A human monoclonal antibody reactive with human prostate

The role of apocrine released proteins in the post-testicular regulation of human sperm function

A unifying hypothesis is presented postulating an apocrine release of several seminal proteins which mix and reaggregate in seminal fluid, thereby eventually forming particles designated either as "prostasomes", "vesiculosomes" or "seminosomes". The term "aposomes" should be restricted to the blebs released from secretory cells in the rat dorsal prostate and coagulating gland. Three different proteins present in human seminosomes along with the respective antibodies have been used to identify the localization, function and hypothetical interaction with spermatozoa. The proteins were (1) seminal vesicle-derived fibronectin, (2) prostate-derived 5'-nucleotidase and (3) a hitherto unidentified 100 kD membrane protein from epididymis, seminal vesicle and prostate. I. Fibronectin is an extracellular matrix protein which is also secreted from the seminal vesicles participating in the formation of the seminal clot. Immunofluorescence and immunoelectron microscopy revealed a relatively broad distribution pattern of fibronectin immunoreactivity on spermatozoa from different donors. Adding a fibronectin antiserum at a moderate dilution to vital spermatozoa in vitro resulted in a significant increase in sperm motility. Purified plasma fibronectin added at various concentrations to a vital sperm preparation was found to inhibit sperm motility in a dose-dependent manner. Measurement of calcium fluxes in individual sperm in the presence of fibronectin showed a significant increase. These findings point to a possible post-testicular regulatory function of seminal fibronectin. 2.5'-Nucleotidase (5'-NT) is an enzyme that hydrolyzes nucleotides such as AMP or IMP into inorganic phosphate and the respective nucleoside. The highest amount and activity of 5'-nucleotidase was present in glandular cells of the prostate; much less was detected in seminal vesicles and epididymis. On spermatozoa, the enzyme was localized on the outer leaflet of the plasma membrane covering the acrosomal region. Addition of purified enzyme to an in vitro incubation system of spermatozoa had no effect on sperm motility. A slight reduction of overall motility, however, was observed after addition of 5'-NT antibody to the spermatozoa. When 5'-nucleotidase inhibitors and adenosine channel antagonists were added to the sperm incubation system, a clear-cut inhibition of sperm motility occurred in a dose-dependent manner. This result is interpreted as indicating a significant role of ecto-5'-nucleotidase in the regulation of sperm motility. 3. A polyvalent antiserum against native human prostasomes recognized antigens in the range of 10-14 kD and of approximately 100 kD, respectively, in seminal fluid and prostate homogenates. Immunohistochemical studies revealed the presence of respective antigens in the epididymis, seminal vesicles and the prostate. Immunoelectron microscopy of ultracryo-sections showed labeling both of the apical plasma membrane in the prostate, as well as intraluminal secretory particles indicating the apocrine i.e. plasma-membrane bounded release of these particles. The secretory elements are termed "seminosomes". An affinity-purified fraction within the antiserum recognizes a 100 kD protein which is present both in the apical plasma membrane of the male genital glands, but also in the sperm head and principal piece of human spermatozoa. Incubation of spermatozoa with seminosomes and the respective purified antiserum had no effect on sperm motility. This is in contradistinction to former reports on motility increase induced by the so-called prostasomes.

Immunohistochemistry of prostasomes from human semen

BACKGROUND

To elucidate the origin of so-called "prostasomes" in human semen, a polyvalent rabbit antiserum was produced against a highly purified preparation of these secretory particles.

METHODS

An immunoaffinity selected fraction of the antiserum contained one antibody which in Western blots of prostate extracts showed a 100 kDa band.

RESULTS

Semithin sections processed for immunohistochemistry by using this immunoselected antibody presented a distinct immunoreaction at the apical plasma membrane of secretory cells. The immunoreaction was not organ specific, but was present also in seminal vesicles, epididymis, salivary glands, and kidney. As spermatozoa present in epididymis and seminal vesicles were likewise immunoreactive, a polytopic origin of the respective antigen was concluded.

