Adult bone-marrow stem cells and their potential in medicine

Effects of the MCF-7 Exhausted Medium on hADSC Behaviour

Stem cells possess the ability to differentiate into different lineages and the ability to self-renew, thus representing an excellent tool for regenerative medicine. They can be isolated from different tissues, including the adipose tissue. Adipose tissue and human adipose-derived stem cells (hADSCs) are privileged candidates for regenerative medicine procedures or other plastic reconstructive surgeries. The cellular environment is able to influence the fate of stem cells residing in the tissue. In a previous study, we exposed hADSCs to an exhausted medium of a breast cancer cell line (MCF-7) recovered at different days (4, 7, and 10 days). In the same paper, we inferred that the medium was able to influence the behaviour of stem cells. Considering these results, in the present study, we evaluated the expression of the major genes related to adipogenic and osteogenic differentiation. To confirm the gene expression data, oil red and alizarin red colorimetric assays were performed. Lastly, we evaluated the expression of miRNAs influencing the differentiation process and the proliferation rate, maintaining a proliferative state. The data obtained confirmed that cells exposed to the medium maintained a stem and proliferative state that could lead to a risky proliferative phenotype.

Osteogenic effect of electromagnetic fields on stem cells derived from rat bone marrow cultured in osteogenic medium versus conditioned medium in vitro

OBJECTIVES

This study assessed possible osteogenic differentiation caused by electromagnetic fields (EMF) on rat bone-marrow-derived stem cells (rBMSCs) cultured in osteogenic medium (OM) or in human adipose-stem cell-conditioned medium (hADSC-CM).

MATERIALS AND METHODS

The rBMSCs were divided into negative and positive control groups, cultured in α-MEM plus 10% FBS or OM respectively. CM and CM + EMF  groups, cultured cells in hADSCs-CM or exposed to EMF (50 Hz, 1 mT) for 30 min/day plus hADSCs-CM, respectively. Cells from the OM + EMF were simultaneously cultured in OM and exposed to EMF. Osteogenesis was investigated through alkaline phosphatase activity, alizarin red staining and real-time PCR.

RESULTS

A meaningfully higher level of ALP activity was observed in the OM + EMF group compared to the other groups. There was a considerable increase in Runx2 expression in the CM + EMF group compared to the positive control and CM groups and a significant increase in Runx2 expression in the OM + EMF in comparison with all other groups after 21 days. Runx2 expression increased significantly in the CM, CM + EMF and positive control groups on day 21 compared to the same groups on day 14. From days 14-21, Ocn expression increased in the CM and CM + EMF groups, but both groups showed a significant decrease compared to the positive controls. CM and EMF had no effect on Ocn expression. On day 21, Ocn expression was significantly higher in the OM + EMF group than in the positive control group.

CONCLUSION

The synergistic effect of EMF and OM increased the expression of Runx2 and Ocn in rBMSCs.

Connexins in the development and physiology of stem cells

Connexins (Cxs) form gap junction (GJ) channels linking vertebrate cells. During embryogenesis, Cxs are expressed as early as the 4-8 cell stage. As cells differentiate into pluripotent stem cells (PSCs) and during gastrulation, the Cx expression pattern is adapted. Knockdown of Cx43 and Cx45 does not interfere with embryogenic development until the blastula stage, questioning the role of Cxs in PSC physiology and development. Studies in cultivated and induced PSCs (iPSCs) showed that Cx43 is essential for the maintenance of self-renewal and the expression of pluripotency markers. It was found that the role of Cxs in PSCs is more related to regulation of transcription or cell-cell adherence than to formation of GJ channels. Furthermore, a crucial role of Cxs for the self-renewal and differentiation was shown in cultivated adult mesenchymal stem cells. This review aims to highlight aspects that link Cxs to the function and physiology of stem cell development.

