Comparative in vitro and in vivo assessment of toxin neutralization by anti-tetanus toxin monoclonal antibodies

Maternal Helminth Infection Causes Dysfunctional B Cell Development in Male Offspring

Infections during pregnancy are known to trigger alterations in offspring immunity, often leading to increased disease susceptibility. Maternal helminth infections correlate with lower Ab titers to certain childhood immunizations and putative decreased vaccine efficacy. The mechanisms that underlie how maternal infection blunts offspring humoral responses are unclear. Using our murine model of maternal schistosomiasis, we found that maternal helminth infection decreases the germinal center response of all offspring to tetanus immunization. However, only male offspring have defects in memory B cell and long-lived plasma cell generation. We found this sex-specific aberration begins during B cell development within the bone marrow via alteration of the IL-7 niche and persists throughout antigenic activation in the germinal center in the periphery. Critically, these defects in males are cell intrinsic, persisting following adoptive transfer to control male pups. Together, these data show that maternal infections can alter both the bone marrow microenvironment and the development of B lymphocytes in a sex-specific manner. This study correlates maternal infection induced defects in early life B cell development with ineffective Ab responses after vaccination.

Advances in optical molecular imaging for neural visualization

Iatrogenic nerve injury is a significant complication in surgery, which can negatively impact patients' quality of life. Currently, the main clinical neuroimaging methods, such as computed tomography, magnetic resonance imaging, and high-resolution ultrasonography, do not offer precise real-time positioning images for doctors during surgery. The clinical application of optical molecular imaging technology has led to the emergence of new concepts such as optical molecular imaging surgery, targeted surgery, and molecular-guided surgery. These advancements have made it possible to directly visualize surgical target areas, thereby providing a novel method for real-time identification of nerves during surgery planning. Unlike traditional white light imaging, optical molecular imaging technology enables precise positioning and identifies the cation of intraoperative nerves through the presentation of color images. Although a large number of experiments and data support its development, there are few reports on its actual clinical application. This paper summarizes the research results of optical molecular imaging technology and its ability to realize neural visualization. Additionally, it discusses the challenges neural visualization recognition faces and future development opportunities.

Molecular correlates of vaccine-induced protection against typhoid fever

BACKGROUNDTyphoid fever is caused by the Gram-negative bacterium Salmonella enterica serovar Typhi and poses a substantial public health burden worldwide. Vaccines have been developed based on the surface Vi-capsular polysaccharide of S. Typhi; these include a plain-polysaccharide-based vaccine, ViPS, and a glycoconjugate vaccine, ViTT. To understand immune responses to these vaccines and their vaccine-induced immunological protection, molecular signatures were analyzed using bioinformatic approaches.METHODSBulk RNA-Seq data were generated from blood samples obtained from adult human volunteers enrolled in a vaccine trial, who were then challenged with S. Typhi in a controlled human infection model (CHIM). These data were used to conduct differential gene expression analyses, gene set and modular analyses, B cell repertoire analyses, and time-course analyses at various post-vaccination and post-challenge time points between participants receiving ViTT, ViPS, or a control meningococcal vaccine.RESULTSTranscriptomic responses revealed strong differential molecular signatures between the 2 typhoid vaccines, mostly driven by the upregulation in humoral immune signatures, including selective usage of immunoglobulin heavy chain variable region (IGHV) genes and more polarized clonal expansions. We describe several molecular correlates of protection against S. Typhi infection, including clusters of B cell receptor (BCR) clonotypes associated with protection, with known binders of Vi-polysaccharide among these.CONCLUSIONThe study reports a series of contemporary analyses that reveal the transcriptomic signatures after vaccination and infectious challenge, while identifying molecular correlates of protection that may inform future vaccine design and assessment.TRIAL REGISTRATIONClinicalTrials.gov NCT02324751.

