Adolescent BCG revaccination induces a phenotypic shift in CD4+ T cell responses to Mycobacterium tuberculosis.

A recent clinical trial demonstrated that Bacille Calmette-Guérin (BCG) revaccination of adolescents reduced the risk of sustained infection with Mycobacterium tuberculosis (M.tb). In a companion phase 1b trial, HVTN 602/Aeras A-042, we characterize in-depth the cellular responses to BCG revaccination or to a H4:IC31 vaccine boost to identify T cell subsets that could be responsible for the protection observed. High-dimensional clustering analysis of cells profiled using a 26-color flow cytometric panel show marked increases in five effector memory CD4+ T cell subpopulations (TEM) after BCG revaccination, two of which are highly polyfunctional. CITE-Seq single-cell analysis shows that the activated subsets include an abundant cluster of Th1 cells with migratory potential. Additionally, a small cluster of Th17 TEM cells induced by BCG revaccination expresses high levels of CD103; these may represent recirculating tissue-resident memory cells that could provide pulmonary immune protection. Together, these results identify unique populations of CD4+ T cells with potential to be immune correlates of protection conferred by BCG revaccination.

HIV BG505 SOSIP.664 trimer with 3M-052-AF/alum induces human autologous tier-2 neutralizing antibodies.

Stabilized trimers preserving the native-like HIV envelope structure may be key components of a preventive HIV vaccine regimen to induce broadly neutralizing antibodies (bnAbs). We evaluated trimeric BG505 SOSIP.664 gp140, formulated with a novel TLR7/8 signaling adjuvant, 3M-052-AF/Alum, for safety, adjuvant dose-finding and immunogenicity in a first-in-healthy adult (n=17), randomized, placebo-controlled trial (HVTN 137A). The vaccine regimen appeared safe. Robust, trimer-specific antibody, B-cell and CD4+ T-cell responses emerged post-vaccination. Five vaccinees developed serum autologous tier-2 nAbs (ID50 titer, 1:28-1:8647) after 2-3 doses targeting C3/V5 and/or V1/V2/V3 Env regions by electron microscopy and mutated pseudovirus-based neutralization analyses. Trimer-specific, B-cell-derived monoclonal antibody activities confirmed these results and showed weak heterologous neutralization in the strongest responder. Our findings demonstrate the clinical utility of the 3M-052-AF/alum adjuvant and support further improvements of trimer-based Env immunogens to focus responses on multiple broad nAb epitopes. KEY TAKEAWAY/TAKE-HOME MESSAGES: HIV BG505 SOSIP.664 trimer with novel 3M-052-AF/alum adjuvant in humans appears safe and induces serum neutralizing antibodies to matched clade A, tier 2 virus, that map to diverse Env epitopes with relatively high titers. The novel adjuvant may be an important mediator of vaccine response.

Human immunoglobulin gene allelic variation impacts germline-targeting vaccine priming.

Vaccine priming immunogens that activate germline precursors for broadly neutralizing antibodies (bnAbs) have promise for development of precision vaccines against major human pathogens. In a clinical trial of the eOD-GT8 60mer germline-targeting immunogen, higher frequencies of vaccine-induced VRC01-class bnAb-precursor B cells were observed in the high dose compared to the low dose group. Through immunoglobulin heavy chain variable (IGHV) genotyping, statistical modeling, quantification of IGHV1-2 allele usage and B cell frequencies in the naive repertoire for each trial participant, and antibody affinity analyses, we found that the difference between dose groups in VRC01-class response frequency was best explained by IGHV1-2 genotype rather than dose and was most likely due to differences in IGHV1-2 B cell frequencies for different genotypes. The results demonstrate the need to define population-level immunoglobulin allelic variations when designing germline-targeting immunogens and evaluating them in clinical trials.

mRNA vaccination boosts S-specific T cell memory and promotes expansion of CD45RAint TEMRA-like CD8+ T cells in COVID-19 recovered individuals.

SARS-CoV-2 infection and mRNA vaccination both elicit spike (S)-specific T cell responses. To analyze how T cell memory from prior infection influences T cell responses to vaccination, we evaluated functional T cell responses in naive and previously infected vaccine recipients. Pre-vaccine S-specific responses are predictive of subsequent CD8+ T cell vaccine-response magnitudes. Comparing baseline with post-vaccination TCRß repertoires, we observed large clonotypic expansions correlated with the frequency of spike-specific T cells. Epitope mapping the largest CD8+ T cell responses confirms that an HLA-A∗03:01 epitope was highly immunodominant. Peptide-MHC tetramer staining together with mass cytometry and single-cell sequencing permit detailed phenotyping and clonotypic tracking of these S-specific CD8+ T cells. Our results demonstrate that infection-induced S-specific CD8+ T cell memory plays a significant role in shaping the magnitude and clonal composition of the circulating T cell repertoire after vaccination, with mRNA vaccination promoting CD8+ memory T cells to a TEMRA-like phenotype.

