Alloreactivity of ex vivo-expanded T cells is correlated with expansion and CD4/CD8 ratio

Background We have demonstrated previously that retroviral-mediated transfer of a suicide gene into bone marrow (BM) donor T cells allows an efficient control of graft-versus-host disease (GvHD) after allogeneic BM transplantation. However, the 12 days of ex vivo culture required for the production of gene-modified cells (GMC), including soluble CD3 monoclonal antibody (MAb)-mediated activation and expansion with interleukin (IL)-2, induced a decrease of GMC alloreactivity and a reversal of their CD4/CD8 ratio. Improving the culture protocol in order to maintain the highest alloreactivity is of critical importance in obtaining an optimal graft-versus-leukemia (GvL) effect. Methods Peripheral blood mononuclear cells were activated with soluble CD3 MAb or CD3 and CD28 MAb co-immobilized on beads and expanded for 12 days in the presence of IL-2, IL-7 or IL-15 before analysis of alloreactivity and phenotype. Results Replacing the CD3 MAb by CD3/CD28 beads led to similar in vitro alloreactivity but improved the expansion and in vivo alloreactivity of GMC. Replacing the IL-2 with IL-7, but not IL-15, or decreasing IL-2 or IL-7 concentrations, improved the in vitro alloreactivity of expanded cells but was associated with lower expansion. Indeed, the alloreactivity of expanded cells was negatively correlated with cell expansion and positively correlated with CD4/CD8 ratio and CD8 expression level. Discussion Quantitative (i.e. low CD4/CD8 ratio) and qualitative (e.g. low CD8 expression) defects may account for the decreased alloreactivity of GMC. Using CD3/CD28 beads and/or IL-7 is more beneficial than CD3 MAb and IL-2 for preventing perturbations of the alloreactivity and phenotype of GMC.

Ex vivo expanded umbilical cord blood T cells maintain naive phenotype and TCR diversity

BACKGROUND

Umbilical cord blood (CB) is a promising source of hematopoietic stem cells for allogeneic transplantation. However, delayed engraftment and impaired immune reconstitution remain major limitations. Enrichment of donor grafts with CB T cells expanded ex vivo might facilitate improved T-cell immune reconstitution post-transplant. We hypothesized that CB T cells could be expanded using paramagnetic microbeads covalently linked to anti-CD3 and anti-CD28 Ab.

METHODS

CB units were divided into three fractions: (1) cells cultured without beads, (2) cells cultured with beads and (3) cells cultured with beads following CD3+ magnetic enrichment. All fractions were cultured for 14 days in the presence of IL-2 (200 IU/mL).

RESULTS

A mean 100-fold expansion (range 49-154) of total nucleated cells was observed in the CD3+ magnetically enriched fraction. Following expansion, CB T cells retained a naive and/or central memory phenotype and contained a polyclonal TCR diversity demonstrated by spectratyping.

DISCUSSION

Our data provide evidence that naive and diverse CB T cells may be expanded ex vivo and warrant additional studies in the setting of human CB transplantation.

IL-2 and IL-15 regulate CD154 expression on activated CD4 T cells

The cellular and humoral immune system is critically dependent upon CD40-CD154 (CD40 ligand) interactions between CD40 expressed on B cells, macrophages, and dendritic cells, and CD154 expressed primarily on CD4 T cells. Previous studies have shown that CD154 is transiently expressed on CD4 T cells after T cell receptor engagement in vitro. However, we found that stimulation of PBLs with maximal CD28 costimulation, using beads coupled to Abs against CD3 and CD28, led to a very prolonged expression of CD154 on CD4 cells (>4 days) that was dependent upon autocrine IL-2 production. Previously activated CD4 T cells could respond to IL-2, or the related cytokine IL-15, by de novo CD154 production and expression without requiring an additional signal from CD3 and CD28. These results provide evidence that CD28 costimulation of CD4 T cells, through autocrine IL-2 production, maintains high levels of CD154 expression. This has significant impact on our understanding of the acquired immune response and may provide insight concerning the mechanisms underlying several immunological diseases.

