Immune response and durability of human papillomavirus antibodies in vaccinated adolescents after hematopoietic stem cell transplantation: a pilot study

Hematopoietic stem cell transplantation (HSCT), preceded by chemotherapy and/or total body irradiation, eradicates hematopoietic cells, including vaccine-primed memory cells. Revaccination is therefore required after HSCT. Human papillomavirus (HPV) vaccination is particularly important in this population because of the increased risk of HPV-associated anogenital and oropharyngeal cancers. While the World Health Organization (WHO) currently recommends a single HPV vaccine dose for immunocompetent adolescents, 3 doses are recommended for immunocompromised individuals. To evaluate the immunogenicity of HPV vaccination in adolescents following HSCT. Two cohorts were studied. Cohort 1 was a quasi-experimental study assessing seroconversion after a 2-dose schedule of HPV vaccination in post-HSCT adolescents aged 9–15 years. Eligible participants were ≥ 1 year post-HSCT and had discontinued immunosuppressive therapy for ≥ 6 months. Participants received 2-dose quadrivalent HPV (qHPV) vaccine at 0 and 6 months. Anti-HPV16 L1 IgG and anti-HPV18 L1 IgG levels were measured 6 months after the first dose and 1 month after the second dose. Cohort 2 was a cross-sectional study evaluating the persistence of anti-HPV16 and anti-HPV18 antibodies in vaccinated post-HSCT adolescents at varying intervals after completion of the vaccination series. Twenty-three participants were enrolled in Cohort 1. Six months after the first vaccine dose, the proportions who seroconverted were 54.5% for HPV 16 and 68.2% for HPV 18. One month after the second dose, the proportions who seroconverted increased to 95.5% for HPV 16 and 90.9% for HPV 18. Local adverse events occurred in 22–39% of participants within 48 h after vaccination, whereas systemic adverse events were infrequent. No serious adverse events were observed. In Cohort 2, 15 participants were included. The interval since the last vaccine dose ranged from 6 to 62 months. All participants had detectable antibodies against HPV16, and all but one had detectable antibodies against HPV18. The findings from this pilot study provide preliminary evidence that a 2-dose HPV vaccination schedule may induce a better antibody response in adolescents after HSCT; however, further studies with larger sample sizes and serial assessment of antibody titers are needed to determine the optimal dosing strategy and long-term durability of immunity.