Autologous Minimally Invasive Cell-Based Therapy for Meniscal and Anterior Cruciate Ligament Regeneration

The meniscus is a fibrocartilaginous tissue that acts as a “shock absorber,” along with performing functions such as stabilization and lubrication of the joint, proprioception, and load distribution. Sudden twisting movements during weight bearing or trauma can cause injury to the menisci, which leads to symptoms such as pain, swelling, and difficulty in performing movements, among others. Conventional pharmacological and surgical treatments are effective in treating the condition; however, do not result in regeneration of healthy tissues. In this report, we highlight the role of cell-based therapy in the management of medial and lateral meniscal and anterior cruciate ligament tears in a patient who was unwilling to undergo surgical treatment. We injected autologous mesenchymal stem cells obtained from the bone marrow and adipose tissue and platelet-rich plasma into the joint of the patient at the area of injury, as well as intravenously. The results of our study corroborate with those previously reported in the literature regarding the improvement in clinical parameters and regeneration of meniscal tissue and ligament. Thus, based on previous literature and improvements noticed in our patient, cell-based therapy can be considered a safe and effective therapeutic modality in the treatment of meniscal tears and cruciate ligament injury.

Study on the Design and Optimization of a Portable Monitoring and Auxiliary Treatment Device for Upper Extremity Lymphedema-Focus on the Rehabilitation Function of the Device

Female patients suffer from the risk of upper limb lymphedema after breast cancer removal surgery. At present, the detection and the adjuvant treatment of this disease are not convenient enough, leading to delay of the disease and increase in the burden of patients. This paper presents a portable monitoring and treatment device for upper extremity lymphedema, enabling patients to monitor the symptoms of upper limb lymphedema and auxiliary rehabilitation. This design utilizes the arm circumference measurement and contrast method to realize symptom monitoring. The device realizes auxiliary rehabilitation using the regional pressure method to imitate traditional manual lymphatic drainage technology. According to the MRI images of volunteers’ upper limbs, the upper arm and forearm’s finite element models are reconstructed in ANSYS. The static simulation experiment is completed. The working mode and parameter design of each rehabilitation module of the device are obtained. The experimental results show that the integrated design principle of monitoring and treatment proposed in this paper has good feasibility, has auxiliary rehabilitation effect, and meets the principle of human comfort. The device can help patients find lymphedema in time and implement auxiliary treatment, which can effectively avoid the further deterioration of lymphedema.

Knee Osteoarthritis: A Review of Pathogenesis and State-Of-The-Art Non-Operative Therapeutic Considerations

Being the most common musculoskeletal progressive condition, osteoarthritis is an interesting target for research. It is estimated that the prevalence of knee osteoarthritis (OA) among adults 60 years of age or older is approximately 10% in men and 13% in women, making knee OA one of the leading causes of disability in elderly population. Today, we know that osteoarthritis is not a disease characterized by loss of cartilage due to mechanical loading only, but a condition that affects all of the tissues in the joint, causing detectable changes in tissue architecture, its metabolism and function. All of these changes are mediated by a complex and not yet fully researched interplay of proinflammatory and anti-inflammatory cytokines, chemokines, growth factors and adipokines, all of which can be measured in the serum, synovium and histological samples, potentially serving as biomarkers of disease stage and progression. Another key aspect of disease progression is the epigenome that regulates all the genetic expression through DNA methylation, histone modifications, and mRNA interference. A lot of work has been put into developing non-surgical treatment options to slow down the natural course of osteoarthritis to postpone, or maybe even replace extensive surgeries such as total knee arthroplasty. At the moment, biological treatments such as platelet-rich plasma, bone marrow mesenchymal stem cells and autologous microfragmented adipose tissue containing stromal vascular fraction are ordinarily used. Furthermore, the latter two mentioned cell-based treatment options seem to be the only methods so far that increase the quality of cartilage in osteoarthritis patients. Yet, in the future, gene therapy could potentially become an option for orthopedic patients. In the following review, we summarized all of the latest and most important research in basic sciences, pathogenesis, and non-operative treatment.

The 'diamond concept' for long bone non-union management

Long bone non-union continues to be a significant worldwide problem. Since its inception over a decade ago, the ‘diamond concept’, a conceptual framework of what is essential for a successful bone healing response, has gained great acceptance for assessing and planning the management of fracture non-unions. Herein, we discuss the epidemiology of non-unions, the basic science of bone healing in the context of the diamond concept, the currently available results and areas for future research.

Insulin producing cells established using non-integrated lentiviral vector harboring PDX1 gene

AIM: To investigate reprogramming of human adipose tissue derived stem cells into insulin producing cells using non-integrated lentivirus harboring PDX1 gene.