High-Throughput IgG Epitope Mapping of Tetanus Neurotoxin: Implications for Immunotherapy and Vaccine Design

Tetanus is an acute, fatal disease caused by exotoxins released from Clostridium tetani during infections. A protective humoral immune response can be induced by vaccinations with pediatric and booster combinatorial vaccines that contain inactivated tetanus neurotoxin (TeNT) as a major antigen. Although some epitopes in TeNT have been described using various approaches, a comprehensive list of its antigenic determinants that are involved with immunity has not been elucidated. To this end, a high-resolution analysis of the linear B-cell epitopes in TeNT was performed using antibodies generated in vaccinated children. Two hundred sixty-four peptides that cover the entire coding sequence of the TeNT protein were prepared in situ on a cellulose membrane through SPOT synthesis and probed with sera from children vaccinated (ChVS) with a triple DTP-vaccine to map continuous B-cell epitopes, which were further characterized and validated using immunoassays. Forty-four IgG epitopes were identified. Four (TT-215-218) were chemically synthesized as multiple antigen peptides (MAPs) and used in peptide ELISAs to screen post-pandemic DTP vaccinations. The assay displayed a high performance with high sensitivity (99.99%) and specificity (100%). The complete map of linear IgG epitopes induced by vaccination with inactivated TeNT highlights three key epitopes involved in the efficacy of the vaccine. Antibodies against epitope TT-8/G can block enzymatic activity, and those against epitopes TT-41/G and TT-43/G can interfere with TeNT binding to neuronal cell receptors. We further show that four of the epitopes identified can be employed in peptide ELISAs to assess vaccine coverage. Overall, the data suggest a set of select epitopes to engineer new, directed vaccines.

Preparation and characterization of a neutralizing murine monoclonal antibody against tetanus toxin

After Clostridium tetani infects the human body, it propagates under anaerobic conditions and produces tetanus neurotoxin (TeNT). TeNT can affect the central nervous system, inhibit the release of neurotransmitters, and result in respiratory failure, which are the root causes of death in tetanus patients. Identifying monoclonal antibodies (mAbs) targeting TeNT with neutralizing activity is urgently needed for the prevention and treatment of tetanus infection. In this study, through immunizing BALB/c mice with tetanus toxoid (TT), we obtained six positive hybridoma cell lines (1A7, 2C7, 3A7, 3H4, 4C1, and 4E12). Antibody isotyping showed that the antibodies are all of the IgG1/κ subclass. Ascites fluid was prepared by allogeneic ascites induction and the antibodies were purified through protein G affinity chromatography columns. Purities of the produced murine mAbs were all greater than 95%. All six antibodies bound to linear epitopes, among which 3A7 bound to the TeNT/L domain and the other five antibodies bound to the TeNT/Hc domain. Moreover, the affinity constants of these six antibodies against the antigen were all in the nanomolar range, and the affinity of 4E12 antibody reached the picomolar range. Results from toxin-neutralization assays in mice showed that 2C7 antibody delayed animal death, while 1A7, 3A7, 3H4, and 4E12 antibodies conferred partial protection. Additionally, 4C1 antibody offered complete protection, as 200 μg of 4C1 antibody fully protected against toxin challenge with 10 LD₅₀ of TeNT and had a window period of 1 h. Antibody epitope grouping results revealed that the binding epitopes of 4C1 antibody were different from those of the other five antibodies. When 4C1 antibody was used in combination with another antibody, the neutralizing activities of antibodies were all evidently enhanced. Specifically, 4C1 combined with 3A7 antibody led to the greatest improvement in neutralizing activities, and 20 μg antibodies total (10 + 10 μg) fully protected against toxin challenge with 10 LD₅₀. When 4E12, 3A7, and 4C1 antibodies were used in combination, 18 μg antibodies total (6 + 6 + 6 μg) completely neutralized 10 LD₅₀ toxin. The present study derived murine mAbs with neutralizing activities and laid the foundation for follow-up therapeutic drug development for TeNT poisoning as well as establishment of TeNT detection methods.

Neutralization of tetanus toxin by a novel chimeric monoclonal antibody

PURPOSE

Tetanus is a life-threatening disease characterized by muscle spasm caused by neurotoxin of Clostridium tetani. Given the current passive immunotherapy of tetanus with human anti-toxin polyclonal antibodies (PAbs) and the limitations of such preparations, neutralizing monoclonal antibodies (MAbs), especially chimeric or human antibodies with reduced immunogenicity might be considered as an alternative source.

METHODS

A mouse-human chimeric MAb, designated c-1F2C2, was generated and its binding specificities to various recombinant fragments of tetanus toxin, generated in E. coli, were determined. In vivo toxin neutralizing activity of c-1F2C2 was evaluated and compared with that of a commercially available human anti-toxin PAb in a mouse model. The possible mechanisms of toxin neutralizing activity of c-1F2C2 were investigated by assessing its inhibitory effects on toxin receptors binding, including GT1b ganglioside receptor and those expressed on PC12 cells.

