mRNA vaccine against malaria tailored for liver-resident memory T cells.

Malaria is caused by Plasmodium species transmitted by Anopheles mosquitoes. Following a mosquito bite, Plasmodium sporozoites migrate from skin to liver, where extensive replication occurs, emerging later as merozoites that can infect red blood cells and cause symptoms of disease. As liver tissue-resident memory T cells (Trm cells) have recently been shown to control liver-stage infections, we embarked on a messenger RNA (mRNA)-based vaccine strategy to induce liver Trm cells to prevent malaria. Although a standard mRNA vaccine was unable to generate liver Trm or protect against challenge with Plasmodium berghei sporozoites in mice, addition of an agonist that recruits T cell help from type I natural killer T cells under mRNA-vaccination conditions resulted in significant generation of liver Trm cells and effective protection. Moreover, whereas previous exposure of mice to blood-stage infection impaired traditional vaccines based on attenuated sporozoites, mRNA vaccination was unaffected, underlining the potential for such a rational mRNA-based strategy in malaria-endemic regions.

A randomised controlled trial of long NY-ESO-1 peptide-pulsed autologous dendritic cells with or without alpha-galactosylceramide in high-risk melanoma.

AIM: We have previously reported that polyfunctional T cell responses can be induced to the cancer testis antigen NY-ESO-1 in melanoma patients injected with mature autologous monocyte-derived dendritic cells (DCs) loaded with long NY-ESO-1-derived peptides together with α-galactosylceramide (α-GalCer), an agonist for type 1 Natural Killer T (NKT) cells. OBJECTIVE: To assess whether inclusion of α-GalCer in autologous NY-ESO-1 long peptide-pulsed DC vaccines (DCV + α-GalCer) improves T cell responses when compared to peptide-pulsed DC vaccines without α-GalCer (DCV). DESIGN, SETTING AND PARTICIPANTS: Single-centre blinded randomised controlled trial in patients ≥ 18 years old with histologically confirmed, fully resected stage II-IV malignant cutaneous melanoma, conducted between July 2015 and June 2018 at the Wellington Blood and Cancer Centre of the Capital and Coast District Health Board. INTERVENTIONS: Stage I. Patients were randomised to two cycles of DCV or DCV + α-GalCer (intravenous dose of 10 × 106 cells, interval of 28 days). Stage II. Patients assigned to DCV + α-GalCer were randomised to two further cycles of DCV + α-GalCer or observation, while patients initially assigned to DCV crossed over to two cycles of DCV + α-GalCer. OUTCOME MEASURES: Primary: Area under the curve (AUC) of mean NY-ESO-1-specific T cell count detected by ex vivo IFN-γ ELISpot in pre- and post-treatment blood samples, compared between treatment arms at Stage I. Secondary: Proportion of responders in each arm at Stage I; NKT cell count in each arm at Stage I; serum cytokine levels at Stage I; adverse events Stage I; T cell count for DCV + α-GalCer versus observation at Stage II, T cell count before versus after cross-over. RESULTS: Thirty-eight patients gave written informed consent; 5 were excluded before randomisation due to progressive disease or incomplete leukapheresis, 17 were assigned to DCV, and 16 to DCV + α-GalCer. The vaccines were well tolerated and associated with increases in mean total T cell count, predominantly CD4+ T cells, but the difference between the treatment arms was not statistically significant (difference - 6.85, 95% confidence interval, - 21.65 to 7.92; P = 0.36). No significant improvements in T cell response were associated with DCV + α-GalCer with increased dosing, or in the cross-over. However, the NKT cell response to α-GalCer-loaded vaccines was limited compared to previous studies, with mean circulating NKT cell levels not significantly increased in the DCV + α-GalCer arm and no significant differences in cytokine response between the treatment arms. CONCLUSIONS: A high population coverage of NY-ESO-1-specific T cell responses was achieved with a good safety profile, but we failed to demonstrate that loading with α-GalCer provided an additional advantage to the T cell response with this cellular vaccine design. CLINICAL TRIAL REGISTRATION: ACTRN12612001101875. Funded by the Health Research Council of New Zealand.

Synthesis and Biological Evaluation of Peptide-Adjuvant Conjugate Vaccines with Increasing Antigen Content.

