The Role of Serotype-Specific Immunological Memory in Pneumococcal Vaccination: Current Knowledge and Future Prospects

Abstract

Streptococcus pneumoniae (S. pneumoniae, pneumococcus) is a major cause of morbidity and mortality worldwide. Achieving long-term immunity against S. pneumoniae through immunization is an important public health priority. Long-term protection after immunization is thought to rely both on protective serum antibody levels and immunological memory in the form of antigen-specific memory B cells (MBCs). Although the ability to achieve protective antibody levels shortly after pneumococcal vaccination has been well documented for the various infant immunization schedules currently in use worldwide, the examination of immunological memory in the form of antigen-specific MBCs has been much more limited. Such responses are critical for long-term protection against pneumococcal colonization and disease. This review summarizes the published literature on the MBC response to primary or booster immunization with either pneumococcal polysaccharide vaccine (PPV23) or pneumococcal conjugate vaccines (PCVs), aiming to elucidate the immunological mechanisms that determine the magnitude and longevity of vaccine protection against pneumococcus. There is evidence that PCVs induce the production of antigen-specific MBCs, whereas immunization with PPV23 does not result in the formation of MBCs. Increased understanding of the immunological factors that facilitate the induction, maintenance and recall of MBCs in response to pneumococcal vaccination could enable the use of MBC enumeration as novel correlates of protection against S. pneumoniae. Ongoing studies that examine MBC response to pneumococcal vaccination in high burden settings will be extremely important in our understanding of long-term protection induced by pneumococcal conjugate vaccines.

Pneumococcal Vaccines: Challenges and Prospects

“…However, the duration of protection induced by these current vaccination schedules remains unclear. A review article by Papadatou et al summarizes the literature on antigen-specific memory B cells (MBCs) induced by pneumococcal vaccination, and highlights the potential use of this novel marker to monitor the duration of vaccine protection [2]. Circulating antibody titers following vaccination are the only currently accepted in vitro correlate of vaccine protection against IPD but other measures are needed for pneumococcal carriage endpoints.…”

Factors influencing PCV13 specific antibody response in Danish children starting in day care

“…A study by Kimaro Mlacha et al found that individuals respond with different dynamics following stimulation with pneumococcal polysaccharide antigens, and children aged 24-36 months with a history of IPD responded quicker than the healthy controls 22 . This may be due to a memory response elicited by the serotype that caused IPD 23 or because the children may have been carrying pneumococcal serotypes beforehand. A study by Ingels et al also showed the importance of evaluating pneumococcal antibody response on an individual level in children at higher risk of IPD 24 .…”

Progress in mucosal immunization for protection against pneumococcal pneumonia

“…As a T-cell independent antigen, polysaccharides can induce serotype-specific antibody, but no immunological memory [7]. Therefore, pneumococcal polysaccharides from prevalent serotypes were chemically conjugated to carrier proteins in order to be protective in children under 2-years-old [7,8]. Today, the World Health Organization (WHO) recommends the inclusion of PCVs in immunisation programmes worldwide for children under 5-years-old [9].…”

“…Today, the World Health Organization (WHO) recommends the inclusion of PCVs in immunisation programmes worldwide for children under 5-years-old [9]. PPV23 is recommended for at risk population >2 years and adults >65 years of age and PCV13 has been adopted in some developed countries for immunisation of adults > 50 years old [8].…”