Rationale for combined use of fetal liver and thymus for immunological reconstitution in patients with variants of severe combined immunodeficiency

Colony-Stimulating Activity of Fetal Liver Cells: Synergistic Role of Stem Cell Factor in Bone Marrow Recovery from Aplastic Anemia

Previously, we and others have shown that fetal liver infusion (FLI) leads to autologous hematopoietic improvement in 40-54% of patients with aplastic anemia. However, whether this recovery was spontaneous or the effect of the infused liver cells was not clear. To dissect the role of FLI in autologous hematopoietic recovery, the colony-supporting potential of fetal liver-conditioned medium (FLCM) was evaluated in bone marrow (BM) cells of normal adult and aplastic anemia patients. In both cases, each sample of FLCM supported the growth of colony-forming cells in semi solid culture medium. The FLCM was assayed for the presence of four principal colony-stimulating cytokines, namely stem cell factor (SCF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and erythropoietin (Epo). While GM-CSF, IL-3, and Epo were present in insignificant amounts or were altogether absent, 50-635 pg/ml of SCF was found in 8 of the 13 FLCM samples tested. Preliminary results of bioneutralization assay indicated the possible role of SCF, secreted by the FL cells, in colony-supporting activity of aplastic anemia and normal BM cells. Overall, our in vitro study implicates the paracrine role of infused FL cells in regenerating autologous hematopoiesis in aplastic anemia patients.

Milestones in the development of pediatric hematopoietic stem cell transplantation--50 years of progress

In the 1950s, the first infusions of hematopoietic stem cells were given as a form of treatment for childhood leukemia. This heralded the beginning of a field that has expanded to include the treatment of immune deficiencies, a variety of leukemias and solid tumors, and then genetic diseases. A number of milestones are highlighted, particularly in regard to the use of alternative sources of hematopoietic stem cells such as unrelated donors, peripheral blood stem cells and umbilical cord stem cells. In addition, newer techniques of using non-myeloablative preparative regimens helped to reduce the toxicity and long-term consequences of hematopoietic stem cell transplant. Many diseases now benefit from the replacement of the marrow stem cells and the provision of a new immune system and improved immune surveillance.

In utero transplantation for thalassemia

In utero hematopoietic stem cell transplantation is a promising approach for the treatment of a variety of congenital hematologic diseases. Although the approach has been successful for immunodeficiency syndromes, attempts thus far to treat the hemoglobinopathies have failed. In most of these cases the late gestational age at transplantation, source of donor cells, or procedure-related complications, provide an explanation for failure. Nevertheless the biology of thalassemia, in the context of prenatal transplantation, requires examination. In contrast to postnatal bone marrow transplant regimens, engraftment after in utero transplantation requires donor cells to effectively complete for developing receptive sites in the recipient hematopoietic microenvironment. Effective prenatal treatment of thalassemia will depend on the ability of normal cells to engraft and complete in the thalassemic microenvironment. Clinical observations after bone marrow transplantation of amelioration of anemia in beta-thalassemia by relatively low degrees of mixed chimerism, and the apparent selective advantage observed for donor erythropoiesis, suggest prenatal transplantation could succeed. Prenatal strategies involving multiple transplants, donor-specific tolerance induction, and postnatal same-donor transplants should be considered.

Early human T cell development: analysis of the human thymus at the time of initial entry of hematopoietic stem cells into the fetal thymic microenvironment

To determine events that transpire during the earliest stages of human T cell development, we have studied fetal tissues before (7 wk), during (8.2 wk), and after (9.5 wk to birth) colonization of the fetal thymic rudiment with hematopoietic stem cells. Calculation of the approximate volumes of the 7- and 8.2-wk thymuses revealed a 35-fold increase in thymic volumes during this time, with 7-wk thymus height of 160 microM and volume of 0.008 mm3, and 8.2-wk thymus height of 1044 microM and volume of 0.296 mm3. Human thymocytes in the 8.2-wk thymus were CD4+ CD8 alpha+ and cytoplasmic CD3 epsilon+ cCD3 delta+ CD8 beta- and CD3 zetta-. Only 5% of 8-wk thymocytes were T cell receptor (TCR)-beta+, < 0.1% were TCR-gamma+, and none reacted with monoclonal antibodies against TCR-delta. During the first 16 wk of gestation, we observed developmentally regulated expression of CD2 and CD8 beta (appearing at 9.5 wk), CD1a,b, and c molecules (CD1b, then CD1c, then CD1a), TCR molecules (TCR-beta, then TCR-delta), CD45RA and CD45RO isoforms, CD28 (10 wk), CD3 zeta (12-13 wk), and CD6 (12,75 wk). Whereas CD2 was not expressed at the time of initiation of thymic lymphopoiesis, a second CD58 ligand, CD48, was expressed at 8.2 wk, suggesting a role for CD48 early in thymic development. Taken together, these data define sequential phenotypic and morphologic changes that occur in human thymus coincident with thymus colonization by hematopoietic stem cells and provide insight into the molecules that are involved in the earliest stages of human T cell development.

