Immunogenicity of Synthetic Peptides Corresponding to Flexible and Antibody-accessible Segments of Mouse Lactate Dehydrogenase (LDH)-C4

Advances in the design of new types of inhaled medicines

Inhalation of small molecule drugs has proven very efficacious for the treatment of respiratory diseases due to enhanced efficacy and a favourable therapeutic index compared with other dosing routes. It enables targeted delivery to the lung with rapid onset of therapeutic action, low systemic drug exposure, and thereby reduced systemic side effects. An increasing number of pharmaceutical companies and biotechs are investing in new modalities-for this review defined as therapeutic molecules with a molecular weight >800Da and therefore beyond usual inhaled small molecule drug-like space. However, our experience with inhaled administration of PROTACs, peptides, oligonucleotides (antisense oligonucleotides, siRNAs, miRs and antagomirs), diverse protein scaffolds, antibodies and antibody fragments is still limited. Investigating the retention and metabolism of these types of molecules in lung tissue and fluid will contribute to understanding which are best suited for inhalation. Nonetheless, the first such therapeutic molecules have already reached the clinic. This review will provide information on the physiology of healthy and diseased lungs and their capacity for drug metabolism. It will outline the stability, aggregation and immunogenicity aspects of new modalities, as well as recap on formulation and delivery aspects. It concludes by summarising clinical trial outcomes with inhaled new modalities based on information available at the end of 2021.

The sperm-specific form of lactate dehydrogenase is required for fertility and is an attractive target for male contraception (a review)

There has been a recent upsurge in the interest about contraceptive development, evidenced by the Contraceptive Special Issue of Biology of Reproduction [1], with research funding from the Male Contraceptive Initiative and the Bill and Melinda Gates Foundation. Support from the Contraceptive Research Branch of the Eunice Kennedy Shriver National Institutes of Child Health and Human Development continues with a marked change in focus in the funding announcements. This has motivated me to reflect on research, mostly from my laboratory starting in the 1960s to the present, on the development of a male contraceptive based on the sperm-specific glycolytic enzyme, lactate dehydrogenase C (LDHC4). This review considers the rationale behind this research, the development paths pursued, obstacles encountered, and the renewed interest in going forward toward development of a male contraceptive mediated by the inhibition of the sperm-specific form of LDHC. I will address how some papers published many years ago are relevant to the present goals of non-hormonal contraception and will mention about innovative technology now available that can advance this project. This review presumably will serve as an instructive guide for a research program with a focused program related to contraception. As an aside, many of the citations in this review are to most of the 26 publications in Biology of Reproduction co-authored by this investigator and collaborators from 1974 through 2020 not long after the first issue of BOR which was published in April 1969.

Study on the antifertility effects of the plasmid DNA vaccine expressing partial brLDH-C4′

Partial cDNA sequence coding forMicrotus brandti radde(Brandt’s vole) testes-specific lactate dehydrogenase (brLDH-C4) was amplified by reverse transcription-polymerase chain reaction (RT-PCR). By inserting the product into the eukaryotic expression vector pCR3.1, pCR3.1-brLDH-C4′ was obtained as the prototype of contraceptive DNA vaccine. Immunization with pCR3.1-brLDH-C4′ in BALB/c mice generated antibodies specific to purified brLDH-C4′ and native mouse LDH-C4 protein. The birth rate of the pCR3.1-brLDH-C4′ immunized mice was found to be decreased significantly (80% lower than that of those immunized with pCR3.1). Functions of the elicited antibodies in sera from pCR3.1-brLDH-C4′ inoculated mice were further explored. The results indicated that the antibodies from the mice injected with pCR3.1-brLDH-C4′ could cause the agglutination of normal sperm suspension, while the ovarian structure and the development of ovarian follicles of these mice were not impaired, which gives a possible explanation for the immunocontraceptive effects of the pCR3.1-brLDH-C4′ DNA vaccine.

Contributions of mass spectrometry to structural immunology

Mass spectrometry has made important contributions to the field of immunology in the past decade. A variety of mass spectrometric-based techniques have been applied to study the structures of macromolecules that play a vital role in the immune response. These include traditional molecular mass measurements to identify post-translational modifications and structural heterogeneity, mass mapping of proteolysis products, sequencing by tandem mass spectrometry and conformational analysis. Antigen-antibody and other immune complexes have been detected by mass spectrometry, providing an avenue to study macromolecular assemblies that are important to immune function. By virtue of the ability of mass spectrometry based techniques to analyze complex biological mixtures, mass spectrometry has also been employed to identify and sequence protein epitopes important in both the humoral and cellular immune responses. This has been achieved through a combination of immunoaffinity and mass spectrometric techniques, and the coupling of high-performance chromatographs to mass spectrometers. These approaches are important for the identification of pathogens and show promise for the early diagnosis of disease associated with viral and bacterial infection and malignancy. These investigations will enable the mechanisms associated with normal and impaired immune function to be elucidated. Mass spectrometry has been utilized to characterize the structure of peptide mimics, multiple antigenic peptides and other constructs in the design of synthetic immunogens. Information derived from these studies will aid in the development of novel therapeutics and vaccines.