Induction of MHC class I expression on immature thymocytes in HIV-1-infected SCID-hu Thy/Liv mice: evidence of indirect mechanisms

The SCID-hu Thy/Liv mouse and human fetal thymic organ culture (HF-TOC) models have been used to explore the pathophysiologic mechanisms of HIV-1 infection in the thymus. We report here that HIV-1 infection of the SCID-hu Thy/Liv mouse leads to the induction of MHC class I (MHCI) expression on CD4+CD8+ (DP) thymocytes, which normally express low levels of MHCI. Induction of MHCI on DP thymocytes in HIV-1-infected Thy/Liv organs precedes their depletion and correlates with the pathogenic activity of the HIV-1 isolates. Both MHCI protein and mRNA are induced in thymocytes from HIV-1-infected Thy/Liv organs, indicating induction of MHCI gene expression. Indirect mechanisms are involved, because only a fraction (<10%) of the DP thymocytes were directly infected by HIV-1, although the majority of DP thymocytes are induced to express high levels of MHCI. We further demonstrate that IL-10 is induced in HIV-1-infected thymus organs. Similar HIV-1-mediated induction of MHCI expression was observed in HF-TOC assays. Exogenous IL-10 in HF-TOC induces MHCI expression on DP thymocytes. Therefore, HIV-1 infection of the thymus organ leads to induction of MHCI expression on immature thymocytes via indirect mechanisms involving IL-10. Overexpression of MHCI on DP thymocytes can interfere with thymocyte maturation and may contribute to HIV-1-induced thymocyte depletion.

Hematopoietic stem cell-based gene therapy for acquired immunodeficiency syndrome: efficient transduction and expression of RevM10 in myeloid cells in vivo and in vitro

Gene delivery via the hematopoietic stem cell (HSC) offers an attractive means to introduce antiviral genes into both T cells and macrophages for acquired immunodeficiency syndrome (AIDS) gene therapy. An amphotropic retroviral vector encoding a bicistronic gene coexpressing RevM10 and the murine CD8alpha' chain (lyt2) was developed to transduce HSC/progenitor cells. After transduction of CD34+ cells isolated from human umbilical cord blood, the lyt2 molecule detected by flow cytometry was used to monitor the level of gene transduction and expression and to enrich RevM10-expressing cells by cell sorting without drug selection. Using this quantitative method, high levels of gene transduction and expression (around 20%) were achieved by high-speed centrifugation of CD34+ cells with the retroviral supernatant (spinoculation). After reconstitution of human bone marrow implanted in SCID mice (SCID-hu bone) with the transduced HSC/progenitor cells, a significant number of donor-derived CD14+ bone marrow cells were found to express the RevM10/lyt2 gene. Finally, replication of a macrophage-tropic human immunodeficiency virus-type 1 (HIV-1) isolate was greatly inhibited in the lyt2+/CD14+ cells differentiated from transduced CD34+ cells after the enrichment of lyt2+ population. Thus, the RevM10 gene did not appear to inhibit the differentiation of HSC/progneitor cells into monocytes/macrophages. The level of retrovirus-mediated RevM10 expression in monocytes/macrophages derived from transduced HSCs is sufficient to suppress HIV-1 replication.

High transdominant RevM10 protein levels are required to inhibit HIV-1 replication in cell lines and primary T cells: implication for gene therapy of AIDS

Expression of antiviral genes in CD4+ T cells has been proposed as a strategy for gene therapy of AIDS. Over the past years, we and others have developed retroviral vectors encoding the RevM10 protein, a dominant-negative mutant of the HIV-1 Rev trans-activator protein. We could demonstrate gene transfer and inhibition of HIV-1 replication in cultured T cell lines and primary T cells. However, little is known about the levels of the antiviral protein required to achieve a therapeutic effect, particularly in primary cells. In this report, we compare different vector designs with regard to expression of the antiviral gene to develop an optimal vector for clinical applications. Our results demonstrate that intracellular steady-state RevM10 protein levels expressed from the Moloney murine leukemia virus (MoMLV), myeloproliferative sarcoma virus (MPSV) or mouse embryonic stem cell virus (MESV) promoters located in the long terminal repeat (LTR) were uniformly higher than from internal promoters (eg CMV, PGK). Analysis of selected vectors in acutely and chronically HIV-infected cell lines suggested that threshold levels of RevM10 expression are required to achieve inhibition of HIV replication. LTR-driven RevM10 expression also yielded high steady-state protein levels in activated primary T cells resulting in inhibition of HIV replication, and there was no apparent difference between the MoMLV, MPSV and MESV-LTR vectors. However, RevM10 expression was down-regulated in resting primary cells and consequently anti-HIV efficacy was significantly reduced. Taken together, the data suggest that relatively high steady-state levels of RevM10 protein are required to achieve inhibition of HIV replication and that the MPSV- and MESV-derived retroviral vectors show no advantage over the MoMLV-based vectors for expression of anti-HIV genes in human T cells.

