Humoral immune responses associated with control of SARS-CoV-2 breakthrough infections in a vaccinated US military population.

BACKGROUND: COVID-19 vaccines have been critical for protection against severe disease following infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) but gaps remain in our understanding of the immune responses that contribute to controlling subclinical and mild infections. METHODS: Vaccinated, active-duty US military service members were enrolled in a non-interventional, minimal-risk, observational study starting in May, 2021. Clinical data, serum, and saliva samples were collected from study participants and were used to characterise the humoral immune responses to vaccination and to assess its impact on clinical and subclinical infections, as well as virologic outcomes of breakthrough infections (BTI) including viral load and infection duration. FINDINGS: The majority of VIRAMP participants had received the Pfizer COVID-19 vaccine and by January, 2022, N = 149 had a BTI. The median BTI duration (PCR+ days) was 4 days and the interquartile range was 1-8 days. Participants that were nucleocapsid seropositive prior to their BTI had significantly higher levels of binding and functional antibodies to the spike protein, shorter median duration of infections, and lower median peak viral loads compared to seronegative participants. Furthermore, levels of neutralising antibody, ACE2 blocking activity, and spike-specific IgA measured prior to BTI also correlated with the duration of infection. INTERPRETATION: We extended previous findings and demonstrate that a subset of vaccine-induced humoral immune responses, along with nucleocapsid serostatus are associated with control of SARS-CoV-2 breakthrough infections in the upper airways. FUNDING: This work was funded by the DoD Joint Program Executive Office for Chemical, Biological, Radiological and Nuclear Defense (JPEO-CBRND) in collaboration with the Defense Health Agency (DHA) COVID-19 funding initiative for the VIRAMP study.

Healthy individuals have T-cell and antibody responses to the tumor antigen cyclin B1 that when elicited in mice protect from cancer.

We previously identified the aberrantly expressed cell cycle regulator cyclin B1 as a tumor antigen recognized by antibodies and T cells from patients with breast, lung, and head and neck cancers. Ordinarily expressed only transiently in the G2/M stage of the cell cycle in normal cells, cyclin B1 is constitutively expressed at high levels in the cytoplasm of these and many other tumor types, leading to its recognition by the cancer patient's immune system. We report here an unexpected observation that cyclin B1-specific antibody and memory CD4 and CD8 T cells are also found in many healthy individuals who have no history of cancer. Moreover, young as well as older healthy people have these responses suggesting that events other than cancer, which occur either early in life or throughout life, may lead to aberrant cyclin B1 expression and anti-cyclin B1 immunity. The role, if any, of immunity to this tumor-associated antigen is not known. We wanted to determine specifically whether immunity to cyclin B1 might be important in the immunosurveillance of cyclin B1+ tumors. We therefore tested in mice the effectiveness of vaccine-elicited anti-cyclin B1 immunity against a cyclin B1+ mouse tumor that was chosen based on our published observation that cyclin B1 overexpression is associated with the lack of p53 function. We found that cyclin B1 DNA prime-protein boost vaccine protected mice from a challenge with a tumor cell line that was established from a tumor arising in the p53(-/-) mouse that spontaneously overexpresses cyclin B1.

GM1 binding-deficient exotoxin is a potent noninflammatory broad spectrum intradermal immunoadjuvant.

Intradermal (i.d.) immunization is a promising route of vaccine administration. Suitable i.d. adjuvants are important to increase vaccine efficacy in poorly responding populations such as the elderly or for dose-sparing strategies in the face of vaccine shortages. Bacterial exotoxins, such as Escherichia coli heat-labile enterotoxin (LT), exert strong immunostimulatory effects through binding to monosialoganglioside (GM1) cell surface receptors; however, injection is hampered by local inflammation. We demonstrate that the injection of LT formulations deficient in GM1 binding by mutation (LT(G33D)) or in vitro ligand coupling does not cause localized edema and inflammation in mice, yet these formulations retain potent adjuvant activity by enhancing functional Ab and cellular immune responses to coadministered Ags. Complete protection against in vivo lethal tetanus toxin challenge and the induction of Ag-specific CTL responses capable of killing target cells in vivo indicated in vivo efficacy of the induced immune responses. LT(G33D) proved superior to standard alum adjuvant regarding the magnitude and breadth of the induced immune responses. Immunizations in complex ganglioside knockout mice revealed a GM1-independent pathway of LT adjuvanticity. Immunostimulation by i.d. LT(G33D) is explained by its ability to induce migration of activated APCs to the proximal draining lymph nodes. LT(G33D) is a promising candidate adjuvant for human trials of parenteral vaccines in general and for current i.d. vaccine development in particular.

Early reconstitution of the T-cell repertoire after non-myeloablative peripheral blood stem cell transplantation is from post-thymic T-cell expansion and is unaffected by graft-versus-host disease or mixed chimaerism.

To study immune recovery after non-myeloablative, reduced-intensity stem cell allografts (NST) and T-cell-depleted myeloablative transplants (TCD), we measured T-cell subset recovery by flow cytometry, T-cell repertoire by spectratyping and thymic T-cell output using a T-cell receptor excision circle (TREC) assay. We found a rapid and comparable increase in lymphocyte numbers in both NST and TCD, supporting the presence of a powerful drive for lymphocyte recovery after transplant. Spectratyping on d 45 and 100 revealed almost complete normalization of the T-cell repertoire in NST patients by d 45, whereas TCD patients demonstrated marked skewing of the repertoire, persisting to d 100. After NST, there was a significantly higher number of TREC-positive CD4+ and CD8+ cells (P = 0.02 and P = 0.01 respectively). However, in both NST and TCD, early T-cell recovery after transplant appeared to result entirely from post-thymic T cells, the expansion pattern of which is most influenced by the starting T-cell dose, but not markedly by graft-versus-host disease (GVHD) or mixed chimaerism. These results define important qualitative differences in the T-cell repertoire according to the type of transplant schedule used.

Immunostimulant patch containing heat-labile enterotoxin from Escherichia coli enhances immune responses to injected influenza virus vaccine through activation of skin dendritic cells.

Vaccine strategies, such as influenza virus vaccination of the elderly, are highly effective at preventing disease but provide protection for only the responding portion of the vaccinees. Adjuvants improve the magnitude and rates of responses, but their potency must be attenuated to minimize side effects. Topical delivery of strong adjuvants such as heat-labile enterotoxin from Escherichia coli (LT) induces potent immune responses. We hypothesized that LT delivered alone in an immunostimulating (LT-IS) patch placed on the skin at the site of injection could augment the immune response to injected vaccines. This was based on the observation that topically applied LT induces migration of activated antigen-presenting cells (APCs) from the skin to the proximal draining lymph node (DLN), and that APCs loaded with antigen by injection in the same anatomical region also migrate to the same DLN. We observed that when influenza virus vaccine is injected and an LT-IS patch is placed to target the same DLN, the influenza virus antibody response is enhanced. Similarly, influenza virus-specific T cells isolated from the lungs show increased levels of gamma interferon and interleukin-4 production. An LT-IS patch placed near an injected vaccine also leads to increased levels of hemagglutination inhibition titers, enhanced mucosal immunoglobulin A responses, and enhanced antigen presentation. Although the mechanisms by which an LT-IS patch exerts its enhancing effects need further study, the enhanced immune responses, ability to safely use potent adjuvants, and simplicity of LT-IS patch application address an important unmet need and provide a new immune enhancement strategy.