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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5625_Библиотеки_им_академика_М_И_Перельмана
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Bacterial Glycolipid Lipid Asand Their Potential
asAdjuvants
Atsushi Shimoyama and Koichi Fukase
560-0043, Japan
4.1 Introduction
Bacterial components have long been known to regulate the immune system[1].
Tumor shrinkage due to bacterial infections has occasionally been reported for the
past hundreds of years[2]. In 1893, Corey etal. first attempted to use immunotherapy for cancer with Streptococcus pyogenes and Serratia marcescens. The immunostimulatory effects of killed Salmonella typhimurium and Mycobacterium
tuberculosis were confirmed in 1916 and 1924, respectively. These immunostimulatory effects, now widely known as the innate immune system, are triggered by recognizing molecular pattern characteristics of pathogens and microbes by various
innate immune receptors in multicellular organisms. Because innate immune stimulants also activate acquired immune responses such as antigen–antibody interactions and cell-to-cell immunity, several studies have been conducted to develop
innate immune stimulants as adjuvants[3], which are vaccine ingredients that
enhance antibody production.
Lipopolysaccharide (LPS), a major glycoconjugate in the outer membrane of
Gram-negative bacteria, is a well-known innate immune stimulator [4]. Lipid A,
which is linked to the terminal of the polysaccharide part via the peculiar acidic
sugar Kdo (2-keto-3-deoxy--mannooctanoic acid), is the active principal of LPS, and
the chemical structure of an authorized Escherichia coli lipid A (1) is described in
Figure4.1. The recognition of LPS/lipid A by Toll-like receptor (TLR) 4/myeloid differentiation protein (MD)2 receptor induces various immune responses, including
cytokine production, nitric oxide production, reactive oxygen species production,
leukocyte migration, and lymphocyte activation, which trigger the host defense system against bacteria. LPS and lipid A are also extremely strong inflammatory agents
and are known as endotoxins, which are the major contributors to sepsis and trigger
serious systemic diseases that cause multiple organ failure, hypotension, and septic
shock [4a]. Canonical E. coli LPS is highly toxic; therefore, its application as an
111
Carbohydrate-Based Therapeutics, First Edition. Edited by Roberto Adamo and Luigi Lay.
© 2024 WILEY-VCH GmbH. Published 2024 by WILEY-VCH GmbH.

112
Polysaccharide
Figure4.1 E. coli LPS and Kdo-lipid A.
adjuvant requires modification to attenuate any inflammatory effects and eliminate
significant toxicity. Monophosphoryl lipid A (MPL) derivative, 3D-MPL (2)
(Figure4.2), has already been developed by GlaxoSmithKline (GSK) and approved as
an adjuvant component[5]. Here, we introduce the structure–activity relationship of
lipid A and the strategy for regulating the immune functions of lipid A for the development of lipid A as an adjuvant.
Figure4.2 Chemical structure of 3D-MPL and lipid IVa.

4.2 Bacterial Glycolipid Lipid A: an Innate Immune Stimulant
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4.2 Bacterial Glycolipid Lipid A: an Innate
Immune Stimulant
In 1892, Pfeiffer (a disciple of the bacteriologist Koch) revealed that Vibrio cholerae
produces two different toxic components: one is a heat-labile exotoxin and the other is
a heat-stable endotoxin [6]. In 1945, Westphal (later the first director of the Max
Planck Institute of Immunobiology and Epigenetics) reported that the active ingredient of endotoxin is LPS, the outer membrane component of Gram-negative bacteria [6]. In 1957, the LPS terminus-acylated disaccharide, glycolipid lipid A, was
reported as the active core of LPS[6]. Shiba and Kusumoto began collaborating with
a German research group and submitted the correct structure of E. coli lipid A (1)
(Figure4.1), and in 1985, they succeeded in the first total synthesis of E. coli lipid A
(1), confirming that lipid A is the active core of endotoxin[7]. Simultaneously,
Qureshi and Takayama identified the lipid A structure [8]. Shiba and Kusumoto
also achieved lipid IVa (3) synthesis (Figure4.2), a precursor of E. coli lipid A[1],
and found that lipid IVa (3) has an immunostimulatory effect in mice but an antagonistic effect in humans[9]. The presence of an antagonist suggested the presence
of receptors, which led to LPS receptor exploratory studies. In 1996, a breakthrough
was achieved by Hoffmann, who revealed that the Toll gene, which regulates dorsoventral axis formation in Drosophila, is essential to the defense mechanism
against the fungus, leading to the discovery of various innate immune receptors[10]. In 1997, TLRs were found to be human homologs of the Drosophila Toll
protein[11], and Beutler identified TLR4 as an LPS receptor in 1998[12]. To date,
10 types of TLRs (TLR1–10) in humans and 12 types (TLR1–9, TLR11–13) in mice
have been identified.
TLRs are membrane glycoproteins containing a leucine-rich repeat motif in the ectodomain and a cytoplasmic signaling domain homologous to the interleukin 1 receptor
(IL-1R), called the Toll/IL-1R (TIR) domain. TLR4 signaling is mediated via various
adaptor molecules (MyD88, TRIF, TIRAP, and TRAM), including the TIR domain
(Figure4.3) [15]. MyD88-mediated signaling activates NF-κB, a transcription factor
involved in inflammation, and induces the production of pro-inflammatory cytokines
such as tumor necrosis factor (TNF)-α and IL-6. These inflammatory cytokines are produced as a protective response against infection. However, TRIF-mediated signaling
leads to the activation of interferon (IFN) regulator 3 (IRF3) and induces the production of the antiviral cytokine type I IFN. Canonical E. coli LPS strongly activates both
signals simultaneously (Figure 4.3), resulting in a massive inflammatory response
leading to lethal toxicity. Therefore, lipid A attenuation and TLR4-signaling pathway
regulation are essential for the development of lipid A-based adjuvants.
To achieve lipid A attenuation and TLR4-signaling regulation, it is essential to
elucidate the molecular basis of lipid A recognition by TLR4. Miyake found that
MD2, an accessory protein to TLR4, is essential for TLR4 signaling[16]. We synthesized a radiolabeled E. coli lipid A analog 4 (Figure4.4), which Miyake used to elucidate the interaction between the TLR4/MD-2 complex and lipid A (Figure4.4)[17].
Miyake also clarified that the species specificity of TLR4/MD-2 is due to differences
in lipid A recognition by MD-2 [18]. Furthermore, X-ray crystallography revealed
113

