Site of Blood Vessel Damage and Relevance of CD18 in a Murine Model of Immune Complex-Mediated Vasculitis

How neutrophils (polymorphonuclear neutrophils, PMNs) damage vessels in leukocytoclastic vasculitis (LcV) mediated by immune complexes (ICs) is unclear. If degradative enzymes and oxygen radicals are released from PMNs while adhering to the inner side of the vessel wall, they could be washed away by the blood stream or neutralized by serum protease inhibitors. We investigated if in LcV PMNs could damage vessels from the tissue side after transmigration. We used CD18-deficient (CD18−/−) mice because the absence of CD18 excludes transmigration of PMNs. When eliciting the Arthus reaction in ears of CD18−/− mice, deposition of ICs was not sufficient to recruit PMNs or to induce IC-mediated LcV. Injection of PMNs intradermally in CD18−/− mice allowed us to investigate if bypassing diapedesis and placing PMNs exclusively on the abluminal side leads to vascular destruction. We found that injected PMNs gathered around perivascular ICs, but did not cause vessel damage. Only intravenous injection of wild-type PMNs could re-establish the Arthus reaction in CD18−/− mice. Thus, PMNs cause vessel damage during diapedesis from the luminal side, but not from the perivascular space. We suggest that in order to shield the cytotoxic products from the blood stream, ICs induce particularly tight interactions between them, PMNs and endothelial cells

Adaptive Immune Response to Model Antigens Is Impaired in Murine Leukocyte-Adhesion Deficiency-1 Revealing Elevated Activation Thresholds In Vivo

Absence of β2 integrins (CD11/CD18) leads to leukocyte-adhesion deficiency-1 (LAD1), a rare primary immunodeficiency syndrome. Although extensive in vitro work has established an essential function of β2 integrins in adhesive and signaling properties for cells of the innate and adaptive immune system, their respective participation in an altered adaptive immunity in LAD1 patients are complex and only partly understood in vivo. Therefore, we investigated adaptive immune responses towards different T-dependent antigens in a murine LAD1 model of β2 integrin-deficiency (CD18−/−). CD18−/− mice generated only weak IgG responses after immunization with tetanus toxoid (TT). In contrast, robust hapten- and protein-specific immune responses were observed after immunization with highly haptenated antigens such as (4-hydroxy-3-nitrophenyl)21 acetyl chicken γ globulin (NP21-CG), even though regularly structured germinal centers with specificity for the defined antigens/haptens in CD18−/− mice remained absent. However, a decrease in the hapten/protein ratio lowered the efficacy of immune responses in CD18−/− mice, whereas a mere reduction of the antigen dose was less crucial. Importantly, haptenation of TT with NP (NP-TT) efficiently restored a robust IgG response also to TT. Our findings may stimulate further studies on a modification of vaccination strategies using highly haptenated antigens in individuals suffering from LAD1

Angiogenin released from ABCB5+ stromal precursors improves healing of diabetic wounds by promoting angiogenesis

Severe angiopathy is a major driver for diabetes-associated secondary complications. Knowledge on the underlying mechanisms essential for advanced therapies to attenuate these pathologies is limited. Injection of ABCB5+ stromal precursors at the edge of nonhealing diabetic wounds in a murine db/db model, closely mirroring human type 2 diabetes, profoundly accelerates wound closure. Strikingly, enhanced angiogenesis was substantially enforced by the release of the ribonuclease angiogenin from ABCB5+ stromal precursors. This compensates for the profoundly reduced angiogenin expression in nontreated murine chronic diabetic wounds. Silencing of angiogenin in ABCB5+ stromal precursors before injection significantly reduced angiogenesis and delayed wound closure in diabetic db/db mice, implying an unprecedented key role for angiogenin in tissue regeneration in diabetes. These data hold significant promise for further refining stromal precursors–based therapies of nonhealing diabetic foot ulcers and other pathologies with impaired angiogenesis

Newly defined ATP-binding cassette subfamily B member 5 positive dermal mesenchymal stem cells promote healing of chronic iron-overload wounds via secretion of interleukin-1 receptor antagonist

