Autologous hematopoietic stem cell transplantation in patients with end-stage liver disease: a 5-year follow-up study of 48 patients.

OBJECTIVE: To investigate the long-term therapeutic effect of autologous hematopoietic stem cell transplantation in patients with End-stage Liver Disease (ESLD). PATIENTS AND METHODS: Forty-eight ESLD patients underwent autologous CD34+ stem cell transplantation were retrospectively reviewed. Changes in clinical and biochemical data, complications, and quality of life were monitored at 3, 6, 12, 36, and 60 months following the stem cell transplantation. Liver biopsies were obtained for histopathological analysis using Ishak system. RESULTS: Marked improvement in clinical and biochemical data was observed during the long-term follow-up. Serum albumin was significantly increased (p<0.001), while total serum bilirubin, prothrombin time (PT), and international normalized ratio (INR) were all significantly decreased (p<0.001). Ishak inflammation and fibrosis scores were significantly decreased with the increased time (p<0.001). The number of patients with ascites, model of end-stage liver disease (MELD) score, Child-Pugh class, and indocyanine green (ICG) score were all markedly reduced with increased time. Meanwhile, the quality of life score of the patients was significantly increased (p<0.001). Six patients died during the 5-years follow-up, and complications occurred in 17 patients. The incidence of complications was significantly associated with mortality of the patients (p<0.05). CONCLUSIONS: The study provided the evidence that autologous CD34+ stem cell transplantation could offer a long-term therapeutic benefit to patients with ESLD. The complications occurred during the process was significantly associated with survival of the patients. Future studies on a large cohort of patients are needed to confirm the long-term effect of stem cell therapy on ESLD.

[MiR-128, a key regulator of oncogenic properties].

MicroRNAs (miRNA) are small noncoding RNAs that are critical regulators of gene function. In the recent years, miRNAs have been increasingly noted for their capacity to regulate key malignant properties of tumor cells. MicroRNA-128 (miR-128) is a brain-enriched miRNA that is normally involved in the development of the nervous system and in the maintenance of neural physiological functions. In tumorcells, miR-128 expression is dysregulated through a variety of genetic and epigenetic events. Dysregulation: of miR-128 has profound effects on tumorigenesis and maintenance of tumor cells through alterations in cellular proliferation, differentiation, metabolism, and apoptosis. This article will review the latest advances in our understanding of miR-128, specifically in the context of clinical and fundamental cancer biology. Further characterization of miR-128 will likely identify its new roles in cancer biology. The use of miR-128 as a diagnostic and/or therapeutic tool may result in improvements in diagnosis, prognosis, and treatment of numerous cancers.

Nicotine increases the resistance of lung cancer cells to cisplatin through enhancing Bcl-2 stability.

BACKGROUND: Nicotine is able to activate mitogenic signalling pathways, which promote cell growth or survival as well as increase chemoresistance of cancer cells. However, the underlying mechanisms are not fully understood. METHODS: In this study, we used immunoblotting and immunoprecipitation methods to test the ubiquitination and degradation of Bcl-2 affected by nicotine in lung cancer cells. Apoptotic assay was also used to measure the antagonising effect of nicotine on cisplatin-mediated cytotoxicity. RESULTS: We demonstrated that the addition of nicotine greatly attenuated Bcl-2 ubiquitination and degradation, which further desensitised lung cancer cells to cisplatin-induced cytotoxicity. In this process, Bcl-2 was persistently phosphorylated in the cells cotreated with nicotine and cisplatin. Furthermore, Akt was proven to be responsible for sustained activation of Bcl-2 by nicotine, which further antagonised cisplatin-mediated apoptotic signalling. CONCLUSIONS: Our study suggested that nicotine activates its downstream signalling to interfere with the ubiquitination process and prevent Bcl-2 from being degraded in lung cancer cells, resulting in the increase of chemoresistance.

Immunohistochemical localization of human kallikreins 6, 10 and 13 in benign and malignant prostatic tissues.