A first-in-human germline-targeting HIV nanoparticle vaccine induced broad and publicly targeted helper T cell responses.

The engineered outer domain germline targeting version 8 (eOD-GT8) 60-mer nanoparticle was designed to prime VRC01-class HIV-specific B cells that would need to be matured, through additional heterologous immunizations, into B cells that are able to produce broadly neutralizing antibodies. CD4 T cell help will be critical for the development of such high-affinity neutralizing antibody responses. Thus, we assessed the induction and epitope specificities of the vaccine-specific T cells from the IAVI G001 phase 1 clinical trial that tested immunization with eOD-GT8 60-mer adjuvanted with AS01B. Robust polyfunctional CD4 T cells specific for eOD-GT8 and the lumazine synthase (LumSyn) component of eOD-GT8 60-mer were induced after two vaccinations with either the 20- or 100-microgram dose. Antigen-specific CD4 T helper responses to eOD-GT8 and LumSyn were observed in 84 and 93% of vaccine recipients, respectively. CD4 helper T cell epitope "hotspots" preferentially targeted across participants were identified within both the eOD-GT8 and LumSyn proteins. CD4 T cell responses specific to one of these three LumSyn epitope hotspots were observed in 85% of vaccine recipients. Last, we found that induction of vaccine-specific peripheral CD4 T cells correlated with expansion of eOD-GT8-specific memory B cells. Our findings demonstrate strong human CD4 T cell responses to an HIV vaccine candidate priming immunogen and identify immunodominant CD4 T cell epitopes that might improve human immune responses either to heterologous boost immunogens after this prime vaccination or to other human vaccine immunogens.

Human immunoglobulin gene allelic variation impacts germline-targeting vaccine priming.

Vaccine priming immunogens that activate germline precursors for broadly neutralizing antibodies (bnAbs) have promise for development of precision vaccines against major human pathogens. In a clinical trial of the eOD-GT8 60mer germline-targeting immunogen, higher frequencies of vaccine-induced VRC01-class bnAb-precursor B cells were observed in the high dose compared to the low dose group. Through immunoglobulin heavy chain variable (IGHV) genotyping, statistical modeling, quantification of IGHV1-2 allele usage and B cell frequencies in the naive repertoire for each trial participant, and antibody affinity analyses, we found that the difference between dose groups in VRC01-class response frequency was best explained by IGHV1-2 genotype rather than dose and was most likely due to differences in IGHV1-2 B cell frequencies for different genotypes. The results demonstrate the need to define population-level immunoglobulin allelic variations when designing germline-targeting immunogens and evaluating them in clinical trials. One-Sentence Summary: Human genetic variation can modulate the strength of vaccine-induced broadly neutralizing antibody precursor B cell responses.

Vaccination induces HIV broadly neutralizing antibody precursors in humans.

Broadly neutralizing antibodies (bnAbs) can protect against HIV infection but have not been induced by human vaccination. A key barrier to bnAb induction is vaccine priming of rare bnAb-precursor B cells. In a randomized, double-blind, placebo-controlled phase 1 clinical trial, the HIV vaccine-priming candidate eOD-GT8 60mer adjuvanted with AS01B had a favorable safety profile and induced VRC01-class bnAb precursors in 97% of vaccine recipients with median frequencies reaching 0.1% among immunoglobulin G B cells in blood. bnAb precursors shared properties with bnAbs and gained somatic hypermutation and affinity with the boost. The results establish clinical proof of concept for germline-targeting vaccine priming, support development of boosting regimens to induce bnAbs, and encourage application of the germline-targeting strategy to other targets in HIV and other pathogens.

Th2-Biased Transcriptional Profile Predicts HIV Envelope-Specific Polyfunctional CD4+ T Cells That Correlated with Reduced Risk of Infection in RV144 Trial.

Ag-specific T cells play a critical role in responding to viral infections. In the RV144 HIV vaccine clinical trial, a rare subset of HIV-specific polyfunctional CD4+ T cells correlated with reduced risk of HIV-1 infection. Polyfunctional T cells are a subset of Ag-specific T cells that are able to simultaneously produce multiple effector cytokines. Little is known about what differentiates polyfunctional T cells from other vaccine-elicited T cells in humans. Therefore, we developed a novel live-cell multiplexed cytokine capture assay to identify, isolate, and transcriptionally profile vaccine-specific polyfunctional CD4+ T cells. We applied these methods to samples from subjects who received the RV144 vaccine regimen, as part of the HVTN 097 clinical trial. We identified two surface receptors (CD44 and CD82) upregulated on polyfunctional T cells and a Th2-biased transcriptional signature (IL-4, IL-5, and IL-13) that predicted the envelope-specific polyfunctional CD4+ T cell profiles that had correlated with reduced risk of HIV infection in RV144. By linking single-cell transcriptional and functional profiles, we may be able to further define the potential contributions of polyfunctional T cells to effective vaccine-elicited immunity.