Synthetic vaccines that induce T cell responses to peptide epitopes are a promising immunotherapy for both communicable and noncommunicable diseases. Stimulating strong and sustained T cell responses requires antigen delivery to appropriately activated antigen presenting cells (APCs). One way this can be accomplished is by chemically conjugating immunogenic peptide epitopes with α-galactosylceramide (α-GalCer), a glycolipid that acts as an immune adjuvant by inducing stimulatory interactions between APCs and type I natural killer T (NKT) cells. Here we investigate whether increasing the ratio of antigen:adjuvant improves antigen-specific T cell responses. A series of conjugate vaccines was prepared in which one, two, four, or eight copies of an immunogenic peptide were covalently attached to a modified form of α-GalCer via the poly(ethoxyethylglycinamide) dendron scaffold. Initial attempts to synthesize these multivalent conjugate vaccines involved attaching the bicyclo[6.1.0]non-4-yne (BCN) group to the adjuvant-dendron structure followed by strain-promoted azide-alkyne cycloaddition of the peptide. Although this approach was successful for preparing vaccines with either one or two peptide copies, the synthesis of vaccines requiring attachment of four or eight BCN groups suffered from low yields due to cyclooctyne degradation. Instead, conjugate vaccines containing up to eight peptide copies were readily achieved through oxime ligation with adjuvant-dendron constructs decorated with the 8-oxo-nonanoyl group. When evaluating T cell responses to vaccination in mice, we confirmed a significant advantage to conjugation over admixes of peptide and α-GalCer, regardless of the peptide to adjuvant ratio, but there was no advantage to increasing the number of peptides attached. However, it was notable that the higher ratio conjugate vaccines required lower levels of NKT cell activation to be effective, which could be a safety advantage for future vaccine candidates.

Synthetic preparation and immunological evaluation of ß-mannosylceramide and related N-acyl analogues.

The synthesis of the invariant natural killer (iNK) T cell agonist ß-mannosylceramide along with a series of fatty amide analogues is reported. Of the six ß-glycosylation protocols investigated, the sulfoxide methodology developed by Crich and co-workers proved to be the most effective where the reaction of a mannosyl sulfoxide and phytosphingosine derivative gave a key glycolipid intermediate as a 95 : 5 mixture of ß- to α-anomers in high yield. A series of mannosyl ceramides were evaluated for their ability to activate D32.D3 NKT cells and induce antitumour activity.

Enhancing T cell responses and tumour immunity by vaccination with peptides conjugated to a weak NKT cell agonist.

Activated NKT cells can stimulate antigen-presenting cells leading to enhanced peptide antigen-specific immunity. However, administration of potent NKT cell agonists like α-galactosylceramide (α-GalCer) can be associated with release of high levels of cytokines, and in some situations, hepatotoxicity. Here we show that it is possible to provoke sufficient NKT cell activity to stimulate strong antigen-specific T cell responses without these unwanted effects. This was achieved by chemically conjugating antigenic peptides to α-galactosylphytosphingosine (α-GalPhs), an NKT cell agonist with very weak activity based on structural characterisation and biological assays. Conjugation improved delivery to antigen-presenting cells in vivo, while use of a cathepsin-sensitive linker to release the α-GalPhs and peptide within the same cell promoted strong T cell activation and therapeutic anti-tumour responses in mice. The conjugates activated human NKT cells and enhanced human T cell responses to a viral peptide in vitro. Accordingly, we have demonstrated a means to safely exploit the immunostimulatory properties of NKT cells to enhance T cell activation for virus- and tumour-specific immunity.

A phase I vaccination study with dendritic cells loaded with NY-ESO-1 and α-galactosylceramide: induction of polyfunctional T cells in high-risk melanoma patients.

Vaccines that elicit targeted tumor antigen-specific T-cell responses have the potential to be used as adjuvant therapy in patients with high risk of relapse. However, the responses induced by vaccines in cancer patients have generally been disappointing. To improve vaccine function, we investigated the possibility of exploiting the immunostimulatory capacity of type 1 Natural killer T (NKT) cells, a cell type enriched in lymphoid tissues that can trigger improved antigen-presenting function in dendritic cells (DCs). In this phase I dose escalation study, we treated eight patients with high-risk surgically resected stage II-IV melanoma with intravenous autologous monocyte-derived DCs loaded with the NKT cell agonist α-GalCer and peptides derived from the cancer testis antigen NY-ESO-1. Two synthetic long peptides spanning defined immunogenic regions of the NY-ESO-1 sequence were used. This therapy proved to be safe and immunologically effective, inducing increases in circulating NY-ESO-1-specific T cells that could be detected directly ex vivo in seven out of eight patients. These responses were achieved using as few as 5 × 105 peptide-loaded cells per dose. Analysis after in vitro restimulation showed increases in polyfunctional CD4+ and CD8+ T cells that were capable of manufacturing two or more cytokines simultaneously. Evidence of NKT cell proliferation and/or NKT cell-associated cytokine secretion was seen in most patients. In light of these strong responses, the concept of including NKT cell agonists in vaccine design requires further investigation.