In this study, we report the beneficial effects of a newly identified dermal cell subpopulation expressing the ATP‐binding cassette subfamily B member 5 (ABCB5) for the therapy of nonhealing wounds. Local administration of dermal ABCB5+‐derived mesenchymal stem cells (MSCs) attenuated macrophage‐dominated inflammation and thereby accelerated healing of full‐thickness excisional wounds in the iron‐overload mouse model mimicking the nonhealing state of human venous leg ulcers. The observed beneficial effects were due to interleukin‐1 receptor antagonist (IL‐1RA) secreted by ABCB5+‐derived MSCs, which dampened inflammation and shifted the prevalence of unrestrained proinflammatory M1 macrophages toward repair promoting anti‐inflammatory M2 macrophages at the wound site. The beneficial anti‐inflammatory effect of IL‐1RA released from ABCB5+‐derived MSCs on human wound macrophages was conserved in humanized NOD‐scid IL2rγ null mice. In conclusion, human dermal ABCB5+ cells represent a novel, easily accessible, and marker‐enriched source of MSCs, which holds substantial promise to successfully treat chronic nonhealing wounds in humans

MAPKinase inhibition after failure of immune checkpoint blockade in patients with advanced melanoma – an evaluation of the multicenter prospective skin cancer registry ADOREG

Objectives: Forty to sixty percent of patients with advanced melanoma show primary resistance to PD-1-based immunotherapy, 30-40% of initial responders also progress. Here, we evaluated the outcome of second-line targeted therapy (TT) after progression on PD-1-based immune checkpoint inhibition (ICI) in BRAFV600-mutated melanoma. In addition, we report data on the activity of re-exposure with PD-1-based regimes. Methods: Patients with advanced (non- resectable stage III or IV, AJCC 2017, 8th edition) melanoma progressing on PD-1-based ICI (nivolumab, pembrolizumab or ipilimumab plus nivolumab) and receiving second-line BRAF plus MEK inhibition were identified from the prospective multicenter skin cancer registry ADOREG. Results: We identified 108 patients with unresectable stage III or stage IV melanoma progressing on first-line ICI (nivolumab, pembrolizumab or ipilimumab plus nivolumab) and receiving second-line combined BRAF/MEK inhibition. Seventy- three percent of the cohort presented with primary PD-1 resistant disease. Median progression-free survival ( PFS) on ICI was 2.6 (95% CI 2.2-2.9) months. Median PFS on subsequent TT was 6.6 (95% CI 5.4 -7.8) months. Median OS from start of second-line TT was 16.0 (95% CI 11.2-20.8) months. The 3-year PFS and OS rates on second-line TT were 16% and 30%. The objective response rate (ORR) and disease control rate (DCR) to TT were 42.6% and 55.6%. In patients with brain metastases, the ORR and DCR were 31.4% and 43.1%. Patients without brain metastases showed an ORR and DCR of 52.6% and 66.7%, respectively. Response to first-line ICI was associated with a numerically higher ORR and DCR to second-line TT and improved OS on TT. Twenty-three patients received third-line ICI of whom two patients showed an objective response. Conclusions: BRAF plus MEK inhibition shows meaningful activity and outcome in patients with advanced melanoma resistant to anti-PD-1- based immunotherapy. Rates of long- term benefit and survival in our study were similar to those reported for treatment-naive patients receiving first-line MAPKi

Syk-Mediated Translocation of PI3Kδ to the Leading Edge Controls Lamellipodium Formation and Migration of Leukocytes

The non-receptor tyrosine kinase Syk is mainly expressed in the hematopoietic system and plays an essential role in β2 integrin-mediated leukocyte activation. To elucidate the signaling pathway downstream of Syk during β2 integrin (CD11/CD18)-mediated migration and extravasation of polymorphonuclear neutrophils (PMN), we generated neutrophil-like differentiated HL-60 (dHL-60) cells expressing a fluorescently tagged Syk mutant lacking the tyrosine residue at the position 323 (Syk-Tyr323) that is known to be required for the binding of the regulatory subunit p85 of the phosphatidylinositol 3-kinase (PI3K) class IA. Syk-Tyr323 was found to be critical for the enrichment of the catalytic subunit p110δ of PI3K class IA as well as for the generation of PI3K products at the leading edge of the majority of polarized cells. In accordance, the translocation of PI3K p110δ to the leading edge was diminished in Syk deficient murine PMN. Moreover, the expression of EGFP-Syk Y323F interfered with proper cell polarization and it impaired efficient migration of dHL-60 cells. In agreement with a major role of β2 integrins in the recruitment of phagocytic cells to sites of lesion, mice with a Syk-deficient hematopoietic system demonstrated impaired PMN infiltration into the wounded tissue that was associated with prolonged cutaneous wound healing. These data imply a novel role of Syk via PI3K p110δ signaling for β2 integrin-mediated migration which is a prerequisite for efficient PMN recruitment in vivo

Senescent BALB/c mice are able to develop resistance to Leishmania major infection.

