Activation of the interleukin 2 pathway precedes CD3-T cell receptor expression in thymic development. Differential growth requirements of early and mature intrathymic subpopulations

An immunomodulating peptide with potential to suppress tumour growth and autoimmunity

Cancers and autoimmune diseases commonly co-exist and immune checkpoint inhibitor therapy (ICI) exacerbates autoimmune pathologies. We recently described a lipidic peptide, designated IK14004, that promotes expansion of immunosuppressive T regulatory (Treg) cells and uncouples interleukin-2 from interferon-gamma production while activating CD8+ T cells. Herein, we report IK14004-mediated inhibition of Lewis lung cancer (LLC) growth and re-invigoration of splenocyte-derived exhausted CD4+ T cells. In human immune cells from healthy donors, IK14004 modulates expression of the T cell receptor α/β subunits, induces Type I IFN expression, stimulates natural killer (NK) cells to express NKG2D/NKp44 receptors and enhances K562 cytotoxicity. In both T and NK cells, IK14004 alters the IL-12 receptor β1/β2 chain ratio to favour IL-12p70 binding. Taken together, this novel peptide offers an opportunity to gain further insight into the complexity of ICI immunotherapy so that autoimmune responses may be minimised without promoting tumour evasion from the immune system.

A novel lipidic peptide with potential to promote balanced effector-regulatory T cell responses

T cell-dendritic cell (DC) interactions contribute to reciprocal stimulation leading to DC maturation that results in production of interleukin-12 (IL-12) and interferon-gamma (IFN-γ). Both cytokines have been implicated in autoimmune diseases while being necessary for effective immune responses against foreign antigens. We describe a lipidic peptide, designated IK14004, that modifies crosstalk between T cells and DCs resulting in suppression of IL-12p40/IFN-γ production. T cell production of interleukin-2 (IL-2) and IFN-γ is uncoupled and IL-12p70 production is enhanced. IK14004 induces expression of activating co-receptors in CD8+ T cells and increases the proportion of Foxp3-expressing CD4+ T regulatory cells. The potential for IK14004 to impact on signalling pathways required to achieve a balanced immune response upon stimulation of DCs and T cells is highlighted. This novel compound provides an opportunity to gain further insights into the complexity of T cell-DC interactions relevant to autoimmunity associated with malignancies and may have therapeutic benefit.

Differential modulation of human multinegative (CD3-4-8-) thymocyte proliferation by monoclonal antibodies to CD45RA or to CD45

Human multinegative (CD3-4-8-19-; MN) thymocytes proliferate optimally in response to anti-CD2 plus anti-CD28 mAb plus PMA or IL-7. The role of CD45 was assessed by the addition of mAb to a CD45 common determinant, or to CD45RA. MN thymocytes are unresponsive to anti-CD2 mAb. Co-stimulation with anti-CD45RA generated 1.6-5.7-fold enhancement of a proliferative response, with maximal enhancement by cross-linkage of CD45RA molecules. The response to anti-CD2/28 mAb was reproducibly enhanced only by immobilized anti-CD45RA. Cross-linking of CD45RA and CD28 through the use of heteroconjugates of mAb did not enhance the co-stimulation by CD45RA. The most marked enhancement by anti-CD45RA occurred in suboptimal activation conditions. In contrast, the response to anti-CD2 or anti-CD2/28 was inhibited by mAb to CD45 common determinants (anti-CD45) in the presence or absence of PMA or IL-7, with the most profound inhibition (6-8-fold) detected in optimal proliferative conditions. Cross-linking of CD45 and CD28 through heteroconjugates of mAb was required as soluble anti-CD45 or immobilized anti-CD45 were unable to mediate inhibition. This inhibitory effect of (anti-CD45 x 28) was specific to MN thymocytes as no inhibition was detectable when peripheral blood T cells were treated with anti-CD2/28 and the same heteroconjugate. The differential effects of anti-CD45 and anti-CD45RA may reflect either CD45 heterogeneity on MN thymocytes, or the physical modulation of a single CD45 molecules by interactions at different epitopes, and the avidity of the relevant CD45 mAb for thymocyte CD45 isoforms may play a role.(ABSTRACT TRUNCATED AT 250 WORDS)

Cutaneous lesions in severe combined immunodeficiency: two case reports and a review of the literature

Two patients with severe combined immunodeficiency (SCID) in whom cutaneous lesions were the first clinical feature were studied. Neither the morphology nor the histology of the lesions was uniform, although we have noted some common findings that can, in subsequent cases, lead us to suspect SCID. The immunologic defects were not uniform, representing the two poles of the spectrum of SCID. We believe that early recognition of the skin lesions is very important, since the patient's life expectancy can be increased by a bone marrow transplantation (1).

Cytokines in T-cell development

The thymus provides a unique environment for the development of T cells, supporting both precursor cell proliferation and differentiation. The control of these processes is unknown but they may be mediated by cytokines, or other soluble factors, or by interactions with specific elements of the thymic stroma. Here, Simon Carding, Adrian Hayday and Kim Bottomly describe cellular, immunochemical and molecular studies of the production and action of cytokines within the human and mouse thymus and demonstrate their essential role in T-cell development.

