Crimean-Congo Hemorrhagic Fever Survivors Elicit Protective Non-Neutralizing Antibodies that Target 11 Overlapping Regions on Viral Glycoprotein GP38

Crimean-Congo hemorrhagic fever virus can cause lethal disease in humans yet there are no approved medical countermeasures. Viral glycoprotein GP38, unique to Nairoviridae, is a target of protective antibodies, but extensive mapping of the human antibody response to GP38 has not been previously performed. Here, we isolated 188 GP38-specific antibodies from human survivors of infection. Competition experiments showed that these antibodies bind across five distinct antigenic sites, encompassing eleven overlapping regions. Additionally, we reveal structures of GP38 bound with nine of these antibodies targeting different antigenic sites. Although GP38-specific antibodies were non-neutralizing, several antibodies were found to have protection equal to or better than murine antibody 13G8 in two highly stringent rodent models of infection. Together, these data expand our understanding regarding this important viral protein and inform the development of broadly effective CCHFV antibody therapeutics.

Long-term Sudan virus Ebola survivors maintain multiple antiviral defense mechanisms

BACKGROUND

The critical issues of sustained memory immunity following ebolavirus disease among long-term survivors (EVD) are still unclear.

METHODS

Here, we examine virus-specific immune and inflammatory responses in 12 Sudan virus (SUDV) long-term survivors from Uganda's 2000-1 Gulu outbreak, 15 years after recovery following in vitro challenge. Total RNA from isolated SUDV-stimulated and unstimulated PBMCs was extracted and analyzed. Matched serum samples were also collected to determine SUDV IgG levels and functionality.

RESULTS

We detected persistent humoral (58%, 7 of 12) and cellular (33%, 4 of 12) immune responses in SUDV long-term survivors and identified critical molecular mechanisms of innate and adaptive immunity. Gene expression in immune pathways, the IFN signaling system, antiviral defense response, and activation and regulation of T- and B-cell responses were observed. SUDV long-term survivors also maintained robust virus-specific IgG antibodies capable of polyfunctional responses, including neutralizing and innate Fc effector functions.

CONCLUSIONS

Data integration identified significant correlations among humoral and cellular immune responses and pinpointed a specific innate and adaptive gene expression signature associated with long-lasting immunity. This could help identify natural and vaccine correlates of protection against ebolavirus disease.

Protective neutralizing antibodies from human survivors of Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever virus (CCHFV) is a World Health Organization priority pathogen. CCHFV infections cause a highly lethal hemorrhagic fever for which specific treatments and vaccines are urgently needed. Here, we characterize the human immune response to natural CCHFV infection to identify potent neutralizing monoclonal antibodies (nAbs) targeting the viral glycoprotein. Competition experiments showed that these nAbs bind six distinct antigenic sites in the Gc subunit. These sites were further delineated through mutagenesis and mapped onto a prefusion model of Gc. Pairwise screening identified combinations of non-competing nAbs that afford synergistic neutralization. Further enhancements in neutralization breadth and potency were attained by physically linking variable domains of synergistic nAb pairs through bispecific antibody (bsAb) engineering. Although multiple nAbs protected mice from lethal CCHFV challenge in pre- or post-exposure prophylactic settings, only a single bsAb, DVD-121-801, afforded therapeutic protection. DVD-121-801 is a promising candidate suitable for clinical development as a CCHFV therapeutic.

Nanobodies Targeting Prostate-Specific Membrane Antigen for the Imaging and Therapy of Prostate Cancer

The repertoire of methods for the detection and chemotherapeutic treatment of prostate cancer (PCa) is currently limited. Prostate-specific membrane antigen (PSMA) is overexpressed in PCa tumors and can be exploited for both imaging and drug delivery. We developed and characterized four nanobodies that present tight and specific binding and internalization into PSMA⁺ cells and that accumulate specifically in PSMA⁺ tumors. We then conjugated one of these nanobodies to the cytotoxic drug doxorubicin, and we show that the conjugate internalizes specifically into PSMA⁺ cells, where the drug is released and induces cytotoxic activity. In vivo studies show that the extent of tumor growth inhibition is similar when mice are treated with commercial doxorubicin and with a 42-fold lower amount of the nanobody-conjugated doxorubicin, attesting to the efficacy of the conjugated drug. These data highlight nanobodies as promising agents for the imaging of PCa tumors and for the targeted delivery of chemotherapeutic drugs.

N-Glycans Mediate the Ebola Virus-GP1 Shielding of Ligands to Immune Receptors and Immune Evasion

The Ebola Virus (EBOV) glycoprotein (GP) sterically shields cell-membrane ligands to immune receptors such as human leukocyte antigen class-1 (HLA-I) and MHC class I polypeptide-related sequence A (MICA), thus mediating immunity evasion. It was suggested that the abundant N-glycosylation of the EBOV-GP is involved in this steric shielding. We aimed to characterize (i) the GP N-glycosylation sites contributing to the shielding, and (ii) the effect of mutating these sites on immune subversion by the EBOV-GP. The two highly glycosylated domains of GP are the mucin-like domain (MLD) and the glycan cap domain (GCD) with three and six N-glycosylation sites, respectively. We mutated the N-glycosylation sites either in MLD or in GCD or in both domains. We showed that the glycosylation sites in both the MLD and GCD domains contribute to the steric shielding. This was shown for the steric shielding of either HLA-I or MICA. We then employed the fluorescence resonance energy transfer (FRET) method to measure the effect of N-glycosylation site removal on the distance in the cell membrane between the EBOV-GP and HLA-I (HLA.A^*0201 allele). We recorded high FRET values for the interaction of CFP-fused HLA.A^*0201 and YFP-fused EBOV-GP, demonstrating the very close distance (<10 nm) between these two proteins on the cell membrane of GP-expressing cells. The co-localization of HLA-I and Ebola GP was unaffected by the disruption of steric shielding, as the removal of N-glycosylation sites on Ebola GP revealed similar FRET values with HLA-I. However, these mutations directed to N-glycosylation sites had restored immune cell function otherwise impaired due to steric shielding over immune cell ligands by WT Ebola GP. Overall, we showed that the GP-mediated steric shielding aimed to impair immune function is facilitated by the N-glycans protruding from its MLD and GCD domains, but these N-glycans are not controlling the close distance between GP and its shielded proteins.