RESULTS

In vivo neutralizing assay showed that c-1F2C2 was able to protect mice against tetanus toxin with an estimated potency of 7.7 IU/mg comparing with 1.9 IU/mg of the commercial human anti-toxin PAb for 10 MLD toxin and 10 IU/mg versus 1.9 IU/mg of the PAb for 2.5 MLD toxin. c-1F2C2 recognized fragment C of the toxin, which is responsible for binding of the toxin to its receptor on neuronal cells. Accordingly, the chimeric MAb partially prevented the toxin from binding to its receptors on PC12 cells (37% inhibition).

CONCLUSION

The chimeric MAb c-1F2C2 displayed similar structural and functional characteristics compared to its murine counterpart and might be useful for passive immunotherapy of tetanus.

Therapeutic effect of CT-P59 against SARS-CoV-2 South African variant

The global circulation of newly emerging variants of SARS-CoV-2 is a new threat to public health due to their increased transmissibility and immune evasion. Moreover, currently available vaccines and therapeutic antibodies were shown to be less effective against new variants, in particular, the South African (SA) variant, termed 501Y.V2 or B.1.351. To assess the efficacy of the CT-P59 monoclonal antibody against the SA variant, we sought to perform as in vitro binding and neutralization assays, and in vivo animal studies. CT-P59 neutralized B.1.1.7 variant to a similar extent as to wild type virus. CT-P59 showed reduced binding affinity against a RBD (receptor binding domain) triple mutant containing mutations defining B.1.351 (K417N/E484K/N501Y) also showed reduced potency against the SA variant in live virus and pseudovirus neutralization assay systems. However, in vivo ferret challenge studies demonstrated that a therapeutic dosage of CT-P59 was able to decrease B.1.351 viral load in the upper and lower respiratory tracts, comparable to that observed for the wild type virus. Overall, although CT-P59 showed reduced in vitro neutralizing activity against the SA variant, sufficient antiviral effect in B.1.351-infected animals was confirmed with a clinical dosage of CT-P59, suggesting that CT-P59 has therapeutic potential for COVID-19 patients infected with SA variant.

A novel single-domain antibody multimer that potently neutralizes tetanus neurotoxin

Tetanus antitoxin, produced in animals, has been used for the prevention and treatment of tetanus for more than 100 years. The availability of antitoxins, ethical issues around production, and risks involved in the use of animal derived serum products are a concern. We therefore developed a llama derived single-domain antibody (VHH) multimer to potentially replace the conventional veterinary product. In total, 28 different tetanus neurotoxin (TeNT) binding VHHs were isolated, 14 of which were expressed in yeast for further characterization. Four VHH monomers (T2, T6, T15 and T16) binding TeNT with high affinity (KD < 1 nM), covering different antigenic domains as revealed by epitope binning, and including 3 monomers (T6, T15 and T16) that inhibited TeNT binding to neuron gangliosides, were chosen as building blocks to generate 11 VHH multimers. These multimers contained either 1 or 2 different TeNT binding VHHs fused to 1 VHH binding to either albumin (A12) or immunoglobulin (G13) to extend serum half-life in animals. Multimers consisting of 2 TeNT binding VHHs showed more than a 10-fold increase in affinity (KD of 4-23 pM) when compared to multimers containing only one TeNT binding VHH. The T6 and T16 VHHs showed synergistic in vivo TeNT neutralization and, when incorporated into a single VHH trimer (T6T16A12), they showed a very high TeNT neutralizing capacity (1,510 IU/mg).

Structural basis of tetanus toxin neutralization by native human monoclonal antibodies

Four potent native human monoclonal antibodies (mAbs) targeting distinct epitopes on tetanus toxin (TeNT) are isolated with neutralization potency ranging from approximately 17 mg to 6 mg each that are equivalent to 250 IU of human anti-TeNT immunoglobulin. TT0170 binds fragment B, and TT0069 and TT0155 bind fragment AB. mAb TT0067 binds fragment C and blocks the binding of TeNT to gangliosides. The co-crystal structure of TT0067 with fragment C of TeNT at a 2.0-Å resolution demonstrates that mAb TT0067 directly occupies the W pocket of one of the receptor binding sites on TeNT, resulting in blocking the binding of TeNT to ganglioside on the surface of host cells. This study reveals at the atomic level the mechanism of action by the TeNT neutralizing antibody. The key neutralization epitope on the fragment C of TeNT identified in our work provides the critical information for the development of fragment C of TeNT as a better and safer tetanus vaccine.

