Biology subjects

Melo, M. B.

Publications and source records attributed to Melo, M. B..

9 recordsLinked to original sources

bioRxiv2026

Germinal centers can persist for up to one year with declining somatic hypermutation and ongoing plasma cell output

The total duration of primary germinal center (GC) responses, and how B cell evolution changes as these responses mature, remain poorly defined. Here, longitudinal sampling of rhesus macaques immunized with HIV Envelope protein revealed that a single slow-delivery prime sustained ongoing GCs for nearly a year without additional antigen. Somatic hypermutation (SHM) accumulated throughout these prolonged responses, but its rate declined substantially over time, independent of both priming strategy and boosting. Over the same period, subdominant non-base Env specificities became increasingly represented within the GC response. Delaying boosting until after primary GC contraction increased recruitment of recalled memory B cells into the GC response. Bone marrow plasma cells were generated throughout prolonged GC maturation, with the timing of their generation modulated by booster timing. Together, these findings reveal how GCs evolve across nearly a year and how this prolonged maturation shapes the memory and plasma cell compartments that underpin long-term humoral immunity.

immunology↗

bioRxiv2026

Atomic layer deposition for core-shell microparticle vaccines enabling programmable antigen delivery to lymph nodes enhance humoral immune responses

Technologies that simplify complex dosing regimens as single-shot immunizations may be important for vaccines against difficult to neutralize pathogens. Here we characterized delivery mechanisms of core-shell microparticles comprising clinically-relevant HIV immunogen formulations spray-dried to form solid spherical microparticles and subsequently coated with a nanoscopic alumina shell using atomic layer deposition (ALD). ALD particles exhibited a time delay in antigen release programmed by the alumina shell followed by prolonged antigen release, which steadily accumulated in antigen-presenting cells at the injection site and draining lymph nodes and accumulated on follicular dendritic cells in B cell follicles. ALD vaccines elicited continuous expansion of antigen-specific germinal center B cells over 8 weeks, serum antibody responses with >10-fold slower antigen-binding off-rates, and 2-fold more long-lived plasma cells compared to traditional bolus vaccination with potent adjuvants. Single administration ALD technology thus promotes key events in the primary immune response important for vaccines against HIV and other challenging pathogens.

immunology↗

bioRxiv2025

Rapid elicitation of a new class of neutralizing N332-glycan independent V3-glycan antibodies against HIV-1 in nonhuman primates.

Sequential immunization is a promising approach to elicit broadly neutralizing antibodies (bNAbs) against the HIV-1 Envelope (Env). However, available protocols are inefficient and involve multiple immunizations over long periods of time. Here, we present WIN332, a new engineered Env-immunogen that induces a new class of neutralizing N332-glycan-independent antibodies to the conserved V3-glycan epitope of Env after a single bolus immunization in nonhuman primates. WIN332 binds to precursors of canonical human N332-glycan-dependent (Type-I) V3-glycan bNAbs but also of a first-of-its-class N332-glycan-independent (Type-II) V3-glycan bNAb. A single immunization elicits neutralizing serum and monoclonal antibodies that are boosted and affinity matured with a heterologous immunogen. EMPEM analysis of serum antibodies, antibody cloning and cryo-EM analysis reveal that WIN332 elicits N332-glycan-independent antibodies with remarkable sequence and binding similarities with the most potent human type-I and type-II V3-glycan bNAbs. Thus, WIN332 is a promising vaccine candidate to streamline V3-glycan bNAb elicitation.

immunology↗

bioRxiv2025

Engineering gene expression dynamics via self-amplifying RNA with drug-responsive non-structural proteins

The design of gene therapies with drug-regulatable expression of therapeutic payloads is of interest for diverse applications. We hypothesized that a regulated expression system based on alphavirus-derived self-amplifying RNAs (saRNAs), which encode 4 non-structural proteins (nsPs) that copy the RNA backbone to enable sustained expression, would have advantages in safety and simplicity of delivery. Here we designed saRNAs where payload expression is regulated by the FDA-approved drug trimethoprim (TMP), by fusing TMP-responsive degradation domains (DDs) to nsPs to regulate RNA self-amplification. Screening a library of nsP-DD fusions, we identified an optimal design with DDs fused to nsP2, nsP3, and the payload, achieving a high fold-change in expression level in response to TMP and low expression in the off state. In mice, this saRNA circuit enabled diverse dynamic expression patterns in response to oral TMP. Implementing this circuit for controlled expression of an HIV antigen, an escalating TMP regimen significantly enhanced germinal center responses critical for B cell affinity maturation. This drug- regulated RNA technology holds potential for vaccines, immunotherapies, and gene therapies.

bioengineering↗

bioRxiv2025

Targeted suppression of type 1 interferon signaling during RNA delivery enhances vaccine-elicited immunity