Multiple viral proteins and immune response pathways act to generate robust long-term immunity in Sudan virus survivors

Background

Profiles of immunity developed in filovirus patients and survivors have begun to shed light on antigen-specific cellular immune responses that had been previously under-studied. However, our knowledge of the breadth and length of those responses and the viral targets which mediate long-term memory immunity still lags significantly behind.

Methods

We characterized antigen-specific immune responses in whole blood samples of fifteen years post-infected survivors of the Sudan virus (SUDV) outbreak in Gulu, Uganda (2000−2001). We examined T cell and IgG responses against SUDV complete antigen and four SUDV proteins; glycoprotein (GP), nucleoprotein (NP), and viral protein 30 (VP30), and 40 (VP40).

Findings

We found survivors-maintained antigen-specific CD4+ T cell memory immune responses mediated mainly by the viral protein NP. In contrast, activated CD8+ T cell responses were nearly absent in SUDV survivors, regardless of the stimulating antigen used. Analysis of anti-viral humoral immunity revealed antigen-specific IgG antibodies against SUDV and SUDV proteins. Survivor IgGs mediated live SUDV neutralization in vitro and FcγRI and FcγRIII antibody Fc-dependent responses, mainly via antibodies to the viral proteins GP and VP40.

Interpretation

We highlight the key role of several proteins, i.e., GP, NP, and VP40, to act as mediators of distinctive and sustained cellular memory immune responses in long-term SUDV survivors. We suggest that the inclusion of these viral proteins in vaccine development may best mimic survivor native memory immune responses with the potential of protecting against viral infection.

Funds

This research was funded by the Defense Threat Reduction Agency (CB4088) and by the National Institute Of Allergy And Infectious Diseases of the National Institutes of Health under Award Number R01AI111516. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Serological and phylogenetic characterization of foot and mouth disease viruses from Uganda during cross-sectional surveillance study in cattle between 2014 and 2017

Here, we report the results of a cross-sectional study designed to monitor the circulation and genetic diversity of foot and mouth disease virus (FMDV) in Uganda between 2014 and 2017. In this study, 13,614 sera and 2,068 oral-pharyngeal fluid samples were collected from cattle and analysed to determine FMDV seroprevalence, circulating serotypes and their phylogenetic relationships. Circulation of FMDV was evidenced by the detection of antibodies against non-structural proteins of FMDV or viral isolations in all districts sampled in Uganda. Sequence analysis revealed the presence of FMDV serotypes A, O, SAT 1 and SAT 2. FMDVs belonging to serotype O, isolated from 21 districts, were the most prevalent and were classified into six lineages within two East African topotypes, namely EA-1 and EA-2. Serotype A viruses belonging to the Africa G-I topotype were isolated from two districts. SAT 1 viruses grouped within topotypes I and IV and SAT 2 viruses within topotypes VII, IV and X were isolated from six and four districts respectively. Phylogenetic analysis of SAT 1 and SAT 2 sequences from cattle clustered with historical sequences from African buffalo, indicating possible interspecies transmission at the wildlife-livestock interface. In some cases, Uganda viruses also shared similarities to viral strains recovered from other regions in East Africa. This 3-year study period provides knowledge about the geographical distribution of FMDV serotypes isolated in Uganda and insights into the genetic diversity of the multiple serotypes circulating in the country. Knowledge of circulating FMDV viruses will assist in antigenic matching studies to devise improved FMDV control strategies with vaccination and vaccine strain selection for Uganda.

The Development and Validation of a Novel Nanobody-Based Competitive ELISA for the Detection of Foot and Mouth Disease 3ABC Antibodies in Cattle

Effective management of foot and mouth disease (FMD) requires diagnostic tests to distinguish between infected and vaccinated animals (DIVA). To address this need, several enzyme-linked immunosorbent assay (ELISA) platforms have been developed, however, these tests vary in their sensitivity and specificity and are very expensive for developing countries. Camelid-derived single-domain antibodies fragments so-called Nanobodies, have demonstrated great efficacy for the development of serological diagnostics. This study describes the development of a novel Nanobody-based FMD 3ABC competitive ELISA, for the serological detection of antibodies against FMD Non-Structural Proteins (NSP) in Uganda cattle herds. This in-house ELISA was validated using more than 600 sera from different Uganda districts, and virus serotype specificities. The evaluation of the performance of the assay demonstrated high diagnostic sensitivity and specificity of 94 % (95 % CI: 88.9-97.2), and 97.67 % (95 % CI: 94.15-99.36) respectively, as well as the capability to detect NSP-specific antibodies against multiple FMD serotype infections. In comparison with the commercial PrioCHECK FMDV NSP-FMD test, there was a strong concordance and high correlation and agreement in the performance of the two tests. This new developed Nanobody based FMD 3ABC competitive ELISA could clearly benefit routine disease diagnosis, the establishment of disease-free zones, and the improvement of FMD management and control in endemically complex environments, such as those found in Africa.

The Ebola-Glycoprotein Modulates the Function of Natural Killer Cells

The Ebola virus (EBOV) uses evasion mechanisms that directly interfere with host T-cell antiviral responses. By steric shielding of human leukocyte antigen class-1, the Ebola glycoprotein (GP) blocks interaction with T-cell receptors (TCRs), thus rendering T cells unable to attack virus-infected cells. It is likely that this mechanism could promote increased natural killer (NK) cell activity against GP-expressing cells by preventing the engagement of NK inhibitory receptors; however, we found that primary human NK cells were less reactive to GP-expressing HEK293T cells. This was manifested as reduced cytokine secretion, a reduction in NK degranulation, and decreased lysis of GP-expressing target cells. We also demonstrated reduced recognition of GP-expressing cells by recombinant NKG2D and NKp30 receptors. In accordance, we showed a reduced monoclonal antibody-based staining of NKG2D and NKp30 ligands on GP-expressing target cells. Trypsin digestion of the membrane-associated GP led to a recovery of the recognition of membrane-associated NKG2D and NKp30 ligands. We further showed that membrane-associated GP did not shield recognition by KIR2DL receptors; in accordance, GP expression by target cells significantly perturbed signal transduction through activating, but not through inhibitory, receptors. Our results suggest a novel evasion mechanism employed by the EBOV to specifically avoid the NK cell immune response.

