# Novel Flow Cytometry Method Detecting Complement C1q Bound to Blood Type A/B IgG Antibody for Preventing Severe Antibody-Mediated Rejection in ABO-Incompatible Kidney Transplantation

## TL;DR

A new flow cytometry method detects complement C1q bound to IgG antibodies in blood type A/B, helping predict severe rejection in incompatible kidney transplants.

## Contribution

The novel FCM-C1q method enables detection of complement-binding anti-blood type antibodies, offering a new tool for predicting antibody-mediated rejection in ABO-incompatible kidney transplants.

## Key findings

- FCM-IgG and C1q levels were significantly higher in type O participants compared to A/B participants.
- High FCM-C1q levels were associated with severe antibody-mediated rejection and poor outcomes in ABO-incompatible kidney transplant recipients.
- Two patients with elevated pre-transplant FCM-C1q and FCM-IgG levels had no or mild rejection post-transplant.

## Abstract

We aimed to develop a novel method for measuring the complement-binding ability of anti-blood type antibodies (ab-Abs), the flow cytometry method for the complement C1q test (FCM-C1q) for detecting antibody-mediated rejection (AMR) caused by ab-Abs in ABO-incompatible kidney transplantation (ABOI-KTx). FCM-C1q distribution was surveyed in 44 healthy participants and 43 dialysis patients (Cohort A). The relationship between AMR and FCM-C1q levels was examined along with ab-Ab titers by the flow cytometry method for the IgG test (FCM-IgG) in 62 ABOI-KTx patients (Cohort B). FCM-IgG and C1q levels were significantly higher in type O participants than in A/B participants in Cohort A. There were minimal differences in the distribution of FCM-IgG and C1q between dialysis and healthy participants. Sixteen cases were suspected of acute rejections (ARs) in Cohort B, of whom nine had AR clinically. One patient with severe AMR was highly suspected of hyperacute rejection along with another patient with severe AMR. Their postoperative FCM-C1q and FCM-IgG levels were elevated. Another two patients showed high FCM-IgG and C1q levels before KTx, and these levels remained low after KTx with no or mild rejection. In conclusion, our results suggest that a high positivity rate for FCM-C1q may predict moderate to severe AMR caused by ab-Abs and poor prognosis in ABOI-KTx.