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Two mRNA vaccines (BNT162b2 and mRNA-1273) against severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) are globally authorized as a two-dose regimen. Understanding the magnitude and duration of protective immune responses is vital to curbing the pandemic. We enrolled 461 high-risk health services workers at the University of California, Los Angeles (UCLA) and first responders in the Los Angeles County Fire Department (LACoFD) to assess the humoral responses in previously infected (PI) and infection naïve (NPI) individuals to mRNA-based vaccines (BNT162b2/Pfizer- BioNTech or mRNA-1273/Moderna). A chemiluminescent microparticle immunoassay was used to detect antibodies against SARS-CoV-2 Spike in vaccinees prior to (n = 21) and following each vaccine dose (n = 246 following dose 1 and n = 315 following dose 2), and at days 31–60 (n = 110) and 61–90 (n = 190) following completion of the 2-dose series. Both vaccines induced robust antibody responses in all immunocompetent individuals. Previously infected individuals achieved higher median peak titers (p = 0.002) and had a slower rate of decay (p = 0.047) than infection-naïve individuals. mRNA-1273 vaccinated infection-naïve individuals demonstrated modestly higher titers following each dose (p = 0.005 and p = 0.029, respectively) and slower rates of antibody decay (p = 0.003) than those who received BNT162b2. A subset of previously infected individuals (25%) required both doses in order to reach peak antibody titers. The biologic significance of the differences between previously infected individuals and between the mRNA-1273 and BNT162b2 vaccines remains uncertain, but may have important implications for booster strategies.

The lack of success of subunit human immunodeficiency virus (HIV) type 1 vaccines to date suggests that multiple components or a complex virion structure may be required. We hypothesized that the failure of current vaccine strategies to induce protective antibodies is linked to the inability of native envelope structures to readily elicit these types of antibodies. We have previously reported on the ability of a formaldehyde-treated, heat-inactivated vaccine to induce modest antibody responses in animal vaccine models. We investigated here whether immunization for HIV with an envelope-modified, formaldehyde-stabilized, heat-inactivated virion vaccine could produce higher-titer and/or broader neutralizing antibody responses. Thus, a clade B vaccine which contains a single point mutation in gp41 (Y706C) that results in increased incorporation of oligomeric Env into virions was constructed. This vaccine was capable of inducing high-titer antibodies that could neutralize heterologous viruses, including those of clades A and C. These results further support the development of HIV vaccines with modifications in native Env structures for the induction of neutralizing antibody responses.

The lack of success of subunit human immunodeficiency virus type 1 (HIV-1) vaccines to date suggests that multiple components or a complex virion structure may be required. We previously demonstrated retention of the major conformational epitopes of HIV-1 envelope following thermal treatment of virions. Moreover, antibody binding to some of these epitopes was significantly enhanced following thermal treatment. These included the neutralizing epitopes identified by monoclonal antibodies 1b12, 2G12, and 17b, some of which have been postulated to be partially occluded or cryptic in native virions. Based upon this finding, we hypothesized that a killed HIV vaccine could be derived to elicit protective humoral immune responses. Shedding of HIV-1 envelope has been described for some strains of HIV-1 and has been cited as one of the major impediments to developing an inactivated HIV-1 vaccine. In the present study, we demonstrate that treatment of virions with low-dose formaldehyde prior to thermal inactivation retains the association of viral envelope with virions. Moreover, mice and nonhuman primates vaccinated with formaldehyde-treated, thermally inactivated virions produce antibodies capable of neutralizing heterologous strains of HIV in peripheral blood mononuclear cell-, MAGI cell-, and U87-based infectivity assays. These data indicate that it is possible to create an immunogen by using formaldehyde-treated, thermally inactivated HIV-1 virions to induce neutralizing antibodies. These findings have broad implications for vaccine development.

Objective: To examine compartmental differences in co-receptor expression on CD4 lymphocytes between blood and gut using endoscopic biopsies. Design: Mucosal and peripheral CD4 T cells from healthy controls were compared for co-receptor expression and vulnerability to infection by HIV-1. Methods: Expression of CCR5 and CXCR4 was quantified by flow cytometry on isolated mucosal CD4 lymphocytes obtained from endoscopic biopsies and blood from healthy controls. Vulnerability to in vitro infection by both R5 and X4 strains was assessed by measuring p24. Results: Biopsies yielded sufficient lymphocytes for flow cytometric characterization and infectivity studies. The percentage of mucosal CD4 T lymphocytes that expressed CCR5 and the per cell expression of CCR5 were both significantly increased compared with that in peripheral blood CD4 T lymphocytes. CXCR4 was expressed on the majority of CD4 lymphocytes in both compartments. In vitro infection of mucosal mononuclear cells supported greater viral replication of both R5 and X4 strains than peripheral blood mononuclear cells. Conclusions: Enhanced expression of CXCR4 and CCR5 on CD4 lymphocytes in normal intestinal mucosa predicts increased vulnerability to infection by both R5 and X4 HIV-1. Endoscopic biopsies provide a useful mucosal tissue sampling technique to identify compartmental immunologic differences that may be exploited by HIV-1 in establishing initial mucosal infection.