Herd Immunity to Ebolaviruses Is Not a Realistic Target for Current Vaccination Strategies

The recent West African Ebola virus pandemic, which affected >28,000 individuals increased interest in anti-Ebolavirus vaccination programs. Here, we systematically analyzed the requirements for a prophylactic vaccination program based on the basic reproductive number (R₀, i.e., the number of secondary cases that result from an individual infection). Published R₀ values were determined by systematic literature research and ranged from 0.37 to 20. R₀s ≥ 4 realistically reflected the critical early outbreak phases and superspreading events. Based on the R₀, the herd immunity threshold (I_c) was calculated using the equation I_c = 1 - (1/R₀). The critical vaccination coverage (V_c) needed to provide herd immunity was determined by including the vaccine effectiveness (E) using the equation V_c = I_c/E. At an R₀ of 4, the I_c is 75% and at an E of 90%, more than 80% of a population need to be vaccinated to establish herd immunity. Such vaccination rates are currently unrealistic because of resistance against vaccinations, financial/logistical challenges, and a lack of vaccines that provide long-term protection against all human-pathogenic Ebolaviruses. Hence, outbreak management will for the foreseeable future depend on surveillance and case isolation. Clinical vaccine candidates are only available for Ebola viruses. Their use will need to be focused on health-care workers, potentially in combination with ring vaccination approaches.

TBE vaccine and post TBE disease Abs drive antibody dependent enhancement of Zika infection

Tick-borne encephalitis (TBE) virus belongs to the Flaviviruses, such as Zika, Dengue, Yellow fever viruses (YFV), etc. Antibody dependent enhancement (ADE) was first described between Dengue 1–4 viruses. Recently the ADE phenomenon was extended to include additional Flaviviruses that are phylogenetically close to Dengue: Zika and YFV. All arthropod borne Flaviviruses are antigenically related, however, the existence and extent of ADE between mosquito-borne and tick-borne Flaviviruses were never addressed. In order to explore ADE associated pathogenesis of sera cross-reactivity, we studied human sera from patients with acute TBE (n=30), vaccinated against TBE (n=76) and a control group without antibodies (Abs) to Flaviviruses (n=30). ELISA assays were used to profile the IgG and IgM serological repertoires to TBE and cross-reactivity to Zika antigen (Ag). Viral plaque assays (VPA) were used to test if TBE Abs cause ADE during infection with Zika virus. Flow cytometry (FACS) was used to measure ADE of Zika infection in U937 cells in the presence of the sera with TBE Abs. We found that 25% of TBE vaccinated subjects and 47% of acute TBE subjects had cross-reactive Abs to Zika Ag in ELISA. Furthermore, serum from 37/40 (92%) TBE positive subjects caused ADE in the VPA assay and 58/60 (96%) caused ADE using the FACS assay. The magnitude of Zika ADE correlated with the titer of TBE Abs. Thereby we demonstrate, that previous vaccination or infection with TBE significantly increases the risk of ADE upon a secondary infection with Zika virus. These results highlight that presence of cross-reactive Abs induced by previous exposure even to a very distantly related Flaviviruses by vaccination or infection dictates the risk of ADE upon secondary infection.

A Serological Point-of-Care Test for the Detection of IgG Antibodies against Ebola Virus in Human Survivors

Ebola virus disease causes widespread and highly fatal epidemics in human populations. Today, there is still great need for point-of-care tests for diagnosis, patient management and surveillance, both during and post outbreaks. We present a point-of-care test comprising an immunochromatographic strip and a smartphone reader, which detects and semiquantifies Ebola-specific antibodies in human survivors. We developed a Sudan virus glycoprotein monoplex platform and validated it using sera from 90 human survivors and 31 local noninfected controls. The performance of the glycoprotein monoplex was 100% sensitivity and 98% specificity compared to standard whole antigen enzyme-linked immunosorbent assay (ELISA), and it was validated with freshly collected patient samples in Uganda. Moreover, we constructed a multiplex test for simultaneous detection of antibodies against three recombinant Sudan virus proteins. A pilot study comprising 15 survivors and 5 noninfected controls demonstrated sensitivity and specificity of 100% compared to standard ELISA. Finally, we developed a second multiplex subtype assay for the identification of exposure to three related EVD species: Sudan virus, Bundibugyo virus and Ebola virus (formerly Zaire) using recombinant viral glycoprotein. This multiplex test could distinguish between the host's immunity to specific viral species and identify cross-reactive immunity. These developed serological platforms consisted of capture ligands with high specificity and sensitivity, in-house developed strips and a compatible smartphone application. These platforms enabled rapid and portable testing, data storage and sharing as well as geographical tagging of the tested individuals in Uganda. This platform holds great potential as a field tool for diagnosis, vaccine development, and therapeutic evaluation.

Sudan ebolavirus long recovered survivors produce GP-specific Abs that are of the IgG1 subclass and preferentially bind FcγRI

Ebolavirus is a highly lethal pathogen, causing a severe hemorrhagic disease with a high fatality rate. To better understand immune correlates of protection by virus specific IgG, we investigated the evolution of the Fcγ receptors (FcγRs)-activating capabilities of antiviral IgG in serum samples of long recovered survivors. To this end, longitudinal serum samples from survivors of Sudan ebolavirus (SUDV) infection, studied over years, were examined for the presence of Ebola-GP specific IgG subclasses, and for their binding to FcγRs. We developed a cell-based reporter system to quantitate pathogen-specific antibody binding to FcγRIIIA, FcγRIIA, FcγRIIB and FcγRI. With this system, we demonstrate that anti-GP-specific stimulation of the FcγRI reporter by survivors’ sera was substantially high one year after acute infection, with a slight reduction in activity over a decade post infection. We further demonstrate that GP-specific IgG1 is by far the seroprevalent subclass that retained and even enhanced its presence in the sera, over ten years post infection; the prevalence of other GP-specific IgG subclasses was considerably reduced over time. In accordance, GP-specific FcγRI reporter response and GP-specific total IgG1 subclass correlated in the studied group of Ebola survivors. These observations are important for further informing Ebola vaccine and therapeutic development.

Marburg virus survivor immune responses are Th1 skewed with limited neutralizing antibody responses

Immune responses that develop in survivors of filovirus infection may indicate critical parameters that could inform rational vaccine development. Stonier et al. characterize immune responses in Marburg virus survivors and demonstrate robust CD4⁺ T cell responses but limited CD8⁺ T cell and neutralizing antibody responses.