Activated NKT Cells Can Condition Different Splenic Dendritic Cell Subsets To Respond More Effectively to TLR Engagement and Enhance Cross-Priming.

The function of dendritic cells (DCs) can be modulated through multiple signals, including recognition of pathogen-associated molecular patterns, as well as signals provided by rapidly activated leukocytes in the local environment, such as innate-like T cells. In this article, we addressed the possibility that the roles of different murine DC subsets in cross-priming CD8(+) T cells can change with the nature and timing of activatory stimuli. We show that CD8α(+) DCs play a critical role in cross-priming CD8(+) T cell responses to circulating proteins that enter the spleen in close temporal association with ligands for TLRs and/or compounds that activate NKT cells. However, if NKT cells are activated first, then CD8α(-) DCs become conditioned to respond more vigorously to TLR ligation, and if triggered directly, these cells can also contribute to priming of CD8(+) T cell responses. In fact, the initial activation of NKT cells can condition multiple DC subsets to respond more effectively to TLR ligation, with plasmacytoid DCs making more IFN-α and both CD8α(+) and CD8α(-) DCs manufacturing more IL-12. These results suggest that different DC subsets can contribute to T cell priming if provided appropriately phased activatory stimuli, an observation that could be factored into the design of more effective vaccines.

An autologous leukemia cell vaccine prevents murine acute leukemia relapse after cytarabine treatment.

Acute leukemias with adverse prognostic features carry a high relapse rate without allogeneic stem cell transplantation (allo-SCT). Allo-SCT has a high morbidity and is precluded for many patients because of advanced age or comorbidities. Postremission therapies with reduced toxicities are urgently needed. The murine acute leukemia model C1498 was used to study the efficacy of an intravenously administered vaccine consisting of irradiated leukemia cells loaded with the natural killer T (NKT)-cell agonist α-galactosylceramide (α-GalCer). Prophylactically, the vaccine was highly effective at preventing leukemia development through the downstream activities of activated NKT cells, which were dependent on splenic langerin(+)CD8α(+) dendritic cells and which led to stimulation of antileukemia CD4(+) and CD8(+) T cells. However, hosts with established leukemia received no protective benefit from the vaccine, despite inducing NKT-cell activation. Established leukemia was associated with increases in regulatory T cells and myeloid-derived suppressor cells, and the leukemic cells themselves were highly suppressive in vitro. Although this suppressive environment impaired both effector arms of the immune response, CD4(+) T-cell responses were more severely affected. When cytarabine chemotherapy was administered prior to vaccination, all animals in remission posttherapy were protected against rechallenge with viable leukemia cells.

A self-adjuvanting vaccine induces cytotoxic T lymphocytes that suppress allergy.

Epitope-based peptide vaccines encompass minimal immunogenic regions of protein antigens to allow stimulation of precisely targeted adaptive immune responses. However, because efficacy is largely determined by the functional status of antigen-presenting cells (APCs) that acquire and present peptides to cells of the adaptive immune system, adjuvant compounds are needed to enhance immunogenicity. We present here a vaccine consisting of an allergen-derived peptide conjugated to a prodrug of the natural killer-like T (NKT) cell agonist α-galactosylceramide, which is highly effective in reducing inflammation in a mouse model of allergic airway inflammation. Unlike other peptide-adjuvant conjugates that directly activate APCs through pattern recognition pathways, this vaccine encourages third-party interactions with NKT cells to enhance APC function. Therapeutic efficacy was correlated with marked increases in the number and functional activity of allergen-specific cytotoxic T lymphocytes (CTLs), leading to suppression of immune infiltration into the lungs after allergen challenge in sensitized hosts.

Resolution of orthogonally protected myo-inositols with novozym 435 providing an enantioconvergent pathway to Ac2PIM1.

