Reprogramming of profibrotic macrophages for treatment of bleomycin-induced pulmonary fibrosis

Fibrotic diseases cause organ failure that lead to ~45% of all deaths in the United States. Activated macrophages stimulate fibrosis by secreting cytokines that induce fibroblasts to synthesize collagen and extracellular matrix proteins. Although suppression of macrophage-derived cytokine production can halt progression of fibrosis, therapeutic agents that prevent release of these cytokines (e.g., TLR7 agonists) have proven too toxic to administer systemically. Based on the expression of folate receptor β solely on activated myeloid cells, we have created a folate-targeted TLR7 agonist (FA-TLR7-54) that selectively accumulates in profibrotic macrophages and suppresses fibrosis-inducing cytokine production. We demonstrate that FA-TLR7-54 reprograms M2-like fibrosis-inducing macrophages into fibrosis-suppressing macrophages, resulting in dramatic declines in profibrotic cytokine release, hydroxyproline biosynthesis, and collagen deposition, with concomitant increases in alveolar airspaces. Although nontargeted TLR7-54 is lethal at fibrosis-suppressing doses, FA-TLR7-54 halts fibrosis without evidence of toxicity. Taken together, FA-TLR7-54 is shown to constitute a novel and potent approach for treating fibrosis without causing dose-limiting systemic toxicities.

Prognostic significance of CD68, CD163 and Folate receptor-β positive macrophages in hepatocellular carcinoma

Cluster of differentiation (CD)68 may be used as a pan-macrophage or M1 marker, whereas CD163 may be used as an M2 marker. Furthermore, folate receptor (FR)β exhibits an M2-like functional profile. In the present study, CD68 and CD163 were used to evaluate and classify tumor-associated macrophages (TAMs). The expression of CD68, CD163 and FRβ by TAMs in hepatocellular carcinoma (HCC) Tissues was investigated. Samples from 105 patients with HCC were evaluated using immunohistochemistry. The results revealed that CD68 and CD163 overexpression was associated with a worse prognosis. The number of CD68 positive cells observed was significantly higher in patients with stage IV cancer. Furthermore, an increase in CD68 positive cells was observed in patients with median tumor size ≥3.5 cm and in patients with poorly differentiated HCC. The number of CD163 positive cells was also significantly increased in patients with median tumor size ≥3.5 cm and in those with poorly differentiated HCC. A low CD163/68 ratio was correlated with a worse outcome. The ratio was significantly lower in patients with stage IV cancer, patients with des-gamma-carboxy prothrombin abnormalities, patients with blood vessel infiltration and patients with intrahepatic metastasis. The number of FRβ positive cells was not correlated with clinicopathological features. The results of the present study indicate that overexpression of CD68 and CD163 may be associated with a worse patient outcome. The evaluation of CD68 and CD163 positive cells in a cancer microenvironment is controversial. TAMs are not simply cells with single markers or restricted M1 or M2 phenotypes; they are more diverse and heterogeneous. Further studies are required to determine the cross-interaction between diverse TAMs and the tumor microenvironment.

Molecular imaging of folate receptor β-positive macrophages during acute lung inflammation

Characterization of markers that identify activated macrophages could advance understanding of inflammatory lung diseases and facilitate development of novel methodologies for monitoring disease activity. We investigated whether folate receptor β (FRβ) expression could be used to identify and quantify activated macrophages in the lungs during acute inflammation induced by Escherichia coli LPS. We found that FRβ expression was markedly increased in lung macrophages at 48 hours after intratracheal LPS. In vivo molecular imaging with a fluorescent probe (cyanine 5 polyethylene glycol folate) showed that the fluorescence signal over the chest peaked at 48 hours after intratracheal LPS and was markedly attenuated after depletion of macrophages. Using flow cytometry, we identified the cells responsible for uptake of cyanine 5-conjugated folate as FRβ(+) interstitial macrophages and pulmonary monocytes, which coexpressed markers associated with an M1 proinflammatory macrophage phenotype. These findings were confirmed using a second model of acute lung inflammation generated by inducible transgenic expression of an NF-κB activator in airway epithelium. Using CC chemokine receptor 2-deficient mice, we found that FRβ(+) macrophage/monocyte recruitment was dependent on the monocyte chemotactic protein-1/CC chemokine receptor 2 pathway. Together, our results demonstrate that folate-based molecular imaging can be used as a noninvasive approach to detect classically activated monocytes/macrophages recruited to the lungs during acute inflammation.