Until recently, immune responses in filovirus survivors remained poorly understood. Early studies revealed IgM and IgG responses to infection with various filoviruses, but recent outbreaks have greatly expanded our understanding of filovirus immune responses. Immune responses in survivors of Ebola virus (EBOV) and Sudan virus (SUDV) infections have provided the most insight, with T cell responses as well as detailed antibody responses having been characterized. Immune responses to Marburg virus (MARV), however, remain almost entirely uncharacterized. We report that immune responses in MARV survivors share characteristics with EBOV and SUDV infections but have some distinct differences. MARV survivors developed multivariate CD4⁺ T cell responses but limited CD8⁺ T cell responses, more in keeping with SUDV survivors than EBOV survivors. In stark contrast to SUDV survivors, rare neutralizing antibody responses in MARV survivors diminished rapidly after the outbreak. These results warrant serious consideration for any vaccine or therapeutic that seeks to be broadly protective, as different filoviruses may require different immune responses to achieve immunity.

Assessing the serological antibody repertoire to Flaviviruses in the endemic population of the Zika forest in Uganda

While the Zika virus has been suspected to cause complications in newborns of women infected during pregnancy, it has circulated in Africa for more --than half a century without any reported cases of microcephaly in children. To assess the prevalence of Zika infections in the Zika forest region we collected human sera samples from 81 people (17–56 years old), who live in Zika forest region, Entebbe, Uganda in 2016, and included both individuals hospitalized with acute febrile illness, as well as health individuals. Elisa assays were used to profile the IgM, IgG serological repertoire to Zika, Dengue 1-4 (DENV1-4) and Yellow Fever (YFV) viruses. We found that 17 individuals (21%) were positive for Zika, 7 of which were hospitalized with acute infection. The hospitalized patients had overall higher antibody titers to Zika. There also were serologically positive samples for: DENV1 n=11 (13.5%); DENV2 n=9 (11%), DENV3 n=4 (5%); DENV 4 n=4 (5%). 11 subjects (13.5%) were positive for YFV. Overall, 49% of the subjects had antibodies to at least one of these Flaviviruses, and 17% had antibodies to two or more Flaviviruses. While serological responses cannot accurately diagnose the specific Flavirvirus infections in these individuals due to significant cross reactivity within this viruses our data suggests that Flavivirus infections are very common in the Zika forest region. While a recent study reported that previous dengue infections may cause antibody dependant enhancement upon subsequent Zika infection, our data suggests that the Zika forest region in which many different Flaviviruses have been circulating for over 50 years may an important region to study such effects in the human population.

Correspondence of Neutralizing Humoral Immunity and CD4 T Cell Responses in Long Recovered Sudan Virus Survivors

Robust humoral and cellular immunity are critical for survival in humans during an ebolavirus infection. However, the interplay between these two arms of immunity is poorly understood. To address this, we examined residual immune responses in survivors of the Sudan virus (SUDV) outbreak in Gulu, Uganda (2000–2001). Cytokine and chemokine expression levels in SUDV stimulated whole blood cultures were assessed by multiplex ELISA and flow cytometry. Antibody and corresponding neutralization titers were also determined. Flow cytometry and multiplex ELISA results demonstrated significantly higher levels of cytokine and chemokine responses in survivors with serological neutralizing activity. This correspondence was not detected in survivors with serum reactivity to SUDV but without neutralization activity. This previously undefined relationship between memory CD4 T cell responses and serological neutralizing capacity in SUDV survivors is key for understanding long lasting immunity in survivors of filovirus infections.

Immune memory to Sudan virus: comparison between two separate disease outbreaks

Recovery from ebolavirus infection in humans is associated with the development of both cell-mediated and humoral immune responses. According to recent studies, individuals that did not survive infection with ebolaviruses appear to have lacked a robust adaptive immune response and the expression of several early innate response markers. However, a comprehensive protective immune profile has yet to be described. Here, we examine cellular memory immune responses among survivors of two separate Ebolavirus outbreaks (EVDs) due to Sudan virus (SUDV) infection in Uganda—Gulu 2000–2001 and Kibaale 2012. Freshly collected blood samples were stimulated with inactivated SUDV, as well as with recombinant SUDV or Ebola virus (EBOV) GP (GP_1–649). In addition, ELISA and plaque reduction neutralization assays were performed to determine anti-SUDV IgG titers and neutralization capacity. Cytokine expression was measured in whole blood cultures in response to SUDV and SUDV GP stimulation in both survivor pools, demonstrating recall responses that indicate immune memory. Cytokine responses between groups were similar but had distinct differences. Neutralizing, SUDV-specific IgG activity against irradiated SUDV and SUDV recombinant proteins were detected in both survivor cohorts. Furthermore, humoral and cell-mediated crossreactivity to EBOV and EBOV recombinant GP_1–649 was observed in both cohorts. In conclusion, immune responses in both groups of survivors demonstrate persistent recognition of relevant antigens, albeit larger cohorts are required in order to reach greater statistical significance. The differing cytokine responses between Gulu and Kibaale outbreak survivors suggests that each outbreak may not yield identical memory responses and promotes the merits of studying the immune responses among outbreaks of the same virus. Finally, our demonstration of cross-reactive immune recognition suggests that there is potential for developing cross-protective vaccines for ebolaviruses.

T and B cell memory responses in 2012 filovirus outbreak survivors (VIR7P.1060)

From 2011 to the present, there have been four confirmed filovirus outbreaks with a fifth case involving a single patient. Four outbreaks/cases were attributed to the Ebolavirus genus, with Marburgvirus responsible for one. With the high lethality rates seen in these outbreaks (generally ~40-90%), and the potentially dramatic disease sequelae, filovirus outbreaks can devastate local communities and present great health risks for affected regions. These issues obviate the need for effective vaccines and therapeutics to limit and manage future outbreaks. In 2012 alone, three outbreaks occurred in Uganda - two of Sudan virus and one Marburg virus. We collected PBMC and serum samples from survivors from each outbreak to evaluate the presence of immune memory and its composition. Serum antibodies displayed broad specificity to Marburg virus and Sudan virus glycoprotein in addition to other proteins. Virtually all serum samples displayed neutralizing activity. PBMCs stimulated with viral and recombinant antigen were evaluated by flow cytometry for functional parameters as well as level of antigen-responsive T cells. Cytokines in the supernatants of these cultures were determined by multiplex ELISA. Cytokine responses were largely pro-inflammatory produced predominantly by CD4 T cells. Establishing immune memory parameters and the nature thereof gives us targets for vaccine development and opens avenues for development of immune-based therapeutics.

