Interaction of CD99 and its ligand upregulates IL-6 and TNF-α upon T cell activation

CD99 has been reported to be involved in T cell regulation. CD99 ligand involvement in the regulation of T cell activation has been postulated. In this study, recombinant CD99 proteins were produced and used as a tool for determining the role of CD99 and its ligand interaction. Recombinant CD99 proteins induced the upregulation of IL-6 and TNF-α expression, but not IFN-γ, in anti-CD3 monoclonal antibody activated T cells. The cytokine alteration was not observed in unstimulated T cells indicating the cytokine upregulation required the signal from T cell activation. The upregulation of IL-6 and TNF-α was, in addition, observed in CD3^- mononuclear cell population including monocytes and NK cells. The recombinant CD99 proteins, however, did not affect either CD25, CD69 or MHC class II expression or T cell proliferation, upon T cell activation. The CD99 ligands were demonstrated to be expressed on monocytes, NK cells and dendritic cells, but not on B and T cells. Our results indicated the presence of CD99 ligands on leukocyte surface. Interaction between CD99 and its ligands involves the regulation of cytokine production.

Association of CD99 short and long forms with MHC class I, MHC class II and tetraspanin CD81 and recruitment into immunological synapses

Background

CD99, a leukocyte surface glycoprotein, is broadly expressed in many cell types. On the cell surface, CD99 is expressed as two distinct isoforms, a long form and a short form. CD99 has been demonstrated to play a key role in several biological processes, including the regulation of T cell activation. However, the molecular mechanisms by which CD99 participates in such processes are unclear. As CD99 contains a short cytoplasmic tail, it is unlikely that CD99 itself takes part in its multi-functions. Association of CD99 with other membrane proteins has been suggested to be necessary for exerting its functions.

Results

In this study, we analyzed the association of CD99 with other cell surface molecules involved in T cell activation. We demonstrate the association of MHC class I, MHC class II and tetraspanin CD81 with CD99 molecules on the cell surface. Association of CD99 with its partners was observed for both isoforms. In addition, we determined that CD99 is a lipid raft-associated membrane protein and is recruited into the immunologic synapse during T cell activation. The implication of CD99 on T cell activation was investigated. Inhibition of anti-CD3 induced T cell proliferation by an anti-CD99 monoclonal antibody was observed.

Conclusions

We provide evidence that CD99 directly interact and form the complex with the MHC class I and II, and tetraspanin CD81, and is functionally linked to the formation of the immunologic synapse. Upon T cell activation, CD99 engagement can inhibit T cell proliferation. We speculate that the CD99-MHC-CD81 complex is a tetraspanin web that plays an important role in T cell activation.

Triggering of CD99 on monocytes by a specific monoclonal antibody regulates T cell activation

CD99, a leukocyte surface glycoprotein, has been implicated in many cellular processes including cell adhesion, cell migration and T cell activation. Our previous study demonstrated the anti-CD99 monoclonal antibody (mAb) clone MT99/3 inhibited T cell activation; however, the mechanism is unclear. In this study, we demonstrated that CD99 expressed on monocytes played a role in the inhibition of T cell activation. Anti-CD99 mAb MT99/3 downregulated the expression of costimulatory molecule CD86, but upregulated IL-6, IL-10 and TNF-α production by monocytes. The inhibitory effect of mAb MT99/3 required cell to cell contact between monocytes and lymphocytes. The soluble mediators produced by monocytes alone were insufficient to induce hypo-function of T lymphocytes. In summary, we demonstrated that ligation of CD99 on monocytes by anti-CD99 mAb MT99/3 could mediate T cell hypo-responsiveness. These findings provide the first evidence of the role of CD99 on monocytes that contributes to T cell activation.

