Deficient antipneumococcal polysaccharide responses in HIV-seropositive patients

In a prospective study, serological responses and opsonic activity towards Streptococcus pneumoniae were measured in 60 HIV-infected patients and 25 controls after the administration of the 23-valent pneumococcal vaccine (PneumovaxR). Serum samples were collected before vaccination and at weeks 1, 2, 4, and 12 after vaccination and were tested for the presence of antibodies against a mixture of capsular polysaccharide antigens (pool) and against type 3 and type 4 antigens (PS3 and PS4), using an ELISA. A serological response was defined as a two-fold or greater increase in serum titer after vaccination. Opsonophagocytosis was measured in patients with a definite response against PS3. Generally, prevaccination antipneumococcal antibody titers were clearly higher in HIV-infected patients than in healthy controls. After vaccination, antipool antibody responses were found in 76% of vaccinated patients; 24% of the patients were non-responders. In patients with more than 0.300 x 10(9) CD4 + cells per liter the percentage of responders was 94%; in patients with fewer than 0.300 x 10(9) CD4 + cells per liter this percentage was 68% (P < 0.05). The antipool response in control subjects was 92%. A serological response to PS3 and PS4 was found in 29% and 49% of the patients, respectively, and was correlated with CD4 + cell count. In controls, these percentages were 48% and 92%, respectively. In 30% of responding patients, antibody titers dropped already to prevaccination levels by week 12 after vaccination. Opsonophagocytosis was not significantly improved by vaccination, probably because of a relatively high preexisting opsonic activity. Although prevaccination conditions may have had an important influence on the study outcome, the results are not in favor of a significant beneficial effect of vaccination with PneumovaxR on antibody formation in HIV-infected patients. This raises further questions as to the relevance of pneumococcal vaccination in this population.