A human monoclonal autoantibody to breast cancer identifies the PDZ domain containing protein GIPC1 as a novel breast cancer-associated antigen

Background

We have been studying the native autoimmune response to cancer through the isolation of human monoclonal antibodies that are cancer specific from cancer patients. To facilitate this work we previously developed a fusion partner cell line for human lymphocytes, MFP-2, that fuses efficiently with both human lymph node lymphocytes and peripheral blood lymphocytes. Using this unique trioma fusion partner cell line we isolated a panel of autologous human monoclonal antibodies, from both peripheral blood and lymph node lymphocytes, which are representative of the native repertoire of anti-cancer specific antibodies from breast cancer patients.

Methods

The current study employs immunocytochemistry, immunohistochemistry, Western blot analysis as well as Northern blots, Scatchard binding studies and finally SEREX analysis for target antigen identification.

Results

By application of an expression cloning technique known as SEREX, we determined that the target antigen for two monoclonal antibodies, 27.B1 and 27.F7, derived from lymph node B-cells of a breast cancer patient, is the PDZ domain-containing protein known as GIPC1. This protein is highly expressed not only in cultured human breast cancer cells, but also in primary and metastatic tumor tissues and its overexpression appears to be cancer cell specific. Confocal microscopy revealed cell membrane and cytoplasmic localization of the target protein, which is consistent with previous studies of this protein.

Conclusion

We have determined that GIPC1 is a novel breast cancer-associated immunogenic antigen that is overexpressed in breast cancer. Its role, however, in the initiation and/or progression of breast cancer remains unclear and needs further clarification.

Native human autoantibodies targeting GIPC1 identify differential expression in malignant tumors of the breast and ovary

Background

We have been studying the native humoral immune response to cancer and have isolated a library of fully human autoantibodies to a variety of malignancies. We previously described the isolation and characterization of two fully human monoclonal antibodies, 27.F7 and 27.B1, from breast cancer patients that target the protein known as GIPC1, an accessory PDZ-domain binding protein involved in regulation of G-protein signaling. Human monoclonal antibodies, 27.F7 and 27.B1, to GIPC1 demonstrate specific binding to malignant breast cancer tissue with no reactivity with normal breast tissue.

Methods

The current study employs cELISA, flow cytometry, Western blot analysis as well as immunocytochemistry, and immunohistochemistry. Data is analyzed statistically with the Fisher one-tail and two-tail tests for two independent samples.

Results

By screening several other cancer cell lines with 27.F7 and 27.B1 we found consistently strong staining of other human cancer cell lines including SKOV-3 (an ovarian cancer cell line). To further clarify the association of GIPC1 with breast and ovarian cancer we carefully studied 27.F7 and 27.B1 using immunocytochemical and immunohistochemical techniques. An immunohistochemical study of normal ovarian tissue, benign, borderline and malignant ovarian serous tumors, and different types of breast cancer revealed high expression of GIPC1 protein in neoplastic cells. Interestingly, antibodies 27.F7 and 27.B1 demonstrate differential staining of borderline ovarian tumors. Examination of different types of breast cancer demonstrates that the level of GIPC1 expression depends on tumor invasiveness and displays a higher expression than in benign tumors.

Conclusion

The present pilot study demonstrates that the GIPC1 protein is overexpressed in ovarian and breast cancer, which may provide an important diagnostic and prognostic marker and will constitute the basis for further study of the role that this protein plays in malignant diseases. In addition, this study suggests that human monoclonal antibodies 27.F7 and 27.B1 should be further evaluated as potential diagnostic tools.

Enhancement of hybridoma formation, clonability and cell proliferation in a nanoparticle-doped aqueous environment

Background

The isolation and production of human monoclonal antibodies is becoming an increasingly important pursuit as biopharmaceutical companies migrate their drug pipelines away from small organic molecules. As such, optimization of monoclonal antibody technologies is important, as this is becoming the new rate-limiting step for discovery and development of new pharmaceuticals. The major limitations of this system are the efficiency of isolating hybridoma clones, the process of stabilizing these clones and optimization of hybridoma cell secretion, especially for large-scale production.

Many previous studies have demonstrated how perturbations in the aqueous environment can impact upon cell biology. In particular, radio frequency (RF) irradiation of solutions can have dramatic effects on behavior of solutions, cells and in particular membrane proteins, although this effect decays following removal of the RF. Recently, it was shown that nanoparticle doping of RF irradiated water (NPD water) produced a stabilized aqueous medium that maintained the characteristic properties of RF irradiated water for extended periods of time. Therefore, the ordering effect in water of the RF irradiation can now be studied in systems that required prolonged periods for analysis, such as eukaryotic cell culture. Since the formation of hybridoma cells involves the formation of a new membrane, a process that is affected by the surrounding aqueous environment, we tested these nanoparticle doped aqueous media formulations on hybridoma cell production.

Results

In this study, we tested the entire process of isolation and production of human monoclonal antibodies in NPD water as a means for further enhancing human monoclonal antibody isolation and production. Our results indicate an overall enhancement of hybridoma yield, viability, clonability and secretion. Furthermore, we have demonstrated that immortal cells proliferate faster whereas primary human fibroblasts proliferate slower in NPD water.

Conclusion

Overall, these studies indicate that NPD water can enhance cell proliferation, clonability and secretion. Furthermore, the results support the hypothesis that NPD water is effectively composed of stable microenvironments.

Optical fiber immunosensor for the detection of IgG antibody to Rift Valley fever virus in humans

This paper describes the development and evaluation of an optical fiber immunosensor (OFIS) for the detection of IgG antibody to Rift Valley fever virus (RVFV) in humans. The OFIS was based on a sandwich enzyme-linked immunosorbent assay (S-ELISA) format, whereby gamma-irradiated RVFV and control antigens were immobilized on the optical fiber surface coated with a mouse anti-RVFV antibody. Data sets derived from field-collected sera in Africa (n=242) were dichotomized according to the results of a virus neutralization test. Compared to standard colorimetric S-ELISA, the OFIS technique was more sensitive in detecting smaller quantity of specific IgG to RVFV in human sera. At cut-off value selected at a 95% accuracy level by the two-graph receiver operating characteristic analysis, the OFIS diagnostic sensitivity was 97.22% and diagnostic specificity 98.86%. Our results demonstrate that the OFIS technology reported here is highly accurate, simple to perform and has the potential to be used in a portable format.