Differential CD147 Functional Epitopes on Distinct Leukocyte Subsets

CD147, a member of the immunoglobulin (Ig) superfamily, is widely expressed in several cell types. CD147 molecules have multiple cellular functions, such as migration, adhesion, invasion, energy metabolism and T cell activation. In particular, recent studies have demonstrated the potential application of CD147 as an effective therapeutic target for cancer, as well as autoimmune and inflammatory diseases. In this study, we elucidated the functional epitopes on CD147 extracellular domains in T cell regulation using specific monoclonal antibodies (mAbs). Upon T cell activation, the anti-CD147 domain 1 mAbs M6-1E9 and M6-1D4 and the anti-CD147 domain 2 mAb MEM-M6/6 significantly reduced surface expression of CD69 and CD25 and T cell proliferation. To investigate whether functional epitopes of CD147 are differentially expressed on distinct leukocyte subsets, PBMCs, monocyte-depleted PBMCs and purified T cells were activated in the presence of anti-CD147 mAbs. The mAb M6-1E9 inhibited T cell functions via activation of CD147 on monocytes with obligatory cell-cell contact. Engagement of the CD147 epitope by the M6-1E9 mAb downregulated CD80 and CD86 expression on monocytes and IL-2, TNF-α, IFN-γ and IL-17 production in T cells. In contrast, the mAb M6-1D4 inhibited T cell function via activation of CD147 on T cells by downregulating IL-2, TNF-α and IFN-γ. Herein, we demonstrated that certain epitopes of CD147, expressed on both monocytes and T cells, are involved in the regulation of T cell activation.

The presence of membrane bound CD99 ligands on leukocyte surface

Objective

CD99, a leukocyte surface molecule, reportedly plays an important role in several cellular processes. However, the role of CD99 in T cell regulation remains unclear, as the CD99 ligand associated with T-cell regulation has not yet been identified. Our previous study showed that recombinant CD99 bound to CD99 ligands was expressed on monocytes, NK cells and dendritic cells. This interaction regulates the expression of IL-6 and TNF-α in CD3 + T cells following T cell activation. In the present study, we confirmed the presence of CD99 ligands in immune cells.

Results

A recombinant CD99-human IgG fusion protein, CD99HIgG, was produced and used to search for CD99 ligand expression in various hematopoietic cell lines. Among several cell lines, THP-1 monocytic cell line showed strong positive reaction for CD99HIgG, and CD99 and CD99 ligand complexes were pulled-down using a DTSSP cross-linker. The study demonstrated the presence of the membrane bound CD99 ligand, and CD99 ligand candidates were identified via LC–MS/MS. These results may be useful to further identify the CD99 ligands, and to fully comprehend the role of CD99 in immunoregulation.

Production of Monoclonal Antibodies against Human Trefoil Factor 3 and Development of a Modified-Sandwich ELISA for Detection of Trefoil Factor 3 Homodimer in Saliva

Background

Human trefoil factor (TFF) peptides consist of three members: TFF1, TFF2 and TFF3. TFF3 is the most abundant TFF peptide in saliva. TFF3 homodimer was suggested to be involved in apoptosis inhibition and malignancy. Determination of TFF3 homodimer expression profiles in saliva may lead to new information about oral biology and diseases. The objective of this study was to generate monoclonal antibodies (mAbs) against TFF3 and apply the produced mAbs for the establishment of ELISA for quantification of dimeric TFF3 in saliva.

Results

With our modified hybridoma technique, three hybridoma clones producing anti-TFF3 mAbs having IgG isotype were generated. The mAbs were specific for TFF3 with no cross-reactivity to other TFFs. Using the generated mAbs, a modified-sandwich ELISA with high sensitivity for the quantification of dimeric TFF3 in saliva was developed. Using this ELISA, the amount of dimeric TFF3 in saliva could be measured.

Conclusions

A modified-sandwich ELISA for the quantification of TFF3 dimeric form was established. The established ELISA will be a valuable tool for facilitating the investigation of the physiological roles and the diagnostic values of TFF3 in oral diseases. The concept of this modified-sandwich ELISA may be applied for the determination of other homodimeric peptides of interest.

Sandwich antibody-based biosensor system for identification of Mycobacterium tuberculosis complex and nontuberculous mycobacteria

Mycobacterial infection, leading to pulmonary disease, remains a world health problem. Clinical symptoms of pulmonary disease caused by Mycobacterium tuberculosis complex (MTBC) and nontuberculous mycobacteria (NTM) are very similar. A rapid method for the differentiation of MTBC and NTM infection is essential for appropriate therapy. In this study, we aim to establish an antibody-based biosensor system for the identification of MTBC and NTM infection. Monoclonal antibodies (mAbs) specific for Ag85B proteins of mycobacteria were generated and characterized. The generated anti-Ag85B mAb clones AM85B-5 and AM85B-8 reacted to Ag85B of Mycobacterium spp.; in contrast, clone AM85B-9 specifically reacted to Ag85B of MTBC. By employing the produced mAbs, single and sandwich antibody-based biosensors using bio-layer interferometry were established for determination of Ag85B proteins. The sandwich antibody-based biosensor system was demonstrated to be suitable for detection of Ag85B protein and identification of MTBC and NTM. Using anti-Ag85B mAbs AM85B-8 and AM85B-9 as immobilized antibodies on sensor chips and using mAb AM85B-5 as secondary antibody, the established sandwich antibody-based biosensor could discriminate MTBC and NTM. The developed biosensor system can be used for culture confirmation of mycobacteria and speciation to MTBC and NTM.

