Irving Goldschneider

Clinical evaluation of group A and group C meningococcal polysaccharide vaccines in infants.

Group A and group C meningoccal polysaccharide vaccines were evaluated in infants. No significant local or systemic reactions were observed with 908 doses of vaccine given to 396 infants between 3 and 12 mo of age. The antibody response varied with the age of the infant, vaccine dose, molecular weight of vaccine, prior immunization with vaccine, and prior exposure to naturally occurring cross-reactive antigens. Only 7% of 3-mo-old infants had detectable antibody responses to primary immunization with 5-200 mug of A vaccine, presumably because of suppressive effects of high concentrations of maternal anti-A. More than 90% of 7- and 12-mo-old infants responded to A vaccine, achieving geometric mean anti-A concentrations of 0.38 and 0.98 mug/ml, respectively. The dose-response curve was flat between 10 and 200 mug of A vaccine. Geometric mean anti-A concentrations of 2.51 and 4.00 mug/ml were induced in 7- and 12-mo-old infants by booster injections of A vaccine. Approximately 90% of 3-mo-old infants had detectable antibody responses to primary immunization with C vaccine. The 100-mug dose appeared to be optimal, resulting in geometric mean anti-C concentrations of 0.49, 1.55, and 2.64 mug/ml in 3-, 7-, and 12-mo-old infants, respectively. Significant booster responses were not observed with C vaccine. Indeed, except for the 10-mug dose, booster injections of C vaccine in 7- and 12-mo-old infants resulted in lower anti-C concentrations than did primary immunizations.

Thymus-homing peripheral dendritic cells constitute two of the three major subsets of dendritic cells in the steady-state thymus

Many dendritic cells (DCs) in the normal mouse thymus are generated intrathymically from common T cell/DC progenitors. However, our previous work suggested that at least 50% of thymic DCs originate independently of these progenitors. We now formally demonstrate by parabiotic, adoptive transfer, and developmental studies that two of the three major subsets of thymic DCs originate extrathymically and continually migrate to the thymus, where they occupy a finite number of microenvironmental niches. The thymus-homing DCs consisted of immature plasmacytoid DCs (pDCs) and the signal regulatory protein α–positive (Sirpα+) CD11b+ CD8α− subset of conventional DCs (cDCs), both of which could take up and transport circulating antigen to the thymus. The cDCs of intrathymic origin were mostly Sirpα− CD11b− CD8αhi cells. Upon arrival in the thymus, the migrant pDCs enlarged and up-regulated CD11c, major histocompatibility complex II (MHC II), and CD8α, but maintained their plasmacytoid morphology. In contrast, the migrant cDCs proliferated extensively, up-regulated CD11c, MHC II, and CD86, and expressed dendritic processes. The possible functional implications of these findings are discussed.

A central role for peripheral dendritic cells in the induction of acquired thymic tolerance

Despite extensive negative selection in the thymus, numerous clones of self-reactive T cells are normally exported to the periphery. In most instances, autoimmunity is prevented by regulatory T (Tr) cells, many of which are also of recent thymic origin. We have demonstrated recently that natural killer (NK) Tr thymocytes (THYr) can be induced by the injection of antigen into the eye, an immunologically privileged site; and that the intravenous infusion of antigen-presenting cells (APCs) from such animals also induces NKT THYr. Furthermore, we have also observed that some of these APCs migrate to the thymus as CD11c(+) dendritic cells (DCs). Other authors have correlated the migration of DCs to the thymus with the generation of CD4(+)CD25(+) THYr. We therefore propose a novel tolerance induction pathway by which tolerogenic DCs routinely transport antigen (both self and nonself) from the periphery to the thymus, where they positively select THYr. We also propose that the ability of tolerogenic DCs to induce acquired thymic tolerance on demand might have important implications for the immunotherapy of autoimmunity and allotransplantation.

Two Developmentally Distinct Populations of Dendritic Cells Inhabit the Adult Mouse Thymus: Demonstration by Differential Importation of Hematogenous Precursors Under Steady State Conditions

Although a variety of lymphoid and myeloid precursors can generate thymic dendritic cells (DCs) under defined experimental conditions, the developmental origin(s) of DCs in the steady state thymus is unknown. Having previously used selective combinations of normal, parabiotic, and radioablated mice to demonstrate that blood-borne prothymocytes are imported in a gated and competitive manner, we used a similar approach in this study to investigate the importation of the hematogenous precursors of thymic DCs. The results indicate that two developmentally distinct populations of DC precursors normally enter the adult mouse thymus. The first population is indistinguishable from prothymocytes according to the following criteria: 1) inefficient (<20%) exchange between parabiotic partners; 2) gated importation by the thymus; 3) competitive antagonism for intrathymic niches; 4) temporally linked generation of thymocytes and CD8αhigh DCs; and 5) absence from prothymocyte-poor blood samples. The second population differs diametrically from prothymocytes in each of these properties, and appears to enter the thymus in at least a partially differentiated state. The resulting population of DCs has a CD8α−/low phenotype, and constitutes ∼50% of total thymic DCs. The presence of two discrete populations of DCs in the steady state thymus implies functional heterogeneity consistent with evidence implicating lymphoid DCs in the negative selection of effector thymocytes and myeloid DCs in the positive selection of regulatory thymocytes.

