SARS-CoV-2 antibody response duration and neutralization following natural infection

Background

The role of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) neutralizing antibody response from natural infection and vaccination, and the potential determinants of this response are poorly understood. Characterizing this antibody response and the factors associated with neutralization can help inform future prevention efforts and improve clinical outcomes in those infected.

Objectives

The goals of this study were to prospectively evaluate SARS-CoV-2 antibody levels and the neutralizing antibody responses among naturally infected adults and to determine demographic and behavioral factors independently associated with these responses.

Methods

Serum was collected from seropositive individuals at baseline, four-weeks, and three-months following their first study visit to be evaluated for antibody levels. Detection of neutralizing antibodies was performed at baseline. Participant demographic and behavioral information was collected via web questionnaire prior to their first visit.

Results

At baseline, higher antibody levels were associated with better neutralization capacity, with 83% of participants having detectable neutralizing antibodies. We found an age-dependent effect on antibody level and neutralization capacity with participants over 65 years having significantly higher levels. Ethnicity, heart disease, autoimmune disease, and COVID symptoms were associated with higher antibody levels, but not with increased neutralization capacity. Work environment during the pandemic correlated with increased neutralization capacity, while kidney or liver disease and traveling out of state after February 2020 correlated with decreased neutralization capacity, however neither correlated with antibody levels.

Conclusions

Our data show that natural infection by SARS-CoV-2 can induce a humoral response reflected by high antibody levels and neutralization capacity.

Systemic checkpoint blockade by PD-L1 single-chain antibody confers potent anti-tumor immunity and long-term survival

Immune checkpoint inhibitors (ICIs) are promising in adjuvant settings for solid tumors and hematologic malignancies. They are currently used in the treatment as monoclonal antibodies in high concentrations, raising concerns of toxicity and adverse side effects. Among various checkpoint molecules, targeting the program cell death protein-1 (PD-1)-programmed death-ligand 1 (PD-L1) axis has garnered more clinical utility than others have. In order to develop a physiologically relevant and systemically stable level of ICIs from a one-time application by genetic antibody engineering, we endeavored using a non-pathogenic, replication-deficient recombinant adeno-associated vector (rAAV), expressing single-chain variable fragments (scFv) of PD-L1 antibody and tested in syngeneic mouse therapy models of MC38 colorectal and EMT6 breast tumors. Results of this study indicated a significant protection against PD-L1-mediated inhibition of CD8+ T cell function, against the growth of primary and secondary tumors, and durable antitumor cytotoxic T lymphocytes activity by adoptive CD8+ T cell transfer. Stable maintenance of PD-L1 scFv in vivo resulted in an increase in PD-1- CD8+ T cells, and a concomitant decrease in regulatory T cells, M2 macrophages and myeloid-derived suppressor cells in the tumor microenvironment. Overall, these data demonstrate the potential of rAAV-PD-L1-scFv as an alternative to mAb targeting of PD-L1 for tumor therapy.

Evaluation of Antibody Response to SARS-CoV-2 mRNA-1273 Vaccination in Patients With Cancer in Florida

Importance

Patients with cancer experience high rates of morbidity and mortality after SARS-CoV-2 infection. Immune response to mRNA-1273 vaccination across multiple cancer types and treatments remains to be established.

Objective

To quantitate antibody responses after mRNA-1273 vaccination among patients with solid tumors and hematologic cancer and to assess clinical and treatment factors associated with vaccine response.

Design, Setting, and Participants

This cohort study included patients with cancer who were aged 18 years or older, spoke English or Spanish, had received their first mRNA-1273 dose between January 12 and 25, 2021, and agreed to blood tests before and after vaccination.

Exposures

Receipt of 1 and 2 mRNA-1273 SARS-CoV-2 vaccine doses.

Main Outcomes and Measures

Seroconversion after each vaccine dose and IgG levels against SARS-CoV-2 spike protein obtained immediately before the first and second vaccine doses and 57 days (plus or minus 14 days) after the first vaccine dose. Cancer diagnoses and treatments were ascertained by medical record review. Serostatus was assessed via enzyme-linked immunosorbent assay. Paired t tests were applied to examine days 1, 29, and 57 SARS-CoV-2 antibody levels. Binding antibody IgG geometric mean titers were calculated based on log10-transformed values.

