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13（ 13 ）〈Original Article〉

Pneumococcal IgG levels against 13-valentpneumococcal conjugate vaccine serotypes inJapanese children with a medical history ofhematopoietic neoplasms and solid tumors
Kenichi Takeshita1,2,*, Naruhiko Ishiwada3, Noriko Takeuchi3,
Yoshiko Takahashi1, Sachiko Naito1, Koo Nagasawa1,
Haruka Hishiki1, Tadashi Hoshino2 and Naoki Shimojo1
1

Department of Pediatrics, Graduate School of Medicine, Chiba University,
1–8–1 Inohana, Chuo-ku, Chiba-shi, Chiba 260–8670, Japan
2
Division of Infectious Diseases, Chiba Childrenʼs Hospital,
579–1 Heta-cho, Midori-ku, Chiba-shi, Chiba 266–0007, Japan3
Department of Infectious Diseases, Medical Mycology Research Center,
Chiba University, 1–8–1 Inohana, Chuo-ku, Chiba-shi, Chiba 260–8673, Japan(Received for publication December 12, 2017)Children aged 6–18 years with a medical history of hematopoietic neoplasm andother immunocompromising conditions are at high risk for invasive pneumococcal
disease (IPD). The Advisory Committee on Immunization Practices in the UnitedStates has therefore recommended that these children be immunized routinely with
13-valent pneumococcal conjugate vaccine (PCV13). Little is known, however,about the immunity of these children to pneumococci of PCV13 serotypes, except
for heptavalent pneumococcal conjugate vaccine (PCV7) serotypes. Serum samples
were therefore collected from Japanese children aged 5–18 years being followed up
for hematological neoplasms or solid tumors, and concentrations of speciﬁc
antibodies against Streptococcus pneumoniae PCV13 (non-PCV7) serotypes were
measured. None of these children had received PCV13. Against all six serotypes, theimmunoglobulin G (IgG) levels of the study patients were lower than those were ofage-matched healthy controls. Children who received chemotherapy within 6 months
prior to sample collection, had lower serotype-speciﬁc IgG levels than those who did
not. These findings indicate that many immunocompromised children notrecommended for routine vaccination owing to their age group did not have PCV13
serotype-speciﬁc IgG levels that could prevent IPD. These results suggest that thevaccination with PCV13 is necessary for children at high risk of IPD.
*Corresponding author, Tel.: ＋81 43 226 2144, Fax: ＋81 43 226 2145, E-mail: take1nek@yahoo.co.jp

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Introduction
Streptococcus pneumoniae is a Gram-positive diplococcus that causes respiratory tract infections such as pneumonia, acute otitis media, and sinusitis. S. pneumoniae can also cause fatal invasive infections, such as sepsis, bacteremia, and bacterial meningitis, regardless of treatment
with appropriate antibiotics. The heptavalent pneumococcal conjugate vaccine (PCV7), licensed
and approved for universal use in the United States in 2000, was ﬁrst introduced in Japan in February 2010. The approved immunization schedule has been described as a 3＋1 schedule, consisting of three doses for the primary series and one booster injection. This vaccine was introduced in
April 2013 for universal use in children aged ＜5 years, resulting in a markedly reduced incidence
of invasive pneumococcal disease (IPD). Following the introduction of PCV7 in Japan, the incidence of IPD-associated non-meningitis in children aged ＜5 years had decreased 56% and the incidence of meningitis had decreased 61%1). However, because the incidence of IPD caused bynon-PCV7 serotypes increased since the introduction of PCV7, PCV7 was replaced in November
2013 by the 13-valent pneumococcal conjugate vaccine (PCV13), which covers an additional six
serotypes.
In the United States, the Advisory Committee on Immunization Practices (ACIP) recommended routine PCV13 vaccination of children aged 6–18 years who had not received the vaccine previously and who had immunocompromising conditions, functional or anatomic asplenia,
cerebrospinal ﬂuid leakage, or cochlear implants2). Similarly, some European countries recommended routine PCV13 vaccinations of these children3). In Japan, PCV13 is routinely administered to children aged ＜5 years and adults aged ≥65 years. Regardless of the underlying conditions, PCV13 is not licensed for children aged ≥6 years. Our previous survey described 26
children aged ≥6 years with IPD in Chiba prefecture, Japan, with 69% having underlying diseases, especially malignancy4). These results indicated that children in this age group, not routinely vaccinated with PCV13, were at high risk for underlying diseases of IPD. However, little is
known about their immunity to PCV13 pneumococcal serotypes not present in PCV7. To assess
the need for PCV13 vaccination of children aged 5–18 years not routinely recommended for
PCV13 vaccination, this study measured levels of pneumococcal serotype-speciﬁc immunoglobulin G (IgG) against serotypes present in PCV13 but not in PCV7.