Colinear synthesis of an antigen-specific B-cell epitope with a 'promiscuous' tetanus toxin T-cell epitope: a synthetic peptide immunocontraceptive

Carrier conjugation is commonly used to provide T-cell help for small, linear peptides containing antigen-specific B-cell epitopes. However, carrier conjugation is expensive, variable and often results in adverse side effects if the conjugate is administered repeatedly. To eliminate the need for carrier conjugation, we examined two synthetic peptides for their ability to elicit sustained antibody titres in female rabbits and baboons. One peptide (hC1-20) was based on the sequence of the sperm-specific isozyme of human lactate dehydrogenase (LDH-C4). This peptide stimulates helper T-cell responses. The other peptide (bC5-19:TT) was a chimera between an LDH-C4 B-cell epitope and a 'promiscuous' T-cell epitope from tetanus toxin which has been shown to bind to and stimulate many different major histocompatibility complex alleles. Both peptides were immunogenic in rabbits and baboons. The chimera elicited consistently high antibody titres and was immunogenic in 19/19 wild-caught female baboons. When 14 bC5-19:TT immunized baboons were mated, their fertility was reduced by 62% compared with controls (P < 0.02). This carrier-free construct can be incorporated into biodegradable microspheres which may provide long-term protection from pregnancy with a single dose.

Induction of native protein reactive antibodies by immunization with peptides containing linear B-cell epitopes defined by anti-porcine ZP3 beta monoclonal antibodies

To identify pertinent target epitopes for contraceptive vaccine development, rabbit polyclonal antibodies were raised against four peptides synthesized from the deduced amino acid (aa) sequence of porcine zona pellucida macromolecule ZP3 beta and coupled to diphtheria toxoid (DT). Synthetic peptides consisted of: P1, 23-37 aa; P2, 164-179 aa with an additional C-terminal cysteine; P3, 246-263 aa with an extra C-terminal cysteine; and P4, 310-321 aa residues corresponding to pZP3 beta precursor protein. Selected sequences were based upon B cell epitopes identified previously by monoclonal antibodies. Immune sera reacted with their respective peptides and DT in an ELISA, and also recognized porcine SIZP and pZP3 beta both in ELISA and Western blot and zona pellucida of porcine oocytes in an indirect immunofluorescence assay. None of the four anti-peptide sera recognized pZP3 alpha in Western blot, emphasizing the specificity of these antibodies to pZP3 beta. The anti-peptide sera, individually, failed to inhibit in vitro attachment of boar sperm to antibody treated zona encased porcine oocytes. However, combinations of immune sera against peptides such as P1 + P4, P2 + P4 and P1 + P2 + P4, did significantly inhibit porcine sperm-oocyte interaction. These results identify combinations of peptides that could potentially be used in the design of an immunocontraceptive vaccine based upon synthetic peptides corresponding to pZP3 beta or its homologues in other species.

Immune responses of chemically modified homologous LDH-C4 and their effect on fertility regulation in mice

PROBLEM

Lactate dehydrogenase-C4 (LDH-C4) is an iso-, allo- and auto-antigen of mammalian sperm. In spite of being cell specific, LDH-C4 does not induce infertility in females of homologous species after immunization. The present study examines the application of homologous LDH-C4 after chemical modifications in the immunological infertility of female mice.

METHODS

LDH-C4 from testes of LACA mice was chemically modified by interacting it with gossypol (gossy-LDH-C4) and glucosylation with lactose (Glu-LDH-C4) in vitro and evaluated for immune responses and induced immunological infertility in allogeneic Balb/c mice after inoculation through intrarectal route using A1(OH)3 as adjuvant.

RESULTS

Native LDH-C4, which elicited high antibody response after immunization with a primary (50 microgram) and three secondary doses (30 micrograms each) at an interval of 15 days each, did not reduce fertility significantly in mice. In contrast, study provides evidence that chemically modified LDH-C4 induces high infertility, since 85-100% of mice failed to conceive in two independent sets of experiments. Mice inoculated with modified LDH-C4 were associated with 2-3 fold anti-LDH-C4 antibody titre compared to antibody response elicited by native LDH-C4. Splenocytes from immunized non-pregnant mice were evaluated for polyclonal activation using Con A as mitogen. It was found that splenocytes primed with native LDH-C4 were significantly more stimulated than the non-immune control cultures. However cells primed with gossy-LDH-C4 were non-reactive to Con A and cells primed with glu-LDH-C4 were suppressed for ConA proliferation.

CONCLUSIONS

It is concluded that LDH-C4-gossypol adduct offers a potential application in the induction of infertility of homologous species in marked contrast to native LDH-C4. Application of A1(OH)3 as adjuvant in the induction of immune response through intra-rectal route has been suggested.