Overexpression of ADAM9 in oral squamous cell carcinoma

Overexpression of a disintegrin and metalloproteinase 9 (ADAM9) has been shown in various types of cancer. Some studies have reported inconclusive findings regarding chromosomal aberrations in the ADAM9-containing region and ADAM9 expression in oral cancer. Therefore, in this study, ADAM9 protein expression was determined and compared between oral squamous cell carcinoma (OSCC) and normal oral tissues, and between oral cancer cell lines and human oral keratinocytes (HOKs). In total, 34 OSCC and 10 healthy paraffin-embedded tissue sections were probed with an anti-ADAM9 antibody, and the immunohistochemical score was determined by multiplying the percentage of positively stained cells with the intensity score. Four different oral cancer and eight independent HOK cell lines were cultured, and the expression of membrane ADAM9 and active ADAM9 at 84 kDa in these cell lines was assayed by flow cytometry and western blot hybridization, respectively. The results showed that the median immunohistochemical score of ADAM9 expression in OSCC tissues was significantly greater than that in normal tissues (P<0.001). Furthermore, among OSCC cases, intense staining of ADAM9 expression was detected in well-differentiated and in moderately-differentiated OSCC; ADAM9 expression was also correlated with an increased degree of cell differentiation (r=0.557; P=0.001). Expression of membrane ADAM9 was present in 3/4 cancer cell lines. Expression of active ADAM9 varied among all the tested cell lines, but significantly higher ADAM9 expression was present in certain cancer cell lines than those in HOKs (P<0.05). In summary, ADAM9 expression is enhanced in OSCC and oral cancer cell lines, suggesting its role in the pathogenesis of oral cancer. Similar to the overexpression of ADAM9 in well-differentiated prostate cancer, high degrees of ADAM9 expression have also been observed in well-differentiated OSCC.

Antibody biosensors for the measurement and characterization of soluble CD147 molecules

BACKGROUND

Soluble CD147 (sCD147) is the shed form of membrane-bound CD147, which is involved in the regulation of cellular functions. The presence of sCD147 in body fluids is associated with several diseases.

OBJECTIVE

In this study, we aimed to establish antibody (Ab) biosensors for the simultaneous differential detection of the general and truncated forms of sCD147.

METHOD

By combining biolayer interferometry technology (BLItz) and different anti-CD147 monoclonal antibodies (mAbs) specific to different extracellular domains of the CD147 molecule, Ab-based biosensors were established to rapidly measure and characterize sCD147 isoforms.

RESULTS

Two types of Ab-biosensors, desginated the single Ab-biosensor and double Ab-biosensor, were established for the measurment and characterization of sCD147 isoforms. For the single Ab-biosensor system, monoclonal antibodies specific for CD147 domain 1 (D1) or domain 2 (D2) were immobilized on the sensor tips and used for the quantification of sCD147 using a BLItz optical interferometric biosensor. For the double Ab-biosensor system, following the single Ab-biosensor step, secondary anti-CD147 mAbs specific for each domain of the CD147 molecule were added and monitored by a BLItz biosensor. By combining the results obtained from the single Ab- and double Ab-biosensors, sCD147 isoforms including the general form (D1 linked to D2) and the truncated forms (sCD147 containing D1 or D2) could be determined.

CONCLUSIONS

This method may be a beneficial tool for the determination of sCD147 isoforms for disease diagnosis and prognosis as well as for the definition of the cellular mechanisms of the immune system.

Impact of the detection of ζ-globin chains and hemoglobin Bart's using immunochromatographic strip tests for α0-thalassemia (--SEA) differential diagnosis

