A tool for evaluating heterogeneity in avidity of polyclonal antibodies.

Diversity in specificity of polyclonal antibody (pAb) responses is extensively investigated in vaccine efficacy or immunological evaluations, but the heterogeneity in antibody avidity is rarely probed as convenient tools are lacking. Here we have developed a polyclonal antibodies avidity resolution tool (PAART) for use with label-free techniques, such as surface plasmon resonance and biolayer interferometry, that can monitor pAb-antigen interactions in real time to measure dissociation rate constant (kd ) for defining avidity. PAART utilizes a sum of exponentials model to fit the dissociation time-courses of pAb-antigens interactions and resolve multiple kd contributing to the overall dissociation. Each kd value of pAb dissociation resolved by PAART corresponds to a group of antibodies with similar avidity. PAART is designed to identify the minimum number of exponentials required to explain the dissociation course and guards against overfitting of data by parsimony selection of best model using Akaike information criterion. Validation of PAART was performed using binary mixtures of monoclonal antibodies of same specificity but differing in kd of the interaction with their epitope. We applied PAART to examine the heterogeneity in avidities of pAb from malaria and typhoid vaccinees, and individuals living with HIV-1 that naturally control the viral load. In many cases, two to three kd were dissected indicating the heterogeneity of pAb avidities. We showcase examples of affinity maturation of vaccine induced pAb responses at component level and enhanced resolution of heterogeneity in avidity when antigen-binding fragments (Fab) are used instead of polyclonal IgG antibodies. The utility of PAART can be manifold in examining circulating pAb characteristics and could inform vaccine strategies aimed to guide the host humoral immune response.

Safety, immunogenicity and non-interference of concomitant Typhoid Vi capsular polysaccharide-tetanus toxoid conjugate vaccine (Typbar-TCV®) and measles or measles-mumps-rubella vaccines in 8-9 months-old Indian children.

We evaluated safety, reactogenicity, and immunogenicity when the WHO-prequalified single-dose Typhoid Vi-polysaccharide conjugate vaccine, Typbar-TCV®, was administered concomitantly with measles (MV) or measles-mumps-rubella (MMR) vaccines in 8- or 9-month-old children. We enrolled 493 children who were randomized 2:1:1:1 to four groups to receive either TCV (0.5 mL intramuscularly) and MV (0.5 ml subcutaneously) concomitantly at 9 months of age (Group 1) with two subgroups given TCV booster 28 days (Group 1A) or 180 days (Group 1B) later, or MV on Day 0 and TCV on Day 28 (Group 2); or TCV at 8 months of age and MV 28 days later (Group 3), or MV only at 9 months of age (Group 4). All children received MMR at 15 months of age. We observed no statistically significant differences between group rates of solicited or unsolicited adverse events assessed throughout the study. Seroconversion rates for measles, mumps, and rubella antibodies were unaffected by concomitant administration with TCV, being similar in Groups 1, 2, and 3 and comparable to Group 4 (Control). IgG anti-Vi antibody titers were similar in all groups after primary Typbar-TCV® vaccination and were not increased by a second dose 28 days later. A small response to a booster dose of Typbar-TCV® given at 180 days did not achieve the high titers observed after the first dose, suggesting that booster vaccination may be more effective after a longer interval than 6 months. Typbar-TCV® can be safely co-administered with measles and MMR vaccines in children aged ≥9 months.Clinical trial registration number: CTRI/2014/04/004532.

An open-label, comparative, single dose, clinical Phase â study to assess the safety and immunogenicity of typhoid conjugate vaccine (Vi-CRM197) in healthy Filipino adults.

An injectable typhoid conjugate vaccine (TCV) provides longer-lasting protection, requires fewer doses, and is suitable for children aged >2 years. In addition, TCV is preferred at most ages owing to its improved immunological properties as it overcomes the limitation of Vi polysaccharide vaccines. Here, we assessed the safety, tolerability, and immunogenicity of a TCV, Vi-CRM197, termed EuTCV, in an open-label clinical phase I study in healthy Filipino adults. This study was conducted in 75 healthy adults aged 18-45 years who were randomized in a 1:1:1 ratio based on the vaccines administered: EuTCV (Test), Typbar-TCV® (WHO prequalified vaccine) and Typhim Vi® (Vi polysaccharide vaccine). The study vaccines were administered at a dose of 25 µg of Vi-CRM197 conjugate by intramuscular injection as a single dose to each of the 25 participants/group, and their immunogenicity and overall safety were assessed for 42 days post-vaccination. All study participants (n = 25/group) completed the trial without dropouts. There were no deaths, SAEs, or events leading to premature withdrawal from the study. Anti-Vi IgG antibody titer (geometric mean titer) of EuTCV group on day 42 was 65.325 [95% CI (36.860, 115.771)], which was significantly higher than that of the WHO prequalified TCV [24.795, 95% CI (16.164, 38.033) p = 0.0055] and the Vi polysaccharide vaccine [7.998, 95% CI (3.800, 16.835) p < 0.0001]. Moreover, the seroconversion rate of EuTCV and Typbar-TCV® was 100%, but that of Typhim Vi® was only 84%. The IgG1-3 subclass titers and serum bactericidal assay results in the EuTCV group showed higher and better bactericidal capacity than the other groups. EuTCV was well tolerated and exhibited an acceptable safety profile in the study population. The Vi-CRM197 conjugate dose of 25 µg may be considered effective in terms of efficacy and safety. ClinicalTrials.gov registration number: NCT03956524.

Adverse events following immunization with typhoid conjugate vaccine in an outbreak setting in Hyderabad, Pakistan.

Pakistan is facing the world's largest outbreak of extensively drug-resistant (XDR) Typhoid. Vaccination campaign for children aged 6 months to 10 years old with Typhoid Conjugate Vaccine (Typbar-TCV®) was conducted in high-risk areas of Hyderabad during 2018. About 207,000 children were vaccinated. Here we report the adverse events following immunization (AEFI) during the campaign. The campaign was carried out using outreach and fixed centre strategy. Community mobilizers visited each household to perform line listing and mobilize parents with age-eligible children. Children were observed for 30 min post-vaccination. Two-pronged strategy was used for ascertainment of AEFI. A 24/7 hotline number was provided to all parents/caretakers (n = 199,861) to report AEFI during 14 days following immunization. An age-stratified (n = 7139 children) were actively followed at days 7 and 14 for the ascertainment of AEFI. All AEFI were examined by three trained medical officers. A structured questionnaire using Brighton collaboration criteria with level 3 diagnostic certainty was used for the recording of AEFI. Data were analysed using Microsoft Excel Office 365. Overall, 499 AEFI (433 in the subset actively followed and 66 self-reported through hotline) were observed. The rate of AEFI was significantly higher among very young children (age group 6 to 12 months) as compared to 2 to 3 years old children (0.54% vs. 0.33% respectively; p-value < 0.001). Fever was the most common AEFI self-reported through the hotline (38/199,861 = 0.02%) and among the subset followed actively for 14 days (206/7139 = 2.89%). Fever was followed by local reactogenicity 10/199,861(0.01%), and 134/7139 (1.88%) through self-reported hotline and active follow-up, respectively. No serious AEFI was observed. Administration of a single dose of Typbar-TCV among children aged 6 months to 10 years old during an outbreak setting of Hyderabad Pakistan was safe.