L. G. Lajtha

Bio: L. G. Lajtha is an academic researcher. The author has contributed to research in topics: Bone marrow & Population. The author has an hindex of 3, co-authored 3 publications receiving 2336 citations.

Conditions controlling the proliferation of haemopoietic stem cells in vitro.

Abstract: A liquid culture system is described whereby proliferation of haemopoietic stem cells (CFU-S), production of granulocyte precursor cells (CFU-C), and extensive granulopoiesis can be maintained in vitro for several months. Such cultures consist of adherent and non-adherent populations of cells. The adherent population contains phagocytic mononuclear cells, “epithelial” cells, and “giant fat” cells. The latter appear to be particularly important for stem cell maintenance and furthermore there is a strong tendency for maturing granulocytes to selectively cluster in and around areas of “giant fat” cell aggregations. By “feeding” the cultures at weekly intervals, between 10 to 15 “population doublings” of functionally normal CFU-S regularly occurs. Increased “population doublings” may be obtained by feeding twice weekly. The cultures show initially extensive granulopoiesis followed, in a majority of cases, by an accumulation of blast cells. Eventually both blast cells and granulocytes decline and the cultures contain predominantly phagocytic mononuclear cells. Culturing at 33°C leads to the development of a more profuse growth of adherent cells and these cultures show better maintenance of stem cells and increased cell density. When tested for colony stimulating activity (CSA) the cultures were uniformly negative. Addition of exogenous CSA caused a rapid decline in stem cells, reduced granulopoiesis and an accumulation of phagocytic mononuclear cells.

Stimulation of differentiation and proliferation of haemopoietic cells in vitro.

Abstract: A liquid culture system, for haemopoietic cells, has been developed using bone marrow cells alone, or co-cultures of thymus and bone marrow cells, inoculated into four ounce medical bottles. After several days growth, such cultures consisted of an attaching population of cells, forming discrete colonies, and a non-attaching population. In the (co-cultures) there was a 2 X enhancement of monolayer colony development compared with the combined total present in the (marrow alone) plus (thymus alone) cultures. Also, better maintenance of non-attaching cells was seen in the (co-cultures). Normal CFUS and CFUC were present in both the (marrow alone) and the (co-cultures) for at least 14 days. In the (marrow alone) cultures, granulocytes in all stages of development were present for the first week, but by 12 days the culture consisted mainly of mono-nuclear cells. In the (co-cultures), however, at 12 days more than 60% of the cells were granulocytes, in all stages of differentiation. (Co-cultures) established using lethally irradiated thymus cells were not able to support this prolonged myeloid differentiation. By feeding the (co-cultures) it was possible to maintain production of (granulocytic) cells for at least ten weeks, although no fully mature granulocytes were observed. After the second feeding, no CFUS were detectable, but variable numbers of agar colony forming cells (not classical CFUC) were present at least for ten weeks.

Studies on the mechanisms of chemical leukaemogenesis.

Abstract: Following a single injection of MNU into “intact” mice, a high incidence of leukaemia (90%) is obtained, with a 50% induction time of 200 days. Immunological studies indicate that the θ antigen is expressed on the leukaemic cells. Thymectomized MNU treated mice had a 50% induction time of 500 days, and the incidence was somewhat lower. Leukaemias failed to develop in MNU treated T lymphocyte deficient animals and in lethally irradiated, or thymectomized lethally irradiated mice reconstituted with MNU treated bone marrow. It is suggested that the T lymphocytes rather than the haemopoietic stem cells or pre-T cells are the “target cells” in MNU leukaemogenesis.

Marrow Stromal Cells as Stem Cells for Nonhematopoietic Tissues

Abstract: Marrow stromal cells can be isolated from other cells in marrow by their tendency to adhere to tissue culture plastic The cells have many of the characteristics of stem cells for tissues that can roughly be defined as mesenchymal, because they can be differentiated in culture into osteoblasts, chondrocytes, adipocytes, and even myoblasts Therefore, marrow stromal cells present an intriguing model for examining the differentiation of stem cells Also, they have several characteristics that make them potentially useful for cell and gene therapy

A metalloproteinase disintegrin that releases tumour-necrosis factor-α from cells

Abstract: Mammalian cells proteolytically release (shed) the extracellular domains of many cell-surface proteins. Modification of the cell surface in this way can alter the cell's responsiveness to its environment and release potent soluble regulatory factors. The release of soluble tumour-necrosis factor-alpha (TNF-alpha) from its membrane-bound precursor is one of the most intensively studied shedding events because this inflammatory cytokine is so physiologically important. The inhibition of TNF-alpha release (and many other shedding phenomena) by hydroxamic acid-based inhibitors indicates that one or more metalloproteinases is involved. We have now purified and cloned a metalloproteinase that specifically cleaves precursor TNF-alpha. Inactivation of the gene in mouse cells caused a marked decrease in soluble TNF-alpha production. This enzyme (called the TNF-alpha-converting enzyme, or TACE) is a new member of the family of mammalian adamalysins (or ADAMs), for which no physiological catalytic function has previously been identified. Our results should facilitate the development of therapeutically useful inhibitors of TNF-alpha release, and they indicate that an important function of adamalysins may be to shed cell-surface proteins.

Identification of the haematopoietic stem cell niche and control of the niche size

Abstract: Haematopoietic stem cells (HSCs) are a subset of bone marrow cells that are capable of self-renewal and of forming all types of blood cells (multi-potential). However, the HSC 'niche'--the in vivo regulatory microenvironment where HSCs reside--and the mechanisms involved in controlling the number of adult HSCs remain largely unknown. The bone morphogenetic protein (BMP) signal has an essential role in inducing haematopoietic tissue during embryogenesis. We investigated the roles of the BMP signalling pathway in regulating adult HSC development in vivo by analysing mutant mice with conditional inactivation of BMP receptor type IA (BMPRIA). Here we show that an increase in the number of spindle-shaped N-cadherin+CD45- osteoblastic (SNO) cells correlates with an increase in the number of HSCs. The long-term HSCs are found attached to SNO cells. Two adherens junction molecules, N-cadherin and beta-catenin, are asymmetrically localized between the SNO cells and the long-term HSCs. We conclude that SNO cells lining the bone surface function as a key component of the niche to support HSCs, and that BMP signalling through BMPRIA controls the number of HSCs by regulating niche size.

Mesenchymal stem cells as trophic mediators.

Abstract: Adult marrow-derived Mesenchymal Stem Cells (MSCs) are capable of dividing and their progeny are further capable of differentiating into one of several mesenchymal phenotypes such as osteoblasts, chondrocytes, myocytes, marrow stromal cells, tendon-ligament fibroblasts, and adipocytes. In addition, these MSCs secrete a variety of cytokines and growth factors that have both paracrine and autocrine activities. These secreted bioactive factors suppress the local immune system, inhibit fibrosis (scar formation) and apoptosis, enhance angiogenesis, and stimulate mitosis and differentiation of tissue-intrinsic reparative or stem cells. These effects, which are referred to as trophic effects, are distinct from the direct differentiation of MSCs into repair tissue. Several studies which tested the use of MSCs in models of infarct (injured heart), stroke (brain), or meniscus regeneration models are reviewed within the context of MSC-mediated trophic effects in tissue repair.