Fetal tissue transplantation, bone marrow transplantation and prospective gene therapy in severe immunodeficiencies and enzyme deficiencies

The successful development of fetal tissue transplantation has resulted in therapeutical solutions for patients with a variety of diseases. Fetal liver transplants as well as bone marrow transplants, can completely cure patients with severe combined immunodeficiency disease. These transplants can also be applied to treat other types of immunodeficiency, hemopathies, and inborn errors of metabolism, in association with immunosuppressive therapy. Despite complete HLA incompatibility between transplanted stem cells and host cells, functional activities of donor-derived T-lymphocytes are not restricted. In severe forms of Di George syndrome, immunological reconstitution can be obtained by fetal thymus transplantation. It is expected that, in the near future, pure stem cell transplants and gene transplants will develop and will provide remarkable solutions for the therapy of a large number of diseases.

The fetal liver as an alternative stem cell source for hemolymphopoietic reconstitution

In mammalian ontogeny, the liver constitutes the primary hematopoietic organ for some time. Fetal liver cells (FLC) are rich in hematopoietic stem cells with a high proliferative potential but contain few post-thymic T cells. In animal studies, FLC restored hematopoiesis without severe graft-versus-host disease. However, genetic disparity between donor and host frequently limited durable engraftment and prevented or protracted complete immune reconstitution in most fully allogeneic recipients. Some children with severe combined immunodeficiency have been cured by FLC infusion, whereas favorable effects in aplastic anemia, acute leukemia, and inborn errors of metabolism have been limited and badly understood. Fetal liver transplantation in animals may serve as a model for the analysis and management of complications associated with the transfer of purified hematopoietic stem cell grafts and aid in the development of future therapeutic strategies requiring rapidly proliferating stem cell populations.

Deficiency of NK activity of HNK-1+ cells after transplantation of fetal thymus and liver or haploidentical soybean agglutinin-treated marrow cells in two severe combined immunodeficiency patients

Two severe combined-immunodeficiency patients successfully transplanted with fetal thymus and liver or haploidentical lectin-treated marrow cells lacked NK activity, with a normal number of HNK1+ cell-defined NK cells. The defect was not due to the inhibiting factor in patients' sera. Their NK cells bound to their targets, but did not lyse them in a single-cell agarose assay, and did not respond to alpha-IFN or IL-2. IL-2 did not stimulated the development of mature NK cells that bear M1 antigens from precursors that lack M1 antigens.

The human thymic microenvironment

Several major points should be emphasized that provide directions for future research. First, using monoclonal reagents we have been able to phenotypically identify four major regions of the human thymus microenvironment: the thymic capsule, interlobular septae and stroma (TE-7+), the subcapsular cortex (TE-4+, Thy-1+, A2B5+, anti-p19+, BB TECS+, TE-3+), the cortex (TE-3+), and the medulla (TE-4+, A2B5+, anti-p19+, BB TECS+). TE-4+ and TE-3+ thymic epithelium constitute HLA+, Ia+ subsets of thymic epithelium that are candidates for cell types of the human thymic microenvironment that might participate in conferring MHC restriction to maturing T lymphocytes. TE-7+ stroma most likely represents the mesodermal-derived thymic component that early in development induces thymic epithelial differentiation. Second, whereas TE-4, anti-p19, and BB TECS antibodies may be thymic epithelial lineage markers, they all react with the basal layer of squamous epithelium of various organs. In particular, in the tonsil, A2B5+, TE-4+ epithelium splays out in the base of tonsillar crypts and morphologically appears similar to thymic medullary epithelial cells. Therefore, these markers of endocrine thymic epithelium may also identify extrathymic areas of T cell differentiation. Third, the concept that thymic epithelium is constantly differentiating in the developed thymus is suggested by the coexpression of TE-4, TE-8, TE-16, and TE-15 antigen by layers of squamous epithelial keratinocytes and by thymic epithelium. That there is a TE-4/TE-8/TE-15 keratinocyte maturation pathway in skin gives credence to the notion that a similar pathway exists from TE-4+, TE-8-, TE-15- endocrine medullary epithelial cells to TE-4-, TE-8+, TE-15+ Hassall's bodies. Fourth, from the literature and the work presented in this review, three phases of thymic microenvironment development can be defined. The first phase is during early fetal development (4 to 8 weeks in humans) when mesodermal-derived fibrous tissue induces endodermal and ectodermal-derived thymic epithelium to proliferate and mature. TE-7+ mesenchymal stroma invaginates TE-4+ thymic epithelium and effects thymic lobulation. The second phase occurs between 9 and 15 weeks fetal development when the thymic primordia is colonized by blood-borne thymocyte precursors. Presumably during this stage, thymic epithelium promotes bone marrow cell colonization of thymus by producing chemoattractant molecules.(ABSTRACT TRUNCATED AT 400 WORDS)