HIV-1-induced thymocyte depletion is associated with indirect cytopathogenicity and infection of progenitor cells in vivo

Direct and indirect cytopathic mechanisms have been proposed to account for the loss of CD4+ T cells after infection with human immunodeficiency virus type 1 (HIV-1). We report here that HIV-1 infection of the human thymus in vivo results in thymocyte depletion by at least two different mechanisms. Thymocytes within multiple stages of differentiation are induced to die of apoptosis; most of these cells are uninfected. Additionally, thymopoiesis is interrupted by direct infection and destruction of intrathymic CD3-CD4+CD8- progenitor cells. These mechanisms are differentially induced by distinct isolates of HIV-1.

Human immunodeficiency virus infection of the human thymus and disruption of the thymic microenvironment in the SCID-hu mouse

Infection with the human immunodeficiency virus (HIV) results in immunosuppression and depletion of circulating CD4+ T cells. Since the thymus is the primary organ in which T cells mature it is of interest to examine the effects of HIV infection in this tissue. HIV infection has been demonstrated in the thymuses of infected individuals and thymocytes have been previously demonstrated to be susceptible to HIV infection both in vivo, using the SCID-hu mouse, and in vitro. The present study sought to determine which subsets of thymocytes were infected in the SCID-hu mouse model and to evaluate HIV-related alterations in the thymic microenvironment. Using two different primary HIV isolates, infection was found in CD4+/CD8+ double positive thymocytes as well as in both the CD4+ and CD8+ single positive subsets of thymocytes. The kinetics of infection and resulting viral burden differed among the three thymocyte subsets and depended on which HIV isolate was used for infection. Thymic epithelial (TE) cells were also shown to endocytose virus and to often contain copious amounts of viral RNA in the cytoplasm by in situ hybridization, although productive infection of these cells could not be definitively shown. Furthermore, degenerating TE cells were observed even without detection of HIV in the degenerating cells. Two striking morphologic patterns of infection were seen, involving either predominantly thymocyte infection and depletion, or TE cell involvement with detectable cytoplasmic viral RNA and/or TE cell toxicity. Thus, a variety of cells in the human thymus is susceptible to HIV infection, and infection with HIV results in a marked disruption of the thymic microenvironment leading to depletion of thymocytes and degeneration of TE cells.

Human cytomegalovirus in a SCID-hu mouse: thymic epithelial cells are prominent targets of viral replication

Animal models of human cytomegalovirus (CMV) infections have not been available to study pathogenesis or to evaluate antiviral drugs. Severe combined immunodeficient mice implanted with human fetal tissues (SCID-hu) were found to support CMV replication and may provide a model for this species-specific virus. When conjoint implants of human fetal thymus and liver were inoculated with a low-passage-number isolate of CMV, strain Toledo, consistent high-level viral replication was detected 5, 12, 15, 28, and 35 days after inoculation and virus replication continued for up to 9 months. Other human tissue implants, including lung and colon, were also found to support viral growth but with greater variability in levels and for a shorter duration. As expected, the species specificity of human CMV was preserved in this model such that virus was detected in the human conjoint thymus/liver implant but not in surrounding mouse tissues. The majority of virus-infected cells were localized in the thymic medulla rather than cortical region of the implant and immunofluorescence analysis identified epithelial cells rather than any hematopoietic cell population as the principal hosts for viral replication. Finally, treatment of infected animals with ganciclovir reduced viral replication, thereby demonstrating the value of this system for evaluating antiviral therapies. This animal model opens the way for a range of investigations not previously possible with human CMV.

Expression of a fetal gamma delta T-cell receptor in adult mice triggers a non-MHC-linked form of selective depletion

Day 14 fetal thymocytes and adult dendritic epidermal T cells (dEC) of all mouse strains express a characteristic non-polymorphic gamma delta T-cell receptor which is rarely found in the adult thymus or lymph nodes. We have made transgenic mice expressing this particular set of receptors on T cells in C3H and C57BL/6 mice. In adult mice of the latter strain, a dramatic depletion of transgene expressing T cells occurs and this effect is primarily mediated by thymic radiosensitive cells. The depletion is genetically dominant but not MHC-linked with major factor(s) mapping to chromosome 18. Taken together, our results show that strain-specific developmental changes in the thymic environment may play a role in shaping the gamma delta TCR repertoire.

Gamma delta T cells in murine epithelia: origin, repertoire, and function

The earliest TCR+ cells to appear during fetal development express products of the gamma and delta loci, and emerge as successive waves of cells bearing different V gamma gene products. These appear to emigrate and seed different epithelia. The TCR repertoire of the first two of these waves, V gamma 3 and V gamma 4, respectively, is extremely restricted. Whether the repertoire of these cells is restricted by selective processes or is shaped by developmental restrictions on rearrangements remains to be determined. These cells may function in surveillance for signals of trauma by recognizing self products induced by cellular stress.

