Mixed chimerism of the resident macrophage population after allogeneic bone marrow transplantation for chronic myeloid leukemia

Tissue-resident immunity in the lung: a first-line defense at the environmental interface

The lung is a vital organ that incessantly faces external environmental challenges. Its homeostasis and unimpeded vital function are ensured by the respiratory epithelium working hand in hand with an intricate fine-tuned tissue-resident immune cell network. Lung tissue-resident immune cells span across the innate and adaptive immunity and protect from infectious agents but can also prove to be pathogenic if dysregulated. Here, we review the innate and adaptive immune cell subtypes comprising lung-resident immunity and discuss their ontogeny and role in distinct respiratory diseases. An improved understanding of the role of lung-resident immunity and how its function is dysregulated under pathological conditions can shed light on the pathogenesis of respiratory diseases.

Immune control of cytomegalovirus reactivation in stem cell transplantation

The reactivation of viruses from latency after allogeneic stem cell transplantation (SCT) continues to represent a major clinical challenge requiring sophisticated monitoring strategies in the context of prophylactic and/or pre-emptive antiviral drugs that are associated with significant expense, toxicity, and rates of failure. Accumulating evidence has demonstrated the association of polyfunctional virus-specific T-cells with protection from viral reactivation, affirmed by the ability of adoptively transferred virus-specific T-cells to prevent and treat reactivation and disease. The roles of innate cells (NK cells) in early viral surveillance, and dendritic cells in priming of T-cells have also been delineated. Most recently, a role for strain-specific humoral responses in preventing early cytomegalovirus (CMV) reactivation has been demonstrated in preclinical models. Despite these advances, many unknowns remain: what are the critical innate and adaptive responses over time, is the origin (e.g. recipient versus donor) and localization (e.g. in parenchymal tissue versus lymphoid organs) of these responses important, how does GVHD and the prevention/treatment thereof (e.g. high dose steroids) impact the functionality and relevance of a particular immune axis, do the immune parameters that control latency, reactivation and dissemination differ, and what is the impact of new antiviral drugs on the development of enduring antiviral immunity. Thus, whilst antiviral drugs have provided major improvements over the last two decades, understanding the immunological paradigms underpinning protective antiviral immunity after SCT offers the potential to generate non-toxic immune-based therapeutic approaches for lasting protection from viral reactivation.

Origin and ontogeny of lung macrophages: from mice to humans

Macrophages are tissue-resident myeloid cells with essential roles in host defense, tissue repair, and organ homeostasis. The lung harbors a large number of macrophages that reside in alveoli. As a result of their strategic location, alveolar macrophages are critical sentinels of healthy lung function and barrier immunity. They phagocytose inhaled material and initiate protective immune responses to pathogens, while preventing excessive inflammatory responses and tissue damage. Apart from alveolar macrophages, other macrophage populations are found in the lung and recent single-cell RNA-sequencing studies indicate that lung macrophage heterogeneity is greater than previously appreciated. The cellular origin and development of mouse lung macrophages has been extensively studied, but little is known about the ontogeny of their human counterparts, despite the importance of macrophages for lung health. In this context, humanized mice (mice with a human immune system) can give new insights into the biology of human lung macrophages by allowing in vivo studies that are not possible in humans. In particular, we have created humanized mouse models that support the development of human lung macrophages in vivo. In this review, we will discuss the heterogeneity, development, and homeostasis of lung macrophages. Moreover, we will highlight the impact of age, the microbiota, and pathogen exposure on lung macrophage function. Altered macrophage function has been implicated in respiratory infections as well as in common allergic and inflammatory lung diseases. Therefore, understanding the functional heterogeneity and ontogeny of lung macrophages should help to develop future macrophage-based therapies for important lung diseases in humans.

Transcriptome analysis highlights the conserved difference between embryonic and postnatal-derived alveolar macrophages

Alveolar macrophages (AMs) reside on the luminal surfaces of the airways and alveoli where they maintain host defense and promote alveolar homeostasis by ingesting inhaled particulates and regulating inflammatory responses. Recent studies have demonstrated that AMs populate the lungs during embryogenesis and self-renew throughout life with minimal replacement by circulating monocytes, except under extreme conditions of depletion or radiation injury. Here we demonstrate that on a global scale, environment appears to dictate AM development and function. Indeed, transcriptome analysis of embryonic host-derived and postnatal donor-derived AMs coexisting within the same mouse demonstrated >98% correlation and overall functional analyses were similar. However, we also identified several genes whose expression was dictated by origin rather than environment. The most differentially expressed gene not altered by environment was Marco, a gene recently demonstrated to have enhancer activity in embryonic-derived but not postnatal-derived tissue macrophages. Overall, we show that under homeostatic conditions, the environment largely dictates the programming and function of AMs, whereas the expression of a small number of genes remains linked to the origin of the cell.

