Human papillomavirus (HPV) vaccines provide excellent protection from infection and disease. The minimum number of doses needed for long-term protection and the potential need for boosters are areas of continuing interest. Studies on the durability of vaccines have focused on antibodies, fewer have analyzed memory immune cells that could provide protection even when antibody levels are low. In this study, subjects who had participated in one of two trials comparing two and three doses (2D, 3D), were given an additional vaccine dose (Gardasil®9, 9vHPV) several years after the initial vaccine doses, and the magnitude of immune responses were compared. Both trials had 2D children who received doses at 0 and 6 months (G1a), 3D children 9-13 (08-001) or 9-14 (V503-010) years old at enrollment in the original trial (G2) and 3D women (age 16-26) (G3). Trial V503-010 had a second 2D group of children vaccinated at 0 and 12 months (G1b). Changes in numbers of HPV specific memory B cells (Bmem) (N = 6 per group, both studies) at 1 month and plasmablasts (PB) (08-001: N = 6 per group, V503-010: G1a N = 12, G1b N = 8, G2 N = 6, G3 N = 28) at 1 week, relative to baseline at the additional dose, were compared among groups. Changes in the geometric mean titers (GMTs) of HPV specific antibodies relative to baseline were compared (N = same as PB). Statistically significant (p < 0.05) increases in the numbers of PB, Bmem and antibody levels (GMT) were seen among subjects receiving an extra vaccine dose relative to baseline. Increases in the number of PB and Bmem were not significantly different among subjects receiving two or three doses. Thus, robust immune responses were observed and did not differ significantly among subjects vaccinated with two or three doses.

Current guidance recommends that adolescents receive a 2-dose human papillomavirus (HPV) vaccine, whereas young adults and immunocompromised persons receive 3 doses. We examined secondary responses of vaccine-elicited memory B cells (Bmem) in naive women receiving 3 doses of the quadrivalent HPV vaccine to understand the quality of B-cell memory generated by this highly effective vaccine. Unexpectedly, we observed a lower Bmem response rate and magnitude of Bmem responses to the third dose than to a booster dose administered at month 24. Moreover, high titers of antigen-specific serum antibody at vaccination inversely correlated with Bmem responses. As the purpose of additional doses/boosters is to stimulate Bmem to rapidly boost antibody levels, these results indicate the timing of the third dose is suboptimal and lend support to a 2-dose HPV vaccine for young adults. Our findings also indicate more broadly that multidose vaccine schedules should be rationally determined on the basis of Bmem responses.

Although licensed human papillomavirus (HPV) vaccines are most efficacious in persons never infected with HPV, they also reduce infection and disease in previously infected subjects, indicating natural immunity is not entirely protective against HPV re-infection. The aim of this exploratory study was to examine the B cell memory elicited by HPV infection and evaluate whether vaccination merely boosts antibody (Ab) levels in previously infected subjects or also improves the quality of B cell memory. Toward this end, the memory B cells (Bmem) of five unvaccinated, HPV-seropositive subjects were isolated and characterized, and subject recall responses to a single HPV vaccine dose were analyzed. Vaccination boosted Ab levels 24- to 930-fold (median 77-fold) and Bmem numbers 3- to 27-fold (median 6-fold). In addition, Abs cloned from naturally elicited Bmem were generally non-neutralizing, whereas all those isolated following vaccination were neutralizing. Moreover, Ab and plasmablast responses indicative of memory recall responses were only observed in two subjects. These results suggest HPV vaccination augments both the magnitude and quality of natural immunity and demonstrate that sexually active persons could also benefit from HPV vaccination. This study may have important public policy implications, especially for the older ‘catch-up’ group within the vaccine's target population.

Licensed human papillomavirus (HPV) vaccines provide near complete protection against the types of HPV that most commonly cause anogenital and oropharyngeal cancers (HPV 16 and 18) when administered to individuals naive to these types. These vaccines, like most other prophylactic vaccines, appear to protect by generating antibodies. However, almost nothing is known about the immunological memory that forms following HPV vaccination, which is required for long-term immunity. Here, we have identified and isolated HPV 16-specific memory B cells from female adolescents and young women who received the quadrivalent HPV vaccine in the absence of pre-existing immunity, using fluorescently conjugated HPV 16 pseudoviruses to label antigen receptors on the surface of memory B cells. Antibodies cloned and expressed from these singly sorted HPV 16-pseudovirus labeled memory B cells were predominantly IgG (>IgA>IgM), utilized diverse variable genes, and potently neutralized HPV 16 pseudoviruses in vitro despite possessing only average levels of somatic mutation. These findings suggest that the quadrivalent HPV vaccine provides an excellent model for studying the development of B cell memory; and, in the context of what is known about memory B cells elicited by influenza vaccination/infection, HIV-1 infection, or tetanus toxoid vaccination, indicates that extensive somatic hypermutation is not required to achieve potent vaccine-specific neutralizing antibody responses.