Contribution of Fc fragment of monoclonal antibodies to tetanus toxin neutralization

BACKGROUND

Monoclonal antibodies (MAbs) against neurotoxin of Clostridium tetani are considered as a novel source of immunoglobulins for passive immunotherapy of tetanus. Toxin neutralization is classically attributed to the Fab and F(ab')2 fragments of antibodies. Herein, we generated Fab and F(ab')2 fragments of three toxin neutralizing mouse MAbs and compared their neutralizing activities to those of their intact molecules.

METHODS

Fab and F (ab')2 fragments of the antibodies were generated by papain and pepsin digestions, respectively, and their toxin neutralizing activities were compared with those of the intact antibodies in an in vivo toxin neutralization assay.

RESULTS

While low doses of the intact MAbs were able to fully protect the mice against tetanus toxin, none of the mice which received Fab or F(ab')2 fragments survived until day 14, even at the highest administered dose. All mice receiving human polyclonal anti-tetanus immunoglobulin or their fragments were fully protected.

CONCLUSION

Reduction in toxin neutralization activities of Fab and F(ab')2 fragments of our MAbs seems to be influenced by their Fc regions. Steric hindrance of the Fc region on the receptor-binding site of the toxin may explain the stronger neutralization of the toxin by the intact MAbs in comparison to their fragments.

Epitope Mapping of Tetanus Toxin by Monoclonal Antibodies: Implication for Immunotherapy and Vaccine Design

Tetanus as a life-threatening disease is characterized by muscle spasm. The disease is caused by the neurotoxin of Clostridium tetani. Active form of tetanus neurotoxin is composed of the light chain (fragment A) and the heavy chain. Fragment A is a zinc metalloprotease, which cleaves the neuronal soluble N-ethylmaleimide-sensitive attachment receptor (SNARE) protein, leading to the blockade of inhibitory neurotransmitter release and subsequent generalized muscular spasm. Two functional domains of the heavy chain are fragment C, which is required for neuronal cell binding of the toxin and subsequent endocytosis into the vesicles, and fragment B, which is important for fragment A translocation across the vesicular membrane into the neuronal cytosol. Currently, polyclonal immunoglobulins against tetanus neurotoxin obtained from human plasma of hyper-immunized donors are utilized for passive immunotherapy of tetanus; however, these preparations have many disadvantages including high lot-to-lot heterogeneity, possibility of transmitting microbial agents, and the adverse reactions to the other proteins in the plasma. Neutralizing anti-tetanus neurotoxin monoclonal antibodies (MAbs) lack these drawbacks and could be considered as a suitable alternative for passive immunotherapy of tetanus. In this review, we provide an overview of the literature discussing epitope mapping of the published neutralizing MAbs against tetanus toxin.

In silico rational design of a novel tetra-epitope tetanus vaccine with complete population coverage using developed immunoinformatics and surface epitope mapping approaches

Presentation of many unwanted epitopes within tetanus toxoid vaccine to lymphocyte clones may lead to production of many unwanted antibodies. Moreover an ideal vaccine must cover all individuals in a population that is dependent to the kinds of human leukocyte antigen alleles. Concerning these issues, our study was aimed to in silico design of a multi-epitope tetanus vaccine (METV) in order to improve population coverage and protectivity of tetanus vaccine as well as reduction of complications. Concerning these issues, a novel rational filtration was implemented to design a novel METV using immunoinformatics and surface epitope mapping approaches. Prediction of epitopes for tetanus toxin was performed in the candidate country in which the frequency had been gathered from almost all geographical distributions. The most strong binder epitopes for major histocompatibility complex class II were selected and among them the surface epitopes of native toxin were selected. The population coverage of the selected epitopes was estimated. The final candidate epitopes had highly population coverage. Molecular docking was performed to prediction of binding affinity of our candidate epitopes to the HLA-DRB1 alleles. At first, 680 strong binder epitopes were predicted. Among them 11 epitopes were selected. Finally, 4 epitopes had the most population coverage and suggested as a tetra-epitope tetanus vaccine. 99.41% of inessential strong binders were deleted using our tree steps filtration. HLA-DP had the most roles in epitope presentation. Molecular docking analysis proved the strong binding affinity of candidate epitopes to the HLA-DRB1 alleles. In conclusion, we theoretically reduced 99.41% of unwanted antibodies using our novel filtration strategies. Our tetra-epitope tetanus vaccine showed 100% population coverage in the candidate country. Furthermore, it was demonstrated that HLA-DP and HLA-DQ had more potential in epitope presentation in comparison to HLA-DRB1.