Human kallikreins 6, 10 and 13 (hK6, hK10 and hK13) are expressed by many normal, mainly glandular tissues, including prostatic epithelium. Some kallikreins may function as tumor suppressors or are downregulated during cancer progression. The aim of this study was to evaluate the immunoexpression of these kallikreins in benign and malignant prostatic tissues and correlate their expression with prostate cancer (PC) prognosis. Included in the study were 25 cases of nonmalignant prostate and 179 cases of PC. Among them, 122 PC cases were immunostained for hK6, 94 for hK10 and 113 for hK13, respectively. The follow-up period for a subset of 68 patients who had undergone radical prostatectomy (RP) was 1-58 months (mean=13.4 +/- 1.7 and median=8.0 months). A cutoff value of 0.2 microg/l of serum PSA was established as a biochemical recurrence threshold. Follow-up information was available for 26/55 RP cases stained for hK6, 14/32 cases stained for hK10 and 25/59 cases stained for hK13. Gleason score (GS) 7 carcinomas were stratified as 7a and 7b, according to the primary grade. PC with GS 2-7a were histologically categorized as low malignant (LM) and PC with GS 7b-10 as high malignant (HM). The immunohistochemical method of streptavidin-biotin-peroxidase using monoclonal and polyclonal antibodies was performed. In the benign prostate and in prostatic intraepithelial neoplasia, a cytoplasmic immunostaining of varying intensity was evident. In PC, the immunoexpression of all kallikreins was decreased: 102/122 cases (84%) were positive for hK6, 73/94 (78%) for hK10 and 97/113 (86%) for hK13, respectively. A statistically significant difference in expression was found, in comparison to nonmalignant prostates (P=0.029, 0.009 and 0.045, respectively). Also, a positive correlation was observed between the immunoexpression of these three kallikreins. Concerning the histological grade, HM-PC expressed all three kallikreins with a slightly higher percentage than LM-PC: 79 vs 88% for hK6, 76 vs 79% for hK10 and 76 vs 92% for hK13. These differences were statistically significant only in the case of hK13 (P=0.024). Serum PSA did not correlate with kallikrein immunoexpression in PC. Furthermore, there was no significant correlation between kallikrein expression and pathological stage or recurrence, in the cases of RP. All three kallikreins are expressed in the nonmalignant and malignant prostate, with cancer tissues demonstrating slightly lower expression. Expression levels did not correlate with aggressiveness and they do not seem to have value for prostate cancer prognosis.

Identification of heat shock protein 90 and other proteins as tumour antigens by serological screening of an ovarian carcinoma expression library.

Serological screening of recombinant cDNA expression libraries has been widely used for the identification of tumour antigens in various cancer types. Identification of tumour antigens in ovarian cancer may facilitate the development of vaccine-based therapies and of disease biomarkers. The purpose of our investigation is to identify tumour antigens in ovarian cancer by using the serological analysis of recombinant cDNA expression libraries method. A recombinant ovarian carcinoma cDNA expression library was screened with ascites fluid, pooled from five ovarian cancer patients. Twelve tumour antigens encoded by known genes were isolated, including ribosomal protein S18, heat shock protein 90, JK-recombination signal binding protein, ribonucleoprotein H1, RAN binding protein 7, TG-interacting factor, eukaryotic translation initiation factor p40 subunit, human amyloid precursor protein-binding protein 1, ribosomal protein L8, CDC23, IQ motif containing GTPase activating protein 1, and ribosomal protein L3. Heat shock protein 90 was chosen for further investigation. The prevalence of hsp90 autoantibodies in ovarian cancer was determined with immunoassay. Sera from 22 normal females, 32 from ovarian cancer (22 stage III/IV, 10 stage I/II), 37 colorectal cancer, 13 breast cancer, 10 lung cancer, 20 benign gynaecologic diseases, and 10 benign breast lesions were screened. Seven (32%) stage III/IV ovarian cancer, 1 (10%) stage I/II ovarian cancer, 1 (3%) colorectal cancer, 1 (8%) breast cancer, and 1 (5%) benign gynaecologic disease sera were found to contain hsp90 autoantibodies. These data support the view that hsp90 autoantibodies are frequently found in late stage ovarian cancer. Hsp90 may, therefore, represent a novel biomarker for ovarian cancer and a candidate ovarian cancer vaccine target.

Higher expression of human kallikrein 10 in breast cancer tissue predicts tamoxifen resistance.