Towards an integrated view of thymopoiesis

One prediction from the complex series of steps in intrathymic T-cell differentiation is that to regulate it the stroma controlling the process must be equally complex: the attraction of precursors, commitment to the T-cell lineage, induction of T-cell receptor (TCR) gene rearrangement, accessory molecule expression, repertoire expansion, major histocompatibility complex (MHC) molecule-based selection (positive and negative), acquisition of functional maturity and migratory capacity must all be controlled. In this review, Richard Boyd and Patrice Hugo combine knowledge of T-cell differentiation with thymic stromal cell heterogeneity to offer an integrated view of thymopoiesis within the thymic microenvironment.

Human thymocytes do not respond to interleukin-2 after removal of mature "bright" CD5 positive cells

Interleukin-2 receptors (IL-2R) are expressed on minor populations of immature and mature human thymocytes. These studies were designed to determine if immature T cells could respond to the mitogen phytohemagglutinin (PHA-P) plus IL-2 in vitro by increasing the expression of IL-2R and by proliferation. Using monoclonal antibodies to CD5 and magnetic immunobeads we were able to remove all mature, "bright" CD5+ cells from nylon wool-purified thymocytes and to obtain less mature cells which consisted almost completely of cells with the CD4+CD8+ phenotype. These immature cells were mostly "dim" CD5+ and less than 5% CD5- and a small percentage expressed the IL-2R. After culture in serum-free medium with PHA-P, these cells showed only a slight increase in the percentage of IL-2R+ cells and the addition of IL-2 did not increase the percentage of IL-2R+ cells and no proliferation was observed. Unseparated, nylon wool-purified thymocytes contained 14% bright CD5+ cells. These bright CD5+ cells had a mature phenotype of CD4+CD8- (52%) and CD4-CD8+ (27%) cells. A small percentage of these cells were IL-2R+. These bright CD5+IL-2R+ cells were predominantly mature CD4+CD8- cells as measured by three-color flow cytometry. After culture with PHA-P and IL-2, the percentage of IL-2R+ cells increased and they were now found not only on CD4+CD8- but also on CD4-CD8+ and on CD4+CD8+ cells. IL-2 plus PHA-P increased proliferation of these cells as compared to those cultured in medium with PHA-P without IL-2. Thus, we show that human immature thymocytes in contrast to mature thymocytes are not responsive to IL-2 as measured by a lack of IL-2R expression and proliferation. These data indicate that mature thymocytes can express a functional high affinity receptor for IL-2 and suggest that immature thymocytes may not possess a (functional) p75 chain of the IL-2R.

Expression and function of CD2 during murine thymocyte ontogeny

CD2, originally recognized as the sheep erythrocyte receptor of human T cells, has been implicated in early T cell development in the thymus. In this report, we examined the expression and functional role of CD2 during murine thymocyte ontogeny by using monoclonal antibodies to murine CD2. Surface expression of CD2 was first detected in Thy-1+ fetal thymocytes at day 14 of gestation and it progressively increased during CD4-CD8- phenotype. Surface IL 2 receptor (CD25) expression was readily detected in surface CD2- cells at day 13 of gestation and the majority of CD2+ cells appeared to be generated from CD25+ cells thereafter. In adult CD4-CD8- thymocytes, the expression of CD2 and CD25 was mutually exclusive. These results indicate that surface CD2 expression is not a prerequisite for CD25 induction during murine thymocyte ontogeny. This was further confirmed by fetal thymus organ culture in which anti-murine CD2 mAb was included. The antibody treatment led to a suppressed CD2 expression on thymocytes; however, there was no effect on the appearance of CD25. Moreover, no influence on the development of mature CD3+ thymocytes was observed after fetal thymus organ culture in the presence of anti-murine CD2 mAb, and a substantial number of CD3+CD2- cells was demonstrated in fetal and adult CD4-CD8- thymocytes. These findings argue against the functional relevance of CD2 expression during early T cell development as proposed in humans.

Factor requirements for activation and proliferation steps of human CD2+CD3-CD4-CD8- early thymocytes

Human CD2+CD3-CD4-CD8- thymocytes were shown to display high in vitro growth ability although their factor requirements for activation and proliferation are not fully known. We have thus isolated these precursors and assayed their activation and proliferation potentials in response to various factors. Our results indicate that these cells proliferate in response to phytohemagglutinin (PHA), recombinant interleukin 2 (rIL 2) and rIL 4. Simultaneous addition of anti-CD2I + III monoclonal antibodies (mAb) and rIL 2 highly increased cell growth while IL 4-induced proliferation was not enhanced upon addition of anti-CD2. Anti-CD2 and PHA, but not IL 2, induced intracytoplasmic Ca2+ influx phosphatidyl inositol turnover as well as IL 2 receptor expression. Sequential studies indicated that CD2 triggering enable many more CD2+ precursors to respond to rIL 2. Endogenous IL 2 synthesis was necessary for PHA-induced cell growth. Neither of these in vitro treatment were able to induce membrane expression of CD3, CD4 or CD8 on CD2+ cells.