Bone marrow T-cell infiltration during acute GVHD is associated with delayed B-cell recovery and function after HSCT.

B-cell immune dysfunction contributes to the risk of severe infections after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Delayed B-cell regeneration is found in patients with systemic graft-versus-host disease (GVHD) and is often accompanied by bone marrow (BM) suppression. Little is known about human BM GVHD. We analyzed the reconstitution kinetics of B-cell subsets in adult leukemic patients within 6 months after allo-HSCT. B-cell deficiency already existed before transplant and was aggravated after transplant. Onset of B-cell reconstitution characterized by transitional B-cell recovery occurred either early (months 2-3) or late (from month 6 on) and correlated highly positively with reverse transcription-polymerase chain reaction quantified numbers of κ-deleting recombination excision circles (KRECs). Delayed recovery was associated with systemic acute GVHD and full-intensity conditioning therapy. Histological analysis of BM trephines revealed increased T-cell infiltration in late recovering patients, which was associated with reduced numbers of osteoblasts. Functionally, late recovering patients displayed less pneumococcal polysaccharide-specific immunoglobin M-producing B cells on ex vivo B-cell activation than early recovering patients. Our results provide evidence for acute BM GVHD in allo-HSCT patients with infiltrating donor T cells and osteoblast destruction. This is associated with delayed B-cell reconstitution and impaired antibody response. Herein, KREC appears suitable to monitor BM B-cell output after transplant.

Apoptosis Susceptibility Prolongs the Lack of Memory B Cells in Acute Leukemic Patients After Allogeneic Hematopoietic Stem Cell Transplantation.

Long-term survival after allogeneic hematopoietic stem cell transplantation requires intact immunosurveillance, which is hampered by lymphoid organ damage associated with conditioning therapy, graft-versus-host disease, and immunosuppression. Our study aimed to identify the mechanisms contributing to sustained low memory B cell numbers after transplantation. Peripheral B and T cell subset recovery and functional marker expression were investigated in 35 acute leukemic patients up to 1 year after transplantation. Apoptosis of B cells after CD40/TLR-9, CD40/BCR, and CD40/BCR/TLR-9-dependent stimulation and drug efflux capacity were analyzed. One half of the patients suffered from infections after day 180. All patients had strongly diminished CD27(+) memory B cells despite already normalized total B cell numbers and fully recovered CD27(-)IgD(-) memory B cells, putatively of extra-follicular origin. Circulating memory follicular helper T cells were reduced in the majority of patients as well. Naïve B cells exhibited a decreased expression of CXCR5, which mediates follicular B cell entry. Additionally, a lower HLA-DR expression was found on naïve B cells, impairing antigen presentation. Upon CD40/TLR-9-dependent activation, B cells underwent significantly increased apoptosis paralleled by an aberrant up-regulation of Fas-L on activated T cells and Fas on resting B cells. Significantly increased B cell apoptosis was also observed after CD40/BCR and CD40/BCR/TLR-9-dependent activation. Drug efflux capacity of naïve B cells was diminished in cyclosporin A-treated patients, additionally contributing to an apoptosis-prone phenotype. We conclude that B cell survival and migration and T cell communication defects are contributing candidates for an impaired germinal center formation of memory B cells after allogeneic hematopoietic stem cell transplantation. Follow-up studies should evaluate effectiveness of revaccinations on the cellular level and should address the long-term sequelae of B cell defects after transplantation.

Utilization of TREC and KREC quantification for the monitoring of early T- and B-cell neogenesis in adult patients after allogeneic hematopoietic stem cell transplantation.

BACKGROUND: After hematopoietic stem cell transplantation (HSCT) T- and B-cell reconstitution from primary lymphoid organs are a prerequisite for an effective early lymphocyte reconstitution and a long-term survival for adult patients suffering from acute leukemia. Here, we asked whether quantification of T cell receptor excision circle, (TREC) and kappa-deleting recombination excision circle (KREC) before and within six month after allogeneic HSCT could be used to measure the thymic and bone marrow outputs in such patients. METHODS: We used a duplex real time PCR assay to quantify the absolute copy counts of TREC and KREC, and correlated the data with absolute cell counts of CD3+CD4+ T-cell and CD19+ B-cell subsets determined by flow cytometry, respectively. RESULTS: By comparing two recently proposed naïve T cell subsets, CD31+ naive and CD31- naive T cells, we found a better correlation for the CD31+ subset with TREC level post alloHSCT, in line with the assumption that it contained T cells recently derived from the thymus, indicating that TREC levels reflected real thymic de novo production. Transitional as well as naïve B cells highly correlated with KREC levels, which suggested an association of KREC levels with ongoing bone marrow B cell output. CD45RO+ memory T cells and CD27+ memory B cells were significantly less correlated with TREC and KREC recovery, respectively. CONCLUSION: We conclude that simultaneous TREC/ KREC quantification is as a suitable and practicable method to monitor thymic and bone marrow output post alloHSCT in adult patients diagnosed with acute leukemia.

