Patients treated with ABA displayed, after two doses of COVID-19 mRNA vaccine, an impaired CD4 and CD4/CD8 T cell response with a reduced release of IFN-γ, as well as IFN-γ-inducible chemokines, such as CXCL9 and CXCL10, in response to peptides of the spike protein. Here, CD4 is linked to COVID-19.