114
Lee and
coworkers [14]
Satow and
coworkers [13]
Figure4.3 Innate immune system activation via TLR4/MD2.
the binding modes of TLR4/MD-2 to agonists and antagonists. The crystal structure
of the complex of human MD-2 with lipid IVa (3) was revealed by Ohto and
Satow[13], and the crystal structure of mouse TLR4/MD-2 complex with Eritoran
(5) (Figure 4.5), a TLR4 antagonist developed by Eisai, was demonstrated by
Lee[14]. In 2009, X-ray crystallography of the human TLR4/MD-2 complex with
E. coli LPS was performed by Lee[19]. The results indicate that five of the six acyl
chains of E. coli lipid A (1) are housed within the hydrophobic pocket of MD-2,
while the remaining acyl chain interacts with the hydrophobic surface of the adjacent TLR4. These interactions trigger the dimerization of the TLR4/MD-2 complex
to activate the immune response. For lipid IVa (3), an antagonist, the lipid A moiety
binds to MD-2in the form in which lipid A is rotated by 180° compared to the agonistic E. coli lipid A (1), and all acyl chains are placed within the MD-2 pocket, thus
not causing TLR4/MD-2 dimerization. Ohto revealed the crystal structure of mouse
TLR4/MD-2with lipid IVa (3); incidentally, lipid IVa (3) acts as an antagonist in
humans but as an agonist in mice[20]. In mice, three of the four acyl chains of lipid
IVa (3) are housed within the MD-2 pocket, and the remaining one interacts with
the hydrophobic surface of the adjacent TLR4, resulting in TLR4/MD-2 dimerization. These studies revealed that differences in the binding mode of lipid A to MD-2
significantly affect TLR4-mediated immune regulation.

Miyake and coworkers [17, 18]
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Lee and coworkers [14, 19]
Lien and coworkers [21]
Figure4.4 Molecular mechanism of TLR4/MD2 dimerization.
Ohto et al. [13]
Ohto et al. [20]
Fukase et al. [22]

116
′ ′
Tanimura et al. [23b]
Fujimoto et al. [23c]
Figure4.5 Chemical structures of various lipid As and lipid A analogs.
Previous structure–activity relationship studies[4a, 24] have revealed that agonistic and antagonistic effects can be controlled by the number of acyl chains and phosphate groups and the chain length (Figures4.4 and4.5). That is, hexa-acylated E. coli
lipid A (1) is an agonist, whereas tetra-acylated lipid IVa (3) is an antagonist. MPL504
(6) (Figure4.5), which is E. coli lipid A (1) without 1-phosphate, shows weaker IL-6-
inducing activity than E. coli lipid A (1)[23]. MPL504 (6) is less dependent on CD14,
a glycosylphosphatidylinositol-anchored receptor known to serve as a co-receptor
for TLR4. Additionally, TLR4/MD2 dimerization in response to MPL is much lower
than the response to E. coli LPS. MPL504 (6) has shown CD14-independent but
MyD88-dependent TNFα-producing ability and TRIF-dependent CD86 upregulation and IFNβ-inducing ability [23b]. Similar to MPL504 (6), MPL505 (7), which
lacks a 4′-phosphate, also exhibits mild immunomodulatory effects. However, while
the ability of MPL504 (6) to induce IL-18 production is lower than that of E. coli
LPS, MPL505 (7) exhibits the same IL-18 induction level as E. coli LPS [23c].
Therefore, these MPLs are expected to be developed as future adjuvants with different adjuvant effects. As described below, such structural modifications help regulate
the effects of lipid A as a potential adjuvant.
LPS consists of an O-antigen polysaccharide part that is characteristic of each
bacterial species, a core oligosaccharide part that has a high degree of commonality