Limited diversity of gamma delta antigen receptor genes of Thy-1+ dendritic epidermal cells

T cells bearing gamma delta antigen receptors constitute minor populations in most peripheral lymphoid tissues but represent the major populations of T cells in certain epithelia, including the epidermis. We show that murine dendritic epidermal cell (dEC) clones express V gamma and V delta gene segments, which are rare in adult T cells but predominate in fetal thymocytes. Analysis of the junctions of the rearranged gamma and delta genes shows a striking homogeneity among the receptors of five dEC clones. Our data support a model in which dECs represent one of perhaps several waves of emigrants from the early fetal thymus, and imply a role for dECs in immune surveillance that is distinct from that of alpha beta- and other gamma delta-bearing T cells.

Delta is the Cx-gene product in the gamma/delta antigen receptor of dendritic epidermal cells

Most T cells bear an antigen receptor that is a protein of a disulphide-linked heterodimer composed of an alpha chain and a beta chain associated with the non-polymorphic CD3 (T3) complex. A small subpopulation of thymic and peripheral T cells, as well as Thy-1+dendritic epidermal cells (dEC), express an alternative CD3-associated dimeric receptor composed of the product of the T-cell antigen receptor (TCR) gamma gene and a fourth chain, designated delta. Recently a new murine TCR constant-region gene, designated Cx, has been cloned and proposed as a candidate for the C delta gene. We have previously demonstrated that murine Thy-1+ dEC cell lines express a CD3-associated disulphide-linked heterodimer composed of a relative molecular mass Mr 41,000 (41K) gamma chain and a 50K delta chain. We have further analysed the receptor of one of these cloned dEC lines, 7-17.1, by endoglycosidase treatment of the isolated gamma and delta chains. The gamma chain was found to contain two N-linked oligosaccharide residues, consistent with the expression of a chain encoded by the V gamma 3 and C gamma 1 gene segments. The delta chain contains at least three N-linked oligosaccharides and has a core size of 38K. Northern blot analysis indicated the presence of abundant Cx messenger RNA in 7-17.1 cells. Immunoprecipitation with two antisera to peptides comprising distinct regions of the Cx sequence indicates that the delta chain is encoded by the Cx gene.

Regulation of T-cell receptor gamma-chain RNA expression in murine Thy-1+ dendritic epidermal cells

The epidermis of normal mice contains two distinct populations of dendritic cells derived from the bone marrow, Ia+ Langerhans cells and Ia- cells that express the Thy-1 alloantigen. The Thy-1-bearing dendritic epidermal cells (Thy-1+ dEC) have a surface phenotype similar to that of very early T-lineage cells, produce IL-2-like growth factors and exhibit cytotoxicity which is not restricted by the major histocompatibility complex (MHC). The relationship of Thy-1+ dEC to the T-cell lineage is unclear. Most T lymphocytes bear a receptor for antigen composed of an alpha chain and a beta chain associated with a nonpolymorphic complex termed CD3 (T3). A minor population carries a receptor in which CD3 is associated with a gamma/delta complex. We have analysed clones of Thy-1+ dEC for rearrangement and expression of the genes for the alpha-, beta- and gamma-chains of the T-cell receptor (TCR). They do not express alpha or beta but do carry a gamma/delta complex. Activation of the cells with Con A is associated with a rapid decrease in the steady-state level of gamma-chain RNA. Because Thy-1+ dEC resemble early stage T lymphocytes, down-regulation of TCR expression may reflect a necessary event during T cell differentiation.

Lack of gene rearrangement and mRNA expression of the beta chain of the T cell receptor in spontaneous rat large granular lymphocyte leukemia lines

Using the murine cDNA clone for the beta chain of the T cell antigen receptor, we have examined four highly cytotoxic rat large granular lymphocyte (LGL) leukemia lines for the expression of unique rearrangements and mRNA transcription of the genes coding for the T cell antigen receptor. In contrast to normal rat T cells and nine rat T cell lines, the LGL leukemia lines exhibited no detectable gene rearrangements in the beta chain locus after digestion of LGL DNA by four restriction enzymes. Northern blots containing RNA from these LGL tumor lines demonstrated a low level of aberrant or nonrearranged beta chain transcription (less than 10 copies per cell) but virtually no translatable 1.3 kilobase message. These results demonstrate that LGL leukemia lines which mediate both natural killer (NK) and antibody-dependent cell-mediated cytotoxicity (ADCC) activities do not express the beta chain of the T cell receptor. The nature of the NK cell receptor for antigen remains elusive.