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A vital function of the immune system is the modulation of an evolving immune response. It is responsible for guarding against a wide variety of pathogens as well as the establishment of memory responses to some future hostile encounters. Simultaneously, it maintains self-tolerance and minimizes collateral tissue damage at sites of inflammation. In recent years, the regulation of T-cell responses to foreign or self-protein antigens and maintenance of balance between T-cell subsets have been linked to a distinct class of cell surface and extracellular components, the immune checkpoint molecules. The fact that both cancer and viral infections exploit similar, if not the same, immune checkpoint molecules to escape the host immune response highlights the need to study the impact of immune checkpoint blockade on viral infections. More importantly, the process through which immune checkpoint blockade completely changed the way we approach cancer could be the key to decipher the potential role of immunotherapy in the therapeutic algorithm of viral infections. This review focuses on the effect of programmed cell death protein 1/programmed death-ligand 1 blockade on the outcome of viral infections in cancer patients as well as the potential benefit from the incorporation of immune checkpoint inhibitors (ICIs) in treatment of viral infections.

Since the pandemic’s onset, a growing population of individuals has recovered from SARS-CoV-2 infection and its long-term effects in some of the convalescents are gradually being reported. Although the precise etiopathogenesis of post-acute COVID-19 sequelae (PACS) remains elusive, the mainly accepted rationale is that SARS-CoV-2 exerts long-lasting immunomodulatory effects, promotes chronic low-grade inflammation, and causes irreversible tissue damage. So far, several viruses have been causally linked to human oncogenesis, whereas chronic inflammation and immune escape are thought to be the leading oncogenic mechanisms. Excessive cytokine release, impaired T-cell responses, aberrant activation of regulatory signaling pathways (e.g., JAK-STAT, MAPK, NF-kB), and tissue damage, hallmarks of COVID-19 disease course, are also present in the tumor microenvironment. Therefore, the intersection of COVID-19 and cancer is partially recognized and the long-term effects of the virus on oncogenesis and cancer progression have not been explored yet. Herein, we present an up-to-date review of the current literature regarding COVID-19 and cancer cross-talk, as well as the oncogenic pathways stimulated by SARS-CoV-2.