Results

The 515 participants were a mean (SD) age of 64.5 (11.4) years; 262 (50.9%) were women; and 32 (6.2%) were Hispanic individuals and 479 (93.0%) White individuals; race and ethnicity data on 4 (0.7%) participants were missing. Seropositivity after vaccine dose 2 was 90.3% (465; 95% CI, 87.4%-92.7%) among patients with cancer, was significantly lower among patients with hematologic cancer (84.7% [255]; 95% CI, 80.1%-88.6%) vs solid tumors (98.1% [210]; 95% CI, 95.3%-99.5%), and was lowest among patients with lymphoid cancer (70.0% [77]; 95% CI, 60.5%-78.4%). Patients receiving a vaccination within 6 months after anti-CD20 monoclonal antibody treatment had a significantly lower seroconversion (6.3% [1]; 95% CI, 0.2%-30.2%) compared with those treated 6 to 24 months earlier (53.3% [8]; 95% CI, 26.6%-78.7%) or those who never received anti-CD20 treatment (94.2% [456]; 95% CI, 91.7%-96.1%). Low antibody levels after vaccination were observed among patients treated with anti-CD20 within 6 months before vaccination (GM, 15.5 AU/mL; 95% CI, 9.8-24.5 AU/mL), patients treated with small molecules (GM, 646.7 AU/mL; 95% CI, 441.9-946.5 AU/mL), and patients with low lymphocyte (GM, 547.4 AU/mL; 95% CI, 375.5-797.7 AU/mL) and IgG (GM, 494.7 AU/mL; 95% CI, 304.9-802.7 AU/mL) levels.

Conclusions and Relevance

This cohort study found that the mRNA-1273 SARS-CoV-2 vaccine induced variable antibody responses that differed by cancer diagnosis and treatment received. These findings suggest that patients with hematologic cancer and those who are receiving immunosuppressive treatments may need additional vaccination doses.

SARS-CoV-2 Period Seroprevalence and Related Factors, Hillsborough County, Florida, October 2020-March 2021

Estimating the actual extent of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is challenging because virus test positivity data undercount the actual number and proportion of persons infected. SARS-CoV-2 seroprevalence is a marker of past SARS-CoV-2 infection regardless of presence or severity of symptoms and therefore is a robust biomarker of infection period prevalence. We estimated SARS-CoV-2 seroprevalence among residents of Hillsborough County, Florida, USA, to determine factors independently associated with SARS-CoV-2 antibody status overall and among asymptomatic antibody-positive persons. Among 867 participants, SARS-CoV-2 period prevalence (October 2020–March 2021) was 19.5% (asymptomatic seroprevalence was 8%). Seroprevalence was 2-fold higher than reported SARS-CoV-2 virus test positivity. Factors related to social distancing (e.g., essential worker status, not practicing social distancing, contact with a virus-positive person, and length of contact exposure time) were consistently associated with seroprevalence but did not differ by time since suspected or known infection (<6 months vs. >6 months).

RANKL-Targeted Combination Therapy with Osteoprotegerin Variant Devoid of TRAIL Binding Exerts Biphasic Effects on Skeletal Remodeling and Antitumor Immunity

Complexities in treating breast cancer with bone metastasis are enhanced by a vicious protumorigenic pathology, involving a shift in skeletal homeostasis toward aggressive osteoclast activity and polarization of immune cells supporting tumor growth and immunosuppression. Recent studies signify the role of receptor activator of NF-κB ligand (RANKL) beyond skeletal pathology in breast cancer, including tumor growth and immunosuppression. By using an osteoprotegerin (OPG) variant, which we developed recently through protein engineering to uncouple TNF-related apoptosis-inducing ligand (TRAIL) binding, this study established the potential of a cell-based OPG^Y49R therapy for both bone damage and immunosuppression in an immunocompetent mouse model of orthotopic and metastatic breast cancers. In combination with agonistic death receptor (DR5) activation, the OPG^Y49R therapy significantly increased both bone remolding and long-term antitumor immunity, protecting mice from breast cancer relapse and osteolytic pathology. With limitations, cost, and toxicity issues associated with the use of denosumab, bisphosphonates, and chemotherapy for bone metastatic disease, use of OPG^Y49R combination could offer a viable alternate therapeutic approach.