Depletion of folate receptor β-expressing macrophages alleviates bleomycin-induced experimental skin fibrosis

OBJECTIVES

Folate receptor β (FRβ)-expressing macrophages have been identified as activated macrophages. Here, we investigated the infiltration of FRβ-expressing macrophages in a murine model of bleomycin (BLM)-induced skin fibrosis and assessed the antifibrotic effects of depletion of FRβ-expressing macrophages in this model using a recombinant immunotoxin to FRβ.

METHODS

A recombinant immunotoxin (anti-FRβ-PE38) was prepared by conjugating the Fv portion of the anti-mouse FRβ heavy chain with truncated Pseudomonas exotoxin A (VH-PE38) and the Fv portion of the anti-mouse FRβ light chain. BLM-induced skin fibrosis mice were intravenously treated with either anti-FRβ-PE38 or VH-PE38 as a control protein. Skin fibrosis was evaluated by the change of skin thickness and hydroxyproline content on Day 29. The TGFβ1 mRNA levels in the treated skin were assessed by quantitative real-time RT-PCR on Day 9.

RESULTS

Numbers of FRβ-expressing macrophages increased in BLM-injected skin. Anti-FRβ-PE38 treatment led to a dramatic reduction in the number of FRβ-expressing macrophages. Additionally, skin thickness and hydroxyproline content, were markedly reduced. TGFβ1 mRNA levels were also down-regulated after the treatment. TGFβ1 expression was enriched in FRβ-expressing macrophages compared with FRβ-negative macrophages.

CONCLUSION

These results indicated that anti-FRβ-PE38 treatment efficiently depleted FRβ-expressing macrophages and consequently alleviated BLM-induced skin fibrosis.

Effect of an immunotoxin to folate receptor beta on bleomycin-induced experimental pulmonary fibrosis

It has been suggested that alveolar and interstitial macrophages play a key role in the pathogenesis of idiopathic pulmonary fibrosis (IPF) by producing proinflammatory and/or fibrogenic cytokines. We showed that inflammatory macrophages expressed folate receptor beta (FRbeta) while resident macrophages in normal tissues expressed no or low levels of FRbeta. In the present study, we examined the distribution of FRbeta-expressing macrophages in the lungs of patients with usual idiopathic pulmonary fibrosis (UIP) and mice with bleomycin-induced pulmonary fibrosis (PF) and tested whether the depletion of FRbeta-expressing macrophages could suppress bleomycin-induced PF in mice. Immunostaining with anti-human or -mouse FRbeta monoclonal antibody (mAb) revealed that FRbeta-expressing macrophages were present predominantly in fibrotic areas of the lungs of patients with UIP and mice with bleomycin-induced PF. Intranasal administration of a recombinant immunotoxin, consisting of immunoglobulin heavy and light chain Fv portions of an anti-mouse FRbeta mAb and truncated Pseudomonas exotoxin A, increased survival significantly and reduced levels of total hydroxyproline and fibrosis in bleomycin-induced PF. In immunohistochemical analysis, decreased numbers of tumour necrosis factor-alpha-, chemokines CCL2- and CCL12-producing cells were observed in the immunotoxin-treated group. These findings suggest a pathogenic role of FRbeta-expressing macrophages in IPF. Thus, targeting FRbeta-expressing macrophages may be a promising treatment of IPF.