Murine Pro-B Cells Require IL-7 and Its Receptor Complex to Up-Regulate IL-7Rα, Terminal Deoxynucleotidyltransferase, and cμ Expression

Phenotypic analysis of bone marrow cells from IL-7 knockout (KO) mice revealed that B cell development is blocked precisely at the transition between pro-B cells and pre-B cells. In contrast, the generation of pre-pro-B cells and pro-B cells appeared to be normal, as judged by total cell numbers, proliferative indexes, D-JH and V-DJH gene rearrangements, and mRNA for recombinase-activating gene-1 (RAG-1), RAG-2, TdT, Igμ, λ5, and VpreB. However, upon closer inspection, several abnormalities in pro-B cell development were identified that could be corrected by injection of rIL-7 in vivo. These included the absence of the subset of late pro-B cells that initiates cμ expression for pre-B cell Ag receptor (BCR) formation, and the failure of pro-B cells to up-regulate TdT and the IL-7Rα (but not the common γ-chain) chain. Similar defects were present in common γ-chain and Jak3 KO mice, but not in λ5 or (excluding cytoplasmic Ig μ heavy chain (cμ)) RAG-1 KO mice, all of which also arrest at the late pro-B cell stage. Consequently, up-regulation of TdT and IL-7Rα expression requires signaling through the high affinity IL-7R, but does not require cμ expression or a functional pre-BCR. Taken together, these results suggest that IL-7 and its receptor complex are essential for 1) up-regulating the expression of TdT and IL-7Rα, 2) initiating the production of cμ, and 3) promoting the formation of a functional pre-BCR in/on pro-B cells. These key events, in turn, appear to be prerequisite both for differentiation of pro-B cells to pre-B cells and for proliferation of these cell subsets upon continued stimulation with IL-7.

Gated Importation of Prothymocytes by Adult Mouse Thymus Is Coordinated with Their Periodic Mobilization from Bone Marrow

The wavelike pattern of fetal T cell neogenesis is largely determined by the intermittent generation and exportation of waves of prothymocytes by the hemopoietic tissues in coordination with their gated importation by the thymus. Having previously shown that the importation of prothymocytes by the adult mouse thymus is also gated and that thymocytopoiesis proceeds in discrete (albeit overlapping) waves, we now demonstrate that prothymocytes are periodically exported in saturating numbers from the adult mouse bone marrow. Experiments in normal, radioablated, and parabiotic mice document the cyclical accumulation (3–5 wk) of prothymocytes in both the steady state and regenerating bone marrow, followed by their release into the blood ∼1 wk before intrathymic gate opening. The results also show that circulating donor-origin thymocyte precursors can transiently (∼1 wk) establish high level chimerism in the bone marrow after the mobilization of endogenous prothymocytes, presumably by occupying vacated microenvironmental niches. Hence, by analogy with the fetal state, we posit the existence of a feedback loop whereby diffusible chemokines of thymic origin regulate the production and/or release of bone marrow prothymocytes during each period of thymic receptivity. Because each resulting wave of thymocytopoiesis is accompanied by a wave of intrathymic dendritic cell formation, these coordinated events may help to optimize thymocyte selection as well as production.

Nucleotide-metabolizing enzymes and lymphocyte differentiation

SummaryInherited deficiencies of adenosine deaminase and purine nucleoside phosphorylase have been found to be associated with certain immunodeficiency syndromes which are characterized by deficiencies of mature peripheral lymphocytes. The immunodeficiency states associated with these enzyme deficiencies are thought to arise from blocks in lymphocyte differentiation. Deficiencies of these enzymes have profound and apparently selective effects on lymphocyte differention. Their discovery has focused attention on previously unknown relationships between purine nucleotide metabolism and lymphocyte development and function. In this article three aspects of nucleotide-metabolizing enzymes and lymphocyte differentiation will be discussed: 1) the distribution of the enzymes among lymphocyte populations at differing stages of differentiation; 2) the possible biochemical mechanisms which give rise to the immunodeficiencies; 3) the stages of lymphocyte differentiation which are affected by the enzyme deficiencies.

