Circulating pneumococcal specific plasma and memory B cells in the elderly two years after pneumococcal conjugate versus polysaccharide vaccination

BackgroundPolysaccharide conjugate vaccines prime for lasting memory responses in children and young adults. The potential value of these vaccines in the elderly is unclear.MethodsWe compared the frequency of circulating pneumococcal capsular polysaccharide (PPS) specific IgG, IgA and IgM plasma and memory cells by cultured ELISpot and supernatant screening two years after vaccination with the 7-valent pneumococcal conjugate vaccine (7vCRM) and/or the 23-valent pneumococcal polysaccharide vaccine (PPV) in 252 adults aged 50–80 years. Some individuals received a six-month boost with 7vCRM or PPV. PPS specific IgG memory detected two years post-primary vaccination was correlated with published matched serum IgG concentration pre- and up to one year post-primary vaccination.ResultsThere was no difference by vaccine schedule in the quantity of plasma or memory cells detected. The concentration of in vitro PPS IgG produced by memory B cells isolated two years post-vaccination correlated with pre-vaccination serum IgG concentration and not with D28 post-vaccination responses regardless of vaccination schedule.ConclusionsThis study shows that circulating memory B cells numbers two years following immunisation with 7vCRM or PPV are best predicted by pre-vaccination serotype specific serum antibody concentration and not early post-vaccination serum antibody responses.