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.

Immune activation and inflammation in HIV-1 infection: causes and consequences

Thorough research on HIV is progressively enabling us to understand the intricate mechanisms that link HIV-1 infection to the onset of immunodeficiency. The infection and depletion of CD4(+) T cells represent the most fundamental events in HIV-1 infection. However, in recent years, the role played by chronic immune activation and inflammation in HIV pathogenesis has become increasingly apparent: quite paradoxically, immune activation levels are directly associated with HIV-1 disease progression. In addition, HIV-1-infected patients present intriguing similarities with individuals of old age: their immune systems are characterized by a loss of regenerative capacity and an accumulation of ageing T cells. In this review, we discuss the potential reasons for the establishment of sustained immune activation and inflammation from the early stages of HIV-1 infection, as well as the long-term consequences of this process on the host immune system and health. A simplified model of HIV pathogenesis is proposed, which links together the three major facets of HIV-1 infection: the massive depletion of CD4(+) T cells, the paradoxical immune activation and the exhaustion of regenerative capacity.

IL-7R alpha versus CCR7 and CD45 as markers of virus-specific CD8+ T cell differentiation: contrasting pictures in blood and tonsillar lymphoid tissue

In humans, circulating CD8(+) memory T cells to a nonpersistent virus (influenza) lie within CCR7(+)CD45RA(-) central memory, whereas memory to Epstein-Barr virus (EBV) latent, EBV lytic, and cytomegalovirus (CMV) antigens are progressively larger in size and are more biased toward CCR7(-)CD45RA(-) effector memory and CCR7(-)CD45RA(+) terminally differentiated compartments. We found that these populations are also distinguished by progressively lower expression of the interleukin-7 receptor (IL-7R alpha) and by lower IL-7 responsiveness; indeed, percentage IL-7R alpha -positive values showed a tight inverse correlation with population size. However, these relationships among size, differentiation phenotype, and IL-7R alpha status in blood did not hold in tonsillar tissue. In tonsil tissue, although EBV reactivities outnumbered their CMV and influenza counterparts, the distinct CCR7/CD45 isoform signatures of the different virus-specific populations were retained. Moreover, all detectable reactivities showed high levels of IL-7R alpha expression. As a discriminator between different virus-specific populations, IL-7R alpha therefore appears to be more susceptible to tissue location than the classical CCR7/CD45 markers.

Improving the ex vivo retroviral-mediated suicide-gene transfer process in T lymphocytes to preserve immune function

The retroviral-mediated transfer of a suicide gene into donor T cells has been proposed as a method to control alloreactivity after hematopoietic stem cell (HSC) transplantation. Gene-modified cells (GMC) may be infused into the patient either at the time of transplantation, together with a T-cell depleted HSC graft, or after transplantation, as a donor lymphocyte infusion. Administration of a so-called pro-drug activating the "suicide" mechanism only after occurrence of GvHD should selectively destroy the alloreactive GMC in vivo, eventually leading to GvHD abrogation. Although phase I-II clinical trials provided vital proof of the principle of GvHD control by suicide-gene therapy, this approach is still suboptimal. Indeed, current gene transfer strategies rely on gamma-retroviral vectors that require extensive T-cell activation and expansion for efficient transduction. Both in vitro and in vivo studies have shown that the activation, cell expansion, transduction and selection steps lead to TCR repertoire alterations and impairment of crucial T-cell functions, such as alloreactivity and anti-EBV reactivity. Thus, improvements of the suicide-gene transfer processes are required in order to preserve T-cell function. This could be achieved by using CD3/CD28 co-stimulation and immunomagnetic selection of transduced cells. In future clinical trials, lentiviral vectors may prove to be a better alternative to gamma-retroviral-mediated gene transfer, by reducing the need for prolonged ex vivo culture.

Preferential retroviral-mediated transduction of EBV- and CMV-specific T cells after polyclonal T-cell activation

Graft-versus-host disease, resulting from the T cells present in allogeneic hematopoietic stem cell (HSC) inoculums, can potentially be treated if a suicide gene has been introduced into the donor T cells. However, the diversity and functionality of the transfused T-cell population, including EBV- (EBV-T) and CMV-specific (CMV-T) CD8+ T cells, which are particularly important for immunosuppressed individuals undergoing HSC transplants, are often modified by the gene transfer protocol. Here, we show that following polyclonal T-cell activation, EBV-T and CMV-T cells are preferentially transduced by oncoretroviral vectors, as compared to the bulk CD8+ T-cell population. This preferential transduction is associated with higher surface levels of PiT-2, the receptor for the amphotropic envelope with which the virions are pseudotyped. Moreover, EBV-T and CMV-T cells proliferate more extensively as compared to bulk CD8+ T cells. Thus, retroviral-mediated transduction can be biased toward a given antigenic specificity, even under conditions of polyclonal stimulation.