METHODS: In this study, human adipose tissue derived stem cells (hADSCs) were obtained from abdominal adipose tissues by liposuction, selected by plastic adhesion, and characterized by flow cytometric analysis. Human ADSCs were differentiated into adipocytes and osteocytes using differentiating medium to confirm their multipotency. Non-integrated lentiviruses harboring PDX1 (Non-integrated LV-PDX1) were constructed using specific plasmids (pLV-HELP, pMD2G, LV-105-PDX1-1). Then, hADSCs were transduced with non-integrated LV-PDX1. After transduction, ADSCs^PDX1+ were cultured in high glucose DMEM medium supplement by B27, nicotinamide and βFGF for 21 d. Expressions of PDX1 and insulin were detected at protein level by immunofluorescence analysis. Expressions of PDX1, neurogenin3 (Ngn3), glucagon, glucose transporter2 (Glut2) and somatostatin as specific marker genes were investigated at mRNA level by quantitative RT-PCR. Insulin secretion of hADSCs^PDX1+ in the high-glucose medium was detected by electrochemiluminescence test. Human ADSCs^PDX1+ were implanted into hyperglycemic rats.

RESULTS: Human ADSCs exhibited their fibroblast-like morphology and made colonies after 7-10 d of culture. Determination of hADSCs identified by FACS analysis showed that hADSCs were positive for mesenchymal cell markers and negative for hematopoietic cell markers that guaranteed the lack of hematopoietic contamination. In vitro differentiation of hADSCs into osteocytes and adipocytes were detected by Alizarin red and Oil red O staining and confirmed their multilineage differentiation ability. Transduced hADSCs^+PDX1 became round and clusters in the differentiation medium. The appropriate expression of PDX1 and insulin proteins was confirmed using immunocytochemistry analysis. Significant expressions of PDX1, Ngn3, glucagon, Glut2 and somatostatin were detected by quantitative RT-PCR. hADSCs^PDX1+ revealed the glucose sensing ability by expressing Glut2 when they were cultured in the medium containing high glucose concentration. The insulin secretion of hADSCs^PDX1+ in the high glucose medium was 2.32 μU/mL. hADSCs^PDX1+ implantation into hyperglycemic rats cured it two days after injection by reducing blood glucose levels from 485 mg/dL to the normal level.

CONCLUSION: Human ADSCs can differentiate into IPCs by non-integrated LV-PDX1 transduction and have the potential to be used as a resource in type 1 diabetes cell therapy.

Characterization of mononucleated human peripheral blood cells

Unspecialized cells that can renew themselves and give rise to multiple differentiated cell types are termed stem cells. The objective of this study was to characterize and investigate, through molecular and biochemical analyses, the stemness of cells derived from isolated mononucleated cells that originated from peripheral blood. The isolated mononucleated cells were separated according to their physical characteristics (adherent and suspension), after 4 to 7 days into a 14-day culturing period in complete medium. Our results revealed that adherent and suspension cells were positive for mesenchymal stem cell (MSC) and hematopoietic stem cell (HSC) markers, respectively. Differentiation of adherent cells into osteoblasts was associated with expression of the OPN gene and increasing ALP enzyme activity, while differentiation of suspension cells into osteoclasts was associated with expression of the TRAP gene and increasing TRAP enzyme activity. In conclusion, molecular and biochemical analyses showed that mononucleated cells consist of MSC (adherent) and HSC (suspension), and both cell types are able to differentiate into specialized cells from their respective lineage: osteoblast (MSC) and osteoclast (HSC).

Activated leukemic oncogenes AML1-ETO and c-kit: role in development of acute myeloid leukemia and current approaches for their inhibition

Acute myeloid leukemia (AML) is a malignant blood disease caused by different mutations that enhance the proliferative activity and survival of blood cells and affect their differentiation and apoptosis. The most frequent disorders in AML are translocations between chromosomes 21 and 8 leading to production of a chimeric oncogene, AML1-ETO, and hyperexpression of the receptor tyrosine kinase KIT. Mutations in these genes often occur jointly. The presence in cells of two activated oncogenes is likely to trigger their malignization. The current approaches for treatment of oncologic diseases (bone marrow transplantation, radiotherapy, and chemotherapy) have significant shortcomings, and thus many laboratories are intensively developing new approaches against leukemias. Inhibiting expression of activated leukemic oncogenes based on the principle of RNA interference seems to be a promising approach in this field.

