Dominant CD8+ T Cell Nucleocapsid Targeting in SARS-CoV-2 Infection and Broad Spike Targeting From Vaccination.

CD8+ T cells have key protective roles in many viral infections. While an overall Th1-biased cellular immune response against SARS-CoV-2 has been demonstrated, most reports of anti-SARS-CoV-2 cellular immunity have evaluated bulk T cells using pools of predicted epitopes, without clear delineation of the CD8+ subset and its magnitude and targeting. In recently infected persons (mean 29.8 days after COVID-19 symptom onset), we confirm a Th1 bias (and a novel IL-4-producing population of unclear significance) by flow cytometry, which does not correlate to antibody responses against the receptor binding domain. Evaluating isolated CD8+ T cells in more detail by IFN-γ ELISpot assays, responses against spike, nucleocapsid, matrix, and envelope proteins average 396, 901, 296, and 0 spot-forming cells (SFC) per million, targeting 1.4, 1.5, 0.59, and 0.0 epitope regions respectively. Nucleocapsid targeting is dominant in terms of magnitude, breadth, and density of targeting. The magnitude of responses drops rapidly post-infection; nucleocapsid targeting is most sustained, and vaccination selectively boosts spike targeting. In SARS-CoV-2-naïve persons, evaluation of the anti-spike CD8+ T cell response soon after vaccination (mean 11.3 days) yields anti-spike CD8+ T cell responses averaging 2,463 SFC/million against 4.2 epitope regions, and targeting mirrors that seen in infected persons. These findings provide greater clarity on CD8+ T cell anti-SARS-CoV-2 targeting, breadth, and persistence, suggesting that nucleocapsid inclusion in vaccines could broaden coverage and durability.

Tremelimumab: research and clinical development.

The immune checkpoint therapy is a relatively recent strategy that aims to tweak the immune system to effectively attack cancer cells. The understanding of the immune responses and their regulation at the intracellular level and the development of fully humanized monoclonal antibodies are the pillars of an approach that could elicit durable clinical responses and even remission in some patients with cancer. Most of the immune checkpoints that regulate the T-cell responses (activation and inhibition) operate through proteins present on the cytoplasmic membrane of the immune cells. Therefore, specific antibodies capable of blocking the inhibitory signals should lead to unrestrained immune responses that supersede the inhibitory mechanisms, which are naturally present in the tumor microenviroment. The best-known and most successful targets for immune checkpoint therapy are the cytotoxic T-lymphocyte antigen-4 and programmed cell death-1 coreceptors. Tremelimumab (CP-675,206) is a fully humanized monoclonal antibody specific for cytotoxic T-lymphocyte antigen-4, which has been successfully used to treat patients with metastatic melanoma and some other cancers. Although still a work in progress, the use of tremelimumab as an immune checkpoint therapeutic agent is a promising approach alone or in combination with other anticancer drugs. Here, we review the use of this antibody in a number of clinical trials against solid tumors.