Recombinant AAV-CEA Tumor Vaccine in Combination with an Immune Adjuvant Breaks Tolerance and Provides Protective Immunity

Carcinoembryonic antigen (CEA) is a human glycoprotein involved in cellular adhesion and expressed during human fetal development. Although expression of CEA largely ceases prior to birth, several human epithelial cancers, including colorectal, gastric, squamous esophageal, and breast carcinomas have been known to overexpress CEA, suggesting its potential as an immunotherapeutic target. Using a transgenic mouse model constitutively expressing human CEA in a spatiotemporal manner as a self-protein and a syngeneic mouse colon cancer cell line, MC38-CEA, overexpressing CEA, we tested the potential of a novel genetic immunotherapy approach against CEA-expressing tumors, using recombinant adeno-associated virus vector encoding CEA (rAAV-CEA) and appropriately timed immune adjuvant application. Results of the study demonstrated breaking of immune tolerance for CEA with this vaccine regimen and an anti-tumor response, resulting in tumor-free survival. Furthermore, tumor challenge of CEA-vaccinated mice with parental MC38 cells not expressing CEA did not result in protection from tumor development, confirming that the protection against tumor development is CEA specific. The study illustrates the feasibility of utilizing rAAV vectors in combination with an immunostimulatory adjuvant to break tolerance to weakly immunogenic self-antigens and for an anti-tumor response.

Effects of Cellular Methylation on Transgene Expression and Site-Specific Integration of Adeno-Associated Virus

DNA methylation is a major epigenetic event that affects not only cellular gene expression but that also has the potential to influence bacterial and viral DNA in their host-dependent functions. Adeno-associated virus (AAV) genome contains a high degree of CpG sequences capable of methylation in its terminal repeat sequences, which are the sole elements retained in AAV-based vectors used in gene therapy. The present study determined the influence of methylation status of the host cell on wild type (wt) AAV integration and recombinant (r) AAV transgene expression in HeLa cells. Results of the study indicated that hypo-methylation significantly enhanced both wtAAV chromosomal integration and transgene expression of rAAV. A direct influence of methylation on AAV integration was further confirmed by methylating the AAVS1 integration sites prior to viral infection with DNA trans-complementation assay. These results signify the importance of epigenetic status of target cells as one of the key factors in long-term transgene expression in AAV gene therapy.

Location of tumor affects local and distant immune cell type and number

INTRODUCTION

Tumors comprise heterogeneous populations of cells, including immune infiltrates that polarize during growth and metastasis. Our preclinical studies on breast cancer (BCa) identified functional differences in myeloid-derived suppressor cells based on tumor microenvironment (TME), prompting variations in host immune response to tumor growth, and dissemination based on tissue type.

METHODS

In order to understand if such variations existed among other immune cells, and if such alteration occurs in response to tumor growth at the primary site or due to bone dissemination, we characterized immune cells, examining localized growth and in the tibia. In addition, immune cells from the spleen were examined from animals of both tumor locations by flow cytometry.

RESULTS

The study demonstrates that location of tumor, and not simply the tumor itself, has a definitive role in regulating immune effectors. Among all immune cells characterized, macrophages were decreased and myeloid dendritic cell were increased in both tumor locations. This difference was more evident in subcutaneous tumors. Additionally, spleens from mice with subcutaneous tumors contained greater increases in both macrophages and myeloid dendritic cells than in mice with bone tumors. Furthermore, in subcutaneous tumors there was an increase in CD4+ and CD8+ T-cell numbers, which was also observed in their spleens.

CONCLUSIONS

These data indicate that alterations in tumor-reactive immune cells are more pronounced at the primary site, and exert a similar change at the major secondary lymphoid organ than in the bone TME. These findings could provide translational insight into designing therapeutic strategies that account for location of metastatic foci.

Immature myeloid cells are critical for enhancing bone fracture healing through angiogenic cascade

Bone fractures heal with overlapping phases of inflammation, cell proliferation, and bone remodeling. Osteogenesis and angiogenesis work in concert to control many stages of this process, and when one is impaired it leads to failure of bone healing, termed a nonunion. During fracture repair, there is an infiltration of immune cells at the fracture site that not only mediate the inflammatory responses, but we hypothesize they also exert influence on neovasculature. Thus, further understanding the effects of immune cell participation throughout fracture healing will reveal additional knowledge as to why some fractures heal while others form nonunions, and lead to development of novel therapeutics modulating immune cells, to increase fracture healing and prevent nonunions. Using novel femoral segmental and critical-size defect models in mice, we identified a systemic and significant increase in immature myeloid cell (IMC) infiltration during the initial phase of fracture healing until boney union is complete. Using gemcitabine to specifically ablate the IMC population, we confirmed delayed bone healing. Further, adoptive transfer of IMC increased bone growth in a nonunion model, signifying the role of this unique cell population in fracture healing. We also identified IMC post-fracture have the ability to increase endothelial cell migration, and tube formation, signaling the essential communication between the immune system and angiogenesis as a requirement for proper bone healing. Based on this data we propose that IMC may play a significant role in fracture healing and therapeutic targeting of IMC after fracture would minimize the chances of eventual nonunion pathology.