CXCR3 promotes the production of IgG1 autoantibodies but is not essential for the development of lupus nephritis in NZB/NZW mice.

OBJECTIVE: Autoantibody immune complexes and cellular infiltrates drive nephritis in patients with systemic lupus erythematosus (SLE) and in murine lupus. The chemokine receptor CXCR3 is assumed to promote cellular infiltration of inflamed tissues. Moreover, CXCR3 deficiency ameliorates lupus nephritis in the MRL/MpJ-Fas(lpr) (MRL/lpr) mouse model of SLE. Hence, CXCR3 blockade has been suggested as a novel therapeutic strategy for the treatment of lupus nephritis. We undertook this study to test the effect of CXCR3 in the (NZB × NZW)F(1) (NZB/NZW) mouse model of SLE. METHODS: CXCR3(-/-) NZB/NZW mice were generated and monitored for survival, proteinuria, and kidney infiltration. Anti-double-stranded DNA (anti-dsDNA) and total IgG1, IgG2a, and IgG2b antibody levels were determined by enzyme-linked immunosorbent assay. T cell and plasma cell infiltrates in the kidneys and interferon-γ production were determined by flow cytometry. Plasma cell infiltrates were measured using enzyme-linked immunospot assay. Kidney tissue was evaluated for pathologic changes. RESULTS: CXCR3(-/-) NZB/NZW mice exhibited reduced production of total and anti-dsDNA antibodies of the IgG1 subclass, but had normal titers of IgG2a and IgG2b antibodies compared to CXCR3(+/+) NZB/NZW mice. Cellular infiltrates and glomerulonephritis were not reduced in CXCR3(-/-) mice. CONCLUSION: CXCR3 has an effect on (auto)antibody production but is not essential for lupus pathogenesis in NZB/NZW mice, indicating that the effect of CXCR3 on the development of kidney disease varies between MRL/lpr and NZB/NZW mice. These results suggest that CXCR3-dependent and -independent mechanisms can mediate lupus nephritis. Hence, therapeutic CXCR3 blockade could be beneficial for only a subgroup of patients with SLE.

Megakaryocytes constitute a functional component of a plasma cell niche in the bone marrow.

Long-lived plasma cells in the bone marrow produce memory antibodies that provide immune protection persisting for decades after infection or vaccination but can also contribute to autoimmune and allergic diseases. However, the composition of the microenvironmental niches that are important for the generation and maintenance of these cells is only poorly understood. Here, we demonstrate that, within the bone marrow, plasma cells interact with the platelet precursors (megakaryocytes), which produce the prominent plasma cell survival factors APRIL (a proliferation-inducing ligand) and IL-6 (interleukin-6). Accordingly, reduced numbers of immature and mature plasma cells are found in the bone marrow of mice deficient for the thrombopoietin receptor (c-mpl) that show impaired megakaryopoiesis. After immunization, accumulation of antigen-specific plasma cells in the bone marrow is disturbed in these mice. Vice versa, injection of thrombopoietin allows the accumulation and persistence of a larger number of plasma cells generated in the course of a specific immune response in wild-type mice. These results demonstrate that megakaryocytes constitute an important component of the niche for long-lived plasma cells in the bone marrow.

Comprehensive CRISPR-Cas9 screens identify genetic determinants of drug responsiveness in multiple myeloma.

The introduction of new drugs in the past years has substantially improved outcome in multiple myeloma (MM). However, the majority of patients eventually relapse and become resistant to one or multiple drugs. While the genetic landscape of relapsed/ resistant multiple myeloma has been elucidated, the causal relationship between relapse-specific gene mutations and the sensitivity to a given drug in MM has not systematically been evaluated. To determine the functional impact of gene mutations, we performed combined whole-exome sequencing (WES) of longitudinal patient samples with CRISPR-Cas9 drug resistance screens for lenalidomide, bortezomib, dexamethasone, and melphalan. WES of longitudinal samples from 16 MM patients identified a large number of mutations in each patient that were newly acquired or evolved from a small subclone (median 9, range 1-55), including recurrent mutations in TP53, DNAH5, and WSCD2. Focused CRISPR-Cas9 resistance screens against 170 relapse-specific mutations functionally linked 15 of them to drug resistance. These included cereblon E3 ligase complex members for lenalidomide, structural genes PCDHA5 and ANKMY2 for dexamethasone, RB1 and CDK2NC for bortezomib, and TP53 for melphalan. In contrast, inactivation of genes involved in the DNA damage repair pathway, including ATM, FANCA, RAD54B, and BRCC3, enhanced susceptibility to cytotoxic chemotherapy. Resistance patterns were highly drug specific with low overlap and highly correlated with the treatment-dependent clonal evolution in patients. The functional association of specific genetic alterations with drug sensitivity will help to personalize treatment of MM in the future.

