impact of the treatment with the inhibitor of JAK-STAT signaling ruxolitimib, are still fragmented to support an informed decision for a third dose for this category of subjects. Here, we show that 76% of MF patients develop spike-specific IgG after the second vaccine dose, but the response has a slower kinetic compared to healthy subjects, suggesting a reduced capability of their immune system to promptly react to vaccination. A reduced ACE2/RBD inhibition binding activity of spike-specific antibodies was also observed, especially in ruxolitimib treated patients. Our results contribute to answer the open question on the induction of the antibody responses in MF patients following vaccination with COVID-19 mRNA vaccines, showing a slow kinetic that support the need for a third dose of SARS-CoV-2 mRNA vaccines.

Evidence of SARS-Cov-2-specific memory B cells six months after vaccination with BNT162b2 mRNA vaccine

SARS-CoV-2 mRNA vaccines have demonstrated high efficacy and immunogenicity, but limited information is currently available on memory B cells generation and long-term persistence. Here, we investigated Spike-specific memory B cells and humoral responses in 145 subjects, up to six months after the BNT162b2 vaccine (Comirnaty) administration. Spike-specific antibody titers peaked 7 days after the second dose and significant titers and neutralizing activity were still observed after six months, despite a progressive decline over time. Concomitant to antibody reduction, Spike-specific memory B cells, mostly IgG class-switched, increased in blood of vaccinees and persisted six months after vaccination. Following in vitro restimulation, circulating memory B cells reactivated and produced Spike-specific antibodies. A high frequency of Spike-specific IgG+ plasmablasts, identified by computational analysis 7 days after boost, positively correlated with the generation of IgG+ memory B cells at six months. These data demonstrate that mRNA BNT162b2 vaccine elicits strong B cell immunity with Spike-specific memory B cells that still persist six months after vaccination, playing a crucial role for rapid response to SARS-CoV-2 virus encounter. One Sentence SummarymRNA BNT162b2 vaccine elicits persistent spike-specific memory B cells crucial for rapid response to SARS-CoV-2 virus encounter