The chemokine receptor CXCR4 is the major coreceptor used for cellular entry by T cell– tropic human immunodeficiency virus (HIV)-1 strains, whereas CCR5 is used by macrophage (M)-tropic strains. Here we show that a small-molecule inhibitor, ALX40-4C, inhibits HIV-1 envelope (Env)-mediated membrane fusion and viral entry directly at the level of coreceptor use. ALX40-4C inhibited HIV-1 use of the coreceptor CXCR4 by T- and dual-tropic HIV-1 strains, whereas use of CCR5 by M- and dual-tropic strains was not inhibited. Dual-tropic viruses capable of using both CXCR4 and CCR5 were inhibited by ALX40-4C only when cells expressed CXCR4 alone. ALX40-4C blocked stromal-derived factor (SDF)-1α–mediated activation of CXCR4 and binding of the monoclonal antibody 12G5 to cells expressing CXCR4. Overlap of the ALX40-4C binding site with that of 12G5 and SDF implicates direct blocking of Env interactions, rather than downregulation of receptor, as the mechanism of inhibition. Thus, ALX40-4C represents a small-molecule inhibitor of HIV-1 infection that acts directly against a chemokine receptor at the level of Env-mediated membrane fusion.

The relationship between host and virus was examined during the initial stages of human immunodeficiency virus type 1 (HIV) infection in a volunteer from the Multicenter AIDS Cohort Study (MACS). The individual was asymptomatic and unaware of his infection during an initial donation of blood and inguinal lymphoid tissue. Proviral DNA, however, was present in cells from both sources, HIV RNA was detected in the plasma, and CD4+ cell levels were reduced by approximately 50% compared with previous donations in the MACS. In a second blood donation 12 days later, plasma HIV RNA increased 200-fold in tandem with viral isolates with an increased growth phenotype in vitro. HIV burden was ultimately suppressed upon seroconversion and the emergence of HIV-specific CD8+ cytotoxic T lymphocytes. These observations provide further evidence that the potential benefits of early treatment may be maximized during the early stages of infection, when viral fitness may be low but is unopposed by immune responses.

Despite considerable evidence that cell activation enhances human immunodeficiency virus-type 1 (HIV-1) replication in vitro, there is very little data on the role of immune activation on in vivo HIV-1 replication. In this study, we examined the effect of influenza vaccination on HIV-1 replication in the peripheral blood of 20 study subjects, and in 14 control subjects who did not receive influenza vaccination. Blood was obtained from each subject on three occasions during the month before vaccination and again on three occasions during the following month. Over the study period, there was little change in levels of proviral DNA in peripheral blood mononuclear cells (PBMCs). However, peak PBMC viral RNA levels after influenza vaccination were significantly increased over the mean of prevaccination values. This change was not observed to the same extent in unvaccinated controls. Therefore, this is the first report showing that HIV-1 replication can increase in temporal association with influenza vaccination. Our results suggest that continued immunologic (antigenic) stimulation may result in increased virus load in vivo. To address the appropriateness of influenza vaccination in HIV-infected patients, expanded studies will be required to examine specific and generalized immune responses to vaccination, and differences in patient response based on disease stage.

Current HIV vaccines in development appear unlikely to prevent infection, but could provide benefits by increasing survival; such vaccines are described as disease-modifying vaccines. We review the current status of vaccines and modeling vaccines. We also predict the impact that disease-modifying vaccines could have in South Africa, where multiple subtypes are co-circulating. We model transmissibility/fitness differences among subtypes. We used uncertainty analyses to model vaccines with four characteristics: (i) take, (ii) duration of immunity, (iii) reduction in transmissibility/fitness, and (iv) increase in survival. We reconstructed, and forecasted, the South African epidemic from 1940 to 2140 (assuming no vaccination). We predict that: (i) incidence will peak in 2014, decline, and stabilize, (ii) prevalence will continue to rise, and (iii) the AIDS death rate curve will peak in 2022. Our predictions show that (over the next 135 years) the epidemic in South Africa will switch from a predominantly Subtype C epidemic to an epidemic driven by other subtypes. We predict that the epidemic could remain unchanged, even with mass vaccination with a vaccine that is equally effective against all co-circulating subtypes. However, if the non-C subtypes are less (or equally) transmissible as Subtype C then disease-modifying vaccines could result in eradication. Thus, in countries where multiple-subtypes are co-circulating it is critical to realize that small biological differences among subtypes will have dramatic consequences for the effectiveness of HIV vaccination campaigns. A slight difference in fitness will determine whether a disease-modifying vaccine has almost no impact on the epidemic or can achieve eradication.