Materials and Methods
Surplus serum samples from routine blood examinations were collected between January
and May 2015 from children aged 5–18 years who were being followed up for hematologicalneoplasms or solid tumors in remission at Chiba University Hospital, Japan. The patients who
had previously received intravenous immunoglobulin within 6 months of the study were ex-Feb. 2018

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15（ 15 ）cluded. Serum concentrations of IgG directed against the pneumococcal serotypes 1, 3, 5, 6A, 7F,
and 19A, which are present in PCV13 but not in PCV7, were measured using WHO-approved enzyme-linked immunosorbent assays5). An IgG level ≥0.35 μg/mL was deﬁned as positive, in accordance with WHO recommendations6). Individual serotype-speciﬁc IgG levels in these children
were compared with those in non PCV vaccinated healthy children (N＝100, age range: 6–19
years) previously described7). Patients background, such as age, sex, underlying conditions, PCV
vaccine history, treatment history were extracted from the medical records.
Statistical analysis was done using StatView version 5.0 (SAS Institute Inc., Cary, North
Carolina, USA). We used the Mann-Whitney U tests for comparing the geometric mean concentrations (GMCs) of IgGs against serotypes and the Fisherʼs exact test for comparing the rates of
positive IgG levels. Differences with a p value ＜0.05 were considered statistically signiﬁcant.
This study was approved by the research ethics committee of Chiba University (No. 1964)
and written informed consent was obtained from the children and/or their legal guardians.

Results
Patient characteristics
Forty-one patients (24 boys, 17 girls; median age, 12 years) were included in this study.
Their underlying diseases included leukemia (56%), lymphoma (12%), solid tumors (27%), andother hematopoietic neoplasms (5%). Nine of the 41 patients (22%) had received PCV7, and one
had received the 23-valent pneumococcal polysaccharide vaccine (PPSV23), but none had received PCV13. Twelve patients (29%) had undergone chemotherapy within 6 months, and six patients (15%) had a history of hematopoietic stem cell transplantation (HSCT) (Table 1).
Serotype-speciﬁc IgG levels
Serotype-speciﬁc IgG levels are shown in Figure 1. The geometric mean concentrations(GMCs) of IgGs against serotypes 1, 3, 5, 6A, 7F, and 19A were 0.75, 0.49, 0.81, 0.67, 0.35, and1.59 μg/mL, respectively. In comparison, the GMCs of IgGs against these six serotypes in agematched healthy Japanese children had been reported to be 1.5, 1.39, 1.95, 2.07, 0.89, and2.67 μg/mL, respectively7), with the IgG levels against all six serotypes being signiﬁcantly lower
in the study patients than in the age-matched controls (Figure 1). When comparing among six serotypes, the GMC of IgG against serotype 7F was lower than others. In addition, lower percentages of study patients than of controls had positive IgG levels (≥0.35 μg/mL) against the six serotypes (Table 2). The serotype-speciﬁc IgG levels of study patients did not correlate with their
total IgG levels.

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Table 1. Patient characteristics (N: 41, Age: range, 5–18 years; median, 12 years）

Effects of chemotherapy and transplantation on serotype-speciﬁc IgG levels
We compared of IgG levels from patients who did and did not receive chemotherapy within
6 months prior to sample collection, and who did and did not have the history of HSCT. Twelve
patients received chemotherapy and their serotype-speciﬁc IgG levels could have been lower, butthere were no statistically signiﬁcant difference against all serotypes (Figure 2). Six children had
a history of HSCT (mean time after transplant, 39 months). The serotype-speciﬁc IgG levels ofthem were higher than those of non-HSCTs but the number of these patients was too small to use
statistical analysis (Figure 3). No other speciﬁc factors were found to inﬂuence the levels of serotype-speciﬁc IgG.

Discussion
Several studies have shown that people with immunocompromising conditions are at risk of
IPD , as are children with immunocompromising conditions such as hematopoietic neoplasms12).
Chemotherapy has a negative effect on the immune system, which may lead to the loss of speciﬁc
antibodies and immunological memory against pathogens. For example, speciﬁc IgG levels
against every PCV7 serotype were found to be lower in 53 children aged 8–18 years with acute
8–11)

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17（ 17 ）Fig. 1. Pneumococcal serotype-speciﬁc IgG levels in study patients (N＝41) and healthy
children (N＝100)

The transverse line at 0.35 is the cut-off value for positive pneumococcal serotype-specific IgG level. Against all 6 serotypes,
the IgG levels of the study patients were significantly lower than those of age-matched healthy Japanese children (p＜0.05).