T7 phage display of Ep15 peptide for the detection of WNV IgG

West Nile virus (WNV) is one of the major emerging infectious diseases in North America. WNV belongs to the genus Flavivirus, and its rapid and extensive global spread has highlighted the necessity for accurate and specific assays for diagnosis of WNV infection. This study presents the first phage displayed peptide based ELISA for detection of WNV immunoglobulin G (IgG). The Ep15 epitope, derived from the WNV E protein DIII, was cloned into a T7 phage display system that was then used as recombinant antigen in a chemiluminescent ELISA format. The phage concentration was optimized at 5 x 10(10)PFU/ml and was used directly after polyethylene glycol concentration. The assay shows a limit of detection at a serum titer of 1:51,200 and a dynamic range from 1:100 to 1:2000. A screen of a panel of 66 human sera samples, and comparison with a commercial kit, revealed a sensitivity of 67% and a specificity of 100%. Considering the ease of antigen preparation, its stability and the optimum display properties of the T7 bacteriophage, it is apparent that this approach can be useful for the preparation of highly sensitive and specific anti-WNV immunoglobulin diagnostic kits.

Development of a highly sensitive, field operable biosensor for serological studies of Ebola virus in central Africa

We describe herein a newly developed optical immunosensor for detection of antibodies directed against antigens of the Ebola virus strains Zaire and Sudan. We employed a photo immobilization methodology based on a photoactivatable electrogenerated poly(pyrrole-benzophenone) film deposited upon an indium tin oxide (ITO) modified conductive surface fiber-optic. It was then linked to a biological receptor, Ebola virus antigen in this case, on the fiber tip through a light driven reaction. The photochemically modified optical fibers were tested as an immunosensor for detection of antibodies against Ebola virus, in animal and human sera, by use of a coupled chemiluminescent reaction. The immunosensor was tested for sensitivity, specificity, and compared to standard chemiluminescent ELISA under the same conditions. The analyte, anti-Ebola IgG, was detected at a low titer of 1:960,000 and 1:1,000,000 for subtypes Zaire and Sudan, respectively. While the same serum tested by ELISA was one order (24 times) less sensitive.

Single-chain bifunctional vascular endothelial growth factor (VEGF)-follicle-stimulating hormone (FSH)-C-terminal peptide (CTP) is superior to the combination therapy of recombinant VEGF plus FSH-CTP in stimulating angiogenesis during ovarian folliculogenesis

Infertility technologies often employ exogenous gonadotropin therapy to increase antral follicle production. In an effort to enhance ovarian response, several long-acting FSH therapies have been developed including an FSH-C-terminal peptide (CTP), where the FSH subunits are linked by the CTP moiety from human chorionic gonadotropin, which is responsible for the increased half-life of human chorionic gonadotropin. We found that administration of FSH-CTP for ovarian hyperstimulation in rats blunted ovarian follicle vascular development. In women, reduced ovarian vasculature has been associated with lower pregnancy rates. We were interested in determining whether vascular endothelial growth factor (VEGF) therapy could enhance ovarian angiogenesis in FSH-CTP-treated rats. Coadministration of systemic FSH-CTP plus recombinant VEGF was compared with treatment with a novel, single-chain bifunctional VEGF-FSH-CTP (VFC) analog. For VFC, the FSH portion targets the protein to the ovary and stimulates follicle growth, whereas VEGF enhances local vascular development. Both in vitro and in vivo studies confirm the dual FSH and VEGF action of the VFC protein. Evaluation of ovarian follicle development demonstrates that administration of combination therapy using VEGF and FSH-CTP failed to increase follicle vasculature above levels seen with FSH-CTP monotherapy. However, treatment with VFC significantly increased follicle vascular development while concurrently increasing the number of large antral follicles produced. In conclusion, we report the production and characterization of a long-acting, bifunctional VEGF-FSH-CTP protein that is superior to combination therapy for enhancing VEGF activity in the ovary and stimulating follicular angiogenesis in rats.

Vaccinia virus interactions with the cell membrane studied by new chromatic vesicle and cell sensor assays

The potential danger of cross-species viral infection points to the significance of understanding the contributions of nonspecific membrane interactions with the viral envelope compared to receptor-mediated uptake as a factor in virus internalization and infection. We present a detailed investigation of the interactions of vaccinia virus particles with lipid bilayers and with epithelial cell membranes using newly developed chromatic biomimetic membrane assays. This analytical platform comprises vesicular particles containing lipids interspersed within reporter polymer units that emit intense fluorescence following viral interactions with the lipid domains. The chromatic vesicles were employed as membrane models in cell-free solutions and were also incorporated into the membranes of epithelial cells, thereby functioning as localized membrane sensors on the cell surface. These experiments provide important insight into membrane interactions with and fusion of virions and the kinetic profiles of these processes. In particular, the data emphasize the significance of cholesterol/sphingomyelin domains (lipid rafts) as a crucial factor promoting bilayer insertion of the viral particles. Our analysis of virus interactions with polymer-labeled living cells exposed the significant role of the epidermal growth factor receptor in vaccinia virus infectivity; however, the data also demonstrated the existence of additional non-receptor-mediated mechanisms contributing to attachment of the virus to the cell surface and its internalization.

Long-acting follicle-stimulating hormone analogs containing N-linked glycosylation exhibited increased bioactivity compared with o-linked analogs in female rats

The effects of altering the number and type of additional carbohydrate moieties on the pharmacokinetic and pharmacodynamic properties of FSH were examined in this report. A series of single-chain follitropins, containing variable numbers of additional N- (or O-) linked carbohydrates, were designed and expressed in Chinese hamster ovary cells. Proper folding, efficient receptor binding, and signal transduction were confirmed by in vitro assays. Pharmacokinetic and pharmacodynamic parameters were evaluated in immature female Sprague Dawley rats. Increasing the number of glycosylation sites with either N- (or O-) linked moieties extended the elimination half-life as much as 2-fold compared with recombinant human FSH (rhFSH). However, there was a maximum elimination half-life such that further glycosylation provided no additional lengthening of the half-life. Conversely, biopotency, as assessed by inhibin A levels 74 h post injection, and follicle production were significantly higher for the N-linked analogs. Rats stimulated with the longest acting analogs (either N- or O-linked) showed significantly higher ovarian weights than rats receiving a single injection of rhFSH. The analog containing four additional N-linked sites (rhFSH-N4) had the greatest number of large, preovulatory follicles. Although the half-life of rhFSH-N4 displayed no further enhancement beyond the other longest acting analogs, this analog exhibited significantly increased biopotency in rats. This work provides the basis for the generation of a series of reagents potentially useful for therapeutic applications.

