Ruth Seggewiss

Immune reconstitution after allogeneic transplantation and expanding options for immunomodulation: an update

Allogeneic hematopoietic stem cell transplantation (HSCT) has advanced to a common procedure for treating also older patients with malignancies and immunodeficiency disorders by redirecting the immune system. Unfortunately, cure is often hampered by relapse of the underlying disease, graft-versus-host disease, or severe opportunistic infections, which account for the majority of deaths after HSCT. Enhancing immune reconstitution is therefore an area of intensive research. An increasing variety of approaches has been explored preclinically and clinically: the application of cytokines, keratinocyte growth factor, growth hormone, cytotoxic lymphocytes, and mesenchymal stem cells or the blockade of sex hormones. New developments of allogeneic HSCT, for example, umbilical cord blood or haploidentical graft preparations leading to prolonged immunodeficiency, have further increased the need to improve immune reconstitution. Although a slow T-cell reconstitution is regarded as primarily responsible for deleterious infections with viruses and fungi, graft-versus-host disease, and relapse, the importance of innate immune cells for disease and infection control is currently being reevaluated. The groundwork has been prepared for the creation of individualized therapy partially based on genetic features of the underlying disease. We provide an update on selected issues of development in this fast evolving field; however, we do not claim completeness.

Protein kinase inhibitors substantially improve the physical detection of T-cells with peptide-MHC tetramers.

Flow cytometry with fluorochrome-conjugated peptide-major histocompatibility complex (pMHC) tetramers has transformed the study of antigen-specific T-cells by enabling their visualization, enumeration, phenotypic characterization and isolation from ex vivo samples. Here, we demonstrate that the reversible protein kinase inhibitor (PKI) dasatinib improves the staining intensity of human (CD8+ and CD4+) and murine T-cells without concomitant increases in background staining. Dasatinib enhances the capture of cognate pMHC tetramers from solution and produces higher intensity staining at lower pMHC concentrations. Furthermore, dasatinib reduces pMHC tetramer-induced cell death and substantially lowers the T-cell receptor (TCR)/pMHC interaction affinity threshold required for cell staining. Accordingly, dasatinib permits the identification of T-cells with very low affinity TCR/pMHC interactions, such as those that typically predominate in tumour-specific responses and autoimmune conditions that are not amenable to detection by current technology.

Profound Inhibition of Antigen-Specific T-Cell Effector Functions by Dasatinib

Purpose: The dual BCR-ABL/SRC kinase inhibitor dasatinib entered the clinic for the treatment of chronic myeloid leukemia and Ph+ acute lymphoblastic leukemia. Because SRC kinases are known to play an important role in physiologic T-cell activation, we analyzed the immunobiological effects of dasatinib on T-cell function. The effect of dasatinib on multiple T-cell effector functions was examined at clinically relevant doses (1-100 nmol/L); the promiscuous tyrosine kinase inhibitor staurosporine was used as a comparator. Experimental Design: Purified human CD3+ cells and virus-specific CD8+ T cells from healthy blood donors were studied directly ex vivo; antigen-specific effects were confirmed in defined T-cell clones. Functional outcomes included cytokine production (interleukin-2, IFNγ, and tumor necrosis factor α), degranulation (CD107a/b mobilization), activation (CD69 up-regulation), proliferation (carboxyfluorescein diacetate succinimidyl ester dilution), apoptosis/necrosis induction, and signal transduction. Results: Both dasatinib and staurosporine inhibited T-cell activation, proliferation, cytokine production, and degranulation in a dose-dependent manner. Mechanistically, this was mediated by the blockade of early signal transduction events and was not due to loss of T-cell viability. Overall, CD4+ T cells seemed to be more sensitive to these effects than CD8+ T cells, and naïve T cells more sensitive than memory T-cell subsets. The inhibitory effects of dasatinib were so profound that all T-cell effector functions were shut down at therapeutically relevant concentrations. Conclusion: These findings indicate that caution is warranted with use of this drug in the clinical setting and provide a rationale to explore the potential of dasatinib as an immunosuppressant in the fields of transplantation and T-cell–driven autoimmune diseases.

