This pilot study demonstrates that CAMR in pediatric renal transplant recipients can be treated successfully and safely with a combination of IVIG and rituximab. This observation should encourage more extensive studies to evaluate this new treatment strategy.

Summary Chronic antibody‐mediated rejection (AMR) is the major cause of late renal allograft loss. There is, however, no established treatment for this condition. We report the results of a prospective pilot study on an antihumoral therapy (AHT) consisting of high‐dose intravenous immunoglobulin G (IVIG) and rituximab in 20 paediatric renal transplant recipients. Donor‐specific HLA antibodies (HLA DSA) were quantified by Luminex‐based bead array technology. Loss of eGFR decreased significantly from 7.6 ml/min/1.73 m² during 6 months prior to AHT to 2.1 ml/min/1.73 m² (P = 0.0013) during 6 months after AHT. Fourteen patients (70%) responded: nine of nine patients (100%) without and five of 11 (45%) with transplant glomerulopathy (P = 0.014). C4d positivity in PTC decreased from 40 ± 18.5% in the index biopsy to 11.6 ± 12.2% (P = 0.002) in the follow‐up biopsy. In four of nine biopsies (44%) C4d staining turned negative. During 2 years of follow‐up, the median loss of eGFR in each of the four 6‐month periods remained significantly lower compared with prior to AHT. Class I DSA declined in response to AHT by 61% (p = 0.044), class II DSA by 63% (p = 0.033) 12 months after intervention. AHT with IVIG and rituximab significantly reduces or stabilizes the progressive loss of transplant function in paediatric patients with chronic AMR over an observation period of 2 years, apparently by lowering circulating DSA and reducing intrarenal complement activation.

Seroconversion after COVID‐19 vaccination is impaired in kidney transplant recipients. Emerging variants of concern such as the B.1.617.2 (delta) and the B.1.1.529 (omicron) variants pose an increasing threat to these patients. In this observational cohort study, we measured anti‐S1 IgG, surrogate neutralizing, and anti‐receptor‐binding domain antibodies three weeks after a third mRNA vaccine dose in 49 kidney transplant recipients and compared results to 25 age‐matched healthy controls. In addition, vaccine‐induced neutralization of SARS‐CoV‐2 wild‐type, the B.1.617.2 (delta), and the B.1.1.529 (omicron) variants was assessed using a live‐virus assay. After a third vaccine dose, anti‐S1 IgG, surrogate neutralizing, and anti‐receptor‐binding domain antibodies were significantly lower in kidney transplant recipients compared to healthy controls. Only 29/49 (59%) sera of kidney transplant recipients contained neutralizing antibodies against the SARS‐CoV‐2 wild‐type or the B.1.617.2 (delta) variant and neutralization titers were significantly reduced compared to healthy controls ( p < 0.001). Vaccine‐induced cross‐neutralization of the B.1.1.529 (omicron) variants was detectable in 15/35 (43%) kidney transplant recipients with seropositivity for anti‐S1 IgG, surrogate neutralizing, and/or anti‐RBD antibodies. Neutralization of the B.1.1.529 (omicron) variants was significantly reduced compared to neutralization of SARS‐CoV‐2 wild‐type or the B.1.617.2 (delta) variant for both, kidney transplant recipients and healthy controls ( p < .001 for all).