Human centrosomal epitope is shared specifically with human lactate dehydrogenase-B isozyme

A rabbit serum (0013) used to identify pericentriolar proteins from isolated centrosomes (Gosti-Testu, F., Marty, M.C., Berges, J., Maunoury, R. and Bornens, M. (1986) EMBO J. 5, 2545-2550) was shown also to react through the same epitope with several non-centrosomal proteins including a major 36 kDa cytosolic antigen. This protein was identified to be human lactate dehydrogenase and the co-distribution of 0013 epitope on the centrosomal protein and on lactate dehydrogenase (LDH) was shown to be specific for human cells (Gosti, F., Marty, M.C., Courvalin, J.C., Maunoury, R. and Bornens, M. (1987) Proc. Natl. Acad. Sci. USA 84, 1000-1004). Human hepatic cells constitute, so far, the only exception to this co-distribution rule. By using this cell type which expresses only the LDH-A4 isozyme, we demonstrate that 0013 epitope is specific for the human LDH-B subunit, making serum 0013 the strongest anti-LDH-B available so far. The evolutionary and physiological significance of this situation is discussed.

Immunogenicity of peptides having pre-determined alpha-helical and alpha-alpha fold topologies

A panel of three synthetic peptides based on the 310-327 region of mouse LDH-C4 was used to examine the effect of peptide conformation on immunogenicity. The peptides, without prior conjugation to carrier molecules, were injected into outbred mice and the antisera were assayed for peptide- and LDH-C4-reactive antibodies by ELISA. An 18-residue random coil peptide (alpha N) and an 18-residue amphipathic alpha-helix peptide (alpha 1) were weakly immunogenic. A conformationally stable 40-residue alpha-alpha fold peptide (alpha 3) was highly immunogenic. The antibodies elicited by alpha 3 reacted strongly with the native molecule by ELISA. Solution-phase binding assays were used to further characterize the specificity of the sera from two mice immunized with alpha 3. Antibodies from one of the mice appeared to recognize the helical portion of the peptides, while antibodies from the other mouse reacted only with the immunogen and may be specific for the non-natural beta bend residues or possibly a topographic determinant peculiar to the anti-parallel helices. Serum from neither mouse was able to recognize the native molecule in solution. Peptides intended to mimic topographic determinants for the purpose of synthetic vaccine development may have to be more complex than those used in this study in order to induce high-affinity antibodies capable of exerting a significant biological effect.

Peptide immunogen mimicry of a protein-specific structural epitope on human choriogonadotropin

It is a challenge to construct synthetic immunogens that elicit antibodies (Abs) both directed to conformational epitopes and specific for a complex protein like human choriogonadotropin (hCG). A monoclonal antibody specific for hCG bound to regions around Lys45 of the alpha subunit (hCG alpha) and Asp112 of the beta subunit (hCG beta). A peptide comprising residues 46 to 55 of hCG alpha and residues 106 to 116 of hCG beta elicited Abs in rabbits that were directed to a discontinuous epitope and were specific for hCG. These Abs inhibited the binding of hCG to its receptor. Thus, a synthetic immunogen can mimic a conformational-specific epitope and can be useful for vaccine development.

Synthesis and biophysical characterization of engineered topographic immunogenic determinants with alpha alpha topology

Model peptides with predetermined secondary, tertiary, and quaternary conformation have been successfully designed, synthesized, and characterized in an attempt to mimic the three-dimensional structure of an antigenic determinant. This work is a continuing effort to map the antigenic structure of the protein antigen lactate dehydrogenase C4 (LDH-C4) to develop a contraceptive vaccine. A putative topographic determinant with alpha alpha topology which associates into four-helix bundles was designed on the basis of the framework model of protein folding. An idealized amphiphilic 18-residue sequence (alpha 1) and a 40-residue alpha alpha fold (alpha 3) have been shown to form stable 4-helix structures in solution with a free energy of association on the order of -20.8 kcal/mol (tetramerization of alpha 1) and -7.8 kcal/mol (dimerization of alpha 3). Both alpha 1 and alpha 3 form stable monolayers at the air-water interface. The CD spectra of Langmuir-Blodgett monolayers are characteristically alpha-helical. Both CD and FTIR spectroscopic studies reval a high degree of secondary structure. The SAXS data strongly suggest that the helices are arranged in a four-helix bundle since the radius of gyration of 17.2 A and the vector distribution function are indicative of a prolate ellipsoid of axial dimensions and molecular weight appropriate for the four-helix bundle. The major contribution to the formation and stabilization of alpha 1 and alpha 3 is believed to be hydrophobic interaction between the amphiphilic alpha-helices. The displayed heptad repeat, helix dipole, ion pairs, and the loop sequence may have also contributed to the overall stability and antiparallel packing of the helices. A detailed structural analysis of a relevant topographic immunogenic determinant will elucidate the nature of antigen-antibody interactions as well as provide insight into protein folding intermediates.