The human tissue kallikreins are secreted serine proteases, encoded by a group of homologous genes clustered in tandem on chromosome 19q13.3-4. Human kallikrein 6 and human kallikrein 10 are two new members of this family. Recently, we developed highly sensitive and specific immunofluorometric assays for human kallikrein 6 and human kallikrein 10, which allow for their quantification in tissue extracts and biological fluids. Both human kallikrein 6 and human kallikrein 10 are found to be down-regulated in breast cancer cell lines, suggesting that they may be involved in breast cancer pathogenesis and progression. In this study, we investigated the potential value of human kallikrein 6 and human kallikrein 10 as prognostic and predictive factors in breast cancer. We quantified human kallikrein 6 and human kallikrein 10 protein levels in 749 breast tumour cytosolic extracts and correlated this data with various clinicopathological variables and patient outcomes. Human kallikrein 6 and human kallikrein 10 are positively correlated with each other. Higher human kallikrein 6 and human kallikrein 10 protein levels are associated with younger age, pre-menopausal, status and tumours which are negative for oestrogen and progesterone receptors. No correlation was found between human kallikrein 6 and human kallikrein 10 levels and tumour size, grade, and nodal status. Survival analysis showed that neither human kallikrein 6 nor human kallikrein 10 are related to the rate of relapse-free and overall survival. In the analysis with respect to response to tamoxifen therapy, although human kallikrein 6 levels were not associated with tamoxifen responsiveness, higher levels of human kallikrein 10 were significantly associated with a poor response rate. This association remained significant in the multivariate analysis. Furthermore, higher human kallikrein 10 levels were significantly related with a short progression-free and post-relapse overall survival after start of tamoxifen treatment for advanced disease. Taken together, our results suggest that although human kallikrein 6 and human kallikrein 10 are not prognostic markers for breast cancer, human kallikrein 10 is an independent predictive marker for response of tamoxifen therapy.

Prognostic value of human kallikrein 10 expression in epithelial ovarian carcinoma.

PURPOSE: Human kallikrein 10 (hK10; also known as the normal epithelial cell-specific 1 gene and protein) is a secreted serine protease, which belongs to the human kallikrein family. It has been reported that hK10 is down-regulated in breast and prostate cancer cell lines and that it may function as a tumor suppressor. Recently, we developed a highly sensitive and specific immunoassay for hK10 and found that this protein is abundantly expressed in ovarian tissue. In this study, we measured quantitatively hK10 levels in ovarian cancer cytosolic extracts and evaluated the prognostic value of this biomarker in ovarian cancer. EXPERIMENTAL DESIGN: Specimens from eight normal ovarian tissues, eight ovarian tissues with benign disease, and 182 ovarian tumors were investigated. RESULTS: hK10 concentration in ovarian tumor cytosols ranged from 0 to 84 ng/mg of total protein, with a median of 2.6. This median was highly elevated in comparison with normal and benign ovarian tissues (P < 0.001). A cutoff of 1.35 ng/mg was selected to categorize tumors as hK10 high and hK10 low. With chi(2) test and Fisher's exact test, high concentration hK10 was found to be associated with advanced disease stage, serous histological type, suboptimal debulking, and large residual tumor (>1 cm; all P < 0.05). hK10 status was additionally correlated with clinical outcome, including progression-free (PFS) and overall survival (OS) using the Cox model. In univariate analysis, we found that patients with hK10 high tumors were more likely to die and relapse, in comparison with patients with hK10 low tumors (hazards ratios for PFS and OS were 1.93 and 2.42, respectively; P < 0.05). Although this correlation disappeared after the entire patient population was subjected to multivariate analysis, it remained significant in the subgroup of patients with stage III/IV ovarian cancer (hazards ratios for PFS and OS were 1.98 and 2.12, respectively; P < 0.05). CONCLUSIONS: Our results indicate that hK10 is a new, independent, unfavorable prognostic marker, especially for late-stage ovarian cancer.

Expression of the normal epithelial cell-specific 1 (NES1; KLK10) candidate tumour suppressor gene in normal and malignant testicular tissue.

The normal epithelial cell-specific 1 (NES1) gene (official name kallikrein gene 10; KLK10) is a new member of the expanding human kallikrein gene family and encodes for a secreted serine protease. Experimental evidence suggests that NES1 controls normal cell growth and may function as a tumour suppressor. NES1 is down-regulated during breast cancer progression. The NES1 gene is highly expressed in testicular as well as in other tissues. In this study, we investigated the expression level of the NES1 gene in cancerous and normal testicular tissues with reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry. In all 14 primary testicular germ-cell tumours examined, the NES1 gene expression was markedly reduced compared to adjacent (paired) normal tissues. We further examined 6 randomly selected primary germ-cell tumours and 8 normal tissues (obtained from different individuals). We confirmed the differential expression of the NES1 gene in germ-cell tumours (GCT) and pre-malignant carcinoma in situ (CIS). Our findings suggest that NES1 may act as a tumour suppressor and may play a role in the pathogenesis and progression of this malignancy.

