# IL-2 Complex Therapy Mitigates Humoral Rejection of Fully Mismatched Skin Allografts by Inhibiting IgG Alloantibody Formation

## TL;DR

This study shows that IL-2 complex therapy can reduce antibody-mediated rejection in skin transplants by limiting harmful antibody production.

## Contribution

The study reveals a novel mechanism by which IL-2 complex therapy inhibits IgG alloantibody formation while preserving IgM.

## Key findings

- IL-2 cplx treatment suppresses germinal center development and Bcl-6 upregulation.
- IL-2 cplx reduces IgG alloantibody production but allows IgM synthesis.
- The therapy shifts antibody production toward low-affinity IgM.

## Abstract

Antibody-mediated rejection (ABMR) caused by donor-specific Abs (DSAs) is still the leading cause of late graft loss following clinical organ transplantation, and effective strategies to combat ABMR are still elusive. We previously showed that rIL-2 complexed with anti-IL-2 mAb clone JES6-1A12 (IL-2 cplx) leads to the selective expansion of regulatory T cells (Tregs) and the prolonged survival of MHC-mismatched skin allografts. Although the grafts were eventually rejected, mice failed to develop DSAs. Here, we investigated the impact of IL-2 cplx on the humoral response and germinal center (GC) reaction during allograft rejection. IL-2 cplx treatment prevents Bcl-6 upregulation, leading to suppressed development of GC T and B cells. The IL-2 cplx-induced impairment of GC development limits IgG allo-Ab production but allows for IgM synthesis. By employing a hapten–carrier system to investigate affinity maturation, we found that IL-2 cplx induces a distinct shift in specific Ab production favoring low-affinity IgM while simultaneously decreasing IgG responses. These findings illuminate the potential of IL-2 cplx therapy for inducing humoral tolerance, potentially paving the way for refining strategies aimed at preventing and treating ABMR.