Longitudinal evaluation of T-cell responses to Pfizer-BioNTech and Janssen SARS-CoV-2 vaccines as boosters in Ghanaian adults

Frank Osei¹Kekeli Korshi Tudzi¹Isaac Otieno Othol²Philip Selorm Segbefia¹Diana Ahu Prah³Evans Nii Armaah-Vedjesu³Abigail Naa Adjorkor Pobee¹Oscar Nii Otto Darko¹Theophilus Brenko¹Doreen Teye-Adjei¹Stella Nartey¹Jones Amo Amponsah¹Vincent Amarh⁴Godfred Futagbi⁵DORCAS OBIRI-YEBOAH²Frederica Partey¹Michael Fokuo Ofori¹Kwadwo Asamoah Kusi^1*

• ¹Department of Immunology, Noguchi Memorial Institute for Medical Research, University of Ghana, Accra, Ghana
• ²Department of Microbiology and Immunology, School of Medical Sciences, University of Cape Coast, Cape Coast, Ghana
• ³West African Centre for Cell Biology of Infectious Pathogens, College of Basic and Applied Sciences, University of Ghana, Accra, Ghana
• ⁴Department of Medical Biochemistry, University of Ghana Medical School, College of Health Sciences, University of Ghana, Accra, Ghana
• ⁵Department of Animal Biology and Conservation Sciences, College of Basic and Applied Sciences, University of Ghana, Accra, Ghana

Introduction: In Ghana, at least five different COVID-19 vaccines based on mRNA or adenovirus vector delivery platforms have been authorized by the Ghana Health Service for vaccination. Although these vaccines have been instrumental in the control of COVID-19, data on the longevity of induced immunity in vaccinated individuals in Ghana is limited. This study aimed at assessing the cellular immune response kinetics among Ghanaians receiving booster vaccinations with the mRNA-based Pfizer and adenovirus-based Janssen COVID-19 vaccines. Methods: We conducted a longitudinal study using 48 Ghanaian adults who had completed primary vaccination series and administered a booster shot with either of the two vaccines. Pre-booster blood samples were collected to serve as the baseline, and post-booster samples at months 3, 6, and 9 for immunological analysis. T-cell responses were assessed using Luminex multiplex assay following stimulation of Peripheral Blood Mononuclear Cells (PBMCs) from study participants with SARS-CoV-2 antigens, whereas immune checkpoint molecules expression was assessed by flow cytometry. Results: Appreciable levels of the Th1 cytokines IL-1β, IL-6, IFN-γ and TNF-α and low levels of IL-2, IL-12 and IL-17A were observed in both groups. The Janssen vaccine booster elicited a more sustained cellular response over the nine months, while the Pfizer vaccine booster group showed signs of response decline after three months. Further sub-analysis showed that persons who received an mRNA-based primary vaccination before a viral vector vaccine booster had more durable cytokine responses. Checkpoint molecules, PD-1, CTLA-4 and TIM-3 were expressed at low levels (<10% of CD4+ or CD8+ T cell population with p-values > 0.05) and comparable between the two groups over the nine months. Discussion/conclusions: Levels of some cytokines were generally more sustained in the Janssen group compared to the Pfizer group. Heterologous vaccine recipients exhibited more efficient cellular immune responses compared to homologous recipients. In addition, T-cell inhibitory molecule kinetics suggests an efficient T-cell activity. These findings may have implications for the overall induction of long-term protective immunity by the two vaccine types.