Generation of a cost-effective cell line for support of high-throughput isolation of primary human B cells and monoclonal neutralizing antibodies.

The isolation of human monoclonal antibodies (mAbs) arising from natural infection with human pathogens has proven to be a powerful technology, facilitating the understanding of the host response to infection at a molecular level. mAbs can reveal sites of vulnerability on pathogens and illuminate the biological function of the antigenic targets. Moreover, mAbs have the potential to be used directly for therapeutic applications such as passive delivery to prevent infection in susceptible target populations, and as treatment of established infection. The isolation of antigen-specific B cells from vaccine trials can also assist in deciphering whether the desired B cells are being targeted by a given vaccine. Several different processes have been developed to isolate mAbs, but all are generally labor-intensive and result in varying degrees of efficiency. Here, we describe the development of a cost-effective feeder cell line that stably expresses CD40-ligand, interleukin-2 and interleukin-21. Sorting of single B cells onto a layer of irradiated feeder cells sustained antibody production that permits functional screening of secreted antibodies in a manner that enables subsequent recovery of B cells for recombinant antibody cloning. As a proof of concept, we show that this approach can be used to isolate B cells that secrete antibodies that neutralize human papilloma virus (HPV) from participants of an HPV vaccine study.

T cell receptor gene therapy targeting WT1 prevents acute myeloid leukemia relapse post-transplant.

Relapse after allogeneic hematopoietic cell transplantation (HCT) is the leading cause of death in patients with acute myeloid leukemia (AML) entering HCT with poor-risk features1-3. When HCT does produce prolonged relapse-free survival, it commonly reflects graft-versus-leukemia effects mediated by donor T cells reactive with antigens on leukemic cells4. As graft T cells have not been selected for leukemia specificity and frequently recognize proteins expressed by many normal host tissues, graft-versus-leukemia effects are often accompanied by morbidity and mortality from graft-versus-host disease5. Thus, AML relapse risk might be more effectively reduced with T cells expressing receptors (TCRs) that target selected AML antigens6. We therefore isolated a high-affinity Wilms' Tumor Antigen 1-specific TCR (TCRC4) from HLA-A2+ normal donor repertoires, inserted TCRC4 into Epstein-Bar virus-specific donor CD8+ T cells (TTCR-C4) to minimize graft-versus-host disease risk and enhance transferred T cell survival7,8, and infused these cells prophylactically post-HCT into 12 patients ( NCT01640301 ). Relapse-free survival was 100% at a median of 44 months following infusion, while a concurrent comparative group of 88 patients with similar risk AML had 54% relapse-free survival (P = 0.002). TTCR-C4 maintained TCRC4 expression, persisted long-term and were polyfunctional. This strategy appears promising for preventing AML recurrence in individuals at increased risk of post-HCT relapse.

Differences in the Selection Bottleneck between Modes of Sexual Transmission Influence the Genetic Composition of the HIV-1 Founder Virus.

Due to the stringent population bottleneck that occurs during sexual HIV-1 transmission, systemic infection is typically established by a limited number of founder viruses. Elucidation of the precise forces influencing the selection of founder viruses may reveal key vulnerabilities that could aid in the development of a vaccine or other clinical interventions. Here, we utilize deep sequencing data and apply a genetic distance-based method to investigate whether the mode of sexual transmission shapes the nascent founder viral genome. Analysis of 74 acute and early HIV-1 infected subjects revealed that 83% of men who have sex with men (MSM) exhibit a single founder virus, levels similar to those previously observed in heterosexual (HSX) transmission. In a metadata analysis of a total of 354 subjects, including HSX, MSM and injecting drug users (IDU), we also observed no significant differences in the frequency of single founder virus infections between HSX and MSM transmissions. However, comparison of HIV-1 envelope sequences revealed that HSX founder viruses exhibited a greater number of codon sites under positive selection, as well as stronger transmission indices possibly reflective of higher fitness variants. Moreover, specific genetic "signatures" within MSM and HSX founder viruses were identified, with single polymorphisms within gp41 enriched among HSX viruses while more complex patterns, including clustered polymorphisms surrounding the CD4 binding site, were enriched in MSM viruses. While our findings do not support an influence of the mode of sexual transmission on the number of founder viruses, they do demonstrate that there are marked differences in the selection bottleneck that can significantly shape their genetic composition. This study illustrates the complex dynamics of the transmission bottleneck and reveals that distinct genetic bottleneck processes exist dependent upon the mode of HIV-1 transmission.

HIV transmission. Selection bias at the heterosexual HIV-1 transmission bottleneck.