Orthogonally protected chiral myo-inositol derivatives are important intermediates for higher order myo-inositol-containing compounds. Here, the use of the immobilized enzyme Novozym 435 to efficiently catalyze the acetylation of the 5R configured enantiomer of racemic 1,2-O-isopropylidene-myo-inositols possessing chemically and sterically diverse protecting groups at O-3 and O-6 is described. The resolutions were successful with allyl, benzyl, 4-bromo-, 4-methoxy-, 4-nitro-, and 4-(3,4-dimethoxyphenyl)benzyl, propyl, and propargyl protection at O-6 in combination with either allyl or benzyl groups at O-3. Bulky protecting groups slow the rate of acetylation. No reaction was observed for 3,6-di-O-triisopropylsilyl-1,2-O-isopropylidene-myo-inositol. The utility of this methodology was demonstrated by the first reported synthesis of an Ac2PIM1 (9), which used both enantiomers of the resolved 3-O-allyl-6-O-benzyl-1,2-O-isopropylidene-myo-inositol in a convergent synthesis.

NKT Agonist-Antigen Conjugates as Cancer Vaccines.

Natural killer T (NKT) cells are a population of innate-like T cells capable of enhancing both innate and adaptive immune responses. Co-delivering an NKT cell agonist and antigen can provide molecular signals to antigen-presenting cells, such as dendritic and B cells, that facilitate strong antigen-specific adaptive immune responses. Accordingly, there has been a significant number of developmental NKT cell-dependent vaccine therapies developed, particularly in the last decade, with many incorporating cancer antigens. In this review, we summarize studies that chemically conjugate the NKT cell agonist and antigen as an effective strategy for agonist-antigen co-delivery to drive antitumor responses.

A Glycolipid-Peptide-Hapten Tricomponent Conjugate Vaccine Generates Durable Antihapten Antibody Responses in Mice.

Eliciting an antihapten antibody response to vaccination typically requires the use of constructs where multiple copies of the hapten are covalently attached to a larger carrier molecule. The carrier is required to elicit T cell help via presentation of peptide epitopes on major histocompatibility complex (MHC) class II molecules; as such, attachment to full-sized proteins, alone or in a complex, is generally used to account for the significant MHC diversity in humans. While such carrier-based vaccines have proven extremely successful, particularly in protecting against bacterial diseases, they can be challenging to manufacture, and repeated use can be compromised by pre-existing immunity against the carrier. One approach to reducing these complications is to recruit help from type I natural killer T (NKT) cells, which exhibit limited diversity in their antigen receptors and respond to glycolipid antigens presented by the highly conserved presenting molecule CD1d. Synthetic vaccines for universal use can, therefore, be prepared by conjugating haptens to an NKT cell agonist such as α-galactosylceramide (αGalCer, KRN7000). An additional advantage is that the quality of NKT cell help is sufficient to overcome the need for an extra immune adjuvant. However, while initial studies with αGalCer-hapten conjugate vaccines report strong and rapid antihapten antibody responses, they can fail to generate lasting memory. Here, we show that antibody responses to the hapten 4-hydoxy-3-nitrophenyl acetyl (NP) can be improved through additional attachment of a fusion peptide containing a promiscuous helper T cell epitope (Pan DR epitope, PADRE) that binds diverse MHC class II molecules. Such αGalCer-hapten-peptide tricomponent vaccines generate strong and sustained anti-NP antibody titers with increased hapten affinity compared to vaccines without the helper epitope. The tricomponent vaccine platform is therefore suitable for further exploration in the pursuit of efficacious antihapten immunotherapies.

Preclinical evaluation of therapeutic vaccines for chronic hepatitis B that stimulate antiviral activities of T cells and NKT cells.

