CD4 and B-cell chronic lymphocytic leukemia: Interactions between CD4+ T and B cells are critical for germinal center reactions.40, 41 Because these lymphocyte subsets decline as a function of both age and CLL disease,2, 42, 43 we compared T cell frequencies in age-matched healthy controls (n=7) as well as treatment-naïve SARS-CoV-2 vaccinees who did (S+NAb+, n=11) versus did not (S+NAb−, n=9) mount a neutralizing antibody response.