Development of a fusion partner cell line for efficient production of human monoclonal antibodies from peripheral blood lymphocytes

We developed a unique fusion partner cell line that is capable of fusing with both human peripheral blood and lymph node lymphocytes at a high efficiency. The cell line was generated by fusing a murine myeloma cell line with a human myeloma cell line, producing a heteromyeloma (B6B11), which was subsequently fused with a human lymph node lymphocyte to produce a trioma (MFP-2). B6B11 and MFP-2 fuse well with human lymphocytes from both spleen and lymph nodes. Interestingly, MFP-2 also fuses with a high efficiency to peripheral blood lymphocytes. The resulting hybrids are stable for extended periods of time and produce human monoclonal antibodies at significant levels. The utility of MFP-2 as a fusion partner was demonstrated by the isolation of several hybridoma cell lines using lymph node and peripheral blood lymphocytes from patients with breast cancer. These hybridomas produce monoclonal antibodies displaying specificity to breast cancer tissue and cell lines.

Development and characterization of a long-acting recombinant hFSH agonist

BACKGROUND

Fusion of the carboxyterminal peptide (CTP) of hCG to FSH results in a follitropin agonist with an extended half-life, presumably due to the four O-oligosaccharides on the CTP. Alternatively, an rhFSH analogue containing additional N-linked carbohydrate is described in this report.

METHODS

A DNA sequence containing two N-oligosaccharide signal sequences was ligated into a vector containing hFSHbeta- and alpha-subunit encoding cDNA, and expressed in CHO-K1 cells. In-vitro bioactivity of the single-chain hormone was assessed in CHO cells expressing the hFSH receptor. Pharmacokinetic values were derived from serial serum assays of the analogue in immature female rats following a single i.v. injection. In-vivo bioactivity was assessed by measuring ovarian weight gain 3 days post-injection.

RESULTS

rhFSH-N2 and native rhFSH induced comparable levels of cAMP in vitro. t(1/2) for native rhFSH, rhFSH-CTP and rhFSH-N2 were 3.7, 7.1 and 7.3 h respectively. Rats receiving rhFSH-N2 had a mean +/- SD ovarian weight 3 days post-i.v. injection (22 +/- 3.6 mg) significantly greater than rats receiving rhFSH and saline (16.7 +/- 1.5 and 15.3 +/- 0.47 mg respectively, P < 0.05).

CONCLUSIONS

rhFSH-N2 has prolonged half-life and increased bioactivity compared with native rhFSH. This rhFSH agonist, and other analogues containing additional N-oligosaccharides may have important clinical applications.

Bacterial expression of a natively folded extracellular domain fusion protein of the hFSH receptor in the cytoplasm of Escherichia coli

We have expressed the extracellular domain of the hFSH receptor as a fusion protein with thioredoxin in the cytoplasm of an Escherichia coli strain that contains mutations in both the thioredoxin reductase and the glutathione reductase genes. The chimeric protein isolated following induction of expression was purified in a soluble form and binds hFSH with an affinity approximating that of native receptor. This truncated form of the receptor displays the same specificity as intact receptor and does not bind hCG. The protein is expressed at levels that exceed 5 mg/L in the bacterial cytoplasm. Expression of the properly folded extracellular domain of the hFSH receptor in the cytoplasm of E. coli allows the facile and economical purification of large quantities of material. This will facilitate the determination of the structure of the hormone-binding domain of this glycoprotein receptor as well as the production of epitope-specific antibodies.

Pharmacokinetics and pharmacodynamics of single-chain recombinant human follicle-stimulating hormone containing the human chorionic gonadotropin carboxyterminal peptide in the rhesus monkey

OBJECTIVE

To compare the pharmacokinetics of a long-acting FSH analog containing the hCG-beta carboxyterminal peptide (recombinant hFSH-CTP) with native recombinant hFSH and describe the pharmacodynamics of recombinant hFSH-CTP after SC injection in female rhesus monkeys.

DESIGN

Rhesus monkey study.

SETTING

Academic research environment.

ANIMAL(S)

Ten female rhesus monkeys.

INTERVENTION(S)

Recombinant hFSH and recombinant hFSH-CTP were administered via a single SC or IV dose to rhesus monkeys, and serial phlebotomy was performed (n = 2 and n = 4 for SC recombinant hFSH and recombinant hFSH-CTP, respectively; for IV dosing, n = 1 in each group). An additional two monkeys were pretreated with SC ganirelix and received SC recombinant hFSH-CTP after confirmation of pituitary suppression.

MAIN OUTCOME MEASURE(S)

Plasma disappearance rate of recombinant hFSH and recombinant hFSH-CTP and serum estradiol levels.

RESULT(S)

The elimination half-life of recombinant hFSH-CTP was twofold and fourfold longer than that for recombinant hFSH after SC and IV dosing, respectively. The absorption half-life was approximately threefold longer for recombinant hFSH-CTP than for recombinant hFSH after SC administration. Recombinant hFSH-CTP stimulates estradiol secretion for 5-7 days after an isolated SC dose.

CONCLUSION(S)

Addition of the hCG-beta carboxyterminal peptide to hFSH-beta results in an FSH analog with longer absorption and elimination half-lives compared with native hormone. This analog is capable of prolonged ovarian stimulation in rhesus monkeys after an isolated SC injection.

Expression and characterization of recombinant beta-subunit hCG homodimer

We have linked two human chorionic gonadotropin (hCG) beta-subunit cDNAs in tandem such that the expressed fusion protein consists of two mature beta-subunits joined through the carboxy terminal peptide of the first beta-subunit. A single glycine residue is inserted between the two subunits in the fusion protein. Chinese hamster ovary (CHO) cells transformed with a clone that contains the fused cDNAs express and secrete a protein that is consistent with it being a beta-hCG homodimer protein. These beta-homodimer molecules can recombine with two free alpha-subunits indicating that both beta-subunits within the homodimer are likely folded in their native conformation. Our data also suggest that the two beta-subunits fold upon each other as a globular protein and do not appear to exist as a simple fusion of two linear beta-subunits. Furthermore, the two beta-monomer subunits in the fusion protein form a stable homodimer that can bind and activate the hLH/CG receptor specifically. Recombination of the fusion protein with alpha-subunits appears to favor an arrangement where two alpha-subunits combine with a single molecule of the fusion protein. The recombined molecule consists of four subunits and is comparable to two tethered hCG moieties, which constitutes a hCG dimer. This hormone dimer can bind and activate the hLH/CG receptor with an activity approximating that of native hCG.

