Faculty Bibliography

Since the latter part of 2020, SARS-CoV-2 evolution has been characterised by the emergence of viral variants associated with distinct biological characteristics. While the main research focus has centred on the ability of new variants to increase in frequency and impact the effective reproductive number of the virus, less attention has been placed on their relative ability to establish transmission chains and to spread through a geographic area. Here, we describe a phylogeographic approach to estimate and compare the introduction and dispersal dynamics of the main SARS-CoV-2 variants-Alpha, Iota, Delta, and Omicron-that circulated in the New York City area between 2020 and 2022. Notably, our results indicate that Delta had a lower ability to establish sustained transmission chains in the NYC area and that Omicron (BA.1) was the variant fastest to disseminate across the study area. The analytical approach presented here complements non-spatially-explicit analytical approaches that seek a better understanding of the epidemiological differences that exist among successive SARS-CoV-2 variants of concern.

Small animal models have been a challenge for the study of SARS-CoV-2 transmission, with most investigators using golden hamsters or ferrets ^1,2 . Mice have the advantages of low cost, wide availability, less regulatory and husbandry challenges, and the existence of a versatile reagent and genetic toolbox. However, adult mice do not transmit SARS-CoV-2 ³ . Here we establish a model based on neonatal mice that allows for transmission of clinical SARS-CoV-2 isolates. We characterize tropism, respiratory tract replication and transmission of ancestral WA-1 compared to variants alpha (B.1.1.7), beta (B.1.351), gamma (P.1), delta (B.1.617.2) and omicron (B.1.1.529). We identify inter-variant differences in timing and magnitude of infectious particle shedding from index mice, both of which shape transmission to contact mice. Furthermore, we characterize two recombinant SARS-CoV-2 lacking either the ORF6 or ORF8 host antagonists. The removal of ORF8 shifts viral replication towards the lower respiratory tract, resulting in significantly delayed and reduced transmission. Our results demonstrate the potential of our neonatal mouse model to characterize viral and host determinants of SARS-CoV-2 transmission, while revealing for the first time a role for an accessory protein this context.

The emergence of recombinant viruses is a threat to public health, as recombination may integrate variant-specific features that together result in escape from treatment or immunity. The selective advantages of recombinant SARS-CoV-2 isolates over their parental lineages remain unknown. We identified a Delta-Omicron (AY.45-BA.1) recombinant in an immunosuppressed transplant recipient treated with monoclonal antibody Sotrovimab. The single recombination breakpoint is located in the spike N-terminal domain adjacent to the Sotrovimab binding site. While Delta and BA.1 are sensitive to Sotrovimab neutralization, the Delta-Omicron recombinant is highly resistant. To our knowledge, this is the first described instance of recombination between circulating SARS-CoV-2 variants as a functional mechanism of resistance to treatment and immune escape.

New mutations conferring resistance to SARS-CoV-2 therapeutics have important clinical implications. We describe the first cases of an independently acquired V792I RNA-dependent RNA polymerase mutation developing in renal transplant recipients after remdesivir exposure. Our work underscores the need for augmented efforts to identify concerning mutations and address their clinical implications.

HIV-1 envelope (Env) conformation determines the susceptibility of infected CD4⁺ T cells to antibody-dependent cellular cytotoxicity (ADCC). Upon interaction with CD4, Env adopts more "open" conformations, exposing ADCC epitopes. HIV-1 limits Env-CD4 interaction and protects infected cells against ADCC by downregulating CD4 via Nef, Vpu, and Env. Limited data exist, however, of the role of these proteins in downmodulating CD4 on infected macrophages and how this impacts Env conformation. While Nef, Vpu, and Env are all required to efficiently downregulate CD4 on infected CD4⁺ T cells, we show here that any one of these proteins is sufficient to downmodulate most CD4 from the surface of infected macrophages. Consistent with this finding, Nef and Vpu have a lesser impact on Env conformation and ADCC sensitivity in infected macrophages compared with CD4⁺ T cells. However, treatment of infected macrophages with small CD4 mimetics exposes vulnerable CD4-induced Env epitopes and sensitizes them to ADCC.