α⁰-Thalassemia is an inherited hematological disorder caused by the deletion of α-globin genes. The Southeast Asian deletion (--^SEA) is the most common type of α⁰-thalassemia observed in Southeast Asian countries. Regarding WHO health policy, an effective α⁰-thalassemia screening strategy is needed to control new severe α-thalassemia cases. In this study, a monoclonal antibody panel was used to develop immunochromatographic (IC) strip tests for detecting the Hb Bart’s and ζ-globin chain. Among 195 samples, all α⁰-thalassemia traits (78 α⁰-thalassemia (--^SEA) and 4 α⁰-thalassemia (--^THAI)) had low MCV or MCH values. The sensitivity, specificity, PPV and NPV of the IC strip tests for ζ-globin and Hb Bart’s for screening α⁰-thalassemia (--^SEA) within the low MCV or MCH samples were 100%, 65.2%, 90.7%, 100% and 96.2%, 47.8%, 86.6%, 78.6%, respectively. All 4 α⁰-thalassemia (--^THAI) traits were negative for ζ-globin chains but positive for Hb Bart’s using the IC strip tests. These results led to a α⁰-thalassemia screening being proposed in which blood samples are first evaluated by MCV, MCH and Hb typing. Samples with high MCV and MCH values are excluded for the presence of the α⁰-thalassemia gene. Samples with low MCV or MCH values are assayed using the developed IC strip tests, where only samples testing positive are further assayed for α⁰-thalassemia by PCR. Patients with Hb H, EA Bart’s or EF Bart’s diseases do not need to use this IC strip assay. Thus, in this study, a simple and cost effective α⁰-thalassemia point of care test was developed.

Ligation of Na, K ATPase β3 subunit on monocytes by a specific monoclonal antibody mediates T cell hypofunction

T cells play a crucial role in orchestrating body immune responses. T cell hyperfunction, however, leads to inflammation and induction of autoimmune diseases. Understanding of T cell regulation mechanisms and successful modulation of T cell responses is beneficial in treatment of disease associated to T cell hyperresponsiveness. Our previous study indicated that monoclonal antibody (mAb) P-3E10, a mAb to Na, K ATPase β3 subunit, inhibited anti-CD3-induced PBMC proliferation. In the current study, we further investigated the mechanism of mAb P-3E10 in the induction of T cell hypofunction. We demonstrated that mAb P-3E10 decreased T cell proliferation and Th1, Th2 and Th17 cytokine production. Monocytes were the cells playing a key role in mediation of mAb P-3E10 induced T cell hypofunction. The inhibition of T cell activation by mAb P-3E10 required cell contact between monocytes and T cells. The mAb P-3E10 induced the down-expression level of MHC class II and CD86 and increased IL-6, IL-10 and TNF-α production of monocytes. We concluded that ligation of the Na, K ATPase β3 subunit on monocytes by mAb P-3E10 arbitrated T cell hypofunction. This mAb might be a promising novel immunotherapeutic antibody for the treatment of hyperresponsive T cell associated diseases.

Characterization and functional analysis of novel circulating NK cell sub-populations

Natural killer (NK) cells are innate lymphoid cells having potent cytolytic function that provide host defense against microbial infections and tumors. Using our generated monoclonal antibody (mAb), named FE-1H10, new NK cell sub-populations in peripheral blood were identified. The molecules recognized by mAb FE-1H10 were expressed on a sub-population of CD3-CD56dim NK cells. The epitope recognized by mAb FE-1H10 was demonstrated to be N-glycan and proven to be different from CD57. Upon K562 stimulation, the CD56dimFE-1H10+ NK cell sub-population exhibited significantly lower cytolytic function with low ability to degranulate and release cytolytic granules compared to the CD56dimFE-1H10- NK cell sub-population. Moreover, the CD56dimFE-1H10+ NK cells produced less IFN-γ and TNF-α than the CD56dimFE-1H10- NK cells. We demonstrated here that mAb FE-1H10 could identify two sub-populations of circulating CD56dim NK cells with different functions. Our discovery of new sub-populations of NK cells improves our understanding of NK cell biology and may lead to the development of new approaches for NK cell therapy.

A modified sandwich ELISA for accurate measurement of HbF in α-thalassemia carriers containing Hb Bart's and Hb Portland 1

Hemoglobin F (HbF) in blood lysate can be accurately measured by various methods, including immunoassay. In this study, we have produced polyclonal antibody (pAb) against HbF and established a modified sandwich-type ELISA for HbF quantification in blood lysates. The modified sandwich ELISA utilized anti-γ-globin monoclonal antibody clones Thal N/B as the capture antibody (Ab) coated on solid-phase, fluorescein isothiocyanate (FITC)-labeled pAb as the detecting Ab, and HPR-labeled anti-FITC Ab as the signal-generating Ab. By using an optimized blood lysate dilution, the HbF could be measured with no interference from hemoglobin Bart's (Hb Bart's) and hemoglobin Portland (Hb Portland 1) presented in α-thalassemia carriers. HbF levels measured by the modified sandwich ELISA were comparable to those quantified by the standard cation-exchange high performance liquid chromatography. We suggested that this modified sandwich ELISA was able to accurately measure HbF levels even in α-thalassemia carriers containing Hb Bart's and Hb Portland 1 and be an alternative method for HbF measurement.