Background & Aims: Liver diseases resulting from chronic HBV infection are a significant cause of morbidity and mortality. Vaccines that elicit T-cell responses capable of controlling the virus represent a treatment strategy with potential for long-term effects. Here, we evaluated vaccines that induce the activity of type I natural killer T (NKT) cells to limit viral replication and license stimulation of conventional antiviral T-cells. Methods: Vaccines were prepared by conjugating peptide epitopes to an NKT-cell agonist to promote co-delivery to antigen-presenting cells, encouraging NKT-cell licensing and stimulation of T cells. Activity of the conjugate vaccines was assessed in transgenic mice expressing the complete HBV genome, administered intravenously to maximise access to NKT cell-rich tissues. Results: The vaccines induced only limited antiviral activity in unmanipulated transgenic hosts, likely attributable to NKT-cell activation as T-cell tolerance to viral antigens is strong. However, in a model of chronic hepatitis B involving transfer of naive HBcAg-specific CD8+ T cells into the transgenic mice, which typically results in specific T-cell dysfunction without virus control, vaccines containing the targeted HBcAg epitope induced prolonged antiviral activity because of qualitatively improved T-cell stimulation. In a step towards a clinical product, vaccines were prepared using synthetic long peptides covering clusters of known HLA-binding epitopes and shown to be immunogenic in HLA transgenic mice. Predictions based on HLA distribution suggest a product containing three selected SLP-based vaccines could give >90 % worldwide coverage, with an average of 3.38 epitopes targeted per individual. Conclusions: The novel vaccines described show promise for further clinical development as a treatment for chronic hepatitis B. Impact and Implications: Although there are effective prophylactic vaccines for HBV infection, it is estimated that 350-400 million people worldwide have chronic hepatitis B, putting these individuals at significant risk of life-threatening liver diseases. Therapeutic vaccination aimed at activating or boosting HBV-specific T-cell responses holds potential as a strategy for treating chronic infection, but has so far met with limited success. Here, we show that a glycolipid-peptide conjugate vaccine designed to coordinate activity of type I NKT cells alongside conventional antiviral T cells has antiviral activity in a mouse model of chronic infection. It is anticipated that a product based on a combination of three such conjugates, each prepared using long peptides covering clusters of known HLA-binding epitopes, could be developed further as a treatment for chronic hepatitis B with broad global HLA coverage.

Physicochemical and biological characterization of synthetic phosphatidylinositol dimannosides and analogues.

Native phosphatidylinositol mannosides (PIMs), isolated from the cell wall of Mycobacterium bovis, and synthetic PIM analogues have been reported to offer a variety of immunomodulating properties, including both suppressive and stimulatory activity. While numerous studies have examined the biological activity of these molecules, the aim of this research was to assess the physicochemical properties at a molecular level and correlate these characteristics with biological activity in a mouse model of airway eosinophilia. To accomplish this, we varied the flexibility and lipophilicity of synthetic PIMs by changing the polar headgroup (inositol- vs glycerol-based core) and the length of the acyl chains of the fatty acid residues (C0, C10, C16, and C18). A series of six phosphatidylinositol dimannosides (PIM2s) and phosphatidylglycerol dimannosides (PGM2s) were synthesized and characterized in this study. Langmuir monolayer studies showed that surface pressure-area (π-A) isotherms were greatly influenced by the length of the lipid acyl chains as well as the steric hindrance and volume of the headgroups. In aqueous solution, lipidated PIM2 and PGM2 compounds were observed to self-assemble into circular aggregates, as confirmed by dynamic light scattering and transmission electron microscopic investigations. Removal of the inositol ring but retention of the three-carbon glycerol unit maintained biological activity. We found that the deacylated PGM2, which did not show self-organization, had no effect on the eosinophil numbers but did have an impact on the expansion of OVA-specific CD4(+) Vα2Vß5 T cells.

The dimethoxyphenylbenzyl protecting group: an alternative to the p-methoxybenzyl group for protection of carbohydrates.

A reliable reagent system for the cleavage of 4-(3,4-dimethoxyphenyl)benzyl (DMPBn) ethers under acidic conditions has been established. Treatment of DMPBn-protected mono- and pseudodisaccharides with TFA in anhydrous CH2Cl2 and 3,4-(methylenedioxy)toluene as a cation scavenger resulted in the selective cleavage of the DMPBn ether giving the corresponding deprotected products in moderate to high yields. Examples are reported which show that allyl, benzyl, and p-bromobenzyl ethers, esters, and glycosidic linkages are stable to these reaction conditions. The selective cleavage of allyl, p-bromobenzyl, and PMB ethers in protected carbohydrates containing DMPBn ethers are also demonstrated. This work establishes the 4-(3,4-dimethoxyphenyl)benzyl ether as an effective and robust alternative to p-methoxybenzyl as a protecting group for alcohols.

Lipid binding orientation within CD1d affects recognition of Borrelia burgorferi antigens by NKT cells.

