*Purpose: Kidney transplant (KT) recipients have an increased incidence of malignancies, including Human Papillomavirus (HPV)-associated cancers. Thus, HPV vaccines may have an important role in preventing HPV-related disease in this population; however, immunogenicity and safety data are lacking. The aim of this study was to examine the immunological response and tolerability to HPV vaccination in children who are likely to need a KT in the future compared to pediatric KT recipients.

*Methods: The quadrivalent HPV vaccine was administered at 0, 2 and 6 months to girls and boys above age 9 recruited from 7 centers associated with the Midwest Pediatric Nephrology Consortium. Participants were recruited from two groups: 1. Pre-transplant (pre-KT), including children with chronic kidney disease stages 3 and 4 or on dialysis. 2. KT recipients at least 6 months post-transplant. The outcome measures consisted of neutralizing antibody concentrations against HPV 6, 11, 16 and 18 using the competitive Luminex immunoassay at 0 and 7 months. Log of the change in geometric mean titers (milli Merck U/mL) between post-vaccination and pre-vaccination and seroconversion rates (defined as reaching a geometric mean titer of ≥ 20 milli Merck U/mL for HPV-6, ≥ 16 milli Merck U/mL for HPV-11, ≥ 20 milli Merck U/mL for HPV-1 and ≥ 24 milli Merck U/mL for HPV-18) were compared. Vaccine tolerability was also assessed.

*Results: A total of 63 participants were recruited: 35 and 28 into the pre-KT and KT groups, respectively. There were no significant differences between the pre-KT and KT groups in terms of age (13.9±2.7 versus 13.1±2.4) or gender. There were no differences in log of the change in geometric mean titers between groups. However, the percentages of subjects who reached seroconversion were overall lower for the KT group, reaching statistical significance for HPV 6 (75.0 versus 97.0, p = 0.01), HPV 11 (67.9 versus 93.9, p = 0.01) and HPV 18 (60.7 versus 87.9, p = 0.01). There were no adverse events in either group.

*Conclusions: The HPV vaccine was well tolerated in this population. KT recipients had lower seroconversion rates compared to their peers in the pre-KT group, reaching statistical significance for all of the serotypes, except HPV 16. This emphasizes the importance of advocating for HPV vaccination prior to KT. However, further studies are needed to determine if for patients who receive the HPV vaccine prior to KT, the antibodies continue to be protective into the post-transplant years and if KT patients who do not seroconvert would benefit from additional doses of the vaccine.

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