*Purpose: The clinical relevance of HLA allosensitization associated with bacterial infection remains poorly defined. The primary objective of this study is to determine the incidence, characteristics, and clinical relevance of post-infectious de novo HLA antibodies (dnHLA) in a cohort of kidney candidates.

*Methods: This retrospective study includes adult kidney patients on the waitlist who (1) had a documented bacterial infection; (2) received a HLA antibody assessment via single-antigen bead (SAB) testing pre- and post-infection; (3) had no other sensitizing events between pre- and post-infectious SAB tests. Epitope analysis was performed using HLA Matchmaker v02. Pathogenic epitopes were identified using IEDB.org.

*Results: Overall, n=9/30 (30%) developed dnHLA Ab with an average rise in cPRA of 53.2±39.8% (Fig 1). The most common route of infection was PD peritonitis (5/9), with Enterococcus being the most commonly cultured organism. The majority of antibodies were class I, but class II antibodies had a higher median MFI compared with class I (p=?) (Fig 2). In contrast, among patients with pre-existing antibodies only class I antibodies showed an increase in MFI post-infection but not class II. There were no clear cross-reactivity patterns to the dnHLA Ab that formed post-infection. Due to limited data in IEDB, epitopes could not be matched to any of the infectious pathogens.

*Conclusions: In this small but well-characterized cohort of waitlisted kidney transplant patients, a significant proportion of patients developed dnHLA Ab after bacterial infection with a concomitant rise in cPRA that could diminish access to transplant. The lack of cross-reactive patterns to these dnHLA Ab indicate they are less likely to be antigen-specific. The MFI strength of these antibodies permit surrogate crossmatches/absorption studies to further evaluate their clinical relevance.

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