Structural and molecular studies of human chorionic gonadotropin and its receptor

Human chorionic gonadotropin (hCG) is a placental hormone that stimulates secretion of the pregnancy-sustaining steroid progesterone. It and other glycoprotein hormones are disulfide-rich heterodimers that share a common alpha chain and distinctive beta chains specific to their particular G protein-linked receptors. We determined the structure of partially deglycosylated hCG at 2.6 A resolution from multiwavelength anomalous diffraction (MAD) measurements of a selenomethionyl hCG crystal. We have also begun three- and four-dimensional structural studies on the biologically active hormone and have determined the structure of the carbohydrate attached to the alpha-subunit. Despite little sequence similarity limited to 10% identity, the alpha and beta subunits of hCG maintain strikingly similar tertiary folds, with cystine-knot motifs at cores of extended hairpin loops. Structural and sequence comparisons indicate an evolutionary homology between the glycoprotein hormone chains and other cystine-knot proteins, notably PDGF, TGF-beta, and NGF. This structural similarity has led us to speculate that early hCG secretion has a broader role than solely the stimulation of the corpus luteum; indeed, levels of hCG, which rise rapidly in the circulation after implantation, are greater than the levels necessary for corpus luteum function. One such role of hCG or its subunits could be as a growth factor that facilitates endometrial receptivity. Our studies of hCG have also identified structural variants, notably in the carbohydrate moiety, that are distinctive for patients with a variety of disorders of pregnancy, including hydatidiform mole and choriocarcinoma. We have also focused our efforts on using information gleaned from the structure of hCG for the design of drug-like molecules that might serve as either agonists or antagonists of hCG. To facilitate these experiments, we have designed a rapid screen for the identification of molecules that might bind the hCG receptor by identifying compounds that disrupt binding of hCG to its receptor. This screen employs a filamentous phage that displays the extracellular domain of the hCG receptor on its surface. Thus far, we have identified a few compounds that disrupt binding of hCG with its receptor at a concentration of approximately 1 micromolar. These "lead" molecules are currently being modified in an attempt to identify a molecule that can disrupt binding of hCG at nanomolar concentrations.

Mutations in the alpha1 subunit of an L-type voltage-activated Ca2+ channel cause myotonia in Caenorhabditis elegans

The control of excitable cell action potentials is central to animal behavior. We show that the egl-19 gene plays a pivotal role in regulating muscle excitation and contraction in the nematode Caenorhabditis elegans and encodes the alphal subunit of a homologue of vertebrate L-type voltage-activated Ca2+ channels. Semi-dominant, gain-of-function mutations in egl-19 cause myotonia: mutant muscle action potentials are prolonged and the relaxation delayed. Partial loss-of-function mutations cause slow muscle depolarization and feeble contraction. The most severe loss-of-function mutants lack muscle contraction and die as embryos. We localized two myotonic mutations in the sixth membrane-spanning domain of the first repeat (IS6) region, which has been shown to be responsible for voltage-dependent inactivation. A third myotonic mutation implicates IIIS4, a region involved in sensing plasma-membrane voltage change, in the inactivation process.

Three-dimensional structures of gonadotropins

Most secreted proteins are modified post-translationally with the addition of carbohydrate. It has been difficult to use crystallography to solve the structures of these proteins due to the inherent heterogeneity of the carbohydrate. The structure of the chemically deglycosylated form (hydrogen fluoride treated) of human chorionic gonadotropin (hCG) has been solved through crystallographic techniques. Unfortunately this form of hCG is not biologically active, and exhibits immunochemical differences from native hormone. In addition, subunit interactions appear altered after chemical deglycosylation as indicated by the increased thermal stability of the HF-treated hormone. The Asn 52 glycan on the alpha-subunit of hCG has been identified as being required for biological activity, it is, therefore, of physiological importance to determine the structure of the hormone with its carbohydrate intact. Also, it has not been possible to obtain crystals of the individual glycosylated subunits of hCG. Therefore an alternative method to solve the structure of the biologically active form of the hormone in solution as well as its separated subunits is necessary. Structural information utilizing NMR techniques can be obtained from native hCG subunits in solution if they can be uniformly labeled with 13C and 15N isotopes. We have developed a universal nonradioactive isotope, labeling medium enriched in 13C and 15N which can be used to express uniformly labeled hCG from Chinese hamster ovary cells suitable for solving the structure of the individual subunits and ultimately that of the native, biologically active hormone. The isotopically labeled recombinant hCG and its purified subunits are essentially identical to urinary hCG on comparison by biochemical, immunochemical, biological activity and the ability of the isolated subunits to recombine to form a biologically active dimer. Mass spectrometric analysis and preliminary structural NMR data indicate that the labeling is uniform and there is greater than 90% incorporation, sufficient for complete structural determination studies. This labeled growth medium represents a technological advance which will enable the rapid solution of the structures of the other glycoprotein hormones, as well as other glycoproteins which have proven unsuitable for crystallographic study.

The Caenorhabditis elegans gene lin-17, which is required for certain asymmetric cell divisions, encodes a putative seven-transmembrane protein similar to the Drosophila frizzled protein

Mutations in the gene lin-17 result in the disruption of a variety of asymmetric cell divisions in Caenorhabditis elegans. We have found that lin-17 encodes a protein with seven putative transmembrane domains. The LIN-17 protein is most similar to the Drosophila Frizzled protein and its vertebrate homologs. Studies using a lin-17-green fluorescent protein translational fusion indicate that lin-17 is expressed in mother cells before asymmetric cell divisions and in both daughter cells after the divisions. Our results suggest that lin-17 encodes a receptor that regulates the polarities of cells undergoing asymmetric cell divisions and raise the possibility that the LIN-17 protein acts as a receptor for the Wnt protein LIN-44, which also controls asymmetric cell divisions.

Activation of V kappa gene rearrangement in pre-B cells follows the expression of membrane-bound immunoglobulin heavy chains

During B cell development V kappa gene rearrangement seems to occur only in mu-positive pre-B cells. To study the role of the mu chain in the activation of the Ig kappa locus, we introduced expression vectors carrying different forms of the mu gene into null pre-B cells. The activation of the Ig kappa locus followed the expression of the membrane form (micron) of the mu chain. The expression of the secreted form (microS) did not result in the activation of the Ig kappa locus. We further show that both forms of the mu chain differ in their intracellular transport in pre-B cells.