Human kallikrein 10: a novel tumor marker for ovarian carcinoma?

BACKGROUND: Human kallikrein 10 (hK10, encoded by KLK10 gene) is a recently discovered member of the human kallikrein family. hK10 is a secreted serine protease. With the development of a highly sensitive and specific immunoassay for hK10, quantification of hK10 in the circulation is now feasible. Our aim was to investigate whether hK10 concentration in serum changes in various malignancies. METHODS: We used a highly specific and sensitive immunofluorometric assay to quantify hK10 protein in 374 serum samples from healthy individuals and patients with various malignancies. RESULTS: Serum hK10 concentration was found to be significantly elevated in 56% of the ovarian cancer patients and such an increase was not observed in serum of healthy individuals or in serum of patients with other types of cancer, with the exception of approximately 15% of patients with gastrointestinal cancer. This hK10 elevation does not correlate well with CA 125. We have further demonstrated that hK10 concentration changes during ovarian cancer progression. CONCLUSION: This is the first report describing that hK10 serum concentration is significantly elevated in the majority of ovarian cancer patients. Our results indicate that hK10 may be a potential new serological marker for ovarian cancer diagnosis and monitoring.

Immunofluorometric assay of human kallikrein 10 and its identification in biological fluids and tissues.

BACKGROUND: The human kallikrein 10 gene [KLK10, also known as normal epithelial cell-specific 1 gene (NES1)] is a member of the human kallikrein gene family. The KLK10 gene encodes for a secreted serine protease (hK10). We hypothesize that hK10 is secreted into various biological fluids and that its concentration changes in some disease states. The aim of this study was to develop a sensitive and specific immunoassay for hK10. METHODS: Recombinant hK10 protein was produced and purified using a Pichia pastoris yeast expression system. The protein was used as an immunogen to generate mouse and rabbit polyclonal anti-hK10 antisera. A sandwich-type immunofluorometric assay was then developed using these antibodies. RESULTS: The hK10 immunoassay has a detection limit of 0.05 microg/L. The assay is specific for hK10 and has no detectable cross-reactivity with other homologous kallikrein proteins, such as prostate-specific antigen (hK3), human glandular kallikrein 2 (hK2), and human kallikrein 6 (hK6). The assay was linear from 0 to 20 microg/L with within- and between-run CVs <10%. hK10 is expressed in many tissues, including the salivary glands, skin, and colon and is also detectable in biological fluids, including breast milk, seminal plasma, cerebrospinal fluid, amniotic fluid, and serum. CONCLUSIONS: We report development of the first immunofluorometric assay for hK10 and describe the distribution of hK10 in biological fluids and tissue extracts. This assay can be used to examine the value of hK10 as a disease biomarker.

Molecular cloning of a novel human gene on chromosome 4p11 by immunoscreening of an ovarian carcinoma cDNA library.

In our efforts to identify immunoreactive antigens in ovarian cancer, we used the method of immunoscreening of an ovarian carcinoma cDNA expression library with ascites fluid from ovarian cancer patients. Among many positive clones, one was found to contain partial sequence of a novel gene. By searching expressed sequence tags (ESTs) and human genome project databases as well as by screening other cDNA libraries and by RT-PCR strategies, we were able to obtain the full-length cDNA sequence (1.4 kb) and establish the genomic organization of this new gene. We also identified two alternatively spliced forms, encoding for slightly different proteins. The longer form (1.4 kb) is predicted to encode for a 27.6 kDa protein of 245 amino acids. The shorter form (1.3 kb) encodes for a truncated protein of 20.7 kDa and 208 amino acids. These proteins are not significantly homologous to any known protein in the GenBank database. This gene is composed of nine exons and eight introns. By fluorescence in situ hybridization (FISH), it was mapped to chromosome 4p11. This gene is highly expressed in many tissues, including testis, brain, placenta, ovary, prostate, and mammary gland. The high level expression of the shorter form is restricted to the central nervous system, including brain, cerebellum, and spinal cord, suggesting that this form may have a unique function in the central nervous system.

Preliminary examination of time-resolved fluorometry for protein array applications.