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in chemical structure across bacterial species, and a lipid A component (Figure4.1).
We also investigated the structure–activity relationship of lipid A connected with
the partial structure of the core oligosaccharide. There are R-mutant bacteria consisting of LPS lacking the O-antigen polysaccharide moiety, and the E. coli Re-mutant
has a Re-LPS (8) consisting of lipid A linked to Kdo disaccharide. To elucidate the
effect of Kdo on lipid A activity, we synthesized Re-LPS (8), Kdo-506 (9), and KdoMPL504 (10) (Figure 4.5), showing for the first time that Kdo enhances lipid A
activity[25].
4.3 Vaccines Containing Natural LPS as Adjuvants
Vaccines are designed to attenuate or inactivate pathogens and their toxins. Most
vaccines for bacteria contain natural bacterial components, and some of which
would act as natural adjuvants. LPS is considered the main natural adjuvant in vaccines derived from Gram-negative bacteria. Here are some examples of vaccines
that contain LPS.
4.3.1 Cholera Vaccines
Live-attenuated and inactivated whole-cell vaccines have been developed for cholera[26]. These vaccines include V. cholerae LPS and act as natural adjuvants.
An injectable whole-cell cholera vaccine was used in the 1960s, mainly in the
USA and Japan, and was administered subcutaneously twice every five to seven
days. The immune response rate was 50%, and protection continued for only six
months. Side effects have been reported, and the World Health Organization recommended its discontinuation.
®
Dukoral
nit, is an oral vaccine that was licensed in Sweden in 1991. This vaccine has an efficacy rate of 85–97% with few side effects. The duration of protection is approximately
two to three years. It is licensed mainly in Europe, Canada, South Asia, and Latin
America.
Live-attenuated oral cholera vaccines, Orochol
using the V. cholerae Inaba strain, whose cholera toxin A subunit (toxic) was deleted.
This vaccine is approved in the same country as Dukoral and has a similar effectivity
rate and effectivity period. However, the production and sale of these vaccines have
been discontinued.
, comprising killed whole bacteria and recombinant cholera toxin B subu-
®
and Mutacol®, were developed
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4.3.2 Salmonella enterica Serovar Typhi Vaccines
Live-attenuated, inactivated whole-cell, and subunit vaccines have been developed
for Salmonella enterica serovar Typhi[27].
®
Vivotif Berna
, derived from the attenuated typhoid Ty21a strain, is an oral liveattenuated vaccine developed in Switzerland. This vaccine is effective for more than
two years and has few side effects. However, the administration of this vaccine to

118
children under five years of age is not recommended. It is licensed in Africa, Europe,
Asia, the USA, and South America.
Inactivated whole-cell vaccines (heat–phenol-inactivated or acetone-inactivated)
were first developed in 1896. However, these have reported side effects, and most
countries have withdrawn the use of these vaccines.
®
Typhim Vi
gen purified from Salmonella Typhi, are subunit vaccines. Because the Vi capsular
polysaccharide antigen was checked by the endotoxin test, LPS was omitted. This
vaccine is effective for several years with a single injection. Its side effects are similar
to those of whole-cell-inactivated vaccines but are relatively mild. It is licensed in
Europe, Africa, Asia, Australia, and the USA.
and Typherix®, using the virulence (Vi) capsular polysaccharide anti-
4.3.3 Other Vaccines
Bexsero®, a vaccine against meningococcal group B (MenB), was developed by
Novartis. It contains a meningococcal outer membrane vesicle, and LPS derived
from meningococcal outer membrane vesicles can function as adjuvants in these
®
vaccines[28]. In contrast, the MenB vaccine Trumenba
protein containing the TLR2ligand bound to the protein antigen[29].
For Bordetella pertussis, subunit and inactivated vaccines have been developed
and are used as diphtheria, tetanus, and pertussis combination vaccine or diphtheria, pertussis, tetanus, and inactivated poliovirus combination vaccine. In most
combination vaccines, the safer acellular pertussis vaccine is commonly used.
However, a more effective whole-cell vaccine is still being used.
Similarly, for other Gram-negative bacteria, such as Haemophilus influenzae
type b and Neisseria meningitidis (serogroups A, B, C, Y, and W-135), vaccines have
also been developed, but all of them are capsular polysaccharide based vaccines;
hence LPS was not included.
Therefore, vaccines that might contain LPS are widely used, and, in some cases,
LPS may act as an adjuvant. In addition, it has been reported that some LPS could
retain their immunostimulatory effects even when administered orally[30], in which
case side effects would decrease compared to injected whole-cell vaccines with LPS.
uses a recombinant lipo-
4.4 LPS and Lipid A in the Environment or Fermented
Foods as Adjuvants
Immunomodulatory functions of LPS and lipid A in the environment or fermented
foods have been reported; thus, LPS and lipid A are attracting attention as safe adjuvant candidates.
The Gram-negative bacterium Pantoea agglomerans, which is widely present in
the soil and plants such as wheat, rice, sweet potato, apple, and pear, has been

