An article published in the Journal of Infectious Diseases by CITF-funded researcher Dr. Deepali Kumar at the University of Toronto evaluated T cell responses in 50 solid organ transplant recipients (SOTR) who demonstrated prior COVID-19 infection. Their findings suggest that even immunocompromised individuals are capable of mounting robust T cell responses following exposure to SARS-CoV-2, but generate weaker responses post-vaccination.

T cells are an important component of the protective immune response to viruses. While most individuals are able to mount a robust T cell response in response to infection with SARS-CoV-2, it is less certain whether immunocompromised individuals, including SOTRs, are capable of generating T cell immunity.

Key points:

  • SOTRs were able to mount SARS-CoV-2-specific CD4 and CD8 T cell responses following a SARS-CoV-2 infection. This phenotype was also consistent with responses observed in the general population (controls).
  • Although similar total blood CD3+ cell levels were observed, SOTRs demonstrated lower CD4 and higher CD8 cell frequencies compared to non-transplant controls. Accordingly, an inverse relationship was observed with spike-specific polyfunctional CD4 T cells more abundant, and CD8 T cells less abundant in SOTRs compared to controls.
  • In SOTRs previously infected with SARS-CoV-2, spike protein-specific CD4 T cells moderately correlated with antibodies against the Spike’s receptor binding domain (RBD).
  • SOTRs with milder COVID outcomes as evidenced by a lower WHO disease score had higher levels of anti-viral CD4 and CD8 T cells compared to those with more severe disease outcomes.
  • They found that mRNA vaccines induced lower levels of polyfunctional IFN-g+ IL-2+ T cells in SOTRs compared to SARS-CoV-2 infection.

Overall, this study provides insights into SARS-CoV-2 T cell immunity among certain populations of immunocompromised individuals and suggests that groups such as SOTRs are capable of mounting polyfunctional T cell responses following exposure to SARS-CoV-2. While vaccinated SOTRs mounted less robust T cell responses compared to naturally-infected SOTRs, the authors acknowledged that age differences may be involved. The authors acknowledge, as well, that, despite the lack of long-term follow up, the observations on impaired T-cell responses in transplant patients provide important information that should inform policy decision on vaccine administration in this population.

Ferreira VH, Marinelli T, Ierullo M, Ku T, Hall VG, Majchrzak-Kita B, Kulasingam V, Humar A, Kumar D. SARS-CoV-2 infection induces greater T-cell responses compared to vaccination in solid organ transplant recipients. J Infect Dis. 2021 Nov 5. doi: 10.1093/infdis/jiab542.