Due to the recrudescence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections worldwide, mainly caused by the Omicron variant of concern (VOC) and its sub-lineages, several jurisdictions are administering an mRNA vaccine boost. Here, we analyze humoral responses induced after the second and third doses of an mRNA vaccine in naive and previously infected donors who received their second dose with an extended 16-week interval. We observe that the extended interval elicits robust humoral responses against VOCs, but this response is significantly diminished 4 months after the second dose. Administering a boost to these individuals brings back the humoral responses to the same levels obtained after the extended second dose. Interestingly, we observe that administering a boost to individuals that initially received a short 3- to 4-week regimen elicits humoral responses similar to those observed in the long interval regimen. Nevertheless, humoral responses elicited by the boost in naive individuals do not reach those present in previously infected vaccinated individuals.

Latent reservoirs in human-immunodeficiency-virus-1 (HIV-1)-infected individuals represent a major obstacle in finding a cure for HIV-1. Hematopoietic stem and progenitor cells (HSPCs) have been described as potential HIV-1 targets, but their roles as HIV-1 reservoirs remain controversial. Here we provide additional evidence for the susceptibility of several distinct HSPC subpopulations to HIV-1 infection in vitro and in vivo. In vitro infection experiments of HSPCs were performed with different HIV-1 Env-pseudotyped lentiviral particles and with replication-competent HIV-1. Low-level infection/transduction of HSPCs, including hematopoietic stem cells (HSCs) and multipotent progenitors (MPP), was observed, preferentially via CXCR4, but also via CCR5-mediated entry. Multi-lineage colony formation in methylcellulose assays and repetitive replating of transduced cells provided functional proof of susceptibility of primitive HSPCs to HIV-1 infection. Further, the access to bone marrow samples from HIV-positive individuals facilitated the detection of HIV-1 gag cDNA copies in CD34+ cells from eight (out of eleven) individuals, with at least six of them infected with CCR5-tropic HIV-1 strains. In summary, our data confirm that primitive HSPC subpopulations are susceptible to CXCR4- and CCR5-mediated HIV-1 infection in vitro and in vivo, which qualifies these cells to contribute to the HIV-1 reservoir in patients.

Although SARS-CoV-2 mRNA vaccination has been shown to be safe and effective in the general population, immunocompromised solid organ transplant recipients (SOTRs) were reported to have impaired immune responses after one or two doses of vaccine. In this study, we examined humoral responses induced after the second and the third dose of mRNA vaccine in different SOTR (kidney, liver, lung, and heart). Compared to a cohort of SARS-CoV-2 naïve immunocompetent health care workers (HCWs), the second dose induced weak humoral responses in SOTRs, except for the liver recipients. The third dose boosted these responses but they did not reach the same level as in HCW. Interestingly, although the neutralizing activity against Delta and Omicron variants remained very low after the third dose, Fc-mediated effector functions in SOTR reached similar levels as in the HCW cohort. Whether these responses will suffice to protect SOTR from severe outcome remains to be determined.

BACKGROUND:T but not B cell numbers are decreased. COVID-19 vaccination thereby provides a model to assess whether lymphopenic platelet donors present compromised humoral immune responses. STUDY DESIGN AND METHODS/METHODS:T cell counts (76-1537 cells/μl). In addition to baseline T cell measurements, antibody binding assays to full-length Spike and the Receptor Binding Domain (RBD) were performed pre- and post-vaccination. Furthermore, pseudo-particle neutralization and antibody-dependent cellular cytotoxicity assays were conducted to measure antibody functionality. RESULTS:T cell levels minimally impacted neutralization, Spike recognition, and IgG Fc-mediated effector functions. DISCUSSION/CONCLUSIONS:Overall, our results indicate that lymphopenic plateletpheresis donors do not exhibit significant immune dysfunction; they have retained the T and B cell functionality necessary for potent antibody responses after vaccination.