Immunostick Test for Detecting ζ-Globin Chains and Screening of the Southeast Asian α-Thalassemia 1 Deletion

Background

Couples who carry α-thalassemia-1 deletion are at 25% risk of having a fetus with hemoglobin Bart’s hydrops fetalis. Southeast Asian deletion (−-(SEA)) is the most common type of α-thalassemia 1 among Southeast Asian populations. Thus, identification of the (−-(SEA)) α-thalassemia 1 carrier is necessary for controlling severe α-thalassemia in Southeast Asian countries.

Results

Using our generated anti ζ-globin chain monoclonal antibodies (mAbs) clones PL2 and PL3, a simple immunostick test for detecting ζ-globin chain presence in whole blood lysates was developed. The procedure of the developed immunostick test was as follows. The immunostick paddles were coated with 50 μg/mL of mAb PL2 as capture mAb, or other control antibodies. The coated immunostick was dipped into cocktail containing tested hemolysate at dilution of 1:500, 0.25 μg/mL biotin-labeled mAb PL3 and horseradish peroxidase-conjugated streptavidin at dilution of 1:1000. The immunostick was then dipped in precipitating substrate and the presence of ζ-globin chain in the tested sample was observed by the naked eye. Upon validation of the developed immunostick test with various types of thalassemia and normal subjects, 100% sensitivity and 82% specificity for detection of the (−-(SEA)) α-thalassemia-1 carriers were achieved. The mAb pre-coated immunostick can be stored at room temperature for at least 20 weeks.

Conclusion

In this study, a novel simple immunostick test for the screening of (−-(SEA)) α-thalassemia 1 carriers was presented. The developed immunostick test, within a single test, contains both positive and negative internal procedural controls.

Neutralizing antibody and T cell responses against SARS-CoV-2 variants of concern following ChAdOx-1 or BNT162b2 boosting in the elderly previously immunized with CoronaVac vaccine

Background

The existence of SARS-CoV-2 variants of concern (VOCs) in association with evidence of breakthrough infections despite vaccination resulted in the need for vaccine boosting. In elderly individuals, information on the immunogenicity of booster vaccinations is limited. In countries where the CoronaVac inactivated vaccine is the primary vaccine, the appropriate boosting regimen is not clear. Immunologic studies of the effects of booster vaccination against VOCs, particularly Delta and Omicron, following CoronaVac in elderly individuals are helpful for policy makers. In this study, we determined the immune responses against VOCs following ChAdOx-1 or BNT162b2 boosting in elderly individuals previously immunized with CoronaVac.

Results

Before boosting, the median % inhibition of neutralizing antibodies (NAbs) against the wild-type (WT), Alpha, Beta, Delta and Omicron variants in the ChAdOx-1 and BNT162b2 groups was 52.8% vs. 53.4, 36.6% vs. 39.9, 5.2% vs. 13.7, 34.3% vs. 44.9, and 20.8% vs. 18.8%, respectively. After boosting with ChAdOx-1 or BNT162b2, the % inhibition of NAbs were increased to 97.3% vs. 97.4, 94.3% vs. 97.3%, 79.9 vs. 93.7, 95.5% vs. 97.5, and 26.9% vs. 31.9% for WT, Alpha, Beta, Delta and Omicron variants, respectively. Boosting with BNT162b2 induced significantly higher NAb levels than boosting with ChAdOx-1 against the Alpha, Beta and Delta variants but not the WT and Omicron variants. NAb levels against Omicron variant were not significantly different before and after boosting with ChAdOx-1 or BNT162b2. To evaluate T-cell responses, S peptides of the WT, Alpha, Beta and Delta variants were used to stimulate T cells. Upon stimulation, the expression of IL-17A in CD8 T cells was higher in the BNT162b2 group than in the ChAdOx-1 boosting group. However, IFN-γ production in CD4 and CD8 T cells did not significantly differ under all vaccination regimens. The expression of FasL in CD4 T cells, but not CD8 T cells, was higher in the BNT162b2-boosted group.

Conclusion

Boosting with either ChAdOx-1 or BNT162b2 in CoronaVac-primed healthy elderly individuals induced high NAb production against all examined VOCs except Omicron. BNT162b2 stimulated higher NAb and some T-cell responses than ChAdOx-1. Vaccine boosting is, therefore, recommended for elderly individuals previously immunized with CoronaVac.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00279-8.