CONCLUSIONS

Prostatsomes therefore should rather be designated as "seminosomes" which more clearly refers to the composite origin of these particles.

Detection by a human monoclonal antibody of a glycoprotein associated with malignant proliferation of mammary epithelial cells

A tumour-associated antigen (TAA.62) with an apparent mol. wt. of 62 kd, identified by a human monoclonal antibody (IgG2, kappa-light chain), was found to be expressed at elevated levels in the cytoplasmic compartment of malignant as compared with normal mammary epithelial cells in both tissues and cultured cells. Increased levels of cytoplasmic expression of the antigen were also observed in malignant cells of cervix, colon, kidney, lung, and stomach. The patterns of expression of TAA.62 in cultured cells mirrored those of tissues and the antigen was expressed at elevated levels in the established breast cancer lines or oncogenically transformed mammary carcinoma cell line (tumourigenic) compared with the immortalised mammary epithelial cell line (non-tumourigenic). Aliquots of TAA.62 were purified to homogeneity from the conditioned-medium of malignant and immortalised breast cells by immunoaffinity chromatography using immobilised anti-TAA.62 antibody, and gel filtration. Both preparations of TAA.62 yielded a single band with an apparent molecular weight of 62 kd under reducing condition on sodium dodecyl sulphate-polyacrylamide gel electrophoresis, and both were identical in terms of size and immunoreactivity to anti-TAA.62 antibody. However, TAA.62(T) isolated from tumourigenic cell lines itself interacted with a cell surface molecule having an apparent molecular weight of 160 kd on both the malignant and immortalised cells: TAA.62(I) isolated from immortalized cell lines, showed no comparable interaction. Scatchard analysis of the concentration-dependent binding of TAA.62(T) to 160 kd-receptor molecule revealed a 2.6 x 10(4) binding sites per cell. The association constant of such binding was determined to be approximately 16.6 nM. Finally, addition of anti-TAA.62 antibody to culture medium resulted in the inhibition of proliferation of the malignant cells, but showed no effect on the normal cells. The results suggest that TAA.62 may interact as a ligand with its 160 kd cell surface receptor with a possible growth related function.

Human-human hybridoma producing monoclonal antibodies against colorectal cancer-associated antigens

Lymphocytes from lymph nodes draining the tumor region in patients with colorectal cancer were fused with two different human B-lymphoblastoid cell lines, LICR-LON-HMy-2 (HMy-2) and WI-L2-729-HF2 (729-HF2), to generate hybridomas synthesizing antibodies reacting with tumor-associated antigens. In this way 220 hybridomas were obtained which produce antibody reacting with colon cancer cells. All established clones produced IgM. Four human monoclonal antibodies have been further analyzed. The cell lines producing these antibodies are all hybrids based on DNA analysis. Three of the antibodies (G4146, B9165 and D4213) showed binding to differentiation antigens by immunocytochemical analysis on different cancer cell lines and normal human leucocytes and by immunohistochemical analysis on sections of frozen malignant and normal tissues, while the fourth (F11348) showed a reaction with all cells and tissues tested. Western blots of tumor extracts showed binding of G4146 to two components from colon cancer cells with Mr of 59 K and 61 K, while B9165 bound to a 43 K component and F11348 to several components with Mr from 30 to 200K. D4213 showed no binding in this analysis. The results obtained demonstrate the successful application of hybridoma technology to produce human monoclonals with reactivity to differentiation antigens.