The advantages of time-resolved fluorometry over conventional fluorometric analysis are well known. However, time-resolved fluorescence has not as yet found wide applications in protein microarray or other multiparametric methods of analysis. Here we describe a general method which is suitable for multiparametric and microarray analysis, based on time-resolved fluorometry. A polystyrene surface is coated with different monoclonal antibodies, specific for certain analytes. The analyte mixtures are then universally biotinylated, using an active biotin ester. After removing excess biotin, the biotinylated samples are applied on the polystyrene surface, incubated and the excess is washed away. The bound moieties are then quantified by adding a universal detection reagent containing streptavidin, labelled with a fluorescent europium chelate. After washing and drying of the solid surface, the immobilized moieties are detected by using solid-phase, laser-excited time-resolved fluorometric analysis. In a preliminary examination of this principle, we have demonstrated that we can correctly identify upregulation of three secreted proteins, following stimulation of a breast carcinoma cell line with various steroids. Our method should be suitable for high-density microarray analysis of proteins, captured by specific monoclonal antibodies or other binding reagents.

The normal epithelial cell-specific 1 (NES1) gene is up-regulated by steroid hormones in the breast carcinoma cell line BT-474.

The normal epithelial cell-specific 1 (NES1) gene encodes a serine protease which was found to be down-regulated in breast cancer. There is evidence that NES1 acts as a tumor suppressor gene in breast cancer cells. To further understand its role in breast tumorigenesis, we investigated the effect of estrogens, androgens, and progestins on NES1 gene expression, in the breast cancer cell line BT-474, at the transcription level. The reverse transcriptase polymerase chain reaction method was used to monitor changes in the NES1 mRNA. Our experiments showed that NES1 gene expression is up-regulated promptly in response to 17 beta-estradiol, 5 alpha-dihydrotestosterone (DHT) and norgestrel stimulation. NES1 gene mRNA started to increase 2 hours after estradiol stimulation and 8 hours after DHT stimulation. The stimulation of NES1 by estradiol can be dramatically blocked by the estrogen antagonists ICI 182,780 and 4-hydroxytamoxifen. Mifepristone (a synthetic antiprogestin) can partially block the up-regulation of the NES1 gene by norgestrel. Dose-response experiments indicated that the lowest stimulatory concentration of 17 beta-estradiol, DHT, and norgestrel is 10(-11) M, 10(-10) M, and 10(-10) M, respectively. The production of NES1 mRNA increased coordinately with increasing concentration of the stimulants. These results suggest that the NES1 gene is primarily regulated by estrogen, but also by androgen and progestin in the breast cancer cell line BT-474. It appears that NES1 may be involved in a pathway that counter balances the action of estrogens and androgens in steroid hormone responsive tissues.

The new human kallikrein gene family: implications in carcinogenesis.

The traditional human kallikrein gene family consists of three genes, namely KLK1 [encoding human kallikrein 1 (hK1) or pancreatic/renal kallikrein], KLK2 (encoding hK2, previously known as human glandular kallikrein 1) and KLK3 [encoding hK3 or prostate-specific antigen (PSA)]. KLK2 and KLK3 have important applications in prostate cancer diagnostics and, more recently, in breast cancer diagnostics. During the past two to three years, new putative members of the human kallikrein gene family have been identified, including the PRSSL1 gene [encoding normal epithelial cell-specific 1 gene (NES1)], the gene encoding zyme/protease M/neurosin, the gene encoding prostase/KLK-L1, and the genes encoding neuropsin, stratum corneum chymotryptic enzyme and trypsin-like serine protease. Another five putative kallikrein genes, provisionally named KLK-L2, KLK-L3, KLK-L4, KLK-L5 and KLK-L6, have also been identified. Many of the newly identified kallikrein-like genes are regulated by steroid hormones, and a few kallikreins (NES1, protease M, PSA) are known to be downregulated in breast and possibly other cancers. NES1 appears to be a novel breast cancer tumor suppressor protein and PSA a potent inhibitor of angiogenesis. This brief review summarizes recent developments and possible applications of the newly defined and expanded human kallikrein gene locus.

Molecular characterization of zyme/protease M/neurosin (PRSS9), a hormonally regulated kallikrein-like serine protease.