Heine and coworkers [34]
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detected during the fermentation process of rye bread [31]. P. agglomerans LPS
exhibits immunostimulatory effects via oral administration [30]. P. agglomerans
lipid A is a mixture of E. coli lipid A (1) and Salmonella minnesota lipid A (11)[32]
(Figure4.6), which are both agonists.
Kurozu (fermented black vinegar), an Asian fermented food, contains LPS derived
from Acetobacter spp. This genus of Gram-negative bacteria is used in acetic acid
fermentation. The chemical structure of Acetobacter pasteurianus LPS[35] and its
lipid A 12[33] (Figure4.6) have been reported recently. Although A. pasteurianus
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Hashimoto et al. [33]
Figure4.6 Chemical structures of various lipid As.

120
LPS had weaker immunostimulating effects than E. coli LPS, A. pasteurianus LPS
and lipid A are still expected to be novel adjuvants because of their safety as foodderived compounds.
The hygiene hypothesis states that exposure to environmental microbes during
early childhood reduces the risk of developing allergic diseases. In the search for
bacteria with an allergy-suppressing ability, Acinetobacter lwoffii F78[34] was found
in livestock feed. A. lwoffii LPS selectively induces T helper 1 (Th1) cell-derived
cytokines, such as IL-12 and IFN-γ, which exhibit anti-allergic effects. A. lwoffii
F78LPS and its lipid A 13 (Figure4.6) have potential as novel adjuvants.
4.5 Synthetic and Semisynthetic Lipid As as Adjuvants
3D-MPL (2)[5] (Figure4.2), which has a 4′-monophosphate structure similar to
MPL504 (6), was developed by GSK. By optimizing the lipid A structure, especially
the acyl and phosphate groups, 3D-MPL (2) has been successfully attenuated and is
currently being derivatized and produced from S. minnesota R595LPS. 3D-MPL (2)
selectively activates the TRIF-dependent pathway of the two signaling cascades
downstream of TLR4/MD2 (Figure4.3).
GSK has developed the liposome adjuvant AS01, a mixture of 3D-MPL (2), cholesterol, and QS21 (a saponin derived from the South American native tree Quillaja
saponaria). AS01was applied to the herpes zoster vaccine, composed of recombinant glycoprotein E of varicella-zoster virus and AS01.
Infectious sporozoites are injected into human blood via salivary glands during
blood collection by Anopheles vector mosquitoes during infection with Plasmodium
falciparum, the causative agent of malaria. Therefore, the development of vaccines
targeting sporozoite surface proteins has been pursued. The recombinant protein
RTS,S consists of a segment of a sporozoite protein and the hepatitis B virus (HBV)
surface antigen, and the malaria vaccine candidate RTS,S/AS01has been developed
by GSK and is currently in phase III clinical trials. Adjuvant AS02, which consists of
3D-MPL (2), oil emulsion, squalene, and QS21, has also been developed by GSK,
and the malaria vaccine RTS,S/AS02 is currently in phase III clinical trials.
GSK has also developed the adjuvant AS04, a mixture of 3D-MPL (2) and aluminum salts. Cell-mediated immune responses are induced by AS04, which exhibits
antiviral effects. AS04 is practically used as an adjuvant for the human papillomavi-
®
rus (HPV) vaccine Cervarix
Furthermore, the MPL mimic RC-529 (14) (Figure4.7) was approved as an adjuvant for the HBV vaccine in Argentina in 2003.
Lipid A adjuvants such as MPL can induce anti-inflammatory cytokines, including IL-10, while modulating the induction of inflammatory cytokines such as IL-6
by their chemical structural modifications[36]; therefore, lipid A adjuvants have a
low risk of developing adjuvant-induced autoimmune diseases.
and the HBV vaccine Fendrix®.
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