Table 2. Rates of positive IgG levels (%)

The percentages of positive IgG levels (≥0.35 μg/mL) of study patients and controls
against the six serotypes. In all serotypes, the positive rates of the study patientswere significantly lower than those of age-matched healthy Japanese children.

lymphoblastic leukemia 9 months after the completion of maintenance chemotherapy than in agematched unvaccinated healthy controls13).
While the incidence of IPD due to PCV7 serotypes has decreased, the incidence of IPD due
to PCV13 serotypes has increased, especially to serotype 19A1). The immunity to PCV13 serotypes in immunocompromised children has not been clariﬁed. A study of PCV13 serotype-speciﬁc IgG levels in 39 children with cancer aged 1–18 years within 12 months after completing
chemotherapy, found that the rates of positive IgG levels were below 50% for eight of 12 serotypes14). However, that study included patients previously immunized with PCV13 and did not18（ 18 ）THE JAPANESE JOURNAL OF ANTIBIOTICS

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Fig. 2. Geometric mean concentrations (GMCs) of serotype-speciﬁc IgG in children who did
and did not receive chemotherapy within 6 months

Serotype-specific IgG levels were lower in patients with (white bars) than without (gray bars) a history of chemotherapy
within 6 months but there were no statistically significant difference against all serotypes.

Fig. 3. Geometric mean concentrations (GMCs) of serotype-speciﬁc IgG in children who did
and did not undergo hematopoietic stem cell transplantation (HSCT)

Serotype-specific IgG levels were higher in patients with (white bars) than without (gray bars) a history of HSCT but there
were no statistically significant difference against all serotypes.

clarify the interval after chemotherapy.
In our study, 62% of the patients were assessed ≥6 months after completing chemotherapy,
and none had been previously immunized with PCV13. To our knowledge, this is the ﬁrst study

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19（ 19 ）to show that IgG levels in Japanese immunocompromised children are low against PCV13 (nonPCV7), as well as PCV7, serotypes.
Our study conﬁrmed that the rates of positive IgG levels in children with hematological neoplasms and solid tumors who were outside recommended ages for routine PCV13 vaccination
were lower than those in healthy unvaccinated children. Based on the results, PCV13 vaccinations may be important for patients with them even if their ages are outside the range recommended for routine vaccination. Other studies have reported that PCV vaccination of immunocompromised patients outside the routine age range is both safe and effective15–19). This study
provides evidence of such PCV vaccinations.
Moreover, we found that the levels of IgG against serotype 7F were lower than those against
other serotypes. We considered that this result was due to a lower frequency of natural exposure
to this serotype20) and because serotype 7F is not a common cause of IPD in Japan21).
Humoral immunity has been reported to recover approximately 6 months after completing
chemotherapy22). Our study found that the GMCs and the rates of positive IgG levels were lower
in patients with a history of chemotherapy within 6 months before the study. These ﬁndings suggested that the ability to produce antibodies had not recovered completely in these patients.
Conditioning chemotherapy regimens before HSCT have been found to eliminate immunocompetent cells, reducing pneumococcal-speciﬁc antibody titers to below preventable levels
within 6–12 months23). Our results showed that post-HSCT patients had higher antibody titers.
However, our study included a small number of patients who had undergone HSCT, indicating aneed for future studies that include larger numbers of patients.
PPSV23 has also been recommended for children aged ≥2 years who are at high risk ofpneumococcal disease2). The ACIP has recommended that immunocompromised children receivea single PCV13 dose, followed by a dose of PPSV23 ≥8 weeks later and a second PPSV23 dose
5 years after the ﬁrst PPSV23 dose24). Despite similar recommendations in Japan, only one patient in this study received PPSV23. People need to be made aware of immunization.
The major limitation of this study was that we did not use serotype-speciﬁc opsonophagocytic assays. To further evaluate protective immunity, opsonization activities (OPAs) should also
be examined. In some cases, serotype-speciﬁc IgG levels did not correlate with the OPA results25).
In conclusion, we measured pneumococcal serotype-speciﬁc IgG levels against PCV13 serotypes in children with hematopoietic neoplasms who were not recommended to receive routine
vaccinations owing to their age. Many of these children did not have sufﬁcient IgG concentrations to prevent IPD. This study suggested that high-risk children in Japan may require vaccination with PCV13.
Acknowledgments
The authors thank the patients and families involved in the study, as well as the pediatric on-20（ 20 ）THE JAPANESE JOURNAL OF ANTIBIOTICS

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Feb. 2018cologists at Chiba University Hospital.
Statement of Financial Support
This study was funded by the MSD and Ministry of Health, Labor and Welfare of Japan.
Naruhiko Ishiwada received research funding and lecture fees from Pﬁzer.
Conﬂicts of Interest
All other authors report no potential conﬂicts of interest.

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