Macrophages and CD4+lymphocytes are the principal target cells for human immunodeficiency virus type 1 (HIV-1) infection, but the molecular details of infection may differ between these cell types. During studies to identify cellular molecules that could be involved in macrophage infection, we observed inhibition of HIV-1 infection of macrophages by monoclonal antibody (MAb) to the tetraspan transmembrane glycoprotein CD63. Pretreatment of primary macrophages with anti-CD63 MAb, but not MAbs to other macrophage cell surface tetraspanins (CD9, CD81, and CD82), was shown to inhibit infection by several R5 and dualtropic strains, but not by X4 isolates. The block to productive infection was postfusion, as assessed by macrophage cell-cell fusion assays, but was prior to reverse transcription, as determined by quantitative PCR assay for new viral DNA formation. The inhibitory effects of anti-CD63 in primary macrophages could not be explained by changes in the levels of CD4, CCR5, or β-chemokines. Infections of peripheral blood lymphocytes and certain cell lines were unaffected by treatment with anti-CD63, suggesting that the role of CD63 in HIV-1 infection may be specific for macrophages.

Inactivation of viral particles is the basis for several vaccines currently in use. Initial attempts to use simian immunodeficiency virus to model a killed human immunodeficiency virus type 1 (HIV-1) vaccine were unsuccessful, and limited subsequent effort has been directed toward a systematic study of the requirements for a protective killed HIV-1 vaccine. Recent insights into HIV-1 virion and glycoprotein structure and neutralization epitopes led us to revisit whether inactivated HIV-1 particles could serve as the basis for an HIV-1 vaccine. Our results indicate that relatively simple processes involving thermal and chemical inactivation can inactivate HIV-1 by at least 7 logs. For some HIV-1 strains, significant amounts of envelope glycoproteins are retained in high-molecular-weight fractions. Importantly, we demonstrate retention of each of three conformation-dependent neutralization epitopes. Moreover, reactivity of monoclonal antibodies directed toward these epitopes is increased following treatment, suggesting greater exposure of the epitopes. In contrast, treatment of free envelope under the same conditions leads only to decreased antibody recognition. These inactivated virions can also be presented by human dendritic cells to direct a cell-mediated immune response in vitro. These data indicate that a systematic study of HIV-1 inactivation, gp120 retention, and epitope reactivity with conformation-specific neutralizing antibodies can provide important insights for the development of an effective killed HIV-1 vaccine.

RANTES (regulated on activation, normal T expressed and secreted), macrophage inflammatory protein (MIP)-1alpha, and MIP-1beta are human immunodeficiency virus (HIV) suppressor factors by virtue of their ability to compete with HIV for access to cell surface R5. Their ability to block HIV infection in vitro is unequivocal; however, their role as HIV suppressor factors in vivo is not firmly established. We therefore conducted a study to test the hypothesis that production of these factors in vitro was a correlate of decreased virus burden in vivo. Moreover, we asked whether higher beta chemokine production could be demonstrated with cells from people who are R5D32 heterozygotes, compared with people who are R5 wild-type homozygotes. Our data support the thesis that RANTES, MIP-1alpha, and MIP-1beta production is associated with decreased in vivo virus load. Moreover, enhanced production of these factors may be explained in part by the genetic background of the host.

The lack of clinical progression in some individuals despite prolonged human immunodeficiency virus type 1 (HIV-1) infection may result from infection with less-pathogenic viral strains. To address this question, we examined the HIV-1 envelope protein from a donor with a low viral burden, stable CD4+ T-lymphocyte counts, and little evidence of CD8+ T-cell expansion, activation, or immune activity. To avoid potential changes in envelope function resulting from selection in vitro, envelope clones were constructed by using viral RNA isolated from uncultured peripheral blood mononuclear cells (PBMC). The data showed that recombinant viruses containing envelope sequences derived from RNA isolated from patient PBMC replicated poorly in primary CD4+ T cells but demonstrated efficient growth in macrophages. The unusual phenotype of these viruses could not be explained solely by differential utilization of coreceptors since the chimeric viruses, as well as an uncloned isolate obtained from the same visit date, can utilize CCR5. In addition, the donor’s own cells appeared resistant to infection with chimeric viruses containing autologous envelope sequences. Genotype analysis revealed that the donor was heterozygous for the previously described 32-bp deletion in CCR5 which may be linked with prolonged survival in HIV-1-infected individuals. These data suggest that the changes in envelope sequences confer properties of viral attenuation, which together with the CCR5 +/Δ32 genotype could account for the long-term survival of this patient.