Biochemical and immunological characterizations of antigens recognised by human monoclonal antibodies

The lymphocytes from lymph nodes of six patients with metastatic mammary carcinomas were hybridised by fusion with a non-secreting variant of murine myeloma cells. Hybrid cells producing human immunoglobulin were detected by screening of culture supernatants using a solid-phase enzyme-linked immunosorbent assay for human IgG or IgM. Reactivity of human immunoglobulins to breast tumour cells was assessed by an indirect immunoperoxidase staining of fresh-frozen breast carcinoma sections. In the initial screening, the tissues used were those removed from the patients who acted as source of lymphocytes for fusion. The hybrid-cells, after repeated cloning, were stable for secretion of immunoglobulins. A total of 14 immunoglobulin G and 51 immunoglobulin M human monoclonal antibodies, showing variable reactivity to mammary carcinoma cells in tissue sections by an indirect immunoperoxidase staining method, were obtained. Two immunoglobulin G monoclonal antibodies (designated HMA-29 and HMA-31) were selected on the basis of their strong reactivity to the tumour cells and utilised to identify their corresponding antigens. The antibodies quantitatively discriminated, as expressed by the degree of staining, malignant from normal or benign mammary epithelia in freshly frozen or formalin-fixed breast tissues. The antibodies also showed reactivity to malignant cells of colon, stomach and lung and to normal cells lining the renal tubules and surface epithelium of colon. As revealed by blocking experiments, the epitopes recognised by these antibodies were not expressed on carcinoembryonic antigens, erythrocytes, lymphocytes, glycoproteins from milk-fat-globule membrane or keratins. The antibody HMA-29 immunoprecipitated a phosphoprotein (Mr = 29,000), and antibody HMA-31 two protein components (Mr = 31,000 and 34,000), from lysates of intrinsically labelled human mammary carcinoma cell line (MCF7). Neither of these proteins were present in detectable amounts in an intrinsically labelled melanoma cell line. Immunoblocking and immunoprecipitation experiments suggested that epitopes recognised by these two antibodies are dissimilar and are expressed on different molecules. The antibodies appear to be useful for functional characterisation of those antigens which are present in elevated levels in malignant compared with normal mammary epithelia.

Use of xenograft tissue for the initial screening of human monoclonal antibodies by immunohistological technique

An indirect avidin-biotin-horseradish peroxidase complex (ABC) method was employed to detect binding activity of human monoclonal antibodies at their early state of production to tissue antigens in either fresh-frozen or formalin-fixed and paraffin-embedded tissue sections. The tissues were obtained from xenograft of human tissues that were grown in immune suppressed BALB/c mice. The reaction was visualized by the use of aminoethylcarbazole (AEC) as chromogen. The procedure described here was as sensitive and, most importantly eliminated an inherent problem associated with the use of human tissue section namely the difficulty in distinguishing binding of the primary human monoclonal antibody from endogenous human immunoglobulins in tissue section.

Growth of human-human hybridomas in serum-free media enhances antibody secretion

Human-human hybridomas derived from fusing lymph node lymphocytes with UC 729-6 were adapted to grow in commercially available serum-free medium and were compared with serum-supplemented [10% fetal bovine serum (FBS)] cultures. Over a 6-d period, no significant changes occurred in the growth of the cells in 10% FBS or serum-free medium. In cultures supplemented with 10% FBS more total proteins were secreted than in serum-free cultures. However, there was an enhanced secretion of three- to four-fold of both immunoreactive human IgG and IgM under serum-free conditions compared to serum-supplemented conditions. Serum-free conditions may provide the appropriate milieu for the increased level of Ig secretion from human hybridomas derived from UC 729-6 in that there are no inhibitors that may be present in serum.