With advancing age, the immune system of animals and humans undergoes characteristic changes, usually resulting in increased susceptibility to infections and malignancies and deficiency in mounting Th2 immune responses. This PhD thesis addresses the question whether the age-related decline in Th2 responses is dominant enough to reduce the generation of Th2 cells and even to bias Tcell differentiation towards a Th1 pattern providing resistance to diseases that require Th1 immune responses for healing. We investigated this issue on the model of experimental leishmaniasis in mice. In this model, genetically resistant mice (like C57) heal cutaneous lesions and clear the infection with L. major by mounting a Th1 immune response with high levels of IFN-gamma; by contrast, genetically susceptible mice (BALB/c) do not heal and succumb under progressive dissemination of the parasites. Surprisingly, susceptible senescent BALB/c mice developed a milder infection than the young ones and in 60% of the cases even healed ulcerations, similarly to the resistant, C57BL/6 mice. Moreover, some senescent BALB/c mice mounted a L. major-specific Th1 response, with elevated release of IFN-gamma upon infection. By sharp contrast, young BALB/c mice developed a susceptibility-characteristic Th2 response. This observation was further sustained by the finding that macrophages from senescent BALB/c mice spontaneously produce higher levels of IL-12 than macrophages from young mice. IL-12 is the main cytokine responsible for the initiation of a host-protective Th1 immune response. Besides aging, we have identified the infection with Murine Hepatitic Virus as a possible second signal, which might have driven the immune response towards a Th1 pattern in senescent mice raised in conventional conditions. Our results are both remarkable and important, as they show for the first time that BALB/c mice might become resistant to infection with L. major without any treatment

Wound healing defect of Vav3−/− mice due to impaired β2-integrin–dependent macrophage phagocytosis of apoptotic neutrophils

Vav proteins are guanine-nucleotide exchange factors implicated in leukocyte functions by relaying signals from immune response receptors and integrins to Rho-GTPases. We here provide first evidence for a role of Vav3 for β2-integrins-mediated macrophage functions during wound healing. Vav3-/- and Vav1-/-/ Vav3-/- mice revealed significantly delayed healing of full-thickness excisional wounds. Furthermore, Vav3-/- bone marrow chimeras showed an identical healing defect, suggesting that Vav3 deficiency in leukocytes, but not in other cells, is causal for the impaired wound healing. Vav3 was required for the phagocytotic cup formation preceding macrophage phagocytosis of apoptotic neutrophils. Immunoprecipitation and confocal microscopy revealed Vav3 activation and colocalization with β2-integrins at the macrophage membrane upon adhesion to ICAM-1. Moreover, local injection of Vav3-/- or β2-integrin(CD18)-/- macrophages into wound margins failed to restore the healing defect of Vav3-/- mice, suggesting Vav3 to control the β2-integrin-dependent formation of a functional phagocytic synapse. Impaired phagocytosis of apoptotic neutrophils by Vav3-/- macrophages was causal for their reduced release of active transforming growth factor (TGF)-β1, for decreased myofibroblasts differentiation and myofibroblastdriven wound contraction. TGF-β1 deficiency in Vav3-/- macrophages was causally responsible for the healing defect, as local injection of either Vav3-competent macrophages or recombinant TGF-β1 into wounds of Vav3-/- mice fully rescued the delayed wound healing. © 2009 by The American Society of Hematology.K.S.-K., A.S., K.L.R., A.G., C.S., and K.D.F. are supported by Deutsche Forschungsgemeinschaft (DFG) grants SFB497-C7 (K.S.-K., A.S.), KFO142 (K.S.-K.), SFB497-C11 (K.L.R., A.G.), DFG SU195/3-1 (C.S.), and SFB497-C6 (K.D.F.).Peer Reviewe