Fibrosis occurs in almost all chronic (inflammatory) diseases such as heart failure, (pulmonary) hypertension, systemic sclerosis, fatty liver disease and graft-versus-host disease. The uncontrolled secretion of extracellular matrix and inflammatory cytokines by dysregulated fibroblasts leads to a gradual loss of tissue function and contributes to 45% of deaths in the western world. Despite a clear medical need, effective antifibrotic therapies are lacking. However, fibroblast activation protein alpha (FAPα) has emerged as a potential fibroblast-specific target. Here, we present a novel strategy using the therapeutic FAPα antibody sibrotuzumab in combination with high affinity Fc receptor expressing NK92 cells (FCR-NK92) to eliminate FAPα⁺ fibroblasts and treat fibrosis.

In the present study, human cardiac (HAF-SRK01), pulmonary (MRC5) and dermal (HFF1) fibroblasts and FCR-NK92 ± sibrotuzumab were used in flow cytometry, cytotoxicity and western blot experiments to assess the antifibrotic potential of NK-mediated antibody-dependent cellular cytotoxicity.

First, we demonstrated specific activation of sibrotuzumab-loaded FCR-NK92 in the presence of human recombinant FAPα as determined by CD107A expression in a flowcytometric degranulation assay. Specific fibroblast killing was determined via europium release assay indicating significant fibroblast lysis after 2h. As therapeutic interventions targeting fibroblasts should be cell-specific to avoid off-target effects, we used a heterocellular culture model (fibroblasts and NK-resistant non-fibroblasts) to characterize the extent of specific fibroblast killing. After 4h, the FAPα⁺ fibroblast population was reduced by approximately 50% in the sibrotuzumab-treated cultures, whereas the non-fibroblast population (FAPα^-) remained unchanged. To evaluate a functional antifibrotic effect, we measured protein expression of collagen 1 by western blot. After overnight co-culture, collagen 1 expression was abolished in all samples treated with FCR-NK92 and sibrotuzumab compared to control.

As of now, antifibrotic cellular immunotherapies remain a largely untapped therapeutic opportunity. The results of our study highlight the promising potential of targeted cellular immunotherapy for the treatment of fibrosis, offering a compelling rationale for further exploration of this approach in the management of debilitating fibrotic diseases.

The authors declare no conflict of interest.