Simultaneous flow cytometric measurement of antigen attachment to phagocytes and phagocytosis

The current available assays cannot differentiate the stages of phagocytosis. We, therefore, established methods for concurrent detection of antigen attachment and engulfment by phagocyte using latex beads coated with lipopolysaccharide, rabbit IgG, and carboxyfluorescein diacetate succinimidyl ester. The generated beads were incubated with whole blood at 37°C for 1 hr and stained with PE-Cy5.5 anti-rabbit IgG antibody. By flow cytometry, attachment and phagocytic processes could be detected, simultaneously. The established method is a valuable tool for diagnosis of phagocytic disorder and study of molecules involved in phagocytosis.

The ligation of CD4 molecules, expressed on monocytes by an anti-CD4 monoclonal antibody, inhibits T cell activation and monocyte mobility

BACKGROUND

CD4, a leukocyte surface glycoprotein, is mainly expressed on CD4+ T cells, but is also expressed on monocytes. The difference in the expression level and structure of CD4 on T cells and monocytes predicts the different functions of this molecule in both cell types. Although the function of CD4 on T cells is well characterized, little is known about that expressed on primary monocytes.

OBJECTIVE

In this study, we investigated the immunoregulation function of CD4 on peripheral blood monocytes.

METHODS

Methods: CD4 molecule on monocyte was ligated by anti-CD4 monoclonal antibody (mAb), MT4/3. The effect of mAb MT4/3 on T cell proliferation, cytokine production, the expression of monocyte costimulatory molecules, monocyte migration, and macrophage differentiation were investigated. Moreover, the molecular weight of CD4 on peripheral blood monocyte was carried out by Western immunoblotting.

RESULTS

We demonstrated that mAb MT4/3 inhibited anti-CD3 induced T cell proliferation, cytokine production, and the expression of monocyte costimulatory molecules. The ligation of only CD4 on monocytes was sufficient to inhibit T cell activation. Moreover, mAb MT4/3 could inhibit monocyte migration in a transwell migration assay, but not affect the differentiation of monocytes to macrophages. Using purified primary monocytes, the molecular weight of CD4 expressed on monocytes was identified as 55 kDa.

CONCLUSIONS

The CD4 molecule expressed on monocytes might play an important role in the regulation of immune responses in both innate and adaptive immunity. Understanding the novel role of CD4 on monocytes in immunoregulation is valuable in the development of new therapeutic approaches.

Levels and durability of neutralizing antibodies against SARS-CoV-2 Omicron and other variants after ChAdOx-1 or BNT162b2 booster in CoronaVac-primed elderly individuals

The outbreak of the SARS-CoV-2 Omicron variant raised the need for vaccine boosting. We evaluated the efficiency of the third booster vaccine, ChAdOx-1 or BNT162b2, in causing a neutralizing antibody (NAb) response and its durability against the Omicron and other variants in elderly individuals previously vaccinated with 2-dose CoronaVac inactivated vaccine. After receiving 2-dose CoronaVac, only 2.2% of subjects had NAbs against the Omicron variant above the cut-off value. Four weeks after boosting, the number of subjects who had NAb levels above the cut-off values in the ChAdOx-1 and BNT162b2 vaccine boosting groups increased to 41.7% and 54.5%, respectively. However, after 12 and 24 weeks of boosting with any vaccines, NAb levels against the Omicron variant dramatically waned. Twenty-four weeks after boosting, only 2% had high levels of NAbs against the Omicron variant. Compared to other variants, the Omicron variant was less responsive to boosting vaccines. The waning rate of NAb levels for the Omicron variant was much faster than that observed in the Alpha, Beta and Delta variants. To combat the Omicron variant, the fourth booster dose is, therefore, recommended for elderly individuals.

Neutralizing antibody and T-cell responses against SARS-CoV-2 variants by heterologous CoronaVac/ChAdOx-1 vaccination in elderly subjects with chronic obstructive pulmonary disease

BACKGROUND

Data on humoral and cellular immune responses against SARS-CoV-2 after receiving heterologous CoronaVac/ChAdOx-1 (CoVac/ChAd) vaccination in subjects with chronic obstructive pulmonary disease (COPD) are still limited. Therefore, we determined the neutralizing antibody (NAb) and T-cell responses against SARS-CoV-2 wild type (WT) and variants of concern (VOCs) in COPD patients.

METHODS

The levels of NAb as well as specific CD4 and CD8 T-cell responses against SARS-CoV-2 WT and VOCs were determined in COPD patients before and after vaccination.