The cDNA for the zyme/protease M/neurosin gene (HGMW-approved symbol PRSS9) has recently been identified. Zyme appears to play a role in Alzheimer disease as well as in breast cancer. In this paper, we describe the complete genomic organization of the zyme gene. Zyme spans 10.5 kb of genomic sequence on chromosome 19q13.3-q13.4. The gene consists of seven exons, the first two of which are untranslated. All splice junctions follow the GT/AG rule, and the intron phases are identical to those of many other genes belonging to the same family, i.e., the kallikreins, NES1, and neuropsin. Fine-mapping of the genomic locus indicates that zyme lies upstream of the NES1 gene and downstream from the PSA and KLK2 genes. Tissue expression studies indicate that zyme is expressed mainly in brain tissue, including spinal cord and cerebellum, in mammary gland, and in kidney and uterus. Zyme is regulated by steroid hormones in the breast carcinoma cell line BT-474. Estrogens and progestins, and to a lesser extent androgens, up-regulate the zyme gene in a dose-dependent manner.

Prostase/KLK-L1 is a new member of the human kallikrein gene family, is expressed in prostate and breast tissues, and is hormonally regulated.

By using the positional candidate gene approach, we were able to identify a novel serine protease gene that maps to chromosome 19q13.3-q13.4. Screening of expressed sequence tags allowed us to establish the expression of the gene and delineate its genomic organization (GenBank accession no. AF135023). We named this gene KLK-L1. Another group, by using a subtraction hybridization method, cloned the same gene and named it prostase (GenBank accession nos. AF113140 and AF113141). Here, we describe the precise mapping and localization of the prostase/KLK-L1 gene between the known genes KLK2 (human glandular kallikrein) and zyme (also known as protease M/neurosin). The direction of transcription of prostase/KLK-L1 is the same as that of zyme but opposite to that of KLK2 and prostate-specific antigen genes. Contrary to the initial impression, prostase/KLK-L1 is expressed at high levels not only in prostate tissue but also in testis, mammary gland, adrenals, uterus, thyroid, and salivary glands. We have further demonstrated with in vitro experiments with the breast carcinoma cell line BT-474 that this gene is expressed and that its expression is up-regulated by androgens and progestins. On the basis of information on other genes that are localized in the same region (prostate-specific antigen, KLK2, zyme, and normal epithelial cell specific-1 gene), we speculate that prostase/KLK-L1 may be involved in the pathogenesis and/or progression of prostate, breast, and possibly other malignancies.

Identification of novel human kallikrein-like genes on chromosome 19q13.3-q13.4.

The human kallikrein gene family is localized on chromosome 19q13.3-q13.4 and currently includes three members: KLK1 or pancreatic/renal kallikrein, KLK2 or human glandular kallikrein and KLK3 or prostate-specific antigen (PSA). The latter two genes are almost prostate-specific and they are used for diagnosis and monitoring of prostate cancer and more recently, in breast cancer applications. In this paper, we analyzed a 300Kb genomic DNA region around chromosome 19q13.3-q13.4 in an effort to map known kallikrein or kallikrein-like genes and identify new kallikrein-like genes. Using the known kallikrein or kallikrein-like genes PSA, KLK2, enzyme and normal epithelial cell-specific 1 gene (NES1) as landmarks, we have identified another six novel genes of which, five have protein homologies and gene structure similarities with other kallikreins or kallikrein-like genes. We conclude, contrary to the current belief, that the human kallikrein gene locus contains a large number of kallikrein-like genes (at least thirteen). In this paper, we present a detailed description of the human kallikrein gene locus, encompassing the already known and newly identified genes. These new genes, like the already known kallikreins, may have utility for diagnosis, monitoring and therapeutics of various cancers including those of the breast, prostate and testis.

Monoclonal anti-human T cell antibody and PAP-s conjugate--preparation and selective cytotoxic properties on leukemic cell.

Pokeweed antiviral protein (PAP-s) was prepared from seeds of Phytolacca americana. Monoclonal antibody against human pan-T lymphocyte Wu71 was linked to PAP-s by a disulfide bond. The results of SDS-PAGE, double immunodiffusion of active monoclonal antibody and PAP-s showed that the conjugate was highly cytotoxic to the human T-leukemic cell line CEM, but not to antigen-negative cell line SP2/O. At a concentration of 10(-9) mol/L, 76.4% of the target cells were killed, as compared with 10.1% at 10(-9) mol/L of free PAP-s. Treatment of the CEM cells with conjugate at 10(-9) mol/L reduced their rate of protein synthesis by 72.4%, as determined with 14C-leucine incorporation. The immunotoxin may be useful for the in-vitro eradication of leukemic cells in autologous bone marrow transplantation to leukemia patients.