Cytotoxic Effects of Rabbit Anti-thymocyte Globulin Preparations on Primary Human Thymic Epithelial Cells.

BACKGROUND: Graft-versus-host disease (GvHD) presents a major cause for morbidity and mortality after allogeneic hematopoietic stem cell transplantation. Rabbit-derived antithymocyte globulin (rATG) treatment reduces the incidence of GvHD after allogeneic hematopoietic stem cell transplantation. However, delayed immune reconstitution following rATG treatment, partly caused by hampered thymic function, is being discussed. The present study aims at elucidating possible cytotoxic effects of 2 commonly used rATG preparations on cultured human thymic stroma, especially thymic epithelial cells (TECs). METHODS: A primary TEC culture was established and the binding and cytotoxicity of 2 rATG preparations to the aforementioned cells were assessed by flow cytometry and immunofluorescence analyses. The release of several cytokines by cultured thymic stroma cells in response to rATG was analyzed via multiplex enzyme-linked immunosorbent assays. RESULTS: Both preparations showed a comparable dose-dependent binding to TECs and exerted a similar complement-independent, dose-dependent cytotoxicity. rATG exposure further resulted in hampered secretion of interleukin (IL)-7, IL-15, and IL-6, cytokines being involved in thymic T cell development and proliferation. Pretreatment with keratinocyte growth factor diminished rATG-induced cytotoxicity of TECs and restored their IL-7 and IL-15 secretion. CONCLUSIONS: Cytotoxic effects on TECs link the rATG-induced thymic damage to the delayed T cell reconstitution, witnessed after rATG treatment. Our data support a combination treatment of rATG and thymus-protective strategies such as keratinocyte growth factor to simultaneously offer sufficient GvHD prophylaxis and overcome delayed T cell reconstitution caused by thymic damage.

A Transgenic Dual-Luciferase Reporter Mouse for Longitudinal and Functional Monitoring of T Cells In Vivo.

Adoptive T-cell therapy (ATT) efficacy is limited when targeting large solid tumors. The evaluation of ATT outcomes using accessory treatment would greatly benefit from an in vivo monitoring tool, allowing the detection of functional parameters of transferred T cells. Here, we generated transgenic bioluminescence imaging of T cells (BLITC) mice expressing an NFAT-dependent click-beetle luciferase and a constitutive Renilla luciferase, which supports concomitant in vivo analysis of migration and activation of T cells. Rapid transferability of our system to preestablished tumor models was demonstrated in the SV40-large T antigen model via both crossbreeding of BLITC mice into a T-cell receptor (TCR)-transgenic background and TCR transduction of BLITC T cells. We observed rapid tumor infiltration of BLITC CD8+ T cells followed by a burst-like activation that mirrored rejection kinetics. Using the BLITC reporter in the clinically relevant H-Y model, we performed female to male transfers and detected H-Y-specific alloreactivity (graft-versus-host disease) in vivo In an H-Y solid tumor model, we found migration of adoptively transferred H-Y TCR-transgenic CD4+ T cells into the tumor, marked by transient activation. This suggests a rapid inactivation of infiltrating T cells by the tumor microenvironment, as confirmed by their expression of inhibitory receptors. In summary, the BLITC reporter system facilitates analysis of therapeutic parameters for ATT, is rapidly transferable to models of interest not restricted to tumor research, and is suitable for rapid screening of TCR clones for tumor rejection kinetics, as well as off-target effects. Cancer Immunol Res; 6(1); 110-20. ©2018 AACR.

Bone Marrow GvHD after Allogeneic Hematopoietic Stem Cell Transplantation.