RESULTS

Four weeks after vaccinations, the median levels of % inhibition of NAb against SARS-CoV-2 WT, Alpha, Beta, and Delta variants were significantly higher compared to pre-vaccination. The induction of NAb against Omicron was very low compared to other variants. At four weeks after vaccination, in comparison to pre-vaccination, the increasing trend of TNF-α-, IFN-γ-, IL-4-, IL-17-, IL-10-, and FasL-producing CD4 T-cells upon stimulation with WT spike peptides were demonstrated. No difference in T-cell responses to spike peptides of Alpha, Beta, and Delta variants and their WT homologs was observed.

CONCLUSION

Heterologous CoVac/ChAd vaccine induced the production of NAb against SARS-CoV-2 WT, Alpha, Beta, and Delta variants, but low for Omicron in COPD patients. Induction of CD4 T-cell subset responses was slightly observed by this vaccine regimen.

CLINICAL TRIALS REGISTRY

This study was approved by the Clinical Trials Registry (Study ID: TCTR20210822002).

Evaluating the immune effector functions induced by humanized anti-CD99 antibody in eliminating T lymphoblastic leukemia/lymphoma cells

Monoclonal antibodies (mAbs) have emerged as targeted immunotherapies with clinical effectiveness and low adverse effects for various cancers. However, antibody drugs for treating aggressive T cell malignancies, T lymphoblastic leukemia/lymphoma (T-ALL/T-LBL), are still limited. Therefore, a potential mAb for treating T-ALL/T-LBL with minimal toxicity to normal cells needs to be developed. We have previously demonstrated that our in-house produced mouse anti-human CD99 mAb MT99/3 and its humanized version, HuMT99/3, which recognize a newly identified epitope of CD99 can induce apoptosis of T-ALL/T-LBL cells without affecting non-malignant peripheral blood cells. Nevertheless, the immune effector functions activated by HuMT99/3 against T-ALL/T-LBL cells remain unexplored. In this study, we evaluated the anticancer activities of HuMT99/3 against T-ALL/T-LBL cells via immune effector functions. T-ALL/T-LBL cell lines were used as target cells, including Jurkat E6.1, MOLT-4, and SUP-T1. The results demonstrated that HuMT99/3 could mediate potent antibody-dependent cellular cytotoxicity (ADCC) activity to kill all cell lines by activating the Fc receptor CD16 on effector cells. HuMT99/3 significantly enhanced the phagocytosis of monocytes on all three malignant T cell lines through antibody-dependent cellular phagocytosis (ADCP) activity. In addition, HuMT99/3 could activate complement to destroy T-ALL cell lines through complement-dependent cytotoxicity (CDC) activity, without affecting the T-LBL cell line and normal PBMCs. Furthermore, the mAb MT99/3 significantly inhibited tumor growth in a T-ALL xenograft model. These findings provide valuable insights into the development of monoclonal antibodies targeting CD99 as promising therapeutics for T-ALL/T-LBL treatment with minimal toxicity to normal peripheral blood cells.

Exploitation of human CD99 expressing mouse myeloma cells as immunogen for production of mouse specific polyclonal antibodies

In this study, we describe the application of a molecular biology technique for the production of mouse polyclonal antibodies (pAbs) specific to human cell surface molecules. Production of the pAb specific to the human CD99 surface molecule was used as the study model. The retroviral expression system was employed to generate human CD99 expressing mouse myeloma cells. After cell sorting and single cell cloning, a myeloma clone which stably expressed high levels of human CD99 on its surface was established. The human CD99 expressing mouse myeloma cells were then used as the immunogen for immunization of BALB/c mice. As endogenous proteins of mouse myeloma cells possess self-non-immunogenicity for BALB/c mice, after immunization, only the expressed human CD99 molecules induce antibody response. After three immunizations, high titers of mouse anti-CD99 pAbs were successfully produced. The produced pAb specifically reacted to both recombinant human CD99 and native CD99 molecules expressed on human blood cells. The established technology is simple and valuable for the production of pAbs specific to human CD99 membrane proteins which can be used for characterization of the CD99 molecule.

