Tetanus toxoid-pulsed monocyte vaccination for augmentation of collateral vessel growth

Clinical improvement and enhanced collateral vessel growth after xenogenic monocyte transplantation

Background: Monocytes (Mo) are the most important mediators in arteriogenesis. Previous results from our group demonstrated the great potential of allogenic Mo transplantation for improving collateral vessel growth, which appeared to be due to a considerable host vs. graft reaction. To prove this hypothesis and introduce this new method in clinical practice, we performed transplantation of human Mo (HuMo) in a mouse model. Methods and results: We ligated the femoral artery of BALB/c mice and transplanted Mo via the tail vein. Perfusion was measured by laser Doppler perfusion imaging (LDPI). We also performed clinical scoring based on behavior, wound healing, signs of inflammation and mobility of the ligated extremity. Finally, arteriogenesis and angiogenesis were examined histologically and by quantitative RT-PCR of the hind limb musculature. LDPI increased within one week after ligation when HuMo were transplanted and increased further up to day 21 (0.63±0.12 (n=12) in HuMo vs. 0.50±0.12 (n=17) in the control group (P<0.01)). A histological evaluation showed significantly more collateral arteries within the adductor muscles after HuMo transplantation. The promotion of collateral vessel growth after HuMo transplantation resulted in better clinical scores (0.33±0.26 (n=12) vs. 3.3 (n=9), SEM; P<0.01). Conclusions: Transplantation of HuMo improves collateral vessel growth and clinical outcomes in mice. These results verify our hypothesis that controlled triggering of the inflammatory mechanism resulted in collateral vessel growth by a local host vs. a graft reaction in the ischemic hind limbs and could represent a further step in the development of a clinical strategy for promoting arteriogenesis.

Intravital Microscopy of Monocyte Homing and Tumor-Related Angiogenesis in a Murine Model of Peripheral Arterial Disease

The therapeutic goal for peripheral arterial disease and ischemic heart disease is to increase blood flow to ischemic areas caused by hemodynamic stenosis. Vascular surgery is a viable option in selected cases, but for patients without indications for surgery such as progression to rest pain, critical limb ischemia, or major disruptions to life or work, there are few possibilities for mitigating their disease. Cell therapy via monocyte-enhanced perfusion through the stimulation of collateral formation is one of a few non-invasive options. Our group examines arteriogenesis after monocyte transplantation into mice using the hindlimb ischemia model. Previously, we have demonstrated improvement in hindlimb perfusion using tetanus-stimulated syngeneic monocyte transplantation. In addition to the effects on the collateral formation, tumor growth could be affected by this therapy as well. To investigate these effects, we use a basement membrane-like matrix mouse model by injecting the extracellular matrix of the Engelbreth-Holm-Swarm sarcoma into the flank of the mouse, after occlusion of the femoral artery. After the artificial tumor studies, we use intravital microscopy to study in vivo tumor-angiogenesis and monocyte homing within collateral arteries. Previous studies have described the histological examination of animal models, which presupposes subsequent analysis to post-mortem artifacts. Our approach visualizes monocyte homing to areas of collateralization in real time sequences, is easy to perform, and investigates the process of arteriogenesis and tumor angiogenesis in vivo.

Factor VII activating protease (FSAP) influences vascular remodeling in the mouse hind limb ischemia model

BACKGROUND

Investigations in factor VII activating protease (FSAP)^-/- mice suggest a role for FSAP in stroke, thrombosis and neointima formation. Here, we analyzed the role of FSAP in vascular remodeling processes related to arteriogenesis and angiogenesis in the mouse hind limb ischemia model.

METHODS AND RESULTS

Femoral artery ligation was performed in mice and exogenous FSAP was injected locally to examine its effect on arteriogenesis in the adductor and angiogenesis in the gastrocnemius muscle over 21 days. Perfusion was decreased by FSAP, which was reflected in a lower arterial diameter and was associated with reduced monocyte infiltration in the adductor muscle. There was increased angiogenesis in the gastrocnemius muscle triggered indirectly by less blood supply to the lower limb. Comparison of wild-type (WT) and FSAP^-/- mice showed that perfusion was not different between the genotypes but there were 2.5-fold more collateral arteries in the adductor muscle of FSAP^-/- mice at day 21. This was associated with a higher infiltration of monocytes at day 3. Capillary density in the gastrocnemius muscle was not altered. Activity of the two major proteolytic pathways associated with vascular remodeling; matrix metalloprotease (MMP)-9 and urokinase-type plasminogen activator (uPA) was elevated in the gastrocnemius but not in the adductor muscle in FSAP^-/- mice.

CONCLUSIONS

Arteriogenesis is enhanced, and this is associated with a higher infiltration of monocytes, in the absence of endogenous FSAP but angiogenesis is unchanged. Exogenous FSAP had the opposite effect on arteriogenesis indicating a possible therapeutic potential of modulating endogenous FSAP.

Isolation and intravenous injection of murine bone marrow derived monocytes

As a subtype of leukocytes and progenitors of macrophages, monocytes are involved in many important processes of organisms and are often the subject of various fields in biomedical science. The method described below is a simple and effective way to isolate murine monocytes from heterogeneous bone marrow. Bone marrow from the femur and tibia of Balb/c mice is harvested by flushing with phosphate buffered saline (PBS). Cell suspension is supplemented with macrophage-colony stimulating factor (M-CSF) and cultured on ultra-low attachment surfaces to avoid adhesion-triggered differentiation of monocytes. The properties and differentiation of monocytes are characterized at various intervals. Fluorescence activated cell sorting (FACS), with markers like CD11b, CD115, and F4/80, is used for phenotyping. At the end of cultivation, the suspension consists of 45%± 12% monocytes. By removing adhesive macrophages, the purity can be raised up to 86%± 6%. After the isolation, monocytes can be utilized in various ways, and one of the most effective and common methods for in vivo delivery is intravenous tail vein injection. This technique of isolation and application is important for mouse model studies, especially in the fields of inflammation or immunology. Monocytes can also be used therapeutically in mouse disease models.