An oligoclonal combination of human monoclonal antibodies able to neutralize tetanus toxin in vivo

The use of antibody-based therapy to treat a variety of diseases and conditions is well documented. The use of antibodies as an antidote to treat tetanus infections was one of the first examples of immunotherapy and remains the standard of care for cases involving potential infections. Plasma-derived immunoglobulins obtained from human or horse pose risks of infection from undetectable emergent viruses or may cause anaphylaxis. Further, there is a lack of consistency between lots. In the search for new formulations, we obtained a series of clonally related human monoclonal antibodies (mAbs) derived from B cells sorted from donors that presented anti-tetanus neutralizing titers. Donors were revaccinated prior to blood collection. Different strategies were used for single-cell sorting, since it was challenging to identify cells at a very low frequency: memory B cell sorting using fluorescent-labeled tetanus toxoid and toxin as baits, and plasmablast sorting done shortly after revaccination. Screening of the recombinant mAbs with the whole tetanus toxin allowed us to select candidates with therapeutic potential, since mAbs to different domains can contribute additively to the neutralizing effect. Because of selective binding to different domains, we tested mAbs individually, or in mixtures of two or three, in the neutralizing in vivo assay specified by Pharmacopeia for the determination of polyclonal hyperimmune sera potency. An oligoclonal mixture of three human mAbs completely neutralized the toxin injected in the animals, signaling an important step for clinical mAb development.

Cooperative binding of anti-tetanus toxin monoclonal antibodies: Implications for designing an efficient biclonal preparation to prevent tetanus toxin intoxication

Oligoclonal combinations of several monoclonal antibodies (MAbs) are being considered for the treatment of various infectious pathologies. These combinations are less sensitive to antigen structural changes than individual MAbs; at the same time, their characteristics can be more efficiently controlled than those of polyclonal antibodies. The main goal of this study was to evaluate the binding characteristics of six biclonal equimolar preparations (BEP) of tetanus toxin (TeNT)-specific MAbs and to investigate how the MAb combination influences the BEPs' protective capacity. We show that a combination of TeNT-specific MAbs, which not only bind TeNT but also exert positive cooperative effects, results in a BEP with superior binding characteristics and protective capacity, when compared with the individual component MAbs. Furthermore, we show that a MAb with only partial protective capacity but positive effects on the binding of the other BEP component can be used as a valuable constituent of the BEP.

Identification of a Tetanus Toxin Specific Epitope in Single Amino Acid Resolution

Vaccinations are among the most potent tools to fight infectious diseases. However, cross-reactions are an ongoing problem and there is an urgent need to fully understand the mechanisms of the immune response. For the development of a methodological workflow, the linear epitopes in the immune response to the tetanus toxin is investigated in sera of 19 vaccinated Europeans applying epitope mapping with peptide arrays. The most prominent epitope, appearing in nine different sera (₉₂₃ IHLVNNESSEVIVHK₉₃₇ ), is investigated in a substitution analysis to identify the amino acids that are crucial for the binding of the corresponding antibody species - the antibody fingerprint. The antibody fingerprints of different individuals are compared and found to be strongly conserved (₉₂₉ ExxEVIVxK₉₃₇ ), which is astonishing considering the randomness of their development. Additionally, the corresponding antibody species is isolated from one serum with batch chromatography using the amino acid sequence of the identified epitope and the tetanus specificity of the isolated antibody is verified by ELISA. Studying antibody fingerprints with peptide arrays should be transferable to any kind of humoral immune response toward protein antigens. Furthermore, antibody fingerprints have shown to be highly disease-specific and, therefore, can be employed as reliable biomarkers enabling the study of cross-reacting antigens.