Prostate cancer-derived cathelicidin-related antimicrobial peptide facilitates macrophage differentiation and polarization of immature myeloid progenitors to protumorigenic macrophages

BACKGROUND

A growing body of evidence indicates a positive correlation between expression of human antimicrobial peptide leucin leucin 37 (LL-37) and progression of epithelial cancers, including prostate cancer (PCa). Although the molecular mechanisms for this correlation has not yet been elucidated, the primary function of LL-37 as a chemotactic molecule for innate immune effector cells suggests its possible association in coordinating protumorigenic mechanisms, mediated by tumor-infiltrating immune cells.

METHODS

To investigate protumorigenic role(s) of cathelicidin-related antimicrobial peptide (CRAMP), a murine orthologue of LL-37, the present study compared tumor growth kinetics between mouse PCa cell lines with and without CRAMP expression (TRAMP-C1 and TRAMP-C1(CRAMP-sh) , respectively) in immunocompetent mice. CRAMP-mediated chemotaxis of different innate immune cell types to the tumor microenvironment (TME) was observed in vivo and confirmed by in vitro chemotaxis assay. The role of CRAMP in differentiation and polarization of immature myeloid progenitors (IMPs) to protumorigenic type 2 macrophages (M2) in TME was determined by adoptive transfer of IMPs into mice bearing CRAMP(+) and CRAMP(-) tumors. To differentiate protumorigenic events mediated by tumor-derived CRAMP from host immune cell-derived CRAMP, tumor challenge study was performed in CRAMP-deficient mice. To identify mechanisms of CRAMP function, macrophage colony stimulating factor (M-CSF) and monocyte chemoattractant protein 1 (MCP-1) gene expression was analyzed by QRT-PCR and STAT3 signaling was determined by immunoblotting.

RESULTS

Significantly delayed tumor growth was observed in wild-type (WT) mice implanted with TRAMP-C1(CRAMP-sh) cells compared to mice implanted with TRAMP-C1 cells. CRAMP(+) TME induced increased number of IMP differentiation into protumorigenic M2 macrophages compared to CRAMP(-) TME, indicating tumor-derived CRAMP facilitates differentiation and polarization of IMPs toward M2. Tumor challenge study in CRAMP deficient mice showed comparable tumor growth kinetics with WT mice, suggesting tumor-derived CRAMP plays a crucial role in PCa progression. In vitro study demonstrated that overexpressed M-CSF and MCP-1 in TRAMP-C1 cells through CRAMP-mediated autocrine signaling, involving p65, regulates IMP-to-M2 differentiation/polarization through STAT3 activation.

CONCLUSION

Altogether, the present study suggests that overexpressed CRAMP in prostate tumor initially chemoattracts IMPs to TME and mediates differentiation and polarization of early myeloid progenitors into protumorigenic M2 macrophages during PCa progression. Thus, selective downregulation of CRAMP in tumor cells in situ may benefit overcoming immunosuppressive mechanisms in PCa.

Anterior gradient protein-2 is a regulator of cellular adhesion in prostate cancer

Anterior Gradient Protein (AGR-2) is reported to be over-expressed in many epithelial cancers and promotes metastasis. A clear-cut mechanism for its observed function(s) has not been previously identified. We found significant upregulation of AGR-2 expression in a bone metastatic prostate cancer cell line, PC3, following culturing in bone marrow-conditioned medium. Substantial AGR-2 expression was also confirmed in prostate cancer tissue specimens in patients with bone lesions. By developing stable clones of PC3 cells with varying levels of AGR-2 expression, we identified that abrogation of AGR-2 significantly reduced cellular attachment to fibronectin, collagen I, collagen IV, laminin I and fibrinogen. Loss of cellular adhesion was associated with sharp decrease in the expression of α4, α5, αV, β3 and β4 integrins. Failure to undergo apoptosis following detachment is a hallmark of epithelial cancer metastasis. The AGR-2-silenced PC3 cells showed higher resistance to Tumor necrosis factor-related apoptosis- inducing ligand (TRAIL) induced apoptosis in vitro. This observation was also supported by significantly reduced Caspase-3 expression in AGR-2-silenced PC3 cells, which is a key effector of both extrinsic and intrinsic death signaling pathways. These data suggest that AGR-2 influence prostate cancer metastasis by regulation of cellular adhesion and apoptosis.