RNA vaccines have emerged as a breakthrough technology, and one promising modality employs alphavirus-derived self-replicating RNA (repRNA) to express vaccine antigens. However, both the lipid nanoparticles (LNP) commonly used to deliver RNA and virus-like amplification of repRNAs trigger innate immune recognition, especially via type I interferon (IFN) signaling. To modulate IFN responses during vaccination, we formulated LNPs co-delivering antigen-encoding RNA together with siRNA targeting the interferon-/{beta} receptor-1 (IFNAR1). siRNA-mediated repression of IFNAR1 increased antigen expression from repRNAs by >10-fold, increased immune cell infiltration, and increased antigen presenting cell activation in the injection site and draining lymph nodes. Compared to repRNA alone, siRNA/repRNA co-delivery increased serum antibody titers >10-fold, dramatically augmented antigen-specific germinal center (GC) B cell responses, and primed 4.4-fold more antigen-specific T cells. Ifnar1 silencing by siRNA co-delivery similarly enhanced mRNA vaccines. Thus, siRNA co-delivery is a readily translatable approach to substantially enhance the immunogenicity of RNA vaccines.

bioengineering↗

bioRxiv2024

Modulation of antigen delivery and lymph node activation in non-human primates by saponin adjuvant SMNP

Saponin-based vaccine adjuvants are potent in preclinical animal models and humans, but their mechanisms of action remain poorly understood. Here, using a stabilized HIV envelope trimer immunogen, we carried out studies in non-human primates (NHPs) comparing the most common clinical adjuvant alum with Saponin/MPLA Nanoparticles (SMNP), a novel ISCOMs-like adjuvant. SMNP elicited substantially stronger humoral immune responses than alum, including 7-fold higher peak antigen-specific germinal center B cell responses, 18-fold higher autologous neutralizing antibody titers, and higher levels of antigen-specific plasma and memory B cells. PET-CT imaging in live NHPs showed that, unlike alum, SMNP promoted rapid antigen accumulation in both proximal and distal lymph nodes (LNs). SMNP also induced strong type I interferon transcriptional signatures, expansion of innate immune cells, and increased antigen presenting cell activation in LNs. These findings indicate that SMNP promotes multiple facets of the early immune response relevant for enhanced immunity to vaccination.

bioengineering↗

bioRxiv2024

'Target-and-release' nanoparticles for effective immunotherapy of metastatic ovarian cancer

Immunotherapies such as checkpoint inhibitors (CPI) are effective in treating several advanced cancers, but these treatments have had limited success in metastatic ovarian cancer (OC). Here, we engineered liposomal nanoparticles (NPs) carrying a layer-by-layer (LbL) polymer coating that promotes their binding to the surface of OC cells. Covalent anchoring of the potent immunostimulatory cytokine interleukin-12 (IL-12) to phospholipid headgroups of the liposome core enabled the LbL particles to concentrate IL-12 in disseminated OC tumors following intraperitoneal administration. Shedding of the LbL coating and serum protein-mediated extraction of IL-12-conjugated lipids from the liposomal core over time enabled IL-12 to disseminate in the tumor bed following rapid NP localization in tumor nodules. Optimized IL-12 LbL-NPs promoted robust T cell accumulation in ascites and tumors in mouse models, extending survival compared to free IL-12 and remarkedly sensitizing tumors to CPI, leading to curative treatments and immune memory.

bioengineering↗

bioRxiv2023

WASP facilitates tumor mechanosensitivity in T lymphocytes

Cytotoxic T lymphocytes (CTLs) carry out immunosurveillance by scanning target cells of diverse physical properties for the presence of antigens. While the recognition of cognate antigen by the T cell receptor is the primary signal for CTL activation, it has become increasingly clear that the mechanical stiffness of target cells plays an important role in antigen-triggered T cell responses. However, the molecular machinery within CTLs that transduces the mechanical information of tumor cells remains unclear. We find that CTLs mechanosensitive ability requires the activity of the actin-organizing protein Wiskott-Aldrich Syndrome Protein (WASP). WASP activation is modulated by the mechanical properties of antigen-presenting contexts across a wide range of target cell stiffnesses and activated WASP then mediates mechanosensitive activation of early TCR signaling markers in the CTL. Our results provide a molecular link between antigen mechanosensing and CTL immune response and suggest that CTL-intrinsic cytoskeletal organizing principles enable the processing of mechanical information from diverse target cells.

immunology↗

bioRxiv2018

Slow delivery immunization enhances HIV neutralizing antibody and germinal center responses via modulation of immunodominance

The observation that humans can produce broadly neutralizing antibodies (bnAbs) against HIV-1 has generated enthusiasm about the potential for a bnAb vaccine against HIV-1. Conventional immunization strategies will likely be insufficient for the development of a bnAb HIV vaccine and vaccines to other difficult pathogens, due to the significant immunological hurdles posed, including B cell immunodominance and germinal center (GC) quantity and quality. Using longitudinal lymph node fine needle aspirates, we found that two independent methods of slow delivery immunization of rhesus macaques (RM) resulted in larger GCs, more robust and sustained GC Tfh cell responses, and GC B cells with improved Env-binding, which correlated with the development of ~20 to 30-fold higher titers of tier 2 HIV-1 nAbs. Using a new RM genomic immunoglobulin loci reference sequence, we identified differential IgV gene usage between slow delivery immunized and conventional bolus immunized animals. The most immunodominant IgV gene used by conventionally immunized animals was associated with many GC B cell lineages. Ab mapping of those GC B cell specificities demonstrated targeting of an immunodominant non-neutralizing trimer base epitope, while that response was muted in slow delivery immunized animals. Thus, alternative immunization strategies appear to enhance nAb development by altering GCs and modulating immunodominance of non-neutralizing epitopes.

immunology↗