Anti-myeloma activity of the novel 2-aminothienopyrimidine Hsp90 inhibitor NVP-BEP800

The 90 kD heat shock protein (Hsp90) molecular chaperone sustains multiple components of oncogenic pathways and has recently emerged as a therapeutic target that is now being clinically tested in a number of malignancies. In order to address formulation issues and to deal with possible resistance mechanisms against small molecule Hsp90 inhibitors, a range of compounds based on different molecular scaffolds are now being developed. The present study preclinically tested the effects of the novel 2‐aminothienopyrimidine class Hsp90 inhibitor NVP‐BEP800, which is suitable for oral formulations, on multiple myeloma cells from established cell lines and on a larger cohort (n = 40) of primary myeloma samples. The drug effectively and specifically killed the majority of primary myeloma cells in coculture with bone marrow stromal cells and reliably entailed molecular consequences of Hsp90 blockade – such as survival pathway breakdown and client protein depletion – in multiple myeloma cells from cell lines as well as from patients. Collectively, the properties of this novel drug support clinical testing in multiple myeloma.

A new direction for gene therapy: intrathymic T cell–specific lentiviral gene transfer

Reports of neoplasia related to insertional activation of protooncogenes by retroviral vectors have raised serious safety concerns in the field of gene therapy. Modification of current approaches is urgently required to minimize the deleterious consequences of insertional mutagenesis. In this issue of the JCI, Adjali and colleagues report on their treatment of SCID mice lacking the 70-kDa protein tyrosine kinase, ZAP-70, with direct intrathymic injection of a ZAP-70-expressing T cell-specific lentiviral vector, which resulted in T cell reconstitution. Using lentiviral vectors and in situ gene transfer may represent a safer approach than using retroviral vectors for ex vivo gene transfer into HSCs, avoiding 3 factors potentially linked to leukemogenesis, namely HSC targets, ex vivo transduction and expansion, and standard Moloney leukemia virus-based retroviral vectors.

In Vitro Culture During Retroviral Transduction Improves Thymic Repopulation and Output After Total Body Irradiation and Autologous Peripheral Blood Progenitor Cell Transplantation in Rhesus Macaques

Immunodeficiency after peripheral blood progenitor cell (PBPC) transplantation may be influenced by graft composition, underlying disease, and/or pre‐treatment. These factors are difficult to study independently in humans. Ex vivo culture and genetic manipulation of PBPC grafts may also affect immune reconstitution, with relevance to gene therapy applications. We directly compared the effects of three clinically relevant autologous graft compositions on immune reconstitution after myeloblative total body irradiation in rhesus macaques, the first time these studies have been performed in a large animal model with direct clinical relevance. Animals received CD34+ cell dose‐matched grafts of either peripheral blood mononuclear cells, purified CD34+ PBPCs, or purified CD34+ PBPCs expanded in vitro and retrovirally transduced. We evaluated the reconstitution of T, B, natural killer, dendritic cells, and monocytes in blood and lymph nodes for up to 1 year post‐transplantation. Animals receiving selected‐transduced CD34+ cells had the fastest recovery of T‐cell numbers, along with the highest T‐cell‐receptor gene rearrangement excision circles levels, the fewest proliferating Ki‐67+ T‐cells in the blood, and the best‐preserved thymic architecture. Selected‐transduced CD34+ cells may therefore repopulate the thymus more efficiently and promote a higher output of naïve T‐cells. These results have implications for the design of gene therapy trials, as well as for the use of expanded PBPCs for improved T‐cell immune reconstitution after transplantation.

53 – Hematopoietic Stem Cell Mobilization and Homing

Hematopoietic stem cells (HSCs) circulate from the extraembryonic yolk sac (YS), the intraembryonic aorta-gonad mesonephros (AGM) region, and the liver during murine embryonic and fetal development, as they colonize organs active in postnatal hematopoiesis. In adult life, the ability of HSCs to enter the circulation, even in low numbers, may be an important aspect of hematopoietic homeostasis. Once released from its attachment, a stem cell undergoes transmural migration through openings in the basement membrane and endothelial lining of a blood sinus and enters the circulation. Mobilization has been achieved in both laboratory and clinical settings. Clarification of the interactions between HSCs and progenitor cells and the components of the marrow microenvironment are central to the understanding of stem cell mobilization and the converse process of “homing”. Homing is defined as migration of HSCs and progenitor cells specifically from the blood to the BM followed by “engraftment” in permissive niches of the microenvironment, where they survive, proliferate, and differentiate into multilineage cells.