Heterosexual transmission of HIV-1 typically results in one genetic variant establishing systemic infection. We compared, for 137 linked transmission pairs, the amino acid sequences encoded by non-envelope genes of viruses in both partners and demonstrate a selection bias for transmission of residues that are predicted to confer increased in vivo fitness on viruses in the newly infected, immunologically naïve recipient. Although tempered by transmission risk factors, such as donor viral load, genital inflammation, and recipient gender, this selection bias provides an overall transmission advantage for viral quasispecies that are dominated by viruses with high in vivo fitness. Thus, preventative or therapeutic approaches that even marginally reduce viral fitness may lower the overall transmission rates and offer long-term benefits even upon successful transmission.

Hypermutable DNA chronicles the evolution of human colon cancer.

Intratumor genetic heterogeneity reflects the evolutionary history of a cancer and is thought to influence treatment outcomes. Here we report that a simple PCR-based assay interrogating somatic variation in hypermutable polyguanine (poly-G) repeats can provide a rapid and reliable assessment of mitotic history and clonal architecture in human cancer. We use poly-G repeat genotyping to study the evolution of colon carcinoma. In a cohort of 22 patients, we detect poly-G variants in 91% of tumors. Patient age is positively correlated with somatic mutation frequency, suggesting that some poly-G variants accumulate before the onset of carcinogenesis during normal division in colonic stem cells. Poorly differentiated tumors have fewer mutations than well-differentiated tumors, possibly indicating a shorter mitotic history of the founder cell in these cancers. We generate poly-G mutation profiles of spatially separated samples from primary carcinomas and matched metastases to build well-supported phylogenetic trees that illuminate individual patients' path of metastatic progression. Our results show varying degrees of intratumor heterogeneity among patients. Finally, we show that poly-G mutations can be found in other cancers than colon carcinoma. Our approach can generate reliable maps of intratumor heterogeneity in large numbers of patients with minimal time and cost expenditure.

Frequent and variable cytotoxic-T-lymphocyte escape-associated fitness costs in the human immunodeficiency virus type 1 subtype B Gag proteins.

Cytotoxic-T-lymphocyte (CTL) escape mutations undermine the durability of effective human immunodeficiency virus type 1 (HIV-1)-specific CD8(+) T cell responses. The rate of CTL escape from a given response is largely governed by the net of all escape-associated viral fitness costs and benefits. The observation that CTL escape mutations can carry an associated fitness cost in terms of reduced virus replication capacity (RC) suggests a fitness cost-benefit trade-off that could delay CTL escape and thereby prolong CD8 response effectiveness. However, our understanding of this potential fitness trade-off is limited by the small number of CTL escape mutations for which a fitness cost has been quantified. Here, we quantified the fitness cost of the 29 most common HIV-1B Gag CTL escape mutations using an in vitro RC assay. The majority (20/29) of mutations reduced RC by more than the benchmark M184V antiretroviral drug resistance mutation, with impacts ranging from 8% to 69%. Notably, the reduction in RC was significantly greater for CTL escape mutations associated with protective HLA class I alleles than for those associated with nonprotective alleles. To speed the future evaluation of CTL escape costs, we also developed an in silico approach for inferring the relative impact of a mutation on RC based on its computed impact on protein thermodynamic stability. These data illustrate that the magnitude of CTL escape-associated fitness costs, and thus the barrier to CTL escape, varies widely even in the conserved Gag proteins and suggest that differential escape costs may contribute to the relative efficacy of CD8 responses.

Vaccine-induced CD8+ T cells control AIDS virus replication.

Developing a vaccine for human immunodeficiency virus (HIV) may be aided by a complete understanding of those rare cases in which some HIV-infected individuals control replication of the virus. Most of these elite controllers express the histocompatibility alleles HLA-B*57 or HLA-B*27 (ref. 3). These alleles remain by far the most robust associations with low concentrations of plasma virus, yet the mechanism of control in these individuals is not entirely clear. Here we vaccinate Indian rhesus macaques that express Mamu-B*08, an animal model for HLA-B*27-mediated elite control, with three Mamu-B*08-restricted CD8(+) T-cell epitopes, and demonstrate that these vaccinated animals control replication of the highly pathogenic clonal simian immunodeficiency virus (SIV) mac239 virus. High frequencies of CD8(+) T cells against these Vif and Nef epitopes in the blood, lymph nodes and colon were associated with viral control. Moreover, the frequency of the CD8(+) T-cell response against the Nef RL10 epitope (Nef amino acids 137-146) correlated significantly with reduced acute phase viraemia. Finally, two of the eight vaccinees lost control of viral replication in the chronic phase, concomitant with escape in all three targeted epitopes, further implicating these three CD8(+) T-cell responses in the control of viral replication. Our findings indicate that narrowly targeted vaccine-induced virus-specific CD8(+) T-cell responses can control replication of the AIDS virus.