Structure and compositional analysis of aluminum oxyhydroxide adsorbed pertussis vaccine

Abstract

Purpose: The goal of this study was to characterize an acellular pertussis vaccine (Tdap) containing genetically modified pertussis toxin (gdPT) and TLR agonist adsorbed to AlOOH adjuvant.

Methods: Several analytical tools including nanoDSF, FTIR, and LD were used to examine the conformation of novel gdPT and the composition of AlOOH adjuvant formulations adsorbed to pertussis vaccine.

Results: DLS particle size results were 9.3 nm and 320 nm for gdPT. For pertussis toxoid (PT), the DLS particle size results were larger at ~440 nm. After adsorption to AlOOH, which was driven by the protein antigen, the size distribution ranged from 3.5 to 22 µm. Two thermal transitions were observed by DSC for gdPT at 70 °C and 102 °C. The main thermal transition was confirmed to be at 72 °C by nanoDSF. All three vaccine formulations showed one thermal transition: Tdap-AlOOH had a thermal transition of 74.6 °C, Tdap-E6020-AlOOH had a thermal transition at 74.2 °C, and Tdap-CpG-AlOOH had a thermal transition at 77.0 °C. Analysis of pertussis toxin (PTx) and gdPT was also performed by FTIR spectroscopy for the purpose of comparison. The second derivative of the FTIR spectra showed an additional feature for PTx at 1685 cm^-1 compared to gdPT. The antigen's amide I and II regions were largely unchanged after adsorption to AlOOH adjuvant as shown by FTIR, suggesting that there were no significant changes in the secondary structure.

Conclusion: gdPT conformation was successfully characterized using an array of analytical methods. All three Tdap formulations have similar thermal stability as shown by nanoDSF, similar size distribution as shown by LD, and similar overall secondary structure as shown by FTIR. In-line particle sizing and IR can be used as in-process characterization tools to monitor consistency of adsorbed vaccine and to confirm product identity.

Keywords: FTIR; PAT; Particle sizing; Pertussis; TLR agonist; Tdap vaccines.

Graphical abstract

Fig. 1

a) Particle size distribution of gdPT protein antigen as measured by DLS. b) Particle size distribution of PTx protein antigen as measured by DLS.

Fig. 2

a) LD particle size distribution of adjuvants and Tdap adsorbed vaccine formulations. AlOOH (black dashed trace), E6020-AlOOH (orange dashed trace), CpG-AlOOH (blue dashed trace), Tdap-E6020-AlOOH (green trace), Tdap-CpG-AlOOH (blue trace) and Tdap-AlOOH (black trace). b) Particle size distribution of adsorbed protein antigens used in a previous formulation of Tdap vaccine and shown for comparison purposes: Diphtheria Toxoid (DT) (dark purple trace), Pertussis Toxoid (PT) (orange trace), Tetanus Toxoid (TT) (light blue trace), Pertactin (PRN) (green trace), Fimbriae (FIM) (blue trace), and Filamentous Haemagglutinin (FHA) (red trace). The size distribution of all adsorbed protein antigens is representative of one lot, five repeats. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3

Overlay of FTIR spectra for gdPT (red trace) and PTx (blue trace). Calculated second derivative of FTIR spectra of gdPT (red trace) and Pertussis Toxin (PTx) (blue trace). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4

a) FTIR spectra of representative samples highlighting prominent absorptions bands from the different AlOOH and Tdap formulations, from 1700 cm⁻¹ to 900 cm⁻¹. a1) shows E6020-AlOOH adjuvant (dashed line) and Tdap-E6020-AlOOH formulations; a2) shows CpG-AlOOH adjuvant (dashed line) and Tdap-CpG-AlOOH formulations; a3) shows AlOOH alone (dashed) and Tdap AlOOH controls. Linear baseline correction with 42 iterations was applied to each spectrum to remove baseline drift. All formulations have an Al-O–H bending absorption band (1065 – 1068 cm⁻¹), and all adsorbed samples have peaks in the Amide I (1600–1700 cm⁻¹) and Amide II (1500–1600 cm⁻¹) region. b) FTIR spectra of representative samples of pre-adsorbed antigens and their AlOOH absorbed counterparts, from 1700 cm⁻¹ to 900 cm⁻¹.

Fig. 5

a) DSC thermogram of gdPT – experimental profile (blue trace) and fitted line (red line). Thermal transitions Tm₁ of gdPT is 70.4 °C, and Tm₂ is 102.1 °C. b) nanoDSF thermal profiles of gdPT (green trace), showing the first derivative of intrinsic fluorescence emission ratio (350 nm/330 nm). Thermal transition (Tm) of gdPT is 72.3 °C. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 6

Thermal profiles of Tdap-AlOOH (black trace), Tdap-E6020-AlOOH (orange trace) and Tdap-CpG-AlOOH (blue trace), showing the first derivative of intrinsic fluorescence emission ratio (350 nm/330 nm). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)