The bone marrow is the origin of all hematopoietic lineages and an important homing site for memory cells of the adaptive immune system. It has recently emerged as a graft-versus-host disease (GvHD) target organ after allogeneic stem cell transplantation (alloHSCT), marked by depletion of both hematopoietic progenitors and niche-forming cells. Serious effects on the restoration of hematopoietic function and immunological memory are common, especially in patients after myeloablative conditioning therapy. Cytopenia and durable immunodeficiency caused by the depletion of hematopoietic progenitors and destruction of bone marrow niches negatively influence the outcome of alloHSCT. The complex balance between immunosuppressive and cell-depleting treatments, GvHD and immune reconstitution, as well as the desirable graft-versus-tumor (GvT) effect remains a great challenge for clinicians.

Eosinophils and megakaryocytes support the early growth of murine MOPC315 myeloma cells in their bone marrow niches.

Multiple myeloma is a bone marrow plasma cell tumor which is supported by the external growth factors APRIL and IL-6, among others. Recently, we identified eosinophils and megakaryocytes to be functional components of the micro-environmental niches of benign bone marrow plasma cells and to be important local sources of these cytokines. Here, we investigated whether eosinophils and megakaryocytes also support the growth of tumor plasma cells in the MOPC315.BM model for multiple myeloma. As it was shown for benign plasma cells and multiple myeloma cells, IL-6 and APRIL also supported MOPC315.BM cell growth in vitro, IL-5 had no effect. Depletion of eosinophils in vivo by IL-5 blockade led to a reduction of the early myeloma load. Consistent with this, myeloma growth in early stages was retarded in eosinophil-deficient ΔdblGATA-1 mice. Late myeloma stages were unaffected, possibly due to megakaryocytes compensating for the loss of eosinophils, since megakaryocytes were found to be in contact with myeloma cells in vivo and supported myeloma growth in vitro. We conclude that eosinophils and megakaryocytes in the niches for benign bone marrow plasma cells support the growth of malignant plasma cells. Further investigations are required to test whether perturbation of these niches represents a potential strategy for the treatment of multiple myeloma.

Persistent autoantibody-production by intermediates between short-and long-lived plasma cells in inflamed lymph nodes of experimental epidermolysis bullosa acquisita.

Autoantibodies are believed to be maintained by either the continuous generation of short-lived plasma cells in secondary lymphoid tissues or by long-lived plasma cells localized in bone marrow and spleen. Here, we show in a mouse model for the autoimmune blistering skin disease epidermolysis bullosa acquisita (EBA) that chronic autoantibody production can also be maintained in inflamed lymph nodes, by plasma cells exhibiting intermediate lifetimes. After EBA induction by immunization with a mCOL7c-GST-fusion protein, antigen-specific plasma cells and CD4 T cells were analyzed. Plasma cells were maintained for months in stable numbers in the draining lymph nodes, but not in spleen and bone marrow. In contrast, localization of mCOL7c-GST -specific CD4 T cells was not restricted to lymph nodes, indicating that availability of T cell help does not limit plasma cell localization to this site. BrdU-incorporation studies indicated that pathogenic mCOL7c- and non-pathogenic GST-specific plasma cells resemble intermediates between short-and long-lived plasma cells with half-lives of about 7 weeks. Immunization with mCOL7c-GST also yielded considerable numbers of plasma cells neither specific for mCOL7c- nor GST. These bystander-activated plasma cells exhibited much shorter half-lives and higher population turnover, suggesting that plasma cell lifetimes were only partly determined by the lymph node environment but also by the mode of activation. These results indicate that inflamed lymph nodes can harbor pathogenic plasma cells exhibiting distinct properties and hence may resemble a so far neglected site for chronic autoantibody production.

Plasma cell survival is mediated by synergistic effects of cytokines and adhesion-dependent signals.

Recent results suggest that plasma cell longevity is not an intrinsic capacity, but depends on yet unknown factors produced in their environment. In this study, we show that the cytokines IL-5, IL-6, TNF-alpha, and stromal cell-derived factor-1alpha as well as signaling via CD44 support the survival of isolated bone marrow plasma cells. The cytokines IL-7 and stem cell factor, crucially important for early B cell development, do not mediate plasma cell survival, indicating that plasma cells and early B cells have different survival requirements. As shown in IL-6-deficient mice, IL-6 is required for a normal induction, but not for the maintenance of plasma cell responses in vivo, indicating that the effects of individual survival factors are redundant. Optimal survival of isolated plasma cells requires stimulation by a combination of factors acting synergistically. These results strongly support the concept that plasma cell survival depends on niches in which a combination of specific signals, including IL-5, IL-6, stromal cell-derived factor-1alpha, TNF-alpha, and ligands for CD44, provides an environment required to mediate plasma cell longevity.