GMP-grade pneumococcal whole-cell vaccine injected subcutaneously protects mice from nasopharyngeal colonization and fatal aspiration-sepsis

Abstract

Mucosal immunization with a killed whole-cell pneumococcal vaccine, given with enterotoxinrelated adjuvants, has been shown to confer multi-serotype protection against colonization of the nasopharynx and middle ear in mice. However, because novel mucosal immunization strategies may be difficult to implement, here we evaluated subcutaneous injection. Strain RM200 was engineered to be capsule-negative, autolysin-negative, and to express a non-toxic mutant pneumolysoid. Liter-scale and 60-L Good Manufacturing Practice (GMP) cultures were grown in bovine-free soy-based medium, killed with chloroform or beta-propiolactone, and injected into C57Bl/6 mice without or with aluminum adjuvant. The adjuvant Al(OH) 3 strongly increased responses, particularly if pre-treated with phosphate. Protection was found in several tested model infections: nasal colonization with a serotype 6B strain and fatal aspiration-sepsis with strains of serotype 3 and 5. Protection against colonization was mechanistically dependent on the presence of CD4+ T cells at the time of challenge; in contrast, in the type 3 aspiration-sepsis model, CD4+ T cells were not required for protection at the time of challenge, suggesting that antibody alone was sufficient to protect against death in this model. Rabbits receiving sequential intramuscular injections in a pilot toxicity study displayed local reactogenicity at injection sites but no clinical signs. The rabbit antiserum thus produced was active in an in vitro phagocytic killing assay and passively protected mice in the type 3 aspiration-sepsis model. Approval is being sought for human trials of this vaccine.

Serotype-independent pneumococcal experimental vaccines that induce cellular as well as humoral immunity

“…These mice similarly displayed accelerated nasopharyngeal clearance, which correlated with their priming for IL-17A responses. Moreover, their plasma antibody responses were >30-fold higher than if nasally immunized, and they were also protected in our model of lethal aspiration pneumonia from type 3 or 5 pneumococci (67). In the lethal model, protection was related to IgG antibody response and was not abrogated by depletion of CD4+ T cells at the time of challenge (67).…”

“…Moreover, their plasma antibody responses were >30-fold higher than if nasally immunized, and they were also protected in our model of lethal aspiration pneumonia from type 3 or 5 pneumococci (67). In the lethal model, protection was related to IgG antibody response and was not abrogated by depletion of CD4+ T cells at the time of challenge (67). WCA antiserum raised by injection in rabbits was passively protective in the aspiration pneumonia model (i.e., immunity could be transferred to naive mice with serum).…”

“…For childhood vaccines in developing nation programs, however, the World Health Organization's "Target Product Profile" presently prefers vaccines to be given by injection. Therefore, WCA was also studied in mice by injection with adsorption to aluminum adjuvants, which are routinely and safely used in human vaccination (67). These mice similarly displayed accelerated nasopharyngeal clearance, which correlated with their priming for IL-17A responses.…”

“…WCA antiserum raised by injection in rabbits was passively protective in the aspiration pneumonia model (i.e., immunity could be transferred to naive mice with serum). Thus, parenteral immunization of mice with WCA revealed a bifunctional immunity: with a nonlethal intranasal challenge, clearance is CD4-dependent and IL-17A-mediated; in a lethal aspiration pneumonia model, survival is CD4-independent and dependent on plasma antibodies (67). Injection of WCA, therefore, might reduce the probability of invasion by accelerating clearance and may also protect systemically in case the mucosal barrier were breached.…”

Contribution of vaccines to our understanding of pneumococcal disease

“…The addition of proteins also increases the possibility that eradication of all pneumococcal carriage may expose a niche for enhanced colonization and disease caused by other pathogens such as staphylococci or Gram-negative bacteria-these concerns remain theoretical at this time. There is renewed interest in whether simple interventions such as whole cell-killed pneumococcal vaccines may play a role in the induction of pneumococcal immunity [64,65]. A re-analysis of the attempts using killed bacterial vaccines to prevent death and pneumonia following influenza during the 1918 pandemic supports the idea that these vaccines may have had some efficacy [60].…”