Ovarian cancer cells with the CD117 phenotype are highly tumorigenic and are related to chemotherapy outcome

Cancer stem cells (CSCs) play an important role in the recurrence and drug resistance of cancer. Isolation and characterization of CSCs from ovarian cancer samples may help to provide novel diagnostic and therapeutic targets in the management of recurrent disease and drug resistance in ovarian cancer. Here, we developed a xenograft model in which cells from 14 samples of human ovarian serous adenocarcinoma tissue or ascites were implanted in immunodeficient mice to test the tumorigenic potential of different populations of ovarian cancer cells. We identified and isolated the tumorigenic cells as CD117(+)Lineage(-) from three different xenografts. As few as 10(3) cells with the CD117(+)Lineage(-) phenotype, which comprise <2% of the xenograft tumor cells, were able to regenerate tumors in a mouse model, a 100-fold increase in tumorigenic potential compared to CD117(-)Lineage(-) cells. The tumors that arose from purified CD117(+)Lineage(-) cells reproduced the original tumor heterogeneity and could be serially generated, demonstrating the ability to self-renew and to differentiate, two defining properties of stem cells. Furthermore, immunohistochemistry analysis of 25 patients with advanced ovarian serous adenocarcinoma revealed positive immunostaining for CD117 in 40% (10 of 25) of patients. CD117 expression was statistically correlated with resistance to conventional chemotherapy (P=0.027). In conclusion, our study demonstrates that human ovarian cancer cells with the CD117(+) phenotype possess the unique properties of CSCs, including self-renewal, differentiation, a high tumorigenic potential, and chemoresistance. Future studies designed to target CD117(+) cancer cells may identify more attractive and effective therapies for treatment of ovarian cancer.

Successful transplant of mesenchymal stem cells in induced osteonecrosis of the ovine femoral head: preliminary results

PURPOSE

Evaluate the bone tissue recovery following transplantation of ovine mesenchymal stem cells (MSC) from bone marrow and human immature dental-pulp stem cells (hIDPSC) in ovine model of induced osteonecrosis of femoral head (ONFH).

METHODS

Eight sheep were divided in three experimental groups. First group was composed by four animals with ONFH induced by ethanol through central decompression (CD), for control group without any treatment. The second and third group were compose by two animals, six weeks after ONFH induction received transplantation of heterologous ovine MSC (CD + oMSC), and hIDPSC (CD + hIDPSC), respectively. In both experiments the cells were transplanted without application of any type of immunosupression protocol.

RESULTS

Our data indicate that both cell types used in experiments were able to proliferate within injured site providing bone tissue recovery. The histological results obtained from CD+hIDPSC suggested that the bone regeneration in such animals was better than that observed in CD animals.

CONCLUSION

Mesenchymal stem cell transplant in induced ovine osteonecrosis of femoral head by central decompression technique is safe, and apparently favors bone regeneration of damaged tissues.

Essential roles of the nitric oxide (no)/cGMP/protein kinase G type-Iα (PKG-Iα) signaling pathway and the atrial natriuretic peptide (ANP)/cGMP/PKG-Iα autocrine loop in promoting proliferation and cell survival of OP9 bone marrow stromal cells

Inappropriate signaling conditions within bone marrow stromal cells (BMSCs) can lead to loss of BMSC survival, contributing to the loss of a proper micro-environmental niche for hematopoietic stem cells (HSCs), ultimately causing bone marrow failure. In the present study, we investigated the novel role of endogenous atrial natriuretic peptide (ANP) and the nitric oxide (NO)/cGMP/protein kinase G type-Iα (PKG-Iα) signaling pathway in regulating BMSC survival and proliferation, using the OP9 BMSC cell line commonly used for facilitating the differentiation of HSCs. Using an ANP-receptor blocker, endogenously produced ANP was found to promote cell proliferation and prevent apoptosis. NO donor SNAP (S-nitroso-N-acetylpenicillamine) at low concentrations (10 and 50 µM), which would moderately stimulate PKG activity, protected these BMSCs against spontaneous apoptosis. YC-1, a soluble guanylyl cyclase (sGC) activator, decreased the levels of apoptosis, similar to the cytoprotective effects of low-level NO. ODQ (1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one), which blocks endogenous NO-induced activation of sGC and thus lowers endogenous cGMP/PKG activity, significantly elevated apoptotic levels by 2.5- and three-fold. Pre-incubation with 8-Bromo-cGMP or ANP, which bypass the ODQ block, almost completely prevented the ODQ-induced apoptosis. A highly-specific PKG inhibitor, DT-3, at 20, and 30 µM, caused 1.5- and two-fold increases in apoptosis, respectively. ODQ and DT-3 also decreased BMSCs proliferation and colony formation. Small Interfering RNA gene knockdown of PKG-Iα increased apoptosis and decreased proliferation in BMSCs. The data suggest that basal NO/cGMP/PKG-Iα activity and autocrine ANP/cGMP/PKG-Iα are necessary for preserving OP9 cell survival and promoting cell proliferation and migration.