Depletion of plasmacytoid dendritic cells inhibits tumor growth and prevents bone metastasis of breast cancer cells

Elevated levels of plasmacytoid dendritic cells (pDC) have been reported in breast cancer patients, but the significance remains undefined. Using three immunocompetent mouse models of breast cancer bone metastasis, we identified a key role for pDC in facilitating tumor growth through immunosuppression and aggressive osteolysis. Following infiltration of macrophages upon breast cancer dissemination, there was a steady increase in pDC within the bone, which resulted in a sustained Th2 response along with elevated levels of regulatory T cells and myeloid-derived suppressor cells. Subsequently, pDC and CD4(+) T cells, producing osteolytic cytokines, increased with tumor burden, causing severe bone damage. Microcomputed tomography and histology analyses of bone showed destruction of femur and tibia. The therapeutic significance of this finding was confirmed by depletion of pDC, which resulted in decreased tumor burden and bone loss by activating tumor-specific cytolytic CD8(+) T cells and decreasing suppressor cell populations. Thus, pDC depletion may offer a novel adjuvant strategy to therapeutically influence breast cancer bone metastasis.

LL-37 as a therapeutic target for late stage prostate cancer

BACKGROUND

The antimicrobial peptide, leucine-leucine-37 (LL-37), stimulates proliferation, angiogenesis, and cellular migration, inhibits apoptosis and is associated with inflammation. Since these functional processes are often exaggerated in cancer, the aim of the present study was to investigate the expression and role of LL-37 in prostate cancer (PCa) and establish its value as a therapeutic target.

METHODS

We evaluated the expression of LL-37 and the murine orthologue, cathelicidin-related antimicrobial peptide (CRAMP) in human and murine prostate tumors, respectively. Compared to normal/benign prostate tissue, both LL-37 and CRAMP were increasingly over-expressed with advancing grades of primary PCa and its metastasis in human tissues and in the transgenic adenocarcinoma mouse prostate (TRAMP) model, correspondingly. We subsequently knocked-down CRAMP in the highly tumorigenic TRAMP-C1 cell line via a RNA interference strategy to examine the importance of CRAMP on cellular proliferation, angiogenesis, invasion, apoptosis, activation of signaling pathways and tumor kinetics.

RESULTS

Abrogation of CRAMP expression led to decreased proliferation, invasion, type IV collagenase, and the amount of phosphorylated Erk1/2 and Akt signaling in vitro. These results were paralleled in vivo. Syngenic implantation of TRAMP-C1 cells subjected to CRAMP knock-down resulted in a decreased tumor incidence and size, and the down-regulation of pro-tumorigenic mechanisms.

CONCLUSIONS

CRAMP knock-down in a murine PCa model analogously demonstrated the tumorigenic contributions of LL-37 in PCa and its potential as a novel therapeutic target for the treatment of PCa and potentially, other cancers over-expressing the peptide.

Therapeutic potential of adult bone marrow-derived mesenchymal stem cells in prostate cancer bone metastasis

PURPOSE

Current evidence indicates that an osteoblast lesion in prostate cancer is preceded by osteolysis. Thus, prevention of osteolysis would reduce complications of bone metastasis. Bone marrow-derived mesenchymal stem cells have the ability to differentiate into osteoblast and produce osteoprotegerin, a decoy receptor for the receptor activator for nuclear factor kappaB ligand, naturally. The present study examined the potential of unmodified mesenchymal stem cells to prevent osteolytic bone lesions in a preclinical mouse model of prostate cancer.

EXPERIMENTAL DESIGN

The human prostate cancer cell line PC3 was implanted in tibiae of severe combined immunodeficient mice. After establishment of the tumor, either unmodified or genetically engineered mesenchymal stem cells overexpressing osteoprotegerin was injected at the site of tumor growth. The effects of therapy were monitored by bioluminescence imaging, micro-computed tomography, immunohistochemistry, and histomorphometry.

RESULTS

Data indicated significant (P < 0.001) inhibition of tumor growth and restoration of bone in mice treated with unmodified and modified mesenchymal stem cells. Detailed analysis suggested that the donor mesenchymal stem cell inhibited tumor progression by producing woven bone around the growing tumor cells in the tibiae and by preventing osteoclastogenesis.

CONCLUSIONS

Overcoming the limitation of the number of mesenchymal stem cells available in the bone can provide significant amelioration for osteolytic damage without further modification.