Monoclonal antibodies in urologic oncology

The sensitivity and specificity of immune reactions have long been recognized. However, since the description of the monoclonal antibody technique certain technical hurdles have been overcome. Monoclonal antibody (mAb) technology allows far more precise understanding of the humoral immune response by allowing dissection of this response into its individual B-lymphocyte populations. Furthermore, the ability to select and expand a particular B-cell clone allows for production of unlimited amounts of a pure antibody "reagent." Each of these reagents may be readily used as a "probe" for its respective antigenic determinant. Panels of these reagents may be used to probe complex biologic structures (e.g., neoplastic cells) and thereby "dissect" them at a molecular level. Murine mAbs are produced by hyperimmunizing a mouse with the antigen of interest. The spleen provides a rich source of B-lymphocytes. These normal B-lymphocytes are incapable of surviving in culture. However, mouse B-lymphocyte tumor cell lines (myelomas) have been previously immortalized in tissue culture. A hybridoma is formed by fusing the normal immunized B-cells with myeloma cells. The hybridoma combines the best features of its parent cells. The immunoglobulin product of each resulting clone is screened against a panel of antigens. This allows selection of those clones producing antibody to the desired antigens. The mAb may be used to purify and/or characterize its respective antigen including definition of the chromosomal site of its gene and factors involved in the regulation of its expression. A large number of mAbs have been produced against renal, bladder, and prostate cancer antigens. These mAbs are allowing a more precise, molecular subclassification of these cancers and providing improved predictability of the natural history of each patient's cancer. Evidence in experimental animals demonstrates that mAbs accumulate at the site of tumor and can lead to the destruction of tumor cells. These encouraging results have prompted clinical trials in patients with metastatic cancer. Such a clinical trial in patients with metastatic renal cancer is currently underway at New York Hospital and Memorial Sloan-Kettering Cancer Center.

Methods of early diagnosis in genitourinary cancer

The commonly employed methods for the early detection of urologic cancers remain the traditional techniques of a carefully performed history and physical examination. Newer developments include, among others, prostate-specific antigen and monoclonal antibodies in prostate cancer, flow cytometry in bladder cancer, computerized axial tomography (CAT) scanning in renal cancer, and ultrasound in testicular cancer. These and other new diagnostic techniques, with further testing and wider use, will hopefully permit the earlier diagnosis of genitourinary cancer.

An evaluation of prostate specific antigen in prostatic cancer

Prostate specific antigen levels were measured in 118 patients with prostatic cancer and 138 control individuals. Prostate specific antigen was sensitive in detecting prostatic cancer. The levels of prostate specific antigen were elevated in 10 per cent of the patients with stage A, 24 per cent with stage B, 53 per cent with stage C and 92 per cent with stage D disease. However, prostate specific antigen levels also were elevated in 9 per cent of the patients with benign prostatic hypertrophy. This lack of specificity in the presence of benign prostatic hypertrophy probably precludes prostate specific antigen from being recommended as a screening test for prostatic cancer. The ultimate role of prostate specific antigen might be as the marker of choice to monitor therapy for prostatic carcinoma.

A method for the blocking of endogenous immunoglobulin on frozen tissue sections in the screening of human hybridoma antibody in culture supernatants

Endogenous immunoglobulin in tissue sections pose a problem in immuno-histochemical techniques employing homologous antibody as primary reagents and enzyme-labelled anti-immunoglobulin for the development. A method for the blocking of endogenous immunoglobulin in human tissue sections by incubation with monomeric pepsin fragments (Fab') of rabbit anti-human immunoglobulin before applying monoclonal antibody was evaluated for the screening of human monoclonal antibody. It was initially demonstrated that Fab' rabbit anti-human IgM and anti-IgG could block endogenous immunoglobulin in human IgM and IgG producing tumors thereby abolishing the binding of subsequently applied peroxidase-labelled anti-IgM or anti-IgG. Frozen sections of human colo-rectal adenocarcinomas show a variable background staining caused by the endogenous immunoglobulin. The background completely disappeared in the IgM system by preincubation with Fab' anti-IgM while the background was clearly reduced but not abolished in the IgG system. A human hybridoma supernatant containing IgM reactive with colo-rectal adenocarcinoma could easily be screened on frozen sections using this method. This approach should be generally useful for the screening of human antibody on human tissue sections.