Invariant natural killer T cells (iNKT cells) respond to CD1d-presented glycolipids from Borrelia burgdorferi, the causative agent of Lyme disease. Although mouse and human iNKT cells respond to different antigens based on subtle differences in their fatty acids, the mechanism by which fatty acid structure determines antigenic potency is not well understood. Here we show that the mouse and human CD1d present glycolipids having different fatty acids, based in part upon a difference at a single amino acid position that is involved in positioning the sugar epitope. CD1d also can bind nonantigenic lipids, however, but unexpectedly, mouse CD1d orients the two aliphatic chains of a nonantigenic lipid rotated 180 degrees, causing a dramatic repositioning of the exposed sugar. Therefore, our data reveal the biochemical basis for the high degree of antigenic specificity of iNKT cells for certain fatty acids, and they suggest how microbes could alter fatty acid biosynthesis as an immune evasion mechanism.

Syntheses and crystal structures of two di-naph-tho[2,1-d:1',2'-f][1,3]dithiepine atropisomers.

The closely related title compounds, 1-(di-naphtho-[2,1-d:1',2'-f][1,3]dithiepin-4-yl)-2,2-di-methyl-propan-1-ol, C26H24OS2, 1 and 2-(di-naphtho-[2,1-d:1',2'-f][1,3]dithiepin-4-yl)-3,3-di-methyl-butan-2-ol, C27H26OS2, 2, both comprise an atrop-isomeric binaphthyl di-thio-acetal unit substituted at the methyl-ene carbon atom with a chiral neopentyl alcohol grouping. The overall stereochemistry of the racemate in each case is defined as aS,R and aR,S. In 1, the hydroxyl group generates inversion dimers via pairwise inter-molecular O-H⋯S hydrogen bonds whereas in 2, the O-H⋯S link is intra-molecular. Weak C-H⋯π inter-actions link the mol-ecules into extended arrays in both structures.

Syntheses and crystal structure of a (2,6-diiso-propyldi-naphtho-[2,1-d:1',2'-f][1,3]dithiepin-4-yl)(phen-yl)methanol atropisomer.

The racemic title compound, C34H32OS2, comprises an atropisomeric binaphthyl di-thio-acetal substituted at the methyl-ene carbon atom with a chiral benzyl alcohol. The two naphthalene ring systems are additionally substituted at the 3,3'-position with isopropyl groups. The overall stereochemistry is defined as aS,R and aR,S. The hydroxyl group forms an intra-molecular O-H⋯S hydrogen bond to one of the sulfur atoms. The crystal structure contains weak C-H⋯π inter-actions that link the mol-ecules into extended arrays.

MAIT cells activate dendritic cells to promote TFH cell differentiation and induce humoral immunity.

Protective immune responses against respiratory pathogens, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus, are initiated by the mucosal immune system. However, most licensed vaccines are administered parenterally and are largely ineffective at inducing mucosal immunity. The development of safe and effective mucosal vaccines has been hampered by the lack of a suitable mucosal adjuvant. In this study we explore a class of adjuvant that harnesses mucosal-associated invariant T (MAIT) cells. We show evidence that intranasal immunization of MAIT cell agonists co-administered with protein, including the spike receptor binding domain from SARS-CoV-2 virus and hemagglutinin from influenza virus, induce protective humoral immunity and immunoglobulin A production. MAIT cell adjuvant activity is mediated by CD40L-dependent activation of dendritic cells and subsequent priming of T follicular helper cells. In summary, we show that MAIT cells are promising vaccine targets that can be utilized as cellular adjuvants in mucosal vaccines.

Synthesis and mass spectral characterization of mycobacterial phosphatidylinositol and its dimannosides.

A family of naturally occurring mycobacterial phosphatidylinositol (PI) and its dimannosides (PIM(2), AcPIM(2), and Ac(2)PIM(2)) that all possess the predominant natural 19:0/16:0 phosphatidyl acylation pattern were prepared to study their mass spectral fragmentations. Among these, the first synthesis of a fully lipidated PIM (i.e., (16:0,18:0)(19:0/16:0)-PIM(2)) was achieved from (±)-1,2:4,5-diisopropylidene-D-myo-inositol in 16 steps in 3% overall yield. A key feature of the strategy was extending the utility of the p-(3,4-dimethoxyphenyl)benzyl protecting group for its use at the O-3 position of inositol to allow installation of the stearoyl residue at a late stage in the synthesis. Mass spectral studies were performed on the synthetic PIMs and compared to those reported for natural PIMs identified from a lipid extract of M. bovis BCG. These analyses confirm that fragmentation patterns can be used to identify the structures of specific PIMs from the cell wall lipid extract.