Exhaustive expansion: A novel technique for analyzing complex data generated by higher-order polychromatic flow cytometry experiments

Background

The complex data sets generated by higher-order polychromatic flow cytometry experiments are a challenge to analyze. Here we describe Exhaustive Expansion, a data analysis approach for deriving hundreds to thousands of cell phenotypes from raw data, and for interrogating these phenotypes to identify populations of biological interest given the experimental context.

Methods

We apply this approach to two studies, illustrating its broad applicability. The first examines the longitudinal changes in circulating human memory T cell populations within individual patients in response to a melanoma peptide (gp100_209-2M) cancer vaccine, using 5 monoclonal antibodies (mAbs) to delineate subpopulations of viable, gp100-specific, CD8+ T cells. The second study measures the mobilization of stem cells in porcine bone marrow that may be associated with wound healing, and uses 5 different staining panels consisting of 8 mAbs each.

Results

In the first study, our analysis suggests that the cell surface markers CD45RA, CD27 and CD28, commonly used in historical lower order (2-4 color) flow cytometry analysis to distinguish memory from naïve and effector T cells, may not be obligate parameters in defining central memory T cells (T_CM). In the second study, we identify novel phenotypes such as CD29+CD31+CD56+CXCR4+CD90+Sca1-CD44+, which may characterize progenitor cells that are significantly increased in wounded animals as compared to controls.

Conclusions

Taken together, these results demonstrate that Exhaustive Expansion supports thorough interrogation of complex higher-order flow cytometry data sets and aids in the identification of potentially clinically relevant findings.

Intraarterial autologous implantation of adult stem cells for patients with Parkinson disease

PURPOSE

To evaluate the feasibility, safety, and effectiveness of intraarterial autologous implantation of adult stem cells for Parkinson disease (PD).

MATERIALS AND METHODS

From June 2006 to August 2008, 36 men and 14 women (mean age, 62.5 years +/- 10.4; range, 38-81 y) with PD (mean duration, 9.3 years; range, 1-28 y) underwent autologous implantation of stem cells with superselective arterial catheterization. Patients were evaluated with clinical and neurologic examinations; internationally recognized scales for the evaluation of PD, disability, activities of daily living, depression, and quality of life (QOL); as well as videos, magnetic resonance (MR) imaging, and MR spectroscopy. Stem cells were implanted in the posterior region of the circle of Willis. Patients were evaluated according to clinical measures. Comparison was made versus data collected from all scales before treatment, as well as videos and spectroscopy in eight patients.

RESULTS

In a mean follow-up of 7.4 months +/- 4.5 (range, 1-18 months), patients showed a median improvement of 51.1% and quartile deviation (QD) of 24.8% on the Unified PD Rating Scale. They showed significant improvement in disability, activities of daily living, depression, and QOL (P < .5). No complications were observed. In eight patients, follow-up MR spectroscopy revealed mean improvements in n-acetylaspartate/creatine ratio from 1.805 to 2.07 (12.8%) and from 1.25 to 1.88 (43.56%) in right and left basal ganglia, respectively, versus preprocedural values (P < .05).

CONCLUSIONS

Treatment of PD with intraarterial autologous implantation of adult stem cells is feasible and safe and results in improved severity of disease and QOL.

