Primary Antibody Responses Against the Novel Pandemic H1N1 and Secondary Antibody Responses Against Seasonal H1N1 Can Be Induced by Vaccination In Patients Early After Allogeneic Stem Cell Transplantation

Abstract 1273

Pandemic influenza (Flu) 2009 and Seasonal Flu are considered a potential health risk for patients after allogeneic stem cell transplantation (alloSCT). However, in a cohort of 137 patients transplanted between October 2006 and December 2009, only 3 patients (2.3%) developed a PCR proven Pandemic Flu infection, and only 1 patient died from multiple super-infections. Moreover, during the Flu season 2009, 5/93 patients (5.3%) transplanted between October 2005 and December 2008 developed a PCR proven Influenza infection and none of them died. These numbers suggest that alloSCT patients were relatively protected against Seasonal and even Pandemic Flu, probably due to earlier Flu antigen exposure. Therefore, we hypothesized that, despite immune impairment after alloSCT, most patients developed secondary and primary antibody responses against Seasonal Flu and neo-antigen containing Pandemic Flu vaccination. To test this hypothesis we measured IgG antibody levels against common Seasonal hemagglutinin (HA), neo-antigens in Pandemic HA and highly conserved cross-reactive re-call antigens shared by Pandemic HA and Seasonal HA in 56 alloSCT patients after vaccination with Seasonal Flu 2009–2010 and Pandemic Flu 2009. To accurately measure antibodies against these antigens, a novel Luminex multiplex bead assay was developed. Recombinant CMV pp65 control protein, native recombinant Seasonal HA (A/Brisbane/59/2007) and Pandemic HA (A/Calefornia/7/2009) were coupled to different Luminex beads which were incubated with plasma samples. To distinguish antibodies against neo-antigenic parts and conserved re-call antigens of Pandemic HA, samples were pre-incubated with or without 0.75 μg HA (A/Brisbane/59/2007) to absorb cross-reacting antibodies against shared parts of Seasonal and Pandemic HA. Finally, samples were stained with PE- labeled Goat α-human IgG and analyzed with a Luminex analyzer. To validate the Luminex bead assay, pp65, Seasonal HA and Pandemic HA positive and negative serum samples were measured with and without pre-incubation with the corresponding protein. In addition, a hemagglutination inhibition assay was performed with Pandemic H1N1 which showed a good correlation with the Luminex assay (r=0.87). Furthermore, specificity of the assay was confirmed by absence of pp65 antibodies in 17 CMV negative patients, whereas in 33/39 (85%) of CMV positive patients antibodies against the immunodominant pp65 protein were detected. To control for vaccination efficacy, 11 healthy donors were vaccinated with Seasonal Flu 2009–2010 followed by 2 Pandemic Flu vaccinations 3 and 6 weeks later. Plasma samples were taken before vaccination, 4 and 12 weeks after Seasonal Flu, and 1 and 8 weeks after Pandemic Flu vaccination. Prior to vaccination all donors had antibodies against Seasonal HA and conserved re-call Pandemic HA, reflecting their previous vaccination with Seasonal Flu 2008–2009. All donors developed secondary antibody responses against Seasonal HA. Highly specific Pandemic HA specific antibodies were present in 1 donor before and 10/11 donors after Pandemic Flu vaccination, indicating that 9/11 donors developed a primary antibody response to neo-antigenic Pandemic HA. To investigate primary and secondary responses after Seasonal and Pandemic Flu vaccination in alloSCT patients, 56 patients followed a similar vaccination and plasma donation scheme. 86% had antibodies against Seasonal HA and 76% against conserved Pandemic HA pre vaccination, probably induced by vaccinations before 2009. 55% developed a secondary antibody response against Seasonal HA 4 –12 weeks post vaccination. Only 5% had neo-antigenic Pandemic HA antibodies prior to vaccination. Excitingly, 57% developed a primary antibody response against neo-antigenic Pandemic HA 8 weeks after Pandemic Flu vaccination. Overall, patients received vaccinations at a median of 443 (range 90–1240) days after alloSCT. Patients vaccinated 90–300, 301–600 and >600 days after alloSCT developed primary antibody responses against neo-antigenic Pandemic HA in 41%, 47% and 80% of the cases, respectively. In conclusion, this detailed analysis of primary and secondary antibody responses against re-call and neo-antigens after Seasonal and 2009 Pandemic HA may explain the low incidence of Flu infections in patients after alloSCT and provides rational arguments to start Flu vaccination from 3 months after alloSCT.