Genetically stable human hybridomas secreting tumor-reactive human monoclonal IgM

Human lymphocytes obtained from regional draining lymph nodes of patients with cancers of the cervix, kidney, prostate, and vulva were immortalized by polyethylene glycol-mediated somatic cell hybridization with either human UC 729-6 or murine P3-NS-1-Ag4-1. Four reactive human IgM-secreting hybridomas, termed CLNH5, MHG7, VLN1H12, and WLNA67 were isolated and characterized. Hybrids obtained by fusions with UC 729-6 have remained tetraploid for over 18 months, have doubling times from 25-35 hours, and have continuously secreted approximately 0.5-5.0 micrograms IgM/10(6) cells/ml per day. MHG7, a mouse-human hybrid, required subcloning every 4-6 months to maintain human IgM secretion. Binding of these human monoclonal antibodies (MoAbs) against a panel of cell lines was assessed by an enzyme-linked immunoassay (EIA). CLNH5 reacted with carcinomas of the cervix, lung, and vulva. MHG7 reacted with carcinomas of the prostate, stomach, and vulva. VLN1H12 reacted with carcinomas of the cervix, lung, prostate, stomach, and vulva. WLNA6 reacted strongly with a carcinoma of the lung. All four human MoAbs failed to react by EIA with hematopoietic cells or normal fibroblast cell lines. The data suggest that regional draining lymph nodes of cancer patients have been primed to produce antibodies against antigens associated with tumor cells and that UC 729-6 served as a genetically suitable vector for the capture and immortalization of these Ig-secreting B lymphocytes.

Variations in the secretion of monoclonal antibodies by human-human hybridomas

A series of human-human hybridomas derived from a single fusion of UC 729-6 with lymph node lymphocytes were examined for the type and nature of macromolecules synthesized and secreted. One hybrid, VLN3G2, secreted fourfold higher IgG than that present in the cytoplasm over 4 days of growth, while the IgM distribution was opposite to that of IgG. VLN5C7, contrary to VLN3G2, contained several-fold more cytoplasmic IgG as well as IgM than the amounts secreted over the same period of time. Of the secreted IgG and IgM by both of these hybridomas, only the IgG showed immunoreactivity against target A431 cell surface antigen(s). Another hybridoma, termed VLN1H12, secreted immunoreactive IgM against target A431 cells, but no detectable IgG. Cytoplasmic proteins prepared by repeated freeze-thaw of the hybridoma cells, membrane proteins obtained by NP-40 extraction of the cell membrane, and secreted proteins present in the supernates of the various hybridomas were assayed by an enzyme-linked immunoassay (ELISA), to understand the discrepancy observed in the immunoglobulins of the cellular and extracellular compartments. The parental UC 729-6 cell line used in these cell fusions produced only trace amounts of immunologically inactive IgM and no detectable IgG. Molecular sieving column chromatography of these hybridoma supernates suggested the presence of intact IgG and IgM molecules and the absence of free heavy chains or hybrid antibodies containing both mu and gamma heavy chains. Intrinsic labeling of VLN3G2 hybridoma cells with 35S-methionine demonstrated the presence of not only a nonimmunoglobulin protein but also a small molecular weight protein-A-binding polypeptide in the culture supernatant. 35S-methionine-incorporated IgG and IgM antibodies, isolated from spent media, cytoplasm, and cell membranes of VLN3G2, also showed binding to protein-A-bearing bacteria. In conclusion, the differences observed in the amounts of secreted MAbs by the human-human hybridomas were not due to the decreased synthesis of these molecules.

Type-A retrovirus particles in heterohybridomas: precaution for human monoclonal antibody purification

Fine structural features of the murine myeloma MHFP-1 and two heterohybridomas secreting human IgM monoclonal antibody were examined. Intracisternal type-A retrovirus particles were found in both MHFP-1 and the heterohydribomas constructed by fusing MHFP-1 and human peripheral blood lymphocytes. The implications of this finding for the purification of human monoclonal antibody for therapeutic applications is discussed.