Abundant Hepatic Gaucher-Like Cells Following Chemotherapy and Bone Marrow Transplantation for Hematologic Malignancy

Cells with a resemblance to Gaucher cells, sometimes called pseudo-Gaucher cells, are seen in the bone marrow of some patients with hematologic malignancy or anemia. These cells are derived from cells of the monocytic lineage but do not show the characteristic inclusions of true Gaucher cells when examined by electron microscopy. Large numbers of Gaucher-like cells were found in the livers at autopsy of 2 patients with hematologic malignancy treated with chemotherapy and bone marrow transplant. Knowledge of this phenomenon may be useful in the interpretation of liver biopsy done on a patient with bone marrow transplant.

Morphology of the bone marrow after stem cell transplantation

In many haematological conditions the only curative option is stem cell (SCT) or bone marrow (BM) transplantation. Little information exists about BM morphology following non-ablative engraftment. During the pretransplantation period and depending on the kind of pretreatment, there may be hypoplasia, residual disease and varying degrees of fibrosis. In the post-transplantation period, after 1-3 weeks of transfusion-dependent pancytopenia, the first signs of successful engraftment are indicated by the recurrence of neutrophils, monocytes and erythrocytes in the peripheral blood. In the BM there is slow regeneration of erythropoiesis, followed by the other lineages of haematopoiesis and increase in reticulin fibres or even a resolution of fibrosis. Diagnostic problems arise when neoplastic lympho- or haematopoiesis are maintained following transplantation. Moreover, there may be a significant graft versus tumour response reaction or an already relapsing disease needing aggressive treatment. On the other hand, a conspicuous dyshaematopoiesis should not be mistaken as representing a myelodysplastic syndrome. The presence of granulomas being treatment-related or a manifestation of intercurrent granulomatous disease has to be considered. More advanced knowledge of the histological features of regenerating BM will certainly aid the recognition of relapsing disease and is needed for the adequate reporting of post-transplant alterations associated with a successful or failing engraftment.

Quantification of clonal hematopoiesis in polycythemia vera

Polycythemia vera (PV) is believed to represent a clonal trilineage myeloaccumulative hematopoietic disorder. This study was undertaken to estimate for the first time the proportion not only of the neoplastic clone but also of clonal and residual nonneoplastic CD34(+) progenitor cells. Chromosomal abnormalities, including trisomy 8 or 9, are phenomena associated in about 20% of PV patients. Therefore, we screened peripheral blood (PB) mononuclear cells of PV patients in the chronic phase of the disease and looked for chromosomal abnormalities performing comparative genomic hybridization. Two of the ten patients revealed cytogenetic changes, including trisomy 8 or 9. To quantify the proportion of cytogenetic abnormal cells in these patients, we applied fluorescence in situ hybridization (FISH) technique on immunomagnetically enriched cell fractions. Ninety percent of the mononuclear cells and up to 79% of PB-derived CD34(+) progenitor cells presented three signals for chromosome 8 or 9. The diagnostic value of FISH to detect trisomies in trephine biopsies was then tested in all patients under study. Although the probability to detect FISH signals in a certain section plane is reduced, constantly 10-15% of the cells revealed three signals. Concerning the CD34(+) progenitor cell pool, a distinct nonclonal population exists in these patients. Our data underline the stem cell character of PV and additionally quantify the proportion of clonal CD34(+) progenitor cells for the first time. The finding of a distinct, not aberrant, CD34(+) progenitor cell population in chronic phase PV may offer perspectives in treatment of the disease. Finally, FISH analysis of bone marrow biopsies can be helpful to consolidate diagnosis of early PV.

Mixed chimerism of bone marrow CD34+ progenitor cells (genotyping, bcr/abl analysis) after allogeneic transplantation for chronic myelogenous leukemia

BACKGROUND

Although CD34 progenitors play a crucial role during bone marrow transplantation (BMT), there is only scant knowledge concerning their lineage-restricted mixed chimerism (MCh).

METHODS

An immunohistochemical and fluorescence in situ hybridization study was performed on bone marrow biopsies derived from 11 patients with chronic myelogenous leukemia after sex-mismatched BMT to quantify the CD34 cell population and their expression. After proper identification by a lineage-specific monoclonal antibody, X chromosome- and Y chromosome-specific probes were used for sex typing and for labeling of the locus commercially available detection systems were applied.

RESULTS

After successful engraftment, 241 progenitor cells were identified at days 9 to 586 of the posttransplant period. Overall incidence of MCh was 24% with a tendency to decline after day 100 to 15%. The gene was detectable in only 10% of these precursors and decreased to less than 4% after more than 6 months. Approximately 0.5 to 5.5 years after BMT in six patients, a manifest leukemic relapse occurred, which was accompanied by a conversion of donor-to-host-type progenitors. This phenomenon involved up to 94% of the 303 evaluable CD34 cells and also included a retrieval of the translocation gene in approximately 50% of this population.

CONCLUSION

The lineage-restricted MCh of progenitors after BMT is in keeping with the assumption that leukemic (bcr/abl ) precursors represent only a fraction of the total host-derived (chimeric) CD34 cells. These residual clonally transformed progenitors survive myeloablative treatment and thus may be the source for a later relapse.