The Preparation and Identification of a Monoclonal Antibody against Domoic Acid and Establishment of Detection by Indirect Competitive ELISA

Domoic acid (DA) is a potent toxin, marine biotoxin, and primarily produced by Pseudo-nitzschia. The DA hapten was coupled with bovine serum albumin (BSA), and ovalbumin (OVA) as carrier proteins. DA-BSA conjugate was used as immunogen and DA-OVA as coating antigen. Cell fusion between spleen cells and sp2/0 myeloma cells developed 1C3 hybridoma clone producing 1C3 monoclonal antibody (mAb). Hybridoma was injected into the mice to produce ascites, and further purified by caprylic acid/ammonium sulfate method. The mAb was of IgG3 subclass, and was specific to DA with high affinity (2.5 × 10⁸ L/mol). Moreover, western blot exhibited significant specificity to the DA antigens. Indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) showed DA working range of 0.006–0.2 ng/mL. The IC₅₀ was 0.03 ng/mL with low limit of detection (LOD) of 0.006 ng/mL. Average DA recovery from spiked shellfish extract was 100.56 ± 2.8% with the coefficient variation of 0.01–0.1%. Hence, mAb producing 1C3 hybridoma was successfully developed and could be used to detect DA in contaminated samples.

Tetanus Neurotoxin Neutralizing Antibodies Screened from a Human Immune scFv Antibody Phage Display Library

Tetanus neurotoxin (TeNT) produced by Clostridiumtetani is one of the most poisonous protein substances. Neutralizing antibodies against TeNT can effectively prevent and cure toxicosis. Using purified Hc fragments of TeNT (TeNT-Hc) as an antigen, three specific neutralizing antibody clones recognizing different epitopes were selected from a human immune scFv antibody phage display library. The three antibodies (2-7G, 2-2D, and S-4-7H) can effectively inhibit the binding between TeNT-Hc and differentiated PC-12 cells in vitro. Moreover, 2-7G inhibited TeNT-Hc binding to the receptor via carbohydrate-binding sites of the W pocket while 2-2D and S-4-7H inhibited binding of the R pocket. Although no single mAb completely protected mice from the toxin, they could both prolong survival when challenged with 20 LD₅₀s (50% of the lethal dose) of TeNT. When used together, the mAbs completely neutralized 1000 LD₅₀s/mg Ab, indicating their high neutralizing potency in vivo. Antibodies recognizing different carbohydrate-binding pockets could have higher synergistic toxin neutralization activities than those that recognize the same pockets. These results could lead to further production of neutralizing antibody drugs against TeNT and indicate that using TeNT-Hc as an antigen for screening human antibodies for TeNT intoxication therapy from human immune antibody library was convenient and effective.

Monoclonal Antibody Combinations that Present Synergistic Neutralizing Activity: A Platform for Next-Generation Anti-Toxin Drugs

Monoclonal antibodies (MAbs) are among the fastest-growing therapeutics and are being developed for a broad range of indications, including the neutralization of toxins, bacteria and viruses. Nevertheless, MAbs potency is still relatively low when compared to conventional polyclonal Ab preparations. Moreover, the efficacy of an individual neutralizing MAb may significantly be hampered by the potential absence or modification of its target epitope in a mutant or subtype of the infectious agent. These limitations of individual neutralizing MAbs can be overcome by using oligoclonal combinations of several MAbs with different specificities to the target antigen. Studies conducted in our lab and by others show that such combined MAb preparation may present substantial synergy in its potency over the calculated additive potency of its individual MAb components. Moreover, oligoclonal preparation is expected to be better suited to compensating for reduced efficacy due to epitope variation. In this review, the synergistic neutralization properties of combined oligoclonal Ab preparations are described. The effect of Ab affinity, autologous Fc fraction, and targeting a critical number of epitopes, as well as the unexpected contribution of non-neutralizing clones to the synergistic neutralizing effect are presented and discussed.

Correlation between ToBI test and in vivo titration for diphtheria and tetanus

Alternatives to animal testing for quality control of biologicals have been a goal since 1959. Instituto Butantan has been developing such methods for quality control of biologicals for human use (vaccines and hyperimmune equine sera) for the last 13 years. In this paper we compare the modified ToBI test and the in vivo seroneutralization test to assess immunogenicity of diphtheria and tetanus vaccines and hyperimmune sera. Data from the last 10 years were statistically analyzed to compare the results for in vivo and in vitro titrations (diphtheria, n = 525 and tetanus, n = 455). The agreement between the tests depended on the serum titer range. For both diphtheria and tetanus components, the correlation and concordance coefficient was higher as the serum titer increased. Overall, the in vitro/in vivo titer ratio did not vary systematically over the range of measurements. These results indicate that although the in vitro ToBI test is not completely able to replace the in vivo serum titration, it is a useful tool to guide the tests during the production process, which can reduce the number of animals used for lot release.