Background/Purpose: Pro-fibrotic macrophages (MØs) are implicated in the pathogenesis of systemic sclerosis (SSc). In prior work, we and others have shown that MØs derived from SSc patients express elevated levels of profibrotic mediators and induce fibroblast activation. Thus, we hypothesize that targeting activated MØs in SSc will provide a novel and effective approach to treat the disease, and that the elimination of these MØs will result in decreased fibrosis. To test this hypothesis, we designed a novel therapeutic approach to eliminate pro-fibrotic MØs using chimeric antigen receptor (CAR) T cells.

Methods: To determine how targeted elimination of MØs alters local and systemic fibrosis, we used bleomycin (BLM) injection and pump mouse models of fibrosis. To study local effects on dermal fibrosis, C57BL/6 mice were injected subcutaneously daily with BLM for 21 days. Macrophage-targeting anti-CD206 CAR T cells, control CAR T cells or vehicle were injected intradermally at Day 0 (n=6 mice/treatment group). Animals were euthanized at day 21 and skin tissue processed for histology and stained by H&E. RNA was extracted and analyzed by qRT-PCR and microarray, and dermal thickness was measured using Image J, where 10 measurements were collected per mouse. To assess systemic effects, either PBS or BLM was administered to C57BL/6J mice via subcutaneously implanted osmotic pumps. Mice were injected via tail vein with media control, control CAR T cells, or anti-CD206 targeting CAR T cells (n=8 mice/treatment group) at Day 6 post-BLM initiation. Tissues (skin and lungs) were harvested on Days 14 and 21 and analyzed using immunohistochemistry, flow cytometry, RT-qPCR, and RNA-seq. Dermal and adipose thickness were measured using Aperio ImageScope.

Results: Local administration of anti-CD206 CAR T cells led to a significant reduction in dermal thickness in the intradermal BLM injection mouse model of skin fibrosis. Moreover, elimination of CD206⁺ MØs during the development of fibrosis resulted in reduction in the expression of genes associated with disease progression. Analysis of dermal tissue in the systemic model showed that injections of anti-CD206 CAR T cells led to significant changes in adipose tissue thickness compared to control T cell and vehicle groups. Consistent with observations in SSc patient skin, BLM-administered mice showed significant reductions in intradermal adipose layer thickness compared with PBS controls. However, intradermal adipose thickness was significantly restored at Days 14 and 21 in mice that received anti-CD206 CAR T cells compared mice that received either media or control T cells.

Conclusion: Our results provide proof-of-concept to support therapeutic targeting of pro-fibrotic MØs in SSc patients, and also implicate a novel role for pro-fibrotic MØs in the regulation of adipocyte transdifferentiation and activation.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cellular-immunotherapy-for-systemic-sclerosis/