Proteomics in bone research

Osteoporosis is prevalent among the elderly and is a major cause of bone fracture in this population. Bone integrity is maintained by the dynamic processes of bone resorption and bone formation (bone remodeling). Osteoporosis results when there is an imbalance of the two counteracting processes. Bone mineral density, measured by dual-energy x-ray absorptiometry has been the primary method to assess fracture risk for decades. Recent studies demonstrated that measurement of bone turnover markers allows for a dynamic assessment of bone remodeling, while imaging techniques, such as dual-energy x-ray absorptiometry, do not. The application of proteomics has permitted discoveries of new, sensitive, bone turnover markers, which provide unique information for clinical diagnosis and treatment of patients with bone diseases. This review summarizes the recent findings of proteomic studies on bone diseases, properties of mesenchymal stem cells with high expansion rates and osteoblast and osteoclast differentiation, with emphasis on the role of quantitative proteomics in the study of signaling dynamics, biomarkers and discovery of therapeutic targets.

c-Kit expression in human normal and malignant stem cells prognostic and therapeutic implications

The human stem cell factor/c-Kit signaling pathway is pivotal for the survival of embryonic, foetal and adult stem cells and for their fundamental role in generating healthy functioning cell and tissue types during embryonic, foetal and adult life. Common biological features between human stem cells and cancer cells include (A) self-renewal, (B) extensive capacity of proliferation, (C) migration to and homing at distant sites and (D) resistance to toxic agents. Given these shared attributes, cancer was proposed to originate from transforming mutation(s) in normal stem cells that dysregulate their physiological programs. This theory has been recently supported by the findings that among all malignant cells within a particular tumour, only cell fraction expressing stem cell markers such as c-Kit named 'cancer stem cells' has the exclusive potential to generate tumour cell population. The involvement of c-Kit and its mutation in various haematological malignancies and solid tumours are reviewed. The impacts of dysregulated c-Kit as oncogenic tyrosine kinase on autocrine stimulation and resistance to chemotherapy of cancer stem cells are evaluated. The significance and efficacy of molecular therapeutic targeting of c-Kit signaling pathway in the management of patients with c-Kit-positive malignancies are appraised.

Cytokine mobilization of bone marrow cells and pancreatic lesion do not improve streptozotocin-induced diabetes in mice by transdifferentiation of bone marrow cells into insulin-producing cells

OBJECTIVE

Transdifferentiation of bone marrow cells (BMC) into insulin-producing cells might provide a new cellular therapy for type I diabetes, but its existence is controversial. Our aim was to determine if those cells could transdifferentiate, even at low frequency, into insulin-producing cells, in testing optimized experimental conditions.

METHODS

We grafted mice with total BMC, genetically labeled either ubiquitarily, or with a marker conditionally expressed under the control of the insulin beta-cell specific promoter. We treated some of the recipients with an agent toxic to beta-cells (streptozotocin) and with cytokines stem cell factor (SCF) and granulocyte-colony stimulating factor (G-CSF).

RESULTS

The contribution of grafted cells could be detected neither for natural turnover (n=6), nor for beta-cell regeneration after pancreatic lesion (n=7), 90 days post-transplantation. Cytokine mobilization of BMC in the blood stream, reported to favor their transdifferentiation into cardiac and neural cells, had never been tested before for beta-cell generation. Here, we showed that injection of SCF and G-CSF did not lead to a detectable level of transdifferentiation (n=7).

CONCLUSIONS

We conclude that BMC cannot spontaneously transdifferentiate into insulin-producing cells in vivo, even after beta-cell lesion and mobilization induced by cytokines. Interestingly, however, treatment by cytokines may have beneficial indirect effects on STZ-induced hyperglycaemia.

Using therapeutic cloning to fight human disease: a conundrum or reality?

The development and transplantation of autologous cells derived from nuclear transfer embryonic stem cell (NT-ESC) lines to treat patients suffering from disease has been termed therapeutic cloning. Human NT is still a developing field, with further research required to improve somatic cell NT and human embryonic stem cell differentiation to deliver safe and effective cell replacement therapies. Furthermore, the implications of transferring mitochondrial heteroplasmic cells, which may harbor aberrant epigenetic gene expression profiles, are of concern. The production of human NT-ESC lines also remains plagued by ethical dilemmas, societal concerns, and controversies. Recently, a number of alternate therapeutic strategies have been proposed to circumvent the moral implications surrounding human nuclear transfer. It will be critical to overcome these biological, legislative, and moral restraints to maximize the potential of this therapeutic strategy and to alleviate human disease.