Optimization of culture conditions for stable expression of recombinant fc-fused human extracellular CD99 in HEK293T cells

CD99 has been demonstrated to play a key role in several biological processes, including the regulation of T-cell activation, cell adhesion, and cell migration. We have also demonstrated that CD99 and its ligands regulate proinflammatory cytokines in NK cells, monocytes and activated T cells. These data suggest CD99 as a potential therapeutic target in cancer. However, the molecular mechanisms by which CD99 and CD99 counter receptors participate in such processes are unclear. High-quality CD99 recombinant proteins produced in large amounts are essential for biological studies and clinical research. In this study, we optimized the various culture conditions for increasing amounts of recombinant protein production with good biological activity. Intracellular immunofluorescence staining was performed to identify the highly expressing CD99HIgG cells. We further investigated the culture conditions for recombinant protein production. A double antibody sandwich enzyme-linked immunosorbent assay was employed to determine the level of secreted CD99HIgG proteins in the culture supernatant of various culture conditions. Later, affinity chromatography using protein G was used to purify CD99HIgG proteins from the culture supernatant of three proper culture conditions. According to our previous report, which utilized Western blotting, the purified CD99HIgG obtained from all tested culture conditions is composed of the CD99 extracellular part fused with the human IgG Fc part in dimer form. For biological activity, the obtained CD99HIgG proteins showed the ability to ligate with the CD99 counter receptor, resulting in the induction of cytokine production.

Exploring the Biological Activity of a Humanized Anti-CD99 ScFv and Antibody for Targeting T Cell Malignancies

CD99, a type I transmembrane protein, emerges as a promising therapeutic target due to its heightened expression in T cell acute lymphoblastic leukemia (T-ALL). This characteristic renders it a potential marker for minimal residual disease detection and an appealing target for antibody-based treatments. Previous studies have revealed that a mouse monoclonal antibody, mAb MT99/3, selectively binds to CD99, triggering apoptosis in T-ALL/T-LBL cells while preserving the integrity of healthy cells. By targeting CD99, mAb MT99/3 suppresses antigen presentation and disrupts T cell functions, offering promise for addressing hyperresponsive T cell conditions. To facilitate clinical translation, we developed a humanized ScFv variant of mAb MT99/3, termed HuScFvMT99/3 in "ScFvkh" design. Structural analysis confirms its resemblance to the original antibody, and the immunoreactivity of HuScFvMT99/3 against CD99 is preserved. The fully humanized version of antibody HuMT99/3 was further engineered, exhibiting similar binding affinity at the 10-10 M level and specificity to the CD99 epitope without antigenic shift. HuMT99/3 demonstrates remarkable selectivity, recognizing both malignant and normal T cells but inducing apoptosis only in T-ALL/T-LBL cells, highlighting its potential for safe and targeted therapy.

Chimeric single-chain variable fragment-human immunoglobulin G crystallizable fragment antibody against GD2 for neuroblastoma targeted immunotherapy

Aim

The present study aims to generate chimeric mouse single-chain variable fragment (scFv) and immunoglobulin G1 (IgG1) crystallizable fragment (Fc) antibody against disialoganglioside (GD2) for the treatment of neuroblastoma (NB). The generated scFv-IgG Fc antibody, lacking first constant domain of heavy chain (CH1), is of a smaller size than the natural antibody and has anti-tumor activity.

Methods

Vector for scFv-IgG Fc antibody was constructed and scFv-IgG Fc antibody was expressed in human embryonic kidney 293T (HEK293T) cell line. Purification of scFv-IgG Fc antibody from the culture supernatant of transfected HEK293T cells was performed by Protein G affinity chromatography. The structure and binding activity of scFv-IgG Fc antibody were verified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), western blotting (WB), and immunofluorescence techniques. Anti-tumor activities by antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) were determined.

Results

Using plasmid fusion-human IgG1-Fc2 tag vector (pFUSE-hIgG1-Fc2), a plasmid vector encoding chimeric mouse scFv and hIgG1 Fc antibody against GD2 was successfully constructed. This vector was transfected into human HEK293T cells to produce scFv-IgG Fc antibody. The transfected HEK293T cells could produce chimeric scFv-IgG Fc antibody against GD2, which lacks the IgG heavy chain CH1 domain but carries CH2 and CH3 domains. The chimeric antibodies could be purified from the culture supernatant of the transfected HEK293T culture in the presence of zeocin drug. The produced GD2 scFv-IgG Fc antibodies, which are smaller in size than the intact antibody, could trigger the killing of GD2 expressed NB cell line SH-SY5Y by ADCC and ADCP mechanisms.

Conclusions

The results indicate that chimeric scFv-hIgG Fc antibody, lacking heavy chain CH1 domain, could mediate antibody induced anti-tumor activities. The small size of this type of chimeric antibody may be employed as anti-GD2 antibody for NB therapy.