Severe acquired immunodeficiency in male homosexuals, manifested by chronic perianal ulcerative herpes simplex lesions

Four homosexual men presented with gradually enlarging perianal ulcers, from which herpes simplex virus was cultured. Each patient had a prolonged course characterized by eight loss, fever, and evidence of infection by other opportunistic microorganisms including cytomegalovirus, Pneumocystis carinii, and Candida albicans. Three patients died; Kaposi's sarcoma developed in the fourth. All were found to have depressed cell-mediated immunity, as evidenced by skin anergy, lymphopenia, and poor or absent responses to plant lectins and antigens in vitro. Natural-killer-cell activity directed against target cells infected with herpes simplex virus was depressed in all patients. The absence of a history of recurrent infections or of histologic evidence of lymphoproliferative or other neoplastic diseases suggests that the immune defects were acquired.

T-lymphocyte differentiation in vitro in severe combined immunodeficiency. Defects of stem cells

A study of T-lymphocyte differentiation was made on fractionated bone marrow cells from normal volunteers and from 11 patients with severe combined immunodeficiency (SCID) using normal thymic epithelial monolayers and their culture supernates as inducing agents. Normal marrow cells could regularly be induced to bear the human T-lymphocyte antigen (HTLA), to form rosettes with sheep erythrocytes (E rosettes), and to respond to the mitogen concanavalin A (Con A) after coculture with the thymic epithelial monolayers or their culture supernates. In contrast, studies of T-cell differentiation on the marrow cells of patients with SCID revealed varying defects, ranging from a complete "absence" of definable T-cell precursors to partial differentiation resulting in acquisition of one (HTLA) or two (HTLA and E rosettes) markers for T lymphocytes. Only in one patient was there induction of all three T-cell markers, namely, HTLA, E rosettes, and responsiveness to Con A. These observations indicate that SCID is a heterogeneous disorder in which defects of differentiation can occur at one or more multiple sites of differentiation leading the the clinical expression of T- and B-cell dysfunction. Further, our studies indicate that in T-cell differentiation, HTLA probably appears before the capacity to form E-rosettes, and development of the latter capacity is followed by a state of responsiveness to mitogens. A scheme of normal differentiation along with the defects of precursor T cells seen in SCID is presented.

On the thymus in the differentiation of "H-2 self-recognition" by T cells: evidence for dual recognition?

In the thymus, precursor T cells differentiate recognition structures for self that are specific for the H-2K, D, and I markers expressed by the thymic epithelium. Thus recognition of self-H-2 differentiates independently of the T cells H-2 type and independently of recognition of nonself antigen X. This is readily compatible with dual recognition by T cells but does not formally exclude a single recognition model. These conclusions derive from experiments with bone marrow and thymic chimeras. Irradiated mice reconstituted with bone marrow to form chimeras of (A X B)F1 leads to A type generate virus-specific cytotoxic T cells for infected targets A only. Therefore, the H-2 type of the host determines the H-2-restricted activity of killer T cells alone. In contrast, chimeras made by reconstituting irradiated A mice with adult spleen cells of (A X B)F1 origin generate virus-specific cytotoxic activity for infected A and B targets, suggesting that mature T cells do not change their self-specificity readily. (A X B)F1 leads to (A X C)F1 and (KAIA/DC) leads to (KAIA/DB) irradiation bone marrow chimeras responded against infected A but not B or C targets. This suggests that cytotoxicity is not generated against DC because it is abscent from the host's thymus epithelium and not against DB because it is not expressed by the reconstituting lymphoreticular system. (KBIB/DA) leads to (KCIC/DA) K, I incompatible, or completely H-2 incompatible A leads to B chimeras fail to generate any measurable virus specific cytotoxicity, indicating the necessity for I-specific helper T cells for the generation of killer T cells. Finally adult thymectomized, irradiated and bone marrow reconstituted (A X B)F1 mice, transplanted with an irradiated thymus of A origin, generate virus-specific cytotoxic T cells specific for infected A targets but not for B targets; this result formally demonstrates the crucial role of thymic epithelial cells in the differentiation of anti-self-H-2 specificities of T cells.