When individuals are infected with HCMV (virus shown in pink), the population of T cells that can detect this virus expands (T cells shown here in purple). Cross-reactivity is a well-known feature of the immune response. Through this process, HCMV infection can activate T cells (shown here in green) that can recognise both HCMV and another pathogen – including the SARS-CoV-2 virus, even if the HCMV infection happened before the COVID-19 pandemic. These cross-reactive T cells may be able to contribute to the immunity of an individual to SARS-CoV-2, as well as to how COVID-19 affects their body.
Image credit: Created with BioRender.com.