Abnormalities in the export and fate of recent thymic emigrants in diabetes-prone BB/W rats

Abnormalities in postthymic T cell development in the BB/W rat model of autoimmune insulin-dependent diabetes mellitus (IDDM) result in part from a lymphopenia (lyp) gene defect. To better characterize these abnormalities, the phenotypes of T cells from diabetes-prone (DP) and diabetes-resistant (DR) coisogenic rats were analyzed by multiparameter flow immunocytometry (FCM). Marked decreases in the numbers of Thy1- RT6+ T cells, most of which are CD8+, were documented in DP rats by live-gating. Conversely, an approximately 3-fold increase was observed in the percentage of Thy1+ RT6- T cells, which normally serve as the precursors of both Thy1- RT6+ and Thy1- RT6- T cell subsets in rats. These results suggested that, at a minimum, an arrest in maturation of the Thy1+ precursors of RT6+ T cells occurs postthymically in DP rats. To determine more precisely the stage(s) in T cell development at which lymphopenia occurs, the export and fate of recent thymic emigrants (RTEs) and their immediate descendants in DP rats was traced after intrathymic (i.t.) labelling with fluorescein isothiocyanate (FITC). The results showed that in DP, as compared with DR, rats: 1) 5-fold fewer RTEs are exported from the thymus per 24 hr; 2) more than 80% of the RTEs are CD4+; 3) most of the immediate descendants of RTEs disappear from the peripheral lymphoid tissues within one week after export from the thymus; and 4) few of the descendants of the RTEs that do survive differentiate into RT6+ T cells. Staining with propidium iodide revealed that a significantly higher proportion of Thy1+ T cells in DP than in DR rats are in cycle (S/G2/M), thereby accounting for their disproportionately high numbers relative to RTEs. These results indicate that, in addition to defective thymic export, most of the immediate descendants of RTEs in DP rats undergo non-productive proliferation and death at the time (3-7 days postthymic) at which their counterparts in DR rats differentiate into Thy1- RT6+ T cells. The resulting deficiency of immunoregulatory T cells, acting in concert with defective intrathymic selection of effector T cell precursors, appears to conspire to markedly enhance the predisposition of DP rats to autoimmunity.

Characterization of RT6 bearing rat lymphocytes: I. Ontogeny of the RT6+ subset

The RT6 alloantigen is present on approximately 70% of peripheral T cells in the rat, but is absent from thymocytes and bone marrow lymphocytes. The results of further phenotypic analysis in the present study demonstrated that the RT6 alloantigen is expressed on approximately 45% of the helper/inducer (CD4; W3/25+) and 80% of the cytotoxic/suppressor (CD8; OX8+) peripheral T-cell subsets. Ontogenetic and thymus ablation studies indicated that the RT6+ T-cell subset is thymus-dependent and normally develops after the appearance of RT6-T cells in neonatal rats, and that the expression of RT6 is a post-thymic maturational event. Furthermore, intrathymic adoptive transfer of bone marrow cells demonstrated that RT6+ T cells are thymus-derived cells. These results show that most if not all RT6+ T cells are the progeny of RT6- T cells. However, they do not exclude the possibility that a separate lineage of RT6- T cells exists, which also has OX8+ and W3/25+ subsets. The possible developmental and functional relationships of RT6- and RT6+ T cells in the rat are discussed.

Cyclical mobilization and gated importation of thymocyte progenitors in the adult mouse: evidence for a thymus-bone marrow feedback loop.

Summary:  It has recently been observed, as in the fetal thymus, that the importation of hematogenous thymocyte progenitors by the adult thymus is a gated phenomenon, whereby saturating numbers of progenitors periodically enter the thymus and occupy a finite number of intrathymic niches. In addition, the mobilization of thymocyte progenitors from the bone marrow appears to be a cyclical process that coincides temporally with the periods of thymic receptivity (open gate). It is proposed that these events are coordinated by a thymus‐bone marrow feedback loop in which a wave of developing triple negative (CD3–CD4–CD8–) thymocytes interacts with stromal cells in the stratified regions of the thymus cortex to sequentially induce the release of diffusible cytokines that regulate the production, mobilization, and recruitment of thymocyte progenitors. The likely components of this feedback loop are described here, as are the properties of the intrathymic vascular gates and niches for thymocyte progenitors. The cyclical production and release of thymocyte progenitors from the bone marrow is placed in the context of a general phenomenon of oscillatory feedback regulation involving all lymphohemopoietic cell lineages. Lastly, the question of whether the gated (as opposed to the continuous) entry of thymocyte progenitors is essential for normal thymocytopoiesis in adult life is discussed.